Two years ago, National Plating Corp.was a small plater in the highly competitive Cleveland area when young Mark Palik, National's third-generation owner, made an all or nothing multimillion-dollar bet on a new highly automated zinc-chloride barrel line. He wanted to take on the area's high-volume platers in the automotive and fastener fields and their rock-bottom prices.
Mark's grandfather, John Palik, started the company in 1946 as a copper, nickel and chromium plating shop. He was aggressive, building the company up to a peak of 60 employees by the late '50s. Active in the industry, John won national awards and was the first president of the National Association of Metal Finishers. He retired in 1970, selling the company to his son Dave who was active in the business. Unlike John, however, Dave was more cautious and decided to downsize the business. He traded off the semi-automatic chromium line for a 10-station cyanide-based zinc barrel line. He was quite content being a much smaller shop with steady, profitable work and fewer frustrations.
By the mid '80s, things were changing. The plating industry was challenged by EPA requirements and the need for expensive waste treatment improvements. Dave Palik had had enough. He did not want to adjust to all these changes; he'd rather sell the company and find a quieter life-style.
When Mark, then a 20-year-old photographer working in California, heard about his father's desire to get out of the business, he decided to give it a shot. "I told him I would come back here and try it for at least the summer," he laughed, "and here I am, eleven years later!"
NATIONAL PLATING'S big line can turn out 20,000 lbs of parts in an hour.
When Mark took over National Plating in 1987, it was time to either commit to big improvements or risk losing the business. For the Palik family, each generation had reacted to its times, applied its own philosophy and been successful in its own way.
It was a small shop at that time, with about eight employees. Mark's plan was clear: respond to this challenge and clean up its act. He immediately began to expand the business and within two years had tripled sales. Today, it employs 40 people.
How did he finance these early expansions? "Hard work," is his quick answer. "We've always had handy people and our own welders. It is not rocket science to build a plating tank. We even built a few of our own barrels at one time. Building your own equipment is a distinct advantage, not something many can do."
The big leap forward. The decision to launch the new line was made two years ago. Business was good, and Mark again wanted to expand. Cost efficiency was the key philosophy behind this major move. "Where prices are going in this industry, it doesn't make sense for anybody with conventional equipment to tackle large volumes of work. We needed to build a line that was so productive and cost efficient that I could run work at the going rate."
MARK PALIK checks the coating thickness using equipment capable of measurements within approximately 1%.
Like the movie Field of Dreams, Mark's theory was "If you build it, they will come." When people asked, however, if he had lined up work for this new line, he had to admit that he had not, but he did have two or three big accounts in mind. "There was no doubt in my mind that when we showed them we could turn massive volumes quickly with better QC and SPC levels than they were getting, they would at least give us an opportunity to be a second source," he explained. "That's all we would need to earn more of their business."
Has it worked? "Yes," he replied with a grin. "Although it was not as easyas I thought it would be." He knew that even with the ups and downs of demand in this business, any plater doing automotive work would have to meet that industry's tough ISO and QS 9000 requirements with the QC and SPC his company had in place.
He was right. This has helped attract new business. "Since we jumped on the large-volume bandwagon, our volume has increased over 300%, sales have doubled, and we were just getting started! We are running the line at about three-fourths capacity now and expect to hit full capacity by year's end. I do not know of any barrel plating line that is more productive."
Because the company did much of the work itself, Mr. Palik pointed out that the investment was probably half what it would have cost had it been engineered and installed by an outside firm. "Although there's no other U.S. barrel line quite like this," he said. "I visited a similarly automated one in Canada that cost more than $4 million."
Another philosophy Mark Palik has always employed is no third shift, even at the busiest of times. He feels that operating around the clock seven days a week cannot be done without sacrificing quality. "We run two shifts five days a week," he said, "eight to twelve hours per shift, depending on how busy we are, and always have available capacity. If we get too busy while running two twelves, we'll just run a Saturday and get caught up."
Features of the new line. Here are the key features that make this new zinc plating line unique and efficient:
Rectification: The line has individual rectification for each plating station. "This gives us the versatility to plate one barrel at 1,000 amps," Mr. Palik explained, "and follow it up with a 100-amp load, thus tailoring plating current to the surface area of the part in each barrel."
Stainless tanks: Another major commitment was to use only stainless steel tanks rather than lined steel tanks. A major initial expense, yes, but one that pays off in reliability and ease of maintenance in the end.
Automatic hoists: Four automatic high-speed hoists were designed and built in-house. They cost about $20,000 each to build, which was a big savings over having to buy them outside.
Barrel automation: With automated barrel handling, the results are consistent cycle to cycle, not varying shift to shift. "Our chromates are constantly on conductivity meters with pumps automatically controlling concentration," he noted. "It is the same every time: concentration, submersion time and end result. On a manual line, you can have an operator counting out the submersion timing and being either faster or slower than the guy on the next shift." The barrels have automatic locking doors. Operators load the barrel and when it turns in one direction, the door locks closed. After processing, turn the barrel the other way, and the door opens and the barrel dumps. This is much faster than standard barrel doors that require manually removing four or five clamps from the door each time you load and unload.
Solution processing: Maintaining bath chemistry is the key to quality control, and here Mr. Palik relies on statistical process control methods and constant monitoring, including daily testing of metal content and chemistry levels. "We use SPC to constantly maintain all chemistry levels," he said. "Everything is charted on the computer. If we got some blistering on a part we ran two months ago, for example, we can go back to our SPC charts and see exactly where our chemistry levels were the day we ran it." Pavco Inc., Cleveland, Ohio, is the main proprietary chemical supplier, and has been instrumental in providing technical support. "Once a week the supplier does an analysis of basically everything we do daily, including a check on the proprietary chemicals, which we cannot do. It can also troubleshoot any problems with its much more sophisticated analytical equipment."
BELT DRYER handles parts carefully.
Thickness testing: Three on-line eddy current testers monitor coating thickness within approximately 5%. This is supplemented by an X-ray test machine that can measure coatings to within approximately 1% on the more complicated surfaces, like parts with threads.
Ventilation: Ventilation is another area of emphasis. "We've spent a lot on ventilation," Mr. Palik recalled. "It is not just having adequate exhausting, you also need to be bringing in more fresh air than you exhaust. We have a big air-makeup unit on our roof, pumping air in and pumping it out. That was a code requirement for us to move into this building. Another was that not only did our chemical storage rooms have to be sprinkled with fire doors, but everything in the building had to be fully sprinkled."
Drying: Here Mr. Palik committed to a belt dryer for his new plating line. Why? "Easier part handling and more pounds per hour than a centrifugal dryer," he replied. "It is less labor intensive and less chance of any violent motion harming the parts. In centrifugal dryers, sometimes parts can kick out, rattle around and get distorted."
Baking and post treatment: Post treatments offered include all the usual plus black chromate, olive drab, bright dipping, lacquer and wax. The new line also offers full capacity baking to help relieve any hydrogen embrittlement of heat-treated parts induced in the plating process.
Help up the learning curve. "You can be two lifetimes in this business and still get stumped. When we do, our supplier can come in with sophisticated equipment, tear apart the plating chemistry and find out what is in the bath that is causing an unusual problem. With our own lab, we are pretty self-sufficient for the day-to-day things, but every once in a while oil or something a new customer is using can cause problems. Many companies are cutting costs by using recycled oil in their manufacturing process. We have probably the best cleaning system around, but can still get something crazy in there now and then. You can bandage many problems by simply throwing in brighteners, but we would much rather analyze the problem and correct it."
AUTOMATED barrels move down the zinc plating line.
Those plating shops serving the auto industry are facing a requirement that all Tier Two suppliers be ISO 9000 registered by year's end. Mark Palik sees that, too, as an opportunity. "We plan to be registered by then," he says. "We're half-way there already."
Although plating demand in the Cleveland area has slacked off since he committed to this new line, Mr. Palik remains optimistic. Once he convinced a few big-volume customers that his small shop was moving into the big time, it didn't take long for the news to spread. "People started talking about the line and the job we were doing for them," he recalled. "Soon people I had called months ago started calling back. Our reputation started paying off."
source http://www.pfonline.com/articles/129804.html
Thursday, June 18, 2009
Fasteners and Finishes
What happened to cadmium? Once the premier coating for corrosion and lubricity, cadmium has faded greatly in automotive use and is predicted to be outdated soon. The reason stems from two major drives in automotive marketing. The first was the decline and final restriction of the coating in overseas vehicles. The EEC (European Economic Community) passed regulations that limited the percentage of toxic metals, including cadmium, to amounts that seemed extreme to American eyes. A strictly adhered to timetable eliminated cadmium in paints (usually yellow, red and white are cadmium based), plastics (used mainly as ultraviolet stabilizers and for a variety of other reasons) and finally for plating. The EEC allowed that if a strong case in the area of safety, etc. could be made for its use, then cadmium could be allowed. However, since the European car manufacturers were building without cadmium, the presence of cadmium in the same components built in America was not justifiable. Back in the States the companies that did not have significant export markets did not worry about the impending ban. Farm, heavy equipment and truck markets were involved almost from the start. The major use of cadmium in automotive applications was as a plating on all metal prevailing torque nuts (locknuts). A drive was on for a substitute plating before the ban's cutoff date. The problem of disposal of plating sludge had been an increasing one for several years as more and more of the authorized landfills closed their gates to cadmium sludge. The price to dispose of the sludge rose so high that most platers began to charge back to their customers a surcharge when cadmium was requested. The EPA and other groups began to circulate reports about the potential hazards of cadmium in the ecosystems and the effects of heavy metals on the human fetus.
This soon led to the second drive to eliminate automotive cadmium. The Title III Act was passed with its list of banned and to-be-banned chemicals. Major OEMs, with the automotive companies leading the way, wanted to create an image of concern. The potential harm was from the plating chemicals and effluent not the finished plating; however, the concern was that some might rub off. It may be perceived that the problem was due to the demand of the OEMs for the dangerous platings. In the spirit of being a good neighbor, the automotive companies would no longer ask for cadmium plating on fasteners.
The search for a substitute was a race against time. Research into any reasonable and some very unreasonable alternatives proceeded. After six or seven months, the list of unacceptables has grown to more than 160, and the ones with promise stood at three or four. Among the rejected ideas were multiple layered plating/organic/lube coatings, an organic so strong that it caused rabbits to go blind within minutes of exposure, and some exotics whose cost placed them within the reach of governmental agencies only. One of the good guys was tin plate. Unfortunately, it was also prone to metal embrittlement, came from some unstable countries and was expensive.
The other alternatives were Magni Corporation's Dorryltone® (later replaced by Dorrylflake) and Dacromet® series of coatings from Metal Coatings International. These last two had the properties that were needed for locknuts. They showed narrow torque bands (for good control in assembly) were readily available, easily applied, economical and non-toxic. One of these two was chosen by the various companies.
This is about where the situation stands today. Some complaints about various aspects of these substitutes have arisen, especially in the areas of corrosion vs. thickness and the fact that the new coatings do not have the same torque/tension values (it takes more torque to produce the same tension, or the new finish is not as slippery as cadmium). While these seem to be the choice of the moment, work is being done on various friction modifiers to increase lubrication. One drawback to these fluids is that they tend to wash off, are not present in reuse situations and require extra labor steps. Topcoats on the two forerunners have also improved the products and further developments look promising.
Cadmium remains available, for a price, in local markets. The surcharge also remains and varies as disposal charges fluctuate. Military remains the largest single customer for cadmium today. Long storage times of assembled components and harsh conditions make the use of cadmium a must in some areas. Hammering the fuse of an atomic bomb that has been in storage for 15 years, to service it, is one place where cadmium would be a first-choice coating for this engineer.
This soon led to the second drive to eliminate automotive cadmium. The Title III Act was passed with its list of banned and to-be-banned chemicals. Major OEMs, with the automotive companies leading the way, wanted to create an image of concern. The potential harm was from the plating chemicals and effluent not the finished plating; however, the concern was that some might rub off. It may be perceived that the problem was due to the demand of the OEMs for the dangerous platings. In the spirit of being a good neighbor, the automotive companies would no longer ask for cadmium plating on fasteners.
The search for a substitute was a race against time. Research into any reasonable and some very unreasonable alternatives proceeded. After six or seven months, the list of unacceptables has grown to more than 160, and the ones with promise stood at three or four. Among the rejected ideas were multiple layered plating/organic/lube coatings, an organic so strong that it caused rabbits to go blind within minutes of exposure, and some exotics whose cost placed them within the reach of governmental agencies only. One of the good guys was tin plate. Unfortunately, it was also prone to metal embrittlement, came from some unstable countries and was expensive.
The other alternatives were Magni Corporation's Dorryltone® (later replaced by Dorrylflake) and Dacromet® series of coatings from Metal Coatings International. These last two had the properties that were needed for locknuts. They showed narrow torque bands (for good control in assembly) were readily available, easily applied, economical and non-toxic. One of these two was chosen by the various companies.
This is about where the situation stands today. Some complaints about various aspects of these substitutes have arisen, especially in the areas of corrosion vs. thickness and the fact that the new coatings do not have the same torque/tension values (it takes more torque to produce the same tension, or the new finish is not as slippery as cadmium). While these seem to be the choice of the moment, work is being done on various friction modifiers to increase lubrication. One drawback to these fluids is that they tend to wash off, are not present in reuse situations and require extra labor steps. Topcoats on the two forerunners have also improved the products and further developments look promising.
Cadmium remains available, for a price, in local markets. The surcharge also remains and varies as disposal charges fluctuate. Military remains the largest single customer for cadmium today. Long storage times of assembled components and harsh conditions make the use of cadmium a must in some areas. Hammering the fuse of an atomic bomb that has been in storage for 15 years, to service it, is one place where cadmium would be a first-choice coating for this engineer.
Monday, June 8, 2009
Choosing Pumps and Filters
Platers and finishers have special requirements compared to the average user of pump and filtration equipment. The solutions are toxic, precious, expensive and corrosive. A certain amount of thought goes into the specification of each component.
Each person in the company has concerns and requirements when selecting pumps and filters. However, each may have a different opinion about the application and equipment. It is important to consider all of the concerns.
Facility manager's concerns.
What are the utility requirements, such as the amp draw of the mo-tors, voltage requirements, power consumption?
Shop air requirements at scfm or psi?
Dimensions of the equipment or a footprint?
Maintenance manager's concerns.
What is required for proper installation?
In addition to items purchased, what components, such as pipe, fittings, valves, electrical components, switches, etc. are needed?
What type of pump is best for the particular application?
Will the pumps be mounted inside or outside the tank?
Questions about in-tank vertical pumps that need to be addressed.
How will chemicals and fumes affect the motors?
Will the motor's coating withstand the harsh environment without peeling and contaminating the solution?
Will the motor bearings hold up? Are the bearings sealed or unsealed and what service is required for them?
What is the service factor of the motors?
Are they insulated for chemical duty?
Will the pumps introduce air into the solution?
Are drip shields available for the motors?
Are all wet-end components compatible with each constituent of the chemical being pumped?
Can the pump run dry without damage?
In electroless plating where the metal tends to plate out and deposit on plastic, can the wet-end components of the pump withstand the effects of stripping solution?
What temperature range will the pump withstand without damage?
What are the psi to temperature ratios the pump will operate under?
Will the pump run against a closed discharge without damage? How long? Will the internal components warp under heat?
Questions to ask when considering a vertical pump mounted outside the tank.
Will the pumped liquid be kept in the pump column or will it pump up the column when under a closed discharge?
Does the pump have a port seal at the mounting plate to protect the motor bearing from corrosive fumes?
What spare parts should be kept in inventory?
Are there any parts susceptible to wear, and what preventive maintenance is needed to keep the pump running at its optimum?
When repairs are necessary, can the pump be removed and repaired at the shop, or does it need to be shipped back to the factory?
Are there factory authorized dealers in the area?
What are the return authorization procedures?
How long is the pump warranty, and what is covered?
Are there any special tools needed for disassembly and repair?
Does the pump have a parts list and operating instructions?
1. TYPICAL VERTICAL pump installations.
In addition to most of the preceding vertical pump concerns, there are more concerns relating to out-of-tank pumps.
The horizontal pump may be a magnetic-driven sealless centrifugal pump, a direct-drive single- or double-seal centrifugal pump, a self-priming centrifugal pump, an air-diaphragm pump or any of a number of other types.
Each of these pumps presents different concerns for the maintenance manager in addition to the concerns presented by the in-tank pumps. The list sometimes seems endless, but each concern is legitimate and must be answered.
What are the Net Positive Suction Heat (NPSH) factors of each pump and application involved?
Is a "flooded suction" to the pump available? If so, is the liquid being pumped or introduced to the suction casing by gravity? With flooded suction available, priming is unnecessary. If not available, either manual priming would be necessary or a priming chamber should be considered.
Can the pump handle abrasives or be run dry? For how long?
The magnetic-driven sealless pump may be considered if the solution contains precious metals or has a low specific gravity (1.4 or lower) or the impeller was trimmed to handle the specific gravity. Magnetic-driven pumps totally isolate the process solution. Since they do not have mechanical seals, packing rings or shaft lip seals, they are referred to as sealless or leakproof. This added measure of safety could reduce environmental concerns and help the user stay within EPA regulations. However, magnetic-driven pumps should never be used with electroless plating solutions or cleaners containing ferrous metal fines. The particles will adhere to the magnet and act like a grinding wheel, eventually destroying the pump.
The mechanical-sealed pump with a single mechanical seal might be considered if the solution is not extremely toxic or contaminated with abrasives, and where slight leakage due to wear or failure of the seal would not present a problem. If temperatures greater than 140F are anticipated, or the solution contains abrasives, a double water flushed seal should be considered to cool and flush the abrasives off the process seal to prevent premature failure.
Pumps with priming chambers are effective when piping from the process tank is plumbed over the side of the tank, and gravity does not introduce liquid to the suction of the pump. If the pump were to be mounted higher than the liquid level in the tank, caution would need to be exercised and the NPSH would need to be calculated and applied. Pumps with priming chambers require priming only at initial startup.
Air-diaphragm pumps are usually the choice for waste treatment to pump heavy or abrasive sludges. These pumps may be used whenever NPSH calculations reveal a shortcoming in centrifugal pumps. With air, the maintenance manager's additional concerns might be as follows.
Is sufficient shop air available to operate the pumps, or will an additional compressor be required?
Would the pumps need oil lubrication for the ball check valves? Are the oil lubrication components standard with the pump, or do they need to be purchased separately?
What noise levels are expected by the pulsation of the pump? Is a muffler included?
Are pulsation dampeners needed on either the pump inlet or discharge plumbing to reduce vibration? Are they included with the pump?
Positive displacement pumps, such as peristaltic, gear or metering pumps, involved in most of the prior mentioned considerations and the addition of bypass pressure-relief valves may be required on the pump discharge.
2. TYPICAL SOLUTION flow patterns using eductor agitation.
Process engineer or chemist's concerns.
Will the chemistry or operation of the process be changed by the operation of the pump, filtration or agitation system? If so, in what ways? Will filtering particles from the solution result in a smoother deposit?
Will the pumps introduce air into the solution that may adhere to the flat surfaces of parts?
Will increased solution flow give better throwing power in low-current-density areas?
Can plating time be reduced?
Will stratification in any area of the process tank be reduced and particles swept off the tank bottom by the agitation?
Will more or less brightener or chemicals be needed because of the increased agitation?
If anode bags are used or curtains installed in front of the anodes, will there be a detrimental effect on the finish due to particles being forced by the pump agitation through the bag and into the solution?
Will the filtration rate be sufficient to remove the particles before they cause roughness on the plated parts?
A turnover rate of 10 to 20 times per hour may be needed to achieve the particle removal speed necessary to prevent this condition from occurring.
The plater's concerns.
Are the pumps, filters, plumbing, valves, agitation eductors or any of the other components such as hoses, etc., in the way?
The anodes must not be shaded with added equipment in front of them that decreases the exchange of positive/negative ions interacting in the bath.
If internal or external auxiliary anodes are needed on occasion, there must be room for immediate insertion and removal without obstruction.
Would the pump suction or discharge interfere with plating?
The shop owner, CEO or general manager's concerns are the bottom line and the greatest return on investment. Concerns may be the following.
Can we get along without it? If not, how did we get along without it until now?
What is the justification for adding or replacing the equipment?
How much will the installation or the additional and/or replacement equipment cost?
How long is the pay back?
Some of the previously cited decision-makers with their various concerns may also have a staff than can influence the decisions. Every member of the staff may have questions about the application. Therefore, whether the selection of the product begins with shop maintenance workers or the CEO, the majority of these concerns need be addressed. Satisfying the needs of the various personnel before selecting the system helps avoid problems.
Filtration media. After the pumps have been specified and turnover agreed upon, filtration media should be considered, if necessary. There are several effective filtration media available that will remove particulates from 100 microns down to submicron levels. The degree of automation required for the use of the equipment should be considered as well.
Media choice is left to the user. However, based on successful installations and past experience, the supplier will usually offer alternative methodologies such as depth-wound filter cartridges, flat paper or cellulose discs, horizontal or vertical plates, bags, cleanable sleeves, disposable fabric or backwashable permanent media. Each media has its pros and cons.
String-wound depth cartridge is the choice of filtration for the average plater because of its simplicity, high-solids-holding capacity and wide range of porosities available to remove progressively smaller particles. A 10-inch by two-and-a-half-inch diameter cartridge is equal to three-and-a-half sq ft of surface media.
For instance, when filtering iron from nickel, acid zinc or cadmium solutions, a filter with dimensions previously described and 15 micron retention will easily hold eight ounces of iron before loading. Sized at one cartridge per 50 gal of plating solution with a suitable pump to achieve an initial solution turnover rate of twice per hour, eight to 12 weeks between cartridge changes is not uncommon. For just a small extra capital investment, the filter chamber size could be doubled and two ten-inch filters per 50 gal of solution could provide 16 to 24 weeks between filter changes.
If mainly iron is filtered, the cartridges can be backwashed or soaked in a dilute acid solution to redissolve the iron. Also, an alkaline cleaner solution could be used to remove some oil and soil buildup in the filter. They could then be carefully rinsed and neutralized for several reuses prior to landfill disposal. If a spare change of filters is kept in stock, one set can be on-line while the other is soaked for reuse. Typically, two to four cartridges of 50 to 100 micron retention per 100 gal work best on cleaners.
One of the most common objections to using string-wound depth filters is that they are too bulky for landfill compared to disc bags. However, whenever any bulky material is sent to landfill for disposal, it is usually processed through a shredder or compactor first. Because of this, depth filters are no more of a problem to dispose of than any other media. Incineration may be considered in the future because polypropylene supports combustion and used cartridges can be used to reduce fuel costs.
Filter cartridges are also available in other configurations such as pleated material, melt-bonded poly-propylene free of organic sizing agents and a number of others, including membranes for electronic grade use. These membranes will filter down to 0.1 micron nominal or absolute, if necessary.
Carbon impregnated fibers as well as granulated carbon filter cartridges are also available in the same size configuration and may be mixed selectively with the other filter cartridges in the filter chamber to achieve carbon adsorption of unwanted organics. Where heavy dirt loads are encountered, it is recommended that the solution be filtered first and then carbon treated in a separate chamber downstream on a bypass.
Disc filter sets, composed of paper, polypropylene or cellulose fiber, are another type of filter media used in industry. The discs may be used alone with paper, or precoated with filter aid to achieve a faster and finer micron retention of the particulate filtered. The downside to discs is their low-solids-holding capacity. They need to be cleaned or serviced often, compared to depth-wound string filters. In heavy particulate applications such as acid zinc or cadmium plating with high iron content, daily cleaning is common, especially on barrel lines.
Wheel platers are the connoisseurs of disc filtration systems. They like them because of their rapid filtration of fine particulates. They buff and polish between steps in many shops, so introduction of buffing compound into the plating bath is common. However, since most buffing compound contains animal fat and greases, carbon needs to be used on the precoat of the discs to remove this organic contamination. When using powdered carbon on the discs, the brighteners in the acid copper and bright nickel baths need to be replenished continuously. If bulk granulated carbon is used on a by-pass in a separate chamber downstream from the filter discs, brightener depletion is much slower.
Bag filters are used in electroless nickel and copper plating because autocatalytic baths have a tendency to plate out on any surface they contact. Bags are the easiest filters to use in these applications, since they are a surface-type media. When they are plated with metal, the operator can see the plate-out and service the bags. When discs or depth filters are used in an enclosed chamber, the operator cannot see the plate-out. Plate- out of the entire bath could occur if the problem is not detected and corrected immediately.
Also, bags are a favorite where high loading of coarse solids occurs, such as in acid dip tanks and running water rinses. If the solution is not slimy and does not coat the bag surface, then the bag will load as vacuum cleaner bag does. However, alkaline cleaner baths are usually slimy, so the particles they contain blind off the bag surface quickly, requiring frequent service. On cleaner or acid dip tanks where oil contamination is a problem, an additional coalescing filter cartridge installed downstream of the bag filter may remove the oil. Auto-gravity filters are also ideal for this application.
Coalescing cartridges will separate any dissimilar liquids with a difference in specific gravity of 0.09 or greater. The prefilter removes the unwanted particulate so the coalescing filter will last indefinitely as long as no particulate is introduced. The oil coalesces from tiny droplets into large ones that float to the top of the water in the chamber. This oil can be manually or automatically bled off. A recycler can then recycle the concentrated oil.
Permanent-media filtration systems are a choice of platers for unattended operation and where disposable filter media or the labor to change it is objectionable. When used in a suitable system, the plating solution is kept clean and the filter media is restored to a clean state each time the system automatically backwashes itself. The up side of this system is that it operates in the top 20 pct of the filtration flow range at all times as compared to non-backwashed media where flow diminishes as the media loads. The backwashable sand filtration system is also an excellent choice for polishing clarified wastewater from the treatment system. A key advantage of the backwashable pressure filtration system is that it cleans itself automatically.
Disposable fabric filtration systems are often referred to as automatic indexing gravity filters. They use an array of tanks, conveyors, pulleys, motors, pumps and float level controls to index disposable filter media over a stationary conveyor. This type of system effectively removes particulates from phosphating solutions, carbonized deposits from quench oil, copper fines from printed circuit board deburring operations and high-solids solutions. The micron retention of the available fabric ranges from one to 125 microns.
Recessed plate filter presses are used in about every precipitation wastewater treatment plant to dewater the underflow of clarifiers. A typical tube-type or slant-plate clarifier with an inverted pyramid bottom or cone achieves approximately 0.5 pct solids on the bottom. If a flat bottom is used and a sludge rake or scraper sweeps the bottom of the clarifier, three pct solids may be achieved if proper flocculation and settling occur. However, the slurry still needs to be thickened to eight or nine pct solids through a sludge thickener before pumping through a filter press, otherwise a much larger press would be needed and would be cost prohibitive.
Where liquids having extremely high solids, usually five to 10 pct, need to be dewatered, an air-diaphragm pump operated from 60 to 90 psi usually is the choice to transfer the thickened slurry through the filter press. The polypropylene filter plates have recessed cavities of one-half to three-quarter inch each with a 20 micron polypropylene filter cloth. As the plates are sandwiched together under pressure, every pair of plates provides a one to one-and-a-half-inch cavity to retain the solids as the slurry is pumped through the plates. This type of filtration system is capable of achieving 30 to 35 pct solids with standard filter cloths. Using membrane-type filter cloths with high psi pumps, solids of up to 60 pct have been achieved. However, the cost of this type of system is much greater than the standard filter press.
Capacities of one-half to 50 or more cubic feet are readily available and applications may be sized accordingly. The general rule of thumb in sizing a filter press for the average plating or printed circuit shop is two-cu-ft capacity minimum for every 25 gpm flow through the clarifier. This sizing arrangement will usually provide a full eight-hour shift before dumping is necessary. The time required to dump and clean a filter press is minimal, usually 15 to 20 min by one worker.
Carbon purification is the choice of platers to adsorb organic contamination from plating solutions, rinses, etches and cleaners.
If total purification is required in a batch treatment, the solution is transferred to a treatment tank and temperature raised above 140F. Hydrogen peroxide is sometimes added to the solution. Three to 12-and-one-half lbs of powdered carbon per 100 gal of solution are added, stirred and allowed to sit four to eight hours. The carbon will settle to the bottom, along with the adsorbed contaminants. The clean liquid can be decanted or pumped back to the process tanks through a filtration media. The carbon sludge is then batch treated and disposed of with the rest of the hazardous waste.
The frequency of the batch carbon treatment procedure may be greatly reduced by circulating the plating solutions continuously through a chamber containing granulated carbon. In this way, a constant balance of brighteners to achieve uniform ductility will be achieved.
An effective way to accomplish purification is to install a separate canister containing granular carbon on a bypass with a valve controlling the flow. After the solution has passed through the filter chamber to remove particulates, a portion (about five to 20 pct) may be directed through the granulated carbon on a continuous basis to remove the unwanted organics and then through a coalescer to remove oil. Granular carbon will remove organic breakdown products of the brighteners as well as oil, grease, etc., without stripping the brightener system.
The canisters holding the carbon have either fine mesh screens or fine retention depth filters of one to three microns to trap any carbon attempting to exit the vessel. This type of granulated carbon canister is also widely used as a portable system on a cart with its own pump, hoses, valves, etc., to recirculate solutions needing carbon treatment.
Caveat Emptor. An experienced sales application consultant will attempt to gather the pertinent data for the application to satisfy all of the concerns of the team involved in the purchase. The ultimate goal is to have a successful installation.
MSDS supply the chemical composition of the materials and must be obtained wherever possible. These documents contain information as to flash points, toxicity and the constituents. It is essential that the chemical compatibility, pH, pressure, temperature, limitation and flow performance curves be researched for the pumps, filters and components of the applications. You also must determine what type and amount of solids are to be removed and how fast. And, are abrasives present or oil or dissimilar liquids that need to be separated? All of this data must be used to select the material and components for the application.
In the end, the rule of Caveat Emptor (let the buyer beware), usually applies. If you let the application consultant make the recommendation, and purchase the product recommended, a reputable manufacturer will stand behind the product. Real products applied to real applications repeatedly offer the customer the greatest assurance and the most peace of mind that the proper product and application have been recommended.
Each person in the company has concerns and requirements when selecting pumps and filters. However, each may have a different opinion about the application and equipment. It is important to consider all of the concerns.
Facility manager's concerns.
What are the utility requirements, such as the amp draw of the mo-tors, voltage requirements, power consumption?
Shop air requirements at scfm or psi?
Dimensions of the equipment or a footprint?
Maintenance manager's concerns.
What is required for proper installation?
In addition to items purchased, what components, such as pipe, fittings, valves, electrical components, switches, etc. are needed?
What type of pump is best for the particular application?
Will the pumps be mounted inside or outside the tank?
Questions about in-tank vertical pumps that need to be addressed.
How will chemicals and fumes affect the motors?
Will the motor's coating withstand the harsh environment without peeling and contaminating the solution?
Will the motor bearings hold up? Are the bearings sealed or unsealed and what service is required for them?
What is the service factor of the motors?
Are they insulated for chemical duty?
Will the pumps introduce air into the solution?
Are drip shields available for the motors?
Are all wet-end components compatible with each constituent of the chemical being pumped?
Can the pump run dry without damage?
In electroless plating where the metal tends to plate out and deposit on plastic, can the wet-end components of the pump withstand the effects of stripping solution?
What temperature range will the pump withstand without damage?
What are the psi to temperature ratios the pump will operate under?
Will the pump run against a closed discharge without damage? How long? Will the internal components warp under heat?
Questions to ask when considering a vertical pump mounted outside the tank.
Will the pumped liquid be kept in the pump column or will it pump up the column when under a closed discharge?
Does the pump have a port seal at the mounting plate to protect the motor bearing from corrosive fumes?
What spare parts should be kept in inventory?
Are there any parts susceptible to wear, and what preventive maintenance is needed to keep the pump running at its optimum?
When repairs are necessary, can the pump be removed and repaired at the shop, or does it need to be shipped back to the factory?
Are there factory authorized dealers in the area?
What are the return authorization procedures?
How long is the pump warranty, and what is covered?
Are there any special tools needed for disassembly and repair?
Does the pump have a parts list and operating instructions?
1. TYPICAL VERTICAL pump installations.
In addition to most of the preceding vertical pump concerns, there are more concerns relating to out-of-tank pumps.
The horizontal pump may be a magnetic-driven sealless centrifugal pump, a direct-drive single- or double-seal centrifugal pump, a self-priming centrifugal pump, an air-diaphragm pump or any of a number of other types.
Each of these pumps presents different concerns for the maintenance manager in addition to the concerns presented by the in-tank pumps. The list sometimes seems endless, but each concern is legitimate and must be answered.
What are the Net Positive Suction Heat (NPSH) factors of each pump and application involved?
Is a "flooded suction" to the pump available? If so, is the liquid being pumped or introduced to the suction casing by gravity? With flooded suction available, priming is unnecessary. If not available, either manual priming would be necessary or a priming chamber should be considered.
Can the pump handle abrasives or be run dry? For how long?
The magnetic-driven sealless pump may be considered if the solution contains precious metals or has a low specific gravity (1.4 or lower) or the impeller was trimmed to handle the specific gravity. Magnetic-driven pumps totally isolate the process solution. Since they do not have mechanical seals, packing rings or shaft lip seals, they are referred to as sealless or leakproof. This added measure of safety could reduce environmental concerns and help the user stay within EPA regulations. However, magnetic-driven pumps should never be used with electroless plating solutions or cleaners containing ferrous metal fines. The particles will adhere to the magnet and act like a grinding wheel, eventually destroying the pump.
The mechanical-sealed pump with a single mechanical seal might be considered if the solution is not extremely toxic or contaminated with abrasives, and where slight leakage due to wear or failure of the seal would not present a problem. If temperatures greater than 140F are anticipated, or the solution contains abrasives, a double water flushed seal should be considered to cool and flush the abrasives off the process seal to prevent premature failure.
Pumps with priming chambers are effective when piping from the process tank is plumbed over the side of the tank, and gravity does not introduce liquid to the suction of the pump. If the pump were to be mounted higher than the liquid level in the tank, caution would need to be exercised and the NPSH would need to be calculated and applied. Pumps with priming chambers require priming only at initial startup.
Air-diaphragm pumps are usually the choice for waste treatment to pump heavy or abrasive sludges. These pumps may be used whenever NPSH calculations reveal a shortcoming in centrifugal pumps. With air, the maintenance manager's additional concerns might be as follows.
Is sufficient shop air available to operate the pumps, or will an additional compressor be required?
Would the pumps need oil lubrication for the ball check valves? Are the oil lubrication components standard with the pump, or do they need to be purchased separately?
What noise levels are expected by the pulsation of the pump? Is a muffler included?
Are pulsation dampeners needed on either the pump inlet or discharge plumbing to reduce vibration? Are they included with the pump?
Positive displacement pumps, such as peristaltic, gear or metering pumps, involved in most of the prior mentioned considerations and the addition of bypass pressure-relief valves may be required on the pump discharge.
2. TYPICAL SOLUTION flow patterns using eductor agitation.
Process engineer or chemist's concerns.
Will the chemistry or operation of the process be changed by the operation of the pump, filtration or agitation system? If so, in what ways? Will filtering particles from the solution result in a smoother deposit?
Will the pumps introduce air into the solution that may adhere to the flat surfaces of parts?
Will increased solution flow give better throwing power in low-current-density areas?
Can plating time be reduced?
Will stratification in any area of the process tank be reduced and particles swept off the tank bottom by the agitation?
Will more or less brightener or chemicals be needed because of the increased agitation?
If anode bags are used or curtains installed in front of the anodes, will there be a detrimental effect on the finish due to particles being forced by the pump agitation through the bag and into the solution?
Will the filtration rate be sufficient to remove the particles before they cause roughness on the plated parts?
A turnover rate of 10 to 20 times per hour may be needed to achieve the particle removal speed necessary to prevent this condition from occurring.
The plater's concerns.
Are the pumps, filters, plumbing, valves, agitation eductors or any of the other components such as hoses, etc., in the way?
The anodes must not be shaded with added equipment in front of them that decreases the exchange of positive/negative ions interacting in the bath.
If internal or external auxiliary anodes are needed on occasion, there must be room for immediate insertion and removal without obstruction.
Would the pump suction or discharge interfere with plating?
The shop owner, CEO or general manager's concerns are the bottom line and the greatest return on investment. Concerns may be the following.
Can we get along without it? If not, how did we get along without it until now?
What is the justification for adding or replacing the equipment?
How much will the installation or the additional and/or replacement equipment cost?
How long is the pay back?
Some of the previously cited decision-makers with their various concerns may also have a staff than can influence the decisions. Every member of the staff may have questions about the application. Therefore, whether the selection of the product begins with shop maintenance workers or the CEO, the majority of these concerns need be addressed. Satisfying the needs of the various personnel before selecting the system helps avoid problems.
Filtration media. After the pumps have been specified and turnover agreed upon, filtration media should be considered, if necessary. There are several effective filtration media available that will remove particulates from 100 microns down to submicron levels. The degree of automation required for the use of the equipment should be considered as well.
Media choice is left to the user. However, based on successful installations and past experience, the supplier will usually offer alternative methodologies such as depth-wound filter cartridges, flat paper or cellulose discs, horizontal or vertical plates, bags, cleanable sleeves, disposable fabric or backwashable permanent media. Each media has its pros and cons.
String-wound depth cartridge is the choice of filtration for the average plater because of its simplicity, high-solids-holding capacity and wide range of porosities available to remove progressively smaller particles. A 10-inch by two-and-a-half-inch diameter cartridge is equal to three-and-a-half sq ft of surface media.
For instance, when filtering iron from nickel, acid zinc or cadmium solutions, a filter with dimensions previously described and 15 micron retention will easily hold eight ounces of iron before loading. Sized at one cartridge per 50 gal of plating solution with a suitable pump to achieve an initial solution turnover rate of twice per hour, eight to 12 weeks between cartridge changes is not uncommon. For just a small extra capital investment, the filter chamber size could be doubled and two ten-inch filters per 50 gal of solution could provide 16 to 24 weeks between filter changes.
If mainly iron is filtered, the cartridges can be backwashed or soaked in a dilute acid solution to redissolve the iron. Also, an alkaline cleaner solution could be used to remove some oil and soil buildup in the filter. They could then be carefully rinsed and neutralized for several reuses prior to landfill disposal. If a spare change of filters is kept in stock, one set can be on-line while the other is soaked for reuse. Typically, two to four cartridges of 50 to 100 micron retention per 100 gal work best on cleaners.
One of the most common objections to using string-wound depth filters is that they are too bulky for landfill compared to disc bags. However, whenever any bulky material is sent to landfill for disposal, it is usually processed through a shredder or compactor first. Because of this, depth filters are no more of a problem to dispose of than any other media. Incineration may be considered in the future because polypropylene supports combustion and used cartridges can be used to reduce fuel costs.
Filter cartridges are also available in other configurations such as pleated material, melt-bonded poly-propylene free of organic sizing agents and a number of others, including membranes for electronic grade use. These membranes will filter down to 0.1 micron nominal or absolute, if necessary.
Carbon impregnated fibers as well as granulated carbon filter cartridges are also available in the same size configuration and may be mixed selectively with the other filter cartridges in the filter chamber to achieve carbon adsorption of unwanted organics. Where heavy dirt loads are encountered, it is recommended that the solution be filtered first and then carbon treated in a separate chamber downstream on a bypass.
Disc filter sets, composed of paper, polypropylene or cellulose fiber, are another type of filter media used in industry. The discs may be used alone with paper, or precoated with filter aid to achieve a faster and finer micron retention of the particulate filtered. The downside to discs is their low-solids-holding capacity. They need to be cleaned or serviced often, compared to depth-wound string filters. In heavy particulate applications such as acid zinc or cadmium plating with high iron content, daily cleaning is common, especially on barrel lines.
Wheel platers are the connoisseurs of disc filtration systems. They like them because of their rapid filtration of fine particulates. They buff and polish between steps in many shops, so introduction of buffing compound into the plating bath is common. However, since most buffing compound contains animal fat and greases, carbon needs to be used on the precoat of the discs to remove this organic contamination. When using powdered carbon on the discs, the brighteners in the acid copper and bright nickel baths need to be replenished continuously. If bulk granulated carbon is used on a by-pass in a separate chamber downstream from the filter discs, brightener depletion is much slower.
Bag filters are used in electroless nickel and copper plating because autocatalytic baths have a tendency to plate out on any surface they contact. Bags are the easiest filters to use in these applications, since they are a surface-type media. When they are plated with metal, the operator can see the plate-out and service the bags. When discs or depth filters are used in an enclosed chamber, the operator cannot see the plate-out. Plate- out of the entire bath could occur if the problem is not detected and corrected immediately.
Also, bags are a favorite where high loading of coarse solids occurs, such as in acid dip tanks and running water rinses. If the solution is not slimy and does not coat the bag surface, then the bag will load as vacuum cleaner bag does. However, alkaline cleaner baths are usually slimy, so the particles they contain blind off the bag surface quickly, requiring frequent service. On cleaner or acid dip tanks where oil contamination is a problem, an additional coalescing filter cartridge installed downstream of the bag filter may remove the oil. Auto-gravity filters are also ideal for this application.
Coalescing cartridges will separate any dissimilar liquids with a difference in specific gravity of 0.09 or greater. The prefilter removes the unwanted particulate so the coalescing filter will last indefinitely as long as no particulate is introduced. The oil coalesces from tiny droplets into large ones that float to the top of the water in the chamber. This oil can be manually or automatically bled off. A recycler can then recycle the concentrated oil.
Permanent-media filtration systems are a choice of platers for unattended operation and where disposable filter media or the labor to change it is objectionable. When used in a suitable system, the plating solution is kept clean and the filter media is restored to a clean state each time the system automatically backwashes itself. The up side of this system is that it operates in the top 20 pct of the filtration flow range at all times as compared to non-backwashed media where flow diminishes as the media loads. The backwashable sand filtration system is also an excellent choice for polishing clarified wastewater from the treatment system. A key advantage of the backwashable pressure filtration system is that it cleans itself automatically.
Disposable fabric filtration systems are often referred to as automatic indexing gravity filters. They use an array of tanks, conveyors, pulleys, motors, pumps and float level controls to index disposable filter media over a stationary conveyor. This type of system effectively removes particulates from phosphating solutions, carbonized deposits from quench oil, copper fines from printed circuit board deburring operations and high-solids solutions. The micron retention of the available fabric ranges from one to 125 microns.
Recessed plate filter presses are used in about every precipitation wastewater treatment plant to dewater the underflow of clarifiers. A typical tube-type or slant-plate clarifier with an inverted pyramid bottom or cone achieves approximately 0.5 pct solids on the bottom. If a flat bottom is used and a sludge rake or scraper sweeps the bottom of the clarifier, three pct solids may be achieved if proper flocculation and settling occur. However, the slurry still needs to be thickened to eight or nine pct solids through a sludge thickener before pumping through a filter press, otherwise a much larger press would be needed and would be cost prohibitive.
Where liquids having extremely high solids, usually five to 10 pct, need to be dewatered, an air-diaphragm pump operated from 60 to 90 psi usually is the choice to transfer the thickened slurry through the filter press. The polypropylene filter plates have recessed cavities of one-half to three-quarter inch each with a 20 micron polypropylene filter cloth. As the plates are sandwiched together under pressure, every pair of plates provides a one to one-and-a-half-inch cavity to retain the solids as the slurry is pumped through the plates. This type of filtration system is capable of achieving 30 to 35 pct solids with standard filter cloths. Using membrane-type filter cloths with high psi pumps, solids of up to 60 pct have been achieved. However, the cost of this type of system is much greater than the standard filter press.
Capacities of one-half to 50 or more cubic feet are readily available and applications may be sized accordingly. The general rule of thumb in sizing a filter press for the average plating or printed circuit shop is two-cu-ft capacity minimum for every 25 gpm flow through the clarifier. This sizing arrangement will usually provide a full eight-hour shift before dumping is necessary. The time required to dump and clean a filter press is minimal, usually 15 to 20 min by one worker.
Carbon purification is the choice of platers to adsorb organic contamination from plating solutions, rinses, etches and cleaners.
If total purification is required in a batch treatment, the solution is transferred to a treatment tank and temperature raised above 140F. Hydrogen peroxide is sometimes added to the solution. Three to 12-and-one-half lbs of powdered carbon per 100 gal of solution are added, stirred and allowed to sit four to eight hours. The carbon will settle to the bottom, along with the adsorbed contaminants. The clean liquid can be decanted or pumped back to the process tanks through a filtration media. The carbon sludge is then batch treated and disposed of with the rest of the hazardous waste.
The frequency of the batch carbon treatment procedure may be greatly reduced by circulating the plating solutions continuously through a chamber containing granulated carbon. In this way, a constant balance of brighteners to achieve uniform ductility will be achieved.
An effective way to accomplish purification is to install a separate canister containing granular carbon on a bypass with a valve controlling the flow. After the solution has passed through the filter chamber to remove particulates, a portion (about five to 20 pct) may be directed through the granulated carbon on a continuous basis to remove the unwanted organics and then through a coalescer to remove oil. Granular carbon will remove organic breakdown products of the brighteners as well as oil, grease, etc., without stripping the brightener system.
The canisters holding the carbon have either fine mesh screens or fine retention depth filters of one to three microns to trap any carbon attempting to exit the vessel. This type of granulated carbon canister is also widely used as a portable system on a cart with its own pump, hoses, valves, etc., to recirculate solutions needing carbon treatment.
Caveat Emptor. An experienced sales application consultant will attempt to gather the pertinent data for the application to satisfy all of the concerns of the team involved in the purchase. The ultimate goal is to have a successful installation.
MSDS supply the chemical composition of the materials and must be obtained wherever possible. These documents contain information as to flash points, toxicity and the constituents. It is essential that the chemical compatibility, pH, pressure, temperature, limitation and flow performance curves be researched for the pumps, filters and components of the applications. You also must determine what type and amount of solids are to be removed and how fast. And, are abrasives present or oil or dissimilar liquids that need to be separated? All of this data must be used to select the material and components for the application.
In the end, the rule of Caveat Emptor (let the buyer beware), usually applies. If you let the application consultant make the recommendation, and purchase the product recommended, a reputable manufacturer will stand behind the product. Real products applied to real applications repeatedly offer the customer the greatest assurance and the most peace of mind that the proper product and application have been recommended.
Fasteners and Finishes
The plating source is often the blame for many automated assembly problems. The manufacturer requests a coating or plating of a certain type from the finisher. When the manufacturer receives the final product he runs off with it, only to call back in a few days to say that the plating is clogging up the assembly process. When the problem involves recalls and expensive warranty costs, the manufacturer may want a percentage paid by the finisher. This month's column talks about the interfaces of finishes with automated assembly tooling, processes and materials.
Automated processes are of two types. The high-tech version is completely controlled by robotic function. The other involves feeder tubes and fancy tools, but has a human operator somewhere in the process. Robotic installation requires that a shipment of material be 100 pct free of foreign material. This is one of the major complaints that assemblers have about finishers in general. Mixed parts occur because some stick in the barrels and are dragged over, stock is mixed in the plant by accident, and sometimes they come mixed to the finisher from the heat treater. Receiving inspection should be a basic requirement of all plating operations.
Robots function tirelessly, but they have an I.Q. of about 15. Installation of a bolt without threads or the wrong size will be attempted. If the part doesn't go in the hole, the robot stops and the system goes down. Mixed stock will not function in automated systems. If the problem is excessive (beyond the point where a simple sorting could separate the parts), special high-speed sorting can be performed. Some companies guarantee 100-pct no-mix conformance, but it costs. The additional charges may have to be passed on to the manufacturer. A small percentage of mixes are generally not a problem unless the assembly process is fully robotic.
While some complaints may be forthcoming, human operators will just toss aside incorrect and damaged parts. The major concern is where the parts jam feed lines and bowls. Then the downtime can be as much as 30 pct, and the manufacturer will come looking for compensation.
The type of finish applied often causes feed and assembly problems. Oil-based coatings tend to coat the plastic feed tubes and clog the system, stopping the flow of parts and the line process. While one common plant solution is to increase the feed pressure, the cure is worse than the problem. The parts tend to break loose suddenly and shoot out the feed tubes at high velocity.
Many new coatings are metallic-based paints. The flaking off of pieces in feed hoppers causes a poor finish on the part, leading to early corrosion. It also causes feed tube and assembly problems with the plating dust. In many areas, the airborne metallic particles are not allowed by OSHA and local environmental regulations. One study on the amount of time that parts spend in a vibratory-type feed hopper showed that not all the parts were fed out after 30 minutes. The last part in several cases took about 45 minutes to clear the bowl. That is a lot of time to be banging around. In addition to flaking and dusting, the likelihood of parts being nicked or otherwise damaged is great. Soft platings are especially prone to damage.
If the part has a recessed head drive, is of a small diameter with fine pitch threads and/or has an integrated washer, it is not a candidate for the thick organics and metallic coatings so popular today. Numerous companies running production coatings today will quote exceptions to the specification if asked to run this type coating on a "problem" part. Sorting for defects associated with these concern areas will use up as much as 35 pct of available labor.
It is a good practice to ask how the parts are going to be used when they arrive for plating. Uses that have potential for poor assembly and fit or will be hopper fed should be discussed with the customer to see if an alternate coating would be acceptable. Parts that are slated for robotic assembly should have a rider attached to the order requesting full sorting and 100 pct no-mix requirements, with an additional charge for this process.
Automated processes are of two types. The high-tech version is completely controlled by robotic function. The other involves feeder tubes and fancy tools, but has a human operator somewhere in the process. Robotic installation requires that a shipment of material be 100 pct free of foreign material. This is one of the major complaints that assemblers have about finishers in general. Mixed parts occur because some stick in the barrels and are dragged over, stock is mixed in the plant by accident, and sometimes they come mixed to the finisher from the heat treater. Receiving inspection should be a basic requirement of all plating operations.
Robots function tirelessly, but they have an I.Q. of about 15. Installation of a bolt without threads or the wrong size will be attempted. If the part doesn't go in the hole, the robot stops and the system goes down. Mixed stock will not function in automated systems. If the problem is excessive (beyond the point where a simple sorting could separate the parts), special high-speed sorting can be performed. Some companies guarantee 100-pct no-mix conformance, but it costs. The additional charges may have to be passed on to the manufacturer. A small percentage of mixes are generally not a problem unless the assembly process is fully robotic.
While some complaints may be forthcoming, human operators will just toss aside incorrect and damaged parts. The major concern is where the parts jam feed lines and bowls. Then the downtime can be as much as 30 pct, and the manufacturer will come looking for compensation.
The type of finish applied often causes feed and assembly problems. Oil-based coatings tend to coat the plastic feed tubes and clog the system, stopping the flow of parts and the line process. While one common plant solution is to increase the feed pressure, the cure is worse than the problem. The parts tend to break loose suddenly and shoot out the feed tubes at high velocity.
Many new coatings are metallic-based paints. The flaking off of pieces in feed hoppers causes a poor finish on the part, leading to early corrosion. It also causes feed tube and assembly problems with the plating dust. In many areas, the airborne metallic particles are not allowed by OSHA and local environmental regulations. One study on the amount of time that parts spend in a vibratory-type feed hopper showed that not all the parts were fed out after 30 minutes. The last part in several cases took about 45 minutes to clear the bowl. That is a lot of time to be banging around. In addition to flaking and dusting, the likelihood of parts being nicked or otherwise damaged is great. Soft platings are especially prone to damage.
If the part has a recessed head drive, is of a small diameter with fine pitch threads and/or has an integrated washer, it is not a candidate for the thick organics and metallic coatings so popular today. Numerous companies running production coatings today will quote exceptions to the specification if asked to run this type coating on a "problem" part. Sorting for defects associated with these concern areas will use up as much as 35 pct of available labor.
It is a good practice to ask how the parts are going to be used when they arrive for plating. Uses that have potential for poor assembly and fit or will be hopper fed should be discussed with the customer to see if an alternate coating would be acceptable. Parts that are slated for robotic assembly should have a rider attached to the order requesting full sorting and 100 pct no-mix requirements, with an additional charge for this process.
Troubleshooting for Electrocoating
Electrocoating provides a decorative and protective finish. Common coating defects may adversely affect these properties, so it is important that electrocoat users develop basic, effective troubleshooting skills.
Troubleshooting process. It is important to understand troubleshooting in order to develop sound, workable solutions to problems. There are five steps to troubleshooting.
1. Define the problem. Defining the problem is the first step in the troubleshooting process. It characterizes the problem by answering several questions:
Isolation—Is the problem in the operation of the system or appearance related?Identification—What type of defect is occurring and does it occur on all parts? Location—Does the problem move around on the part or is it always in the same area? Timing—When did the problem start? Duration—Is it constant or sporadic?
Problems do not occur without something having changed. Problems are not solved unless something is changed.
2. Identify the root cause. Identifying possible root causes is step two in the troubleshooting process. It is necessary to understand common causes for the defects. There could be several bath variables and process areas to investigate. Commonly asked questions include the following.
Correlation—What are the common causes for this type of defect? Have there been any recent changes made to the line? Is there a correlation between tank parameter test data and the appearance of the problem?
Mechanical—Is the testing equipment functioning properly? Procedural—Have the testing procedures been followed?
3. Determine corrective action. Determining the appropriate corrective action is the next step in the troubleshooting process. This step is probably the most time consuming. Developing a logical plan that tests one variable at a time is crucial to identifying potential solutions. Answering the following questions should help develop a practical action plan.
Which variables can be tested on line quickly?
Which variables can be tested with little disruption to production?
Which variables can be tested on line in the paint lab?
Which variables need technical support from the suppliers?
4. Implement corrective action. Implementing corrective action is the success step in the troubleshooting process. As each variable is tested, it will either be eliminated or identified as a possible solution. There may be multiple solutions and in rare cases there may be no solution. In the cases where no solutions have been found, it is necessary to start the troubleshooting process again by redefining the problem.
5. Follow-up. Follow-up is the last step in the troubleshooting process. It involves determining what permanent changes are needed to prevent the problem from recurring. This troubleshooting model provides guidance for identifying, reacting to and solving problems and if properly followed and documented, it can provide a faster response for future problems.
Preventive action methods. Troubleshooting should be more than a reaction to problems. Preventive maintenance is often overlooked as a tool to guard against problems and defects. It is not possible to list every housekeeping item or maintenance program associated with an electrocoat system, but there are essential mechanical, chemical and substrate considerations.
Tank agitation. Agitation of a paint tank is necessary for paint suspension, filtration and removing excess heat generated from pumping and coating. Proper agitation is dependent on the header/eductor system and the circulation pump. Broken or misaligned eductors can cause appearance defects in production and dead zones in the paint tank. A malfunctioning pump can cause poor bath circulation, foam and appearance defects. Excessive tank agitation can cause parts to fall. The velocity of the paint in recirculation lines should normally fall between seven and ten fps. Semi-annual tank cleanings should be performed to check agitation, and weekly cleaning of the pump screens will prevent blockage.
Oven. The oven is critical to the final coating appearance and the desired performance properties. It is recommended that the oven buildup be monitored and cleaned out when necessary. Oven temperature recorders should be run semi-annually to ensure correct oven balance and dehydration zone temperatures.
Rectifier. The rectifier should be checked yearly for ripple. It should not exceed five pct under anticipated load conditions. The amperage and voltage displays should also be checked to ensure calibration accuracy. There should be no stray voltage to the paint tank during non-production hours.
Electrodes. The electrodes should be checked weekly for degradation, proper operation of supply and return flows and to ensure electric leads are connected. Periodic checks of each electrode's amperage draw can be used to monitor anode performance. It is important to maintain a 4:1 or lower ratio of coating surface to electrode (based on a two-minute immersion time).
Anolyte/catholyte. The anolyte/catholyte is needed to remove excess acid/base from the paint bath and should be checked for proper liquid level, proper functioning of the conductivity set-point indicator and probe, water supply availability and that the supply and return flows are operational.
Racking. Racking includes design, part loading and cleaning. There should be specially designed racks available for odd-shaped parts and spring-loaded hooks for small parts. It is recommended to have one contact point for part grounding and to handle them in a way as to eliminate liquid pooling, air pockets, falling off and contact with other parts. Maintaining clean racks and contact points will help prevent rack buildup and coating failures. The grounding system should be checked yearly for wear and good contact.
Rinsing. Ensure the rinse system is operating monthly without any plugged or misdirected nozzles. Make sure spraying is contained within the tank, and the recirculated rinse flow is balanced from stage to stage. Check for a buildup of paint solids and parts that have fallen in the tank. The headers should be cleaned periodically to remove any settled material from the piping and pressure maintained between five and ten psi.
Filtration. Filtration of the electrocoat tank includes both bag filters and ultrafilters. Bag filters should be changed when the pressure differential inlet to outlet is five psi. If oil absorbent media is being used, it should be changed frequently. The ultrafilter flux rate should be checked daily using the site gauges and cleaner per the manufacturer's recommendations. Most manufacturers recommend a cleaning at 70 pct of the stabilized flux rate, or membranes can be irreversibly fouled, shortening life span and making them more difficult to clean. The ultrafilter pump should be monitored by pressure gauges.
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Cleaning process. Proper cleaning parameters will allow for removal of substrate contaminants such as stamping oils, surface dirt, fibers and weld smut. Whether an acid or alkaline cleaner is used, the concentration and the process time must be maintained and monitored daily. This includes any auxiliary cleaning steps such as shot blasting and pickling. A clean substrate is necessary for proper pretreating and coating. Dirty or contaminated substrate surfaces will cause final appearance and/or performance problems leading to rejected parts and rework.
Pretreatment process. Pretreatment functions as a conversion coating for improved paint adhesion and performance. It is crucial that this process be closely monitored and followed per the supplier's recommendations. The four basics to optimum pretreatment chemistry require monitoring of time, temperature, pressure and concentration. Routine testing for proper coating weights and crystal morphology should also be performed because the final appearance and performance of the electrocoated part is only as good as its preparation.
Water. High-quality water is essential for operation of an electrocoat system. Quality water is characterized by low conductivity, less than 10 micro mhos/cm for deionized or 20 micro mhos/cm for reverse osmosis, low silica levels and microbe free. It is recommended to have a minimum of two water sources, either two alternately functioning units or one unit plus water storage capability. Resin bed cleanings and regeneration procedures should be followed.
Substrate. Substrate quality is the first consideration in achieving a quality finish. There are many types of metals used in electrocoating ranging from aluminum to cold-rolled steel and from galvanized to heat treated metals. Using the first in, first out rule will keep substrates clean. Protective storage conditions will aid in the prevention of flash rusting and other surface defects.
Operating parameter effects. All systems, from cleaner and pretreatment through electrocoat, have specifications that recommend optimal ranges of operation. Understanding how each specification affects the appearance and performance of the coating will allow for corrective adjustments. Also, through accurate testing and charting, a historical picture of the system can be built and the occurrence of defects minimized.
Bath solids. This includes the pigments and non-volatile components of paint. Low bath solids cause lower film thickness, decreased throwing power, higher rupture voltage and higher ultrafilter flux rate. Low bath solids occur from normal excessive replenishment additions of paste.
Pigment to binder ratio. Low pigment to binder ratios cause higher gloss, decreased throwing power, less hiding and more cratering. Low pigment levels occur from excessive replenishment additions of resin and settling in the tank. High pigment to binder ratios cause lower gloss, increased throwing power, settling in the bath and rinses, and it makes the film more sensitive to water spotting. High pigment levels occur from excessive additions of paste.
Bath pH. High bath pH for cationic systems can cause tank settling, dirt, a decrease in ultrafilter permeate rates and sensitivity to streaking. High pH can occur from excessive anolyte purges, excessive replenishment and caustic contamination from carryover or deionized water. Low pH occurs from excessive acid levels and can cause redissolution. Potential causes of low pH are deficient anolyte purges, anolyte leakage in the paint tank, insufficient membrane surface, membranes surface plugging, excessive acid additions and acid contamination from carryover or poor quality deionized water.
Low bath pH for anionic systems also can cause tank settling, dirt, a decrease in ultrafilter permeate rates and sensitivity to streaking. Low bath pH occurs from excessive ultrafilter purge, excessive replenishment, and acid contamination from carryover or deionized water. High pH occurs from insufficient ultrafilter purges, excessive amine additions and caustic contamination from carryover or poor quality deionized water.
Bath conductivity. Low bath conductivity can cause poor throwing power, low film build and roughness. Low conductivity is caused by excessive ultrafilter purges and low bath solids. High bath conductivity can cause rupturing, high film build and roughness. High conductivity is caused by high bath solids and ionic contamination from carryover or poor quality deionized water.
Solvent. Low solvent levels can cause low film builds, higher rupture voltages, sensitivity to streaking (phosphate mapping), lower gloss and poor flow or orange peel. Low solvent levels are a result of inadequate solvent additions and excessive ultrafilter purges.
High solvent levels can cause high film builds, lower rupture voltages, higher gloss and poor throwing power. High solvent levels are a result of excessive solvent additions.
Common Electrocoat Defects. Coating defects are numerous and this section will not address every one, but it will provide some common defects related to the electrocoat tank, potential causes and their solutions.
Cratering. Craters are bowl-shaped depressions with material in the center and raised circular edges. They are usually caused by contamination of the bath, rinses or substrates with particulates or incompatible oils. These contaminants can be from the substrate forming process, greases or lubricants and other processes that allow airborne contaminants to enter the system. Craters may also be caused by post tank contamination of parts. This can come from chain oils, conveyor drips and blow out of contamination in the oven. Often it is difficult to identify the cause of cratering without close investigation of the line. A permanent solution to cratering must be to identify and eliminate the source. Short-term solutions are using oil absorbent media inside of bag filters, increasing the pigment to binder ratio and in some severe cases diluting the contaminant with fresh feed.
Rupturing is the bursting of the deposited film by an excessive generation of heat (anodic) and electrical sparking/gassing at the film/substrate interface (cathodic). Rupture defects are caused by excessive voltage, excessive ripple, high film build, electrode/counter electrode in close proximity and bath contamination. By racking the parts according to substrate type, size and weight, the voltage can be adjusted as necessary. Rupture can also be due to high bath temperature, solvent levels and bath solids. The cathode or anode should be a safe distance away from its counter electrode. Bath contamination by ionic species can be removed by ultrafiltering to drain and replacing with deionized water.
Roughness is indicated by patches on a cured film that exhibits an alternately non-uniform and smooth appearance. Patchy roughness can be due to ionic contamination, low solvent levels and substrate irregularities. Ionic contamination is typically brought into the bath through part carryover, poor water quality and anolyte/catholyte malfunctions. Adding solvents can also help smooth the overall coating appearance. Using clean, high-quality substrates and controlling pretreatment will minimize the non-uniformity of the cured electrocoat film.
Redissolution is where all or part of the electrocoat film washes off or dissolves. Redissolution can seriously limit the high transfer efficiency of an electrocoat system. It occurs in the paint bath or post rinses and can be caused by excess solubilizer, high solvent levels and line stoppages. Excess solubilizer and high solvent levels in the bath lead to aggressive permeate post rinses that dissolve the deposited coating during rinsing. This can be eliminated by maintaining proper bath pH and solvent levels. The amount of time the ware is in the bath and rinse stages during the line stoppages should be minimized.
Dirt. Dirt has three sources, process, environmental and oven. Process dirt develops within the bath or rinses from inadequate solubilizer levels, pump shear, altered circulation and improper filtration. In the early stages, dirt appears on a horizontal surface, but in severe cases it can affect all surfaces. Environmental dirt is caused by airborne particles that fall into the bath or settle on the ware. Electrocoat areas exposed to vehicular traffic, ventilation fans, and grinding/sanding operations are susceptible. Oven dirt is caused by condensation of electrocoat by-products that flake off when drying. On a cured part, oven dirt is more surface oriented, while process and environmental dirt is somewhat imbedded in the paint film.
Streaking. Streaking in an electrocoat film can be due to pretreatment, rinsing and racking. Pretreatment variations can cause differences in ware surface conductivity. This defect is usually a telegraphing or mapping of the pretreatment through the electrocoat film or an electrocoat film phenomenon. Rinsing issues include low solvent or solubilizer levels in the rinse stages and clogged or misaligned rinse nozzles. The greater the length of time from paint bath to post rinse can increase drying of the dragout, making it difficult to rinse. Dirty racks and improper racking also can be sources of drips or spots.
Pinholing/outgassing is a pattern of relatively small, random volcano-like holes in the electrocoat film that penetrates to the substrate. Pinholing is primarily seen on galvanized/zinc-coated substrates, but can be caused by poor metal quality and rectifier problems. Galvanized and other zinc-coated substrates may inherently have surface microvoids. These microvoids may allow for the gasses normally generated in the electrocoat process to be trapped under the electro-coating. During curing, the gasses blow out through the electrocoating, leaving a volcano-like hole. Poor metal quality, metal that cannot be pretreated evenly and voltage spikes from an unfiltered rectifier can cause rapid electrodeposition. This does not allow the normal gasses generated in the process to escape, therefore holes result.
Foaming/air entrapment. Foaming is typically caused by pump problems, poor tank circulation and improper part loading. Cavitating pumps allow for aeration of the electrocoat bath and poor tank circulation does not allow gas to dissipate. Odd-shaped ware entering the electrocoat bath at an angle or through surface foam can also be a reason for air entrapment.
Gloss variations can be caused by several factors, including pigment to binder ratios, solvent levels and solubilizer levels. Pretreatment variations cause gloss differences not only part to part, but also on one part. Cure time and temperature also affect the final gloss.
Color variations can be caused by iron contamination, improper cure and poor tank agitation. Iron contamination can cause a yellowing or browning of the coated film. Oven problems can discolor cured films. Poor tank agitation can cause pigment pooling that can cause a streaked or blotched discoloration on products.
Throwing power. Poor throwing power is usually related to low voltage, low bath solids, low conductivity, high solvent levels and insufficient deposition time. By increasing some or all of these variables and decreasing solvent and bath temperature, throwing power will increase. Throwing power also can be impacted by the addition of auxiliary electrodes close to areas where more film build is needed.
Thin coating. These coats may be caused by poor contact, a faulty rectifier, inadequate electrode surface, high part loading, low voltage and low bath temperature and inadequate deposition time. Clean hooks, proper electrical supply and maintaining the proper coating surface to electrode ratio is essential to proper film build. High part loading can cause an overall film-build decrease. Film build can be increased by increasing voltage, bath temperature and deposition time.
Orange peel is related to iron contamination and low solvent levels. Iron contamination can be caused by fallen parts, exposed mild steel and leaking anolytes. This type of contamination, although ionic, cannot be ultrafiltered from the bath. Coating out, adding fresh feed to dilute the contamination and eliminating the source are the recommended solutions. Increased solvent levels can improve the flow characteristics of the electrocoating, eliminating the orange peel.
The "Big Four" electrocoating troubleshooting areas include the troubleshooting process, establishing preventive maintenance schedules, controlling operating parameters and classifying common electrocoat defects. Troubleshooting electrocoating will help users develop effective skills needed to promote optimum electrocoating.
Troubleshooting process. It is important to understand troubleshooting in order to develop sound, workable solutions to problems. There are five steps to troubleshooting.
1. Define the problem. Defining the problem is the first step in the troubleshooting process. It characterizes the problem by answering several questions:
Isolation—Is the problem in the operation of the system or appearance related?Identification—What type of defect is occurring and does it occur on all parts? Location—Does the problem move around on the part or is it always in the same area? Timing—When did the problem start? Duration—Is it constant or sporadic?
Problems do not occur without something having changed. Problems are not solved unless something is changed.
2. Identify the root cause. Identifying possible root causes is step two in the troubleshooting process. It is necessary to understand common causes for the defects. There could be several bath variables and process areas to investigate. Commonly asked questions include the following.
Correlation—What are the common causes for this type of defect? Have there been any recent changes made to the line? Is there a correlation between tank parameter test data and the appearance of the problem?
Mechanical—Is the testing equipment functioning properly? Procedural—Have the testing procedures been followed?
3. Determine corrective action. Determining the appropriate corrective action is the next step in the troubleshooting process. This step is probably the most time consuming. Developing a logical plan that tests one variable at a time is crucial to identifying potential solutions. Answering the following questions should help develop a practical action plan.
Which variables can be tested on line quickly?
Which variables can be tested with little disruption to production?
Which variables can be tested on line in the paint lab?
Which variables need technical support from the suppliers?
4. Implement corrective action. Implementing corrective action is the success step in the troubleshooting process. As each variable is tested, it will either be eliminated or identified as a possible solution. There may be multiple solutions and in rare cases there may be no solution. In the cases where no solutions have been found, it is necessary to start the troubleshooting process again by redefining the problem.
5. Follow-up. Follow-up is the last step in the troubleshooting process. It involves determining what permanent changes are needed to prevent the problem from recurring. This troubleshooting model provides guidance for identifying, reacting to and solving problems and if properly followed and documented, it can provide a faster response for future problems.
Preventive action methods. Troubleshooting should be more than a reaction to problems. Preventive maintenance is often overlooked as a tool to guard against problems and defects. It is not possible to list every housekeeping item or maintenance program associated with an electrocoat system, but there are essential mechanical, chemical and substrate considerations.
Tank agitation. Agitation of a paint tank is necessary for paint suspension, filtration and removing excess heat generated from pumping and coating. Proper agitation is dependent on the header/eductor system and the circulation pump. Broken or misaligned eductors can cause appearance defects in production and dead zones in the paint tank. A malfunctioning pump can cause poor bath circulation, foam and appearance defects. Excessive tank agitation can cause parts to fall. The velocity of the paint in recirculation lines should normally fall between seven and ten fps. Semi-annual tank cleanings should be performed to check agitation, and weekly cleaning of the pump screens will prevent blockage.
Oven. The oven is critical to the final coating appearance and the desired performance properties. It is recommended that the oven buildup be monitored and cleaned out when necessary. Oven temperature recorders should be run semi-annually to ensure correct oven balance and dehydration zone temperatures.
Rectifier. The rectifier should be checked yearly for ripple. It should not exceed five pct under anticipated load conditions. The amperage and voltage displays should also be checked to ensure calibration accuracy. There should be no stray voltage to the paint tank during non-production hours.
Electrodes. The electrodes should be checked weekly for degradation, proper operation of supply and return flows and to ensure electric leads are connected. Periodic checks of each electrode's amperage draw can be used to monitor anode performance. It is important to maintain a 4:1 or lower ratio of coating surface to electrode (based on a two-minute immersion time).
Anolyte/catholyte. The anolyte/catholyte is needed to remove excess acid/base from the paint bath and should be checked for proper liquid level, proper functioning of the conductivity set-point indicator and probe, water supply availability and that the supply and return flows are operational.
Racking. Racking includes design, part loading and cleaning. There should be specially designed racks available for odd-shaped parts and spring-loaded hooks for small parts. It is recommended to have one contact point for part grounding and to handle them in a way as to eliminate liquid pooling, air pockets, falling off and contact with other parts. Maintaining clean racks and contact points will help prevent rack buildup and coating failures. The grounding system should be checked yearly for wear and good contact.
Rinsing. Ensure the rinse system is operating monthly without any plugged or misdirected nozzles. Make sure spraying is contained within the tank, and the recirculated rinse flow is balanced from stage to stage. Check for a buildup of paint solids and parts that have fallen in the tank. The headers should be cleaned periodically to remove any settled material from the piping and pressure maintained between five and ten psi.
Filtration. Filtration of the electrocoat tank includes both bag filters and ultrafilters. Bag filters should be changed when the pressure differential inlet to outlet is five psi. If oil absorbent media is being used, it should be changed frequently. The ultrafilter flux rate should be checked daily using the site gauges and cleaner per the manufacturer's recommendations. Most manufacturers recommend a cleaning at 70 pct of the stabilized flux rate, or membranes can be irreversibly fouled, shortening life span and making them more difficult to clean. The ultrafilter pump should be monitored by pressure gauges.
ELECTROCOATED golf car from Yamaha Motor Corp.
Cleaning process. Proper cleaning parameters will allow for removal of substrate contaminants such as stamping oils, surface dirt, fibers and weld smut. Whether an acid or alkaline cleaner is used, the concentration and the process time must be maintained and monitored daily. This includes any auxiliary cleaning steps such as shot blasting and pickling. A clean substrate is necessary for proper pretreating and coating. Dirty or contaminated substrate surfaces will cause final appearance and/or performance problems leading to rejected parts and rework.
Pretreatment process. Pretreatment functions as a conversion coating for improved paint adhesion and performance. It is crucial that this process be closely monitored and followed per the supplier's recommendations. The four basics to optimum pretreatment chemistry require monitoring of time, temperature, pressure and concentration. Routine testing for proper coating weights and crystal morphology should also be performed because the final appearance and performance of the electrocoated part is only as good as its preparation.
Water. High-quality water is essential for operation of an electrocoat system. Quality water is characterized by low conductivity, less than 10 micro mhos/cm for deionized or 20 micro mhos/cm for reverse osmosis, low silica levels and microbe free. It is recommended to have a minimum of two water sources, either two alternately functioning units or one unit plus water storage capability. Resin bed cleanings and regeneration procedures should be followed.
Substrate. Substrate quality is the first consideration in achieving a quality finish. There are many types of metals used in electrocoating ranging from aluminum to cold-rolled steel and from galvanized to heat treated metals. Using the first in, first out rule will keep substrates clean. Protective storage conditions will aid in the prevention of flash rusting and other surface defects.
Operating parameter effects. All systems, from cleaner and pretreatment through electrocoat, have specifications that recommend optimal ranges of operation. Understanding how each specification affects the appearance and performance of the coating will allow for corrective adjustments. Also, through accurate testing and charting, a historical picture of the system can be built and the occurrence of defects minimized.
Bath solids. This includes the pigments and non-volatile components of paint. Low bath solids cause lower film thickness, decreased throwing power, higher rupture voltage and higher ultrafilter flux rate. Low bath solids occur from normal excessive replenishment additions of paste.
Pigment to binder ratio. Low pigment to binder ratios cause higher gloss, decreased throwing power, less hiding and more cratering. Low pigment levels occur from excessive replenishment additions of resin and settling in the tank. High pigment to binder ratios cause lower gloss, increased throwing power, settling in the bath and rinses, and it makes the film more sensitive to water spotting. High pigment levels occur from excessive additions of paste.
Bath pH. High bath pH for cationic systems can cause tank settling, dirt, a decrease in ultrafilter permeate rates and sensitivity to streaking. High pH can occur from excessive anolyte purges, excessive replenishment and caustic contamination from carryover or deionized water. Low pH occurs from excessive acid levels and can cause redissolution. Potential causes of low pH are deficient anolyte purges, anolyte leakage in the paint tank, insufficient membrane surface, membranes surface plugging, excessive acid additions and acid contamination from carryover or poor quality deionized water.
Low bath pH for anionic systems also can cause tank settling, dirt, a decrease in ultrafilter permeate rates and sensitivity to streaking. Low bath pH occurs from excessive ultrafilter purge, excessive replenishment, and acid contamination from carryover or deionized water. High pH occurs from insufficient ultrafilter purges, excessive amine additions and caustic contamination from carryover or poor quality deionized water.
Bath conductivity. Low bath conductivity can cause poor throwing power, low film build and roughness. Low conductivity is caused by excessive ultrafilter purges and low bath solids. High bath conductivity can cause rupturing, high film build and roughness. High conductivity is caused by high bath solids and ionic contamination from carryover or poor quality deionized water.
Solvent. Low solvent levels can cause low film builds, higher rupture voltages, sensitivity to streaking (phosphate mapping), lower gloss and poor flow or orange peel. Low solvent levels are a result of inadequate solvent additions and excessive ultrafilter purges.
High solvent levels can cause high film builds, lower rupture voltages, higher gloss and poor throwing power. High solvent levels are a result of excessive solvent additions.
Common Electrocoat Defects. Coating defects are numerous and this section will not address every one, but it will provide some common defects related to the electrocoat tank, potential causes and their solutions.
Cratering. Craters are bowl-shaped depressions with material in the center and raised circular edges. They are usually caused by contamination of the bath, rinses or substrates with particulates or incompatible oils. These contaminants can be from the substrate forming process, greases or lubricants and other processes that allow airborne contaminants to enter the system. Craters may also be caused by post tank contamination of parts. This can come from chain oils, conveyor drips and blow out of contamination in the oven. Often it is difficult to identify the cause of cratering without close investigation of the line. A permanent solution to cratering must be to identify and eliminate the source. Short-term solutions are using oil absorbent media inside of bag filters, increasing the pigment to binder ratio and in some severe cases diluting the contaminant with fresh feed.
Rupturing is the bursting of the deposited film by an excessive generation of heat (anodic) and electrical sparking/gassing at the film/substrate interface (cathodic). Rupture defects are caused by excessive voltage, excessive ripple, high film build, electrode/counter electrode in close proximity and bath contamination. By racking the parts according to substrate type, size and weight, the voltage can be adjusted as necessary. Rupture can also be due to high bath temperature, solvent levels and bath solids. The cathode or anode should be a safe distance away from its counter electrode. Bath contamination by ionic species can be removed by ultrafiltering to drain and replacing with deionized water.
Roughness is indicated by patches on a cured film that exhibits an alternately non-uniform and smooth appearance. Patchy roughness can be due to ionic contamination, low solvent levels and substrate irregularities. Ionic contamination is typically brought into the bath through part carryover, poor water quality and anolyte/catholyte malfunctions. Adding solvents can also help smooth the overall coating appearance. Using clean, high-quality substrates and controlling pretreatment will minimize the non-uniformity of the cured electrocoat film.
Redissolution is where all or part of the electrocoat film washes off or dissolves. Redissolution can seriously limit the high transfer efficiency of an electrocoat system. It occurs in the paint bath or post rinses and can be caused by excess solubilizer, high solvent levels and line stoppages. Excess solubilizer and high solvent levels in the bath lead to aggressive permeate post rinses that dissolve the deposited coating during rinsing. This can be eliminated by maintaining proper bath pH and solvent levels. The amount of time the ware is in the bath and rinse stages during the line stoppages should be minimized.
Dirt. Dirt has three sources, process, environmental and oven. Process dirt develops within the bath or rinses from inadequate solubilizer levels, pump shear, altered circulation and improper filtration. In the early stages, dirt appears on a horizontal surface, but in severe cases it can affect all surfaces. Environmental dirt is caused by airborne particles that fall into the bath or settle on the ware. Electrocoat areas exposed to vehicular traffic, ventilation fans, and grinding/sanding operations are susceptible. Oven dirt is caused by condensation of electrocoat by-products that flake off when drying. On a cured part, oven dirt is more surface oriented, while process and environmental dirt is somewhat imbedded in the paint film.
Streaking. Streaking in an electrocoat film can be due to pretreatment, rinsing and racking. Pretreatment variations can cause differences in ware surface conductivity. This defect is usually a telegraphing or mapping of the pretreatment through the electrocoat film or an electrocoat film phenomenon. Rinsing issues include low solvent or solubilizer levels in the rinse stages and clogged or misaligned rinse nozzles. The greater the length of time from paint bath to post rinse can increase drying of the dragout, making it difficult to rinse. Dirty racks and improper racking also can be sources of drips or spots.
Pinholing/outgassing is a pattern of relatively small, random volcano-like holes in the electrocoat film that penetrates to the substrate. Pinholing is primarily seen on galvanized/zinc-coated substrates, but can be caused by poor metal quality and rectifier problems. Galvanized and other zinc-coated substrates may inherently have surface microvoids. These microvoids may allow for the gasses normally generated in the electrocoat process to be trapped under the electro-coating. During curing, the gasses blow out through the electrocoating, leaving a volcano-like hole. Poor metal quality, metal that cannot be pretreated evenly and voltage spikes from an unfiltered rectifier can cause rapid electrodeposition. This does not allow the normal gasses generated in the process to escape, therefore holes result.
Foaming/air entrapment. Foaming is typically caused by pump problems, poor tank circulation and improper part loading. Cavitating pumps allow for aeration of the electrocoat bath and poor tank circulation does not allow gas to dissipate. Odd-shaped ware entering the electrocoat bath at an angle or through surface foam can also be a reason for air entrapment.
Gloss variations can be caused by several factors, including pigment to binder ratios, solvent levels and solubilizer levels. Pretreatment variations cause gloss differences not only part to part, but also on one part. Cure time and temperature also affect the final gloss.
Color variations can be caused by iron contamination, improper cure and poor tank agitation. Iron contamination can cause a yellowing or browning of the coated film. Oven problems can discolor cured films. Poor tank agitation can cause pigment pooling that can cause a streaked or blotched discoloration on products.
Throwing power. Poor throwing power is usually related to low voltage, low bath solids, low conductivity, high solvent levels and insufficient deposition time. By increasing some or all of these variables and decreasing solvent and bath temperature, throwing power will increase. Throwing power also can be impacted by the addition of auxiliary electrodes close to areas where more film build is needed.
Thin coating. These coats may be caused by poor contact, a faulty rectifier, inadequate electrode surface, high part loading, low voltage and low bath temperature and inadequate deposition time. Clean hooks, proper electrical supply and maintaining the proper coating surface to electrode ratio is essential to proper film build. High part loading can cause an overall film-build decrease. Film build can be increased by increasing voltage, bath temperature and deposition time.
Orange peel is related to iron contamination and low solvent levels. Iron contamination can be caused by fallen parts, exposed mild steel and leaking anolytes. This type of contamination, although ionic, cannot be ultrafiltered from the bath. Coating out, adding fresh feed to dilute the contamination and eliminating the source are the recommended solutions. Increased solvent levels can improve the flow characteristics of the electrocoating, eliminating the orange peel.
The "Big Four" electrocoating troubleshooting areas include the troubleshooting process, establishing preventive maintenance schedules, controlling operating parameters and classifying common electrocoat defects. Troubleshooting electrocoating will help users develop effective skills needed to promote optimum electrocoating.
Understanding Vibratory Finishing Revisited
Vibratory finishing has not changed much during the years. Several years ago, Products Finishing published a series of articles by John Kittredge. These articles have good, pertinent information that is still valid for the vibratory finishing industry today. The series covered media, compound solution, equipment and parts.
Four elements are significant in vibratory finishing: parts, media, compound solutions and equipment. These link to form an interdependent network, or Tetrahedron of Interdependence. These elements depend on each other to such an extent that if one fails, the process fails.
MediaMedia is one of the supporting parts; however, it is also supported by the other three parts.
Functions. The chips or stones in vibratory finishing are called media. While there are many variations, from aggressive grades capable of removing large quantities of metal from parts in short cycles to media that cannot cut at all. Each type has the following functions:
1. Separate and cushion parts. Parts are mixed with media in a random distribution. The ratio of parts to media helps control the amount of contact the parts have among themselves. If insufficient media is between the parts, they will collide. Media cushions this impact so that irreparable damage does not occur. This is not important for forgings, but is a key consideration of preplate finishing of die castings.
2. Contact critical edges and surfaces. Certain media shapes may lead to a false sense of security. Plastic cones are popular and available in a variety of sizes. That pointed end can touch all areas of a part, but if the cone is large and not a blend of sizes, the pointed end does not do much work.
3. Provide proper degree of cut or luster. Abrasive media will cut. More and bigger abrasive will result in more cut. Non-abrasive media can only produce luster.
1. TETRAHEDRON OF INTERDEPENDENCE shows close relationship of equipment, media, compound solution and parts.
4. Resist lodging in parts. If media sticks in the parts, someone must remove it. If this is difficult, the cost of removal may exceed the cost of the process. To prevent lodging, manufacturers of media produce a great variety of shapes and sizes.
5. Permit separation from parts. Any time you mix parts and media, the two must eventually be separated. The efficiency of this operation depends on the equipment available, but also on the shape and size of the media and parts.
Abrasive media has distinct functions. It releases abrasive slowly into the system. It can cut and deburr edges. It can develop the required surface smoothness and will last as long as possible.
Media wears and exposes fresh grains. Media also wears against other media, which it is designed to do. This keeps media clean and ready to cut with fresh abrasive.
The rate of media wear varies with use. Media designed for rotary barrels will wear out too fast in higher energy equipment such as vibratory systems. Media designed for vibratory use wears out too fast in barrels and other centrifugal equipment.
Abrasive particle size controls the depth of cut. Bigger particles cut deeper and produce rougher surfaces. The hardness of the abrasive should be greater than the material being cut. This cutting action removes burrs and changes the surface contour.
Surface smoothness can be measured using a capacitive sensing probe. Units are read in microinches or micrometers, AA or arithmetic average. Developing good, smooth, low-micro-inch surfaces is easily done, but care must be exercised. Fast cutting products give rougher surfaces at their minimum capability.
The ideal media lasts forever, and this can happen with non-abrasive media such as steel, but not with abrasive media. Heavy-cutting grades wear faster.
Non-abrasive media peens or pound edges and surfaces. It also deburrs edges lightly while brightening surfaces. It also experiences little or no wear or loss.
2. TUB vibrator processes parts as shown here
Since non-abrasive media cannot cut and energy is imparted to it, it can only pound surfaces and edges. No scratch pattern develops; instead, a series of small, uniform dents is imparted to the surface of the work.
The small dents are followed by more and more pounding until the surface gets brighter. This occurs quickly with steel media on malleable metals, but may never develop on hard steels.
Media wears primarily by rubbing against other pieces of media until abrasive grains fall out or are cut away. With no abrasive, cutting stops and so does wear.
Media has an amazing influence on the vibratory finishing process. However, for the media to work, the solution system must behave, the equipment must perform and the parts must be uniform and above all, people must not make waves too high for the process to get through.
Compound SolutionThe compound solution is the least understood and most frequently abused part of the mass finishing process. It has the following functions:
1. Control pH, foam and water hardness. Many compounds are buffered to prevent big changes in pH from taking place. Mass finishing solutions vary from a pH 1 to 14. The most popular range is from 4 to 14.
Some foam is necessary in most applications, especially those involving cleaning. Foam holds the solution in place on the surface of the parts and media. Without foam, process cycles are greatly extended or cleaning just does not occur.
Too much foam kills the action in a vibratory machine. It cushions the mass so effectively that cutting can literally come to a stop. In rotary barrels or centrifugal barrels, however, foam merely moderates action.
In the U.S. water hardness varies from low to high, and public water supplies are often quite different from water drawn from a well in the same area. These great variations in hardness strain the solution since it tried to equalize the differences.
2. Wet surfaces. If the compound solution will not wet or spread on the surface to be cleaned, it will not clean well. Wetting is dependent on concentration.
3. Emulsify oily soils. Physical action improves the speed and stability of emulsification. Because vibratory finishers are excellent scrubbers, they clean well. Media continually works the soils, allowing sometimes-marginal cleaners to "get away with it."
4. Remove tarnish or scale. Both high- and low-pH compound solutions can chemically attack tarnish and scale. These oxides of the metal darken the surfaces and lower reflectivity. Highly alkaline solutions remove rust or scale from some steel. These alkaline solutions can produce light, bleached metal surfaces. Strongly acidic solutions vigorously attack rust and other metal oxides. Unfortunately, they also attack the base metal unless the solution is properly inhibited.
3. ROUND vibrator with no elevation on the chamber
5. Suspend soils. Soil removed or made during the process can redeposit on the parts, media and/or lining of the chamber. Excessively hard water contributes to the problem. Usually a special compound is needed to overcome this.
6. Control lubricity. For years, it was believed that the solution had to be slippery to burnish or brighten a part. This is often true in rotary barrels. In vibratory equipment, excessive slip brings everything to a halt. Traction is lost. Media stops rolling, and nothing happens to the parts. Lubricity should not be completely eliminated, since some lubricity does assist the cutting of the compounds.
7. Control part color. Coloring or darkening parts in vibratory finishing is caused by oxidation or dirt impregnation. Highly alkaline surfaces can bleach out surfaces and acidic compounds can give too clean a surface.
8. Prevent corrosion. The only way to stop corrosion is to include an inhibitor in the compound solution. Some inhibitors are effective on ferrous metals, while others are more effective on non-ferrous metals or those that will oxidize.
9. Provide cooling. If a vibratory process were to run dry, friction would generate high temperatures quickly. The solution cools the mass of media and parts. Low flow rates do not carry away heat as fast. Then more oxidation occurs. Elevated temperatures are seldom needed, even for severe cleaning problems.
Solution FeedThere are three major types of solution-feed systems: batch, recirculation and flow-through. Batch is the simplest system. It is used in barrels and vibrators with no drains. Recirculation systems mix a solution in the tank and pump it into the process, allowing it to drain back into the tank for reuse. This sounds efficient, however the high rate of soil production creates severe contamination problems. Flow-through systems pump fresh solution into the machine, allow it to act and then drain it. Compound flow-through means the parts see only clean media. The solution is always the same strength. There is no sludge tank to clean.
There are three methods of adding compound: manual, batch premix and automatic.
With the manual procedures, you add compound and water manually using a measuring device. In the batch premix method the solution is held in a tank where it is mixed prior to being pumped into the machine. Automatic addition employs a compound-metering pump and rotameter for measuring flow rate of water.
EquipmentEquipment serves several functions.
1. Process parts. The equipment must do the deburring, cleaning, surface conditioning or burnishing.
2. Separation. Separation skills are high on the normal system capability list. The simplest separators are screens. For parts with projections that would cause them to hang up on screens, the tie rod deck is a good choice. It allows parts to slide down parallel rods while the media drops through. Or the inverse if the parts are smaller than the media.
3. Control mass action. Equipment must have adjustments so that more aggressive or gentler work can be done. Tub-type vibratory equipment has a variable-weight system to adjust energy input. Generally, there is a single shaft mounted directly underneath the tub. On each end is an eccentric weight that has some variability in its mass. More weight, more amplitude, faster cutting, rougher surfaces, greater media wear.
The rotational speed of the eccentric weights is another variable. Higher speed generally promotes faster cut, rough surfaces and greater media wear rates.
In round vibratory equipment, the eccentric weights are mounted on each end of a vertical shaft or motor in the center tube of the tub. The amount of weight on the top eccentric generally controls the speed of mass travel around the tub, while the amount on the bottom controls the rollover rate of the mass.
TABLE I - Media-to-Part Volumetric Rates
Media-to-PartRatio by Volume
Normal Commercial Application
0:1
No media. Part-on-part. Used for beating off burrs. No media for cutting.
1:1
Equal volumes of media and parts. Forgings, sand castings; to produce crude, very rough surfaces.
2:1
More gentle, more separation. But still allows relatively severe part-on-part damage.
3:1
About minimum for non-ferrous parts. Considerable part-on-part contact. Fair-to-good for ferrous metals.
4:1
Probably average for non-ferrous parts. Good for ferrous metals.
5:1
Good for non-ferrous metals. Minimal part-to-part contact.
6:1
Very good for non-ferrous parts. Common for preplate on zinc with plastic media.
8:1
For higher quality preplate finishes.
10:1 to 20:1
Even better. Used for very irregularly shaped, fragile parts.
Infinite
Absolutely no part-to-part contact. One part per machine or compartment or the part is fixtured.
PartsThe most important of the Tetrahedron of Interdependence is parts. Without the parts, there would be no process. And, depending on the requirements for the parts, the process is designed, equipment is chosen, media and compound solution are selected. Only when a new process is set up to use existing equipment is the procedure changed. Normally, the parts dictate all else.
There are seven significant purposes of vibratory finishing.
1. Clean. Cleaning can be done with little or no increase in cost, quickly and without heat. Typical parts cleaned commercially in vibratory units include machined engine components, stampings, copper plumbing fittings, brass forgings, plastics, ceramics, rubber and wood.
2. Deburr or radius. This is the best known use of vibratory finishing. All metals, ceramics and some plastics can be deburred. Deburring prevents people from cutting themselves and makes parts feed through automatic feeders more easily.
3. Improve surfaces. Rough surfaces need to be smoothed before they take a high-quality electroplate, paint or anodize. Surface roughness values below 10 microinches AA are common and with good preplate plastic media, values below five microinches are commercially achieved.
4. Brighten. Brightening or burnishing metal surfaces is a good, viable application of mass finishing. It is done easily to the more malleable metals using non-abrasive media. Aluminum, copper, brass and mild steels can be brightened in 10 to 30 min depending on finish quality required and starting surface quality. Harder metals such as stainless, some brasses and other steels take 30 min to several hours.
5. Inhibit. Sensitive metals, including powdered iron, cast iron, copper, brass, zinc and steels of all types will corrode unless protection is provided. Metal surfaces will look cleaner and brighter for longer if they are properly inhibited.
6. Dry. To prevent corrosion or discoloration or to improve parts handling, parts should be dried. Spin basket, hot-air conveyors and dryers filled with ground corncobs can be used.
7. Transfer. Mass finishing is capable of any degree of automation. The easiest transfer to use and one of the most effective is a simple conveyor belt. In-house handling of parts is also important.
Big, heavy parts can crush media, leading to premature media breakdown and higher costs. Crushed or whole media can stick or lodge in parts and be carried out of the vibrator.
One of the worst effects parts can have on media is to soil the media. Oils are especially bad for media if the compound solution cannot remove them rapidly enough. Oil stops cutting and parts emerge dirty or dark.
An important relationship between media and parts is the media-to-parts volumetric ratio. In a mass finishing process, the amount of contact between parts is controlled by the ratio of parts to media. Machine settings control the force of these contacts. This is a statistical phenomenon based on the probabilities involved. If you want smooth parts, keep media levels up. Don't overload the machine with parts.
Parts and people. People make parts. Or at least they control the machines that make the parts. When the quality of the parts is maintained, the vibratory finishing process is consistent. If part quality strays, expect the process to as well.
People make decisions. They make changes that affect the parts. The process cannot. People will muddle the process or keep it simple.
Smart people take every possible advantage of the mechanical process. They insist the process run the same everyday. People rely on the vibratory finishing process and they learn how to use it as an excellent quality control tool.
Four elements are significant in vibratory finishing: parts, media, compound solutions and equipment. These link to form an interdependent network, or Tetrahedron of Interdependence. These elements depend on each other to such an extent that if one fails, the process fails.
MediaMedia is one of the supporting parts; however, it is also supported by the other three parts.
Functions. The chips or stones in vibratory finishing are called media. While there are many variations, from aggressive grades capable of removing large quantities of metal from parts in short cycles to media that cannot cut at all. Each type has the following functions:
1. Separate and cushion parts. Parts are mixed with media in a random distribution. The ratio of parts to media helps control the amount of contact the parts have among themselves. If insufficient media is between the parts, they will collide. Media cushions this impact so that irreparable damage does not occur. This is not important for forgings, but is a key consideration of preplate finishing of die castings.
2. Contact critical edges and surfaces. Certain media shapes may lead to a false sense of security. Plastic cones are popular and available in a variety of sizes. That pointed end can touch all areas of a part, but if the cone is large and not a blend of sizes, the pointed end does not do much work.
3. Provide proper degree of cut or luster. Abrasive media will cut. More and bigger abrasive will result in more cut. Non-abrasive media can only produce luster.
1. TETRAHEDRON OF INTERDEPENDENCE shows close relationship of equipment, media, compound solution and parts.
4. Resist lodging in parts. If media sticks in the parts, someone must remove it. If this is difficult, the cost of removal may exceed the cost of the process. To prevent lodging, manufacturers of media produce a great variety of shapes and sizes.
5. Permit separation from parts. Any time you mix parts and media, the two must eventually be separated. The efficiency of this operation depends on the equipment available, but also on the shape and size of the media and parts.
Abrasive media has distinct functions. It releases abrasive slowly into the system. It can cut and deburr edges. It can develop the required surface smoothness and will last as long as possible.
Media wears and exposes fresh grains. Media also wears against other media, which it is designed to do. This keeps media clean and ready to cut with fresh abrasive.
The rate of media wear varies with use. Media designed for rotary barrels will wear out too fast in higher energy equipment such as vibratory systems. Media designed for vibratory use wears out too fast in barrels and other centrifugal equipment.
Abrasive particle size controls the depth of cut. Bigger particles cut deeper and produce rougher surfaces. The hardness of the abrasive should be greater than the material being cut. This cutting action removes burrs and changes the surface contour.
Surface smoothness can be measured using a capacitive sensing probe. Units are read in microinches or micrometers, AA or arithmetic average. Developing good, smooth, low-micro-inch surfaces is easily done, but care must be exercised. Fast cutting products give rougher surfaces at their minimum capability.
The ideal media lasts forever, and this can happen with non-abrasive media such as steel, but not with abrasive media. Heavy-cutting grades wear faster.
Non-abrasive media peens or pound edges and surfaces. It also deburrs edges lightly while brightening surfaces. It also experiences little or no wear or loss.
2. TUB vibrator processes parts as shown here
Since non-abrasive media cannot cut and energy is imparted to it, it can only pound surfaces and edges. No scratch pattern develops; instead, a series of small, uniform dents is imparted to the surface of the work.
The small dents are followed by more and more pounding until the surface gets brighter. This occurs quickly with steel media on malleable metals, but may never develop on hard steels.
Media wears primarily by rubbing against other pieces of media until abrasive grains fall out or are cut away. With no abrasive, cutting stops and so does wear.
Media has an amazing influence on the vibratory finishing process. However, for the media to work, the solution system must behave, the equipment must perform and the parts must be uniform and above all, people must not make waves too high for the process to get through.
Compound SolutionThe compound solution is the least understood and most frequently abused part of the mass finishing process. It has the following functions:
1. Control pH, foam and water hardness. Many compounds are buffered to prevent big changes in pH from taking place. Mass finishing solutions vary from a pH 1 to 14. The most popular range is from 4 to 14.
Some foam is necessary in most applications, especially those involving cleaning. Foam holds the solution in place on the surface of the parts and media. Without foam, process cycles are greatly extended or cleaning just does not occur.
Too much foam kills the action in a vibratory machine. It cushions the mass so effectively that cutting can literally come to a stop. In rotary barrels or centrifugal barrels, however, foam merely moderates action.
In the U.S. water hardness varies from low to high, and public water supplies are often quite different from water drawn from a well in the same area. These great variations in hardness strain the solution since it tried to equalize the differences.
2. Wet surfaces. If the compound solution will not wet or spread on the surface to be cleaned, it will not clean well. Wetting is dependent on concentration.
3. Emulsify oily soils. Physical action improves the speed and stability of emulsification. Because vibratory finishers are excellent scrubbers, they clean well. Media continually works the soils, allowing sometimes-marginal cleaners to "get away with it."
4. Remove tarnish or scale. Both high- and low-pH compound solutions can chemically attack tarnish and scale. These oxides of the metal darken the surfaces and lower reflectivity. Highly alkaline solutions remove rust or scale from some steel. These alkaline solutions can produce light, bleached metal surfaces. Strongly acidic solutions vigorously attack rust and other metal oxides. Unfortunately, they also attack the base metal unless the solution is properly inhibited.
3. ROUND vibrator with no elevation on the chamber
5. Suspend soils. Soil removed or made during the process can redeposit on the parts, media and/or lining of the chamber. Excessively hard water contributes to the problem. Usually a special compound is needed to overcome this.
6. Control lubricity. For years, it was believed that the solution had to be slippery to burnish or brighten a part. This is often true in rotary barrels. In vibratory equipment, excessive slip brings everything to a halt. Traction is lost. Media stops rolling, and nothing happens to the parts. Lubricity should not be completely eliminated, since some lubricity does assist the cutting of the compounds.
7. Control part color. Coloring or darkening parts in vibratory finishing is caused by oxidation or dirt impregnation. Highly alkaline surfaces can bleach out surfaces and acidic compounds can give too clean a surface.
8. Prevent corrosion. The only way to stop corrosion is to include an inhibitor in the compound solution. Some inhibitors are effective on ferrous metals, while others are more effective on non-ferrous metals or those that will oxidize.
9. Provide cooling. If a vibratory process were to run dry, friction would generate high temperatures quickly. The solution cools the mass of media and parts. Low flow rates do not carry away heat as fast. Then more oxidation occurs. Elevated temperatures are seldom needed, even for severe cleaning problems.
Solution FeedThere are three major types of solution-feed systems: batch, recirculation and flow-through. Batch is the simplest system. It is used in barrels and vibrators with no drains. Recirculation systems mix a solution in the tank and pump it into the process, allowing it to drain back into the tank for reuse. This sounds efficient, however the high rate of soil production creates severe contamination problems. Flow-through systems pump fresh solution into the machine, allow it to act and then drain it. Compound flow-through means the parts see only clean media. The solution is always the same strength. There is no sludge tank to clean.
There are three methods of adding compound: manual, batch premix and automatic.
With the manual procedures, you add compound and water manually using a measuring device. In the batch premix method the solution is held in a tank where it is mixed prior to being pumped into the machine. Automatic addition employs a compound-metering pump and rotameter for measuring flow rate of water.
EquipmentEquipment serves several functions.
1. Process parts. The equipment must do the deburring, cleaning, surface conditioning or burnishing.
2. Separation. Separation skills are high on the normal system capability list. The simplest separators are screens. For parts with projections that would cause them to hang up on screens, the tie rod deck is a good choice. It allows parts to slide down parallel rods while the media drops through. Or the inverse if the parts are smaller than the media.
3. Control mass action. Equipment must have adjustments so that more aggressive or gentler work can be done. Tub-type vibratory equipment has a variable-weight system to adjust energy input. Generally, there is a single shaft mounted directly underneath the tub. On each end is an eccentric weight that has some variability in its mass. More weight, more amplitude, faster cutting, rougher surfaces, greater media wear.
The rotational speed of the eccentric weights is another variable. Higher speed generally promotes faster cut, rough surfaces and greater media wear rates.
In round vibratory equipment, the eccentric weights are mounted on each end of a vertical shaft or motor in the center tube of the tub. The amount of weight on the top eccentric generally controls the speed of mass travel around the tub, while the amount on the bottom controls the rollover rate of the mass.
TABLE I - Media-to-Part Volumetric Rates
Media-to-PartRatio by Volume
Normal Commercial Application
0:1
No media. Part-on-part. Used for beating off burrs. No media for cutting.
1:1
Equal volumes of media and parts. Forgings, sand castings; to produce crude, very rough surfaces.
2:1
More gentle, more separation. But still allows relatively severe part-on-part damage.
3:1
About minimum for non-ferrous parts. Considerable part-on-part contact. Fair-to-good for ferrous metals.
4:1
Probably average for non-ferrous parts. Good for ferrous metals.
5:1
Good for non-ferrous metals. Minimal part-to-part contact.
6:1
Very good for non-ferrous parts. Common for preplate on zinc with plastic media.
8:1
For higher quality preplate finishes.
10:1 to 20:1
Even better. Used for very irregularly shaped, fragile parts.
Infinite
Absolutely no part-to-part contact. One part per machine or compartment or the part is fixtured.
PartsThe most important of the Tetrahedron of Interdependence is parts. Without the parts, there would be no process. And, depending on the requirements for the parts, the process is designed, equipment is chosen, media and compound solution are selected. Only when a new process is set up to use existing equipment is the procedure changed. Normally, the parts dictate all else.
There are seven significant purposes of vibratory finishing.
1. Clean. Cleaning can be done with little or no increase in cost, quickly and without heat. Typical parts cleaned commercially in vibratory units include machined engine components, stampings, copper plumbing fittings, brass forgings, plastics, ceramics, rubber and wood.
2. Deburr or radius. This is the best known use of vibratory finishing. All metals, ceramics and some plastics can be deburred. Deburring prevents people from cutting themselves and makes parts feed through automatic feeders more easily.
3. Improve surfaces. Rough surfaces need to be smoothed before they take a high-quality electroplate, paint or anodize. Surface roughness values below 10 microinches AA are common and with good preplate plastic media, values below five microinches are commercially achieved.
4. Brighten. Brightening or burnishing metal surfaces is a good, viable application of mass finishing. It is done easily to the more malleable metals using non-abrasive media. Aluminum, copper, brass and mild steels can be brightened in 10 to 30 min depending on finish quality required and starting surface quality. Harder metals such as stainless, some brasses and other steels take 30 min to several hours.
5. Inhibit. Sensitive metals, including powdered iron, cast iron, copper, brass, zinc and steels of all types will corrode unless protection is provided. Metal surfaces will look cleaner and brighter for longer if they are properly inhibited.
6. Dry. To prevent corrosion or discoloration or to improve parts handling, parts should be dried. Spin basket, hot-air conveyors and dryers filled with ground corncobs can be used.
7. Transfer. Mass finishing is capable of any degree of automation. The easiest transfer to use and one of the most effective is a simple conveyor belt. In-house handling of parts is also important.
Big, heavy parts can crush media, leading to premature media breakdown and higher costs. Crushed or whole media can stick or lodge in parts and be carried out of the vibrator.
One of the worst effects parts can have on media is to soil the media. Oils are especially bad for media if the compound solution cannot remove them rapidly enough. Oil stops cutting and parts emerge dirty or dark.
An important relationship between media and parts is the media-to-parts volumetric ratio. In a mass finishing process, the amount of contact between parts is controlled by the ratio of parts to media. Machine settings control the force of these contacts. This is a statistical phenomenon based on the probabilities involved. If you want smooth parts, keep media levels up. Don't overload the machine with parts.
Parts and people. People make parts. Or at least they control the machines that make the parts. When the quality of the parts is maintained, the vibratory finishing process is consistent. If part quality strays, expect the process to as well.
People make decisions. They make changes that affect the parts. The process cannot. People will muddle the process or keep it simple.
Smart people take every possible advantage of the mechanical process. They insist the process run the same everyday. People rely on the vibratory finishing process and they learn how to use it as an excellent quality control tool.
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