Getting Better All the Time

Innovation and trend-setting technology have always driven suppliers of zinc plating processes. To “future-proof” the survival of the zinc plating industry, we must be able to provide customers with the products they need now as well as innovations they will need many years down the road. This article provides a look at some technology advancements either just released to the market or currently under development at our company. Consider these forward-thinking strategies an effort to sail smoothly through any “future shock.”
Next-Generation Tri Black ChromateTo find out where we’re heading with trivalent black chromates, we first have to see where we’ve been and where we are. Prior to the European Union’s End-of-Life Vehicle (ELV) directive and the restriction of hexavalent chromium on finished zinc-plated parts, the two-part silver-Cr6+ was the staple chromate for producing a black finish. Although expensive, somewhat labor-intensive and at times inconsistent in color, the two-part hex black had a successful run dating back to the late 1940s. When the two-part hex black chromate solution was tweaked just right and parts were processed by an experienced “dipper,” the finish was jet black with a high-intensity gloss.
With the demise of hexavalent chromates, first-generation trivalent black passivates came to market in early 2000. These processes had multiple problems, including poor corrosion protection, unsatisfactory appearance and color, and short solution life.
Trivalent black passivates currently in use reflect the great strides made in appearance, corrosion protection, and solution life. All these are improved and the processes are a little more like the old two-part hex black. However, they still employ multiple additives and controllers to maintain the solution. This can become labor-intensive due to the constant tweaking required to produce an acceptable and consistent black finish. Line operators are required to perform numerous analyses each shift to determine chrome content and operating levels in the tanks. After laboratory analysis, a somewhat unscientific approach of guessing and juggling of additives is needed to “bring the solution back.” Table 1 lists the attributes of second-generation trivalent black passivates.
Table 1: Second-Generation Trivalent Black Chromates Attribute Comments Appearance Improved gloss-black and scratchability, still some inconsistency Film thickness 100–200 nm Performance 96+ hr to first white rust Chromate additives Still require multi-component additives, polymer and chrome-based sealers Solution life, Maximum zinc content, ppm Improved; may last a couple of days to many weeks 5,000–8,000 Notes Improved polymer and chrome-based sealers, Better process stability, Continue to be complicated and laborious to run consistently
The key to developing the next generation of trivalent black passivates will be to create a true one-component chromate that is easy to use and maintain, such as Columbia Chemical’s just-introduced TriVecta UniBlack. This new trivalent black passivate offers what all future passivates will be required to provide—a consistent gloss black appearance, high corrosion protection and tolerance to zinc build-up for economical operation. Table 2 compiles requirements and a “wish list” for the next-generation one-part black passivate.
One of the biggest complaints from users of today’s trivalent black passivates is the inability to run the process on a daily basis without constantly babysitting the solution or requiring the supplier to camp out at the shop to maintain the solutions. A true one-component chromate has to be stable and contain all trivalent chromium salts, acid salts, metal salts and other proprietary chemicals as one “make-up/starter” product and as the replenisher.
Table 2: Next-Generation One-Part Black Trivalent Chromate Attribute Comments Appearance Uniform gloss-black, scratch-resistant Chromate film thickness, nm 400+ Salt-spray performance 144+ hr to first white rust Chromate additives True one-part chromate and one-part sealer Solution life Excellent life, cost-effective chemical replenishment Maximum zinc content, ppm 20,000+ Notes Wide operating window (pH, temp, immersion time), Very easy to use, no juggling components, True reactive sealer reacts with chromate film
Zinc build-up has always been a chromate killer, regardless of whether it was in hexavalent or trivalent chromates. Since trivalent chromates are much more sensitive, new technologies must slow down the build-up of zinc and increase tolerances of the dissolved zinc metal. As zinc builds, higher levels of chromate additives are required to compensate for this contaminant growth. Zinc lowers corrosion protection and causes the finish to have a mottled gray appearance.
Another critical component of future one-part trivalent black processes is chromate “mileage.” The present two-part trivalent black passivates require high replenisher additions to maintain salt-spray performance and appearance. This is due to the low oxidation state (inability to promote chromate film growth), depletion and precipitation of key process components, characteristics of the zinc deposit (leveling, brightness, thickness) and hypersensitivity to solution temperature and pH.
Cobalt-Free ChromatesWith the painful yet successful switch from hex to trivalent chromates, the need for even more environmentally friendly passivates is on the horizon. The EU’s Restriction of Hazardous Substances (RoHS) directive requires periodic review of new scientific evidence, with the intent of adding potentially hazardous substances to the prohibited list.
Current two-part trivalent black passivates can process relatively small amounts of work before zinc build-up requires dumping of solution. New one-part passivate tolerates more than 20,000 ppm zinc and is able to process significantly more surface area. Figures do not account for solution drag-out. Cobalt is being considered as a “high-priority substance/material” for addition to the list of RoHS prohibited substances. Selection of these high-priority hazardous substance candidates is based on criteria that addresses both environmental and human health impacts. Environmental impact includes the formation of hazardous substances during collection and treatment of electrical and electronic equipment or during recycling or incineration. The impact on human health encompasses whether or not the substance has carcinogenic, mutagenic or toxic properties.
If and when cobalt is moved from the RoHS watch list to the active prohibited substance list, other expensive, exotic substances will be needed to meet industry specifications. This is evident from our experience with the elimination of hexavalent chromium, when more expensive substances such as trivalent chromium, cobalt and chelating acids were required to meet automotive and general zinc plating specifications. Avenues now being explored to replace cobalt include:
Formulating trivalent chromates with integrated silica compounds Adding specially formulated organic compounds Adding organo-metallic compounds Adding expensive transition metals. Looking back at the initial changeover from hexavalent to trivalent chromates, elimination of cobalt will surely increase product costs and force chemical suppliers and plating operators to invest the necessary time to master the non-cobalt learning curve.
Comparison of chromate consumption of current (left) versus next-generation one-part passivates shows the newer system can process about three times more surface area. Figures do not account for solution drag-out. No Nitric or NitratesNitric acid and its related acid salts are also on the potential RoHS hit list due to U.S. Environmental Protection Agency (EPA) National Primary Drinking Water Regulations, extremely hazardous substance listing requirements, and other pending regulations.
Nitric acid and its related acid salts has been workhorses for chromate technologies for many, many years. Nitric acid activates the zinc deposit surface, promotes chromate film growth and provides clarity and color. For this reason, future R&D efforts must center on formulations to replace this key component.
Total elimination of nitric acid from trivalent chromates will increase use of other acids and their salts, such as sulfuric, hydrochloric and hydrofluoric. Chelating and non-chelating acids will also need to be incorporated into new formulations. As with most substances that become regulated, non-nitric acid trivalent chromates will be initially more expensive, more difficult to use, and have appearance and performance problems.
Improved Zn-Ni Alloy ProcessesAs zinc-nickel alloy plating continues to grow, improvements in appearance, brightness, and chromate receptivity are required to satisfy this higher-end market. Table 3 highlights deficiencies and areas for improvement needed for today’s alkaline zinc-nickel alloy process.
Table 3: Characteristics of Current Alkaline Zinc-Nickel Alloy Plating Processes Appearance Matte to moderate bright Chromate receptivity Can produce dark, discolored, mottled finish Deposit distribution Acceptable; better than acid zinc-nickel Nickel distribution Excellent over a range of current densities Cathode efficiency Low; slow plating speed Operating range Narrow zinc, caustic, temperature and proprietary additive range Notes Sensitive to carbonate build-up, Inability to treat contaminants
Table 4: Next-Generation Alkaline Zinc-Nickel Alloy Plating Appearance Full bright Chromate receptivity Provides true chromate color and appearance, does not darken or mottle appearance Deposit distribution Excellent, comparable to present advanced alkaline zinc processes Nickel Distribution Maintain over a range of current densities Cathode Efficiency High, comparable to present advanced alkaline zinc processes Operating Range Must have a wide zinc, caustic soda, temperature and proprietary additive range
Low cathode efficiency (slow plating speed) is a primary target area for future product development. Probably the biggest complaint today from platers is low bath efficiency, which equates to slow plating and low output. Platers want the high efficiency, quick plating and high output they presently get from their alkaline zinc (non-alloy) plating lines, which have much higher cathode efficiency and deliver more than 50% more output. In today’s ultra competitive zinc market, this is a tremendous benefit and profit maker.
Comparison of cathode efficiency of current alkaline zinc-nickel alloy process and current alkaline zinc (non-alloy) process. The latter delivers much higher cathode efficiency and 50%+ more output. Future zinc-nickel alloy chemistries will have to deliver at least the same efficiency and output presently found in today’s advanced alkaline zinc processes. Table 4 provides additional requirements for next-generation alkaline zinc-nickel alloy processes.
Although acid zinc-nickel alloy plating is a much smaller market than alkaline zinc-nickel, it has one nice attribute: its ability to plate heat-treated and hardened steel. The process’s high cathode efficiency (90%+) provides two things: immediate deposit initiation and fast plating speed. In the alkaline bath, parts gas heavily and polarize before initiating the first phase of zinc deposition. This can take up to 10 min before even the first layer of zinc-nickel starts to deposit on the part. Acid baths, in contrast, start plating and laying down zinc-nickel as soon as the part is hit by current.

But unlike alkaline alloy processes, acid zinc-nickel bath has poor deposit distribution that makes it unsuitable for most rack applications. Because a “true throwing power/covering power” process for non-alloy acid zinc has yet to be developed, it is going to be a real struggle to develop one for acid zinc-nickel—development would be much easier if there was already a platform to work from. Regardless, throwing power, even if it is on a micro or limited basis, is another area that must be investigated and improved.
Table 5 is a summary of present-day acid zinc-nickel alloy plating, while Table 6 outlines areas for improvement in a next-generation chemistry.
Table 5: Characteristics of Current Acid Zinc-Nickel Alloy Plating Processes Appearance Matte to semi-bright Chromate receptivity Can produce dark-dull-satin appearance Plate distribution Poor, comparable with present acid chloride zinc processes Nickel distribution Fair, deposits more nickel at higher current densities Notes Anodes polarize, Requires elevated bath temperature due to high chloride contentSolution easily precipitates, difficult to maintain filtration
Table 6: Wish List for Next-Generation Acid Zinc-Nickel Alloy Plating Appearance Full bright, comparable to acid chloride zinc Chromate receptivity Provides true chromate color and appearance, does not darken or mottle appearance Plate distribution Provides some covering and throwing power Nickel distribution Maintains over range of current densities Notes No polarization of anodes, Economical to operate, does not require elevated temperatures or bath chemistry
Summing UpUpcoming changes and environmental/human health mandates relating to zinc plating can be viewed as either an impending disaster for our industry or a fantastic opportunity for suppliers. Without doubt, the change from hexavalent passivates to trivalent passivates was difficult, labor-intensive and expensive. However, the zinc plating industry as a whole became much better.
The same will hold true with the next round of prohibited substances. New processes will create a win-win situation for the environment and for human health, and will also raise the bar on performance requirements for finished zinc-plated components.
Source pfonline.com/articles/030902.html

How Clean Is Clean?

A feature article in a recent issue of Products Finishing asked the same question as the headline of this story (March 2008). The article then went on to describe multiple standards and methods for determining the level of cleanliness of your parts, ranging from simple water break testing to complicated elemental and particle analysis using scanning electron microscopes and other sophisticated equipment.
A German supplier of precision cleaning and surface inspection equipment now has its own answer. Advanced Clean Production GmbH (ACP; Esslingen) says its PartSens device is the first ever to allow direct measurement and documentation of particulate contamination on component surfaces.
The device features a large measuring probe that ACP says significantly expands the potential range of applications, enabling rapid cleanliness checks of, for example, sheet metal blanks and automotive body panels. The probe has a measuring surface of 20 × 15 mm and allows for efficient, random sample testing of component surfaces for particulate cleanliness, according to the company. It can detect particulate contamination with sizes down to 25 µm, and measurement can be performed either manually or automatically.
The PartSens inspection system has a measuring surface of 20 x 15 mm and is equipped with optical filters that produce high-contrast images of surfaces being inspected. The result is precise, reliable measurement of particulate cleanliness on a variety of flat and shaped sheet metal surfaces.
The system works by using direct side lighting to illuminate the surface being inspected. Integrated optical filters produce images with extremely high contrast, assuring reliable inspection even under difficult conditions such as inspection of surfaces with complex geometries.
Testing is a simple procedure consisting of passing the measuring probe over the surface to be inspected. An integrated video display allows real-time visualization of the surface under test, and the number of particles, along with their size, orientation and position is represented in the live image.
The company says the instrument lets users reach reliable conclusions regarding the number, the size and size distribution of particles on the inspected surface. The system lets users program particle count, size and other characteristics in accordance with customer-specific requirements, documenting the required cleanliness of part surfaces. And, ACP says, the fact that measurement results are available immediately allows users to react without delay to problems, thus avoiding expensive rework and scrap.
Documentation of test results is via an integrated thermal report printer. Measured values and live images can also be saved to a USB memory stick for documentation and later analysis at a PC.
In automotive plants, inspecting sheet metal blanks before press forming is a typical application for the new measuring system, according to ACP. The company says a large U.S. automobile manufacturer is already using the system to inspect auto body panels for cleanliness before painting. Further applications include monitoring of production environments and examination of the degree of cleanliness achieved during cleaning.
source pfonline.com/articles/1208tn1.html

New Approach to Internal Deburring and Cleaning

A patented process for rapidly cleaning and deburring complex internal passages in castings and other components is being marketed. (Kalamazoo, MI).
Opposing nozzles can create a 360° blast pattern, and flow through intersecting passageways to provide rapid cleaning and deburring of castings and other parts with complex internal geometry. . Developed by Steve Carpenter, president of Hammond distributor (Grand Rapids, MI), the Recipro-Blast process uses opposing blast streams to create turbulence inside the component being processed. The turbulence created by the opposing streams aggressively removes internal burrs, burned-on sand and leftover mold or core materials from difficult-to-reach passages and highly cored and deep components. Nozzle and part movement are servo-controlled.
Carpenter explains that the system grew out of his foundry experience. “When I worked in foundries, first as a chief engineer and then as a plant manager, a common problem was cleaning interior part passages, especially small IDs with long or irregular sections,” he says. “In an effort to create turbulence that could be controlled, we tried introducing blast streams from opposing ends with some amazing results.”
Carpenter continued to develop the process, then patented it and sold the marketing rights to Hammond. He says it can replace labor-intensive hand cleaning, molten salt cleaning, rotary brushes, extensive external wheel blasting and other processes such as thermal deburring.
In simple terms, the process uses two or more opposing blast nozzles to impart reflective, random energy to the blast media at a chosen area inside the part. According to Carpenter, Recipro-Blast is much more effective and much faster than conventional blasting for internal deburring and cleaning.
From the outside, Recipro-Blast does not appear radically different than a conventional abrasive blasting system. “With a conventional lance, energy is lost because the abrasive is forced to turn an abrupt corner at the nozzle tip,” he explains. “This decelerates the blast media and reduces its effectiveness. However, two opposing nozzles create a mushroom effect and gives the added benefit of a 360° blast pattern, if desired.”
Nozzles used in the process do not have to be directly opposing, Carpenter says. “This is advantageous where part configurations don’t allow opposing nozzles, such as water jacket passages and oil galleries in engine blocks and turbocharger housings.”
Hammond has several systems in operation and is marketing the process to manufactures of hydraulic/pneumatic manifolds, valve fittings and bodies, and transmission components.
According to Carpenter, the process is also applicable for peening of internal surfaces. “Peening of normal surfaces is usually accomplished with a small-diameter lance with outlets exiting the lance at an angle,” he explains. “In peening, ideal effects are accomplished with the stream striking the desired surface at an angle approaching 90°. In the Recipro-Blast system, the angle can be varied by adjusting the pressure from side to side or changing the nozzle diameter. And, the system allows the abrasive to strike in a 360° pattern if desired, and at angles up to and past 90° with significant intensity and speed of coverage.”
Cutaway of passages in a hydraulic valve casting before (left) and after cleaning using the reciprocating blast system shows how the system rapidly removes sand and other casting debris. In one application, the process reduced time to treat internal surfaces of fuel system components from 10 min with a conventional lance to 10 sec.
Other applications for Recipro-Blast involves deburring of internal surfaces of precision components such as valves, metering devices, rectangular and tubular parts. “Most openings in tubular parts—holes, slots and others—are created from outside to inside, leaving burrs on the interior surface,” Carpenter says. “These can be removed using any of several methods, including thermal deburring, mechanical brushing, hand deburring, high-pressure water, conventional blasting, vibratory finishing and additional machine operations. All these have advantages and disadvantages, but the Recipro-Blast allowed consistent burr removal in a matter of seconds per part with a relatively low cost of installation.”
The system can use a variety of media for abrasive blasting and peening. Media choices include ceramic beads; glass beads; carbon, stainless steel and zinc cut wire; cast aluminum, stainless or steel beads; and dry ice.
source pfonline.com/articles/0209tn1.html