Deciding which zinc alloy will work best...
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Finishing a 650-pound steel plate would have been unthinkable on a hand-line but is handled easily on the new zinc-iron line.
It was just 2 years ago when our company newsletter, Anoplate News carried the banner "Which Zinc?" However, the history of zinc plating at Anoplate dates back to the traditional cyanide zinc formulations, which Geduld's Zinc Plating states is how the majority of commercial zinc plating was done from 1935 to 1975. Anoplate's humble beginnings in cyanide zinc plating began in 1960. Over a period of years, scientific advances and environmental progress helped introduce various acid zinc and low cyanide baths that were installed and certainly served their purpose at Anoplate.
Despite the limitations of acid zinc, including brittle deposit, difficulty in painting and poor thickness uniformity on rack work, the process performed well for barrel applications and for those customers who desired an almost nickel-like, decorative appearance. However, by 1995, with increasing pressure to minimize cyanide use, Anoplate still needed to find an alternative to cyanide zinc plating.
There was no specific customer pushing for any huge volume of zinc or zinc-alloy deposition. Our hand lines, with a small, overhead rail hoist, took care of most of our needs. However, by the mid-90s the size of the parts became larger and delivery issues arose. Also, we sometimes had trouble with quick turnaround, and we were looking at expanding our zinc capabilities. In addition, we toyed with the idea of offering a zinc alloy, again with no direct customer input, just recognizing growth in the marketplace and perhaps an opportunity.
In 1998, we purchased a 40,000-sq-ft building across the street from our present facilities. This gave us time to plan and design new shop layouts. As a typical growing job shop, we had modified departments and various lines within the shop over time without an entire overhaul or redesign. Typical space constraints were obvious in our existing 70,000-sq-ft facility. The new building gave us the opportunity to design, upgrade and expand some existing departments. There were many finishes that we put on our "wish list," including, zinc, anodizing, tin and black oxide. With an empty building, we could fulfill our wishes after major infrastructure needs were met.
An interdisciplinary task force of quality, engineering, environmental operations, finance and production representatives took on the task of compiling diverse wishes and expectations, blending them with the reality of experience and a newer, more environmentally friendly zinc and finite funding to arrive at a final design. Mike Florczykowski, Anoplate's chief environmental officer, assumed the role of project engineer. Using a team of outside suppliers, our personnel and his own experience as a facilities engineer with a Fortune 500 firm, the task was accomplished in timely fashion once a final design and budget was agreed upon.
The former building owners had used the facility as a packaging warehouse, so the plant floor had limited electric, no steam, heat or water. It took nearly 6 months to get the physical plant in order prior to installing the zinc plating line. While the physical plant was put in order, the zinc line design criteria were developed and a bid package released. By the time the physical plant was ready, the 42-tank hoist line and all of its ancillary equipment had been bid and awarded. Installation and startup occurred in less than 90 days. Included in the line, beyond the normal cleaning setup for steel, was a periodic reverse cleaning tank for weld scale removal and a die-cast cleaning line. The supplemental treatments included trivalent clear chromate through olive drab as well as two black chromates and a final sealer for boosting corrosion resistance.
During line design, we faced two questions. "Which zinc?" and "Which alloy?" If any. A 6-month study was conducted on 8 proposed zinc processes, and MacDermid's Isobrite™ 424 alkaline noncyanide system was chosen. Based on our tests, the process demonstrated good throwing/covering power, and it was more tolerant to normal contaminants. The system did not have harmful hazardous additives nor were there compounds present that would interfere with our waste treatment operation. With the possible need for conforming electrodes, the alkaline zinc formulation allowed us to use common steel anode material.
The line has a 4,200-gal zinc bath holding 3 flight bars. A zinc generator is used for dissolving the zinc and additions are made to keep the zinc concentration at 1.1 to 1.3 oz/gal. This is a safe range to balance covering power versus efficiency.
Now we get to the other half of the two-part question, "Which alloy?" Once again, no specific customer needs, just a realization that market forces were at work and that there was an improved zinc out there. We had to go out and make the best decision based on the merits of the process and competitive pressure. Upstate New York already had significant capacity in both zinc-nickel and zinc-cobalt plating. That was one reason for looking at zinc-iron. Next, a modest portion of our work increase was in the area of "zinc black" requests. Zinc-iron alloys have the best success with blackening, and a nonsilver-bearing black chromate solution specifically formulated for zinc-iron deposits ensured higher reliability due to its light stability. The potential for rework, months after finishing, due to black zinc degrading over time to an olive drab color, was eliminated.
It is important to note that the corrosion resistance of most zinc alloys is superior to straight zinc deposits. It is common to have salt spray results for zinc-iron deposits in the 750 to 1,000-hr range. The plating literature, supported by automotive industry standards, suggests that there are good corrosion results using straight zinc plating with various organic polymer topcoats.
Typically used for fasteners and similar hardware, such topcoats improve the corrosion resistance while improving the torque-tension range or holding power of the fastener as well. With most sheet metal and machined parts that Anoplate processes, however, conductivity is a major factor and organic topcoats create nondesirable, nonconductive coatings over our zinc. So the zinc-iron deposit gives us one more finish in our repertoire of more than 100 metal finishing processes.
A major technical issue regarding zinc-iron plating helped with our decision. Zinc-iron yields a uniform composition across a range of current densities. For example, to blacken a complex chassis properly and uniformly, the iron content must be in the upper part of the alloy range (0.3 to 0.8%). Variable composition in zinc-nickel and zinc-cobalt lead to difficulty in chromating as well as increased process control and analytical support. The only known drawback of blackened zinc-iron is that when subjected to moderate heat for a prolonged time, the otherwise outstanding corrosion resistance can suffer. Because of this, it is advisable to test the black zinc-iron deposits under actual operating conditions.
The new zinc facility and its accompanying environmental control and related physical plant equipment did not fill the new Building 400. Recall the other expansion departments on our "wish list?" Well, we are close to completing a black oxide line. Acid-proof floors, exhausts, hoist and tanks are in place. Well before spring, that department will move across the street. A realigned hardcoat department installation, along with its new computer process control support will be operational this summer in its expanded department. This expansion is long overdue and will double our current hardcoat anodize capacity.
What will the future hold? Relieving the space crunch in our original facility will allow for further department redesign so that we can offer customers more efficient finishing lines, faster turnaround and competitive pricing. In our new building, the support functions such as environmental operations and boiler room were located such that it would permit for easy production expansion, if needed, on to our contiguous seven-acre woods. Anoplate and its 170 employees are poised for the new millennium, as we celebrate our 40th year in business.blog comments powered by Disqus