Zinc plating back in 1960, when Anoplate was founded by purchasing a small metal finisher by the name of Noxon Plating Works, contained the old standby, standard high cyanide, 4 ½ ounces per gallon zinc metal bath.  As early as 1855 patents were issued on the use of cyanide zinc plating, but it was not until the early 1920s when Blum and workers at the National Bureau of Standards developed the workhorse formulation which was the standard for about 50 years.  It was in the early 1970s, that the industry accepted the fact that much lower cyanide and higher caustic soda formulations as reported by R. Bair in December 1972 Products Finishing magazine.  Anoplate still maintains a small quantity of low cyanide zinc solution for certain fussy difficult to cover jobs.  It still is an easier to use and a more “forgiving” bath.

The next development at Anoplate was to install a small acid zinc bath.  You know how difficult it is to change an old workhorse.  It was very slow to be accepted.  The advent of increased pressure to be more environmentally sound precipitated this first attempt at removal of one cyanide source.  Finally some malleable castings came in for plating and with the typical over-voltage condition we got lots of gassing but little plating.  This was one of the “strong points” of newer acid zinc baths and beautiful, bright castings were the result.  Over the years, bright acid zinc has become the main bath in our hand plating and barrel department.

Now acid zinc baths have existed much longer than cyanide formulations.  Why were they not popular earlier?  Until the early 1930s, the majority of zinc plating was carried out using dull acid zinc baths.  In fact for over 80 years those formulations were used by the high-speed wire and sheet electro galvanizing industry.  The principal problem as far as job shop were concerned was that the dull acid zinc baths had poor covering power and their inability to plate reasonable thickness at low current densities without excessive plate buildup at higher current densities (edges).  In 1966, Schloetter Laboratories of Germany patented the basis for today’s modern bright acid zinc baths, which overcame most of the concerns.  Very bright acid zinc is now available from our hand/barrel zinc department.

We are not done yet with the development of zinc baths available at Anoplate.  With the tightening of thickness requirements, we had to overcome this “distribution” concern that acid baths have on “box shaped” parts.  Sheet metal enclosures are a major portion of our zinc requirements and that is where alkaline non-cyanide solutions show dramatic success.  With the installation of our 42 tank, ten foot long hoist line in building 400, it was imperative that as much uniformity of thickness be designed into the processing as possible.  Since the efficiency of the recent alkaline non-cyanide zinc formulations is higher at low current densities and lower at high current densities (edges), a much more uniform thickness range occurs on complex shapes.  Non-cyanide alkaline was the chosen bath.  This is especially important with sheet metal boxes containing pre-installed studs and fasteners.  Today, all three baths have their place in our zinc departments.

What about the future of zinc?  When this article was first published in Anoplate NEWS and subsequently picked up by Products Finishing magazine in 2000, we questioned whether or not Anoplate would ever be out of cyanide zinc plating.  Actually our last cyanide zinc bath was replaced in late 2008.  It’s wasn’t so much the danger of handling or working with cyanide (we still employ it for silver and cadmium plating as well as some stripping operations) as the improvements made suppliers of alternative zinc plating baths.  Zinc alloy baths, most notably zinc-iron, zinc-nickel, and zinc-cobalt are today inseparable from “zinc thinking”.  In most cases, these alloy deposits over steel offer anodic protection, similar to plain zinc, but with greatly improved salt spray life.  At Anoplate, zinc-iron was the alloy bath of choice due to its excellent blackening ability and improved light stability.  One of the keys to zinc remaining the corrosion protective coating of choice has been the development of good substitutes for the hexavalent chromate post dips.  European legislation which banned the use of hexavalent chromium in products, namely RoHS, WEEE and ELV, forced the industry to develop and deploy trivalent or non-chromium based post treatments for zinc plating.  It didn’t take long for Anoplate to adopt these new alternatives as in many cases, the new non-hexavalent products outperformed their predecessors.  We’re still struggling to find an aesthetically appealing black trivalent chromate, that is one that can be used without use of a blackened non-conductive topcoat but that search will continue until an acceptable product is found.  Every year we discover new or improved solutions to existing problems.  A Brazilian doctor, with very limited financial resources once said, “dar um jeito” which loosely translated is “no problem is unsolvable and no barrier too great to cross”.

For your zinc plating needs or to discuss a particular metal finishing application or project please call us at (315) 471-6143. You can also e-mail us at sales@anoplate.com.