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the premier coating for corrosion and lubricity, cadmium has faded greatly in automotive use and is predicted to be outdated soon.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.blog comments powered by Disqus