Dacromet is a trademark of Metal Coatings International, and it represents Dacromet coating Supplier. This is a means of applying a sacrificial coating of zinc. My understanding is it offers greater corrosion resistance than zinc electroplating (probably because it’s thicker).
Salt spray testing is not a meaningful method to predict the lifestyle of zinc-based coatings though. The security they afford in real life originates from the formation of stable and insoluble zinc carbonate corrosion products which develop with time with exposure to the carbon dioxide in the open air.
“The Perfect Finish” is something the business has sought for years. It is really an elusive concept which vast amounts of money happen to be spent developing, testing and qualifying possible alternative finishes, but the majority of these efforts have already been futile. Each finish, from phosphate to cadmium, has weaknesses and strengths that really must be weighed for each application. Utilizing these considerations, progress can be created toward using the materials that have the nearest resemblance towards the strengths of cadmium which are required and, consequently, accepting their weaknesses.
This paper describes an investigation study conducted on eight finishes that are potential replacements for cadmium. Information is specific to fasteners in relation to clamp load and corrosion, both cosmetic and galvanic. The scope was broadened to know many aspects of each finish to provide engineers information vital to recommending their use as cadmium substitutes and exposing weaknesses of each finish. One inorganic alternative was discovered as a drop-in replacement for cadmium, and the other two were found to closely resemble cadmium’s performance in every respects aside from electrical conductivity.
Because cadmium offers excellent corrosion resistance, consistent torque-tension, bimetallic compatibility and thickness within standard thread tolerances, it really has been most engineers’ finish preferred by many years. It really is still found in many applications that cannot sacrifice the qualities that Zinc Flake Coating offers.
Initially, automotive OEMs established a deadline to get rid of cadmium by 1995. Chrysler enacted testing programs to fill the hole in their fastener finish requirements.1 Chrysler conducted a Form of Experiment (DOE) to qualify alternatives that met strict performance requirements and also followed OSHA and EPA regulations. This DOE resulted in the selection of the Dacromet 320® L coating system since it closely resembled cadmium in fastener applications. Consequently, Chrysler was compliant with OSHA and EPA regulations ahead of the established deadline. Metal Coatings International Inc. (MCII) was involved with this DOE.
Due to the extreme utilization of its equipment in critical situations, the military continued to use cadmium for many applications. The delay in switching from cadmium-plated hardware proved beneficial because automotive OEMs compiled many details in that time. The military sorted with the data produced by automotive qualifications and selected zkqjlg coatings that performed well in the predetermined areas, which in-turn resulted in a substantial cost savings.
Three years ago, the Army embarked over a cadmium replacement journey, testing numerous finishes as potential candidates.2 Although no “perfect finish” was discovered, this testing ended in the qualification of the solvent-based coating that closely resembled Full Automatic Dip Spin Coating Machine DST S800+ in relation to corrosion protection, bi-metallic compatibility and clamp load retention. The weaknesses exposed were lack of conductivity, high coating thickness and the dependence on a supplemental lubricant to fulfill Army torque charts. Another attribute that must definitely be considered is the fact this coating was solvent-based and thus rich in volatile organic compounds (VOC). Because of the VOC content, application facilities required expensive air treatment equipment to reduce pollution that otherwise would have escaped into the environment.