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 really a meaningful way to predict the lifestyle of zinc-based coatings though. The protection they afford in the real world originates from the development of stable and insoluble zinc carbonate corrosion products that develop with time with contact with the fractional co2 in the open air.
“The Ideal Finish” is one thing the market has sought for a long time. It is really an elusive concept where vast amounts of money have already been spent developing, testing and qualifying possible alternative finishes, but most of these efforts happen to be futile. Each finish, from phosphate to cadmium, has strengths and weaknesses that must definitely be weighed for each application. Utilizing these considerations, progress can be produced toward utilizing the materials that have the nearest resemblance for the strengths of cadmium that are required and, consequently, accepting their weaknesses.
This paper describes a research study conducted on eight finishes that are potential replacements for cadmium. Information is specific to fasteners with regards to clamp load and corrosion, both cosmetic and galvanic. The scope was broadened to comprehend many components 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 found to become a drop-in alternative to cadmium, and another two were found to closely resemble cadmium’s performance in all respects aside from electrical conductivity.
Because cadmium offers excellent corrosion resistance, consistent torque-tension, bimetallic compatibility and thickness within standard thread tolerances, it has been most engineers’ finish of choice for many years. It is actually still used in many applications that cannot sacrifice the qualities that Zinc Flake Coating offers.
Initially, automotive OEMs established a deadline to eliminate cadmium by 1995. Chrysler enacted testing programs to fill the hole in their fastener finish requirements.1 Chrysler conducted a Design of Experiment (DOE) to qualify alternatives that met strict performance requirements and in addition adhered to OSHA and EPA regulations. This DOE led to the selection of the Dacromet 320® L coating system because it closely resembled cadmium in fastener applications. Consequently, Chrysler was compliant with OSHA and EPA regulations prior to the established deadline. Metal Coatings International Inc. (MCII) was associated with this DOE.
Due to the extreme usage of its equipment in critical situations, the military continued to utilize cadmium for a lot of applications. The delay in switching from cadmium-plated hardware proved beneficial because automotive OEMs compiled much information in that time. The military sorted through the data produced by automotive qualifications and selected zkqjlg coatings that performed well within the predetermined areas, which in-turn resulted in a substantial cost benefits.
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 led to the qualification of a solvent-based coating that closely resembled dip spin coating for green plating equipment with regards to corrosion protection, bi-metallic compatibility and clamp load retention. The weaknesses exposed were absence of conductivity, high coating thickness and also the dependence on a supplemental lubricant to satisfy Army torque charts. Another attribute that really must be considered is that this coating was solvent-based and thus loaded with volatile organic compounds (VOC). Due to the VOC content, application facilities required expensive air treatment equipment to lessen pollution that otherwise might have escaped in to the environment.