Dacromet is actually a trademark of Metal Coatings International, and it represents Dacromet coating. It is a method of applying a sacrificial coating of zinc. My understanding is it gives greater corrosion resistance than zinc electroplating (probably because it’s thicker).
Salt spray tests are not just a meaningful approach to predict the lifestyle of zinc-based coatings though. The protection they afford in real life arises from the development of stable and insoluble zinc carbonate corrosion products which develop over time with being exposed to the carbon dioxide inside the open air.
“The Perfect Finish” is one thing the market has sought for years. It is really an elusive concept on which huge amounts of money happen to be spent developing, testing and qualifying possible alternative finishes, but most of these efforts have already been futile. Each finish, from phosphate to cadmium, has weaknesses and strengths that must be weighed for every application. Using these considerations, progress can be created toward utilizing the materials which have the closest 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. Details are specific to fasteners in terms of clamp load and corrosion, both cosmetic and galvanic. The scope was broadened to understand many aspects of each finish to provide engineers information vital to recommending their use as cadmium substitutes and exposing weaknesses of every finish. One inorganic alternative was discovered to become a drop-in replacement for cadmium, and the other two were found to closely resemble cadmium’s performance in all respects with the exception of electrical conductivity.
Because cadmium offers excellent corrosion resistance, consistent torque-tension, bimetallic compatibility and thickness within standard thread tolerances, this has been most engineers’ finish of choice for many years. It is actually still utilized in many applications that cannot sacrifice some of the qualities that Best Zinc Flake Coating Line Manufacturer offers.
Initially, automotive OEMs established a deadline to get rid of cadmium by 1995. Chrysler enacted testing programs to fill the hole in the 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 ended in the selection of the Dacromet 320® L coating system as 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 associated with this DOE.
Due to the extreme utilization of its equipment in critical situations, the military continued to utilize cadmium for many applications. The delay in switching from cadmium-plated hardware proved beneficial because automotive OEMs compiled much information during that time. The military sorted from the data created by automotive qualifications and selected zkqjlg coatings that performed well inside the predetermined areas, which in-turn resulted in a substantial cost savings.
36 months ago, the Army embarked over a cadmium replacement journey, testing numerous finishes as potential candidates.2 Although no “perfect finish” was found, this testing led to the qualification of any 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 insufficient conductivity, high coating thickness as well as the reliance upon a supplemental lubricant to meet Army torque charts. Another attribute that really must be considered is that this coating was solvent-based and for that reason loaded with volatile organic compounds (VOC). As a result of VOC content, application facilities required expensive air treatment equipment to lessen pollution that otherwise could have escaped in to the environment.