Dacromet is actually a trademark of Metal Coatings International, and it represents Dacromet coating Manufacturer. It is a method of applying a sacrificial coating of zinc. My understanding is it provides higher corrosion resistance than zinc electroplating (probably because it’s thicker).
Salt spray testing is not a meaningful way to predict the life span of zinc-based coatings though. The safety 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 fractional co2 within the outside.
“The Ideal Finish” is one thing the industry has sought for many years. It is an elusive concept where 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 good and bad points that really must be weighed for each and every application. Using these considerations, progress can be created toward using the materials who have the nearest resemblance to the strengths of cadmium which can be required and, consequently, accepting their weaknesses.
This paper describes an investigation study conducted on eight finishes which are potential replacements for cadmium. Information is 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 offer engineers information vital to recommending their use as cadmium substitutes and exposing weaknesses of each and every finish. One inorganic alternative was discovered to become a drop-in alternative to cadmium, and another two were found to closely resemble cadmium’s performance in every respects with the exception of 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 of choice for several years. It really is still used in many applications that cannot sacrifice any of 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 its fastener finish requirements.1 Chrysler conducted a Form of Experiment (DOE) to qualify alternatives that met strict performance requirements and in addition followed OSHA and EPA regulations. This DOE ended in selecting the Dacromet 320® L coating system since it closely resembled cadmium in fastener applications. As a result, Chrysler was compliant with OSHA and EPA regulations ahead of the established deadline. Metal Coatings International Inc. (MCII) was included in this DOE.
Because of the extreme use of its equipment in critical situations, the military continued to utilize cadmium for most 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 produced by automotive qualifications and selected zkqjlg coatings that performed well inside the predetermined areas, which in-turn resulted in a substantial cost savings.
Three years ago, the Army embarked on a cadmium replacement journey, testing numerous finishes as potential candidates.2 Although no “perfect finish” was discovered, this testing resulted in the qualification of any 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 insufficient conductivity, high coating thickness and the dependence on a supplemental lubricant to fulfill Army torque charts. Another attribute that must be considered is the fact that this coating was solvent-based and for that reason high in volatile organic compounds (VOC). Due to the VOC content, application facilities required expensive air treatment equipment to lessen pollution that otherwise could have escaped in to the environment.