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There is an increasing demand for hexavalent chrome-free coatings that have equal corrosion resistance and wear resistance. TOPCOAT 107, Griekspoor’s economical hexavalent chrome-free alternative to nickel chrome plating, scores very high on both aspects. In this article you read more about the corrosion resistance of TOPCOAT 107.
Chemical resistance and quality of application: a soldi duo
The corrosion resistance of TOPCOAT 107 stems from the chemical resistance of the coating material and the quality of the Griekspoor flame spraying application.
The exact composition of TOPCOAT 107 is confidential but we can give a glimpse of the materials in the alloy. In 2017 we challenged ourselves to create a hexavalent chrome-free coating with superb durability. We started with a nickel based superalloy. Nickel, however, is tough but not hard enough to serve as a coating for piston rods. Therefore we added carbides to the alloy. This balanced mix resulted in a hardness of 950-1400 HV0.3 delivering excellent wear resistance. As several tests have shown we have developed the holy grail in coatings.
TOPCOAT 107 is used in the most severe of conditions and because of that we aimed high for the coating’s corrosion resistance. Among other things the coating had to be able to perform for years in high temperatures with high salinity. A lot of the piston rods we treat are used in tropical conditions where they are constantly exposed to salt water.
Besides that a high chemical resistance was an important premise. Corrosion is deterioration of metals due to electrochemical reactions. Coating has to prevent this but cylinder heads are often uncoated on the inside. Around scrapers and seals cylinder heads corrosion may occur. The corrosion leads to the formation of iron oxide which in turn may lead to pH levels as low as pH 2. This acidic environment usually affects the piston rod coating adversely but TOPCOAT 107 has such a high corrosion resistance that it can even withstand these severely acidic environments.
The quality of the coating process is the final touch in the remarkable achievements of TOPCOAT 107. If the coating is not compacted enough when applied it may lead to leaks. Combined with salt water these leaks can cause corrosion of the base material, pushing even the best alloys off of the piston rod. To prevent this we meticulously monitor the coating process and we test the coatings continuously. Standardised electrochemical porosity tests and polarisation curve testing, both performed in-house, ensure the highest quality of coating and the best corrosion resistance.
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