This rust proofing treatment was discovered and patented by Mr Sherard Cowper-Coles at the turn of the 20th century and became an established process in the 1920’s until the present day.   

The process involves an interaction at a controlled temperature of 380 to 450ºC between the base metal and zinc dust during which a zinc alloy is produced at the interface.  Beyond the alloy interface, a layer of almost pure zinc can be built up by prolonging the treatment. The coating thickness would typically be 25µm Delta layer alloy and 15µm Gamma layer of zinc.  The process is in accordance with the UK standard BS4721 or to customer specifications.

Because the process is primarily one of impregnation (60% +) rather than deposition (as with galvanising),  there is a reduced tendency for build up on external corners.  This factor is particularly important for the rust proofing of threaded components such as those employed in various AV Mount applications.

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