New Thick Film Chromate finishes for Zinc Barrel Line

Following a series of production trials with various customers, CP Plating has introduced two new thick film trivalent chromate finishes to our Zinc Barrel plating line. The two new chromates meet and exceed AS 1789-2003 designation C, class 2 classified coatings. The chromate is available in two distinctly different iridescent finishes, one giving a blue appearance and the other yellow.

There are several advantages to the trivalent thick film chromates. The first being that they are hexavalent chromium free solutions able to meet current automotive requirements. This also means that our waste treatment system has to convert one less product containing hexavalent chromate to trivalent chromate before processing.

Secondly, thick film trivalent chromates provide significant improvements over the thin film trivalent chromates for corrosion protection. In some cases the improvement is over five times that of some thin film trivalent chromates. This is essential for barrel electroplating processes, as the thickness of zinc is limited by the process itself resulting in a reduction of protection provided by the zinc layer alone.

The final major factor leading to our decision was that the thick film yellow trivalent chromate gave CP Plating a much more durable option for post plating heat treatment, as compared to yellow hexavalent chromate. The option to be able to heat treat finished barrel work between 190 and 210 deg C allows us to perform hydrogen embrittlement relief without causing the chromate to fail prematurely under corrosion testing.

The new iridescent thick film blue trivalent chromate replaces our current thin film blue trivalent chromate on the barrel plating line. The new yellow iridescent thick film trivalent chromate is currently working as an alternative, to the current gold/yellow hexavalent chromate and will be under consideration as a full replacement over the coming months. The new chromates for the barrel plating line work in well with our current rack plating line chromates. The thin film clear/silver trivalent chromate used on the rack plating lines is quite thick and borders on a thick film designation as indicated by its slight iridescent appearance. We are still supplying a gold/yellow hexavalent chromate on the rack line, but should corrosion testing prove favourable, CP Plating might consider replacing it with a thick film trivalent chromate instead!

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