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Improve the quality of the zinc yellow chromate coating

2004

Hello!

In the zinc plus yellow chromate process,we have came across some difficulties and we are actually seeking for some solutions.

First of all we put the metal parts-which they are actually of small volume-in plastic cylindrical barells which they rotate in the solutions and they move automatically through a PLC system.At first they are being plated with zinc (the zinc plating is about 0,0004 in)and then the yellow chromate conversion coating is applied.The objects remain in the yellow chromate solution for about 1 minute.

At the end of the yellow coating process,the metal parts are rinsed with water.

After the parts are dried, we observe a red rust corrosion on the surface of the parts.

We have supposed some reasons for not having a successful yellow chromate coating.

We are wondering if the fact that the objects are not dived in the solution separately but the whole quantity-which means that they come in touch-may cause some kind of problem.We are still not so sure if 1 minute is enough time for a successful yellow coating.and finally we are still wondering whether the drying process has to be done under some specific conditions referring to the temperature,the pressure etc.thanks you in advance.

We would be grateful having a prompt reply

IRAKLIS SAATSOGLOU
roda s.a - THESSALONIKI, GREECE

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2004

The problem that you had is simple you need work your yellow chromate in 1.6 to 1.8 in ph the time is no more than 15 to 20 seconds.

A minute is a long time in then you strip the zinc plate.

You need minimum 5 microns to support the yellow chromate.

Best Regards.

Gabriel Ramirez Nuñez
- Toluca, Mexico