Technical Resources Area
Main Site  |  Technical Index   |  Data Sheets  |  Processing Guides  |  Enquiry Form  |  Service Conditions		Tel: +44 (0) 1252 733777	Close window

PRE-TREATMENTS FOR STAINLESS STEEL

1) Mechanical Pre-treatments

Stainless steel has a smooth surface therefore needs to be etched to create a good mechanical key. This will enhance any chemical key that is inherently produced by the coating. Although steel grit can produce the profile, it may embed itself into the stainless steel surface. If this happens then bimetallic corrosion may occur later in service. The recommended abrasive is aluminium oxide. Guyson produce a brown aluminium oxide that is cost effective. Plascoat would recommend a profile of 30 to 50 microns. The profile is achieved by the size of the grit, the gun nozzle design, the gun pressure, the distance from the work piece and the spray time. If the profile cannot be easily achieved we would advise the applicator to seek advice from the supplier of the abrasive.

2) Chemical Pre-treatment

It is very difficult to chemically pre-treat stainless steel. It is necessary to remove the oxide layer and the traditional method uses nitric and hydrofluoric acids. These are not user friendly and I would not recommend their use. Zinc phosphates will not react with this oxide layer and so cannot be used. However iron phosphates, which work in a different way, can react, but on their own they do not produce a strong enough key. Henkel have done some work for us on a low grade stainless steel called Cromweld 3CR12 and found that a Zirconium passivator after the iron phosphate gave a good result. This passivator may work on other stainless steels that have been iron phosphated but this must be verified.

3) Summary

From the above the best and most consistent pre-treatment for stainless steels is a 30 to 50 micron profile produced using brown aluminium oxide grit. For thermoset powder coating a profile of 50 microns may be better. These recommendations are valid for powder coating in general as well as for Plascoat PPA571.