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-----How to do olive drab phosphate or chromate conversion coating
Phosphating is a coating usually done on steel components as a base for paint or as a final finish for parts which are intended to remain oily. As a paint base it improves corrosion resistance and paint adhesion. As a free-standing finish it doesn't offer significant corrosion resistance by itself, but is a good oil-retention surface and the phosphate plus oil is corrosion resistant.
Chromate conversion coating cannot be applied directly onto steel parts, but is a finish applied after zinc plating to deter white rust. Chromates can be applied rather lightly or rather heavily; olive drab chromates are the thickest and most corrosion resistant.
Q. I am looking for the materials needed and process instructions to phosphate coat or chromate conversion coat steel parts; the finished product should be a very dark Olive drab green.
Thank you,
Jeff Kubosh- South Houston, Texas
2003
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A. Hello, Mr. Kubosh--
Steel can't be chromated directly (rather, the steel is zinc plated and the chromate is applied to the zinc plating). Phosphating is therefore probably more promising from an economics viewpoint. Phosphate finishes need to be kept oiled for proper corrosion resistance, and thread 219/62 discusses the possibility of applying an olive drab post-dip to the phosphate, and thread 204/57 observes that colored oils are available. That may be an answer for you. Good luck.
Ted Mooney, P.E.
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