Metal finishing Q&As since 1989

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Rust Formation Post Phosphate Pressure Wash

Our company utilizes a Pressure Island spray system for degreasing tubular and sheet steel parts in preparation for powder coating. We have a problem with rust forming once the parts are dry and before we can powder coat them. The time interval is brief. We are using a no rinse system from Oakite [Chemetall]. The description is "Gardobond A 4961". We monitor the ph level, concentration of solution and temperature closely. Yet, we are getting rust. My question is: Is there a no rinse phosphate degreasing and cleaning system out there that will work with a pressure washer and not rust?

Ron Isles
reproductions - La Mirada, California, USA
2002

Hi Ron,

Flash rust is a troublesome problem when applying an iron phosphate by spray wand. Given the right conditions, a surface that has just been phosphated can corrode quite easily.

Normally, the phosphating product will be formulated to prevent the formation of flash rust. It's not possible in this forum to know how your current product is formulated.

George Gorecki
- Naperville, Illinois
2002

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Ron,

I notice that this product is "optionally" non-rinse. I think you would be better to use a monoethanolamine based cleaner which would offer some rust protection and overpaintability. Pint performance of any process will be governed by water quality and the ionic content of the process.

Roger Bridger
- Croydon, UK
2002

I agree that flash rust and high pressure spray systems can be a challenge in certain circumstances. FYI there is a high pressure system that will be hitting the market shortly that will have separate stages for phosphate, rinse, and sealer which can help solve your problem.

Dan Martelli
- Menlo Park, California, USA
2004