Metal finishing Q&As since 1989

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Pre treatment of steel after shotblasting.

 

I am service development manager at a company which reconditions wheelchairs.We remove all of the old paint finish via a shotblasting process, prior to a respray in polyester powder coat finish. Is it necessary to carry out any further pre treatment after shotblasting to ensure a good 'key' for the powder coat?

Alan J. Dodds
Remploy - Coventry, West Midlands, UK

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Dear Mr. Dodds,

Normally, a blasting operation is a good preparation for powdercoating. Some points to consider:

- Blasting should be done with angular-shape material in order to get enough surface profile (Saw-tooth shape)
- De-dusting after blasting must be done very thoroughly
- Be aware: since you have no conversion-coat (i.e. phosphating)the anti-corrosion resistance would be fairly poor, but this will be probably no problem with wheel-chairs

Hope to have helped you,

Remmelt Bosklopper
- Enschede, The Netherlands

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It's nice to see companies that refurbish and/or reuse resources. Blasting is a good way to clean and prepare the surface of the substrate. You must remember that blasting media (abrasive material) can potentially reintroduce oils, soils and other contaminants to the surface. Liquid topcoats generally are more forgiving when dealing with these contaminants, however, powder coating is not as forgiving. For optimum durability and customer satisfaction, the substrate should be at least washed thoroughly and if possible be phosphated.

Bob Utech
Benson, Minnesota