Q: I have a question regarding cleaning steel before powder coating. We powder coat mainly welded parts made with hot-rolled steel. Our paint line is composed of steps:
- 1. A shot blaster
- 2. 5 stage cleaning stations (alkaline clean, rinse, phosphate, rinse, rinse/seal)
- 3. Dry-off oven
- 4. Powder coat booth
- 5. Cure oven
We have been hearing of a theory that you get the same results even after eliminating completely steps 2 and 3 listed above. I always learned and believed that you have to clean the steel before you powder coat. Is that possible to eliminate the steps 2 and 3 and still have the same quality application of powder coat on steel? If yes, what are the long-term effects?
A: I think that you have been getting spurious information regarding the criticality of proper pretreatment. High-quality pretreatment is essential when powder coating cold-rolled steel, and it is even more so when coating hot-rolled steel that has welds. The shot blasting makes a huge difference in the surface readiness for the phosphating steps. It ensures that there is minimal mill scale and/or smut. The cleaning step dissolves away any incidental oils, dirt, or handling contaminants. Rinsing eliminates the alkaline cleaner, which would otherwise contaminate the low-pH phosphate. The phosphate creates a chemical bridge for the powder to anchor to the metal. The final rinse/seal provides additional insurance for corrosion resistance.
Otherwise, your system as it operates today was set up properly to provide a high level of performance. Whoever engineered it knew what they were doing. It’s encouraging to encounter an operation doing things right. Keep up the good work.