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topic 9779

Pre treatment issues


We run our Paintline on alternate days or twice a week. There is a five stage pretreatment,

1. Degreasing
2. Water rinsing
3. Zinc phosphating
4. Water rinsing
5. Di water rinsing before Powder painting.

What we obseve when we run the conveyor line in the first few carriers there is "Yellowing" observed on the components after phosphating. Our chemical supplier says, the chemical bath prepared requires "iron content" from the components. He suggests few dummy carriers to be left with steel sheets will solve the issue.

We need any other practical solution without wasting steel sheets..?

Nanda V Srikakulam
Otis - Bangalore, India


I have used 0000 steel wool [linked by editor to product info at Rockler] to provide iron content to a fresh bath. You can just take a piece of steel wool or even clean scrap steel and throw it in the bath. The phosphate bath will dissolve Fe ions from the steel part. If you use scrap steel, make sure it is clean and free from any oils or other soils that could contaminate the phosphate bath.

Patrick Patton
- Westlake, Ohio, USA

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