Metal finishing Q&As since 1989

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Pre-treatment Problem

2004

Dear Sir,

We are painting automotive components having .6mm as the sheet thickness and roughness of less than 1 on the sheet. We get variable results in our spray washer line which is 9 stages. Some times there is powder after phosphating or yellowness and patches after phosphating. Can somebody give some help to us so that we can overcome this problem. We feel that sheet is not up to the mark and it is creating the problem. Please help me.

Regards,

Srikant Dubey
Pre-treatment - Noida, U.P., INDIA

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Sounds unlikely that there is any problem with your sheet. There could be 101 things out of control in your Pretreatment Line. Enlist the help of your Proprietary cocktail supplier.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

2004

I don't think your substrates is the source of your problem. Please do check your phosphating parameter, i.e., operating temperature, filter and tank volume. Yellowness and patches on the surfaces indicate the following process ( DI Water Cleaning?) is not up to the standard and make sure process before phosphathing such as water rinsing, adjust the pH to be a bit alkaline (ph 7.5-8.0).

Romi Sabihin
- Sg Buloh, Selangor, Malaysia
2004