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USE OF DI WATER IN WATER TREATMENT PLANT FOR RINSING IN POWDER COATING PLANT

Hi there!

I just want to know the importance of D.I water in chemical treatment on ferrous surfaces prior to Powder Coating. We do have spray booth type state of art equipments but the D.I plant isn't working properly and was out of order for some time. I am wondering how important it is to use this D.I water and what Impact does it make on the surface finish. At the moment we are getting uneven Phosphating on our products. It seams like some flood has passed by and have left some bluish lines on it.

Can any one suggest some measures to be taken please!

Regards,
Raza

M. Ahsen Raza
- Karachi, Pakistan
2007

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Hi, Raza. I don't know quite what you mean by "suggest some measures to be taken". Obviously, getting the DI unit back in service is important. If you are asking whether parts that were not rinsed need to be rejected, or even recalled from the field, I don't think anyone has enough info to answer that.

Very good rinsing, either DI or with an additive, is necessary between phosphatizing and painting for maximum corrosion resistance. The usual procedure is to develop a robust treatment system, test that it works as planned, and then carefully adhere to it. Unfortunately , the question of the severity of the impact if you don't adhere to the plan is generally not answerable. Sorry, I am not personally familiar with a bluish "high water mark" effect, but maybe another reader is.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
February , 2007

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2007

The answer to your DI questions depends on the quality of your tap water. Some places have near DI quality tap water and others have terrible water.
The typical reason for a DI system not working is simply that it is not being taken care of per the DI system manufacturers instruction sheet.
It is penny wise and pound foolish to run a system any longer than it is supposed to before regeneration. You get very bad water and sometimes it will damage the resin. Not having a proper filter and carbon pack ahead of the resin tanks will give much shorter regeneration times and probable resin failure.

James Watts
- Navarre, Florida

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Mr. Raza,
The Powder Coat Institute sells books that will answer all of your questions, you need more information than can be presented here. Your chemical vendor should also be helping you set up your system.

Sheldon Taylor
supply chain electronics
Wake Forest, North Carolina
2007

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2007

Dear sir,

'getting uneven Phosphating on our products. It seams like some flood has passed by and have left some bluish lines on it'

1. check the NOZZLE if your process is auto spray.
if you use zinc phosphate
2. check/add the conditioner to get the fine crystal phosphate coating
3. check the free acid, total acid, accelerator. free acid have to in range 1.0 to 1.2

Jaff
- Malaysia