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Powder coating - problems in pretreatment

2006

Hello everyone,

My question is about a problem that we are experiencing quite a long time and unfortunately that isn't solved yet.

Our powder coating line consists of 5 main divisions:
Degreasing, Rinsing, Preheating, Coating, Post-heating

We use an acidic iron phosphate compound in degreasing bath (%1 mixed with tap water). pH is generally around 4.0 and bath is kept at 60 °C. This compound is sprayed on 1008 cold drawn steel wires through nozzles. After preheating at about 370 °C, the wires are dipped into polyamide powder.

Most of the time, we can see "pin-holes" on several wires when the process is finished. We tried to change process parameters like temperature, PH, etc but nothing worked. Last month we shut down the degreasing pumps and saw that pinholes disappeared! But, we had adhesion problems without phosphating. So, we can't live with or without degreasing step. We think about changing the chemical we use, but contents are all same.

So, 2 questions:
1. Do you have any suggestions?
2. We sent tap water to a lab for chemical analysis and results show 30,000 ppm of sulphate(SO4) in water. Do iron phosphate react with sulphate?

Thank you for your time
Best Regards

Levent Subasi
factory - Ankara, TURKEY

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Hello,
Your rinse should be purified water(R/O or DI). Since you are using a 2-stage system, make sure you are skimming the oil off of the top of the water daily in the 1st stage(oil will appear after the pumps are shut off and the water cools) so that it is not re-deposited onto the parts later. Make sure that the phosphate has a cleaning agent in it. It probably does, but ask you're chemical supplier anyway. You're concentration looks a bit low, 2-2.5% might be better, you'll probably end up using something to increase the pH if you run the con. higher, but if it produces a better part it will be worth it.

Sheldon Taylor
supply chain electronics
Wake Forest, North Carolina
2006

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The SO4 concentration is 30, not 30000. So, you can forget about question 2.

But question 1 is still valid of course...

Levent Subasi
- Ankara, Turkey
2006

Please advise me how do you heat your degreasing tank/liquid?

Nit N.
- Thailand
2006

Please let me know your tank size ,chemical additions per each tank.

Dr Halim Polat
- Istanbul, Turkey
2006