The Problem-Solution Series: Part 4

Streaks, Spots, Solution?

Problem: 

The pretreated part appears to have streaks and spots, but I thought I did everything right. How do I get rid of them or stop this from happening?

Origins/ Causes: 

There are several reasons that these spots and streaks could begin appearing. Here is a handy list of just a few of the causes:

• Soils are not being efficiently removed
• Parts are not fully rinsed, or the rinse is contaminated
• Drying off of the coating is occurring between stages
• The phosphate coating weight is too low

Solutions: 

If…

• It seems that the soils are not being removed, you may need to test the cleaning stage. This means that you should determine if the proper choice of chemicals and process conditions have been chosen (remember: acid conditions clean inorganic soils and alkaline conditions clean organic soils)
• The parts are not fully rinsed or there is contamination, orient the pars for maximum coverage. Also, clean and adjust the spray nozzles for maximum coverage. As always, ensure that you are maintaining high rinse tank purity.
• You notice that dry-off is occurring between stages, allow sufficient time for adequate drainage, yet not enough time for dry off. If possible, reduce the temperatures, and utilize the fog nozzles and adjust them for maximum coverage.
• The phosphate coating weight is too low, adjust the processing conditions. Make the necessary adjustments by either increasing the temperature, lengthening the time, or both. In addition, increase the phosphate and/or accelerator concentration.

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