When To Dump The Chemical Tanks

Q. I manage the finishing line at my plant. We use a three-stage iron phosphate system, and we seem to be using a lot of pretreatment chemicals. The operator tells me he dumps the cleaner when he thinks it is not cleaning the parts, and he dumps the phosphate when the parts look off-color. Can I establish a scientific program to indicate when the chemicals should be dumped? I think we should consider conductivity, grease and oil, solid residue, and coating weight. All of these should be related to humidity resistance and salt spray resistance tests.

Can you help? W. S.

 

A. Back when I had a real job as a scientist at a large research lab, I could have undertaken such a program. Your request is beyond the scope of this column. It is also beyond the scope of most plants. To do it, you must have access to sophisticated equipment and trained technicians. However, I’m sure this information is available from chemical suppliers, who pay lab people to conduct such programs. Talk to your sales rep about your concerns.

On the other hand, there are rules of thumb for determining when to dump phosphate chemical baths. A couple of examples: dump when the free oil in the cleaner tank reaches 3 to 5%, and dump when the amount of chemical addition needed to balance the phosphate tank equals the original charge.