Ask the Expert Question-and-Answer Archive

by Ron Joseph

May, 2003

Evaluating Pretreatment Cleaners

Q. Can you evaluate the cleaning efficiency of one cleanser vs. another based on the results of the ASTM B117 salt spray test? Example: Suppose the phosphate coatings and film thickness were the same when using two different paint line cleansers. But after looking at the parts run in the salt spay test one batch vs the other shows a higher frequency of red rust development. Also, the red rust may develop at earlier time periods during a 370 hour salt spray test. Would this be unexplainable (all things being equal), or are there cause and effect reasons for rust that can be attributed to the cleansers assuming you have adequate paint coverage and adhesion?

A. You can definitely use the ASTM B117 salt spray test to evaluate the effectiveness of a pretreatment system. If all your process parameters are equal, then in general you can say that the longer the coated panels run in the salt spray cabinet, the more effective is the pretreatment system.

Bear in mind that when you evaluate a new pretreatment system you must also consider the replenishment rate; namely how often you need to add chemicals to the tank. Consider also whether the chemicals are supplied as liquids or powders; whether sludge is formed during the phosphating process, temperature at which the process must operate, etc.

Therefore, a thorough evaluation incorporates all of these factors, and not only corrosion resistance.