Feed-Over Test

Q. Could you tell us about the “feed-over test”? We are trying to replace our current electrocoat supplier and want to use this test, but we have not been able to find any literature about it.  —G.G.

A. The feed-over test is a simulation test performed in a laboratory. It is used to determine the operational feasibility and chemical compatibility of two different electrocoat paints when mixed together in the e-coat tank. The feed-over test is necessary to confirm and verify the potential replacement of one electrocoat paint supplier with another without outside disposal of the existing electrocoat bath.  

Electrocoat suppliers do not like their paints to be mixed with another supplier’s paint and, in most cases, will not recommend the user to do that. In some cases, the e-coat user has no other alternative, however, and the feed-over test is the necessary due diligence to ensure proper functioning and proper performance of the electrocoat bath.  

For example, your electrocoat tank is operating with paint A and you would like to start using another e-coat paint, paint B. Additionally, you would like to start feeding paint B over your existing e-coat bath with paint A without having to dump the entire existing bath. Your strategy is to start feeding the new paint B over the existing paint A as regular paint make-up feed. The feed-over test will determine the minimum initial percent of paint B necessary in the bath for the tank to operate and perform properly. 

The test typically covers mix ranges from 20 to 90 percent of new paint versus old paint. In most cases, the electrocoat bath needs to have at least 20 percent of the new paint for the bath to deposit properly. Depending on the compatibility of resins, solvents and operating pH, greater percentages may be needed. The greater the starting percentage of new paint, the lower the risk with the future feed-over and conversion. 

The feed-over test itself involves coating out panels at the different mix percentages to determine application voltages, film thickness, visual appearance, corrosion performance and any other relevant physical, chemical or corrosion characteristics and properties deemed necessary for the required specification.

Prior to the actual feed-over and conversion, the electrocoat user must develop a strategy for reducing existing paint bath volume to make room for the minimum starting percentage of new paint volume needed. This volume reduction is typically accomplished by controlled draining of clean or raw UF permeate without making it up with DI water. Once the volume reduction of the existing bath is accomplished, the new paint can be added to return the bath to operating level. Once this is accomplished, the electrocoat user can start the regular feed-over procedures to maintain percent solids in the bath.