Q. We manufacture shelving for retail outlets and painted them on a spray paint line for years with no problems. We recently installed an electrocoating system where everything is new, including the cleaner stages, chemicals, type of paint and curing ovens. Now we are having problems with the presence of emulsified oils in our alkaline cleaner which messes up the finish on our products. How can we remove the emulsified oils? W.D.
A. Chemically, you can either change the stamping lubricant or change the cleaning solution chemicals. Physically, you can remove emulsified oils from the alkaline cleaner solution by ultrafiltration. Ultrafilters separate particles from solutions by using selective membranes. This often is done in the pretreatment stages of high-volume finishing lines. With ultrafiltration, the oil is essentially removed as concentrated emulsion from the cleaner solution, and the cleaned solution is then returned to the cleaner stage. This not only makes disposal of emulsified oil concentrate simpler, it also extends the life of the cleaner solution. Ultrafiltration can be done batch-wise or on a continuous basis, depending on the size of the unit and the rate of production.