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. 

Q. I work for a specialty silver plating company that restores silver-plated candelabras, silverware and other household items. Our silver plating bath has been well-maintained in terms of testing and maintaining proper chemical composition, but we have noticed over the last few months that the plated deposits are more difficult to polish and buff. Do you have any suggestions for resolving this problem? S.L.

A. Start by checking the current density in the bath. Low current density will enable you to deposit silver, but if it is at the very low end of the suggested range you can get harder-than-normal silver deposits. There are several types of impurities that will cause silver deposits to become hard and difficult to polish and buff, including the presence of iron and high chlorides. Lead, tin, nickel and organics also can cause this problem. To remove the unwanted organics, filter the plating solution through activated carbon. Keep in mind, however, that activated carbon treatment will also remove desirable organic additives, so you will most likely have to reconstitute the bath with the required additives. To remove most of the “tramp” metals mentioned above, dummy the bath at 2 asf for 12 to 24 hrs.