Q. Our company makes packaging machines, and I am the quality control engineer responsible for all finishing operations. We paint castings, sheet metal guards and machined parts. We are presently solvent-cleaning in two dip tanks prior to painting. One tank is 6 × 3 × 2 ft, and the other is 5 × 3 × 2 ft. We use our own solvent blend made up of hydrocarbons, but this material is flammable and has a nauseating odor. We are looking for an inexpensive, nonflammable liquid cleaner. E.C.
A. Solvent cleaning by dipping in tanks containing flammable solvents could be an invitation to disaster. It is not only dangerous as far as fire safety is concerned, but also from a product-quality viewpoint. Finish quality could suffer because solvent dip tanks become contaminated with residual oily soils as soon as the first part is dipped. As this operation continues, the concentration of oily soils increases. This can result in oily soils residue on the parts, reducing paint adhesion. If you must use this cleaning method, the soils level in the solvent has to be monitored and the solvent changed often.
Years ago, I would have told you to get a vapor degreaser system using 1,1,1-trichloroethane or trichloroethylene. In these devices the hot vapors, which were always clean, condensed on the cooler metal surfaces, dissolving the oily soils and flushing them off the parts. The U.S. Environmental Protection Agency declared them unhealthy to mankind (and rightfully so), and you know the rest of the story
Today, prepaint cleaning has changed radically. New cleaning materials that meet environmental standards and new process equipment to apply these material are available.
I highly recommend reading the Parts Cleaning sections of this and the February 2012 issue of Products Finishing which are devoted to parts cleaning, including the Parts Cleaning Clinic by David S. Peterson. These issue have everything you need to know about parts cleaning, including advertisements by producers of cleaning materials and equipment. One of the February articles even mentions my good friend Dr. Clifford Schoff and the work of his ASTM subcommittee. If you don’t have a copy of the issue, get one.