Solvent Wiping

Q. I am the Engineering Manager in our plant. Our company’s finishing specs call for the use of toluene for solvent wiping before painting. The surfaces are typically mild steel, to be painted later. What other solvents serve as good cleaners? Goals include: low toxicity, high flash point, and residue-free qualities. Chlorinated solvents for any purpose are highly regulated in our state and are out of the question. B. L.

 

A. In my opinion, solvent wiping is a poor cleaning method using the best solvent. Since the cleaning solvent becomes contaminated with the oily soils removed, there is too much danger of recontaminating surfaces due to infrequent solvent and wiper changes. Therefore, I recommend it only as a last resort. I am also concerned about your statement “to be painted later.” Degreased surfaces must be painted as soon as possible to prevent flash rusting.

If you must solvent wipe, use materials like mineral spirits, odorless mineral spirits or VM&P naphtha. They have higher flash points than toluene and are less toxic. It is important to change wipers and solvents frequently.

More sensible and environmentally friendly cleaning methods are ultrasonic cleaning and spray washing using aqueous cleaners. Multi-stage portable spray washers have been commercially available for many years. Suppliers of spray washers are listed under Cleaning Systems aqueous or CFC-free, on pages 269-270, of the 2006 Products Finishing Directory and Technology Guide. Suppliers of ultrasonic cleaners are listed under Cleaning Equipment, ultrasonic, on pages 268-269, of the same Directory.