Steel surface preparation prior to galvanizing is of paramount importance in delivering complete, optimum-quality zinc coatings. Some surface residues, such as mill lacquer, welding slag, varnish, water-insoluble paints, adhesives, and sand used in the making of castings, are not removed by the standard chemical cleaning methods involved in the galvanizing process.
Abrasive blast-cleaning, or other mechanical methods, should be used to remove residues that cannot be chemically cleaned from the steel surface prior to delivering the steel to the galvanizer. Typically, pipe and tube are coated with organic lacquers very difficult to remove by chemical cleaning. When pipe comes from the steel supply house, the coating may be tough to identify. Mill lacquers and varnish require extra effort and time to remove. To lower costs and minimize turnaround times, any mechanical cleaning should be performed at the fabrication facility.
There are numerous mechanical cleaning methods used to remove these common residues, including:
- Abrasive blasting / wheel-abrading
- Barrel and vibratory finishing
- Brush- and hand-finishing
- Grinding and polishing
Contact your galvanizer when planning to use steel coated with lacquer or other products to determine whether the coating can be removed at the galvanizing plant.