Q. We have a small paint tank that needs replaced. We want to use a steel tank but we need to find a liner that is compatible with the electrocoat for insulation and safety of the electrical charge. Can you tell us where to find liners and how to install them? —R.S.
A. Electrocoat paint tanks must be electrically isolated from the charged liquid electrocoat in the bath to provide the safety necessary for line operators to maintain and operate piping and valving around the equipment without getting shocked. As a result, it is necessary that electrocoat tanks be constructed of non-conductive plastic materials like PP or HDPE; otherwise isolation liners must be used. The liners can be drop-in liners or coated-on liners. Coated-on liners are the most frequently used in the automotive industry.
In addition to the electrical isolation, the liners must also provide chemical compatibility with the pH of the electrocoat paint (acidic if cathodic and alkaline if anodic) as well as not leach out any contamination into the paint tank such as plasticizers or pigments.
Typical coated-on liners used in the industry are two-component coatings containing epoxy or phenolic resins. Oftentimes, the coatings incorporate some glass flake to provide improved wear protection against erosion, additional structural stability and improved electrical insulation by lowering the permeability of the liner.
Coated-on liners for electrocoat lines are typically applied by manual methods—either trowel or roller—to a film thickness of 140 to 160 mils. The applied coating needs at least 24 hours drying time before placed into service and in contact with electrocoat paint, preferably 48 hours.
Surface preparation of the steel tank is critical prior to the application of the coating material. Sand or water must be used to blast the steel to clean the surface and improve adhesion of the coating. No rust or welding residues can remain on any of the surfaces of the tank. The application of a primer is oftentimes necessary so the materials come in as a basecoat and as a top-coat.
The keys to success for the application of the coating materials in electrodeposition tanks are the quality of the product and the proper professional installation. Experienced personnel to clean and prepare the tanks, install, test and inspect the lining system are essential. The liner must be holiday tested to make sure there are not defects or electrical paths for electrical current to flow or leak. The coated-on liners should remain in service continuously for many years with no repair.
When repairs are needed, they are usually only spot patches. In some cases, the original topcoat can be removed and new topcoat troweled in place.
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This paper is a peer-reviewed and edited version of a presentation delivered at NASF SUR/FIN 2012 in Las Vegas, Nev., on June 12, 2012.