Spot Weld Marks
On certain sheet metal parts made of 16-gauge cold rolled steel, we have trouble with spot weld marks showing through the paint finish. How do we eliminate this problem?
Q. I’m the plating and paint shop foreman of a company that makes office machines. In order to get a first-rate finish, we use a five-stage washer to apply an iron phosphate. After dry-off, we apply an epoxy primer and then a polyurethane topcoat to all painted parts with an electrostatic spray gun. Total dry film thickness is 3 mils. On certain sheet metal parts made of 16-gauge cold rolled steel, we have trouble with spot weld marks showing through the paint finish. How do we eliminate this problem? B.F.
A. It is often difficult to hide surface defects with a paint film, even at a 3-mil dry film thickness. Paints, as well as powder coatings, tend to conform to the surface on which they are applied. Paints over spot weld marks, which come in two forms—holes and ridges—will follow the rules of surface coatings. These surface defects can only be eliminated by cosmetic repair, requiring hand work. I suggest you fill the holes using a body putty or filling compound and then sanding them smooth. If the weld marks are ridges, they can be removed by hand-grinding using a power tool.
RELATED CONTENT
-
Cleaning Limescale from Galvanized Steel
How do you clean white lime scale and rust spots on galvanize?
-
Top Reasons to Switch to a Better Cleaning Fluid
Venesia Hurtubise from MicroCare says switching to the new modern cleaning fluids will have a positive impact on your cleaning process.
-
Alkaline Cleaning Guide
Gregg Sanko, Senior Chemist, Oakite Products, Inc. provides an overview of the alkaline cleaning process.