Masking Options for Raised Numbers

Q. We have an aluminum casting that is 18 × 12 inches with raised numbers on one edge. I want to powder coat it if I can find an easy way to leave the tops of the lettering bare aluminum. The part is not flat enough to machine the paint off in production. On other items we powder coat, we wipe the area we don’t want painted, but due to the complexity of the numbering, I don’t think this would work. Masking individual numbers would not be practical due to the small size. Is there another method you could suggest that will leave the number tops unpainted and the rest of the part coated?  A.B.

A. I cannot think of any simple way to do what you want. You can apply a mask material before coating or remove the powder after coating. Options for masking are application of tape or other soft mask products or a custom made hard mask. Options for removal are blow off, vacuum off or removal by abrasion using a machine or hand sanding. I cannot see the size of the numbers, but it sounds challenging. Since the pre-mask route sounds impractical, you may have more success removing the powder after application.

Response from A.B: Thanks for the response. I’ve done some testing with sanding and it may work. I used an auto body type hard rubber sanding block and 180 grit wet paper and was able to remove the paint from the top of the numbers and not scratch the recessed area. The block followed the surface nicely so the out of flat did not cause a problem. For production, I will make guides to keep the operator from sanding outside the lines.