Q. We machine large quantities of small (0.5" × 0.25" × 0.25") steel alloy parts which have small feather burrs. The surfaces are hard to work for a good pre-coat finish, resulting in coating adhesion problems. Do you have a finishing solution? —L.D..
A. Blasting is a standard process for coating adhesion, and the removal of burrs is important for coating adhesion on the part edges. Blasting the parts in a basket blaster is the least expensive way to automate the process for small parts. With the right media, this process can remove the feather burrs and obtain a pre-coat profile in a single operation.
Check with the coating manufacturer for the specification profile required; this will determine the media. If there is no specification on media, my recommendation is an 80-120-grit aluminum oxide blast with air pressure at 60-80 psi.
The basket in an air blast system is positioned at a 45-degree angle and then filled to one-third of the way with parts. The blast nozzle is fixtured and positioned through the open top of the basket such that it will blast the bottom corner of the basket at a distance of approximately 6" from the parts. As the parts rotate by the nozzle for about 15 minutes, the entire group of parts should be uniformly finished and deburred.
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.
Metal fabricators that laser-cut with oxygen take steps to prepare parts better for powder coating.
When choosing vibratory media, understand the size, shape, starting roughness condition and metallurgical structure of the part.