Powder Coat Stripping on Aluminum Parts
What is an efficient process for removing rejected powder coating from 6-inch 6061 aluminum without damaging the substrate?
Q. Our factory produces aluminum powder coated parts for the recreational motor-sports industry. We need an efficient process to remove rejected powder coating without damaging the surface from a 6-inch 6061 aluminum part. —P.B.
A. This is a very common problem. Many parts are painted wrong, damaged after painting or need to be re-worked. A finishing system in these situations is generally running lower production (hopefully), but needs to be efficient.
This is a manual pressure blast cabinet application, blasting with a type 11 (urea)
2040, mesh-size plastic blast media. Blasting pressure is generally between 40 and 60 psi. The blast nozzle should be held at an angle for maximum stripping action.
Plastic blasting media is softer than the substrates being blasted, (3.0 to 4.0 Mohs hardness) resulting in blasting without damaging surfaces. Plastic abrasives are used for coating and paint stripping on aluminum, fiberglass, composites, plastics and other soft metals. Plastic media are also used for mold cleaning, de-flashing, deburring, die-castings, circuit boards and stripping aircraft components.
Plastic blast media is used to remove various layers of coatings on rejected automobile paint surfaces. It can also remove paint without removing the anodized surfaces beneath. Plastic media is not good for rust removal.
There are a number of plastic materials used for blasting. The most common are: Type 1 (polyester), the softest plastic at 3 Mohs hardness; Type 11 (urea), the most widely used and more aggressive on sensitive applications with a 3.5 Mohs hardness; Type 111 (melamine), the most aggressive for difficult surfaces with a 4.0 Mohs hardness; and Type V (Acrylic), which has the longest life, for delicate parts with a 3.5 Mohs hardness.
Plastic blasting media removes powder coating from aluminum faster than any other mechanical finishing process while minimizing surface damage.
Immersion tin and lead-free hot air solder leveling (HASL) coatings based on SnCu or SnAgCu alloys are widely used as surface finish materials for printed circuit boards (PCB). These coatings prevent the underlying copper from corrosion and preserve its solderability during lead-free assembly processes and for a long storage life of PCBs.
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.
Surface finish types for commercially supplied stainless steel sheet are detailed in various standards. ASTM A480-12 and EN10088-2 are two; BS 1449-2 (1983) is still available, although no longer active. These standards are very similar in that they define eight grades of surface finish for stainless steel. Grade 7 is “buff polished,” while the highest polish—the so-called mirror polish—is designated Grade 8