brighten surfaces. Liquid, selective media, calibrated vibration and special compounds can also be used to cushion against damage. Most die castings go through a mechani- cal deburring operation prior to post-trim fi nishing, though ad- ditional operations may be required for 100% burr-free specifi cations. Surface Conversion Coating:
Deburring is usually followed by a conversion coating to remove any remaining oil, diecast part release agents and other contaminants. Where final painting is specified, this coating serves as preparation and primer. In many non-cosmet- ic applications, this conversion coating serves as the component’s final finish. Environmentally friendly Triva-
lent clear chromium is now a prov- en, economical alternative to widely used hexavalent chromium coatings, off ering high corrosion resistance for aluminum, magnesium and zinc die castings. With a bright fi nish, it meets stricter EPA regulations and RoHS European Union mandates, avoiding concerns with prohibited toxic hexavalent chromates. Combined Conversion Coat-
ings/Functional Finishes: Where a diecast component has a specific functional requirement, such as added corrosion protection, added durability and/or semi-decorative appearance, one of the combined conversion-functional finishes is often recommended. A com- bined coating replaces the use of a surface conversion coating, which serves as either a paint base or the part’s final finish. Final Cosmetic Surface Finish:
While fi nal painting or plating of diecast housings and compo- nents is most often specifi ed for cosmetic purposes, and to sustain their decorative appearance over the life of the part, other func- tional purposes of a fi nal applied fi nish may be of equal, or of even greater, importance. T ese include: maximizing corrosion resistance, heat dissipation, and surface per- formance under abuse, and adding
Nov/Dec 2015 | METAL CASTING DESIGN & PURCHASING | 37
Fig. 5. While advanced technology can execute most corner designs, gentle radii will reduce fi nishing steps.
greater insulation properties. A wide range of painting appli-
cations is available for die castings in matching fi nished, mating parts produced in other production pro- cesses. T ese fi nal fi nishes include powder coatings in fi nishes from fi ne to coarsely textured, liquid paint polyurethane and water-based
fi nishes applied at various thick- ness/texture levels. Component masking is an essential part of virtually all cosmetic surface finish applica- tions and required to assure part areas that must not receive finish coatings are protected during processing. Required protective
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