Is burn-off the only way that rejected parts can be salvaged? The burn-off process damages some of our parts. Thanks for any help you can give us on this issue. D.B.
While burn-off is the best way to remove e-coat from hooks, racks and hangers, it may not be the best way to salvage rejected parts. If the parts are of a design (metal thickness and substrate) to sustain the temperature and time to burn off the coating, this is still the best method to salvage the parts. Total removal of coating and re-coating should produce the most consistent final coating. However there are alternatives to burn-off and re-coating.
If the part design does not permit burn-off, removal of the entire coating is still an option with a chemical stripper or blasting with plastic media of very fine shot (or grit). Seams, hems and welds are sources of “bleed-out” if chemical stripping is used which can generate more problems. Rinsing and baking after stripping along with some mechanical clean up (sanding or wire brushing) can make stripping an alternative. Blasting is usually labor intensive and very operator dependent.
Another alternative to total removal of the coating and re-coating is to partially remove the coating in the defected area and re-coating with a compatible liquid coating. Sanding, blasting or wire brushing are usually labor intensive and very operator dependent. If the e-coat is totally removed to bare metal a “halo” may appear after re-coating with a liquid. E-coating again before applying the liquid can usually solve this.
If the e-coat is a primer, see if partial removal of the e-coat without re-coating is acceptable. If this is not acceptable, try e-coating again or consider a flash primer prior to top-coating.
The cost of all of these salvage methods needs to be monitored along with the success rate of the rework. It is sometimes more cost effective to scrap the parts than try to rework them. While this may not seem very reasonable, it will bring the true cost of the reject to light and encourage reducing the rejects versus reworking them.
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