Metal Finishing Guide Book

2013

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p procedures when blast-cleaning the surface. By sectioning and polishs ing a sample of the coating and in substrate, one could easily meas sure the blast profile even though s the job had been conducted years t before (Figure 7). b Figure 9. Extensive solvent entrapment on the underside of an epoxy coating, resulting in poor wetting and inadequate adhesion to the substrate. Figure 10. Top of epoxy coating showing extensive pinholes and craters. Figure 11. Top coat blistering due to extensive solvent entrapment in the under coat. Figure 12. Multiple layers of paint leads to tremendous internal pressures. 6. 6 Wood Coatings A cabinet maker applied a lacquer from Company A for finishing f kitchen cabinets. After the cabinets were installed, several customn ers complained the coating easily e chipped off when something was c dropped onto the wood. The probd lem was exacerbated when someone le bumped into the corners or edges b of the wood. o The cabinet maker then changed to a different lacquer and clear coat t from Company B and the results f appeared to be fine. Upon microa scopic investigation, it was clear that the original finish was so t brittle that when the paint conb sultant touched it with the tip s of an X-Acto¨ knife, the coating o shattered into small pieces and s there was essentially no adhesion t between the lacquer and the wood b (see Figure 8). When the replace( ment coating was examined, some m of the clear coat broke away from the underlying lacquer, but the t coating system remained in good c condition. There were no comc plaints that the new coating system p failed in the field. f 7. 7 Delamination of epoxy primer One of the most common reasons O for paint delamination is solvent f entrapment. Figure 9 illustrates a e micrograph taken with a stereom microscope showing extensive solm vent entrapment on the underside v of the coating. Although this was o barely visible with the naked eye, b it became obvious under approxi531

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