Products Finishing

SEP 2018

Products Finishing magazine is the No. 1 industrial finishing publication in the world. We keep our readers informed about the latest news and trends in plating, painting, powder coating, anodizing, electrocoating, parts cleaning, and pretreatment.

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Page 26 of 59

Learn more at SOLUTIONS FOR YOUR WORLD Powder Coating Systems Electrostatic application technology Spray finishing and fluid handling Precision engineered finishing technology Five Brands. One Mission. Deliver Superior Finishing Solutions. Infrared curing and Chain-on-edge machines PRODUCTS FINISHING — 25 thus lower gloss due to the inhibiting effect of dissolved aluminum during etching. It was possible to reason that increasing aluminum in the low caustic step prevented the caustic to etch the surface deeply, consequently increasing the masking capability of the acid etch process. Additionally, higher dissolved aluminum content also forced the caustic to attack the sharp zones around the pits, thus levelling the surface and creating a uniform appearance. Figure 2 shows the SEM analyses on the first set of samples. The results are in accordance with the findings from 3D profiling, in which Samples B and C show similar surface texture to Sample D (acid etch control sample): pits with sharp edges distributed throughout the surface. The surface of Sample A resembles that of Sample E (long-life caustic etch control sample), which has smooth-edged alkaline pits with intermetallics reemerging from the aluminum matrix. On Samples A and E, due to the abrasive nature of the caustic etching step, even the grain boundaries were noticeable because of the preferential etching, which decreased the uniform appearance. Table 4 shows the surface gloss values achieved by changing the process times in the low caustic step for Samples A, B and C. From these results, we can see the hindering influence of dissolved aluminum. The same gloss values were achieved for low-aluminum-content Sample A3 in 1 minute and for high- aluminum-content Sample C4 in 3.5 minutes. Samples A3, B and C4 were chosen for further investigation due to their relevant surface gloss values. Table 5 and Figure 3 show the 3D profiling results alongside the surface roughness values, which indicate a similar surface topology. The major difference in the results appears to be between Samples A and C, where Sample A exhibits sharper peaks due to the shorter process time in low caustic, decreasing the uniform surface topology. Sample C shows the highest surface roughness and highest differ- ence in high and low points due to the LOW CAUSTIC ETCH BATHS

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