Corrosion Corner Figure 4. Coating drool The anomaly in Figure 4 is referred to as a drool. Drools form toward container bottoms when coating material drips from the spray nozzle used to apply the coating to the container. I’ve not observed instances where drools caused or contributed to corrosion. Figure 5. Nip in a laminated aluminum foil package (~0.3 mm wide along the minor axis) The anomaly in Figure 5 is on a laminated aluminum foil bag inserted into traditional metal aerosol containers. This type of anomaly is referred to as a nip. Nips are common, but have not yet been shown to cause or contribute to bag metal or polymer corrosion. Figure 6. Distorted inclusion in aluminum metal (~0.65 mm wide along the minor axis) The anomaly in Figure 6 was formed from an inclusion in the aluminum metal. Inclusions are alloying materials in aluminum alloys that precipitate when the molten aluminum alloy is cooled to room temperature. The inclusion in Figure 6 was originally a spherical particle that was distorted into an oval during container fabrication. This type of anomaly could cause container pitting corrosion. Figure 7. Crack in aluminum foil used for laminated foil bags Figure 7 has an example of a crack in the aluminum foil between layers of polymer films. This type of laminate is used to fabricate the internal bags inserted into traditional aerosol containers. Cracks in the aluminum foil are common. Product leakage could occur through a crack whenever product diffuses through a laminate film. The examples shown in this month’s Corrosion Corner are a few of those used in our Elements of Spray Package (Aerosol) Corrosion short course. This 1.5 day short course provides an introduction to all aspects of spray package corrosion, corrosion testing and corrosion prevention. More info: www.pairodocspro.com. Please send your questions/comments/suggestions to rustdr@ pairodocspro.com. Back issues of Corrosion Corner are available on CD from ST&M. Thanks for your interest and I’ll see you in August. SPRAY 22 Spray July 2013 Continued from page 20
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