Waterborne Metallic Paints: A Comparison of the Degradation Caused by Various Pumps During Circulation

The type of pump (lobe, centrifugal, or piston) used in a circulation system determines the degree of mechanical and shear degradation inflicted upon the pigments present in a waterborne metallic paint. The visible effect of degrading the performance of a metallic paint is the extreme variation encountered in the appearance of the resulting automotive finish. We have determined through multiple angle spectrophotometry that lobe and centrifugal pumps initially cause a similar amount of degradation to the two-tone effect exhibited by a metallic finish. The degradation effect associated with a lobe pump was observed to dramatically increase with extended usage of the pump. Piston pumps were discovered to cause the least amount of paint degradation. A centrifugal pump having open impellers performed similar to a centrifugal pump with closed impellers. This paper describes the results of our investigation highlighting the effect that various pumps have on the gonioapparent characteristics exhibited by a metallic finish.