A company making metal fasteners added an electrostatic paint line that gave managers grief almost as soon as it began operating.
The line uses steel baskets to hold 100-lb loads of small metal parts in a caustic cleaning solution, take them through primer pretreatment, then through application of 360 Vdc for electrostatic painting. Finally the baskets travel through a 350°F curing oven. The baskets had to turn and tumble, so they hung from a conveyor on a stub axle. But this axle-to-basket connection also had to carry the voltage needed for painting.
Once in operation, the poor electrical contact between the axle and baskets, coupled with the relatively high voltage, led to arcing and sparking. It was intense enough to eat away at the metal components, including entire sections of overhead conveyor chain. To solve the problem, Graphite Metallizing Co., Yonkers, N.Y., recommended a Graphalloy bearing in a cast-iron housing. The graphite/metal alloy conducts electricity well, so the new part made for better current flow, which stopped the arcing. The bearing could also withstand the caustic detergent and high temperatures.