Abstract
The rusting of ball bearings caused by vapour from the insulating varnish in electric motors was investigated by measuring the corrosive acid vapour using ion chromatographic analyser. It was found that formic acid evolved depending on the kind of varnishes, and that the amount had good correlation with the extent of rusting of bearings tested in a relative humidity of 70 percent. Based on the limit of formic acid present, a quantitative evaluation of varnish-induced rusting and classification of varnishes are presented.
