Insulative coatings for electrical steels

摘要

An aqueous coating solution for forming an insulative coating directly on electrical steels and on steels having a mill glass thereon. The aqueous solution comprises an aluminum-magnesium phosphate premix solution and a colloidal silica solution. The premix solution also comprises from about 10 to about 45 parts by weight Cr2O3 for every 100 parts by weight H2PO4- calculated as H3PO4 on a water-free basis, from about 5 to about 20 parts of a compound chosen from the class consisting of boric acid, vanadium pentoxide and mixtures thereof per 100 parts H2PO4- calculated as H3PO4 on a water-free basis and additional Mg++ up to that amount which will go into solution. The colloidal silica solution is present in an amount of from that amount which will form a good glass up to 40 volume percent to provide a coating solution having a premix solution to colloidal silica solution volume ratio up to 1.5:1.