A machinist had pressed a new prelubricated porous sintered

A machinist had pressed a new prelubricated, porous sintered bronze bearing in an electric moto. The rotor shaft would not fit into the bearing. Measuring the bore, the machinist discovered that it was a few thousandths of an inch undersize. he removed it, put it in a lathe, and bored out the excess material. The bearing was pressed it again, the motor assembled, and put into use. A few days later the motor was back in the sho with the bearing burned out. What had happened to this prelubricated, sintered bearing to cause this failure?

Solution

Porous sintered bronze bearing are susceptible to expansion due to heat. As the machinist tightly pressed the bearing to the exact size of the shaft without keeping any clearance for expansion due to heat, after few days of operation the heat generated in the bearing caused it to expand and without any clearance it caused failure.