First, the oil level is too low, so that reduce the amount of oil into the bearings. Second, the oil failed, water into the impurities or emulsified metamorphism. Third, oil ring does not rotate, bearing oil supply interruption. Fourth, lack of bearing cooling water. Fifth, bearing damage. Sixth, the rolling bearings, in addition to the above reasons, the bearing cover exerts too much pressure on the bearing, crushed its radial clearance, loss of flexibility.