Why is the bearing burned or locked?

Why is the bearing burned or locked?
1. Improper selection of bearing clearance.
For example, C3 group clearance should be selected, but ordinary group clearance is actually selected. As the bearing will continue to accumulate heat during operation, the shaft diameter, inner ring and rolling element will expand. The expansion of the outer ring is relatively small due to good heat dissipation conditions. In general, the bearing clearance becomes smaller, and even a large negative clearance appears.
At this time, the compressive stress between the rolling element and the raceway increases, the lubrication condition decreases, the boundary lubrication phenomenon will appear, and even the dry friction between local steel and steel will occur. Therefore, the temperature continues to rise, and the base oil in the grease will gradually volatilize. Such a vicious cycle will lead to overheating and burning of the bearing, and the rolling element will become blue and black after annealing, At this time, the friction of the bearing increases sharply, and the rolling element stops rotating, squeezing the cage and locking the bearing.
2. If the size deviation of the bearing seat hole is too small or the size deviation of the shaft is too large, the bearing ring is extruded and deformed to reduce the clearance. Thus, the phenomenon of burning and locking occurs.
3. Foreign matters, such as iron filings, burrs, sand particles, cotton thread, etc., are padded between the outer diameter of the bearing and the bearing seat hole or between the inner diameter of the bearing and the shaft surface. It will also squeeze the deformation of the bearing and reduce the clearance. Thus, the phenomenon of burning and locking occurs.