(1) Cause Analysis

① Fracture of the alloy bearing bush in a ball mill

The alloy bearing bush may suddenly fracture during operation. The main cause of such fracture is vibration and natural wear of the mill, which leads to fatigue of the alloy material, initiation of micro‑cracks, gradual propagation and interconnection of these cracks, and ultimately fracture of the alloy bearing bush.

② Fracture of the cast iron spherical bearing block in a ball mill

The spherical bearing block (spherical seat) in a ball mill is generally cast from grey cast iron HT20‑40. It has internal cooling water passages, an inner circular surface with an alloy bearing bush embedded or babbitted, and an outer spherical surface. Both the inner and outer surfaces are ground. Under uniform loading conditions, it is not prone to fracture. However, in northern regions, sudden water stoppage in winter – or stoppage due to operational error – causes water to freeze inside, leading to internal expansion. Under this expansion stress, the spherical bearing block fractures. In some cases, the block contains fatal casting defects such as blowholes or micro‑cracks, which cause fracture under operating load.

(2) Repair Methods

① Emergency repair method for a fractured alloy bearing bush in a ball mill

If the thickness of the fractured alloy bearing bush is 5 mm or more, fusion welding (build‑up welding) can be used as an emergency repair. The specific procedure is as follows:

a. First, melt bearing alloy of the same material into welding rods (shape is not critical).

b. Then, using oxy‑acetylene welding, melt the fractured area of the bearing bush into a groove shape.

c. Next, carry out build‑up welding. The welded surface must be flat. After welding, it should be ground smooth with a grinding wheel, followed by scraping and fitting.

For fractured alloy bearing bushes with a thickness of less than 5 mm, repair is generally not worthwhile; it is better to replace them with a new bush.

② Emergency repair method for a fractured cast iron spherical bearing block in a ball mill

A fracture in the cast iron spherical bearing block can be repaired by welding at the fractured location. The specific procedure is as follows:

a. Clean the fractured area of the cast iron spherical bearing block thoroughly, removing all dirt and contaminants from the crack and its surrounding region.

b. Align the broken pieces (if the part has a crack but is not completely broken, locate the starting and ending points of the crack), and cut a V‑shaped groove at the fracture (or crack) and clean the groove thoroughly.

c. Preheat the spherical bearing block to about 300 °C using charcoal. While it is hot, weld it with ductile cast iron welding rods using oxy‑acetylene welding. The welded surface must be smooth and not protruding. After welding, allow the part to cool naturally indoors, then grind the welded surface smooth with a grinding wheel.

d. During installation, grind the spherical bearing block again, mainly to check whether the welded part has deformed. If deformation is found, re‑grind it until at least 75% of the spherical contact surface is in contact before putting it back into service.