Oxy-Acetylene Surfacing Repair of Ball Mill Sliding Bearing - Literature Study Note

Publication Overview

This technical note by Zhang Qibin, published in Mining Machinery (Vol. 28, No. 10, 2000, pp. 84-85), describes the application of oxy-acetylene flame surfacing to repair the sliding bearing (bush) of a ball mill at Qidaogou Iron Mine Concentrator. The work falls under the classification TG455 (surfacing welding) and addresses a common maintenance challenge in mineral processing operations.

Technical Background and Failure Analysis

Ball mills in ore processing circuits operate under continuous heavy loading, with the trunnion or head shaft supported by sliding bearings or trunnion bearings. The bearing bush (axial bearing pad) is subjected to:

• High contact stresses at the sliding interface
• Corrosive attack from mill slurry containing abrasive particles and chemicals
• Thermal cycling from frictional heating
• Potential for seizure if lubrication is compromised

When the bearing bush surface is worn or damaged, the dimensional clearance between the bush and the shaft changes, leading to abnormal vibration, accelerated wear, and potential catastrophic bearing failure. Surfacing repair allows restoration of the original geometry and, if appropriate, improvement of surface hardness and wear resistance.

Oxy-Acetylene Surfacing Process Characteristics

The oxy-acetylene process offers several advantages for bearing repair: it requires no electrical supply (suitable for remote mine sites), produces low heat input compared to arc welding, and allows precise control of the molten pool. However, it also has limitations including lower deposition efficiency, potential for oxidation inclusions, and difficulty in achieving deep penetration.

Metallurgical Considerations

The bearing bush material is typically a medium-carbon steel (such as 45 steel or 50 steel) or a manganese bronze for sliding applications. For steel bushes, the surfacing filler metal must be carefully selected to avoid:

• Excessive dilution leading to soft layers incapable of resisting wear
• Formation of brittle phases at the weld interface
• Cracking due to hydrogen absorption from the flame process

Post-surfacing machining is essential to restore the bearing bore to precise dimensional tolerances (typically H7 or H8 for clearance fits). The machined surface must be smooth enough to maintain hydrodynamic lubrication under operating conditions.

Quality Assurance and Service Experience

Following surfacing and machining, the repaired bearing undergoes:

1. Dimensional verification using bore gauges and micrometers
2. Hardness profiling across the surfacing layer to confirm uniformity
3. Visual and magnetic particle inspection for surface defects
4. Functional test under reduced load before full operational return

The paper demonstrates that oxy-acetylene surfacing, when properly executed with attention to process parameters and post-weld treatment, provides a reliable and economical repair method for sliding bearings in mineral processing equipment. The technique is particularly valuable for components where disassembly is difficult or where replacement parts are unavailable.

Study Insights

This case reinforces the importance of matching the repair technique to the component's service conditions and the available resources at the repair site. Oxy-acetylene surfacing, while a traditional method, remains relevant in situations where arc welding equipment is impractical or where the low-heat-input characteristic is advantageous for thin-walled or heavily alloyed components. The bearing repair described here exemplifies the broader principle in maintenance metallurgy: a well-executed surfacing repair can extend component life significantly while avoiding the cost and downtime associated with complete replacement.