Ball mills are core grinding equipment in industries like mining and cement. Damage to the pinion gears in their transmission systems can directly impact production continuity. Pinion repair requires a comprehensive assessment of feasibility based on the damage type, material, and operating conditions.

I. Common Damage Types and Repair Solutions

Broken Tooth Repair

If a pinion has a partially broken tooth (e.g., the broken tooth length accounts for ≤65%), an online welding repair process can be used. For example, a 3.4m Φ coal mill had a 330mm broken tooth (65% of the tooth length) on its pinion. After repair, the pinion was reinforced with drilled stainless steel bolts, welded with nickel-based weld material, and manually reshaped. The repair resulted in normal test runs and continued operation for a year without any issues. This solution is suitable for soft tooth surface materials such as 40CrNiMo, but requires strict control of the preheating temperature (280-320°C) and post-weld dehydrogenation treatment (320-350°C) to prevent secondary cracking.

Bearing Seat Wear

For bearing mating surface wear, polymer composite repair technology offers advantages. This process requires no disassembly of the gear shaft. By cleaning the base surface, applying the composite material, and curing it, the original dimensional accuracy is restored. In one case, the repaired pinion shaft operated smoothly at only 30%-50% of the cost of a new replacement.

II. Repair Cost Assessment

Repair costs are significantly affected by the extent of damage and the process. A simple broken tooth repair costs approximately 2,000-3,000 yuan (including labor and materials), while repairing a worn bearing seat can cost as little as a few hundred yuan. In contrast, replacing a new pinion typically costs over 10,000 yuan and requires 7-15 days of downtime. For urgent production needs, online repair can significantly reduce downtime losses.

III. Decision Recommendations

Prioritized repair scenarios: No spare parts in stock, time-sensitive downtime, and minimal damage (such as a single tooth fracture or localized wear).

Replacement scenarios: Severe wear on multiple teeth, hardened material that cannot be welded, or excessive vibration after repair. Note that hardened gears (such as 20CrMnTi) are generally recommended for direct replacement due to their poor weldability.