4 Common Girth Gear Failures and How to Prevent Them (A Maintenance Guide)

A sudden failure of your girth gear isn’t just a repair job—it’s a critical production emergency. Hours of unplanned downtime translate directly into tens or hundreds of thousands of dollars in lost revenue. The key to avoiding this scenario isn’t just reactive repair; it’s proactive understanding and prevention.

At Luoyang Hengchang Heavy Machinery Co., Ltd., with over 20 years of designing and manufacturing heavy-duty girth gears for the mining and cement industries, we’ve analyzed countless failure cases. This guide distills that experience into a clear breakdown of the five most common girth gear failures, their root causes, and, most importantly, actionable steps you can take to prevent them.

1. Tooth Flank Wear & Pitting
   What it looks like: Gradual loss of material on the tooth surface, often accompanied by small, crater-like pits (pitting). This leads to loss of the original tooth profile.

Root Causes:
Inadequate or Contaminated Lubrication: The primary cause. Insufficient oil film leads to metal-to-metal contact.

Abrasive Contamination: Dust, grit, or process material ingress acts as a grinding compound.

Material Fatigue: Repeated high-load cycles cause subsurface cracks that propagate to the surface.

How to Prevent It:

Implement a Strict Lubrication Regime: Use the manufacturer-recommended, high-viscosity EP (Extreme Pressure) gear oil. Establish and follow precise relubrication intervals.

Upgrade Sealing Systems: Inspect and maintain gear guards and lip seals regularly to prevent contaminant ingress.

Conduct Regular Oil Analysis: A scheduled oil analysis program can detect wear metals and contamination before visible damage occurs.

2. Tooth Root Crack & Fracture
   What it looks like: A visible crack originating at the root of the gear tooth, which can propagate and lead to a complete tooth break-off—a catastrophic failure.

Root Causes:

Overloading & Shock Loads: Exceeding design torque or experiencing severe material jams in the mill.

Improper Heat Treatment: Incorrect hardening can create a brittle microstructure prone to cracking.

Manufacturing Defects: Subsurface casting porosity or inclusions that act as stress concentrators.

Insufficient Root Fillet Radius: Poor design or machining leaves a sharp corner where stress concentrates.

How to Prevent It:

Operate Within Design Limits: Train operators to avoid practices that cause shock loading.

Invest in Quality Manufacturing: Source gears from suppliers who employ rigorous Ultrasonic Testing (UT) and Magnetic Particle Inspection (MPI) to detect internal and surface flaws before installation.

Regular NDT Inspections: Schedule periodic in-situ inspections using dye penetrant or magnetic particle testing during maintenance shutdowns to catch cracks early.

3. Misalignment & Improper Meshing
   What it looks like: Uneven wear pattern across the tooth face (e.g., wear concentrated on one end), excessive vibration, and a characteristic “howling” or “chattering” noise during operation.

Root Causes:

Foundation Settlement: Over time, the mill or kiln foundation can shift unevenly.

Incorrect Initial Installation: Poor alignment during the last gear replacement or mill overhaul.

Worn or Damaged Bearings: Support bearing failure allows the pinion shaft to drift.

Thermal Expansion: Inadequate accounting for thermal growth in the system design.

How to Prevent It:

Precision Laser Alignment: Dump the straight-edge and feeler gauge. Use modern laser alignment systems for both initial installation and annual verification. Tolerances should be within 0.05 mm per meter of face width.

Implement a Bearing Monitoring Program: Use vibration analysis and temperature sensors to predict bearing failures before they affect alignment.

4. Bolt Loosening & Shearing
   What it looks like: Loose or missing flange bolts, elongated bolt holes, or bolts that have sheared off completely. This compromises the structural integrity of a segmented gear or its attachment to the shell.

Root Causes:

Insufficient Preload/Torque: Bolts were not tightened to the correct specification during installation.

Vibration: High operational vibrations can work bolts loose over time.

Lack of Locking Mechanisms: Reliance on standard nuts without proper lock