Bearing Failure: Causes and Analysis Made Simple

Introduction

Types of Bearing Failure: A Simple Classification

• Failures that start from the outside (surface-related issues)
• Failures that start from the inside (material-related issues)

Failures That Start from the Outside

Worn or Abraded Surfaces

• What it looks like: The bearing surface appears rough or “rubbed” instead of smooth.
• Why it happens: Bearings are designed for rolling friction, not sliding. If there’s sliding, it means something is causing the bearing to slip instead of roll.
• Possible causes:
  • Insufficient load: The bearing isn’t under enough pressure to maintain proper rolling.
  • Contamination: Dirt or debris is interfering with the rolling motion.
  • Internal jamming: Something inside the bearing is preventing smooth rotation.
• Think about it: If your bearing looks like it’s been “rubbed” the wrong way, it’s time to check for sliding issues.

Scratched Surfaces

• What it looks like: Visible scratch marks on the bearing surface.
• Why it happens: Scratches usually occur when foreign objects, like dirt particles, get trapped in the bearing.
• Possible causes:
  • Contamination: Particles have entered the bearing.
  • Interference: Other machine parts are rubbing against the bearing.
  • Overloading or poor lubrication: This can cause the rolling elements to slide instead of roll, leading to scratches.
• Ever wonder how a tiny speck of dirt can cause so much damage? It’s like a grain of sand in your shoe—small but painful!

Dented or Pitted Surfaces

• What it looks like: Indentations or small pits on the bearing surface.
• Why it happens: Dents and pits can form due to various reasons, including impact, vibration, or electrical issues.
• Possible causes:
  • Large area material loss: Such as the cage or the raceway has been worn thinner. This could indicate poor lubrication or contamination.
  • Single dents: If the dents are spaced similarly to the rolling elements, the bearing might have been overloaded while stationary or subjected to rough handling during installation.
  • Tiny, dense pits: These are often caused by electrical erosion, which can be seen under a magnifying glass.
  • Plastic deformation: The entire bearing surface is deformed, usually due to excessive impact loads.
• Pro tip: If your bearing looks like it’s been through a war zone, check for impact or electrical issues.

Broken or Fractured Bearings

• What it looks like: The bearing ring, cage, or rolling element is cracked or split.
• Why it happens: Breakage is a clear sign of excessive stress or improper handling.
• Possible causes:
  • Ring fracture:
    • Axial cracks: Check for improper fitting or overheating.
    • Circumferential cracks: Look for signs of fatigue (shell-like patterns) or impact (plastic deformation).
  • Cage fracture:
    • Cages aren’t designed to handle heavy loads. If broken, check for excessive wear or operational issues like frequent starts or vibration.
• Quick question: If your bearing cage is broken, is it always a quality issue? Not necessarily—it’s often due to how the bearing is used.

Failures That Start from the Inside

• What it looks like: The bearing surface may have uneven, somewhat flat pits.
• Why it happens: This is often due to subsurface fatigue, where the bearing material weakens over time under repeated stress.
• Possible causes:
  • Check the bearing’s load and fatigue life. If these are within normal limits, the issue might be with the bearing’s material quality, such as impurities in steel.
• Did you know? Internal failures are less frequent because modern bearings are made from high-quality steel(Such as spherical roller bearing 24048 CC W33). If you see this type of failure, it might be time to review your bearing supplier.

Summary: It’s Often About Application, Not Just Quality

• External failures are usually linked to operational issues like contamination, improper loading, or poor lubrication.
• Internal failures are more likely related to material fatigue or quality issues.