Hammering a rolling bearing during mounting, especially with point contact, causes damage due to the delicate internal design and extremely high contact stresses involved. Let’s break it down technically and visually:
Why It Damages the Bearing
1. Point Load OverstressRolling bearings are designed to handle distributed loads through rolling elements (balls or rollers), not sharp impulse forces.
A hammer hit introduces a highly concentrated force at one location (point contact), far exceeding material yield limits in that tiny area.
Result: Micro-cracks, indentations (brinelling), and even raceway deformations.2. False Brinelling and True Brinelling
If the hit is on a static bearing, it may leave permanent dimples where balls press into the race.
This destroys the smoothness of the raceway → vibration, noise, and premature failure.
3. Internal Misalignment
Hammering on one ring (usually the outer) causes impact force to travel through the rolling elements to the opposite ring.
This misaligns the inner ring vs. outer ring and may cause fractures in cages or rollers.
4. Surface Hardness Breakdown
Bearing raceways and balls are precision-ground and heat-treated (often >60 HRC). These surfaces are brittle on purpose.
A hammer hit introduces plastic deformation → destroys heat-treated layer → early spalling.
5. Cage Deformation or Fracture
Cages are thin and designed only to guide balls or rollers—not absorb axial impact.
Hammering can break or deform cages → misrouting of rolling elements → catastrophic failure.
Best Practice Instead
Use a bearing heater (induction or hot plate) to expand the inner ring thermally, then slide it onto the shaft.
Or use a bearing mounting tool set that applies force evenly to the ring being mounted (inner ring for shaft, outer ring for housing).
Image (Crying Bearing)
The artwork perfectly shows:
Left: Happy bearing waiting to be properly installed.
Right: Damaged and sad after being hammered — symbolizing internal pain no one sees until failure.
Summary
Never hammer bearings into place. Even one improper blow may cut the bearing life to a fraction — from 50,000 hours to 500 hours — and result in unexpected breakdowns in critical machinery.
