How does excessive temperature affect bearing friction?

The core effects of high temperature on bearing friction are:

1. Lubrication Failure

At high temperatures, base oil evaporates (mineral oil volatilizes significantly above 80°C), causing a sharp drop in viscosity (30%-50% for every 10°C increase in temperature). This leads to insufficient oil film thickness (<0.1μm), causing oil film rupture. The friction coefficient rises from 0.001-0.005 to above 0.1, creating a vicious cycle of "high temperature → oil film rupture → increased frictional heat → higher temperature." Simultaneously, the grease oxidizes and decomposes (for example, lithium-based grease above 120°C), generating acids that corrode the metal and carbide deposits that cause abrasive wear.

2. Material Degradation

Bearing steel hardness decreases with increasing temperature (HRC60 decreases significantly above 200°C), leading to plastic deformation in the contact zone (sag/bulge in the raceway). Differential thermal expansion causes abnormal clearances: loosening of the inner ring increases sliding friction; interference fit of the outer ring may cause seizure of the rolling elements, increasing the friction coefficient from 0.001-0.005 for rolling friction to 0.1-0.3 for sliding friction.

3. Deterioration of Contact Conditions
After the oil film ruptures, high temperatures in localized micro-regions (up to hundreds of degrees Celsius) trigger metal micro-welding, which in turn causes adhesive wear and metal shedding. High temperatures accelerate oxidative wear (the cyclical formation and shedding of oxide films such as Fe₃O₄), reducing dimensional accuracy. Impurities ingress after seal failure exacerbates abrasive wear.

4. Indirect Impacts
The effects of thermal deformation and abnormal clearance increase vibration (for example, increasing acceleration from 0.1g to 1g). Impact friction destabilizes the oil film, creating a secondary cycle of "vibration-friction-heating."

Summary: High temperatures destroy lubrication, weaken materials, and deteriorate contact, causing friction to degenerate from fluid lubrication to boundary/dry friction, accompanied by a combination of adhesive, oxidative, and abrasive wear. Continuous high temperature will cause abnormal noise, jamming or even burning. The operating temperature must be controlled to ≤70-90℃ (depending on the bearing and grease type).