What effects will occur if the temperature is too high or too low when installing self-aligning roller bearings by heating?
Release time:
2025-06-18
What effects will occur if the temperature is too high or too low when installing self-aligning roller bearings by heating?
When installing self-aligning roller bearings by heating, temperature control is a crucial step to ensure installation quality and bearing lifespan. Both excessively high and low temperatures can significantly affect bearing performance, the installation process, and subsequent usage. The specific hazards are as follows:
I. Effects of Excessively High Temperature (>120℃)
1. Deterioration of Material Properties
Hardness Reduction:
The common material for bearings is high-carbon chromium bearing steel (such as GCr15), with a tempering temperature typically ranging from 150℃ to 180℃. If the heating temperature exceeds 120℃, the material undergoes "secondary tempering", resulting in a decrease in hardness (for example, from 62HRC to below 58HRC), directly weakening the bearing's fatigue resistance and wear resistance.
Change in Microstructure:
High temperatures cause the decomposition of martensite, forming tempered sorbite or troostite, leading to a decrease in material toughness and an increase in brittleness, which can result in roller fractures or raceway cracks during operation.
2. Failure of Dimensional Accuracy
Excessive Expansion of Inner Hole:
High temperatures can cause the inner hole to expand beyond the required fit (for instance, a 100mm inner diameter bearing expands approximately 0.12mm at 130℃; if the interference fit only requires 0.05mm, it may lead to excessive clearance after installation), causing loose fit between the bearing and the shaft, resulting in slippage, overheating, and even burning during operation.
Deformation of Retainer:
If the retainer is made of plastic (such as PA66) or brass, it may soften and deform at temperatures above 100℃ (the softening temperature of plastic retainers is approximately 120℃), causing rollers to misalign, jam, and potentially leading to bearing seizure.
3. Damage to the Lubrication System
If the bearing is pre-lubricated with grease, high temperatures can cause the grease to carbonize and dry out (the drop point of common lithium-based grease is about 180℃, but it oxidizes and deteriorates at temperatures above 120℃), losing its lubricating effect. After installation, the friction coefficient increases sharply during operation, leading to overheating and failure of the bearing.
4. Safety Hazards
When using oil bath heating, temperatures exceeding 120℃ can cause mineral oil to vaporize and produce flammable gases, posing a fire risk. With induction heating, high temperatures may cause the bearing surface to oxidize, forming oxide scales, which can scratch the shaft neck or inner hole during installation.
II. Effects of Excessively Low Temperature (<80℃)
1. Excessive Installation Resistance
Insufficient Expansion of Inner Hole:
If the temperature is too low, the expansion of the inner hole may not meet the minimum clearance required for the interference fit (for example, an interference fit of 0.05mm requires an expansion of approximately 0.075mm, but at 70℃, the actual expansion is only 0.077mm), resulting in insufficient clearance between the bearing and the shaft. Forcing the installation can:
Scratch the surface of the shaft neck or inner hole, damaging the fit accuracy;
Generate installation stress, increasing vibration and noise during operation.
2. Insufficient Interference Fit
If the temperature is too low and the expansion does not reach the minimum clearance required for the interference fit (for example, an interference fit of 0.05mm requires an expansion of 0.075mm, but the actual expansion is only 0.06mm), the bearing may experience axial movement or circumferential slippage during operation, causing:
Wear on the shaft surface (fretting wear);
Heating and annealing of the inner ring, and even the "running ring" phenomenon (relative rotation between the inner ring and the shaft).
3. Reduced Installation Efficiency
Insufficient temperature requires multiple heating or forced press-fitting, not only prolonging the installation time but also potentially causing local overheating of the bearing due to repeated heating (such as when using flame heating), exacerbating material damage.
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