The Concept of Combining Rolling Bearings
When it comes to the combination of rolling bearings, it's essential to understand how the selection and layout of bearings impact the overall performance and longevity of mechanical systems. Properly combining bearings ensures smooth operation, minimizes wear, and enhances system efficiency.
The key aspects of bearing combination include:
- Shaft support end layout
- Interaction between bearings and adjacent components
- Smoothness and sealing of the bearing assembly
- Improving the stiffness of the entire bearing system
1. Fixed at Both Ends (Two-Way Fixed)
This method is typically used for short shafts operating under normal temperatures (with a span L < 400mm). The support usually employs a two-way one-way fixing method, where each bearing does not experience axial force in one direction. When the shaft operates, there may be a small amount of thermal expansion. Therefore, an axial gap of 0.25–0.4 mm should be left between the bearing cap and the outer end face of the shaft. This allows for proper thermal expansion without causing damage.
Features: The shaft can move freely in both directions. Suitable for shafts with minimal temperature changes.
Notes: Be mindful of thermal expansion. Leave a gap of 0.2–0.3 mm between the bearing cap and the outer end face.
2. One End Fixed, One End Free (Swimming Support)
This approach is ideal for long shafts or when the working temperature is high. The thermal expansion of the shaft must be accommodated. In this setup, one end is fixed to bear axial forces, while the other end is allowed to move freely. This prevents loosening and ensures the shaft remains stable during operation.
At the floating end, the inner ring of the bearing should be axially fixed to the shaft—often using an elastic ring. If a cylindrical roller bearing is used as the floating support, the outer ring should be fixed to the housing. This allows the roller and raceway to move, accommodating the shaft’s elasticity.
Features: One end is fixed in both directions, while the other end is free to move.
Application: Best suited for long shafts with significant temperature fluctuations.
3. Adjustment of Bearing Combination
Proper adjustment of the bearing clearance and pre-tightening is crucial for optimal performance:
- Clearance Adjustment: Can be achieved by adjusting the thickness of the bearing cover or base, or by moving the bearing outer ring gland with screws.
- Pre-Tightening: Helps improve accuracy, stiffness, and reduce vibration. It involves applying a specific axial force to ensure proper clearance.
- Orientation Adjustment: Ensures that on-axis components like gears and pulleys are aligned correctly for precise operation.
4. Fit Between Bearing and Shaft
The inner ring of the rolling bearing fits with the shaft using the base hole system. Meanwhile, the outer ring fits with the housing bore using the base shaft system. These standard fits ensure secure and reliable connections.
5. Assembly and Disassembly of Rolling Bearings
Rolling bearings often have a shorter lifespan than the entire machine. They may need frequent replacement due to damage or wear. When disassembling, it's important to avoid transmitting force through the rolling elements, as this can cause plastic deformation. Special tools are recommended for safe removal, and the layout of the shaft should allow for easy access.
Related Bearing Knowledge
- Bicycle bearings, drive components, and cleaning methods
- NTN cylindrical bore bearing installation using press fit
- Analysis of common quality defects in bearing parts after heat treatment
- Classification of rolling bearings based on size and heating devices
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