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Is a Smaller Radial Clearance Better for Bearings?
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By: 创始人
- Aug 29, 2025
- 1 Visit
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When selecting bearings, many users may mistakenly assume that a smaller radial clearance yields better performance. However, this is not a universal rule—the optimal radial clearance depends entirely on the bearing’s operating conditions, and a one-size-fits-all approach to minimizing clearance can lead to premature bearing failure or reduced equipment efficiency. Below is a detailed explanation of bearing radial clearance classification, selection principles, and key considerations for practical applications.
1. Classification of Bearing Radial Clearance
According to China’s National Standard GB/T 4604-93 (equivalent to international standards for rolling bearings), the radial clearance of rolling bearings is divided into five distinct groups, with clearance values increasing in a specific order:
| Clearance Group | Clearance Magnitude | Description |
|---|---|---|
| Group 2 | Smallest | Specialized for scenarios requiring ultra-precise rotation |
| Group 0 | Standard | Default choice for general operating conditions |
| Group 3 | Larger than Group 0 | For applications with moderate special requirements (e.g., slight temperature fluctuations) |
| Group 4 | Larger than Group 3 | Suitable for high-speed or high-temperature environments |
| Group 5 | Largest | Reserved for extreme conditions (e.g., heavy loads with significant thermal expansion) |
Among these, Group 0 (standard clearance) is the most widely used, as it meets the needs of most general-purpose equipment under normal operating parameters.
2. Principles for Selecting Radial Clearance
The core of radial clearance selection is to match the clearance to the bearing’s operating environment, load type, and precision requirements. Specific guidelines are as follows:
2.1 General Operating Conditions: Choose Standard Clearance (Group 0)
For bearings used in ordinary mechanical equipment (e.g., conveyors, general-purpose motors, or pumps) that operate at normal temperatures (20–60°C), use common interference fits (e.g., 过渡配合 /transition fits between the inner ring and shaft, or clearance fits between the outer ring and housing), and bear moderate, stable loads—Group 0 (standard clearance) is the most cost-effective and reliable choice. It balances rotational flexibility and load-bearing stability, avoiding both excessive clearance (which causes vibration and noise) and insufficient clearance (which leads to friction and overheating).
2.2 Special Operating Conditions: Adjust Clearance Based on Needs
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High temperature, high speed, low noise, or low friction requirements: Opt for larger radial clearances (Groups 3, 4, or 5).
At high temperatures, bearing components (inner ring, outer ring, rolling elements) expand thermally; a larger initial clearance compensates for this expansion, preventing the clearance from becoming too small or even negative (a state where components are pressed together, causing severe friction). For high-speed bearings (e.g., in centrifugal separators or precision fans), larger clearance reduces centrifugal force-induced friction between rolling elements and raceways, lowering noise and heat generation. -
Precision rotation scenarios: Select smaller radial clearances (Group 2).
Equipment requiring ultra-high rotational precision—such as precision spindles (e.g., in CNC machine tools, optical instruments, or semiconductor manufacturing equipment)—needs minimal radial clearance. A smaller clearance minimizes axial and radial runout of the spindle, ensuring stable rotation accuracy and reducing vibration during high-precision machining or measurement. -
Roller bearings: Maintain a small amount of working clearance.
Roller bearings (e.g., cylindrical roller bearings, tapered roller bearings) rely on line contact between rolling elements and raceways to bear heavy loads. A small working clearance ensures uniform load distribution across the roller surface, avoiding localized stress concentrations and extending bearing service life.
2.3 Special Case: Split Bearings Have No Radial Clearance
Split bearings (a type of bearing with a split inner or outer ring, often used in large-scale equipment like marine propellers or industrial turbines) are designed with zero radial clearance in their original state. This is because their split structure requires tight assembly to ensure coaxiality between the inner and outer rings; any initial clearance would cause misalignment during operation, leading to uneven load distribution.
3. Key Note: Installed Working Clearance ≠ Original Clearance
It is critical to recognize that the actual working clearance of a bearing after installation is smaller than its original clearance before installation. This reduction stems from two main factors:
- Elastic deformation due to load: When the bearing operates under rotational load, the inner ring, outer ring, and rolling elements undergo slight elastic deformation. This deformation narrows the gap between components, reducing the effective radial clearance.
- Interference fit effects: Most bearings use interference fits between the inner ring and the shaft (to prevent the inner ring from slipping on the shaft during rotation). The interference fit compresses the inner ring slightly, which in turn reduces the radial clearance between the inner ring, rolling elements, and outer ring.
For this reason, when selecting radial clearance, it is necessary to account for the expected reduction in clearance after installation—ensuring that the final working clearance still meets the equipment’s operational requirements.