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The Ultimate Guide to Measuring Bearing Clearance
In mechanical engineering and manufacturing, bearings are key components that ensure smooth operation and long life of mechanical equipment. The performance of a bearing depends not only on its design and manufacturing quality, but also on the bearing clearance. Bearing clearance refers to the gap between the bearing rolling elements and the inner and outer rings, which has a significant impact on the noise, vibration, heat generation and load distribution of the bearing. This article will delve into the concept, classification, calculation methods of bearing clearance and its impact on bearing performance, and provide detailed formulas and data support.
Bearing clearance refers to the gap between the bearing rolling elements and the inner and outer rings when no external load is applied. Depending on the direction of measurement, bearing clearance can be divided into radial clearance and axial clearance.
1. Radial clearance: In the no-load state, when the inner ring of the bearing is fixed, the amount of movement of the outer ring in the radial direction, that is, the displacement perpendicular to the axis direction.
2. Axial clearance: In the no-load state, when the inner ring of the bearing is fixed, the amount of movement of the outer ring in the axial direction, that is, the displacement parallel to the axis direction.
Bearing clearance grade
Bearing clearance grades are classified according to their size, and each grade is suitable for different working conditions and applications. Common clearance grades include C2, CN, C3, C4, and C5.
C2 level clearance
Class C2 has smaller clearance and is suitable for applications that require higher bearing accuracy and stability, such as precision instruments and motors. Due to its small clearance, this type of bearing has low noise and vibration during operation, and is suitable for high-precision mechanical equipment.
CN level clearance
Grade CN is normal clearance and is suitable for most general applications such as industrial machinery and vehicles. It provides a good balance, ensuring the bearing’s operational stability while adapting to general load and temperature changes.
C3 level clearance
Grade C3 has larger clearance and is suitable for applications with high temperatures or larger loads, such as motors and heavy-duty machinery. Larger clearance can compensate for thermal expansion caused by rising temperatures and prevent bearing failure due to overheating.
Grade C4 and Grade C5 clearance
Grades C4 and C5 have larger clearances than grade C3 respectively and are suitable for applications with higher temperatures or greater loads. These levels of clearance are used for equipment under extreme working conditions, such as high temperature environments or overloaded mechanical equipment, to ensure that the bearings can still operate stably under harsh conditions.
| Clearance Class | Radial Clearance (µm) | Axial Clearance (µm) | Application Examples |
|---|---|---|---|
| C2 | Less than Normal (10-20) | Less than Normal (10-25) | High precision, low noise applications |
| CN (Normal) | Normal (20-40) | Normal (25-50) | General industrial applications |
| C3 | Greater than Normal (40-70) | Greater than Normal (50-90) | High temperature or heavy load applications |
| C4 | Greater than C3 (70-100) | Greater than C3 (90-130) | Very high temperature or very heavy load |
| C5 | Greater than C4 (100-130) | Greater than C4 (130-160) | Extreme conditions with maximum clearance |
Measuring bearing clearance
Measuring bearing clearance is a key step to ensure stable performance of bearings under actual operating conditions. The following describes the different types of internal bearing clearance and their calculation formulas.
Measured internal bearing clearance (Δ1)
The measured internal bearing clearance is measured under a specific load, including load-induced elastic deformation (δfo). The calculation formula is:
Δ1=Δ0+δfo
Δ1 is the measured internal bearing clearance
Δ0 is the theoretical internal bearing clearance
δfo is the elastic deformation caused by load
Theoretical internal bearing clearance (Δ0)
Theoretical internal bearing clearance is the radial internal bearing clearance measured under no load and does not include elastic deformation. For rolling bearings, the elastic deformation is zero, so the formula simplifies to:
Δ0=Δ1
Remaining internal bearing clearance (Δf)
Residual internal bearing clearance is the bearing clearance after the machine is assembled but before it is put into service, excluding elastic deformation but accounting for ring expansion or compression. The calculation formula is:
Δf=Δ0+δf
δf is the change caused by ring expansion or compression
Effective internal bearing clearance (Δ)
The effective internal bearing clearance is the bearing clearance produced by the machine due to the operating temperature, excluding elastic deformation due to load. The calculation formula is:
Δ=Δf−δt=Δ0−(δf+δt)
δt is the change caused by the temperature difference between the inner and outer rings
Factors affecting bearing clearance
Several factors can affect bearing clearance, including temperature changes, load changes, installation quality and operating speed.
Temperature change
Increased temperatures cause bearing components to expand, affecting clearance. The heat generated during operation causes the inner and outer rings of the bearing to expand, reducing clearance. To avoid bearing failure due to thermal expansion, it is important to select the appropriate clearance grade. The formula is as follows:
δt=αΔtDe
δt is the reduction in radial bearing clearance caused by the temperature difference between the inner and outer rings (unit: mm).
α is the linear thermal expansion coefficient of bearing steel, which is approximately 12.5 × 10⁻⁶/℃.
Δt is the temperature difference between the inner and outer rings (unit: ℃).
De is the outer ring channel diameter (unit: mm), for ball bearings: De=(4D+d), for rolling bearings: De=(3D+d).
Loading change
Different loading conditions can cause changes in clearance, especially axial loads. When the bearing is subjected to axial load, the rolling elements will displace in the axial direction and change the clearance. Therefore, actual load conditions need to be considered when designing and selecting bearings.
Installation quality
Improper installation may change the bearing’s clearance and affect its performance. For example, an over-tight installation can compress the bearing, reduce clearance, and increase friction and wear. Too loose installation will increase the clearance and lead to unstable operation.
Running speed
During high-speed operation, centrifugal force will cause the bearing assembly to deform and change the clearance. In order to ensure that the bearing remains stable at high speeds, it is important to select the appropriate clearance grade.
Conclusion
Bearing clearance is an important parameter for bearing performance. The correct understanding and calculation of bearing clearance is crucial to the installation, operation and life of the bearing. By understanding the different types of bearing clearances and how they are calculated, engineers can better select and use bearings to meet various operating conditions and application needs. I hope this article can help readers fully understand the importance of bearing clearance and apply this knowledge in practical work to improve the operating efficiency and reliability of equipment.