Bearings
Dimensional accuracy of bearings
Why is it important?
In precision engineering and high-tech applications such as machine tools, medical equipment and aerospace technology, the dimensional accuracy of bearings is crucial. Standard bearings with tolerance class P0 are often not accurate enough for applications where high running accuracy and higher speeds are required. For the situations, higher precision bearings that meet strict ISO standards are used.
Overview of tolerance classes
Different standards define the precision of bearings. The table below shows how DIN, ISO and AFBMA (ABEC) standards correspond to each other:
| DIN standard | ISO standard | AFBMA (American) standard |
|---|---|---|
| Default = P0 | ISO-0 | ABEC-1 |
| More accurate than P0=P6 | ISO-6 | ABEC-3 |
| Semi-precision class = P5 | ISO-5 | ABEC-5 |
| Precision class = P4 | ISO-4 | ABEC-7 |
Some manufacturers use intermediate tolerance levels. The above classes are primarily found in ball and angular contact bearings and are referred to as suffixes, such as 6212 P6.
Practical applications for precise bearings
The choice of a bearing depends heavily on the specific requirements of the application. Some examples of applications requiring higher dimensional accuracy:
- CNC machines: High precision and minimal vibration are required for precise machining.
- Medical equipment: For example, MRI scanners and surgical instruments, where precision is essential.
- Aerospace: Bearings in aircraft engines and satellites must withstand extreme conditions without loss of accuracy.
Overview of standards
To standardize the dimensional accuracy of bearings worldwide, there are several standards institutes and organizations:
- DIN (Deutsches Institut für Normung): German standard for technical components, including bearings.
- ISO (International Organization for Standardization): International organization that establishes standards, including precision bearings.
- AFMBA (Anti-Friction Bearing Manufacturers Association): American standards organization for bearings.
- ABEC (Annular Bearing Engineers Committee): Part of AFBMA, focuses specifically on precision bearings.