When rolling elements are subjected to load, contact stresses develop at the interface between the rolling elements and the inner and outer rings. During operation, the inner and outer rings and the rolling elements undergo relative rotational motion, Consequently, the contact stress fluctuates. When the contact stress exceeds the specified limit, fatigue cracks form beneath the surface layer and gradually propagate towards the surface. This leads to fatigue pitting on the rolling surfaces of the inner and outer rings, resulting in diminished rotational precision, increased noise, impact, and vibration in precision bearings. Thus, pitting constitutes a failure mode for precision rolling bearings. Let us now examine the impact of fatigue pitting on troubleshooting precision bearing failures.
Methods to extend the service life of precision bearings:
The longevity of precision bearings is intrinsically linked to their production, manufacturing, installation, and application. Ensuring excellence at each stage enables bearings to achieve optimal operational conditions and prolong their service life.
1. Selection and handling of dimensional tolerances for shafts and bearing housings: After pressing the bearing into the housing, it should rotate freely without binding. If rotation is noticeably impeded, the shaft dimensions are excessive; reduce the dimensional tolerance. Conversely, if the bearing exhibits a pronounced ‘looseness’ sensation after press-fitting onto the shaft, the shaft's dimensional tolerance may be too large, or its concentricity may be inadequate. Therefore, in controlling the dimensional tolerances of precision bearings and bearing housings, concentricity must be prioritised. At present, many manufacturers focus solely on dimensional tolerances without addressing concentricity.
2. Installation Method: As precision bearings are high-accuracy components, improper installation readily damages their cross-section, rendering them unusable. Specialised presses are required for installation; striking with hammers is inadvisable. When pressing onto a shaft, apply force only to the inner ring; when pressing onto a large ring, apply force only to the large ring. When installing using pneumatic or hydraulic presses, ensure horizontal alignment during lateral riveting. Any misalignment will damage the bearing cross-section and compromise the precision bearing's guide wires.
3. Contamination Prevention: When mounting bearings onto motor rotors for dynamic balancing, iron filings generated during balancing may enter precision bearings. Therefore, ensure the rotor achieves proper dynamic balance before bearing installation. Some manufacturers introduce oil or vegetable oil into the bearing chamber for lubrication to facilitate installation. However, operators struggle to control the quantity of oil or vegetable oil within the precision bearing chamber. Excessive oil or vegetable oil may cause the bearing to adhere to the shaft during rotation. Do not apply oil or vegetable oil to the precision bearing chamber. If application is necessary, ensure no accumulation occurs within the chamber during operation.
4. Prevention of Paint Rust: Paint rust typically affects enclosed motors. During initial installation, the motor operates with minimal noise. However, after prolonged storage in warehouses, the motor's noise level increases significantly. Upon disassembly, severe rusting of the precision bearings is often observed. Previously, many manufacturers attributed this issue to the precision bearings themselves.