A trial operation is conducted to insure that the bearings are properly mounted.
In the case of compact machines, rotation may be checked by manual operation at first.
If no abnormalities, such as those described below, are observed, then further trial operation proceeds using a power source.
- Knocking ...
due to flaws or insertion of foreign matter on rolling contact surfaces.
- Excessive torque (heavy) ...
due to friction on sealing devices, too small clearances, and mounting errors.
- Uneven running torque ...
due to improper mounting and mounting errors.
For machines too large to allow manual operation, idle running is performed by turning off the power source immediately after turning it on. Before starting power operation, it must be confirmed that bearings rotate smoothly without any abnormal vibration and noise.
Power operation should be started under no load and at low speed, then the speed is gradually increased until the designed speed is reached.
During power operation, check the noise, increase in temperature and vibration.
If any of the abnormalities listed in "Table 15-5 Bearing noises, causes, and countermeasures" and "Table 15-6 Causes and countermeasures for abnormal temperature rise" are found, operation must be stopped, and inspection for defects immediately conducted.
The bearings should be dismounted if necessary.
Table 15-5 Bearing noises, causes, and countermeasures
|Flaw noise (similar to noise when punching a rivet)
Rust noise (similar to noise when punching a rivet)
Brinelling noise (Unclear siren-like noise)
|Flaw on raceway
Rust on raceway
Brinelling on raceway
|Improve mounting procedure, cleaning method and rust preventive method. Replace bearing.
|Flaking noise (similar to a large hammering noise)
|Flaking on raceway
|Dirt noise (an irregular sandy noise.)
|Insertion of foreign matter
|Improve cleaning method, sealing device.
Use clean lubricant. Replace bearing.
|Fitting noise (drumming or hammering noise)
|Improper fitting or excessive bearing clearance
|Review fitting and clearance conditions. Provide preload.
Improve mounting accuracy.
|Flaw noise, rust noise, flaking noise
|Flaws, rust and flaking on rolling elements
|Squeak noise (often heard in cylindrical roller bearings with grease lubrication, especially in winter or at low temperatures)
|If noise is caused by improper lubrication, a proper lubricant should be selected.
In general, however, serious damage will not be caused by an improper lubricant if used continuously.
|Abnormally large metallic sound
Insufficient amount of or improper lubricant
|Review fitting, clearance.
Adjust preload. Improve accuracy in processing and mounting shafts and housings. Improve sealing device.
Refill lubricant. Select proper lubricant.
Table 15-6 Causes and countermeasures for abnormal temperature rise
|Too much lubricant
|Reduce lubricant amount. Use grease of lower consistency.
|Select proper lubricant.
|Review fitting and clearance conditions and adjust preload.
|Improve accuracy in processing and mounting shaft and housing. Review fitting. Improve sealing device.
Normally, listening rods are employed for bearing noise inspections.
The instrument detecting abnormalities through sound vibration and the Diagnosis System utilizing acoustic emission for abnormality detection are also applicable.
In general, bearing temperature can be estimated from housing temperature, but the most accurate method is to measure the temperature of outer rings directly via lubrication holes.
Normally, bearing temperature begins to rise gradually when operation is just starting; and, unless the bearing has some abnormality, the temperature stabilizes within one or two hours.
Therefore, a rapid rise in temperature or unusually high temperature indicates some abnormality.