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Dismounting and Cleaning of Rolling Bearings

Bearings are dismounted for periodic inspection or replacement. If the removed bearing is to be reused or it is removed only for inspection, dismounting needs to be conducted as carefully as mounting, taking care not to damage the bearing or individual components. Since it is particularly difficult to dismount bearings that are tightly fitted, sufficient consideration should be given at the design stage to the structure surrounding the bearing so that the bearing can be easily dismounted. It is also important to design and manufacture dismounting tools as required.

All possible preparations must be made for dismounting bearings by studying the dismounting method, the sequence of procedures, and the fitting conditions of the bearing as displayed in drawings. When investigating the cause of bearing failure, the bearing also needs to be treated carefully, as described above, to preserve the condition of the bearing prior to dismounting. In the course of dismounting a bearing, take care not to scratch the bearing, wipe off any grease, or remove dust, dirt or iron powder, since these actions may prevent identifying the cause of the failure. Although a loosely fitted bearing can be easily dismounted, exercise extreme care when the bearing is tightly fixed.

When bearings used for a given period of time are dismounted for inspection, they should be cleaned. First inspect the old grease coating the bearing, then clean the bearing and examine its condition. Dismounted bearings should first be given a preliminary cleaning followed by a finishing rinse. During preliminary cleaning, it is better to use a brush to gently remove any grease containing dust, dirt, or abrasive powder, without rotating the bearing.

New bearings are always coated with an anti-corrosion agent prior to packaging. Generally, these bearings do not need to be cleaned only to remove the anti-corrosion agent. Since only a thin coating of anti-corrosion agent covers the surface of the bearing, there should not be any harmful effect from leaving the agent on the bearing, even when mixed with a lubricant or lubrication grease. Greater damage can be caused by cleaning the bearing in an environment exposed to contaminated oil, dust, or dirt.

Nevertheless, removing the anti-corrosion agent is recommended for small bearings used in high-speed operations or for bearings that will use low-viscosity or mist lubrication. Therefore, in principle, bearings should be cleaned when they are being examined; when dust and dirt have adhered to the bearing; or when the machine using the bearing operates at a level of speed or accuracy that would be impaired by even the slightest resistance to bearing rotation.

Kerosene is generally used as a cleaning agent. Low-viscosity spindle oil may be jet sprayed. Compressed air is also used to remove dust and dirt from the bearing, unless the applied air contains moisture or dust and dirt; air usually contains moisture that often condenses into water droplets at the tip of the nozzle. Therefore, due care must be exercised when using compressed air. In addition, since cleaning a bearing while rotating the bearing by blowing it with compressed air can damage the raceway, the inner and outer ring must be fixed to prevent the bearing from rotating.

When storing a cleaned bearing, it should be thoroughly dried and coated with an anticorrosion agent. When applying grease, be sure to rotate the bearing to ensure uniform distribution to every part of the bearing.