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Koyo Technical Information

11. Handling of bearings

• General instructions
• Mounting methods
  • b.1. Press fit of bearings with cylindrical bore bearings
  • b.2. Shrink fit of bearings with cylindrical bore bearings
• Test run
• Maintenance and checking
• Checking of bearings

a. Handling of bearings

1) General remarks

• Bearings are highly precise products. Handle carefully to keep them free from dirt and dust as well as from impact.
• Use suitable handling jigs.
• Keep bearings away from moisture or perspiration to prevent corrosion.

2) Storing
Bearings are treated to prevent corrosion at the time of shipment. If they are stored unused for a long period of time, place on a shelf more than 30cm high from the floor, at 65% or less humidity and at 20. Keep them away from the strong sun. Do not place them near the window, where moisture condensation is likely.

3) Pre-installation preparations
Do not clean off anti-corrosion oil on the bearing when it is used under normal conditions. When it is used in an application of extremely high precision or at high speed, remove anti-corrosion oil with unpolluted cleaning oil, assemble quickly, and inject lubricant.

4) Inspection of shaft and housing
Before assembly, inspect the shaft and housing, and apply machine oil or other appropriate material to the mating surfaces of the individual components.

b. Mounting methods

b.1. Press fit of bearings with cylindrical bore bearings

Mounting methods	Descriptions
1) Using press fit(the most widely used method)	As shown in the Fig., a bearing should be mounted slowly with care, by using a fixture to apply force evenly to the bearing. When mounting the inner ring, apply pressure to the inner ring only. Similarly, in mounting the outer ring, press only the outer ring.
	(Inner ring press fit)	(Outer ring press fit)	(Inner ring press fit)
2) Using bolts and nuts (screw hole should be provided at the shaft end)	If interference is required on both the inner and outer ring of non-separable bearings, use two kinds of fixtures as shown in the Fig. and apply force carefully, as rolling elements are easily damaged. Be sure never to use a hammer in such cases. (Simultaneous press fit of inner ring and outer ring)
3) Using hammers(only when there is no alternative measure)

b.2. Shrink fit of cylindrical bore bearings

Fig.12-1 Heating temperature and expansion of inner rings

[Remarks]
1 Thick solid lines show the maximum interference value between bearings (class 0) and shafts (r6,p6,n6,m5,k5,js5) at normal temperature.

2 Therefore, the heating temperature should be selected to gain a larger “expansion of the bore diameter” than the maximum interference values.

c. Test run

To ensure that the bearing has been installed in a correct way, perform test runs to check out the following:

1) Rotational conditions

a) Knocking – Contaminants or damaged raceway may impair smooth rotation.
b) Excessive friction – Friction on the sealing device, error in mounting, or too small clearance may cause torque to become too high.
c) Fluctuations in running torque – Incorrect installation or error in mounting may make running torque uneven.

2) Abnormal noise

Check for any abnormal bearing noise by using a sound-locating bar or hearing aids. Because expertise is required to identify noise, it is desirable to have an experienced person to perform the check.

Table 12-2 Bearing noises, causes, and countermeasures

3) Abnormal generation of heat
After the start of operation, bearing temperature rises gradually and becomes constant within one to two hours. Temperature should be monitored and recorded continuously during operation for evaluation by comparison.
Trouble may cause irregular changes in temperature, such as a sudden rise.

Table 12-3 Causes of and countermeasures for abnormal temperature rise

d. Maintenance and checking

To ensure that bearings can demonstrate their optimal performance and provide service over a long time, regular maintenance and inspection are required. Inspect uninstalled bearings by the following procedure:

1) Cleaning
When a bearing is uninstalled, check how much lubricant is remaining first. Clean the bearing with anhydrous, neutral light oil or kerosene. Warm alkalic solution or other material may be used as necessary. Clean the bearing preliminarily under cleaning oil, removing grease and sticking foreign matter with a brush or other tool. Do not rotate the bearing excessively during the preliminary cleaning.

After such foreign matter is removed, perform finishing cleaning while rotating the bearing slowly. Provide anti-corrosion treatment promptly when the cleaning is complete.

2) Checking
To determine whether the removed bearing can be used further, examine the bearing rings, rolling elements and cage carefully. If any of the damages shown in the Examples of Bearing Failures is found, use a new bearing.

e. Checking of bearings

1) Noise checking

Check for any abnormal bearing noise by using a sound-locating bar or hearing aids. Because expertise is required to identify noise, it is desirable to have an experienced person to perform the check.

Table 12-2 Bearing noises, causes, and countermeasures

2) Temperature checking

After the start of operation, bearing temperature rises gradually and becomes constant within one to two hours. Temperature should be monitored and recorded continuously during operation for evaluation by comparison. Trouble may cause irregular changes in temperature, such as a sudden rise.

Table 12-3 Causes of and countermeasures for abnormal temperature rise

3) Lubricant checking

This method detects abnormalities from the foreign matter, including dirt and metallic powder, in lubricants collected as samples. This method is recommended for inspection of bearings, which cannot be checked by close visual inspection, and large size bearings.