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  1. Maintenance of Bearings
  2. Lubrication: Too Much vs. Too Little
  3. What Are ABEC GRADES in Bearings?
  4. Internal Clearances

1.Maintenance of Bearings

If not particularly prescribed , rolling bearings lubricated with grease are usually adopted for motors. Except close-type ball bearings , all other bearings are of open type so as to prevent from being over-greased by facilitating the injection and discharge of grease. Tips of maintenance are listed and explained below :

Tips for maintenance :

  1. Additional supply of grease should be given to the newly procured motors before they are started running , or to the motors have stopped running for more than 2 months before they are re-started for running.
  2. After motors having started running . additional grease should be supplied at intervals and according to the quantities shown on nameplate.
  3. The discharged grease should be removed timely

After stopping running for a long period (more than 2 months) :

  1. Make sure checks described in item 1 and 4 have been completed .
  2. After beginning running , grease should be injected at once . The quantity to be injected is shown on nameplate .
  3. Temperature rise around bearings after beginning running .
  4. Loudness and tone of bearing noise .
  5. Noise and vibration of the motor .
  6. Vibration of the bearing

2. Lubrication: Too Much vs. Too Little                                                                              

While many bearings can fail due to lack of lubrication, over-lubrication is considered one of the major causes of bearing failure. Many lubrication programs are based on preventive maintenance programs in which bearings are lubricated according to a time-based schedule with predetermined amounts of lubrication applied. While useful, if this practice is followed without any feedback regarding the condition of a bearing, it may, in fact, lead to an over-lubricated condition that will eventually lead to bearing failure. Many maintenance departments are therefore switching to a combination of preventive and condition-based lubrication (Figure A).A condition-based lubrication program requires trending of bearing decibel levels. A baseline decibel level is set, along with (if possible) a baseline sound sample, and an inspection schedule is established for periodic testing. When a bearing sound level exceeds 8 dB with no change in the sound quality (usually a smooth, "rushing" sound), the bearing is considered in need of lubrication. A lubrication technician, while listening to the bearing, will then apply lubricant, a little at a time, until the baseline level is reached. Stopping at that point prevents over-lubrication.

Other causes of bearing failure include improper installation, corrosive atmospheres, particle contamination, faulty alignment, and use of the wrong lubricant.

Tips for maintenance :

  1. Additional supply of grease should be given to the newly procured motors before they are started running , or to the motors have stopped running for more than 2 months before they are re-started for running.
  2. After motors having started running . additional grease should be supplied at intervals and according to the quantities shown on nameplate.
  3. The discharged grease should be removed timely

After stopping running for a long period (more than 2 months) :

  1. Make sure checks described in item 1 and 4 have been completed .
  2. After beginning running , grease should be injected at once . The quantity to be injected is shown on nameplate .
  3. Temperature rise around bearings after beginning running .
  4. Loudness and tone of bearing noise .
  5. Noise and vibration of the motor .
  6. Vibration of the bearing

3. What Are ABEC GRADES in Bearings?

The ABEC scale is a system for rating the manufacturing tolerances of precision bearings. The system was developed by the Annular Bearing Engineering Committee or Council (ABEC) of the American Bearing Manufacturers Association (ABMA). The American Bearing Manufacturers Association was formerly known as the Anti-Friction Bearing Manufacturers Association.

What Does ABEC Mean?
The ABEC scale is a system for rating the manufacturing tolerances of precision bearings. The system was developed by the Annular Bearing Engineering Committee or Council (ABEC) of the American Bearing Manufacturers Association (ABMA). The American Bearing Manufacturers Association was formerly known as the Anti-Friction Bearing Manufacturers Association.

Bearings rated under the ABEC system are typically called "precision bearings", and they are rated with a number from 1 to 9, with the higher number assigned to bearings manufactured against a higher standard of precision (high number = tighter tolerances = more expensive bearing).

What Does Tolerance Mean?
Tolerance is the amount of variation from an absolute exact measurement that is permitted during the manufacturing process.

Other Bearing Rating Systems
ABEC is only one system for rating bearing tolerances. The International Standards Organization (ISO) and the German National Standards Organization (DIN) use similar scales to rate the precision of bearings. In the ISO and DIN systems, a smaller number means a tighter tolerance and a larger number means a looser tolerance. This is just the opposite of the ABEC system. See the following table for equivalents.





4. Internal clearance

The internal clearance of a ball bearing is composed of a radial component, the radial clearance, and an axial component, the axial clearance. Both clearances are determined before assembly and zero load. The operational clearance is the residual radial clearance after assembly at normal working conditions of the ball bearing.

The radial clearance corresponds to the relative radial displacement under no load of one ring compared to the other.

The radial clearance is not considered a quality criteria. A radial clearance, which is not correctly adapted to the fit on the shaft and on the housing nor to the operational conditions, may have an influence over the behavior and service life of the bearing.

The normal radial clearance CN is defined in order to get a final, requested positive clearance after assembly in normal adjustment and operating conditions. Other standardized clearances are ranged into classes according to the following designations:

● C2 Clearance smaller than CN
● CN (C0) Normal clearance
● C3 Clearance greater than CN
● C4 Clearance greater than C3

In addition, WIB has defined two non-standard radial clearance ranges,

for which the centre value may freely be defined. They are identified as:

● R (Regular): band width 6 µm.
● L (Large): band width 10 µm.

In the bearing designation, the R or L designations are followed by the centre value of the selected clearance.

Example 1)  623-2Z Y P5R20 - Indicates a radial clearance of 6 µm with values between 17 and 23 µm: (17+23)/2=20.

Example 2)  623-2Z Y P5L20 - Indicates a radial clearance of 10 µm with values between 15 and 25 mm: (15+25)/2=20


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