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BEARING HANDLING

14.6 Maintenance and Inspection 14.6.2 Bearing Failures and Measures Type of Failure Probable Causes Measures

14.6.1 Detecting and Correcting Irregularities In general, if rolling bearings are used correctly they Scoring Inadequate initial lubrication, excessively Use a softer grease and avoid rapid
will survive to their predicted fatigue life. However, they hard grease and high acceleration when acceleration.
In order to maintain the original performance of a often fail prematurely due to avoidable mistakes. Scoring or smearing between raceway starting.
bearing for as long as possible, proper maintenance In contrast to fatigue life, this premature failure is and rolling surfaces.
and inspection should be performed. If proper caused by improper mounting, handling, or lubrication,
procedures are used, many bearing problems can be entry of foreign matter, or abnormal heat generation. Spiral scoring or smearing of raceway Raceway rings are not parallel and Correct the mounting, apply a preload, or
avoided and the reliability, productivity, and operating For instance, the causes of rib scoring, as one surface of thrust ball bearing. excessive speed. select another bearing type.
costs of the equipment containing the bearings are all example of premature failure, may include insufficient
improved. It is suggested that periodic maintenance lubrication, use of improper lubricant, faulty lubrication Scoring or smearing between the end face Inadequate lubrication, incorrect mounting Select proper lubricant and modify the
be done following the procedure specified. This system, entry of foreign matter, bearing mounting
periodic maintenance encompasses the supervision error, excessive deflection of the shaft, or any of the rollers and guide rib. and large axial load. mounting.
of operating conditions, the supply or replacement of combination of these. Thus, it is difficult to determine
lubricants, and regular periodic inspection. Items that the real cause of some premature failures. Cracks Excessive shock load, excessive Examine the loading conditions, modify the
should be regularly checked during operation include If all the conditions at the time of failure and previous to Crack in outer or inner ring. interference in fitting, poor surface fit of bearing and sleeve. The fillet radius
bearing noise, vibration, temperature, and lubrication. the time of failure are known, including the application, cylindricality, improper sleeve taper, large must be smaller than the bearing chamfer.
If an irregularity is found during operation, the cause the operating conditions, and environment; then by fillet radius, development of thermal
should be determined and the proper corrective actions studying the nature of the failure and its probable cracks and advancement of flaking.
should be taken after referring to Table 14.2. causes, the possibility of similar future failures can be
If necessary, the bearing should be dismounted reduced. The most frequent types of bearing failure, Crack in rolling element. Advancement of flaking, shock applied to Be carefull in handling and mounting.
and examined in detail. As for the procedure for along with their causes and corrective actions, are Broken rib. the rib during mounting or dropped during
dismounting and inspection, refer to Section 14.5, listed in Table 14.3. handling.
Inspection of Bearings.
Fractured cage. Abnormal loading of cage due to incorrect Reduce the mounting error and review the
NSK BEARING MONITOR (Bearing Abnormality
Detector) Indentations mounting and improper lubrication. lubricating method and lubricant.
Indentations in raceway in same pattern
It is important during operation to detect signs of as rolling elements. Shock load during mounting or excessive Use care in handling.
irregularities early before damage becomes severe. load when not rotating.
The NSK Bearing Monitor (see Page C5) is an
instrument that checks the condition of bearings Indentations in raceway and rolling Foreign matter such as metallic chips Clean the housing, improve the seals, and
and gives a warning of any abnormality, or it stops elements. or sand. use a clean lubricant.
a machine automatically in order to prevent serious
trouble. In addition, it helps to improve maintenance Abnormal Wear Vibration of the bearing without rotation Secure the shaft and housing, use oil as a
and reduce its cost. False brinelling (phenomenon similar to during shipment or rocking motion of lubricant and reduce vibration by applying
brinelling) small amplitude. a preload.

Table 14.3 Causes and Measures for Bearing Failures

Fretting Slight wear of the fitting surface. Increase interference and apply oil.

Type of Failure Probable Causes Measures

Flaking Wearing of raceway, rolling elements, rib, Penentration by foreign matter, incorrect Improve the seals, clean the housing, and
Flaking of one-side of the raceway of use a clean lubricant.
radial bearing. and cage. lubrication, and rust.

Flaking of the raceway in symmetrical Abnomal axial load. A loose fit should be used when mounting Creep Insufficient interference or insufficient Modify the fit or tighten the sleeve
patterm. Out-of-roundness of the housing bore. the outer ring of free-end bearings to allow tightening of sleeve.
axial expansion of the shaft. Seizure Review the internal clearance and bearing
Flaking pattern inclined relative to the Discoloration and melting of raceway, Insufficient clearance, incorrect fit, supply an adequate amount of the
raceway in radial ball bearings. Flaking Correct the faulty housing. rolling elements, and ribs. lubrication, or improper mounting. proper lubricant and improve the mounting
near the edge of the raceway and rolling method and related parts.
surfaces in roller bearings. Improper muonting, deflection of shaft, Use care in mounting and centering, select Electric Burng Melting due to electric arcing.
inadequate tolerances for shaft and a bearing with a large clearance, and Fluting or corrugations. Install a ground wire to stop the flow of
Flaking of raceway with same spacing as housing. correct the shaft and housing shoulder. electricity or insulate the beaning.
rolling elements.
Large shock load during mounting, rusting Use care in mounting and apply a rust
Premature flaking of raceway and rolling
elements. while bearing is out of operation for preventive when machine operation is

Premature flaking of duplex bearings. prolonged period. suspended for a long time. Corrosion & Rust

Insufficient clearance, excessive load, Select proper fit, bearing clearance, and Rust and corrosion of fitting surfaces and Condensation of water from the air, or Use care in storing and avoid high
improper lubrication, rust, etc. lubricant. bearing interior. fretting. temperature and high humidity, treatment
Penetration by corrosive for rust prevention is necessary when
substance(especially varnish-gas, etc). operation is stopped for long time.
Selection of varnish and grease.
Excessive preload. Adjust the preload.

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