Three factors affecting NSK bearing failure
Three factors affecting NSK bearing failure
2022年4月23日
Essential factors of Koyo imported bearing noise
Essential factors of Koyo imported bearing noise
2022年4月23日

Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent

  • Internal factors mainly refer to the three factors that determine the quality of Timken imported bearings, such as structural design, manufacturing process and material quality.
  • First, the reasonable design and advanced nature of the structure will lead to longer TIMKEN bearing life. The manufacturing of bearings generally goes through multiple processing processes such as forging, heat treatment, turning, grinding and assembly. The rationality, advanced nature and stability of all the processing technologies will also affect the life of TIMKEN imported bearings. 
  • Among them, the heat treatment and grinding processes that affect the quality of Timken imported bearings are often more directly related to the failure of bearings. In recent years, the research on the metamorphic layer of the bearing working surface shows that the grinding process is closely related to the surface quality of Timken imported bearings.
  • The metallurgical quality of Timken imported bearing materials was once the main factor affecting the early failure of Timken imported rolling bearings. With the progress of Metallurgical Technology (such as vacuum degassing of bearing steel), the quality of raw materials has been improved. The proportion of raw material quality factor in Timken imported bearing failure analysis has decreased significantly, but it is still one of the main influencing factors of Timken imported bearing failure. Proper material selection is still a factor that must be considered in bearing failure analysis.
  • The main task of Timken imported bearing failure analysis is to find out the main factors causing bearing failure according to a large number of background materials, analysis data and failure forms, so as to put forward targeted improvement measures, prolong the service life of Timken imported bearings and avoid sudden early failure of Timken imported bearings.
  • For sealed Timken imported bearings, appropriate grease has been filled during production; For the bearing, a sealing device is also set in the main engine to prevent the leakage of lubricating grease.
  • There is a problem of how much grease should be injected into Timken imported bearings.
  • Too little grease injection is easy to cause lack of grease or dry friction and affect service life. Excessive grease injection will lead to a large amount of grease leakage, which will not only pollute the environment, but also cause waste. It can be seen that the amount of grease injected into Timken imported bearing is the less the better on the premise of ensuring the full lubrication of Timken imported bearing.
  • Advantages and disadvantages of grease lubrication under normal working conditions, grease lubrication can be used for most Timken imported bearing applications.
  • The advantage of grease is that it is easier to retain in Timken imported bearing configuration, especially in applications where the vertical axis or axis is inclined at a certain angle. The grease also has the function of sealing, which can prevent the influence of pollutants, moisture or moisture on Timken imported bearings. The application of grease will cause the temperature of the bearing to rise, especially if the speed is too high.
  •  In most cases, the Timken inlet bearing can be completely filled with grease only at the initial stage, while the Timken inlet bearing seat is only filled with an appropriate amount of grease and left with a certain free space. Before fully reaching the working speed, the excess grease must be discharged from the bearing during the running in stage, so that an appropriate amount of grease can be left in the Timken inlet bearing. When the operating temperature drops significantly, it indicates that the grease has run in with the bearing and is evenly distributed in the Timken imported bearing configuration.
  •  The so-called constant pressure preload is a method of giving appropriate preparatory load to the bearing by using coil spring and Belleville spring. In use, even if the relative position of the bearing changes, the preloading method. In use, even if there is a change in the relative position of the walking out, the preload can be roughly maintained at a certain level.
  • Preload line diagram of SKF imported bearing after constant pressure preload. The rigidity of preload spring is usually very small compared with that of bearing. Therefore, the displacement straight line of spring is approximately parallel to the horizontal axis. Therefore, the rigidity of single bearing with constant pressure preload is the same as that of pre applied preload
  • The rigidity of the single bearing with axial load is roughly the same. Comparison of rigidity between SKF imported bearing and bearing monomer after positioning preload and constant pressure preload.
  • According to the rigidity comparison of preloading methods, the comparison of positioning preload and constant pressure preload is as follows. After fag bearing installation, in order to check whether the installation is correct, operation inspection shall be carried out. Small machinery can be rotated by hand to confirm whether it rotates smoothly.
  •  The inspection items include poor operation caused by foreign matters, scars and indentation, unstable torque caused by poor installation and poor processing of mounting base, excessive torque caused by too small clearance, installation error and sealing friction, etc. If there is no abnormality, the power operation can be started.
  • Large machinery cannot rotate manually, so the power shall be cut off immediately after no-load start, and the machinery idles. Check whether there is vibration, noise, contact of rotating parts, etc. after confirming that there is no abnormality, enter the power operation.
  • Power operation, starting from no-load and low speed, slowly increase to the rated operation under the specified conditions. During the test run, the inspection items are whether there is abnormal sound, FAG bearing temperature change, lubricant leakage or discoloration, etc. If any abnormality is found, stop the operation immediately, check the machinery, and remove the bearing for inspection if necessary.
  • Fag bearing temperature can generally be inferred from the external temperature of bearing pedestal. However, it is more accurate to directly measure the temperature of the bearing outer ring by using the oil hole. The bearing temperature rises gradually from the beginning of operation, and the temperature is usually stable after 1 ~ 2 hours.
  • If the bearing is not installed properly, the temperature will rise sharply, resulting in abnormal high temperature. The reasons are too much lubricant, too small bearing clearance, poor installation, excessive friction of sealing device, etc. In the case of high-speed rotation, the wrong selection of fag bearing structure and lubrication mode is also the reason.
  • The rotation of fag bearing is checked with stethoscope, and there are strong metal noise, abnormal sound, irregular sound and other indications of abnormality. The reasons are poor lubrication, poor accuracy of shaft or bearing seat, bearing damage, foreign matter intrusion, etc. 
  • Using lead pressure method to detect the clearance of NTN imported bearing is more accurate than using feeler gauge, but it is more troublesome. The aluminum wire used for testing should be soft, and the diameter should not be too large or too small. The ideal diameter is 1.5 ~ 2 times of the gap. In practical work, soft lead wire is usually used for testing.
  • During the inspection, first open the NTN inlet bearing cover, select the lead wire with appropriate diameter, cut it into a small section with a length of 15 ~ 40mm, put it on the journal and the interface between the upper and lower bearings, cover the bearing cover, tighten the fixing bolts according to the specified torque, then loosen the bolts, remove the bearing cover, detect the thickness of the flattened lead wire with a micrometer, and calculate the average value of the top clearance of the NTN inlet bearing.
  • If the top clearance is too small, a pad can be added on the joint surface of the upper and lower tiles. If it is too large, the pad shall be reduced, scraped or the tile shall be poured again.
  • Adjustment of bearing bush tightening force: in order to prevent the possible rotation and axial movement of the bearing bush during the working process, in addition to the interference and stop parts, the bearing bush must also be compressed with NTN imported bearing cover.
  •  The measurement method is the same as the top clearance measurement method. In addition to measuring the thickness of soft lead wire, the bearing bush tightening force can be calculated (expressed by the elastic deformation of the bearing bush after compression)
  • Generally, the pressing force of bearing bush is 0.02 ~ 0.04 mm. If the pressing force does not meet the standard, it can be adjusted by increasing or decreasing the thickness of the gasket at the joint surface of NTN inlet bearing and bearing seat, and the pad back is not allowed to be padded.
  • In addition to radial clearance, the sliding NTN inlet bearing should also ensure axial clearance. When detecting the axial clearance, move the shaft to an extreme position, and then measure the displacement of the shaft from one extreme position to another with a feeler gauge or dial indicator, that is, the axial clearance.
  • When the clearance of sliding NTN inlet bearing does not meet the regulations, it shall be adjusted. Split bearings often use shims to adjust the radial clearance (top clearance). Koyo imported bearings show strong regularity and good repeatability in their use. When the normal high-quality bearing (Koyo imported bearing) is used at the beginning, the vibration and noise are relatively small, but the spectrum is scattered and the amplitude is small, which may be caused by some defects in the manufacturing process, such as surface burrs.
  • After moving for a period of time, the vibration and noise maintain a certain level, and the spectrum is very single, with only one or two times the frequency. The frequency spectrum above three times of power frequency rarely appears, and the bearing state is very stable and enters the stable working period.Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  • After continued operation and entering the later stage of use, the vibration and noise of Koyo imported bearing began to increase, and sometimes abnormal sound appeared, but the vibration increased slowly. At this time, the bearing kurtosis began to suddenly reach a certain value. We believe that at this time, the imported bearing of Koyo shows initial failure.Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  • At this time, it is required to closely monitor the imported Koyo bearing and pay close attention to its changes. Since then, the bearing kurtosis value began to decline rapidly and close to the normal value, while the vibration and noise began to increase significantly, and the increase amplitude began to accelerate. When the vibration exceeded the vibration standard (such as ISO2372 standard), the bearing kurtosis value also began to increase rapidly. Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  • When both the vibration standard and the kurtosis value also exceeded the normal value (the relative standard of kurtosis available), we believe that the bearing has entered the late fault production, and the equipment needs to be repaired in time, Replace the Koyo imported bearing.Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  • Koyo imported bearings show late fault characteristics. The time from the occurrence of serious faults (generally bearing damage, such as shaft holding, burns, sand frame spalling, raceway, bead wear, etc.) is usually less than one week. The larger the equipment capacity, the faster the rotating speed, and the shorter the interval. Therefore, in the actual Koyo imported bearing fault diagnosis, once the late fault characteristics are found, the bearing fault should be determined and the maintenance should be arranged as soon as possible. Although the bearing is metal, it will also be damaged. Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  • No matter what hard material it is, it will be damaged, but the degree of damage is different. We all know that Timken bearings are of good quality and made of good steel. Steel is a very solid material, but it will also be damaged. Timken bearings run in the machine every day, and it is easy to damage Timken bearings due to constant friction, Therefore, we should also prevent the damage of Timken bearing, maintain the bearing well, and do not use the bearing indiscriminately, causing unnecessary losses to ourselves.Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  • So how to deal with the bearing damage. If the bearing is used correctly, it can be used until the fatigue life is reached. However, there will be accidental and premature damage, which can not be resistant to use. This early damage, as opposed to fatigue life, is the quality service limit known as failure or accident. Most of them are caused by careless installation, use and lubrication, foreign matters invading from the outside, and insufficient research on the thermal effects of shafts and shells. Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  • As for the damage state of the bearing, such as the clamping damage of the ring and retaining edge of the roller bearing, these reasons can be considered. These reasons also coincide with insufficient lubricant, unfitness, defects of the oil supply and drainage structure, invasion of foreign matters, bearing installation error and excessive deflection of the shaft. Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent.Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  • Therefore, only investigating the bearing damage, it is difficult to know the real cause of the damage. However, if you know the use machinery, service conditions, the structure around the bearing, understand the situation before and after the accident, and investigate the damage state of the bearing and several causes, you can prevent the recurrence of similar accidents.Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
Static load action of NSK bearing equivalent

Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent

  • Generally, the shaft adopts double support structure, and the radial position of the shaft is jointly limited by two supports. Each support shall have a radial positioning radial or angular contact bearing. The axial position can be limited by two supports in one direction, and the axial displacement in two directions can also be limited by one support. In general, different axial positioning methods can obtain different operation accuracy. Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  • Therefore, when designing the supporting structure, the specific scheme of axial positioning should be selected according to the operation accuracy and working conditions of the shaft. Angular contact bearings are installed in pairs in three ways. Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  • The opposite installation of the wide end faces of the outer rings of two SKF bearings is called back-to-back installation. The action points of the two supporting forces fall outside the supporting span. This arrangement is widely used because of its large support span, good rigidity when the shaft is cantilevered, and the tendency of separation of the inner and outer rings when the shaft is heated and extended, so the shaft will not get stuck. Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  • However, if pre tightening installation is adopted, the pre tightening amount will be reduced when the shaft is heated. The opposite installation of the narrow end faces of the two bearing outer rings is called face-to-face installation. The force action point of the two supports falls within the support span. Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  • This arrangement has the advantages of simple structure, convenient assembly, disassembly and commissioning, so it is also widely used. It is mainly used for short shafts and occasions with low temperature rise, but pay attention to reserve clearance. The axial clearance should not be too large, which will reduce the operation accuracy of the shaft.Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  •  When the axial load is large and multiple bearings are required to bear it at the same time, the series mode of relative installation of wide and narrow outer ring of SKF Bearing is often adopted. The force action points of each SKF Bearing fall on the same side of the bearing, so it is called in-line arrangement, also known as series connection. Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  • When adopting this arrangement, pay attention to the structure and manufacturing to ensure that each SKF imported bearing can bear the load as evenly as possible. In order to maintain the flexible rotation of the shaft, in the design of the supporting structure, while meeting the requirements of axial positioning accuracy, the requirements of free expansion of the shaft due to heating should also be considered. Axial positioning and axial expansion are corresponding. Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent
  • The axial position adjustment of the shaft is to meet the special requirements of some meshing transmission. For example, in worm drive, the worm axis must fall in the middle plane of the worm gear to ensure its correct engagement, so it is required that the worm gear shaft can adjust its position in the axial direction. In bevel gear transmission, the pitch cone apex of two bevel gears must coincide, so it is required that both bevel gear shafts can be adjusted axially.Static load action of NSK bearing equivalentStatic load action of NSK bearing equivalent