Influence of bearing load on accuracy
Influence of bearing load on accuracy
2022年5月18日
Troubleshooting and maintenance of bearing damage
Troubleshooting and maintenance of bearing damage
2022年5月20日

Cause analysis of common bearing quality faults

The first is to identify and check the rolling sound of common bearing

 

  • We can use sound detector to check the rolling sound and sound quality of Timken bearing in operation. Because Timken bearing will emit abnormal sound and irregular sound even if there is slight peeling and other damage, it can be distinguished by sound detector to prevent it in advance.
  • Secondly, the vibration of Timken bearing in operation is identified and checked
  • Timken bearing vibration is very sensitive to the damage of Timken bearing. For example, peeling, indentation, corrosion, crack, wear, etc. will be reflected in the vibration measurement of Timken bearing. Therefore, the vibration can be measured by using a special Japanese Timken bearing vibration meter (frequency analyzer, etc.), and the specific situation of abnormality can not be inferred through frequency division. Cause analysis of common bearing quality faults
  • The measured values are different due to the service conditions of Timken bearing or the installation position of sensor, so it is necessary to analyze and compare the measured values of each machine in advance to determine the judgment standard.Cause analysis of common bearing quality faults
  • After that, check according to the temperature of Timken bearing
  • The temperature of Timken bearing can generally be inferred from the temperature outside the Timken bearing chamber in Japan. It is more appropriate if the outer ring temperature of Timken bearing can be directly measured by oil hole.Cause analysis of common bearing quality faults
  •  Usually, the temperature of Timken bearing rises slowly with the start of operation and reaches a stable state after 1-2 hours. The normal temperature of Timken bearing varies with the heat capacity, heat dissipation, speed and load of the machine.Cause analysis of common bearing quality faults
  •  If the lubrication and installation parts are appropriate, the Timken bearing temperature will rise sharply and abnormal high temperature will occur. At this time, the operation must be stopped and necessary preventive measures must be taken. Cause analysis of common bearing quality faults
  • According to a large number of test data, since the temperature is affected by lubrication, speed, load and environment, the value in the table only represents the approximate temperature range. Cause analysis of common bearing quality faults
  • Using the thermal sensor, the working temperature of Timken bearing can be monitored at any time, and the automatic alarm or stop when the temperature exceeds the specified value can be realized to prevent the occurrence of combustion shaft accident
  • In order to improve the actual fitting accuracy of NTN bearing during installation, it is necessary to accurately measure the fitting surface dimensions of the inner hole and outer circle of NTN bearing by using the measurement methods and tools that do not deform the NTN bearing. NTN bearing
  • All the measurement items related to the inner diameter and outer diameter can be measured, and the measured data can be comprehensively analyzed. Based on this, the dimensions of the installation parts of Japanese NTN bearing that accurately match the shaft and seat hole can be measured. When actually measuring the corresponding size and geometry of the matched shaft and seat hole, it shall be carried out under the same temperature conditions as when measuring NTN bearing.NTN bearing
  • In order to ensure a high actual matching effect, the roughness of the surface of the shaft and seat hole matched with the NTN bearing shall be as small as possible.NTN bearing
  • During the above measurement, two groups of marks indicating the direction of large deviation shall be made on the outer circle and inner hole of NTN bearing and the corresponding surface of shaft and seat hole on both sides close to the assembly chamfer, so as to align the large deviation of matching two sides with the same direction during actual assembly, so that the deviation of both sides can be partially offset after assembly.NTN bearing
  • The purpose of making two groups of orientation marks is to comprehensively consider the compensation of deviation, not only improve the rotation accuracy of the supports at both ends, but also partially eliminate the coaxiality error of the seat hole between the two supports and the journal at both ends. NTN bearing
  • The implementation of surface strengthening measures on the mating surface, such as sand blasting, using a precision plug with a slightly larger diameter to plug the primary inner hole, etc., are conducive to improving the mating accuracy.NTN bearing

The gloves apply on his hands,common bearing

  • Before the bearing is delivered for routine inspection, its oil seal package can be removed, and it can be immersed in washing gasoline or acid free kerosene containing 3% engine oil. Turn its outer ring and carefully wash the junction of cage, rolling element and raceway. Cause analysis of common bearing quality faults
  • The bearings that have been dried or dried shall be dripped with lubricating oil as required and delivered for inspection immediately. At this time, there is no oil film protection on the outer surface of the bearing, and it is not allowed to directly touch the skin of hands during the whole inspection process. Cause analysis of common bearing quality faults
  • The operator shall wear clean gloves or apply antirust agent on his hands, but the antirust agent on his hands must be avoided from mixing into the rolling surface of the bearing, otherwise the measurement results will be deviated.Cause analysis of common bearing quality faults
  • After the inspection, the bearing shall be immediately delivered for use or treated with anti rust inventory. The whole inspection process shall also be completed quickly to avoid corrosion caused by too long. Note that using pure gasoline without engine oil for cleaning will also cause corrosion.Cause analysis of common bearing quality faults
  • Before inspection, the bearing must be placed on a metal plate in the inspection site together with the gauge block, standard parts and measuring instruments used for inspection, so as to homogenize the temperature and room temperature of these objects quickly.Cause analysis of common bearing quality faults
  • Bearing temperature is too high: during the operation of the mechanism, the part where the bearing is installed is allowed to have a certain temperature. When touching the shell of the mechanism with your hand, it should be normal not to feel hot. Otherwise, it indicates that the bearing temperature is too high.Cause analysis of common bearing quality faults
  • The lubricating oil viscosity is too high or the lubricating oil quality does not meet the requirements; The mechanism assembly is too tight (insufficient clearance); The bearing assembly is too tight; The bearing race rotates on the shaft or in the shell; Excessive load; Broken bearing cage or rolling element, etc.Cause analysis of common bearing quality faults
  • Bearing noise: the rolling bearing is allowed to make slight running noise during operation. If the noise is too loud or there is abnormal noise or impact sound, it indicates that the bearing is faulty.Cause analysis of common bearing quality faults
  • The causes of rolling bearing noise are complex: Cause analysis of common bearing quality faults
  • Metal spalling on the raceway surface: the bearing rolling body and the inner and outer raceway surfaces are subjected to periodic pulsating load, resulting in periodic contact stress. When the number of stress cycles reaches a certain value, fatigue spalling will occur on the working surface of rolling element or inner and outer race raceway.
  • It is a comprehensive technology to judge and predict the reliability and service performance of the bearing through the fault and deterioration of the bearing and the performance state parameters, identify and judge the position, cause and risk degree of the abnormal situation, and determine the repair and improvement methods. 
  • Bearing fatigue failure is a surface form of failure, which is mainly manifested in the initiation, propagation and fracture process of fatigue crack, and the long-term impact of load failure under alternation. Cracks are in two ways:
Cause analysis of common bearing quality faults

From the surface layer common bearing

  • From the surface, this is the role of the external load caused by the plastic deformation of the working surface and the periodic change of the contact stress of the strain hardened surface during the rolling contact process of the bearing, and finally the formation of the surface crack between the two from the developing inner surface of the small crack. Due to the lubricant on the working surface and the open force, the crack is severely hit on the wall, forcing the crack to move forward;
  • From the surface layer, under repeated pressure, the contact of the surface will initially produce cracks at a certain depth at the place where the surface is exposed, and from the angle along the surface direction to a certain depth, from behind the surface of the contact surface, and beyond the surface, and finally form corrosion stripping, leaving a horse pit.common bearing
  • From the bearing surface, or from the cracks in the surface layer, these two objectives (carburization, quenching and other surface heat treatment of parts). If there are uneven hardness, organization, and non-uniform internal stress and other disadvantages, the contact stress is generally affected by the opposite underground cracks. If the surface quality of parts is poor, there is a defect (oxidation, decarburization), poor friction or lubrication, and from the surface cracks.
  •  The methods to control the sound of raceway are: select low-noise bearings, that is, bearings with small waviness, and carefully select the service conditions. Raceway noise often affects the noise of the whole machinery. Reducing raceway noise can reduce the noise of the whole machinery.
  • the mating surfaces of the inner and outer rings of the bearing are worn. Due to this kind of wear, the matching relationship between the bearing and the shell, the bearing and the shaft is damaged, resulting in the axis deviation from the correct position and abnormal noise when the shaft moves at high speed. When the bearing is tired, the metal on its surface will peel off, which will also increase the radial clearance of the bearing and produce abnormal noise. 
  • After the bearing is worn and loose, the cage is loose and damaged, which will also produce abnormal noise and damage to the bearing. During the disassembly and inspection of rolling bearing, the fault and damage cause of bearing can be judged according to the damage of bearing.
  •  If the load of the bearing is too large, it will aggravate this fatigue. In addition, improper bearing installation and shaft bending will also produce raceway spalling. The fatigue spalling of bearing raceway will reduce the operation accuracy of shaft and cause vibration and noise of mechanism.
  • Therefore, the fault diagnosis technology of bearing is not a simple fault detection (or monitoring) technology, nor is it a simple point inspection and instrumentation. 
  • Correctly, quickly and effectively collect signals, process data, identify and judge manually or automatically. In order to determine the scientific repair cycle, necessary tests and estimates of fatigue and wear life should also be carried out according to the mechanism of various faults.
  • It is required to thoroughly clean the original oil traces left in any hidden parts. After the bearing is cleaned, the attached cleaning oil shall be drenched and dried on the workbench lined with clean neutral lining paper, or dried slowly in the far-infrared oven. The bearing ring, cage or any rolling element shall not be rotated during the whole process from washing oil drying to air drying or drying.
  • Before the bearing is delivered for routine inspection, its oil seal package can be removed, and it can be immersed in washing gasoline or acid free kerosene containing 3% engine oil. Turn its outer ring and carefully wash the junction of cage, rolling element and raceway. 
  • It is required to thoroughly clean the original oil traces left in any hidden parts. After the bearing is cleaned, the attached cleaning oil shall be drenched and dried on the workbench lined with clean neutral lining paper, or dried slowly in the far-infrared oven. The bearing ring, cage or any rolling element shall not be rotated during the whole process from washing oil drying to air drying or drying.
  • The bearings that have been dried or dried shall be dripped with lubricating oil as required and delivered for inspection immediately. At this time, there is no oil film protection on the outer surface of the bearing, and it is not allowed to directly touch the skin of hands during the whole inspection process. 
  • The operator shall wear clean gloves or apply antirust agent on his hands, but the antirust agent on his hands must be avoided from mixing into the rolling surface of the bearing, otherwise the measurement results will be deviated.
  • After the inspection, the bearing shall be immediately delivered for use or treated with anti rust inventory. The whole inspection process shall also be completed quickly to avoid corrosion caused by too long. Note that using pure gasoline without engine oil for cleaning will also cause corrosion.
  • Before inspection, the bearing must be placed on a metal plate in the inspection site together with the gauge block, standard parts and measuring instruments used for inspection, so as to homogenize the temperature and room temperature of these objects quickly.
  • The causes of bearing fracture include defect and overload. When the external load exceeds the material strength limit, the part fracture is called overload fracture. During the operation of the bearing, defects such as overheating tissue and local burns will also occur, resulting in defect fracture.Cause analysis of common bearing quality faults
  • During the operation of the bearing, sometimes foreign hard particles or hard foreign matters or wear debris on the metal surface will be squeezed between the bearing surfaces, which will cause furrow like abrasion of the bearing. Cause analysis of common bearing quality faults
  • These hard foreign matters enter the interior of the bearing through the lubricating medium. With the continuous operation of the bearing, local friction generates heat, which is easy to cause local deformation of the friction surface and friction micro welding, or even local melting, and then bite.Cause analysis of common bearing quality faults
  • Generally speaking, the bearing itself does not produce noise. What we call noise is actually the sound effect of vibration between the bearing and the surrounding structure directly or indirectly.
  • Excitation caused by the change of the number of loaded rolling elements. When a radial load is loaded on a bearing, the number of loaded rolling elements will change slightly during operation, that is: 2-3-2-3 This causes an offset in the direction of the load. Cause analysis of common bearing quality faults
  • The resulting vibration is inevitable, but can be reduced by axial preloading, which is applied to all rolling elements (not applicable to cylindrical roller bearings in bearings).Cause analysis of common bearing quality faults
  • When the waviness of components is closely matched between the bearing ring and the bearing seat or transmission shaft, the bearing ring may be deformed by matching with the shape of adjacent components. If deformation occurs, vibration may occur during operation. Therefore, it is important to machine the bearing pedestal and drive shaft to the required tolerances.Cause analysis of common bearing quality faults
  • Local damage due to incorrect operation or installation, a small part of the bearing raceway and rolling element may be damaged. During operation, rolling over damaged bearing parts will produce specific vibration frequency. Vibration frequency analysis can identify damaged bearing components.Cause analysis of common bearing quality faults
  •  Vibration behavior in applications in many applications, the stiffness of sliding bearings is the same as that of surrounding structures. Because of this feature, as long as the bearing (including preload and clearance) and its configuration in the application are correctly selected, it is possible to reduce the vibration in the application.Cause analysis of common bearing quality faults