Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
2022年6月6日
Advantages of NTN bearing in application
2022年6月8日

Various failure causes and precautions of NTN bearing

The deformation capacity is lost locally, NTN bearing

  • In severe cases, metal peeling and large-area random scratches occur on the contact surface; In general, the mechanical damage of Koyo imported bearing refers to the appearance of groove marks at different levels on the alloy surface of bearing bush. Contact surface damage and ablation exist at the same time. The main reason for bearing mechanical damage is that the bearing surface is difficult to form oil film or the oil film is seriously damaged.Various failure causes and precautions of NTN bearing
  • Plastic deformation and cold work hardening occur on the outer surface layer, and Koyo imported bearing is under the repeated action of cylinder pressure (impact load). The deformation capacity is lost locally, and the grain is gradually formed and continuously expanded. Then, with the falling off of wear debris, the loaded outer layer forms a hole.Various failure causes and precautions of NTN bearing
  •  Generally, when the bearing bush is pitted, the pit first appears, and then the pit gradually expands and causes the cracking of the alloy layer interface. The crack extends along the parallel direction of the interface until it peels off. Various failure causes and precautions of NTN bearing
  • The main reason for bearing cavitation is that the sudden change of the cross section of structural elements such as oil groove and oil hole causes strong disorder of oil flow. Bubbles are formed in the vacuum area with disorder of oil flow, and then cavitation occurs due to the collapse of bubbles due to the increase of pressure. Cavitation usually occurs in the high load area of the bearing, such as the lower bearing bush of the crankshaft main bearing.Various failure causes and precautions of NTN bearing
  • Due to the overload of the engine, the fatigue pitting corrosion of Koyo imported bearings refers to. Make the bearing overheat and the bearing clearance is too large, resulting in fatigue damage, fatigue pitting or fatigue falling off in the middle of the bearing. This kind of damage is mostly caused by overload, excessive bearing clearance, or unclean lubricating oil and foreign matters mixed in it. Various failure causes and precautions of NTN bearing
  • Therefore, when using, attention should be paid to prevent the bearing from overload and do not run at too low or too high speed; Adjust the engine to a stable state at idle speed; Ensure the normal bearing clearance and prevent the engine speed from being too high or too low; Check and adjust the working condition of the cooling system to ensure that the working temperature of the engine is appropriate.Various failure causes and precautions of NTN bearing
  • The chemical impurities (acid oxides, etc.) in the lubricating oil oxidize the bearing alloy to form acidic substances. The corrosion area of the bearing alloy is generally impure lubricating oil. Cause the bearing alloy to fall off locally and form irregular small cracks or pits. The main causes of bearing alloy corrosion are improper selection of lubricating oil, poor corrosion resistance of bearing data, or rough engine operation and high temperature.Various failure causes and precautions of NTN bearing
  • Local high temperature is formed, and there is a small convex metal surface in direct contact between the journal and the friction pair of Koyo bearing. In case of lack of lubrication and poor cooling, the bearing alloy will be blackened or partially burned. This fault is often caused by too tight fit between journal and bearing; Lack of lubricating oil pressure is also easy to burn the bearing. The following table lists the main analysis items: analysis item selection method
  • For the type of bearing whose rigidity can meet the rigidity required by the mechanical shaft system, in the machine tool spindle and automobile final reducer, while improving the rigidity of the shaft, we must also improve the rigidity of the bearing. The deformation of roller bearing under load is smaller than that of ball bearing. Applying preload (negative clearance) to the bearing can improve the rigidity. This method is suitable for angular contact ball bearings and tapered roller bearings.Various failure causes and precautions of NTN bearing
  • The installation space of SKF Bearing can be accommodated in the bearing installation space. Because the rigidity and strength of the shaft are paid attention to when designing the shaft system, the shaft diameter, i.e. the inner diameter of the bearing, is generally determined first. However, rolling bearings have a variety of size series and types, and the appropriate bearing type should be selected from them.
  • The type of bearing with the required rotation accuracy. The spindle of machine tool, gas turbine and control machine require high rotation accuracy, high speed and low friction respectively. At this time, SKF bearings with accuracy above grade 5 should be used.Various failure causes and precautions of NTN bearing
  • The installation and disassembly frequency and methods of regular inspection of installation and disassembly. When the installation and disassembly are frequent, the cylindrical roller bearing with separable inner ring and outer ring, needle roller bearing and tapered roller bearing are more convenient. Tapered hole self-aligning ball bearings and tapered hole self-aligning roller bearings can be easily assembled and disassembled by using fasteners or withdrawal sleeves.Various failure causes and precautions of NTN bearing
  • The size, direction and nature of load bearing load are rich in changes, such as the size of load, whether there is only radial load, whether the axial load is one-way or two-way, the degree of vibration or impact, etc. After considering these factors, choose the appropriate SKF Bearing type.Various failure causes and precautions of NTN bearing
Various failure causes and precautions of NTN bearing

The speed adapt to the NTN bearing mechanical speed.

 

  • The analysis of the relative inclination between the inner ring and the outer ring causes the relative inclination between the inner ring and the outer ring of the bearing, and select the bearing type that can adapt to this service condition. If the relative inclination between the inner ring and the outer ring is too large, the bearing will be damaged due to internal load. Therefore, the type of bearing that can withstand this inclination should be selected.Various failure causes and precautions of NTN bearing
  • The speed can adapt to the SKF Bearing type of mechanical speed. The limit speed of the bearing is not only taken from the bearing type, but also limited to the bearing size, cage type, accuracy grade, load conditions and lubrication mode. Therefore, these factors must be considered in the selection. The following bearings are mostly used for high-speed rotation: deep groove ball bearings, angular contact ball bearings and cylindrical roller bearings.Various failure causes and precautions of NTN bearing
  •  If there are bumps, rust layers, wear debris, sand particles, dust and soil on the assembly surface of NTN bearing and its matched parts, one is that the bearing is difficult to install, resulting in incorrect assembly position; Second, these attachments form abrasives and are easy to wear the working surface of the bearing, affecting the assembly quality. Various failure causes and precautions of NTN bearing
  • , before installation, carefully inspect the surface of journal, bearing housing hole, shoulder end face and the mating surface of connecting parts such as bushing, washer and end cover. If there is any rust layer, file it off with a fine file and polish it with a fine abrasive cloth. At the same time, remove the attachments on the bearing assembly surface and its connecting parts.Various failure causes and precautions of NTN bearing

Use of NTN bearings

  • Precautions for use: rolling bearing is a precision component, and its use must be carried out with corresponding caution. No matter how high-performance bearings are used, if they are not used properly, the expected high performance will not be obtained. Precautions for the use of bearings are as follows:Various failure causes and precautions of NTN bearing
  • Keep the bearing and its surroundings clean. Even small dust that cannot be seen by the eyes will affect the bearing. Therefore, keep the surrounding clean so that the dust will not invade the bearing.Various failure causes and precautions of NTN bearing
  • Use with care. Strong impact on the bearing during use will produce scars and indentation, which will become the cause of the accident. In serious cases, it will crack and fracture, so we must pay attention to it.Various failure causes and precautions of NTN bearing
  • Use appropriate operating tools. Avoid replacing with existing tools, and appropriate tools must be used. Such as special sleeve, press, etc.Various failure causes and precautions of NTN bearing
  • Pay attention to the corrosion of the bearing. When operating the bearing, the sweat on the hand will become the cause of rust. Pay attention to operate with clean hands and try to wear gloves.Various failure causes and precautions of NTN bearing
  • Do not unpack the bearing before the installation preparation is completed to avoid pollution.
  • Selection and control of tolerance of shaft and NTN bearing chamber: NTN bearing shall rotate flexibly without blocking feeling after being pressed into NTN bearing. If there is obvious inflexible rotation, it indicates that the size of the shaft is too large and the tolerance should be reduced.Various failure causes and precautions of NTN bearing
  •  If the NTN bearing rotates by hand after being pressed into the shaft, there is an obvious “rusty” feeling, it may be that the tolerance of the shaft is too large or the roundness of the shaft is not good. Therefore, when controlling the tolerance of shaft and NTN bearing chamber, it is also necessary to control the roundness. At present, many domestic manufacturers only control the tolerance, not the roundness.Various failure causes and precautions of NTN bearing
  • Assembly method of NTN bearing: because NTN bearing is a high-precision product, if it is not assembled properly, it is easy to damage the NTN bearing channel, resulting in the damage of NTN bearing. NTN bearing shall be equipped with a special mold during assembly, which can not be knocked at will. When pressing the shaft, only a small ring can be stressed, and when pressing a large ring, only a large ring can be stressed. Various failure causes and precautions of NTN bearing
  • Air pressure or hydraulic pressure is required during assembly. During press assembly, the upper and lower touch shall be outside the horizontal state. If there is inclination, the NTN bearing channel will be damaged due to stress and the NTN bearing will produce conduction sound.Various failure causes and precautions of NTN bearing
  • Prevention of assembly foreign matters: when NTN bearing is installed on the rotor for dynamic balance, it is easy to enter the iron filings generated during dynamic balance into the NTN bearing, so it is necessary to perform dynamic balance before installing NTN bearing. In order to facilitate assembly, some manufacturers apply some oil or grease in the NTN bearing chamber for lubrication effect during assembly, but it is often difficult for the operator to control the amount.Various failure causes and precautions of NTN bearing
  •  If more oil or grease is accumulated in the NTN bearing chamber, it is easy to enter the NTN bearing along the shaft when the NTN bearing rotates. NTN bearing chamber shall not be coated with oil or grease. If it is necessary to do so, it shall be controlled and there shall be no accumulation in NTN bearing chamber.Various failure causes and precautions of NTN bearing
  • Prevention of paint rust: paint rust is characterized by frequent occurrence in sealed motors. The sound of the motor is very good during assembly, but after being placed in the warehouse for some time, the abnormal sound of the motor becomes very large, and there is serious rust when removing NTN bearings. In the past, many manufacturers thought it was the problem of NTN bearing. After our continuous publicity, now the motor factory has realized that it is mainly the problem of insulating paint. Various failure causes and precautions of NTN bearing
  • The main reason for this problem is that the acidic substances volatilized from the insulating paint form corrosive substances at a certain temperature and humidity, which corrodes the NTN bearing channel and leads to the damage of NTN bearing. At present, the problem can only be to select good insulating paint and assemble after drying and ventilation for a period of time.Various failure causes and precautions of NTN bearing
  • The service life of NTN bearing is closely related to manufacturing, assembly and use. It must be done well in each link in order to make NTN bearing in the running state, so as to prolong the service life of NTN bearing.Various failure causes and precautions of NTN bearing

Metal spalling on the raceway surface NTN bearing

  • Ina bearing temperature is too high: when the mechanism is running, the part where the bearing is installed is allowed to have a certain temperature. When touching the mechanism shell by hand, it should be normal not to feel hot. Otherwise, it indicates that the bearing temperature is too high.Various failure causes and precautions of NTN bearing
  • The reasons for the high temperature of INA Bearing are: the quality of lubricating oil does not meet the requirements or deteriorates, and the viscosity of lubricating oil is too high; 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.Various failure causes and precautions of NTN bearing
  • INA 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. The reason for the noise of rolling bearing: it is more complex. It is the wear of the mating surfaces of the inner and outer rings of the bearing. Due to this kind of wear, the matching relationship between INA Bearing and shell, bearing and shaft is damaged, resulting in the axis deviation from the correct position and abnormal noise when the shaft moves at high speed. Various failure causes and precautions of NTN bearing
  • 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. Insufficient bearing lubrication, dry friction and bearing breakage will produce abnormal sound. The bearing will shake and damage the retainer. During the disassembly and inspection of rolling bearing, the fault and damage cause of bearing can be judged according to the damage of bearing.Various failure causes and precautions of NTN bearing

 

  • The rolling element of INA Bearing and the raceway surfaces of inner and outer rings are subjected to periodic pulsating load, resulting in periodic contact stress. When the number of stress cycles reaches a certain value, it will be produced on the working surface of rolling element or inner and outer race raceway
  • Fatigue peeling. If the load of ina bearing is too large, this fatigue will be exacerbated. 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.
  • INA Bearing burn: the burned bearing has a return fire color on its raceway and rolling element. The causes of burns are generally insufficient lubrication, unqualified or deteriorated lubricating oil quality, and tight assembly of ina bearings.Various failure causes and precautions of NTN bearing
  • Plastic deformation: uneven pits appear on the contact surface between raceway and roller of INA Bearing, indicating plastic deformation of bearing. The reason is that under the action of large static load or impact load, the local stress on the working surface of the bearing exceeds the yield limit of the material, which generally occurs on ina bearings rotating at low speed.Various failure causes and precautions of NTN bearing
  • INA Bearing Race crack: the crack of bearing race may be caused by too tight bearing fit, loose bearing or inner ring, deformation of INA Bearing containing parts, poor surface processing of ina bearing installation, etc.Various failure causes and precautions of NTN bearing

Broken cage: the reason is insufficient lubrication, broken rolling element, 

  • seat ring skew, etc.Various failure causes and precautions of NTN bearing.Various failure causes and precautions of NTN bearing
  • The metal of the cage adheres to the rolling element, which may be due to the rolling element being stuck in the cage or insufficient lubrication.Various failure causes and precautions of NTN bearing
  • Serious wear of race raceway: foreign matters may fall into the race, insufficient lubricating oil or inappropriate lubricating oil brand. In order to ensure the performance of rolling bearings and maintain long-term use under good conditions, NTN imported bearings must be inspected and maintained. This inspection and maintenance is very important to prevent faults in advance.
  •  It is hoped that regular inspection and maintenance can be carried out according to the operation standards suitable for the operating conditions of the machine. Generally, the following methods are adopted: the inspection under the operating state is based on the rolling sound, vibration Check the temperature and the nature of the lubricant, and judge the supplement or replacement time of the lubricant.
  • NTN imported bearing inspection: fully observe the bearings removed due to the regular inspection and replacement of the machine, and check the condition of the raceway surface, whether there is damage and whether it can be reused. Due to the clearance of NSK imported bearing, the inner and outer rings will move relatively under the action of load, which will reduce the stiffness of NSK imported bearing, cause the radial and axial vibration of the shaft, and affect the working accuracy and service life of the machine.Various failure causes and precautions of NTN bearing

 In order to reduce this vibration, for high-precision and high-speed mechanical equipment

  •  The preloading method is often adopted when installing NSK imported bearing, that is, a certain load (radial or axial) is given to NSK imported bearing in advance during installation to eliminate its original clearance, and make NSK imported bearing body and inner and outer rings produce elastic deformation, so as to prevent relative movement between inner and outer rings during operation. 
  • The temperature of IKO imported bearing can generally be inferred from the temperature outside the bearing chamber. It is more appropriate if the oil hole can be used to directly measure the temperature of the outer ring of the bearing.
  • Generally, the temperature of IKO inlet bearing starts to rise slowly with the operation of the bearing, and reaches a stable state after 1-2 hours. The normal temperature of IKO imported bearing varies with the heat capacity, heat dissipation, speed and load of the machine. Various failure causes and precautions of NTN bearing
  • If the lubrication and installation parts are appropriate, the 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.Various failure causes and precautions of NTN bearing
  • The working temperature of IKO imported bearing can be monitored at any time by using the thermal sensor, and the automatic alarm or stop when the temperature exceeds the specified value can be realized to prevent the occurrence of combustion shaft accident.Various failure causes and precautions of NTN bearing
  • High temperature often indicates that IKO imported bearing is in abnormal condition. High temperature is also harmful to the lubricant of IKO imported bearings. Sometimes bearing overheating can be attributed to the lubricant of the bearing. If the temperature of the bearing exceeds 125 ℃ for a long time, the service life of the bearing will be reduced. The causes of high temperature bearings include insufficient or excessive lubrication and lubricant. It contains impurities, excessive load, bearing ring damage, insufficient clearance, high friction caused by oil seal, etc.Various failure causes and precautions of NTN bearing
  • Therefore, it is necessary to continuously monitor the bearing temperature, whether it is measuring the bearing itself or other important parts. If the operating conditions remain unchanged, any temperature change can indicate that a fault has occurred.Various failure causes and precautions of NTN bearing