Maintenance and repair methods for reducing NTN imported bearing noise
Maintenance and repair methods for reducing NTN imported bearing noise
2022年4月15日
Six precautions for selecting NTN imported bearing
Precautions for select NTN imported bearing
2022年4月16日

Various failure 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.
  •  Therefore, 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.
  • 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:
  • 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.
  • 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.
  • Use appropriate operating tools. Avoid replacing with existing tools, and appropriate tools must be used. Such as special sleeve, press, etc.
  • 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.
  • 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. 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.
  • 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. 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.
  • 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.
  •  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.
  • 4. 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. 
  • 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.
  • 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.
  • However, the infinity of bearings can only be “completed” under the conditions of the laboratory, and such conditions are difficult and too expensive for bearings used on site under certain working conditions.
  • When SKF Bearing is used on site, its working load is often greater than its corresponding fatigue durability limit load. After working for a certain period of time, it will be unable to continue to use because its own data reaches the fatigue limit sooner or later. 
  • Even if the working load of some SKF bearings is lower than their corresponding durability limit load, they will be worn out due to the bearing pollution problem that is difficult to eradicate. In short, the bearings in field operation can not fully meet the conditions of the above laboratories, and the slight lack of any of these conditions will shorten the service life of the bearings, which leads to the problem of bearing life.
  • Generally speaking, the service life of rolling bearing refers to the professional service period that the rolling bearing can continuously meet the working performance and working accuracy actively requested under the practical service conditions (including working conditions, environmental conditions, maintenance and home care conditions, etc.).
  • Bearing roundness error inspection roundness error is measured in the deviation of the radius of the hole, and a certain measuring instrument shall be used. At present, general measuring tools are widely used in practical production, such as inner diameter dial gauge.
  •  At this time, the roundness error of bearing should be evaluated by half of the large difference in diameter. This method is called two-point method. It has low measurement accuracy, but it has certain application value.
  • (2) The inspection method of the cylindricity error of the bearing cylindricity error inspection hole is the same as that of the IKO bearing cylindricity error of the outer cylindrical surface. In practice, it is difficult to accurately check the cylindricity error of the hole in production, so it can often be controlled by the parallelism of the outer bus of the inner hole, that is, the drum, saddle and cone errors of the cylindrical surface can be controlled. These errors can be checked and controlled with ordinary general measuring tools, which is convenient and applicable.
  • Inspection of hole coaxiality error
  • The coaxiality of the hole refers to the level that the axis of the measured cylindrical surface is not coaxial with the reference axis., A comprehensive gauge can be used to check the coaxiality error of the two holes. If the gauge can pass through the reference hole and the measured hole, the coaxiality will pass, but it will fail. At this time, the step diameter of the comprehensive gauge shall be within the size of the two holes; It is required that the shape error of the two holes is small.
  • How to measure the dimensions of bearings and bearing holes
  • Measurement of bearing hole
  • For the measurement of the bearing hole, the inner diameter gauge can be used to check the reference size on the outer diameter micrometer, and the roundness and cylindricity of the bearing hole also need to be measured. Burning out the bearing often reduces the diameter of the bearing hole at the opening and the roundness is out of tolerance, which is very bad for the normal task of the bearing. 
  • The connecting rod bearing cap will shift and make the roundness of the bearing hole out of tolerance. The roundness error of IKO bearing hole should be controlled within the size service, while the cylindricity should be strictly controlled.
  • Measurement of primary dimension of IKO bearing
  • Bearing thickness: fix the outside micrometer and change the measuring head from plane to spherical surface, which can be used to measure the bearing thickness. The thickness of the bearing should be controlled within the limit of 0.005 ~ 0.010 mm, otherwise the inner diameter of the bearing will be out of tolerance. The bearing has slight thinning near the opening, which should be paid attention to during measurement.
  • Common tightness of bearing and bearing hole: the common tightness is guaranteed by the free spring opening and residual surface height of the bearing. Under the method of measuring the height of the remaining surface: assemble the bearing according to the rules, tighten the bolts of the bearing cover to the regular torque, loosen one of the bolts, and measure the clearance at the interface of the bearing cover with a feeler gauge, which shall be within the limit of 0.05 ~ 0.15mm.
  • Bearing inner diameter: before measurement, install the bearing according to the rules and tighten the bolts of the bearing cover according to the regular torque. Measure with the inner diameter gauge after correcting the reference size on the outer diameter micrometer. Avoid the thinning area during measurement. The difference between the inner diameter of the bearing and the outer diameter of the corresponding journal is the common clearance.
  • Coaxiality of the inner hole of the main bearing: the coaxiality error of the inner hole of the main bearing is mainly formed by the coaxiality error of the bearing hole, and the cause of the coaxiality error of the bearing hole is the deformation of the cylinder block. When the radial circular runout of the main journal is within the regular public service, reflect on the eating and closing marks of the main journal and the bearing. If the eating and closing marks of each main IKO bearing are in a clear position and clarify that the coaxiality error is large, it can be handled by scraping, boring the bearing or changing the cylinder block, otherwise it is difficult to ensure the normal task of the generator.
  • For the use of bearings, noise is very common. Even the low-noise bearings in Koyo imported bearings have the same situation. So why does it make noise? Today I will introduce its essence to you.
  • The raceway sound of Koyo imported bearing and its control method raceway sound is a smooth and continuous sound generated by the rolling body rolling on the raceway surface when Koyo imported bearing is running. It is a unique basic sound that will occur in all rolling bearings. 
  • The general bearing sound is the sound of raceway plus other sounds. The raceway sound of ball bearing is irregular, and its frequency is above 1000Hz. Its main frequency does not change with the speed, but its total sound pressure level increases with the speed. For the bearing with loud raceway sound, the sound pressure level of raceway sound decreases with the increase of viscosity; For bearings with low raceway noise, the sound pressure level changes from decrease to increase when the viscosity increases to more than 20mm2 / s.
  • The greater the rigidity of the bearing pedestal, the lower the total sound pressure level of the raceway sound. If the radial clearance is too small, the total sound pressure level and dominant frequency of raceway sound will increase sharply with the decrease of radial clearance. Various failure causes and precautions of NTN bearing
  • 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.

 Various failure causes and precautions of NTN bearing

Various failure causes and precautions of NTN bearing
  • Impact sound of rolling element and its control method when the ball bearing or cylindrical roller bearing of larger model runs at low speed under pure radial load, due to the small centrifugal force of the rolling element, the rolling element in the non load area will impact the cage or raceway and make noise. But as the speed increases, the sound will disappear. The control methods of impact sound of rolling elements are: appropriately reduce the radial clearance, and use the bearing of cage with reasonable structure and flexible material.
  • The rolling sound of imported Koyo bearings and its control method rolling sound is the harsh metal friction sound that can occur in cylindrical roller bearings on all occasions. Most of it occurs in larger types of grease lubricated bearings, which is more likely to occur in greases with degraded base oil performance and hardly occurs in oil lubrication. In addition, it is easy to occur in winter. When bearing pure radial load, it is easy to occur in the case of large radial clearance, and it is easy to occur in a specific speed range with different models and sizes, both continuously and intermittently. Various failure causes and precautions of NTN bearing
  • Special processing methods for the outer ring raceway can prevent the occurrence of rolling sound. If necessary, this kind of bearing can be selected, or the radial clearance of the bearing can be appropriately reduced, the lubricating grease with excellent performance can be used and the rigidity of the parts matched with the bearing can be improved. In order to ensure the working condition of NTN bearing, it is necessary to avoid damage as much as possible. What should we do?Various failure causes and precautions of NTN bearing
  • Generally, 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 called the quality service limit of 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.
  • As for the damage state of NTN bearing, for example, the clamping damage of the ring retaining edge of roller bearing can be considered as the reason. These reasons can also coincide with insufficient lubricant, unsuitable, defects of oil supply and drainage structure, intrusion of foreign matters, bearing installation error and excessive deflection of shaft.Various failure causes and precautions of NTN bearing
  • 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, the situation before and after the accident, and combined with the damage state of the bearing and several causes, you can prevent the recurrence of similar accidents. The use factors of Koyo bearings mainly refer to whether the installation, adjustment, use and maintenance, maintenance and repair meet the technical requirements.Various failure causes and precautions of NTN bearing
  • According to the technical requirements of Koyo bearing installation, use, maintenance and repair, monitor and inspect the load, speed, working temperature, vibration, noise and lubrication conditions of the running bearing, find out the causes immediately and adjust them to make them return to normal. The installation condition is one of the primary factors in the use factors. Various failure causes and precautions of NTN bearing
  • The improper installation of the bearing often leads to the change of the stress state between the parts of the whole bearing. The bearing operates in an abnormal state and ends its service life early. The internal factors mainly refer to the three factors that determine the quality of Koyo bearing, such as structural design, manufacturing process and material quality. Precautions: use accurately machined NTN bearing pedestal and shoulder
  • The thermal sensor can monitor the working temperature of the bearing at any time, and automatically alarm or stop when the temperature exceeds the specified value to prevent the occurrence of combustion shaft accident. High temperature often indicates that the bearing is in an abnormal condition. High temperature is also harmful to the lubricant of the bearing. 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. NTN bearing is used to measure the bearing itself or other important parts. If the operating conditions remain unchanged, any temperature change can indicate that a fault has occurred. The periodic measurement of bearing temperature can be aided by thermometer, such as digital thermometer, which can accurately measure the bearing temperature and display it in ℃ or Fahrenheit.
  • Generally, the temperature of the bearing can be inferred from the temperature outside the bearing chamber. If the oil hole can be used to directly measure the temperature of the outer ring of the bearing, NTN bearing is more suitable. Usually, the temperature of the bearing starts to rise slowly with the operation of the bearing, and reaches a stable state after 1-2 hours. 
  • The normal temperature of the bearing varies with the heat capacity, heat dissipation, speed and load of the machine. 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. Proper material selection is still a factor that must be considered in bearing failure analysis.
  • The main task of NSK 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 the bearing and avoid sudden early failure of the bearing. The installation condition is one of the primary factors in the use factors. 
  • The improper installation of the bearing often leads to the change of the stress state between the parts of the whole bearing, and the NSK bearing operates in an abnormal state and fails early. According to the technical requirements of bearing installation, use, maintenance and repair, monitor and inspect the load, speed, working temperature, vibration, noise and lubrication conditions borne by the running bearing, find out the cause immediately and adjust it to make it return to normal.
  • First of all, the reasonable design and advanced nature of the structure will lead to longer 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 bearings. The heat treatment and grinding processes that affect the quality of finished bearings are often related to the quality of bearings