Three principles of how to prolong the service life of NTN bearings
Three principles of how to prolong the service life of NTN bearings
2022年5月12日
Precautions for using SKF Bearing
Precautions for using SKF Bearing
2022年5月12日

Diagnosis method of fag bearing cage

Advantages of fag bearing in application

  • High speed motorized spindle is the core component of high-speed machine tool. The accuracy of each part of motorized spindle unit is usually μ Class m, if runout is generally 1 ~ 3 μ m. The spindle stiffness is generally 100-300n/ μ m.Advantages of NTN bearing in application 
  • Therefore, the precision error and deformation of each part of the motorized spindle are very small. However, when running at high speed, NTN bearing generates a lot of heat, resulting in high temperature rise of NTN bearing and thermal deformation. Advantages of NTN bearing in application
  • The error caused by thermal deformation is much larger than the accuracy error and deformation. Moreover, the thermal deformation directly changes the preload condition of NTN bearing, affects the stiffness characteristics of NTN bearing and the machining accuracy of motorized spindle, and even leads to the thermal bite of NTN bearing and the destruction of motorized spindle. Diagnosis method of fag bearing cage 
  • The heating problem of motorized spindle reduces its reliability in practical production and application. Therefore, thermal analysis of NTN bearing and mastering the thermal characteristics of NTN bearing are extremely important to improve the stability and reliability of motorized spindle machining. Diagnosis method of fag bearing cage
  • Advantages of NTN bearing in application
    High speed precision angular contact ball NTN bearing is a kind of NTN bearing widely used in machine tool spindle unit. Taking this kind of NTN bearing as the research object, this paper makes a meaningful thermal characteristic analysis and calculation of high-speed precision spindle NTN bearing system.Advantages of NTN bearing in application
  • It is common for ina bearing to fail during operation, so there is no need to make a fuss. In case of failure, judgment and treatment are the key. Let’s explain the causes of common faults of INA Bearing.Advantages of NTN bearing in application
  • Ina bearing temperature is too high: when the mechanism is running, the part where ina bearing is installed is allowed to have a certain temperature. When touching the mechanism shell with hands, it is normal not to feel hot. Otherwise, it indicates that the ina bearing temperature is too high.

Advantages of NTN bearing in application

  • 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;Diagnosis method of fag bearing cage
  •  The mechanism assembly is too tight (insufficient clearance); Ina bearing assembly is too tight; INA Bearing Race rotates on the shaft or in the shell; Excessive load; Breakage of ina bearing cage or rolling element, etc.Advantages of NTN bearing in application
    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 ina bearing is faulty. The causes of noise produced by rolling ina bearing are relatively complex. 1) it is the wear of the mating surfaces of the inner and outer rings of INA Bearing. Advantages of NTN bearing in application
  • Due to this kind of wear, the matching relationship between   NTN bearing in applicationand shell.
     INA Bearing and shaft is damaged, resulting in the axis deviation from the correct position and abnormal noise when the shaft moves at high speed. When ina bearing is tired, its surface metal will peel off, which will also increase the radial clearance of INA Bearing and produce abnormal sound.Advantages of NTN bearing in application
  •  Insufficient lubrication of INA Bearing, dry friction and breakage of INA Bearing will produce abnormal sound. Diagnosis method of fag bearing cage

Advantages of NTN bearing in application

  •  After the ina bearing is worn and loose, the cage is loose and damaged, which will also produce abnormal noise and damage to the INA Bearing. During the disassembly and inspection of rolling INA Bearing, the fault and damage cause of ina bearing can be judged according to the damage of INA Bearing.Advantages of NTN bearing in application
  • Metal spalling on the raceway surface: 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, fatigue spalling will occur on the working surface of rolling element or inner and outer race raceway. Advantages of NTN bearing in application
  • If the load of ina bearing is too large, this fatigue will be exacerbated. In addition, improper installation of INA Bearing and shaft bending will also produce raceway spalling. The fatigue spalling of INA Bearing Raceway will reduce the operating accuracy of the shaft and cause vibration and noise of the mechanism.Advantages of NTN bearing in application
  • carefully check whether the journal is smooth and whether there are defects such as rust and bruise, and try to eliminate them first; Then, check the contact between the journal and the shaft. The inspection method is to apply a thin layer of display agent (such as red lead powder, red Qian oil, etc.) on the shaft diameter.Diagnosis method of fag bearing cage
  •  then install the journal in the Koyo bearing, rotate it two or three times in the positive and negative directions by hand, take out the shaft, and check the distribution of coloring points on the Koyo bearing. If the distribution of coloring points is abnormal or does not move at all, start scraping and grinding.Diagnosis method of fag bearing cage
  • During scraping and grinding, the principle of first heavy and then light, scraping heavy and leaving light, scraping large and leaving small shall be adopted according to the situation. For the first few times, the hand can be heavier and scrape off more metal, so as to achieve better contact quickly. When the contact area reaches 50%, it should be scraped gently. Diagnosis method of fag bearing cage
  • After each scraping, wipe the tile surface, apply the display agent on the journal for inspection, and then scrape and grind according to the contact condition until it meets the technical requirements. Indicator can be used for scraping and grinding inspection, but for precision Koyo bearings with high requirements for contact points, indicator cannot be used in the later stage of scraping and grinding. Diagnosis method of fag bearing cage
  • Because the coloring point on the Koyo bearing is too large after coating the display agent, it is difficult to judge the actual contact situation. At this time, the journal can be wiped clean, directly put in the Koyo bearing for verification, and then take out the shaft. It can be seen that the bright spot on the Koyo bearing is the contact point. Then scrape and grind the bright spot until it meets the technical requirements.Diagnosis method of fag bearing cage
  • During scraping and grinding, not only the contact point shall meet the technical requirements, but also the side clearance and contact angle shall meet the technical requirements. Generally, the contact point shall be studied first, and the contact angle shall be taken into account at the same time, and then the side clearance shall be scraped. Diagnosis method of fag bearing cage
  • However, there should be no obvious boundary between the contact part and the non-contact part. When wiping the surface of Koyo bearing with fingers, no trace should be detected.Diagnosis method of fag bearing cage
Diagnosis method of fag bearing cage

Advantages of NTN bearing in application

 

  •  Its fault can not impact the inner and outer rings and rolling elements. In principle, it is not among the diagnostic objects.fag bearing
  • However, the diagnosis system found a large number of cage faults. The mechanism is:Diagnosis method of fag bearing cage
  • When the cage window is broken, the lost objects generated by fracture vibration and friction enter the grease, which is recognized by the system as “free impurity mode” and gives an alarm;Diagnosis method of fag bearing cage
  • Or the lost object adheres to the inner and outer rings and the working surface of the rolling element and is judged as the fault of the parasitic working surface by the system in the “parasitic impurity mode” and gives an alarm;
  • After opening the fag bearing, it is found that it is the cage fault rather than the fault of the specific alarm object (inner and outer rings and rolling elements). This “quasi misdiagnosis” is harmless to a set of fag bearings – it is a “diagnosis” for the fag bearings.Diagnosis method of fag bearing cage
  • The reliability of this “parasitic fault mode” is not 100%, so there are some missed diagnosis of cage fault.Diagnosis method of fag bearing cage
  • The main mechanism is that even if the cage window strip falls off, it will not impact with the rolling parts during uniform speed operation. In this regard, the author has made a test on fag bearing of diesel locomotive axle box: insert a 1m long iron wire between fag bearing cages, and even insert a saw blade. The locomotive runs back and forth for dozens of times in the servicing depot. After decomposition and inspection, the fault parts are intact.Diagnosis method of fag bearing cage
  • Mechanical analysis shows that only in emergency braking and when the grease is very thin, the falling window strip can impact with the rolling body. Accordingly, the 4th generation of the diagnostic system plans to launch the “broken bar detection braking method”, that is, when the braking preparation reverse detection is carried out after the forward rotation detection is completed, the braking method detection is inserted.Diagnosis method of fag bearing cage
  • However, because the material of the cage is softer than that of the inner and outer rings and the rolling element, even if there is an impact with the rolling element during braking, its value is also very small. This brings difficulties to the detection. In particular, FAG bearings of railway freight cars can not be detected after changing to plastic cages.Diagnosis method of fag bearing cage
  • The use of plastic steel cage can not only prevent fracture with the flexibility and uniformity of the cage, but also because even if the cage material is lost in grease, it will not be as dangerous as steel, which is a wise move.Diagnosis method of fag bearing cage

method of fag bearing is a part without rolling working surface.

 

  • Grinding is usually a semi finishing or finishing process of the inner ring channel, which plays a decisive role in the roundness of the finished inner ring channel. In addition to the accuracy and dynamic characteristics of the grinding process system, the roundness of the inner ring channel grinding is also closely related to the grinding process parameters. Diagnosis method of fag bearing cage
  • The former has been valued by many scholars and has carried out a lot of research, which greatly improves the roundness of grinding inner ring channel. With the improvement of grinding process system accuracy and dynamic characteristics, grinding process parameters have become the main factor affecting roundness. Diagnosis method of fag bearing cage
  • Therefore, the study of the influence law of grinding process parameters on roundness is of great significance to reasonably select process parameters, ensure the grinding roundness of imported bearing channels, and then optimize the process parameters of grinding imported bearing channels.Diagnosis method of fag bearing cage
  • The groove of imported bearing inner ring usually adopts variable feed rate cut in grinding, and its grinding cycle can be divided into four stages: workpiece rapid approach, coarse feed, fine feed and no feed grinding. The main factors affecting the roundness of the grinding inlet bearing channel can be summarized as follows:  Diagnosis method of fag bearing cage
  •  the accuracy of the process system in the grinding process, which depends on the accuracy of the grinder and the positioning principle, structural parameters and accuracy of the fixture;  Diagnosis method of fag bearing cage
  • The dynamic characteristics of the process system, especially the balance state of the grinding wheel: in the process of dressing and grinding, the grinding wheel is unbalanced, which will cause forced vibration, Diagnosis method of fag bearing cage
  • Due to the difference between the relative position of the dresser and the grinding wheel when dressing the grinding wheel and the relative position of the workpiece and the grinding wheel when grinding, and the different stiffness of the process system in these two different cases, the vibration causes the surface of the workpiece to be out of round. 、Diagnosis method of fag bearing cage
  • The grinding process parameters will affect the contact stiffness between the grinding wheel and the workpiece, the wear process of the grinding wheel and the damping characteristics of the vibration of the process system, so as to affect the vibration characteristics of the grinding process, Finally, it is reflected in the geometric shape (i.e. roundness) and other surface quality of the grinding workpiece:  Diagnosis method of fag bearing cage
  •  the original error mapping of the workpiece caused by the elastic deformation of the process system: by analyzing the variation law of the geometric error of the workpiece in the grinding cycle, it can be seen that the geometric error mapping of the workpiece after grinding mainly depends on the stiffness of the process system, the grinding process parameters, the wear speed of the grinding wheel and the original error of the workpiece?.Diagnosis method of fag bearing cage
  •  Considering the above factors, when the stiffness and dynamic characteristics of the process system are certain (especially the grinding wheel must be well balanced), the roundness error of the grinding workpiece mainly depends on the grinding process parameters. Diagnosis method of fag bearing cage
  • Therefore, through the stepwise regression modeling of the grinding roundness test data, select important parameters from multiple process parameters and gradually introduce the regression equation, so as to establish the optimal regression equation of the relationship between grinding roundness and process parameters.Diagnosis method of fag bearing cage
  • Machine tool vibration caused by unbalanced grinding wheel or other factors will seriously affect the roundness of grinding workpiece. Keeping the good working state of the machine tool and the good balance of the grinding wheel is the prerequisite for the application of the roundness mathematical model. In addition, the hardness, structure, particle size and abrasive type of grinding wheel, as well as the composition of coolant, will have a certain impact on the roundness of grinding.Diagnosis method of fag bearing cage

The service life and smoothness of directly affects the service life of the method of fag.

  • Generally, the index of speed limit can be found in the fag bearing model table. What does it mean?
  • When NSK Bearings exceed a certain operating speed, they will begin to generate uncontrollable internal heat.Diagnosis method of fag bearing cage
  • The speed limit varies with NSK bearing type, size, lubrication system, internal design of NSK bearing and working load. In addition, the speed limit will vary depending on the type of synthetic NSK bearing seal used (depending on the speed of the seal contact area).Diagnosis method of fag bearing cage
  • The term “speed limit” generally refers to the estimated speed, revolutions per minute, at which NSK Bearings will remain serviceable.Diagnosis method of fag bearing cage
  • The limit speed of grease lubrication and oil lubrication will be given in the general dimension table. This value is based on NSK bearing installed on horizontal shaft, suitable lubrication operation and light load. Raceway noise is a kind of stable and continuous noise excited by the rolling body rolling in the raceway when ina bearing rotates. People pay attention to it only when its sound pressure level or tone is extremely high. In fact, the sound energy excited by the raceway sound is limited. Diagnosis method of fag bearing cage
  • For example, under normal conditions, the high-quality 6203ina bearing raceway sound is 25 ~ 27db. This kind of noise is typical of single row deep groove ball ina bearing bearing bearing bearing bearing radial load. It has the following characteristics: A. noise and vibration are random; b. The vibration frequency is above 1kHz; c. No matter how the rotating speed changes, the main frequency of noise is almost unchanged, while the sound pressure level increases with the increase of rotating speed; d. Diagnosis method of fag bearing cage
  • When the radial clearance increases, the sound pressure level increases sharply; When the rigidity of INA Bearing Pedestal increases, the lower the total sound pressure level is, even if the speed increases, the total sound pressure level does not increase much; f. The higher the viscosity of lubricant, the lower the sound pressure level, but for grease lubrication, its viscosity and the shape and size of soap fiber can affect the noise value.Diagnosis method of fag bearing cage
  • The sound generation source of raceway is caused by the natural vibration of ferrule after being loaded. The elastic contact between the ferrule and the rolling body constitutes a nonlinear vibration system. When the lubrication or machining accuracy is not high, the natural vibration related to this elastic feature will be excited, and when it is transmitted to the air, it will become noise. Diagnosis method of fag bearing cage
  • As we all know, even if the advanced manufacturing technology is adopted to process INA Bearing parts, there will always be small geometric errors in varying degrees on the working surface, resulting in small fluctuations between the raceway and the rolling body and exciting the natural vibration of the vibration system.Diagnosis method of fag bearing cage

The first is to identify and check the rolling sound of NTN 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.Diagnosis method of fag bearing cage
  • 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. 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.Diagnosis method of fag bearing cage
  • 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. Diagnosis method of fag bearing cage
  • 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.Diagnosis method of fag bearing cage
  •  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. Diagnosis method of fag bearing cage
  • 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. 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