Effect of regular maintenance on service life of Timken cross roller bearing
Effect of regular maintenance on service life of Timken cross roller bearing
2022年6月5日
Various failure causes and precautions of NTN bearing
Various failure causes and precautions of NTN bearing
2022年6月7日

Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing

Installation position of the NTN one-way bearing

  • Measure the size of the shaft and bearing seat hole to determine their mutual matching accuracy. The matching requirements are: the inner ring and the shaft adopt interference fit with an interference amount of 0 ~ +4 um (under the condition of light load and high accuracy of 0); Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • Clearance fit shall be adopted between the outer ring and the bearing seat hole, with a clearance of 0 ~ +6um (but when the bearing at the free end uses one-way bearing, the clearance shall be increased); The roundness error between the shaft and the seat hole surface is less than 2um, the end face parallelism of the spacer used for NTN bearing is less than 2um, and the runout of the inner end face and the outer end face of the shaft shoulder is less than 2um; The runout of the bearing seat hole shoulder to the axis is less than 4um; The fluctuation of the inner end of the front cover of the main shaft to the axis should also be less than 4um.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • Installation position of the front bearing at the fixed end on the shaft: clean the bearing with clean kerosene and measure the bottom. For grease lubrication, the organic solvent containing 3% ~ 5% grease is injected into the one-way bearing for degreasing and cleaning, and then the oil gun is used to fill a certain amount of grease into the NTN bearing (accounting for about 10% ~ 15% of the bearing space); Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • Heat the bearing to 20 ~ 30 ℃, and install the bearing into the shaft end with an oil press; Press the tightening sleeve on the shaft and press the bearing end face with appropriate pressure to make it axially positioned; Roll the belt of the spring scale on the outer ring of the bearing, and check whether the specified preload has a large change by measuring the starting torque (even if the bearing is correct, the preload may change due to improper matching or cage deformation).Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • We need to install the bearing shaft assembly into the seat hole: heat the seat hole to raise the temperature by 20 ~ 30 ℃, and install the one-way bearing shaft assembly into the seat hole with continuous and gentle pressure; Adjust the front cover so that the fastening amount of the front cover is 0.02 ~ 0.05um.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  •  Take the outer end face of the bearing seat as the benchmark, push the dial indicator head against the journal surface, and rotate the shaft to measure its runout. The error is required to be less than 10um; Position the dial indicator on the shaft, the gauge head collides with the inner surface of the rear seat hole, and rotate the shaft to measure the coaxiality of the front and rear seat holes of the bearing seat.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • clean
  • When the NTN bearing is removed for inspection, the appearance record shall be made by means of photography. In addition, confirm the amount of remaining lubricant and sample the lubricant before cleaning the bearing.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • The cleaning of one-way bearing is divided into rough cleaning and fine cleaning, and the metal grid can be placed at the bottom of the container.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • During rough cleaning, use a brush to remove grease or adhesion in the oil. At this time, if the NTN bearing is rotated in the oil, the rolling surface may be damaged due to foreign matters.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • During fine cleaning, rotate the bearing slowly in oil and carefully.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • The commonly used cleaning agent is neutral water-free diesel oil or kerosene, and warm lye is sometimes used as required. No matter what kind of detergent you use, you should always filter it to keep it clean.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • After cleaning, coat the NTN bearing with antirust oil or grease immediately.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • Inspection and judgment
  • In order to judge whether the removed one-way bearing can be reused, the dimensional accuracy, rotation accuracy, internal clearance, mating surface, raceway surface, cage and sealing ring shall be emphatically checked.
  • The inspection results can be judged by those who use NTN bearings or are proficient in bearings. The shaft parts of the machine tool, especially the main shaft, are generally assembled with the thrust ball bearing and rotate at a very high speed, sometimes they will produce very high heat. Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • If this phenomenon is not eliminated in time, it will cause the NTN bearing to overheat and cause the temperature of the corresponding parts of the machine tool to rise, resulting in thermal deformation. In serious cases, the spindle and tailstock will be unequal in height, which will not only affect the accuracy and machining accuracy of the machine tool itself, but also burn out the bearing.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • The rated fatigue life refers to the total number of revolutions in which 90% of NTN bearings do not appear spalling caused by rolling fatigue when a group of bearings of the same model are operated under the same conditions. When the rotating speed is constant, the rated fatigue life is usually expressed by the total operating time.
  • When studying the service life of thrust ball bearings, we should not only consider the fatigue life, but also consider several service limits according to the performance of the bearings. For example, grease life of grease lubricated bearings. The noise life, wear life, etc. are based on different uses, and the use limit benchmarks are different. Therefore, most of them have pre selected the experience limit.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • Therefore, it is difficult to know the real cause of NTN bearing damage only by investigating NTN bearing damage. However, if we know the operating machinery, operating conditions, the structure around the bearing, understand the situation before and after the accident, and investigate the bearing damage status and several causes, we can prevent similar accidents from happening again.
  • The judgment of NTN bearing availability is mainly determined by considering the bearing damage degree, mechanical performance, importance, operating conditions and the period until the next maintenance. If there are the following defects, it can no longer be used, and the thrust ball bearing must be replaced with a new one. Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • There are cracks or notches on any one of the inner ring, outer ring, rolling element and cage. Before installing the equipment, the components should be carefully inspected. Today, we will talk about the fine inspection of the installation cost of IKO bearing, an important component of the operating equipment.
  • Check all parts in the bearing and remove all burrs. Clean the shaft and shoulder and measure the tolerance and shape of the shaft and bearing housing. Check the oil seal. Please contact the seller. Please unpack the bearing before installation. Try to ensure that IKO bearings are not polluted by dust.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • Except for the bearing inner hole and outer surface. Other parts of the rust inhibitor do not need to be wiped off. Easy to use oil and solvent for cleaning and dry in the air. Large bearings are usually sealed with a thick layer of grease like rust inhibitor. Before installation, it can be removed by cleaning.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • Spacious and clean workplace, under normal temperature, with correct installation methods and tools. The installation site shall be free of metal sand, cement powder and other foreign matters. If possible, the parts to be installed with IKO bearings shall be moved to the refurbishment factory. If it cannot be installed immediately after unpacking, the machine shall be covered and the bearing shall be kept free from the pollution of the surrounding environment.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • The packing and packaging of the bearings are both. Please unpack them before installation. Use lint free cloth to clean the bearing inner hole and outer ring surface. Be careful not to use cotton waste cloth. The bearings that will be lubricated with very low or high temperature grease, especially synthetic grease, should be completely cleaned to avoid the adverse effect of rust on the performance of the lubricating oil.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • Take out processing
  • Sweat on your hands during operation will cause rust, so keep your hands clean and dry, and wear gloves if necessary. Bearings can only be removed from their original packaging for cleaning before assembly. If only a few sets of bearings are taken out of several packages sealed with volatile corrosion inhibitor paper, the package shall be resealed immediately: the protective gas phase of VCI paper can only be maintained in the closed package, and the taken IKO bearings shall be immediately greased and oiled.Comprehensive calibration method for routine inspection and maintenance of NTN one-way bearing
  • Compatibility and miscibility
  • The antirust oil used for bearings can be compatible with and mixed with lubricating oil and mineral oil-based grease. If thickeners other than synthetic lubricants and lithium based composite soaps are used, their compatibility shall be tested. In case of incompatibility, especially when using polytetrafluoroethylene (ptff) or cycloalkyl fluoroether based lubricant or lubricant containing polyurea thickener, or if the lubricant is changed or the bearing is subject to pollution, the antirust oil shall be cleaned before greasing.
  • clean
  • IKO bearings must be dried after cleaning and immediately lubricated with antirust oil or grease to avoid corrosion! When disassembling the lower Koyo bearing for maintenance, first record the bearing appearance, confirm the residual lubricant, and then clean the bearing after sampling the lubricant for inspection. As a cleaning agent, gasoline and kerosene are commonly used. The cleaning of the removed bearings can be divided into rough cleaning and fine cleaning.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

After it is roughly clean, NTN one-way bearing

  •  Put the metal mesh pad at the bottom of the container respectively, so that the rolling bearings do not directly contact the dirt of the container. During fine cleaning, if the bearing rotates with dirt, it will damage the Koyo surface of the bearing, which should be paid attention to. In the coarse cleaning oil, use a brush to remove the grease and adhesion. After it is roughly clean, turn to fine cleaning.
  • Fine cleaning is to carefully clean the rolling bearings while rotating them in the cleaning oil. In addition, the cleaning oil should always be kept clean.
  • In order to judge whether the disassembled bearing can be reused, the needle roller bearing shall be checked after cleaning. Carefully check the state of raceway surface, Koyo surface and mating surface, the wear of cage, the increase of bearing clearance and whether there is any damage or abnormality related to the decline of dimensional accuracy. For non separable small ball bearings, use one hand to support the inner ring horizontally, and rotate the outer ring to confirm whether it is smooth.
  • Excessive grease. Then it is time to change the lubricant of the rolling bearings. After draining the old engine oil, if possible, the needle roller bearing lubricated with engine oil should be filled with fresh engine oil and the machine should be rotated at a low speed for several minutes. Make the oil collect residual pollutants as much as possible, and then drain the oil. 
  • When replacing the grease of the grease lubricated Koyo bearing, the separator used should avoid any part of the outer spherical bearing with cotton. These residual fibers may be wedged between Koyo parts and cause damage, especially for the application of small bearings.
  • There are many kinds of dimension forms of scale bearings, so scale bearings are used in the design of mechanical devices.
  • Its nature, size and direction are changeable. In general, the rated base load is shown on the dimension table. However, axial load and radial load are also important factors in selecting suitable rolling bearings. When the sizes of ball and needle roller bearings are matched, rolling bearings usually have high load capacity and bear large vibration and impact loads.
  • In terms of bearing speed, the bearing is determined according to the bearing type, size, accuracy, cage type, load, lubrication mode, cooling mode and other factors.
  • In some cases, Koyo bearings need to apply preload to increase rigidity. This procedure is usually used for deep groove ball bearings, centripetal thrust ball bearings and tapered roller bearings. Inner and outer ring offset, shaft bending, shaft or bearing housing tolerance changes, and matching errors will lead to inner and outer ring eccentricity. 
  • To prevent excessive eccentric angle, self-aligning ball bearing, self-aligning roller bearing, or self-aligning bearing seat are better choices. Voice frequency and torque, rolling bearings are manufactured according to high-precision standards, so voice and torque are small. Deep groove ball bearings and cylindrical roller bearings are used for occasions with special requirements for low noise and low torque.
  • Bearing tolerance, bearing dimensional accuracy and rotation accuracy are based on ISO and JIS standards. For machines requiring high accuracy and high-speed operation, it is recommended to use bearings with accuracy of grade 5 or above. Deep groove ball bearings, radial thrust ball bearings or cylindrical roller bearings are suitable for machines with high operation accuracy. 
  • Rigidity, when the contact surface between the moving elastic body and the raceway of the bearing is under pressure, it will produce elastic deformation. Some machines need to minimize elastic deformation. Roller bearings produce less elastic deformation than ball bearings.
  • When using the Koyo bearing, if it is to be used, the rolling bearing must be checked to check its vibration amplitude, sound, temperature and lubricant (whether there is any change in color and viscosity, and whether there is any foreign matter). 
  • Keep in mind that the amount of lubricant used must be moderate. If there is too much waste, it will not play its due role. In the process of use, do not exceed the limit speed. If the operating temperature exceeds 100 ℃, the oil should be replaced 2-3 times a year.