Generally, if the bearing is used correctly, it can be used until the fatigue life is reached. However, there may be accidental damage prematurely, and may not be able to withstand use. This kind of early damage, as opposed to fatigue life, is the quality use limit called failure or accident. It is mostly caused by careless installation, use, and lubrication, foreign objects invaded from the outside, and insufficient research on the thermal effects of shafts and housings.
Regarding the damage state of the bearing, such as: the jam of the ring and the rib of the roller bearing, the reasons can be considered: insufficient lubricant, incompatibility, defects in the oil supply and drainage structure, foreign matter intrusion, bearing installation error, shaft deflection If the song is too big, these reasons will overlap.
Therefore, it is difficult to know the real cause of the damage only by investigating bearing damage. However, if you know the machinery used, the conditions of use, the structure around the bearing, the situation before and after the accident, combined with the damage state of the bearing and several reasons, you can prevent similar accidents from happening again.
a. The thickness of the inner and outer spacers must be matched, and the parallelism between the two sides of the spacer should not exceed 0.002mm.
b. Bearings must be selected. The inner diameter difference and outer diameter difference of each group of bearings should be between 0.002 mm and 0.003 mm, and should be kept between 0.004 mm and 0.008 mm with the housing hole and between 0.0025 mm and 0.005 mm with the journal. In actual installation, it is best to fit the bearing with the thumb of both hands.
c. The roundness of the bearing seat hole and the journal, the coaxiality at both ends of the housing hole, and the radial runout of the journal should not exceed 0.003mm.
d. The end faces of the parts that are in contact with the end faces of the bearing rings should be colored for inspection, and the contact area should not be less than 80%.
e. Must be installed directionally. That is, the highest point of radial runout of all bearing inner rings is aligned with the lowest point of journal radial runout, and the highest point of radial runout of bearing outer ring should be in a straight line when installed in the housing hole.
There may be many factors that affect the service life of rolling bearings, which can be further explained from the use factors and internal factors.
The use factor mainly refers to whether the installation adjustment, use and maintenance, maintenance and repair meet the technical requirements. According to the technical requirements of rolling bearing installation, use, maintenance and maintenance, the load, speed, working temperature, vibration, noise and lubrication conditions of the running bearing are monitored and checked. If an abnormality is found, the cause will be immediately found and adjusted to make it Back to normal. The installation condition is one of the primary factors in the use factors. The bearing is often caused by improper installation, which causes the stress state of the various parts of the bearing to change. The bearing runs in an abnormal state and ends its service life early.
The large or small force applied when installing the bearing will affect the performance and life of the bearing, and also cause damage to the bearing. The following are four tips that need to be paid attention to in the process of applying force.
1. The applied force should be stable and uniform, without impact. This requires the use of oil pressure or tools that can apply a smooth pulling force or pressure. When hammering is really necessary, it must be passed through a softer copper sleeve. The falling metal is buffered, and the striking force is as gentle as possible. It is best to use a copper rod or copper hammer for hammering.
2. The application of force should continue until the work is completed. For example, when the bearing is installed, the application of force should be stopped when the bearing is just installed in the correct position to ensure that the end face of the ring (washer) is against the seat hole or the end face of the shaft's shoulder, and it cannot be squeezed. It's too tight to fit in place.
3. The resultant force of the applied force passes through the axis of the bearing as much as possible, which requires that the force application point is uniform, symmetrical and stable, and the force is applied through a spherical surface or parallel to the axis.
4. Avoid applying force through rolling elements, which requires applying force through the inner ring when assembling and disassembling the inner ring (shaft ring), and applying force through the outer ring when assembling and disassembling the outer ring.
(1) The resultant force of the applied force passes through the axis of the bearing as much as possible, which requires the application point to be uniform, symmetrical and stable, applying force through a spherical surface or parallel to the axis.
(2) The applied force should be stable and uniform, and should not be impacted. This requires the use of oil pressure or tools that can apply a stable tension or pressure. When hammering is really necessary, it must be passed through a soft copper sleeve. The non-falling metal is buffered, and the striking force is as gentle as possible. It is best to use a copper rod or copper hammer for hammering.
(3) Avoid applying force through the rolling elements, which requires applying force through the inner ring when assembling and disassembling the inner ring (shaft ring), and applying force through the outer ring when assembling and disassembling the outer ring.
(4) The drag force should continue to the extent it should be. For example, when the bearing is installed, the force should be stopped when the bearing is just installed in the correct position to ensure that the end surface of the ring (washer) abuts against the end surface of the seat hole or the shoulder of the shaft. It cannot be squeezed too tightly, nor can it be installed incorrectly.
1. It is not allowed to drill, groove, chamfer, or car end face on the bearing during installation. Otherwise, it is easy to cause deformation of the bearing ring, which affects the accuracy and life of the bearing. At the same time, the cut metal easily enters the working surface of the bearing, accelerating the wear of the raceway and rolling elements, and causing premature damage to the bearing.
2. It is not allowed to directly hit the bearing ring with a hand hammer during installation. The reference end face of the bearing is installed close to the shaft shoulder inward. The reference end surface of the bearing is distinguished according to whether the bearing end surface is typed or not. For deep groove ball bearings, self-aligning ball bearings, cylindrical roller bearings, spherical roller bearings and needle roller bearings, the end surface without letters is used as the reference surface; angular contact For ball bearings and tapered roller bearings, the end face with letters is used as the reference surface.
3. The pressure should be applied to the end face of the ring with installation interference fit during installation, that is, when it is installed on the shaft, the pressure should be applied to the end surface of the bearing inner ring; when it is installed in the bearing housing hole, the pressure should be applied outside the bearing Circle end face. It is not allowed to pass pressure through rolling elements and hold.
4. For bearings with a tight fit of the inner ring and a slip fit of the outer ring, when installing, the non-separable type should first install the bearing on the shaft, and then install the shaft together with the bearing into the housing hole of the bearing housing; For the separable type, the inner and outer rings can be installed separately.
5. In order to prevent the bearing installation from tilting, the center line of the shaft and the bearing hole must coincide during installation. If the installation is not correct, the bearing must be pulled out through the end face of the inner ring when reinstallation is required. Whether the bearing is installed correctly or not has a direct impact on its life and the accuracy of the main engine. If it is installed improperly, the bearing will not only have vibration, high noise, low accuracy, large temperature rise, but also the risk of being stuck and burned; on the contrary, if it is installed properly, it will not only ensure accuracy, but also greatly extend its life. Therefore, after the bearing is installed, it must be inspected.
Adjusting the axial clearance For the installation axial clearance of tapered roller bearings, you can use the adjustment nut on the journal, the adjustment washer and the thread in the bearing seat hole, or use the pretension spring to adjust. The size of the axial clearance is related to the arrangement of the bearing, the distance between the bearings, and the material of the shaft and the bearing seat, and can be determined according to the working conditions.
For tapered roller bearings with high loads and high speeds, when adjusting the clearance, the effect of temperature rise on the axial clearance must be considered, and the reduction in clearance caused by the temperature rise must be estimated, that is, the axial clearance It needs to be adjusted to be larger.
For low-speed and vibration-bearing bearings, clearance-free installation or pre-load installation should be adopted. Its purpose is to make the rollers and raceways of tapered roller bearings make good contact, evenly distribute the load, and prevent the rollers and raceways from being damaged by vibration and impact. After adjustment, the size of the axial clearance is checked with a dial indicator.