The assembly inspection and adjustment of rolling bearings need to be restated
The equipment needs regular maintenance and adjustment at the initial stage of operation and throughout its life, especially the bearings. Due to the lack of experience of the operator, the bearing cannot be inspected and adjusted according to the regulations, resulting in improper clearance, resulting in the bearing running inside and outside the circle, stuck and not rotating, high temperature rise and early damage. These faults are mostly caused by the failure to adjust the bearing clearance in time as required in the initial stage of use (including reassembly after disassembly). Therefore, the assembly, inspection and adjustment of rolling bearings need to be redone.
1. Cleaning and inspection of rolling bearings
(1) Cleaning of rolling bearings the bearings that have just been removed are usually cleaned with gasoline or diesel. When cleaning, prepare a sufficient amount of gasoline or diesel oil first, put the bearing into the oil, hold the inner ring of the bearing with one hand, and slowly rotate the outer ring of the bearing with the other hand. When the grease and dirt on the raceway, rolling element and cage are all removed, gently rotate the inner ring of the bearing by hand, without stopping and rotating freely. When the oil runs out, put it on clean paper for drying.
For new bearings, do not unpack the bearings until they are ready for assembly. The oil painted on the bearing before leaving the factory is used for rust prevention, not for lubricating the working bearing. Due to long-term storage, the grease is invalid and aging, and the bearing may rust. Therefore, it is also necessary to clean the new bearings.
(2) Inspection of rolling bearings
Radial wear inspection shall be carried out for radial rolling bearings with non adjustable clearance after cleaning, and they shall be replaced unless they exceed the wear limit. The following table gives the limit division value of the radial rolling bearing after wear for users' reference.
The adjustable radial thrust bearing has been adjusted during assembly. After the equipment is put into normal operation for several hours, the bearing clearance should be readjusted according to the provisions of the manual.
2. Assembly of rolling bearings
Here, only two methods, hammering method and heating method, are briefly introduced. The press assembly method needs to be equipped with a press of appropriate tonnage and contact, which is simple and convenient to operate.
(1) In the hammering method, when hitting the inner and outer rings of the bearing with a brass rod, it is necessary to prevent the bearing from being crooked, and strike symmetrically along the periphery of the bearing.
(2) The heating assembly method has large interference and is suitable for the assembly of large heavy-duty bearings. The bearing is placed in the oil groove with bracket, and the heating temperature is appropriate at 80~100 ℃. It must not contact the groove bottom to prevent dirt from entering or local annealing of the bearing. This method is easy to form assembly conditions and can be widely used for batch assembly and single piece maintenance. The bearing with dust cover or sealing ring cannot be heated, otherwise it will cause lubricant loss. The heating method can also be electric induction heating, and the temperature and time should be well controlled.
3. Disassembly of rolling bearing
The disassembly of the bearing is for regular maintenance. If the removed bearing is ready to continue to be used, the disassembly force must not be applied through the rolling element during disassembly. If the interference fit bearing is difficult to disassemble, special attention should be paid not to damage the bearing and its matching parts.
The inner ring of the bearing is interference fit with the shaft, and the outer ring is clearance fit with the bearing seat. If the bearing is installed in the separate seat hole, the shaft and the bearing can be removed from the seat together, and then the bearing can be removed from the shaft with a press. Special tools can also be used to remove the bearing from the shaft (with wedges). When disassembling separable bearings, special pullers or presses can also be used to remove the bearing outer ring from the seat hole.
When disassembling large bearings, the oil pressure method can simplify the disassembly work. However, the premise of using this method is that it can be used only when the mating part of the bearing has oil passages and oil grooves for the introduction of high-pressure oil. In addition, as with the installation of bearings, the bearings can also be removed after heating.
4. Inspection and adjustment of rolling bearing clearance
When the clearance of the rolling bearing is small, the manufacturing accuracy of the parts is defective, the assembly method is improper, and the force is uneven, which will cause the bearing to deform. As a result, the bearing will run out of the inner and outer circles so that it will be stuck and damaged in the early stage. When the bearing clearance is too large, although there is no jamming, due to the non-uniformity of the inertia rotation torque and axial load on the bearing force, the bearing produces sliding friction, causing accelerated damage to the rolling element and inner and outer rings. Therefore, it is very important to adjust the bearing clearance reasonably during machine assembly and maintenance.
(1) Except for the inspection of non adjustable rolling bearings, non adjustable bearings refer to single row radial ball bearings, self-aligning ball bearings and self-aligning roller bearings. Since the radial clearance of these bearings has been determined according to the standard during manufacturing, it cannot be adjusted. The main purpose of the inspection is to find out the assembly quality of the bearings and whether the working bearings reach the wear limit, and decide whether to choose or not.
There are several methods to check whether there is fit clearance in the bearing. More accurate methods include feeler gauge inspection and dial indicator inspection. The most commonly used method is to rotate the bearing by hand to check the flexibility of rotation. The bearing should be flexible and stable without obvious braking, but without jumping and abnormal noise. The other method is to hold the bearing moving ring by hand and shake the bearing installed on the shaft left and right along the axis to see whether there is easy to find axial movement, but there should be no excessive movement. The above two methods are relatively reliable, but the operator needs some experience. After the bearing room is determined, the axial movement shall be reasonably adjusted according to the bearing model, load and installation method. The axial movement of bearings at different positions is different, generally between 0.5~1.2mm.
(2) Remove the inspection clearance of adjustable rolling bearings. Adjustable rolling bearings refer to angular contact ball bearings, tapered roller bearings, etc. these bearings must determine and adjust the axial runout during assembly and use. Various adjustable axial runouts can be found in the bearing installation and repair manual. Generally, the centripetal thrust with an inner diameter of 50~100mm and the axial clearance of tapered roller bearings are 100~180 μ M, which can also be determined according to experience.
The inspection methods for adjusting the axial clearance of rolling bearings include: dial indicator inspection, feeler gauge inspection, shaking by hand or inspection according to the flexibility of rotation. This method is more useful and intuitive.
① Check with a dial indicator: after the dial indicator base is fixed, place the top of the dial indicator on the end face of the shaft or on the end face of the parts on the shaft, and pry it in two directions along the axis with a crowbar. At this time, the limit difference indicated by the dial indicator is the axial clearance.
② Check with a feeler gauge: place the feeler gauge between the outer race raceway and the roller, rotate the inner race by hand, and the thickness of the feeler gauge that can just pass is the vertical distance between the inner surface of the outer race of the bearing and the roller surface. It must be noted that the relationship between this distance and axial clearance and radial clearance is shown in the figure below.
P -- vertical distance between inner surface of outer race of bearing and roller surface
S -- axial clearance
β- The included angle between the outer race raceway bus and the bearing centerline! Standard series β= 10。- 16。
γ- Radial clearance
③ Check according to the rotation flexibility: when the bearing is installed in a closed structure or the work site cannot be checked by the above methods, it can only be checked according to the axial displacement or rotation flexibility. When checking with this method, the rotating shaft should not have visible braking phenomenon, and the rotation should be stable and flexible.
(3) Adjustment of rolling bearing clearance
There are two basic forms of adjustable clearance bearing or non adjustable clearance bearing. That is, the axial division of the non adjustable bearing is adjusted by adding a pad between the side cover and the box, or the axial division is adjusted by the inner race nut to achieve the purpose of free rotation of the rotating body.
When using the inner race nut to adjust the axial clearance of tapered roller bearing, it is necessary to use the torque corresponding to the nut to tighten the nut according to the specified torque, and then screw the nut back to an appropriate angle according to the allowable shaft displacement, and lock it with a non-return pad. All equipment shall be maintained and adjusted for speed at the initial stage of operation or after bearing replacement.
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