Needle roller bearing is a kind of roller bearing with cylindrical roller, our daily life is commonly used in cars or motorcycles, etc., that needle roller bearing in use is inevitably some failure, according to the understanding of needle roller bearings, tell you about some common failure factors of needle roller bearings, and related to eliminate bearing failure methods. Needle roller bearings common failures and their causes. 1、Failure form. (1) bearing rotation difficulties, heat. (2) bearing operation with strange sound. (3) bearing vibration. (4) inner seat ring peeling, cracking; (5) outer seat ring peeling, cracking. (5) outer seat ring spalling, cracking. (6) bearing raceway and rolling body indentation. 2, the cause of failure analysis. (1) Inspection before assembly is not careful. Before assembling the bearings should be cleaned and carefully check the inner and outer seat ring, rolling body and cage, whether there is rust, burrs, bruises and cracks; check whether the bearing clearance is appropriate. Whether the rotation is light and free, there is no sudden card stop phenomenon; At the same time check the shaft diameter and bearing seat hole size, roundness and cylindricity and its surface whether there are burrs or four convex inequality. For the open bearing seat, require the bearing cover and bearing base joint surface and the outer ring of the outer circle between the surface, should leave 0.1mm ~ 0.25mm clearance, in order to prevent the outer seat on both sides of the “tile mouth” at the “clip help” phenomenon resulting in the reduction of clearance, wear Speed up, so that the bearing premature damage. (2) Improper assembly. Improper assembly will lead to the above-mentioned forms of bearing failure, as well as the following situations. A. Improper fit. Bearing bore and shaft fit using the base hole system, bearing outer circle and bearing seat hole fit using the base shaft system. Generally in the normal load conditions of the work of the centrifugal pump, centrifugal machine, reducer, motor and centrifugal compressor shaft and bearing inner seat ring, using J5, js5, js6, k5, k6, m6 with, bearing seat hole and bearing outer seat ring using j6, J7 with. Rotating seat ring (most of the bearing inner seat ring for rotating seat ring, outer seat ring not for rotating seat ring, a small number of bearings are the opposite), usually using interference fit, can avoid the seat ring under load in the shaft diameter and bearing seat hole of the mating surface rolling and sliding. But sometimes due to the shaft diameter and bearing seat hole size measurement inaccurate or fit surface roughness does not meet the standard requirements, resulting in too large interference fit, so that the bearing seat ring by a large squeeze, resulting in the bearing itself to reduce the radial clearance, so that the bearing rotation difficulties, heat, increased wear or jamming, serious will cause the bearing inside and outside the seat ring in accordance with the installation of cracking. Do not rotate the seat ring often use clearance or interference is not large fit, so do not rotate the seat ring is likely to produce a small creep, and seat ring and rolling body contact surface constantly replaced, seat ring raceway wear uniform. Also can eliminate the shaft due to thermal elongation and make the bearing in the rolling body of the phenomenon of axial jamming. But too much clearance with, will not rotate the seat ring with the rolling body rotation, resulting in the shaft (or bearing seat hole) and the inner seat ring (or outer seat ring) occurring serious wear, and friction so that the bearing heat, vibration. B. Improper assembly method. Bearing and shaft diameter or bearing seat hole interference is small, more use press-in method assembly. The simplest method is to use brass rod and hand hammer, in a certain order to symmetrically tap the bearing with interference with the seat ring, so that the bearing is smoothly pressed into. In addition, can also be used to soft metal casing by hand hammer or pressed into the press. If the operation is not proper, it will make the seat deformation and cracking, or hand hammer hit in the non-perfection with the seat, it will make the raceway and rolling body indentation or bearing indirectly destroyed. C. improper temperature control during assembly. Needle roller bearing in assembly, if its interference with the shaft diameter is large, generally use the hot installation method assembly. The bearing is put into the oil barrel with oil, and the oil barrel is heated with hot water or flame outside, the process requires the oil temperature to be heated at 80℃~90℃, usually not more than 100℃, at most not more than 120℃. The bearings are quickly removed and set on the journal after heating. If the heating temperature is too high due to improper temperature control, the bearings will be tempered and the hardness will be reduced, and the bearings will be easily worn, spalled or even cracked during operation. D. Improper adjustment of clearance when assembling. Needle roller bearing clearance is divided into radial clearance and axial clearance, its function is to ensure the normal operation of the rolling body and lubrication and compensation of thermal elongation. For the clearance adjustable bearing, because of its axial clearance and radial clearance between the positive proportion, so the installation is as long as the axial clearance is adjusted to obtain the required radial clearance, and cut they are generally used in pairs (that is, installed in both ends of the shaft or one end), therefore, only need to adjust the axial clearance of a bearing can be. Generally use shims to adjust the axial clearance, some can also use screws or thrust bad adjustment. For the clearance can not be adjusted needle roller bearing, because its radial clearance in the manufacturing has been determined according to the standard, can not be adjusted, such bearings installed in the shaft diameter or bearing seat hole, the actual radial clearance is called assembly radial clearance, assembly to make the size of the assembly radial clearance just in operation can cause the necessary work radial clearance, to ensure that the bearing flexible rotation. This kind of bearing in work, because the shaft in the temperature rise when the heat elongation and make its inner seat ring relative displacement, so that the bearing radial clearance is reduced, and even make the rolling body in the inner and outer seat ring between the card. If the double bearing needle roller bearing in a bearing (another bearing fixed in the shaft and bearing seat) and the side cover between the axial clearance, can avoid the above phenomenon. From the above, regardless of the gap can be adjusted or gap can not be adjusted needle roller bearings, they are assembled to adjust the axial clearance (but some gap can not be adjusted bearings do not have to stay axial clearance), in order to compensate for the shaft in the temperature rise when the thermal elongation, so as to ensure the normal operation of the rolling body. If the axial clearance is too small, it will cause the bearing rotation difficulties, heat, and even make the rolling body stuck or broken; if the axial clearance is too large, it will lead to the operation of the sound, and even cause serious vibration or make the cage damage. E. Improper coupling alignment. Most of the input shaft of the running equipment is connected with the power shaft through the coupling, so the coupling must be corrected when assembling, so that the active shaft and the driven shaft are on the same axis. (3) Poor lubrication. Needle roller bearings use lubricating oil (or grease) have a certain working temperature, when the temperature is too high, it will deteriorate, so as to lose the lubricating effect, so that the bearing is burned due to high temperature. In addition, the lubricant (or grease) itself bad texture or operation of the oil (grease) is not timely, will also cause the bearing temperature rise or produce strange sound. (4) Rotor imbalance. Generally speaking, the rotor of the operating equipment should be balanced dynamically and statically before assembly, so the bearing will not be a problem. But some rotors in the process of operation due to the corrosion of the medium or solid impurities wear, or shaft bending, it will lead to the generation of unbalanced centrifugal force, so that the bearing heat, vibration, raceway serious wear, until the destruction. (5) Inspection and replacement is not timely. During the operation of the bearings, check them regularly according to the regulations. If there is heat, strange sound, vibration, etc., stop in time to find the cause and eliminate the fault. If the bearings are found to have serious fatigue spalling, oxidation and rust, worn pits, cracks, hardness reduced to HRC<60, or excessive noise that cannot be adjusted, they should be replaced in time. If the inspection and replacement are not timely, it will cause serious damage to the bearings and even the rotor, thus affecting normal production. In addition, improper bearing disassembly, vibration caused by loose equipment foot bolt, will also lead to bearing raceway and rolling body indentation, bearing inner and outer seat ring cracking. Eliminate the needle roller bearing failure methods. (1) when replacing the bearing, the new bearing should be carefully checked, while the shaft diameter and bearing seat hole and rotor for meticulous inspection. (2) assembly and disassembly of bearings, strict implementation of the overhaul process, careful operation, to avoid damage to the bearing caused by improper installation and disassembly. (3) Timely oiling and oil change to ensure that the working condition of the bearings is always in good condition. (4) Check carefully during operation, and eliminate any hidden trouble in time.

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