Common Fault Analysis And Elimination Method of Needle Roller Bearing

Time：2020.12.31  Source：Roller Bearings Suppliers

Needle roller bearings are roller bearings with cylindrical rollers, which often appear in automobiles or motorcycles in our daily lives. The roller is elongated relative to its diameter. This kind of roller is called a needle roller. Despite the small cross-section of the bearing, the bearing still has a high load-carrying capacity. Needle roller bearings are equipped with long and thin rollers, so the radial structure is compact, and their inner diameter and load capacity are the same as other types of bearings. The smallest, especially suitable for support structures with limited radial installation dimensions. However, some failures will inevitably occur in the process of using needle roller bearings.

1.The inspection before assembly is not careful

Before the bearing is assembled, it shall be cleaned and carefully checked for rust, burr, bruise and crack on the inner and outer seat ring, rolling body and cage of the bearing. Check whether the bearing clearance is suitable. Whether the rotation is light and free, whether there is a sudden stop phenomenon; Check the size, roundness and cylindricity of the bearing diameter and bearing seat hole, and check whether there is a burr or four-convex inequality on the surface. For the open bearing seat, it is required that a gap of 0.1mm~0.25mm should be set aside between the joint surface of the bearing cover and bearing base and the outer round surface of the outer seat ring, so as to prevent the gap from being reduced and wear accelerating caused by the phenomenon of "clamping" occurring at the "tile mouth" on both sides of the outer seat, causing premature damage to the bearing.

2. Improper assembly

Improper assembly can lead to various failure forms mentioned above, as well as the following situations:

A. Improper coordination:

The base hole system is used for bearing the inner hole and shaft, and the base shaft system is used for bearing the outer circle and bearing housing hole.J5, JS5, JS6, K5, K6, M6 are used for shaft and bearing inner seat ring of centrifugal pump, centrifuge, reducer, motor and centrifugal compressor under normal load, and J6, J7 is used for bearing seat hole and bearing outer seat ring. A rotating seat ring (the inner seat ring of most bearings is a rotating seat ring, the outer seat ring is not a rotating seat ring, and a few bearings are opposite), usually adopts an interference fit, which can prevent the seat ring from rolling and sliding on the matching surface of the bearing diameter and bearing seat hole under the action of load. Need WSBC 22212 E, click here to learn more. 

But sometimes due to the size of the diameter of the axle and bearing hole measurement inaccuracy or cooperate with surface roughness, do not meet the standard requirements to cause excessive interference fit, the bearing race is being squeezed from a large, resulting in the radial clearance of bearing itself is reduced, the bearing rotating difficulties, fever, wear or jammed, caused serious bearing inner and outer race cracking when installing. Non-rotating seat ring usually adopts clearance or small interference fit, so that non-rotating seat ring may produce tiny crawling, and make the seat ring and rolling body contact surface constantly change, seat ring raceway wears a uniform. At the same time, it can also eliminate the phenomenon of axial sticking of the rolling body in bearing due to thermal elongation. But too large clearance, will not rotate the seat along with the rolling body rotation, resulting in the shaft (or bearing seat hole) and inner seat ring (or outer seat ring) serious wear, and friction makes the bearing hot, vibration.

B. Improper assembly method:

When the interference of bearing and bearing diameter or bearing housing hole is small, it is usually assembled by pressing method. The simplest method is to use the copper bar and hand hammer to strike the seat ring with the interference fit symmetrically in a certain order to make the bearing press in smoothly. In addition, the soft metal casing can be driven by a hand hammer or press. If the operation is not proper, it will make the seat ring deformation and cracking, or hammer hit on the seat ring with non-interference fit, it will make the racetrack and rolling body produce indentation or indirect damage to the bearing.

C. Improper temperature control during assembly:

When assembling needle roller bearings, if the interference between them and the axial diameter is large, the method of hot assembly is generally adopted. The bearing is put into the oil barrel containing oil, the oil barrel is heated with hot water or flame outside, the process requires the temperature of the heated oil to be controlled at 80℃~90℃, generally not more than 100℃, not more than 120℃. After the bearing is heated, quickly remove the suit and attach it to the journal. If the improper temperature control causes the heating temperature to be too high, it will cause the bearing to temper and reduce the hardness, and the bearing will be easy to wear, flake and even crack in operation.

D. Improper clearance adjustment during assembly:

The clearance of needle roller bearing is divided into radial clearance and axial clearance. Its function is to ensure the normal operation and lubrication of the rolling body as well as to compensate for the thermal elongation. Click here to learn more about WSBC 22208 E. 

Forbearing clearance can be adjusted, because of its axial gap and the radial gap there is a direct proportion relationship between, so the installation is adjusted axial clearance can be obtained as long as the radial clearance, but they are usually in pairs used (i.e. in the ends of the shaft or end), as a result, only need to adjust a bearing axial clearance. Adjust axial clearance with gasket commonly, some also can use a screw or thrust bad adjustment. For needle roller bearing clearance shall not adjust, because the radial clearance as defined by the standard in manufacturing has been good, can't adjust, such loading on the diameter of the axle bearing or bearing hole after the actual radial clearance is called assembly radial clearance, assembly time to assemble the size of the radial clearance is right to make necessary work in the operation of radial clearance, to ensure that the flexible bearing rotation. When this kind of bearing is working, the relative displacement of the inner seat ring will occur because the shaft is stretched when the temperature rises, thus reducing the radial clearance of the bearing and even making the rolling body get stuck between the inner and outer seat rings. The above phenomenon can be avoided if an axial clearance is set apart between one bearing (the other bearing is fixed on the shaft and in the bearing housing) and the side cover in the double bearing needle roller bearing.

It can be seen from the above that, whether the clearance can be adjusted or the clearance can not be adjusted needle roller bearings, they should be adjusted in the assembly of axial clearance (but some clearance can not be adjusted bearings do not need to keep axial clearance), to compensate the thermal elongation of the shaft when the temperature rises, so as to ensure the normal operation of the rolling body. If the axial clearance is too small, it will cause bearing rotation difficulty, heat, or even make the rolling body stuck or damaged; If the axial clearance is too large, it will cause abnormal sound in operation, and even cause serious vibration or damage to the cage.

3. Methods to eliminate needle roller bearing faults

(1) When the bearing is replaced, the new bearing should be carefully checked, and the axle diameter, bearing seat hole, and rotor should be carefully checked;

(2) When assembling and disassembling bearings, strictly implement the maintenance process and operate carefully to avoid bearing damage caused by improper assembly and disassembly;

(3) Timely refueling and oil changes to ensure that the working condition of the bearing is always in good condition;

(4) Check carefully during operation, find out hidden trouble and eliminate it in time.

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