Abstract: Rolling bearing is a kind of precision component that is assembled carefully. It is very important to ensure the assembly quality and improve the working efficiency. In the process of use, the faults and damages should be maintained and repaired in time.

Keywords: rolling bearing assembly method, failure, damage, repair

1 Structural characteristics of rolling bearing

Rolling bearing is a kind of bearing with rolling friction property, which is generally composed of inner ring, outer ring, rolling element and cage. A smooth groove raceway is arranged on the inner and outer rings, and the rolling body can roll along the raceway to form friction. It has the advantages of small friction, high efficiency, small axial size, convenient assembly and disassembly, and is one of the important parts of the machine. Due to its structure, the rolling bearing has a certain clearance, so during the assembly of the bearing, the appropriate clearance should be controlled and adjusted to ensure normal operation and prolong the service life of the bearing.

2 Assembly method of rolling bearing

The assembly method of rolling bearing shall be determined according to the structure, type, size and matching property of bearing components. The normal assembly of rolling bearing, no matter the shaft or hole, is generally interference fit. The common assembly methods of interference fit include temperature difference method, press in method, etc. At the mechanical assembly site, the temperature difference method is used less, mainly because the operation is more complex. The temperature difference method is simpler than the heating method for assembly. Generally, liquid nitrogen is used, which has the advantages of large temperature difference, large linear expansion and clean. Install the bearing into the hole and soak the bearing directly in liquid nitrogen. The heating method is troublesome. In order to heat evenly, it is generally necessary to boil the parts (bearings) in liquid. If the bearing is boiled, the requirements are relatively high. The heating medium should be clean and the temperature should be well controlled. The biggest disadvantage of the temperature difference method is that the volume of parts is limited. For example, when assembling the lathe spindle, it is necessary to install the spindle and gears on the shaft at the same time. The temperature difference method is simply unable to do this. The indentation method is the most widely used. One hammer and one copper rod can complete the task. There are still many differences and precautions in operation. When installing bearings, try to use a non impact method. If a press is used, hammering is not good for the protection of parts and bearings. For bearings with small specifications and small interference, use a manual press, such as a lead screw type, or even a vise. Large size bearings generally require hydraulic pressure. When installing the bearing, pay attention to whether the bearing is inclined at any time at the beginning, and adjust the force position in time to prevent damage to the mounting hole or shaft. Of course, the preparation before installation is also very important. Clean the installation surface of the parts and remove the burrs at the orifice and shaft end. After cleaning, apply clean engine oil, etc. to the mounting surface. Be careful in your preparations. If the bearing cannot be assembled in place due to burr, dust, etc. grinding into the assembly surface, it will be more serious later, and often fall into a dilemma, even the entire shaft or parts will be scrapped. In many cases, the bearing can only be installed or removed by knocking, and the impact is inevitable. So the hammer skill is also an important basic training for fitters. Knocking is different for different loading and unloading methods. If the copper rod is used, it can only be knocked symmetrically from left to right. Do not use too much force each time, and gradually knock the bearing in. Generally speaking, it is better to strike symmetrically on both sides instead of three-point striking. Another better method is to pad a cylinder with a size similar to the outer or inner ring of the bearing on the bearing, and hit this end of the cylinder with a hammer (a special tool made by ourselves, and the knocked end is dead). When the bearing is already in place (all of it enters the hole or shaft), the knocking force can be greater. In fact, in this case, in principle, the bearing should be hit in place with as few strokes as possible. Because the striking feature is that frequent tapping will produce riveting effect, but it is easy to damage the surface of the shaft or hole. ① Assembly of cylindrical bore bearings. When the inner ring of the bearing fits tightly with the shaft, and the outer ring fits loosely with the housing, the bearing should be installed on the shaft first. When pressing, a copper sleeve should be placed on the end face of the bearing, and then the bearing and the shaft should be installed together into the bearing seat hole. When the outer ring of the bearing is closely matched with the bearing seat hole and the inner ring is loosely matched with the shaft, press the bearing into the bearing seat hole before installing it into the shaft. The installation method of the bearing is mainly determined by the size of the fit interference. When the interference is small, knock the inner and outer rings of the bearing with a copper rod and sleeve evenly. When the interference is large, press the bearing with a pressure machine. When the interference is large, use the hot assembly method. ② Tapered bore bearing assembly. When the interference is small, it can be directly installed on the tapered journal. For tapered hole bearings with large size or interference that are difficult to disassemble frequently, hydraulic sleeve method is used for assembly. ③ Assembly of thrust bearing. The thrust ball bearing can be divided into loose ring and tight ring. The inner hole of the loose ring is larger than the inner hole of the tight ring. It has clearance with the shaft and can rotate relative to the shaft. The tight ring fits the shaft tightly and is relatively static with the shaft. During assembly, make sure that the tight ring rests on the plane of the rotating part and the loose ring rests on the plane of the stationary part.

3 Failure and damage of rolling bearing

There are two kinds of faults of rolling bearings. One is that the temperature of the bearing installation part is too high, and the other is that the bearing runs with noise. The temperature of one bearing is too high. When the mechanism is running, a certain temperature is allowed at the position where the bearing is installed. When touching the mechanism housing with hands, it should be normal not to feel hot, otherwise, it indicates that the bearing temperature is too high. The reasons for high bearing temperature are: the quality of lubricating oil does not meet the requirements or deteriorates, and the viscosity of lubricating oil is too high; The mechanism assembly is too tight (insufficient clearance); The bearing assembly is too tight; The bearing race rotates on the shaft or in the housing; {HotTag} The load is too large; Broken bearing cage or rolling element, etc. The second is bearing noise. The rolling bearing is allowed to make a slight running noise during operation. If the noise is too loud or there is abnormal noise or impact, it indicates that the bearing is faulty. The noise of rolling bearing is caused by complex reasons, mainly due to the wear of the mating surfaces of the inner and outer rings of the bearing. Due to this kind of wear, the matching relationship between the bearing and the housing, and between the bearing and the shaft is destroyed, which causes the axis to deviate from the correct position and produces abnormal noise when the shaft is moving at high speed. When the bearing is fatigued, the metal on its surface will peel off, which will also increase the radial clearance of the bearing and produce abnormal noise. In addition, the insufficient lubrication of the bearing, the formation of dry friction, and the crushing of the bearing will produce abnormal noise. If the bearing is worn and loose, the cage will become loose and damaged, which will also cause abnormal noise. Damage of rolling bearing. ① The metal on the raceway surface peels off. The rolling element of the bearing and the raceway surfaces of the inner and outer rings are subject to periodic pulsating loads, resulting in periodic contact stresses. When the number of stress cycles reaches a certain value, fatigue peeling will occur on the working surface of the rolling element or inner and outer ring raceways. If the load of the bearing is too large, this fatigue will be aggravated. In addition, if the bearing is installed incorrectly and the shaft is bent, the raceway will also peel off. The fatigue peeling of the bearing raceway will reduce the running accuracy of the shaft and cause vibration and noise of the mechanism. ② Bearing burns. The raceway and rolling element of the burnt bearing have a fire back color. Burns are generally caused by insufficient lubrication, unqualified or deteriorated lubricating oil, and tight bearing assembly. ③ Plastic deformation. Uneven pits appear on the contact surface between the raceway and the roller of the bearing, indicating that the bearing has plastic deformation. The reason is that under the action of large static load or impact load, the local stress on the working surface of the bearing exceeds the yield limit of the material, which generally occurs on bearings rotating at low speed. ④ The bearing race is cracked. Cracks in the bearing race may be caused by the tight fitting of the bearing, looseness of the foreign or inner ring of the bearing, deformation of the bearing's containing parts, poor surface processing of the installed bearing, etc. ⑤ The cage is broken. The reasons are insufficient lubrication, broken rolling elements, and skewed seat rings. ⑥ The metal of the cage adheres to the rolling element. The main reason is that the rolling element is stuck in the cage or the lubrication is insufficient. ⑦ The race race is severely worn. It is mainly caused by foreign matters falling into the seat ring, insufficient lubricating oil or improper lubricating oil brand.

4 Maintenance and repair of rolling bearing

In case of any fault, wear or damage of rolling bearing during use, it shall be adjusted and repaired in time. If the bearing clearance is too small and the lubrication is poor, it shall be adjusted and re lubricated in time; If there are sundries entering the bearing, the bearing shall be cleaned and re lubricated in time. Lubricants commonly used in rolling bearings are lubricating oil and grease. When the circumferential speed of the shaft is less than (4~5) m/s, grease lubrication is used because the grease is not easy to lose and is not affected by temperature. {TodayHot} can be used for a long time by adding grease once. Lubricating oil lubrication is mainly used for bearings with high speed and high working temperature, which can dissipate heat due to low friction resistance. When the journal is worn when disassembling the bearing, it can be repaired by chrome plating. When the bearing seat hole is worn, it can be repaired by spraying or inlaying, and the size requirements can be met by machining. Only after careful cleaning and lubrication before assembly and early resolution of abnormalities found during use can failures be reduced, the service life of bearings be extended and productivity be improved.

More about ITS Spherical Roller Bearing:

Spherical roller bearing is a bearing with drum shaped rollers assembled between the inner ring with two raceways and the outer ring with spherical raceways. spherical roller bearing has two rows of rollers, which mainly bear radial load and axial load in either direction. It has high radial load capacity, especially suitable for working under heavy load or vibration load, but can not bear pure axial load. The outer race of this kind of bearing is spherical, so its centering performance is good and can compensate the coaxiality error.

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