Analysis of bearing troubleshooting methods

    It is not uncommon for the bearing to malfunction during operation, so there is no need to make a fuss. A failure has occurred and it is critical to judge and deal with it. Today we will explain the common faults of FAG bearings and how to eliminate them.
1. Bearing temperature is too high
When the mechanism is running, the part where the bearing is installed is allowed to have a certain temperature. When the body of the mechanism is touched by hand, it should be normal to not feel hot, otherwise the bearing temperature is too high.
The reasons for the bearing temperature being too high are: the quality of the lubricating oil does not meet the requirements or deteriorates, the viscosity of the lubricating oil is too high; the assembly of the mechanism is too tight (the gap is insufficient); the bearing assembly is too tight; the bearing race rotates on the shaft or inside the casing; Large; bearing cage or rolling body fragmentation.
2. Bearing noise
Rolling bearings allow a slight running noise during operation. If the sound is too loud or there is abnormal noise or impact, the bearing is faulty.
The causes of noise generated by rolling bearings are more complicated. One is the wear of the inner and outer rings of the bearing. As a result of this wear, the bearing and the housing, the bearing and the shaft are broken, causing the axis to deviate from the correct position and produce an abnormal sound when the shaft is moving at a high speed. When the bearing is fatigued, the surface metal peeling off will also increase the radial clearance of the bearing to produce abnormal noise. In addition, insufficient bearing lubrication, dry friction, and bearing crushing can produce abnormal sounds. After the bearing wears loose, the cage is loose and damaged, and the abnormal bearing damage will also occur.
When the rolling bearing is disassembled and inspected, the bearing failure and the cause of damage can be judged according to the damage of the bearing.
Rolling surface metal peeling
The bearing rolling elements and the inner and outer ring raceways are subjected to periodic pulsating loads, resulting in periodic changes.
Contact stress. When the number of stress cycles reaches a certain value, fatigue peeling occurs on the rolling element or the inner and outer ring raceways. If the bearing load is too large, this fatigue will be exacerbated. In addition, the bearing is not installed correctly, the shaft is bent, and the raceway is peeled off. Fatigue spalling of the bearing races reduces the accuracy of the shaft and causes vibration and noise in the mechanism.
2. Bearing burns
Burned bearings have a tempering color on the raceways and rolling elements. The causes of burns are generally insufficient lubrication, the quality of the lubricant does not meet the requirements or deterioration, and the bearing assembly is too tight.

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Talking about the use of new self-lubricating plastic sliding bearing on the isolating switch

The use of new self-lubricating plastic sliding bearings on the isolating switch

First, the isolation switch definition



The Disconnector is mainly used to reliably isolate the part of the high-voltage power distribution device that needs to be powered off from the live part to ensure the safety of the maintenance work. When the isolating switch is in the sub-position, there is an insulation distance and an obvious disconnection mark between the contacts in accordance with the specified requirements; in the combined position, it can carry the current under normal loop conditions and under abnormal conditions (such as short circuit) within a specified time. Current switching device


Second, the working principle of the isolation switch


The contacts of the isolating switch are all exposed to the air and have obvious breaking points. The isolating switch has no arc extinguishing device and therefore cannot be used to cut off the load current or short circuit current. Otherwise, under the action of high voltage, the breaking point will generate a strong arc. It is difficult to extinguish itself, and may even cause arcing (relative to ground or phase-to-phase short circuit), burning equipment, endangering personal safety. This is a serious accident called "loading isolation switch". The isolating switch can also be used to switch between certain circuits to change the way the system operates. For example, in a double bus circuit, an isolated switch can be used to switch a running circuit from one bus to another. At the same time, it can also be used to operate some small current circuits; aluminum plate spot welding machine


Third, the use of the sliding bearing of the rotating part of the isolating switch


The contact of the isolating switch, that is, the separating action of the isolating knife can be completed by manual and electric control, but in any case, it is required that the rotating parts can smoothly run under any circumstances, which requires the bearing of each rotating part to be longer. After the pause of time, it can still ensure normal operation; in order to ensure the normal operation of the isolating switch during the annual maintenance process, it is required that the sliding bearing of each rotating part can resist high and low temperature staggering all the year round and can still be used after the end face cover fails. Resist the erosion of various external factors, such as salt fog, acid rain, oxidative corrosion and other natural factors.

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In the early days, the domestic and foreign isolating switch manufacturers were able to solve the various rotating parts of the isolating switch. After the long-term stop, the metal sliding bearings were used in all rotating parts, such as powder metallurgy bearings, copper alloy bearings and three-layer composite. Bearings; although these bearings have adopted the self-lubricating process, they can not change the disadvantages of metal bearings, such as the lubricant is easy to dry, the corrosion and rust after the cover fails, etc. The isolation switch can not ensure the normal operation after long-term stop. . At present, the domestic use of a certain proportion of the three-layer composite bearing, although the inner diameter of the working surface is sintered with a lubricating layer, but this layer of lubricating layer thickness is only 0.03mm, when the lubricating layer works off the surface of the rotating shaft and the underlying metal copper powder layer or low The direct contact of carbon steel may result in rust and adhesion of the shaft and the surface of the metal bearing after a long pause, and the isolating switch has a risk of failure. In order to completely solve these risks, European isolation switch manufacturers first began to try to use new plastic self-lubricating bearings and after years of use prove that engineering plastic self-lubricating bearings become the most effective means of isolating switches to solve the risk of rotational failure.

Common quality defects in bearing parts after heat treatment

Common quality defects of bearing parts after heat treatment include: quenching microstructure overheating, underheating, quenching cracks, insufficient hardness, heat treatment deformation, surface decarburization, soft spots, etc.
Overheat
Overheating of the microstructure after quenching can be observed from the rough mouth of the bearing part. However, the exact microstructure must be observed to determine the degree of overheating. If coarse needle-shaped martensite appears in the quenched structure of GCr15 steel, it is quenched and superheated. The formation may be caused by excessive overheating of the quenching heating temperature or excessive heating and holding time; or it may be due to the serious banding of the original structure, forming a local martensite needle-like coarseness in the low carbon zone between the two zones. Local overheating caused. The retained austenite increases in the superheated structure, and the dimensional stability decreases. Due to the overheating of the quenched structure, the coarse crystal of the steel causes the toughness of the part to decrease, the impact resistance is lowered, and the life of the bearing is also lowered. Excessive heat can even cause quenching cracks.
2. Underheat
If the quenching temperature is low or the cooling is poor, the tortite structure exceeding the standard is formed in the microstructure, which is called the underheated structure, which lowers the hardness and sharply reduces the wear resistance, which affects the bearing life.
3. Quenching crack
The crack formed by the internal stress of the bearing part during the quenching and cooling process is called quenching crack. The causes of such cracks are: due to excessive heating temperature of quenching or too rapid cooling, the microstructure stress when the thermal stress and metal mass volume change is greater than the fracture strength of the steel; the original defects of the working surface (such as surface micro cracks or scratches) Trace) or steel internal defects (such as slag inclusions, severe non-metallic inclusions, white spots, shrinkage residuals, etc.) form stress concentration during quenching; severe surface decarburization and carbide segregation; insufficient tempering after quenching of parts Or not tempered in time; the cold punching stress caused by the previous process is too large, forging and folding, deep turning tool marks, sharp edges and corners of the oil groove. In short, the cause of quenching crack may be one or more of the above factors, and the existence of internal stress is the main reason for the formation of quenching cracks. The quenching crack is deep and slender, the fracture is straight, and the fractured surface has no oxidation color. It is often a longitudinal straight crack or annular crack on the bearing ring; the shape on the bearing steel ball is S-shaped, T-shaped or ring-shaped. The microstructure of the quenching crack is that there is no decarburization on both sides of the crack, and the difference is obvious with forging cracks and material cracks.

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What aspects should be considered when choosing a bearing clearance?

 When choosing a bearing clearance, the following aspects should be considered:

      1, the working conditions of the bearing, such as load, temperature, speed, etc.;

      2. Requirements for bearing performance (rotational accuracy, friction torque, vibration, noise);

      3. When the bearing and the shaft and the housing hole are in an interference fit, the bearing clearance is reduced;

      4. When the bearing is working, the temperature difference of the inner jacket ring causes the bearing clearance to decrease;

      5. The bearing clearance is reduced or increased due to the different expansion coefficients of the shaft and the outer casing material.

      6, according to the experience of use, the most suitable working clearance of the ball bearing is close to zero; roller bearings should maintain a small amount of working clearance. In components requiring good bearing rigidity, the bearings allow a certain amount of preload. It is specifically pointed out here that the so-called working clearance refers to the clearance of the bearing under actual operating conditions. There is also a kind of play called the original play, which refers to the play before the bearing is not installed. The original clearance is larger than the installation clearance. Our choice of clearance is mainly to choose the right working clearance. Valve inlet pump

      7. The clearance values ​​specified by national standards are divided into three groups: basic group (0 group), small clearance auxiliary group (1, 2 group) and large clearance auxiliary group (3, 4, 5 groups). When selecting, under normal working conditions, the basic group should be preferred, so that the bearing can get the proper working clearance. When the basic group does not meet the usage requirements, the auxiliary group clearance should be used. The large clearance auxiliary group is suitable for interference fit between the bearing and the shaft and the housing hole. The temperature difference between the inner and outer rings of the bearing is large. The deep groove ball bearing needs to bear a large axial load or needs to improve the centering performance. Reduce the bearing friction torque and other occasions; the small clearance auxiliary group is suitable for the requirements of higher rotation accuracy, strict control of the axial displacement of the housing hole, and the need to reduce vibration and noise.

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