Causes of damage to the clutch release bearing

      Causes of damage to the clutch release bearing
1. Working conditions and stress of clutch release bearing
The separation bearing is subjected to axial load, impact load, and radial centrifugal force during high-speed rotation during use. Further, since the fork thrust and the reaction force of the separation lever are not in the same straight line, a torsional moment is also formed. Clutch release bearings have poor operating conditions, intermittent high-speed rotation and high-speed friction, high temperature, poor lubrication conditions, and no cooling conditions.
2. Reasons for damage to the clutch release bearing
The damage of the clutch release bearing has a lot to do with the driver's operation, maintenance and adjustment. The causes of the damage are as follows:
1) The operating temperature is too high to cause overheating
Many drivers often turn the clutch halfway when turning or decelerating, and some of the gears are placed on the clutch pedal. Some vehicles have too large free travel adjustment, which makes the clutch separation incomplete, in a semi-engaged and semi-detached state. The dry friction causes a large amount of heat transfer to the separation bearing. The bearing is heated to a certain temperature, and the butter melts or dilutes the flow, so that the temperature of the separation bearing is further increased, and when the temperature reaches a certain level, it burns out.
2) wear and tear without lubrication
The clutch release bearing is lubricated with butter. There are two ways to add the butter. For the 360111 release bearing, the rear cover of the bearing should be opened to fill the grease during maintenance or when the transmission is removed, and then the rear cover should be reinstalled. For the 788611K release bearing, it can be removed and placed in molten grease for digesting, and then taken out after cooling to achieve the purpose of lubrication. In actual work, the driver easily overlooks this, resulting in a lack of oil in the clutch release bearing. The amount of wear of the separated bearing in the case of no lubrication or less lubrication is often several to several tens of times the amount of wear after lubrication. As the wear increases, the temperature will also increase greatly, which makes it more vulnerable.
3) Free travel is too small or too many loads
According to the requirements, the clearance between the general clutch release bearing and the separating lever is 2.5mm, which is reflected in the free travel of the clutch pedal is 30-40mm, the free travel is too small or there is no free travel at all, which will make the separation lever and The release bearing is in a normally engaged state. According to the principle of fatigue failure, the longer the bearing working time, the more serious the damage; the more the number of loads, the more likely the separation bearing is to cause fatigue damage. Moreover, the longer the working time, the higher the temperature of the bearing, and the easier it is to burn, reducing the service life of the separation bearing.
4) In addition to the above three reasons, whether the separation lever is adjusted flat, whether the separation bearing return spring is good or not, has a great influence on the damage of the separation bearing.

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What are the common quality defects of 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

    The microstructure after quenching can be observed from the rough mouth of the bearing part, but the 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 tends to be 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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