Maintenance technology of bearing under working condition
Maintenance technology of bearing under working condition
2022年5月24日
Preventive measures for bearing running noise and overheating
Preventive measures for bearing running noise and overheating
2022年5月26日

Cause analysis of common bearing quality faults

Mechanical damage common bearing

  • It is a comprehensive technology to judge and predict the reliability and service performance of the bearing through the fault and deterioration of the bearing and the performance state parameters, identify and judge the position, cause and risk degree of the abnormal situation, and determine the repair and improvement methods. Cause analysis of common bearing quality faults
  • Therefore, the fault diagnosis technology of bearing is not a simple fault detection (or monitoring) technology, nor is it a simple point inspection and instrumentation.Cause analysis of common bearing quality faults
  •  Correctly, quickly and effectively collect signals, process data, identify and judge manually or automatically. In order to determine the scientific repair cycle, necessary tests and estimates of fatigue and wear life should also be carried out according to the mechanism of various faults.Cause analysis of common bearing quality faults
  • Bearing fatigue failure is a surface form of failure, which is mainly manifested in the initiation, propagation and fracture process of fatigue crack, and the long-term impact of load failure under alternation. Cracks are in two ways:Cause analysis of common bearing quality faults
  • From the surface, this is the role of the external load caused by the plastic deformation of the working surface and the periodic change of the contact stress of the strain hardened surface during the rolling contact process of the bearing, and finally the formation of the surface crack between the two from the developing inner surface of the small crack. Due to the lubricant on the working surface and the open force, the crack is severely hit on the wall, forcing the crack to move forward;Cause analysis of common bearing quality faults
  • From the surface layer, under repeated pressure, the contact of the surface will initially produce cracks at a certain depth at the place where the surface is exposed, and from the angle along the surface direction to a certain depth, from behind the surface of the contact surface, and beyond the surface, and finally form corrosion stripping, leaving a horse pit.Cause analysis of common bearing quality faults
  • From the bearing surface, or from the cracks in the surface layer, these two objectives (carburization, quenching and other surface heat treatment of parts). If there are uneven hardness, organization, and non-uniform internal stress and other disadvantages, the contact stress is generally affected by the opposite underground cracks. If the surface quality of parts is poor, there is a defect (oxidation, decarburization), poor friction or lubrication, and from the surface cracks. 
  • The methods to control the sound of raceway are: select low-noise bearings, that is, bearings with small waviness, and carefully select the service conditions. Raceway noise often affects the noise of the whole machinery. Reducing raceway noise can reduce the noise of the whole machinery.
  • Before the bearing is delivered for routine inspection, its oil seal package can be removed, and it can be immersed in washing gasoline or acid free kerosene containing 3% engine oil. Turn its outer ring and carefully wash the junction of cage, rolling element and raceway.Cause analysis of common bearing quality faults
  •  It is required to thoroughly clean the original oil traces left in any hidden parts. After the bearing is cleaned, the attached cleaning oil shall be drenched and dried on the workbench lined with clean neutral lining paper, or dried slowly in the far-infrared oven. The bearing ring, cage or any rolling element shall not be rotated during the whole process from washing oil drying to air drying or drying.Cause analysis of common bearing quality faults
  • The bearings that have been dried or dried shall be dripped with lubricating oil as required and delivered for inspection immediately. At this time, there is no oil film protection on the outer surface of the bearing, and it is not allowed to directly touch the skin of hands during the whole inspection process. 
  • The operator shall wear clean gloves or apply antirust agent on his hands, but the antirust agent on his hands must be avoided from mixing into the rolling surface of the bearing, otherwise the measurement results will be deviated.Cause analysis of common bearing quality faults
  • After the inspection, the bearing shall be immediately delivered for use or treated with anti rust inventory. The whole inspection process shall also be completed quickly to avoid corrosion caused by too long. Note that using pure gasoline without engine oil for cleaning will also cause corrosion.Cause analysis of common bearing quality faults
  • Before inspection, the bearing must be placed on a metal plate in the inspection site together with the gauge block, standard parts and measuring instruments used for inspection, so as to homogenize the temperature and room temperature of these objects quickly.Cause analysis of common bearing quality faults
  • Bearing temperature is too high: during the operation of the mechanism, the part where the bearing is installed is allowed to have a certain temperature. When touching the shell of the mechanism with your hand, it should be normal not to feel hot. Otherwise, it indicates that the bearing temperature is too high.Cause analysis of common bearing quality faults
  • The reasons for high bearing temperature include: 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 shell; Excessive load; Broken bearing cage or rolling element, etc.Cause analysis of common bearing quality faults
  • Bearing noise: the rolling bearing is allowed to make slight running noise during operation. If the noise is too loud or there is abnormal noise or impact sound, it indicates that the bearing is faulty.Cause analysis of common bearing quality faults
  • The reason for the noise of rolling bearing: it is more complex. It is 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 shell, the bearing and the shaft is damaged, resulting in the axis deviation from the correct position and abnormal noise when the shaft moves at high speed. Cause analysis of common bearing quality faults
  • When the bearing is tired, the metal on its surface will peel off, which will also increase the radial clearance of the bearing and produce abnormal noise. Insufficient bearing lubrication, dry friction and bearing breakage will produce abnormal sound. 
  • After the bearing is worn and loose, the cage is loose and damaged, which will also produce abnormal noise and damage to the bearing. During the disassembly and inspection of rolling bearing, the fault and damage cause of bearing can be judged according to the damage of bearing.
  • Metal spalling on the raceway surface: the bearing rolling body and the inner and outer raceway surfaces are subjected to periodic pulsating load, resulting in periodic contact stress. When the number of stress cycles reaches a certain value, fatigue spalling will occur on the working surface of rolling element or inner and outer race raceway. Cause analysis of common bearing quality faults
  • If the load of the bearing is too large, it will aggravate this fatigue. In addition, improper bearing installation and shaft bending will also produce raceway spalling. The fatigue spalling of bearing raceway will reduce the operation accuracy of shaft and cause vibration and noise of mechanism.Cause analysis of common bearing quality faults
  • Bearing burn: the burned bearing has a return fire color on its raceway and rolling element. The causes of burns are generally insufficient lubrication, unqualified or deteriorated lubricating oil quality, and too tight bearing assembly.Cause analysis of common bearing quality faults
  • 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 the bearing rotating at low speed.Cause analysis of common bearing quality faults
  • The causes of bearing fracture include defect and overload. When the external load exceeds the material strength limit, the part fracture is called overload fracture. During the operation of the bearing, defects such as overheating tissue and local burns will also occur, resulting in defect fracture.
  • During the operation of the bearing, sometimes foreign hard particles or hard foreign matters or wear debris on the metal surface will be squeezed between the bearing surfaces, which will cause furrow like abrasion of the bearing. 
  • These hard foreign matters enter the interior of the bearing through the lubricating medium. With the continuous operation of the bearing, local friction generates heat, which is easy to cause local deformation of the friction surface and friction micro welding, or even local melting, and then bite.
  • Generally speaking, the bearing itself does not produce noise. What we call noise is actually the sound effect of vibration between the bearing and the surrounding structure directly or indirectly.
  • Excitation caused by the change of the number of loaded rolling elements. When a radial load is loaded on a bearing, the number of loaded rolling elements will change slightly during operation, that is: 2-3-2-3 This causes an offset in the direction of the load. Cause analysis of common bearing quality faults
  • The resulting vibration is inevitable, but can be reduced by axial preloading, which is applied to all rolling elements (not applicable to cylindrical roller bearings in bearings).Cause analysis of common bearing quality faults
  • When the waviness of components is closely matched between the bearing ring and the bearing seat or transmission shaft, the bearing ring may be deformed by matching with the shape of adjacent components. If deformation occurs, vibration may occur during operation. Therefore, it is important to machine the bearing pedestal and drive shaft to the required tolerances.Cause analysis of common bearing quality faults
Cause analysis of common bearing quality faults

Bearing cavitation common bearing

  • Local damage due to incorrect operation or installation, a small part of the bearing raceway and rolling element may be damaged. During operation, rolling over damaged bearing parts will produce specific vibration frequency. Vibration frequency analysis can identify damaged bearing components. Cause analysis of common bearing quality faults
  • Vibration behavior in applications in many applications, the stiffness of sliding bearings is the same as that of surrounding structures. Because of this feature, as long as the bearing (including preload and clearance) and its configuration in the application are correctly selected, it is possible to reduce the vibration in the application.Cause analysis of common bearing quality faults
  • Let’s briefly introduce the rolling sound of the bearing first. The size and sound quality of the rolling sound should be checked by the sound detector. The problem will be accurately judged with advanced tools. Even if the bearing has slight peeling and other damage, it will emit abnormal sound and irregular sound, which can be distinguished by the sound detector.Cause analysis of common bearing quality faults
  • Then check the vibration of the bearing to see if the damage of the bearing is very sensitive. Whether peeling, indentation, corrosion, crack, wear, etc. will be reflected in the bearing vibration measurement. Therefore, the vibration can be measured by using a special bearing vibration measuring instrument (frequency analyzer, etc.), and the specific situation of abnormality can not be inferred by frequency division. Cause analysis of common bearing quality faults
  • However, the values measured by each machine are different due to the service conditions of the bearing or the installation position of the sensor, so it is necessary to analyze and compare the measured values of each machine in advance to determine the judgment standard.Cause analysis of common bearing quality faults
  • In severe cases, metal peeling and large-area random scratches occur on the contact surface; In general, bearing mechanical damage refers to different levels of groove marks on the alloy surface of bearing bush. Contact surface damage and ablation exist at the same time. The main reason for bearing mechanical damage is that the bearing surface is difficult to form oil film or the oil film is seriously damaged.Cause analysis of common bearing quality faults
  • Plastic deformation and cold work hardening occur in the outer layer, and the sliding bearing is subjected to repeated action of cylinder pressure (impact load). The deformation capacity is lost locally, and the grain is gradually formed and continuously expanded. Then, with the falling off of wear debris, the loaded outer layer forms a hole. Generally, when the bearing bush is pitted, the pit first appears, and then the pit gradually expands and causes the cracking of the alloy layer interface.Cause analysis of common bearing quality faults
  •  The crack extends along the parallel direction of the interface until it peels off. The main reason for the cavitation of sliding bearing is that the sudden change of the cross section of structural elements such as oil groove and oil hole causes the strong disorder of oil flow. 
  • Bubbles are formed in the vacuum area of oil flow disorder, and then cavitation occurs due to the collapse of bubbles due to the increase of pressure. Cavitation usually occurs in the high load area of the bearing, such as the lower bearing bush of the crankshaft main bearing.
  • fatigue pitting
  • Due to the overload of the engine, bearing fatigue pitting refers to. Make the bearing overheat and the bearing clearance is too large, resulting in fatigue damage, fatigue pitting or fatigue falling off in the middle of the bearing. This kind of damage is mostly caused by overload, excessive bearing clearance, or unclean lubricating oil and foreign matters mixed in it. 
  • Therefore, when using, attention should be paid to prevent the bearing from overload and do not run at too low or too high speed; Adjust the engine to a stable state at idle speed; Ensure the normal bearing clearance and prevent the engine speed from being too high or too low; Check and adjust the working condition of the cooling system to ensure that the working temperature of the engine is appropriate.Cause analysis of common bearing quality faults
  • The chemical impurities (acid oxides, etc.) in the lubricating oil oxidize the bearing alloy to form acidic substances. The corrosion area of the bearing alloy is generally impure lubricating oil. Cause the bearing alloy to fall off locally and form irregular small cracks or pits. The main causes of bearing alloy corrosion are improper selection of lubricating oil, poor corrosion resistance of bearing data, or rough engine operation and high temperature.Cause analysis of common bearing quality faults
  • Bearing melting
  • Local high temperature is formed, and there is a small convex metal surface in direct contact between the journal and the bearing friction pair. In case of lack of lubrication and poor cooling, the bearing alloy will be blackened or partially burned. This fault is often caused by too tight fit between journal and bearing; Lack of lubricating oil pressure is also easy to burn the bearing.

Bearing alloy corrosion common bearing

  • There are great differences between the working surface and the core of bearing parts in terms of state, structure and performance requirements, but the overall heat treatment often makes it impossible to take into account, and the potential of materials can not be brought into full play. 
  • The application of material surface strengthening technology can not only better solve the differences in structure and requirements between the surface and the core, but also further make the surface obtain some special working properties to meet the requirements of the bearing working under specific conditions. This is of great significance in the development of modern science and technology. Cause analysis of common bearing quality faults
  • The traditional surface strengthening method belongs to the category of heat treatment. The surface strengthening methods such as laser, electron beam and ion beam developed in modern times not only apply some high and new technologies to the surface strengthening of materials, but also go beyond the scope of traditional heat treatment and form a new technical field.
  •  Therefore, the current surface strengthening technology can form a variety of classification methods from different angles. According to the physical and chemical process of surface strengthening technology, it can be roughly divided into five categories: surface deformation strengthening, surface heat treatment strengthening, chemical heat treatment strengthening, surface metallurgy strengthening and surface film strengthening.Cause analysis of common bearing quality faults
  • The metal surface layer is plastically deformed by mechanical methods to form a hardened layer with high hardness and high strength. This surface strengthening method is called surface deformation strengthening, also known as work hardening. Including shot blasting, sand blasting, cold extrusion, rolling, cold rolling and impact, explosion impact strengthening, etc. Cause analysis of common bearing quality faults
  • The characteristics of these methods are: the strengthening layer dislocation density increases and the sub crystal structure is refined, so as to improve its hardness and strength and reduce the surface roughness value, which can significantly improve the surface fatigue strength of parts and reduce the sensitivity of fatigue notch. This strengthening method has the advantages of simple process and remarkable effect. 
  • There is no obvious boundary between the hardened layer and the matrix, the structure is coherent, and it is not easy to fall off in use. Most of its methods have been applied in the bearing industry: the surface impact strengthening of rolling element is the application of this kind of method, and precision rolling has become a new ferrule processing and strengthening method.
  • Quenching the surface layer of parts by means of solid-state phase transformation and rapid heating is called surface heat treatment, commonly known as surface quenching. Including flame heating quenching, high (medium) frequency induction heating quenching, laser heating or electron beam heating quenching, etc. The characteristics of these methods are: local heating and quenching of the surface, small deformation of the workpiece; Fast heating speed and high production efficiency; The heating time is short, and the surface oxidation decarburization is very slight.Cause analysis of common bearing quality faults
  • Continuous vacuum dryer, this model is a comprehensive development of structural spray drying and freeze drying. Its working process is carried out in a low-temperature environment. The dry environment should maintain a low-temperature state. Cause analysis of common bearing quality faults
  • First, the equipment itself should be equipped with high-performance cooling parts. Second, the heat dissipation ability of the equipment itself is better, which requires that the performance of the bearing must meet the requirements of low-temperature resistance and high heat dissipation.Cause analysis of common bearing quality faults
  • Vacuum disc continuous dryer is mainly used to dry heat sensitive materials, and its drying process is carried out under negative pressure. In the processing process, due to the different space pressure, the equipment may have a small amount of expansion and contraction changes, which will have a great impact on the equipment components for a long time.Cause analysis of common bearing quality faults
  • which requires the bearing to have higher toughness and the performance that the clearance can be adjusted freely in a small range. To ensure the purchase of bearing products with the above performance, it is necessary to further understand the bearing code interpretation.Cause analysis of common bearing quality faults
  • Double cone rotary vacuum dryer is mainly used to dry powder, granular and fibrous materials. According to these dry materials, it can be judged that the working environment is dirty and there is a lot of floating dust, which requires high dust-proof performance of the bearing. 
  • Another is the mechanism of the equipment itself. This model adopts two-stage elastic connection mode of belt / chain, so the equipment operates stably. In order to achieve high-speed and stable operation of the equipment, the rotating parts are bearings.