Characteristics of engine sliding NSK bearing damage
Characteristics of engine sliding NSK bearing damage
2022年5月15日
Maintenance measures to prevent bearing failure
Maintenance measures to prevent bearing failure
2022年5月17日

Selection and use of fag bearings

Selection of bearing clearance: fag bearings

  • Selection of bearing model: the bearing model is generally selected by the user’s technicians according to the service conditions and load of supporting products. The business personnel mainly know whether the user’s actual load is consistent with the selected fag bearing. 
  • If the bearing fails to meet the use requirements, they should advise the customer to change the model as soon as possible, but there will be no problem in selecting the model unless special products.
  • Selection of bearing clearance: when purchasing bearings, users generally only tell what model and grade they are in, and rarely put forward requirements for the clearance of fag bearings. Business personnel must ask about the service conditions of bearings, including bearing speed, temperature and fit tolerance, which are directly related to the selection of bearing clearance. Generally, CM clearance is adopted for motors with speed below 3500 rpm. Selection and use of fag bearings
  • For example, relatively large clearance is required for high-temperature and high-speed motors. After assembly, the bearing clearance will be reduced due to the increase of inner hole and the reduction of outer circle. The reduction of clearance = interference × 60% (unless the bearing housing is aluminum). For example, if the clearance before bearing assembly is 0.01mm and the interference during assembly is 0.01mm, the clearance after bearing assembly is 0.004mm. Selection and use of fag bearings
  • Theoretically, the noise and service life of the bearing reach a good state when there is zero clearance, but considering the problems such as temperature rise in actual operation, the clearance of fag bearing after assembly is 0.002mm-0.004mm.Selection and use of fag bearings
  • Selection of grease: the selection of grease is generally based on the speed, temperature resistance, noise requirements and starting torque of the bearing, and the business personnel are required to understand the performance of various greases.Selection and use of fag bearings
  • Selection of bearing sealing type: the lubrication of fag bearing can be divided into oil lubrication and grease lubrication. Oil lubricated bearings are generally formal bearings, and grease lubricated bearings are generally sealed with dust covers or rubber seals. Selection and use of fag bearings
  • The dust cover is suitable for parts with high temperature or good service environment. The seals are divided into contact seal and non-contact seal. The contact seal has good dust-proof performance but large starting torque, and the non-contact seal has small starting torque, but the sealing performance is not as good as the contact seal.Selection and use of fag bearings
  • At present, the bearing has been professionally manufactured in automobile motor bearing, household appliance motor bearing, motorcycle bearing, health motor bearing and other industries, so that the noise and service life of fag bearing can reach a good state.Selection and use of fag bearings
  • From the objective demand of the machine tool industry, angular contact ball bearing motorized spindle, liquid (dynamic) hydrostatic bearing motorized spindle and gas bearing motorized spindle are not only the focus of market development, but also the focus of academic research. Angular contact ball bearing is suitable for high-speed rolling bearing. It has the advantages of low friction resistance, low power consumption, low cost, easy serialization and standardization.Selection and use of fag bearings
  •  It has high limit speed, high precision and high stiffness. It has been widely used in machining centers, CNC milling machines, lathes, internal grinding machines and high-speed engraving and milling machines. Its main technical difficulty lies in improving accuracy, service life and reliability. Liquid (dynamic) hydrostatic spindle is supported by liquid “oil film”, which has significant “error homogenization effect” and damping and vibration reduction. The rotation accuracy is much higher than that of rolling bearing spindle. Selection and use of fag bearings
  • It has high stiffness, small wear and long service life. It has been widely used in precision and ultra precision machine tools. Its main technical difficulty is to control the temperature rise and thermal deformation of spindle at high speed. Gas fag bearing motorized spindle is supported by “air film”, and its rotation accuracy and limit speed are higher than liquid (dynamic) static pressure motorized spindle and rolling bearing motorized spindle. Selection and use of fag bearings
  • It has good thermal stability. It is an indispensable core component of ultra precision machine tool and printed circuit board (PCD) drilling machine. Its deficiency lies in low bearing capacity and high process requirements.Selection and use of fag bearings
  • Magnetic bearing is also an important spindle support mode. It has high limit speed and no wear during operation. Its technical difficulty lies in how to improve the dynamic stiffness and damping performance, so as to ensure high machining accuracy while realizing high speed. The core research content of magnetic suspension spindle is the control of mechanical system characteristics and electromagnetic characteristics.Selection and use of fag bearings
  • In the process of using NTN bearing, due to its own quality and external conditions, its bearing capacity, rotation accuracy and antifriction energy performance will change. When the performance index of the bearing is lower than the use requirements and can not work normally, it is called bearing damage or failure. Once the bearing is damaged and other accidents occur, its machine and equipment will stop running and its function will be damaged.Selection and use of fag bearings
Selection and use of fag bearings

Grinding heat of fag bearings

  • Therefore, it is necessary to investigate and deal with the causes in a short time and take corresponding measures. Of course, the damage of NTN bearing is much more complex than that of general mechanical parts. 
  • The damage of rolling bearing is characterized by many manifestations and complex causes. In addition to the internal factors of bearing design and manufacturing, most of the damage of bearing is due to improper use, such as suitable selection cloth (see instructions to customers) and unreasonable support design, Improper installation, poor lubrication, poor sealing and other external factors.Selection and use of fag bearings
  • It is of great significance to study the formation and causes of NTN bearing damage. On the one hand, it can improve the use method, use the bearing correctly and give full play to the due efficiency of the bearing. On the other hand, it is helpful to develop new products with better performance. Selection and use of fag bearings
  • This paper not only describes the precautions, installation methods and operation supervision in the use of rolling bearings, but also focuses on the forms and causes of bearing damage and the countermeasures that should be taken
  • Grinding heat of bearing
  • In the grinding process of NTN bearing, the contact area between grinding wheel and workpiece consumes a lot of energy and generates a lot of grinding heat, resulting in local instantaneous high temperature in the grinding area. It can be found that the instantaneous temperature in the grinding area can be as high as 1000 ~ 1500 ℃ in 0.1 ~ 0.001ms. Selection and use of fag bearings
  • Such instantaneous high temperature is enough to make the surface layer at a certain depth of the working surface produce high-temperature oxidation, amorphous structure, high-temperature tempering, secondary quenching, and even burn cracking.Selection and use of fag bearings
  • Surface oxide layer
  • Under the action of instantaneous high temperature, the steel surface reacts with oxygen in the air to form an extremely thin (20 ~ 30nm) thin layer of iron oxide. It should be noted that there is a corresponding relationship between the thickness of oxide layer and the total thickness of surface grinding metamorphic layer. This shows that the thickness of oxide layer is directly related to the grinding process and is an important symbol of grinding quality.Selection and use of fag bearings
  • Amorphous structure layer
  • When the instantaneous high temperature in the grinding area makes the workpiece surface reach the molten state, the molten metal molecular flow is evenly coated on the working surface and cooled by the base metal at a very fast speed to form a very thin amorphous structure layer. It has high hardness and toughness, but it is only about 10nm, which is easy to be removed in precision grinding.Selection and use of fag bearings
  • High temperature tempering layer
  • The instantaneous high temperature in the grinding area can make the surface heated to a certain depth (10 ~ 100nm) higher than the tempering heating temperature of the workpiece. When the austenitizing temperature is not reached, with the increase of the heating temperature, the surface layer by layer will produce the microstructure transformation of re tempering or high-temperature tempering corresponding to the heating temperature, and the hardness will also decrease. The higher the heating temperature, the more severe the decrease of hardness.Selection and use of fag bearings
  • Two layer quenching layer
  • When the instantaneous high temperature in the grinding area heats the surface layer of the workpiece above the austenitizing temperature (AC1), the austenitized structure of the layer is re quenched into martensitic structure in the subsequent cooling process. Selection and use of fag bearings
  • For the workpiece with secondary quenching burn, the high-temperature tempering layer with very low hardness must be under the secondary quenching layer.Selection and use of fag bearings

Contact angle fag bearings

  • The journal and sliding bearing shall be in uniform and fine contact, and there shall be a certain fit clearance.
  • It refers to the center angle of the contact surface between the journal and the sliding bearing. The contact angle shall not be too large or too small. Too small contact angle will increase the pressure of sliding bearing, and in serious cases, it will cause large deformation of sliding bearing, accelerate wear and shorten service life; If the contact angle is too large, it will affect the formation of oil film and can not get good liquid lubrication.Selection and use of fag bearings
  • The experimental research shows that the limit of contact angle of sliding bearing is 120 °. When the sliding bearing is worn to this contact angle, the liquid lubrication will be destroyed. Therefore, the smaller the contact angle is, the better without affecting the compression condition of the sliding bearing.Selection and use of fag bearings
  •  From the theoretical analysis of friction distance, when the contact angle is 60 °, the friction torque is small. Therefore, it is suggested that for sliding bearings with speed higher than 500r / min, the contact angle should be 60 °, and for sliding bearings with speed lower than 500r / min, the contact angle can be 90 ° or 60 °.Selection and use of fag bearings
  • What should be done when the bearing temperature rises:Selection and use of fag bearings
  • When the bearing temperature rises, first judge whether there is misoperation. If it does rise, do the following:
  • Check whether the oil level of the oil gauge is normal. If not, check whether the oil drain valve of the oil tank is tightly closed. If it has been closed tightly, oil shall be added. If it is oil leakage from the sealant pad, it shall be shut down for treatment.Selection and use of fag bearings
  • Take an oil sample to observe whether the oil color has changed, and test to see whether it has deteriorated. If the deterioration is confirmed, stop the machine and replace it with new oil.Selection and use of fag bearings
  • Check whether the bearing has abnormal sound and whether the bearing swing is abnormal.Selection and use of fag bearings
  • Check the oil pressure of the governor. If the oil pressure is low, the cooling water hydraulic valve may be closed.
  • Check whether the cooling water pressure, water flow and pipeline system are normal. If the water pressure is low, the filter may be blocked and cannot be handled in time, it can be shut down for treatment. When it is confirmed that it can work, it can be put into use.Selection and use of fag bearings
  • First, let’s look at the reasons for the increase of bearing temperature:Selection and use of fag bearings
  • It may be the deterioration of the oil quality of the bearing, the uncleanness of the oil itself or the deterioration of the oil during operation. For example, the increase of water in the oil will increase the acidity of the oil, reduce the lubricating effect of the oil, corrode the bearing bush and increase the bearing temperature.Selection and use of fag bearings
  • The interruption of cooling water of the bearing may be caused.Selection and use of fag bearings
  • 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 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. Selection and use of fag bearings

    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.Selection and use of fag bearings

  •  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.Selection and use of fag bearings

  • 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.

  • 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.

  •  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.

  • In order to maintain the original performance of the bearing in good condition for as long as possible, it is necessary to maintain and repair in order to prevent accidents, ensure the reliability of operation and improve productivity and economy. 
  • Maintain the operation standard of corresponding mechanical operation conditions and carry out it regularly. The contents include monitoring the operation status, replenishing or changing the lubricant, and regular disassembly inspection. As maintenance items in operation, there are bearing rotation sound, vibration, temperature, lubricant state, etc.
  • Bearing cleaning: when disassembling the lower bearing for maintenance, first record the appearance of the bearing, confirm the residual amount of lubricant, and wash the bearing after sampling the lubricant for inspection. As a cleaning agent, gasoline and kerosene are commonly used.
  • The cleaning of the removed bearing is divided into coarse cleaning and fine cleaning. They are placed in the container respectively. First, put the metal mesh bottom so that the bearing does not directly contact the dirt of the container. During rough cleaning, if the bearing rotates with dirt, it will damage the rolling surface of the bearing, which should be paid attention to. In the coarse cleaning oil, use a brush to remove the grease and adhesion. After it is roughly clean, turn to fine cleaning.
  • According to the load acting on the bearing and the rotation condition of the ferrule, the load borne by the ferrule can be divided into three types: fixed load, rotating load and back and forth shaking load.
  • Fixed load
  • The resultant radial load is borne by part of the region of the ferrule raceway and transmitted to the corresponding part of the region of the appropriate surface of the shaft or shell. This load is called fixed bearing load.
  • The unique feature of the fixed load is that the synthetic radial load is relatively static with the ferrule. Generally, loose ferrules can be used to bear fixed load.
  • Load shedding
  • The synthetic radial load vector acting on the bearing ring rotates along the circumferential direction of the raceway, is successively borne by each part of the raceway, and is transmitted to each part of the outer surface of the shaft housing hole accordingly. This kind of load is called off load, also known as cyclic load.
  • The unique feature of load shedding is that the synthetic radial load vector rotates relative to the ferrule. The ferrule bearing the transfer load and the shaft or shell hole shall be suitable for filtering or interference. If you think it is appropriate to use the gap and install it properly, there will be slip between you and me, which will cause friction damage and friction heating of the contact surface, rapidly increase the temperature and quickly destroy the bearing. 
  • The volume of the desired interference is determined according to the operating conditions, and the principle is that when the bearing is working under the load effect, it will not cause the “crawling” phenomenon of the actuating ferrule on the appropriate surface in the shaft or housing hole.
  • The synthetic radial load vector acting on the bearing ring relatively swings back and forth within a certain area of the ring raceway, which is borne by a certain area of the raceway and transmitted to a certain area on the surface of the shaft or shell hole, or the load acting on the bearing is impact load and oscillation load, and its load direction or number often changes. This load is called swing load, also known as non directional load.
  • When the bearing bears back and forth shaking load, especially when bearing heavy load, the inner and outer rings should be considered appropriate and the interference should be used appropriately. 
  • When the inner ring swings and rotates back and forth, it is generally considered appropriate by the inner ring, but it is appropriate to use it when the transfer load is removed. However, sometimes the outer ring must be able to swim towards the bearing outside the housing or when its load is light, it can be considered appropriate to use a slightly looser outer ring than the rotating load.