In the production, the rolling bearing “fever” is often encountered. If the cause analysis is unclear, the treatment is not timely, and the measures are not proper, it will often be half the effort, and even cause a bad accident such as bearing burnout and gear reducer. In the following, combined with the typical cases that the author encountered in the production and debugging process, the paper analyzes and summarizes the specific problems in the design, installation, lubrication, assembly and other links for your reference. 1. Bearing fever due to improper lubrication 1.1 Bearing lubrication part design is inherently insufficient ZB's No. 1 kiln head surplus fan had many bearing burnout accidents in the year of 2003 (in the initial stage of production), and after on-site investigation, it was found that there was a problem with the oil mark design of the bearing housing. When the oil level is engraved under the oil mark, the actual measurement, the lowest row of balls of the bearing has just touched the oil surface, and only when the oil level is displayed on the upper scale line can the operation be satisfied. When the oil level is close to the lower engraving line, the lubrication condition deteriorates. At first, the bearing temperature rises slowly. The on-site personnel did not pay enough attention to the bearing fever alarm. Once the temperature rise reaches a certain level, it will rise sharply in a very short time. Burn out the bearing. Therefore, incorrect labeling of the oil mark will cause misleading to the inspection and maintenance personnel. After finding out the reasons, the refueling standard line was redefined. Another example is the high-speed shaft bearing of CL's rotary kiln reducer. After only 2~3 hours of starting, the bearing suddenly smokes. The reason for the accident analysis was that the oil return hole in the high-speed shaft bearing housing was too low, and most of the oil coming from the oil pipe directly flowed into the reduction gear box from the oil return hole. Adjust the angle of the oil return hole to keep a certain amount of oil in the bearing housing After the bit, it runs normally. 1.2 Lubrication pipe is blocked by foreign matter Because the lubrication management is not strict, the container is dirty during the oil-changing process, or the pipe welding and pickling are not standardized, which causes the welding slag and other debris to enter the oil pipe and block the oil hole. It is more common in the previous project. For example, the raw material grinding reducer of ZB Company is blocked by the oil circuit. The cement grinding reducer of TH Company is also the long-term high temperature of the bearing caused by the oil circuit being blocked by the cotton yarn. In particular, when the high-speed shaft bearing of the reducer of TH company is used to check the oil quantity, it is always impossible to see how much oil can be added in the high-speed bearing. After completely removing the oil pipe and purging it with high-pressure air, it is found that two fine pieces are blocked inside. Cotton rope! In addition, in the process of replacing the reducer bearing, TH Company also found that the bearing eccentric sleeve is too thin (the oil hole of the eccentric sleeve can be larger than the diameter of the oil hole of the bearing itself), so the oil hole is reamed. deal with. Since the bearings of various parts of the hardened gear reducer are generally forcedly lubricated by the thin oil station, the oil pipes of each lubrication point are in parallel relationship. It is difficult to find the blockage of individual oil pipes when observing the total oil quantity and oil return quantity, so there is experience. The maintenance personnel will carefully check the temperature of each tubing and judge whether the oil passage is unblocked according to the temperature difference of the tubing. Generally, the oil pipe temperature is lower than other pipes. PY's inspectors have discovered that the high-speed shaft tubing temperature of the reducer in the kiln is low and finally confirms the serious hidden danger of the tubing blockage, thus avoiding a major accident. 1.3 Lubricating oil (fat) deterioration or refueling is not timely The lubricating oil (or grease) used in the rolling bearing has a certain working temperature. When the temperature is too high, the water in the bearing housing enters the water, and the ash enters the ash, severe oxidation, emulsification and the like may occur, thereby losing the lubricating effect and causing the bearing to be heated. Burned. In addition, the lubricating oil (or grease) itself is poor in texture or the fueling (fat) in operation is not timely, which is also a common phenomenon, such as belt conveyor roller bearings into the rainwater, rotary feeder bearings and Fuller pump bearings into the coal powder or raw The powder will cause the bearing temperature to rise or produce abnormal sound. 1.4 Lubrication of the cooler of the lubrication line is blocked, resulting in poor cooling effect Especially in summer production, this problem is particularly common, and individual manufacturers do not hesitate to increase or parallel the cooler to enhance the cooling effect. Because of the serious scaling of the high-temperature fan cooler, frequent bearing alarms have been encountered in various branches. A more effective treatment is to pickle and descale the cooler before entering the summer. 2. Bearing heat due to improper installation 2.1 Design bearing a fever caused by insufficient expansion This situation is more likely to occur on long-axis equipment such as large wind turbines and crushers, which is also a relatively easy part of equipment design, manufacturing, installation and maintenance personnel. Typical case CX company's rotary kiln rear exhaust fan has experienced intense heat generation at the free end of the fan at the initial stage of production. Because of the thermal expansion of the rotor main shaft and the bearing end cover after the thermal expansion of the rotor main shaft, the high temperature generated in a short period of time The bearing end cap and the rotor main shaft end face are welded together. Therefore, when installing and accepting the new fan, it is necessary to pay attention to whether the axial clearance of the free end bearing can meet the expansion requirement of the working condition. The method for calculating the amount of shaft expansion is simple: △L=L×(t-t0)×0.000012 Where: ΔL—the amount of expansion of the shaft; mm; L—the length of the shaft between the bearing blocks; mm; T—condition temperature; °C; T0—the ambient temperature at which the device is installed; °C. It should be noted that in the summer installation, the amount of shrinkage of the equipment during the winter season should also be considered, which is especially important for the northern region. Generally speaking, the temperature difference between the winter and the summer in the cold regions of the north can reach 80 °C. If the shaft with a length of 3 m is installed in the summer, the maximum shrinkage in winter (when the machine is stopped) can be close to 3 mm. 2.2 Bearings caused by skewed bearing fever If the bearing is installed in a skewed position, the ball will not roll in the correct position of the bearing raceway, or even cause a large axial end force of the ball end face and the inner race of the bearing seat and the outer race stop, causing the bearing to overheat. If the bearing is not correct, it will take a lot of effort to check. The LY company's limestone crusher bearing heat is the case. The solution is to suck the dial indicator on the shaft, and the needle hits the end face of the bearing outer ring to check the end face jump. The end face runout value is controlled within 0.05. It is also possible to directly check the clearance on the left and right sides of the bearing with a feeler gauge. 2.3 Fever caused by improper assembly of the bearing itself (1) Improper cooperation The inner hole of the bearing and the shaft are matched by the base hole, and the outer circumference of the bearing and the bearing housing hole are made by the base shaft. Generally, under normal load conditions, the shaft and the inner race of the bearing are matched by j5, js5, js6, k5, k6, m6, and the bearing seat hole and the bearing outer race are matched by j6 and j7. Rotating races, usually with an interference fit, can prevent the race from rolling and sliding on the shaft diameter and the mating surface of the housing bore under load. However, due to the inaccurate measurement of the shaft diameter and the bearing housing hole or the roughness of the mating surface does not meet the standard requirements, the excessive interference fit is caused, and the bearing race is greatly squeezed, resulting in the radial clearance of the bearing itself. The reduction makes the bearing difficult to rotate, generates heat, and the wear is intensified or stuck. In severe cases, the inner and outer races of the bearing are cracked during installation. The non-rotating seat often adopts a gap or a small interference, so that the rotation of the seat may cause a slight creep, and the contact surface of the race with the rolling element is continuously replaced, and the raceway of the race is evenly worn. At the same time, it is also possible to eliminate the axial jam of the rolling elements in the bearing due to the thermal elongation of the shaft. However, if the gap is too large, the non-rotating seat will rotate together with the rolling elements, causing severe wear of the shaft (or the bearing housing hole) and the inner race (or the outer race), and the friction causes the bearing to heat and vibrate. TH's cement grinding reducer was burned out after only two hours of operation after replacing the new bearing. Initially, the gap between the eccentric sleeve for fixing the bearing and the outer race of the bearing caused the vibration of the reducer. During maintenance, many pockmarks were found on the inner surface of the eccentric sleeve, and at the same time, the solid tooth glue was applied, which caused the bearing outer race to be unable to generate axial displacement, and thus could not be burned out if the shaft expansion requirement could not be satisfied. (2) Improper assembly method When the bearing and the shaft diameter or the bearing housing hole have a small interference, the press-in method is often used for assembly. The easiest way is to use a copper rod and a hand hammer to symmetrically tap the bearing with an interference fit in a certain order to make the bearing smoothly pressed in. In addition, it is also possible to use a sleeve made of soft metal to be hammered in or pressed by a press. If improperly operated, the seat will be deformed and cracked, or the hammer will be hit on the non-interference fit seat, which will cause the raceway and the rolling element to be indented or the bearing to be indirectly damaged. (3) Improper temperature control during assembly When the rolling bearing is assembled, if it has a large interference with the shaft diameter, it is generally assembled by hot charging. The bearing is placed in the oil drum filled with organic oil. The outside of the oil drum is heated by hot water or flame. The temperature of the oil required for heating is controlled at 80 °C ~ 90 °C, generally not exceeding 100 °C, and not exceeding 120 °C. After the bearing is heated, it is quickly taken out and placed on the journal. If the temperature is not properly controlled, the heating temperature will be too high, which will cause the bearing to temper and the hardness will decrease. During operation, the bearing will be prone to wear, peeling, excessive temperature rise and even cracking. It should be noted that when oil is used to “boil” the bearing, the bearing should be placed flat in the oil drum, and a wooden block or steel bracket with a height of about 50 mm should be placed between the bearing and the bottom of the cylinder. The instrument or thermometer controls the oil temperature. Since the oil bath heating method is inconvenient for measuring the bearing expansion amount, temperature control, and installation, it is recommended to use an electromagnetic induction heater. (4) Improper adjustment of bearing clearance during assembly The gap of the rolling bearing is divided into a radial gap and an axial gap, and its function is to ensure the normal operation and lubrication of the rolling elements and to compensate for the thermal elongation. For a bearing with adjustable clearance, because of the proportional relationship between the axial clearance and the radial clearance, the installation is to obtain the required radial clearance as long as the axial clearance is adjusted, and they are generally For the use (that is, at the two ends or one end of the shaft), therefore, it is only necessary to adjust the axial clearance of one bearing. However, for the reducer, attention should be paid to the tooth surface engagement when adjusting the bearing clearance. Generally, the axial gap is adjusted by a gasket (pressing wire method), and some can also be adjusted by screws or thrust rings. If the gap adjustment is too large or the end cap of the reducer is loose during operation, the bearing clearance will be too large, which will not only cause the vibration of the bearing itself, the noise is large, the cage is easy to be damaged, etc., and the gear surface meshing is further caused by the gear reducer. Tooth accident. For example, DY's No. 2 kiln reducer, SS company No. 1 kiln coal mill reducer's teething accident is mainly caused by excessive bearing axial clearance and tooth surface misalignment. For rolling bearings with non-adjustable clearance, the radial clearance is determined according to the standard at the time of manufacture and cannot be adjusted. After such bearings are installed in the shaft diameter or in the bearing housing bore, the actual radial clearance is called assembly. Radial clearance, the assembly should be such that the radial clearance of the assembly can just cause the necessary working radial clearance during operation to ensure flexible rotation of the bearing. When such a bearing is in operation, the shaft is relatively displaced due to the temperature rise when the temperature rises, so that the radial clearance of the bearing is reduced, and even the rolling elements are caught between the inner and outer races. This can be avoided by leaving an axial gap between one of the double-bearing rolling bearings (the other bearing is fixed on the shaft and in the housing) and the side cover. A typical example is PY's No. 2 grate cooler No. 9 fan. The 8-disc bearing was replaced within one month. Finally, it was suspected that the bearing quality was not good and it was changed to an imported bearing, which still did not help. The real reason is that when the maintenance personnel replace the bearing, the gasket added between the upper and lower bearing housings is lost, so that after the upper cover is pressed, the outer ring deformation of the bearing is flattened, the radial clearance becomes small or almost zero, and the bearing runs once. When heat is generated and the expansion is blocked, it will burn out due to rapid high temperature. In the worst case, the bearing will be burned after running for an hour or two. After checking the lead wire of the fan bearing, it was found that the over-winning amount of each part of the mating surface of the bearing seat was very different, and the most parts were added with 0.23mm gasket. The minimum part had almost no added gasket, and only the sealing glue was used to compensate. . After the bearing clearance is suitable, the operating temperature is about 40 °C, and everything is normal. 2.4 Coupling misalignment can also cause bearing heating or failure The input shaft of most operating equipment is connected to the power shaft through the coupling, so the alignment of the coupling must be performed during assembly so that the drive shaft and the driven shaft are on the same axis. 80% of the heating of the motor tile is caused by poor alignment. Such as PY company raw material grinding reducer motor tile. XC company's cement mill reducer coupling itself processing error too Large, causing poor alignment, high motor bearing temperature, and large equipment vibration. In addition, during the installation process of the coupling, it is necessary to pay attention to the relative position mark of the coupling end of the active end and the driven end to avoid too much deviation of the pin hole and cause the pin to be installed too tightly. 3. Rotor imbalance Some rotors are subject to corrosion of the medium or wear of solid impurities during operation, or the shaft is bent, resulting in unbalanced centrifugal force, which causes the bearing to heat up, vibrate, and the raceway is severely worn until it is destroyed. This is especially important for circulating fans in the mill system. Due to the serious wear of the impeller, the balance of the rotor after wear is poor, and the vibration of the fan is large, which often causes the bearing to fail prematurely. 4. Check that the replacement is not timely If the bearing is found to have severe fatigue flaking, oxidative corrosion, worn pits, cracks, and hardness reduced to HRC<60, or if excessive noise cannot be adjusted, it should be replaced in time. If the inspection or replacement is not timely, it will cause the bearing to have heat, abnormal sound, vibration, etc., or even serious damage to the rotor, thus affecting normal production. In addition, improper bearing disassembly and vibration caused by loosening of the anchor bolts of the equipment may also cause indentation of the bearing raceway and the rolling elements, and cracking of the inner and outer races of the bearing. During the operation of the bearing, the inspection shall be carried out according to the specified cycle.
5. Bad bearing quality
Rolling bearing parts work in the form of point contact or line contact for a long time under high alternating contact stress. The accuracy, longevity and reliability of the mainframe are largely determined by the bearings. Whether it is an ordinary bearing or a special special bearing, the mainframe puts high demands on its life, performance and reliability. Therefore, in the purchase and acceptance of the bearing must pay attention to inspection, first of all to use the products of regular brand-name manufacturers, the key parts even use original imported bearings, such as SKF bearings, NSK bearings, TIMKEN bearings and FAG bearings. Special parts should be specially designed, such as bearings for roller presses and vertical grinding rolls.
Although the rolling mill bearings of PY and JY have been specially ordered, due to the unstable quality of large-scale domestic bearing manufacturing, there has been a phenomenon of pitting and peeling on the inner surface of the rolling ring, causing the bearing to be fever and the roller press to frequently stop.
6. Improper bearing selection
When selecting the bearing, pay attention to the limit speed and load capacity of the bearing, and do not exceed the speed and overload.
7. Bearing heat caused by comprehensive factors
AQ's first-stage exhaust fan (model: Y6-2x40-14NO30F) has affected production due to frequent bearing heating problems. The final settlement of this matter lasted more than two years, and the direct cost was more than 300,000 yuan.
At first, the bearing inner ring of the impeller was caused by the fever of the free end of the impeller, and the shaft was welded together. The grinding wheel was used to repair the journal and the production was maintained. Because there is a fear that the part is not well matched (the fan vibration is too large), it will cause long-term hidden danger to the production. The rotor main shaft and the bearing housing were replaced again during the overhaul. After the replacement, the free end bearing heats up, and then the coupling side bearing heats up. After half an hour, the temperature rise will reach 80 °C. Repeatedly, the kiln system could not operate normally. The main reasons for the problems are as follows:
(1) The main reason for the initial free-end bearing heating and burning is that the outer ring pressure is relatively tight, and the bearing cannot be axially displaced with the expansion of the main shaft. Another reason is that the actual fit between the inner race and the shaft is insufficient (or has become a transition fit). When the temperature rise of the system gas is small, the bearing is only slightly slightly heated and does not affect the operation. However, if the process system is abnormally operated and the gas temperature is too high, the amount of expansion is insufficient. A slip occurs between the inner ring and the shaft, and the adhesion is burned out.
(2) After the rotor main shaft and the free end bearing housing are replaced, the free end bearing heats up because the joint angle is not blunt when the tile seat is processed, and the "clamping" phenomenon occurs after the bearing is installed. For new housings, attention should be paid to the inspection during assembly and, if necessary, to the requirements of “scraping”.
(3) The coupling side bearing heat is caused by the poor verticality of the bearing and the main shaft, the outer race being skewed, and the ball running position is not correct. Because it is an old bearing, once the shaft temperature is abnormal, the bearing position changes greatly, and it will cause heat when it deviates from the original raceway position. In addition, during the operation of the fan, the top of the base of the motor is smashed, and the displacement of the motor, resulting in poor alignment accuracy of the coupling, is also one of the important reasons.
(4) The return oil pipe of the bearing seat is relatively thin, the temperature in winter is low, and the oil return is slow. Because the bearing oil leaks axially, the post personnel reduce the oil supply of the bearing. Objectively reducing the oil supply and circulation of the bearing lubricant is also an important reason for the excessive temperature rise of the bearing. In response to this situation, we have increased the oil supply pressure on site. (Reducing the opening of the return line valve at the gas station safety valve)
