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Common Faults and daily maintenance of rolling mill bearings

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Analysis of 1. common faults and causes

 

Mill bearings may be damaged due to various reasons during operation, such as improper assembly, poor lubrication, moisture and foreign body intrusion, corrosion and overload, which may lead to premature damage to bearings. Even if the installation, lubrication and use and maintenance are normal, after a period of operation, the bearing will appear fatigue spalling and wear and can not work properly. In short, the fault causes of mill bearings are very complex, and the common faults and causes are analyzed as follows.

 

1.1 Fatigue peeling

 

The inner and outer raceways and the surface of the rolling body of the rolling bearing bear both the load and the relative rolling. Due to the action of alternating load, cracks are formed at a certain depth (maximum shear stress) under the surface. Then it extends to the contact surface to make the surface flake. Fatigue spalling will cause the impact load, vibration and noise increase during operation. In general, fatigue spalling is often the main cause of rolling bearing failure.

 

1.2 Wear

 

Due to the invasion of dust and foreign body, the surface wear will be caused by the relative movement of the raceway and rolling body, and the poor lubrication will also aggravate the wear. The wear results increase the clearance of the bearing, increase the surface roughness, reduce the bearing operation accuracy, and increase the vibration and noise. Therefore, to a certain extent, the wear limit the bearing life.

 

1.3 Plastic deformation

 

Dents or scratches are formed on the surface of the raceway when the shaft is subjected to excessive impact or static loads, or when additional loads are caused by thermal deformation, or when foreign bodies with high hardness invade. This will cause the bearing to produce violent vibration and noise during operation, and once there is an indentation, the impact load caused by the indentation will further cause the spalling of the nearby surface.

 

2. routine maintenance

 

2.1 Inspection of bearings during operation

 

Listen, observe and measure bearings regularly according to maintenance procedures. Listening is to use one end of the listening rod to the bearing axial end cover and the radial housing of the bearing seat, and the other end to listen to whether the bearing has impact sound and mechanical friction sound during operation. Observation is to observe the operating environment, installation position, vibration deviation, lubrication and so on, whether there are bad working conditions. Measurement is the use of thermometers, vibrators, the bearing for regular testing. Using these methods, the bearing is periodically checked to determine whether the bearing is in normal condition.

 

2.2 Inspection of bearings at rest

 

Check the fastening condition of the relevant parts to confirm whether the parts are in the correct position, any loose anomalies, etc. In addition, the bearing lubrication is tested to detect whether there are foreign bodies in the lubricating oil. When the diameter of the foreign body is less than the minimum working clearance of the bearing, the foreign body can be stirred with the lubricating oil through the clearance. When the diameter of the foreign body is larger than the working clearance of the bearing, the foreign body is crushed or crushed into thin dust to stick to the bearing surface or embedded in it. Crushed foreign debris, if not embedded in the working surface, into the lubricating oil, will be more bearing wear. So that the bearing fatigue spalling. Causes the working surface temperature to rise. The lubricating oil then loses its function. When the bearing fails, the foreign body is crushed or embedded in the rolling body, the oil film is destroyed quickly, resulting in the shaft being damaged by working in the dry friction state.

 

2.3 Post-disassembly inspection of bearings

 

When the roll is changed, the cleaning agent can be used to clean the bearing, blow dry with compressed air, and then check the roller, cage, raceway. Roller, raceway appear dents, pitting and other phenomena, depending on the specific situation to replace. At the same time, the necessary bearing seal is replaced to prevent the poor seal from affecting the bearing life. If the bearing seal is poor and the emulsion enters the bearing, it will cause water pollution to the lubricating oil or grease, which will lead to the decrease of the fatigue strength of the bearing material and the easy crack. At the same time, the sealing is poor, the iron oxide into the bearing failure lubrication conditions, so that the bearing element surface wear.

 

2.4 Installation of bearings

 

2.4.1 press installation

 

Press installation generally uses press, can also use bolts and nuts, when forced to use hand hammer to hit the installation of the occasion, in the inner ring pad pad operation. This practice has often become the cause of bearing installation operation damage, so it is limited to the use of small interference, can not be used for large or medium or large bearings. Such as deep groove ball bearings such as non-separated bearings, the inner ring, outer ring need to be installed interference, then need to pad the pad operation, with screw or oil pressure to press the inner ring and outer ring at the same time. The outer ring of the ball bearing is easy to tilt, so that it is not interference fit, and it is best to install the pad. Such as cylindrical roller bearings, tapered roller bearings and other separate bearings, the inner ring, outer ring can be installed on the shaft and shell, respectively, when the installation of the inner ring and outer ring, the key is to firmly close the two, so that the center of the two do not deviate, force will cause raceway surface jam.

 

2.4.2 hot pack

 

Large bearings require a lot of force when pressed, so it is difficult to press in. Therefore, the bearing is heated in oil to expand and then installed on the shaft, which is widely used in the installation of large bearings. Using this method can make the bearing avoid unnecessary external force and complete the installation operation in a short time. The heating temperature of the bearing is based on the size of the bearing and the required interference. The bearing is heated to about 100℃~120℃. In order to make the bearing not directly contact the bottom of the oil tank, it is best to consider placing the bearing on the metal mesh table or hoisting the bearing to 20℃~30℃ higher than the required temperature. After installation, the bearing cools down and the width direction shrinks, so fasten it with shaft nuts or other appropriate methods to prevent cracks between the inner ring and the bearing retaining shoulder.

 

2.5 Inspection after bearing is installed

 

After the bearing installation, in order to check whether the installation is correct, to check the operation, you can use hand rotation to confirm whether the rotation is smooth. Inspection items due to foreign bodies, scars, indentation caused by poor operation, due to poor installation, poor processing of the installation seat caused by uneven rotation torque, due to too small clearance, installation error, sealing friction caused by excessive torque and so on. If there is no exception, you can start running. Check if there is vibration, sound, rotating parts have contact, etc., confirm that there is no abnormal into the power operation. Operation inspection starts at low speed without load and slowly increases to rated conditions. The inspection items in trial operation are: abnormal sound, transfer of bearing temperature, leakage of lubricant and discoloration. In case of abnormal operation during trial operation, stop operation immediately, check mechanical equipment and unload bearing inspection if necessary.

 

3. Conclusion

 

Through the analysis of common faults and causes of bearings and the establishment of scientific and reasonable maintenance rules, it can effectively improve the service life of bearings, reduce the incidence of accidents, reduce spare parts consumption, ensure production time, and provide a strong guarantee for reducing cost and increasing efficiency.


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