Mill bearing common faults and routine maintenance

Mill bearings during operation may be due to various reasons, such as poor assembly, moisture and foreign matter invasion, corrosion and overload, leading to premature bearing damage. Even if it is installed, lubricated, and used and maintained normally, the bearing will fatigue peel off and wear out after a period of operation, and it will not work properly. In short, the cause of the failure of the rolling mill bearing is very complex, and its common faults and causes are analyzed as follows.

01、Common malfunctions Fatigue spalling

Roller bearing inner and outer raceway and rolling element surface both bear the load and relative rolling, due to the effect of sophistry load, the first to form a crack at a certain depth below the surface (the maximum shear stress), and then extended to the contact surface to peel the surface pit, and finally The development of mass spalling is the Fatigue spalling phenomenon. Fatigue spalling can cause increased shock loads, vibrations, and noise during operation. Fatigue spalling is often the main cause of failure of rolling bearings.

Worn

Due to intrusion of dust and foreign matter, the raceways and rolling elements will cause surface Worn when they move relative to each other, and poor lubrication will exacerbate Worn. Worn results in increased bearing clearance, increased surface roughness, reduced bearing operation accuracy, and vibration and vibration. Noise also increases. Thus, to some extent, the amount of Worn limits the bearing life.

Plastic deformation

When the bearing receives a large impact load or static load, or additional load due to thermal deformation, or a high degree of hardness of foreign objects invade the surface of the raceway will form dents or scratches. This will cause the bearings to generate severe vibration and noise during operation, and once indentation occurs, the impact load caused by the indentation will further cause the nearby surface to fall off.

02、Routine maintenance Inspection during operation

According to the maintenance regulations, the bearings are subjected to regular listening, observation and measurement. Listening is to use the radial shell of one end of the listening bar facing the axial end cap of the bearing and the bearing seat, and the other end of the bar is listening to whether the bearing has impact noise and mechanical friction sound during operation. The observation is to observe the operating environment, installation location, vibration offset, lubrication conditions, etc., and whether there is any bad working condition. Measurement is the use of thermometers, vibrometers to carry out regular inspections of the bearing seats. Use these methods to periodically check the bearing to determine if the bearing is in a normal condition.

Checking at rest

Check the tightening of the relevant parts and check whether the parts are in the correct position or if there is any looseness or other abnormalities. In addition, bearing lubrication is tested to detect the presence of foreign materials in the lubricant. When the foreign body diameter is less than the minimum working clearance of the bearing, foreign matter can be agitated with the lubricant through the gap, so that the rolling element work surface friction; when the foreign body diameter is greater than the bearing working gap, foreign matter is crushed or rolled into a thin dust adhered to the bearing Surface or embedded in it. If the crushed foreign material debris enters the lubricating oil without being embedded in the working surface, the bearing Worn will be aggravated, so that the bearing will cause Fatigue spalling, causing the working surface temperature to increase and the lubricating oil to lose its effect and cause the bearing to fail. After foreign matter is crushed or embedded in the rolling element, the oil film is quickly damaged, causing the bearing to work under friction and being damaged.

Bearing removal inspection

When the roll is replaced, a cleaning agent can be used to clean the bearing, dry it with compressed air, and then inspect the rolling elements, cage, and raceway. Rolling body, raceway dents, pitting and other phenomena, depending on the circumstances to be replaced. At the same time, if necessary, replace the bearing seal to prevent bearing failure due to poor seal life. If the bearing is badly sealed and the emulsion enters the bearing, it will cause water contamination to the lubricating oil or grease, which will lead to a decrease in the fatigue strength of the bearing material and cause cracks. At the same time, if the seal is poor, the iron oxide skin at the time of rolling enters the bearing and breaks the lubrication conditions, causing the wear particles Worn on the surface of the bearing element.

03、Bearing installation Push-in installation

Push-in installation generally uses a press, but also uses bolts and nuts. When it is necessary to use a hammer to beat, but to pad the inner ring work, this approach has become the main reason for bearing installation damage. Therefore, it is only limited to cases where the amount of interference is small. It cannot be used for large-interference or large- and medium-sized bearings. For non-separable bearings such as deep groove ball bearings, the inner and outer rings require the installation of the interference, and the pads are required to be used. The screw or oil pressure presses the inner and outer rings at the same time. Self-aligning ball bearing outer ring is easy to tilt, even if it is not an interference fit, it is also best to pad the block installation. Cylindrical roller bearings, tapered roller bearings and other separate bearings, can be installed on the inner ring and outer ring to the shaft and shell, and then merge the inner ring and outer ring, the key is to firmly close the two, so that There is no deviation from the center of the two. Pressing in and out will cause a raceway surface card injury.

Hot loading

Large bearings require a lot of force when they are pressed in, and they are difficult to press. Therefore, the bearing heater is generally used to heat the inner ring of the bearing to 100°C~120°C, and the inner ring is quickly inserted into the roller. After installation, the bearing cools down and the width direction also shrinks. Use a shaft nut or other suitable method to tighten it to prevent gaps between the inner ring and bearing shoulders.

04、Mounted bearing inspection Post-installation inspection

After installation of the bearing is completed, in order to check whether the installation is correct, check the operation and confirm that it is smooth by rotating it by hand. There are unsmooth operation due to foreign matter and indentation, uneven rotation torque due to poor mounting, poor seating processing, excessive torque caused by loose clearance, mounting error, and seal friction. If no abnormality can start running. Check for vibrations and sounds, contact with rotating parts, etc. Check that there is no error and then perform power operation. The operation check starts from the no-load low speed and gradually increases to the rated condition operation. The test items in the test run are: whether there is abnormal noise, whether the temperature rise of the bearing is normal, and whether the lubricant leaks or discolors. If there is any abnormality during the test operation, the operation shall be suspended immediately, the equipment shall be inspected, and if necessary, the bearing inspection shall be dismantled.

By analyzing common malfunctions and causes of rolling mill bearings and formulating scientific and reasonable maintenance procedures, it can effectively increase the service life of bearings, reduce the accident rate, reduce the consumption of spare parts, ensure the production time, and provide strong guarantee for cost reduction and efficiency increase.

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