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Bearing science - bearing inspection

Bearing science - bearing inspection

2021-07-20

Check the vibration of bearings and the temperature of bearings

First, the vibration of bearings

Bearing vibration is very sensitive to bearing damage, such as peeling, indentation, rust, crack, wear, and so on will be reflected in the bearing vibration measurement, so, using a special bearing vibration measurement device (frequency analyzer, etc.) can measure the size of vibration, through the frequency can not infer the specific situation of abnormal. The measured values are different due to the use conditions of bearings or the installation position of sensors, etc., so it is necessary to analyze and compare the measured values of each machine in advance to determine the judgment standard.

Two, the temperature of the bearing

The temperature of the bearing can generally be inferred by the temperature outside the bearing. If the oil hole can be used to directly measure the temperature of the bearing outer ring, it is more appropriate.

Usually, the temperature of the bearing begins to rise slowly with the operation of the bearing and reaches a stable state after 1-2 hours. The normal temperature of the bearing is different due to the heat capacity, heat dissipation, speed, and load of the machine. If the lubrication and installation department is appropriate, the bearing temperature will rise sharply, and there will be abnormal high temperatures. At this time, the operation must be stopped and the necessary preventive measures must be taken.

The use of thermal sensors can monitor the working temperature of bearings at any time, and realize automatic alarm or stop when the temperature exceeds the specified value to prevent the occurrence of burning shaft accidents. The high temperature often indicates that the bearing has been in an abnormal situation. High temperature is also harmful to the lubricant of bearings. Sometimes bearing overheating can be attributed to the lubricant of the bearing. If the temperature of the bearing exceeds 125℃ for a long time, the life of the bearing will be reduced. Causes of high-temperature bearings include insufficient lubrication or excessive lubrication, lubricant. It contains impurities, excessive load, damaged bearing ring, insufficient clearance, and high friction caused by oil seal, and so on. Therefore, it is necessary to continuously monitor the bearing temperature, whether measuring the bearing itself or other important parts. If the operating conditions are unchanged, any temperature change may indicate a failure.

Regular measurement of bearing temperature can be made with the help of thermometers, such as SKF digital thermometers, which can accurately measure bearing temperature and display in units according to ℃ or Fahrenheit temperature. The importance of bearings means that when damaged, it will cause the shutdown of the equipment, so it is best to install a temperature detector for this kind of bearings. Under normal circumstances, the bearing will have a natural temperature rise after fresh lubrication or re-lubrication and last for one or two days.

Check the rolling sound of bearings

The sound meter is used to check the size and sound quality of the rolling sound of the bearing in operation. Even if the bearing has slight damage such as peeling, it will emit abnormal and irregular sounds, which can be distinguished by the sound meter. Hearing is a common way to identify irregular movements. For example, detecting the abnormal noise of a part with an electronic stethoscope is often used by experienced operators. If the bearing is in a good continuous state, it will emit a low whine sound. Sharp hissing, squeaking, and other irregular sounds often indicate that the bearing is in poor continuous rotation. The shrill squeaking noise may be due to improper lubrication. Improper bearing clearance can also cause metallic sound. 


The dent of the concave track on the bearing outer ring track will cause vibration and cause smooth and clear sound. If the knocking scars caused by the installation will also produce noise, the noise will vary with the height of the bearing speed. If there is intermittent noise, it means that the rolling parts may be damaged. This sound occurs when the damaged surface is rolled, and contaminants in the bearing often cause a hissing sound. Severe simultaneous damage can produce irregular and loud noises. Bearing damage can be detected by hearing, but usually at this time has arrived the bearing must be replaced immediately. Therefore, a better approach is to use Electronic Condition Monitoring such as SKF. Compared with the old method of using a stick or screw screwdriver against the bearing box and the other end against the ear, the new invention ensures a safer and more accurate estimation of the bearing condition

Stop inspection of rolling bearing

\ Regular inspection of bearing seal is very important to maintain the bearing in the best condition. The most favorable inspection time is scheduled during the regular downtime inspection period. Importance of clean bearings: It is important to keep bearings and lubrication clean. Clean the surface of the machine before inspection, and then remove the parts around the bearing. 


The oil seal is a very fragile part, so it needs to be carefully removed, do not apply excessive force, and then carefully check the oil seal and its surrounding parts, if it has shown bad symptoms, be sure to replace, bad oil seal will lead to bearing damage and lead to equipment shutdown. Check the lubricant and rub the lubricant between the two fingers. If there are pollutants, you can feel them. Or apply a thin layer of lubricant on the back of the hand, and then seal the light for inspection. Replace Lubricant Oil Lubricant bearings After removing the old oil, if possible, fill in fresh oil and let the machine run at low speed for a few minutes. 


As far as possible, make the oil collect residual contaminants, and then remove the oil. It is best to filter the oil before use. Grease lubricated bearings should be avoided with cotton contact with any part of the bearing when replacing the grease, because these residual fibers may wedge into the rolling parts and cause damage, especially the application of small bearings need to pay more attention to this problem. When inspecting the bearing, do not expose the bearing to pollutants or moisture. If work is interrupted, the machine should be covered with oil-paper plastic film or similar material. If the unmasked bearing is cleaned without disassembly and inspection may be performed, it shall be cleaned with a coating brush coated with petroleum spirit and then dry with a non-pilling cloth or blow dry with compressed air (be careful not to allow the bearing assembly to start rotation). 


The track surfaces, retainers, and beads of bearings are examined with a small mirror and a probe similar to that used by dentists. If the bearing is not damaged, re-lubrication should be performed according to the lubrication instructions provided by the machine manufacturer or as recommended on pages 204 to 247 of this book. Do not clean the bearings with encrypted caps or dustproof; Just wipe the outside surface. If the bearing is damaged, it needs to be replaced. Replacing bearings during regular downtime is far more economical than the loss of sudden downtime caused by bearing damage.

bearing inspection

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