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Easy Diagnosis of Bearing Status


1、 Monitoring  bearings by auscultation


By using the auscultation method to monitor the working condition of bearing. The common tool is a wooden handle long screw driver. you can also use a hard plastic tube with an outer diameter of about φ20mm. Relatively speaking, monitoring with an electronic stethoscope is more conducive to improving the reliability of monitoring.
1) Sound characteristics of bearing in normal working condition
When the bearing is in normal working condition, the operation is smooth, brisk, and there is no stagnation. The sound is harmonious and no noise, and a uniform and continuous “beep” sound or a low “boom” sound can be heard. The noise intensity is not large.
2)  Bearing failure reflected by abnormal sound
(1)The bearing emits a even and continuous "sisi" sound, which is generated by the rolling element rotating in the inner and outer rings and contains irregular metal vibration sounds independent of the rotational speed. Generally, the amount of grease in the bearing is insufficient and should be supplemented.
If the equipment is down for long time, especially in low temperature conditions in winter, the sound of “sa sa” will sometimes be emitted during the bearing operation, which is related to the smaller radial clearance of the bearing and the smaller penetration of the grease. The bearing clearance should be properly adjusted to replace the new grease with a larger penetration.
(2)The bearing emits a uniform periodic "huahua" sound in a continuous "click" sound, which is caused by scratches, grooves, and rust spots on the rolling elements and the inner and outer ring raceways.
(3)The period of the sound is proportional to the speed of the bearing. Bearings should be replaced
The bearing emits a discontinuous "stalk" sound that is caused by the rupture of the cage or the inner and outer rings. The bearing must be replaced immediately.
(4) The bearing emits an irregular, uneven “beep” sound, which is caused by impurities such as iron filings and sand particles falling inside the bearing.The sound intensity is small and has no connection with the number of revolutions. The bearings should be cleaned, regreased or oil changed.
(5)The bearing emits a continuous and irregular "sasa" sound, which is generally related to the loose fit of the inner ring of the bearing and the shaft or the loose fit of the outer ring with the bearing hole. When the sound intensity is large, the bearing coordination should be checked and the problem should be repaired in time.

(6)The bearing emits a continuous squeaking noise. This sound is caused by poor lubrication of the bearing or lack of oil, or partial contact of the rolling element, such as the deflection of the inner and outer ring raceways, and the tightness of the inner and outer rings of the bearing. . The bearings should be inspected in time to identify the problem and treat it symptomatically.


3)Requirements for monitoring using an electronic stethoscope


(1)During the monitoring process, similar monitoring points should be selected as much as possible, or monitoring points with close working conditions should be used to compare the sounds. It is found that the abnormalities should be treated as defective and must be inspected in depth. For a single device, in order to overcome the incompatibility shortcomings, the sound recording of the monitoring point under normal conditions can be used as a comparison basis for future monitoring.
(2) Select the location of the monitoring point, the vibration direction to be measured should be consistent with the sensitive direction of the sensor, so that the measurement direction is the direction with the largest vibration intensity. The sensor should be at right angles to the surface to be measured, and the error should be controlled within 10°.
(3) The measuring surface is required to be clean and flat, so that there is no rust and no paint, and the concave portion is polished to make it smooth and flat.

(4)The measuring force of the pressure probe is preferably 10-20N.


3、Monitoring of  bearings by measurement


 By measuring the temperature rise during bearing operation, it is generally difficult to monitor local damage such as fatigue flaking, cracks or indentations, especially in the early stages of damage. When the bearing rises after a long period of normal operation, the problem generally reflected is not only quite serious, but also rapidly develops, causing bearing damage failure. At this time, intermittent monitoring often leads to leakage. If the temperature of the bearing is more than 70-80 °C during the monitoring, stop the inspection immediately.
 For newly installed or re-adjusted rolling bearings, the temperature rise of the new ones can be monitored by the temperature measurement method to judge the installation and adjustment quality of the bearings, especially if the clearance is too tight. . The timely adjustment of the problem is found to help extend the service life of the rolling bearing.

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