Monitoring Rolling Bearings with the Magnetic Plug Method:
1. Requirements for Monitoring Rolling Bearings with Magnetic Plugs
(1) Magnetic plugs are only suitable for monitoring key main bearings that are lubricated with oil and have oil returned through dedicated pipelines.
(2) Magnetic plugs should be installed as close as possible to the monitored main bearings, on the main oil return passage, without being obstructed by oil filters, oil pumps or other hydraulic components in between.
(3) To improve monitoring efficiency, a rotary oil storage tank with an oil return inlet and outlet can be fabricated. The tank should be made into an inverted conical platform, and the magnetic plug should be installed at the bottom of the tank. The oil inlet of the tank should be inclined at a certain angle to allow lubricating oil to enter tangentially. This helps to separate wear particles from the rotating lubricating oil and facilitate their precipitation at the bottom. The particles enter the magnetic plug through a small hole and adhere to the end of the magnetic steel.
2. Morphological Characteristics of Wear Particles Under Normal Conditions
During the running-in period and normal operation of rolling bearings, the size of generated wear particles is generally 0.01-0.015 mm, mixed with a small amount of metal powder. The quantity of wear debris generated by new bearings during the running-in period is higher than that during normal operation. After entering the normal operation period, the quantity of wear debris and metal powder will decrease significantly. Under a microscope, the wear debris presents an elongated shape with an irregular cross-section.
3. Morphological Characteristics of Defective Wear Particles
The main failure mode of rolling bearings is fatigue pitting. The size of wear debris formed by rolling fatigue and spalling is generally 0.025-0.05 mm, and sometimes large debris is mixed with a small amount of metal powder. The wear debris from steel balls of ball bearings is generally approximately circular, showing a rose petal shape with radial separation; the wear debris in raceways presents a roughly circular surface fracture form; the wear debris of roller bearings is generally rectangular, with a length 2-3 times the curled width; the wear debris in raceways is usually irregularly rectangular.
Precautions for Monitoring Rolling Bearings with the Temperature Measurement Method:
By measuring the temperature rise of bearings during operation, it is usually difficult to monitor local damages in rolling bearings such as fatigue spalling, cracks or indentations, especially in the early stage of damage, where it is almost impossible to detect any problems. When the temperature of a bearing rises after long-term normal operation, the reflected problems are usually not only severe but also develop rapidly, leading to bearing damage and failure. Intermittent monitoring at this time often results in missed detection. If the bearing temperature exceeds 70-80℃ during monitoring, the equipment should be shut down for inspection immediately.
For newly installed or readjusted rolling bearings, the temperature measurement method can be used to monitor the temperature rise within a specified period to determine the quality of bearing installation and adjustment, especially in cases where excessive tight clearance may cause an abnormal temperature rise. Timely adjustment upon discovering problems helps to extend the service life of rolling bearings.
