1. Requirements for monitoring rolling bearings using magnetic plugs

(1) Magnetic plugs are only suitable for monitoring critical main bearings that are oil-lubricated and have oil returning via dedicated return lines.

(2) Magnetic plugs should be installed as close as possible to the main bearing being monitored, situated on the main return line, without any obstruction from filters, oil pumps or other hydraulic components.

(3) To improve monitoring efficiency, a swivel-type oil reservoir with return inlets and outlets may be fabricated. The reservoir should be designed as an inverted frustum of a cone, with the magnetic plug installed at the base. The inlet of the reservoir should be angled to allow the lubricating oil to enter tangentially. This facilitates the separation of wear particles from the circulating lubricating oil, allowing them to settle at the bottom, pass through small holes into the magnetic plug, and be adsorbed onto the ends 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 the wear particles generated is generally 0.01–0.015 mm, mixed with some metal powder. New bearings produce a greater quantity of abrasive particles during the running-in period than during normal operation; once normal operation is established, the quantity of abrasive particles and metal powder decreases significantly. Under a microscope, the abrasive particles appear fine and short in shape, with irregular cross-sections.

3. Morphological characteristics of failure-related abrasive particles

The primary failure mode of rolling bearings is fatigue pitting. Particles formed by rolling fatigue and spalling are generally 0.025–0.05 mm in size, though larger fragments may occasionally be present, mixed with some metal powder. Particles from the balls in ball bearings typically appear roughly circular, arranged in a radial pattern resembling rose petals; particles from the raceways appear as roughly circular fragments with fractured surfaces; In roller bearings, the fragments from the rollers usually take the form of curled rectangles with a length equal to 2–3 times their width; the fragments from the raceways generally appear as irregular rectangles.

The fundamental performance requirements for materials used in rolling bearings depend on the operating characteristics of the bearing. Generally speaking, steel for bearing manufacture should possess the following properties:

1. High contact fatigue strength.

2. High wear resistance.

3. High elastic limit and yield strength.

4. High and uniform hardness.

5. Adequate impact toughness.

6. Good dimensional stability.

7. Good corrosion resistance.

8. Good machinability.

For bearing materials operating under special conditions, they must also possess specific properties suited to those conditions, such as resistance to high temperatures, low temperatures, corrosion, radiation and magnetism.