Mechanical wear and chemical corrosion are common in rotating machinery and are the main loss factors of its components, and there is a special loss phenomenon that does not belong to mechanical wear and chemical corrosion, but is related to discharge.
When the shaft current generated by the instantaneous excessive current or unbalanced magnetic field passes through the bearing, when the voltage between the bearing ring and the rolling element once exceeds the insulation breakdown threshold, the current passes through the rolling element and the lubricating oil film, and is transmitted from one ring of the bearing to the other, and a concentrated discharge occurs in the contact zone between the ring and the rolling element, resulting in local heating in a very short time interval, so that the contact area melts and welds together.
This trace of attrition is generally in the following two states:
1.Scrub-likeThis trace often appears on the surface of bearings, sealing rings, thrust rings, and journals, and sometimes this kind of trace appears on the gear teeth, and when this trace appears in a large area, the surface of the component loses its metal luster, as if it has been oxidized;However, in the early stages of such marks, it is difficult to distinguish with the naked eye under a microscope of 50 to 100 times, this kind of scar is a small pit one by one, the inner wall of the pit is smooth and shiny, which is different from mechanical wear and chemical corrosion, it is obviously a trace of melting, and only the instantaneous high heat caused by partial discharge can produce this phenomenon.
2.Scratch-likeThis kind of scratch is very similar to mechanical scratch in appearance, but it is different from mechanical scratch, which has angular scratches at the turn, and ordinary mechanical scratches caused by small particles cannot have such a sudden turn, and it can be found under the microscope that the bottom of this scratch is also smooth and shiny, and the depth of similar scratches in a certain area is roughly the same;The inside of mechanical scratches is usually not very smooth, and the shades are different, indicating that the scratches are produced by high heat melting, and are also caused by electrical discharge.
Shaft currents can electrolyze the motor or bearing, causing damage to the bearing, and can also ionize the grease inside the bearing, causing the grease to degrade and fail. The degree of bearing damage depends on factors such as bearing type, current intensity, duration, bearing load, bearing clearance, rotational speed and lubricant.
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