During the operation of the equipment, when abnormal friction occurs on the relative moving metal surface, wear particles will be produced and fall into the oil tank. Therefore, the wear particles are directly related to the abnormal operation of the fan gearbox and are the reflection of the internal wear information of the equipment. Ferrography analysis technology can identify the type of wear particles, count the number of wear particles, and then evaluate the wear status and operation status of mechanical equipment.

According to the shape, texture and color of wear particles, the ferrographic wear particles in gear box can be divided into five categories.

(1) normal particles. The normal wear particles are lamellar with smooth surface, and the long axis size is 0.5-15 μ m, or even smaller, as shown in Fig. (a). Normal wear particles are particles produced on the surfaces of two friction pairs of gearbox under normal sliding wear mechanism, which have little effect on the gearbox.

(2) fatigue particles. The fatigue wear particles are flat and flake, the size is more than 15 μ m, the surface is smooth, and the contour is randomly zigzag, as shown in Fig. (b). When a large number of the abrasive particles appear, the gearbox has failed and should be shut down for maintenance.

(3) sliding particles. The size of the long axis of the sliding abrasive is generally more than 15 μ m, and there are scratches on the surface, as shown in Fig. (c). The appearance of the wear particles indicates that the gear is abnormal between the pitch line and the tooth root, and between the pitch line and the tooth top. It is necessary to further inspect the gearbox by combining with other methods such as vibration signal analysis.

(4) cutting particles. The average width of the particles is 2-5 μ m, as shown in figure (d). It is a sign of abnormal wear of equipment friction pair that there are more cutting abrasive particles in gear box. At this time, the internal lubricating oil contains more impurities, so it is recommended to replace the lubricating oil.

(5) oxide particles. The oxide wear particles are black particles, as shown in figure (E). When a large number of oxide wear particles appear, the gearbox has poor lubrication and serious corrosion, and its internal lubricating oil is insufficient, so it needs to be injected with lubricating oil.