As an important part of the mine hoist, the head pulley wheel device bears the entire lifting load, which is related to the safety production of the whole mine. The traveling wheel of the head sheave pulley wheel device usually adopts the wear-resistant alloy sliding bearing bush structure. In the process of long-term ore or material lifting, the bearing bush will be worn or burnt, and often needs to be replaced or repaired. Combined with the example of Yunding coal industry in Yimei Coal Mine, the causes of bearing bush damage are analyzed, and effective improvement measures are proposed to prolong its service life.

Bearing bush damage analysis and replacement

1 Structure of head sheave pulley wheel

Most of the multi rope head sheave pulley wheel devices adopt the combined welding structure of hub, rim and channel steel, which is mainly composed of wheel body, crown wheel shaft, bearing seat, bearing bush, bearing, polymer liner, clamp, etc., as shown in Figure 1.

The number of wheel bodies of the multi rope crown wheel is matched with the number of wire ropes of the lifting equipment, which is generally composed of 2, 4, 6 or 8. One wheel body is a fixed wheel, which is connected with the head sheave pulley wheel shaft through a flat key. The rest of the wheel bodies are traveling wheels, which are connected with the head sheave pulley wheel shaft through bearing pads. The main advantage of this structure is that when the linear speed of each steel wire rope is different during the normal operation of the hoisting equipment, the traveling wheels, the traveling wheels and the fixed wheels can rotate each other to prevent the sliding friction between the steel wire rope and the liner, which can extend the service life of the liner and effectively protect the steel wire rope.

1 - head sheave pulley wheel shaft; 2 - Fixed wheel; 3 - Traveling wheel; 4 - Polymer liner; 5 - Bearing bush; 6-Clamp; 7 - Bearing pedestal; 8-Bearing

Through analysis, the direct cause of bearing bush wear or burning is poor bearing bush lubrication. When the bearing bush of the head sheave pulley wheel device is short of oil, when it is running, the formation of the lubricating oil film between the bearing bush and the head sheave pulley wheel shaft is blocked, and the sliding lubrication between the two becomes dry friction. In addition, the bearing bush material is relatively soft compared with the head sheave pulley wheel shaft material, which will cause the bearing bush to wear or burn. At this time, the friction between the head sheave pulley wheel shaft and the bearing pad due to the relative operation is borne by the fixed bolt between the bearing pad and the hub. Under the long-term positive and negative rotation operation and impact, the fixed screw will be gradually cut off. The dry friction between the head sheave pulley wheel shaft and the bearing bush or the extrusion of the sheared screw in the inner hole of the traveling hub will cause abnormal noise when the crown wheel is running.

In addition to wear and burning of bearing bush, it may also cause scratches due to solid debris, as shown in Figure 3. The main reason for this result is that there are bumps on the shaft or burrs between the shaft and the bearing bush are not cleaned up during installation, which fall off and mix  with lubricating oil during work. Secondly, if the grease is used for a long time and is often operated under high load and high temperature, the impurities in the grease will increase and these impurities will also scratch the bearing bush.

Preventive measures for bearing bush damage

(1) Solve the lubrication problem of bearing bush. The scheme mainly includes: ① increase the oil storage capacity of the bearing bush oil groove, and replace the screw inside the existing bearing bush.

The oil tank is changed into a longitudinal and transverse staggered structure (i.e., "well shaped" structure). As shown in Figure 5, the oil storage capacity of the "well shaped" bearing pad structure is more than 3-5 times that of the spiral structure; ② Shorten the oiling period of bearing pads. Due to the high derrick of the crown wheel, manual oil gun injection is time-consuming and laborious, and the maintenance time is long. It is considered to use the automatic oiling device of the crown wheel, which is convenient and fast; ③^ Select the appropriate brand of lubricating oil and ensure the purity of lubricating oil during installation and filling. There are many types of lubricating oil in the market. It is recommended to use No. 2 lithium base grease or its equivalent.

(2) Improve the material performance of bearing bush. The ordinary copper alloy bearing bush is replaced by graphite inlaid copper bush, which can achieve self-lubricating effect and prolong the service life of the bearing bush when the runner is short of oil, as shown in Figure 6

(3) Prevent the connecting bolts of bearing shells from being cut off. The main schemes are as follows: ① Increase the number of connecting bolts of bearing pads to improve the strength of connecting bolts; ② Add locating blocks at the flange end of bearing pads to reduce the force on the connecting bolts, as shown in Figure 7; ③ Improve the processing technology of bearing pads, so that there is no gap after the installation of two petal bearing pads; ④ Increase the thickness of the bearing bush to ensure that the fit clearance between the inner surface of the bearing bush and the shaft reaches the specified value.

4 Conclusion

As the main force bearing component of the lifting system, the use and maintenance of the bearing bush of the head sheave pulley wheel device is particularly important. Combined with the case of Yunding Coal Industry, this paper analyzes the causes of bearing bush damage, and formulates corresponding preventive measures, which greatly extends the service life of bearing bush and reduces the economic losses caused by bearing bush replacement.