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Analysis of the fracture of the roller journal of the belt conveyor

by:YiFan Conveyor     2021-07-09
Belt conveyors are widely used in food, medicine, tobacco, logistics and other industries due to their advantages such as large capacity, easy installation, and easy protection. Then in the process of use, there will be the cause of the belt conveyor roller journal fracture. Let's analyze it in detail below: 1. Load analysis The belt loading conveyor is driven by the motor through the reducer to roll the automatic roller, and the meshing of a pair of synchronous gears completes the main, The driven roller rolls together, and the static friction between the conveyor belt and the surface of the roller is used to complete the conveying of the loading conveyor belt. During operation, because the roadway is rugged and changeable, the load of the conveyor changes with the change of the slope. At the same time, in the practice of underground production, the size of the coal also changes with the changes of the coal mining surface conditions, which constitutes a conveyor. The load is complex and changeable, and the moment load on the roller shaft is constantly changing, especially in the case of tight parking when the load is heavy, the backstop when the conveyor is reversed, and the forced launching of the heavy load. Under working conditions, the drum shaft has to receive the largest torque and is impactful. If such severe working conditions exist frequently and for a long time, the drum shaft must accept huge and repeated impact loads. Under the effect of impact load, the shaft is prone to failure. When installing, the center lines of the automatic roller and the driven roller must be parallel to each other. Otherwise, the roller shaft must receive radial shear stress. The greater the parallelism error, the greater the shear stress on the roller shaft. 2. Analysis of the cracked surface of the broken shaft. It can be seen from the fracture of the broken shaft that there are two distinct areas on the cracked surface, namely the fatigue cracking zone and the instantaneous breaking zone. Judging from the fracture section, there are significant fatigue streaks in the fatigue area on the fracture. It clarifies that the shaft damage is attributed to fatigue damage. The share of the instantaneous fracture area is about 50%. It can be considered that the overload degree of the shaft is relatively large during the operation. In view of the area, the grinding is relatively rough, indicating that after the fatigue crack occurs, the crack growth rate is too large due to the excessive overload, and the fatigue crack growth period accounts for a small share in the total life. The two sections have not been frictional When entering the transient period, the fracture is fibrous from the transient region, indicating that the final cracking is attributed to resistant cracking. Therefore, it can be judged from the tracing and analysis of the fracture that the shaft cracking is attributed to multi-source fatigue cracking caused by stress concentration. In addition, according to the structural analysis of the broken shaft, it is found that the fillet radius of the 80mm-90mm shaft shoulder transition is small, as long as 2mm-3mm, the stress will be large, which is also one of the important reasons for the early cracking of the shaft. 3. Analysis of steel composition and heat treatment. According to the operating conditions and technical requirements of the belt conveyor roller shaft, combined with the introduction of related materials, the shaft should be made of medium-carbon alloy structural steel with good hardenability, and their hardenability is relatively good. After quenching and tempering, the combination of strength and toughness is better. In order to further improve the fatigue strength, the hardness after heat treatment can be increased to about HB300. In order to smooth the stress concentration at the transition of the shaft shoulder, the fillet radius should be appropriately increased to improve the machine and the quality. During the mid-frequency quenching operation of the keyway, attention should be paid to prevent the heat-affected zone from reaching the transition of the shaft shoulder. If part of the surface roll strengthening is selected to improve the fatigue strength of this area, it can form the surface residual compressive stress that is conducive to the fatigue strength at the fillet transition. . Through the above analysis, the following conclusions can be drawn: 1 The belt conveyor has a large azimuth gradient, a large amount of coal, and frequent heavy-duty parking or starting, so that the shaft receives a large and repeated impact load, and it occurs prematurely. Tired and damaged. It is advocated to shorten the length of the belt loading conveyor as much as possible when using a belt conveyor in a steeply inclined position, and appropriately control the amount of coal, strengthen the handling of the belt conveyor, and prevent frequent parking, especially heavy-duty parking or starting. 2 The quality of heat treatment is poor. The keyway of the shaft needs to be treated by intermediate frequency quenching. Improper operation during quenching makes the transition of the journal change in the heat affected zone of intermediate frequency quenching. The unfavorable residual stress in the heat affected zone and the slight shape change of the shaft The stress at the place is concentrated and superimposed, which is one of the reasons for the fatigue cracking in the early stage of the shaft. It is advocated to improve the quality of heat treatment and prevent the transition of journal change from being in the heat-affected zone of heat treatment.
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