A scraper conveyor is a continuous transportation equipment that conveys bulk materials by means of a moving scraper chain. The SGB-520/22 scraper conveyor is mainly used for transportation in economic common mining faces of medium and low thick coal seams. This product features a compact and simple structure, smooth transmission, convenient installation and maintenance, reliable operation, and flexible process layout. It can not only convey horizontally but also at an incline. It can be used either as a single machine or in combination with multiple units. The sprocket is one of the important components of the scraper conveyor, and its characteristics have a direct impact on the service life of the scraper conveyor. The sprocket drive used in the sprocket wear analysis is a common traction sprocket, which has a relatively large sliding motion at the meshing point. Under harsh working conditions, it will cause relatively severe wear.
The reasons for the severe wear of the scraper sprocket chain socket are as follows:
The greater the adhesive wear load and the higher the surface temperature, the more severe the adhesion phenomenon will be.
For metallic materials of a certain hardness, wear tests conducted under different pressures obtained the curve graph of the relationship between the wear rate and the pressure. When the pressure reaches more than one-third of the material’s hardness, severe wear will occur. According to the stress distribution map, it can be known that the contact point of the maximum stress is the place with the maximum pressure, and its value is 884.4 MPa. Since the quenching hardness at the chain socket is HRC48 to 52, the corresponding hardness value is 4800MPa. Therefore, the pressure is far less than one-third of the material’s hardness, so adhesive wear is not the main form of scraper sprocket wear.
Contact fatigue wear
The friction pair between the scraper sprocket and the chain is under alternating contact stress, and fatigue pitting corrosion is prone to form on its friction surface. The indicator for judging the contact fatigue strength of metals is the contact fatigue limit, which is the maximum stress at which pitting corrosion does not occur under a certain number of stress cycles. After surface quenching treatment, the contact fatigue limit σ0H of 40Cr is HRC17 +200, and the calculated σ0H is 1016MPa. According to the stress distribution diagram, it can be known that the maximum stress value of the scraper sprocket chain socket is 884.4 MPa. Its value is very close to the contact fatigue limit allowed on the surface of the scraper sprocket. At the maximum stress, it is relatively easy to cause pitting failure. However, due to the poor lubrication conditions of the sprocket and the chain, pitting corrosion cannot form in time and has already caused wear. At this point, the main form of damage is wear rather than pitting corrosion. Contact fatigue wear is the main form of sprocket wear, which basically determines the service life of the scraper sprocket.
Abrasive wear
As the chain inevitably comes into contact with pulverized coal, a small amount of pulverized coal adheres to it and is carried to the contact point of the scraper sprocket chain socket. The pulverized coal contains a little sharp and hard sand, which will cause the surface material of the scraper sprocket to fall off during the friction process. This is abrasive wear. Abrasive wear is related to the hardness of the friction material and the hardness of the abrasive. From the graph showing the influence of abrasive hardness on wear, it can be seen that when the hardness of the abrasive approaches that of the friction material, it causes high-speed wear of the friction material. As the coal powder is mixed with a small amount of sharp and hard sand, this is also one of the main reasons for accelerating the wear of the scraper sprocket.
Corrosion wear
In addition to the adhesive wear, contact fatigue wear and abrasive wear mentioned above, the scraper sprocket may also be affected by corrosion wear. In some coal mining faces, the environment may be relatively humid and there may be some corrosive substances. For instance, the sulfur element contained in coal may form acidic substances under specific conditions. When the scraper sprocket is exposed to such an environment for a long time, chemical reactions will occur on its surface, causing the metal material to gradually corrode and thereby weakening the strength and performance of the sprocket. Corrosion and wear can make the surface of the scraper sprocket rough and uneven, not only accelerating the occurrence of other forms of wear, but also possibly causing fatigue cracks in the sprocket, further shortening its service life.
The manufacturing process and installation accuracy impact on wear
In addition, the manufacturing process and installation accuracy of the scraper sprocket will also have a significant impact on wear. If there are processing errors in the manufacturing process of the sprocket, for instance, the precision of the sprocket tooth profile is not high, it will lead to an unsmooth meshing between the scraper sprocket and the chain, increasing additional friction and stress concentration, thereby accelerating wear. Similarly, during the installation process, if the installation position of the sprocket is inaccurate or the tension of the chain is inappropriate, it will also cause the sprocket to bear uneven loads, leading to accelerated local wear. Therefore, during the design, manufacture, installation and maintenance of the sprocket, every link needs to be strictly controlled to reduce wear, extend the service life of the sprocket, and thus ensure the stable operation of the scraper conveyor.
In Conclusion
The scraper conveyor, as an important conveying equipment in the economic common coal mining face of medium and low thick coal seams, has many advantages such as compact structure and smooth transmission. However, the wear problem of its key component, the scraper sprocket, is rather prominent, directly affecting the service life and operational reliability of the equipment. The main forms of scraper sprocket wear include contact fatigue wear and abrasive wear. Meanwhile, adhesive wear has a relatively small impact under specific conditions, while corrosive wear cannot be ignored in specific environments such as humidity. In addition, the manufacturing process and installation accuracy of the scraper sprocket will also have a significant impact on wear.
Contact fatigue wear is caused by the fact that the surface of the scraper sprocket and the chain is prone to fatigue pitting under alternating contact stress. Although it is mostly manifested in the form of wear due to poor lubrication conditions, it is still the main factor determining the service life of the scraper sprocket. Abrasive wear is caused by sharp sand particles contained in the coal powder carried by the chain, which cause the surface material of the sprocket to fall off during the friction process. To reduce the wear of the scraper sprocket and extend the service life of the equipment, it is necessary to strictly control each link in the process of design, manufacturing, installation and maintenance, optimize the working environment of the scraper sprocket, improve its wear resistance, and ensure the stable and efficient operation of the scraper conveyor in coal mining work.
