YAN Fangqiang^1a，1b，LI Bo¹，XIA Rui^1a，1b，DONG Yingwei^1a，WANG Xuewen^1a，1b，SHAO Yunliang²

1a. College of Mechanical Engineering，1b. Shanxi Key Laboratory of Fully Mechanized Coal Mining Equipment，Taiyuan University of Technology， Taiyuan 030024， China；2. Jiangsu Asian Star Anchor Chain Co. ， Ltd. ， Taizhou 214533， China

Abstract

Objective Rib spalling is a sudden and frequent issue in coal mining operations, often caused by the working conditions of the scraper conveyor. It leads to localized bulk material accumulation and impacts the conveyor system. This study investigates the effects of rib spalling on coal bulk material and the dynamic performance of scraper conveyor’s chain drive system. By examining variations in rib spalling strength and the falling posture of crushed material, this study aims to reveal their effects on system forces and stability, providing theoretical support for the design optimization of scraper conveyor.

Methods In this study, a fractured rib spalling model was constructed using the discrete element method (EDEM) to simulate the falling process of crushed coal particles and their interaction with surrounding structures. The scraper conveyor was modeled using the multibody dynamics (MBD) method to capture the dynamic response of the chain drive system under impact loading. Then, a rigid-discrete coupling simulation was performed to simultaneously track bulk fragmentation and the resulting force responses. To represent typical coal wall degradation scenarios, three rib spalling strength levels were simulated using the rock integrity coefficient and a quasi-rock strength estimation method. Three distinct falling postures, including normal, reverse, and vertical falls, were considered to evaluate their influence on contact positions and force transmission. Finally, the integrated models were used to obtain the numbers of crushed particles and key dynamic parameters, such as scraper and chain forces in multiple directions, enabling a quantitative analysis of system behaviors under varying spalling conditions.

Results and Discussion The results showed that lower rib spalling strength led to more severe crushing, with a correlation coefficient of -0. 99 between spalling strength and the number of crushed particles. After impact, scraper forces increased to 874. 5, 1 843. 4, and 692 N, respectively, across the three different spalling strength levels, eventually leading to logging. This was due to the accumulation of fine particles between the scraper and the trough, which caused significant force fluctuations in the z-and x-directions. Among the different falling postures, vertical falls caused the smallest spalling volume. The posture of the falling material mainly influenced the dynamic response through changes in impact direction. Normal and reverse falls caused significant impacts in the z-direction between the scraper and the chain ring. Vertical falls caused impacts on the central plate, leading to chain expansion on both sides and affecting x-direction force transmission. The blockage of the gap between the central plate and chain ring by fine particles generated during crushing was the main cause of x-direction force variation.

Conclusion This study reports the effects of different rib spalling strengths and falling postures on coal bulk crushing and dynamic behavior of the scraper conveyor. It is found that the lower rib spalling strength leads to more severe crushing, with the most significant force responses in the z-direction of the scraper conveyor. Both the position and posture of falling particles affect the stability of the chain drive system by influencing the entry of fine particles into critical components. Specifically, low-strength rib spalling and asymmetric falling postures severely exacerbate force fluctuations in the system. The research results provide a theoretical basis for optimizing the design and operation of scraper conveyor.

Keywords：rib spalling; coal crushing; scraper conveyor; chain drive system; coupling simulation

Funding：The research was supported by the National Natural Science Foundation of China （Grant No. 52476157）， the Fundamental Research Program of Shanxi Province （Grant No. 02103021223080 and 202203021221051）， the Teaching Innovation and Reform Project of Higher Education Institutions in Shanxi Province （Grant No. J20240344）， and the Teaching Reform Project for Postgraduate Education in Shanxi Province （Grant No. 2024JG045）.