For armoured face conveyors (AFC) in coal mines, fracture and jam phenomena of the chain are common failure patterns in the chain assembly. These failure patterns are caused by chain's severe vibrations from uneven loads on the conveyor. However, due to limitations of harsh operating environment in coal mines, performing underground experiments is difficult to obtain real vibration signals. Multi-body dynamic simulation is an efficient approach to analyse the complex dynamic behaviour of chain assembly in the AFC. In order to determine the actual dynamic properties of chain assembly in the AFC under different operating conditions, multi-body simulation was used to analyse the vibration properties of the chain assembly. In this study, theoretical analysis of contact force between horizontal and vertical rings, and between sprocket wheel and rings in the chain assembly was initially performed. Rigid and rigid-flexible coupling models of the chain assembly were then established. Dynamic simulations through two types of models, that is, rigid and rigid-flexible coupling models were conducted under full-, half-and empty load conditions using the ADAMS software. Trends of contact force, stress, and velocity of horizontal and vertical rings under various working conditions were obtained, and vibration properties of the chain assembly were analysed based on the corresponding curves. Results indicate that the maximum velocity is 1.75 m/s in the rigid simulation, whereas the maximum velocity is 3.0 m/s in the rigid-flexible coupling simulation. The rigid-flexible coupling method is proven to be more accurate and feasible in describing the dynamic properties of the chain assembly than the rigid method. The proposed method should be preferentially utilized in performing multi-body dynamic simulation of the chain assembly in the AFC. This study provides references for the structural optimization and design of the chain assembly in mining AFC.

The effects of the spiral line for pick arrangement on the cutting load of a boom type roadheader's cutting head were investigated. For this purpose, cutting heads with equal and unequal pitch angle and various numbers of spiral lines were designed for the same cutting head body. The cutting head with unequal pitch angle of spiral lines was specifically designed to avoid tool-holder overlap at the top section without adjustments and reduce the manufacturing difficulties. The cutting process of different cutting heads were simulated by finite element method using ANSYS/LS-DYNA and the time history curve of the traversing force, vertical force, axial force, and resultant force on the cutting head were obtained. The results indicate that the load stability of the cutting head with unequal pitch angle was worse than the equal pitch angle cutting head. For cutting heads with various numbers of spiral lines, the head with 3 spiral lines shows the best performance, considering the force values and fluctuations of the cutting head. The analysis provides a reliable basis for optimization of the design of boom type roadheader cutting heads.

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The chain drive system is the most important subsystem in a mining scraper conveyor. Compared with the general chain drive system, that in a scraper conveyor is highly coupled. The rings on a chain come in contact not only with the sprocket wheels but also with the central chutes and scrapers. In order to improve the reliability of the scraper conveyor, a contact analysis of the chain drive system based on its meshing properties was performed. Vogit model-based translational and rotating models of the chain drive system were first introduced. A finite element model of the chain drive system was then established. Contact simulations were conducted using the software LS-DYNA. Von Mises stress and contact pressure curves on various dangerous areas of the horizontal ring, vertical ring, and sprocket wheel were obtained. The von Mises stress and the contact pressure of the rings and the sprocket wheel were compared, and their differences were analysed. Results indicate that the maximum contact pressure for the horizontal and vertical rings is considerably larger than the maximum von Mises stress. The maximum contact pressure for the horizontal ring exceeds 2000 MPa, which is 90 % larger than the von Mises stress (1100 MPa). Meanwhile, the contact pressure for the sprocket wheel is considerably less than the von Mises stress. Therefore, the failure mode of the rings and the sprocket wheels differs. Contact analysis based on meshing properties is useful in describing the dynamic properties of the chain drive system in detail. This study provides guidance for overcoming chain break and jam problems in scraper conveyors.

The scraper conveyor is the unique transport equipment in coal mining face. Its chain drive system is the core subsystem. The dynamic characteristics of the chain drive system need monitoring for a safe mining. Existing monitoring methods include controlling the chain tension, chain speed and motor current. However, the above-mentioned methods have many disadvantages, such as difficult and costly to implement in mining face, due to the poor working environment and the limitations of the scraper conveyor's structure. This study proposes a monitoring method for the dynamic characteristics of the scraper conveyor on the basis of the speed difference between the head and the tail sprockets. Such an initiative is carried out to study the dynamic characteristics of the scraper conveyor under real working conditions and describe its running state. The speed difference of the head and tail sprockets under different chain speeds, terrains, and loads is monitored and studied. Research results show that the average and maximum speed differences are 0.797% and 0.990%, respectively. Due to the complex terrain, the tighter the scraper chain gets, the smaller the difference of the rotational speed is, compared with the flat working condition. The speed difference under load greatly increases compared with no load. Research results provide data support for the research of the chain drive system dynamics of the scraper conveyor. These results will also provide a new idea for the monitoring of the operating state of the scraper conveyor.

The cutting unit of a mining shearer is composed of a drum, gear transmission and hydraulic height adjusting mechanism. To obtain the dynamic characteristics of crucial components in the coal cutting process, a model of a drum cutting coal was constructed using LS-DYNA. The model of gear transmission was constructed with Adams, and a model of the hydraulic height adjusting system was constructed with AMESim. Data transmission and co-simulation of these three models were implemented with MATLAB. Changes of the meshing force, acceleration and amplitude-frequency characteristics of key gears under different conditions were obtained. From the research, we conclude that it is effective and feasible to apply the multi-software co-simulation used by this paper to research a complex mechanical-hydraulic system such as a shearer cutting unit; supports from a hydraulic cylinder can decrease the meshing force of gears to some extent; and the meshing force of gears increases significantly as the mining height of the drum increases.

The scraper conveyor is the key coal transportation equipment on the coal mining face. The conveyor often encounters the influence of abnormal working conditions, such as stuck chains, broken chains, and impact loads, which have a great effect on the smooth operation of the scraper chain and seriously affect the safety of coal production. If the chain breaks during the test, the broken link may fly out and hurt the tester. The test risk of the scraper conveyor under abnormal working conditions is relatively large; hence, the test research is impossible to carry out. The combination of experiment and simulation is used to carry out the research. The dynamic characteristic test bed of the chain drive system is created to collect the speed of the sprocket and the acceleration of the scraper. The two groups of data are obtained by simulation, and the accuracy of the simulation is verified by comparing the test data with the simulation data. The dynamic characteristics of the chain drive system under abnormal working conditions are analyzed by simulation. Results show that the longitudinal velocity of the link dramatically changes, the contact force increases by 5.4 times, and the link vibrates under impact loads. When the chain is stuck, the speed of the running direction suddenly changes, and the chainring vibrates. The contact force between the chainrings increases by 7.2 times compared with the smooth operation. When the chain is broken, the acceleration in the running direction of the link dramatically changes. This study provides a basis and reference for the further optimization design of the chain drive system and detection of the abnormal working conditions.

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