Introduction: In existing coal enterprises, many medium-sized mines use inclined shaft tandem hoisting as the main hoisting method. Due to the high equipment turnover rate and frequent lifting, there are generally various hidden dangers that restrict and threaten mine safety production, such as low transportation efficiency and high accident rate. Problems of Inclined Shaft Tandem Hoisting 1. Introduction to Inclined Shaft Tandem Hoisting System Inclined shaft tandem hoisting is a multi-level, multi-plate hoisting system. In mines built in the 1970s and early 1980s, the main hoisting was mostly inclined shaft tandem hoisting and inclined shaft skip hoisting (see Flowchart 1 of Inclined Shaft Tandem Hoisting System). After the coal from the working face is transported to the coal storage bins at each level, it is loaded into mine cars through the loading port, transported by locomotives in the horizontal roadway, and then hoisted to the surface by multi-level, multi-plate hoisting of the inclined shaft winch. Then, the dispatching winch pulls it to the surface, where it is tipped over in a cage, and finally, it is screened into the bin by the coal preparation belt. 2. Insufficient hoisting capacity, high production accident rate, and the inability to pull out coal are prominent problems of inclined shaft tandem hoisting. Take the Meihe Coal Mine No. 3 of Liaoyuan Mining Group as an example. The mine began production in 1978, with a designed annual output of 450,000 tons. It has two shafts: the main hoisting shaft has an inclination angle of 23 degrees and uses a double-hook tandem hoisting system. The auxiliary shaft also has an inclination angle of 23 degrees and is responsible for transporting personnel, unloading materials, hoisting gangue, and serving as a return air shaft. From its commissioning until a system upgrade in 1992, the mine's output increased year by year, averaging 830,000 tons per year. With over 800 cars pulled by shifts and nearly 10,000 operations, the long-distance transportation led to frequent accidents, resulting in coal shortages. The accident rate hovered between 7% and 15%, severely impacting and restricting the mine's production. 3. Inclined shaft tandem hoisting, due to its complex processes, numerous pieces of equipment, and long transport distances, also presents another negative problem: a large number of workers and high costs for track and equipment maintenance. The 450,000-ton mine had over 300 mine cars, locomotives, and various specialized equipment specifically for hauling coal, along with over 2,000 meters of transport railway. The annual maintenance costs and equipment wear and tear of various equipment exceed 1.2 million yuan. Furthermore, many aspects of the inclined shaft hoisting system only perform useful work when heavily loaded; nearly half of the electrical and mechanical power consumption is wasted when unloaded. These high costs and ineffective losses significantly increase the costs of the coal industry. 4. The most serious problem with inclined shaft hoisting is safety. Ensuring safe production is the primary task in coal production. The high-frequency turnover and complex procedures of the equipment in the inclined shaft hoisting system pose a significant threat to the personal safety of transportation workers who are constantly working around the vehicles. During operation, the connecting pins are frequently inserted and removed thousands of times, and the winch hooks are swung and attached hundreds of times. Inevitably, loose pins and unreliable connections occur. Due to inadequate maintenance of hundreds of mine cars and thousands of meters of railway, derailment and runaway accidents are impossible to prevent. Taking the No. 3 mine as an example, according to mine history records, in the 15 years before the 1992 renovation, there were 11 runaway accidents and 16 serious personal injury accidents. The numerous problems existing in inclined shaft hoisting systems have rendered them inadequate for rapidly developing production needs. Bottlenecks affecting production, substantial costs, and serious safety threats have compelled enterprises to seriously consider system upgrades. Advantages of using steep-angle belt conveyors for upgrades: 1. Introduction to Steep-Angle Belt Conveyor Systems: Steep-angle belt conveyors are a type of continuous transport equipment widely used in newly built mines. They use steel wire rope core belts as the traction mechanism and load-bearing body. They offer high belt strength, long transport distances, large transport capacity, simple equipment, and smooth start-up, making them the preferred equipment for inclined shaft upgrades. Their rotation system is shown in Figure 2. The belt conveyor consists of the following parts: Drive unit—motor, coupling device, reducer, main drive drum, and idler drum. The unloading section consists of an unloading drum, a sweeper, and a magnetic separator. The middle section includes a wire rope core conveyor belt, idlers, a frame, and a belt breakage protection device. The tail section consists of a tail drum, a tail frame, and a tensioning trolley. The conveyor belt winds around the drive drum, redirecting drum, tail tensioning redirecting drum, unloading drum, and drive drum, forming a loop supported by the frame and idlers to achieve uninterrupted continuous transport. 2. The steep-angle belt conveyor has a large transport capacity and long transport distance. It uses a wire rope core conveyor belt with high strength (up to 6000 N/mm). As the main hoisting mechanism for inclined shafts, it has the following advantages: 1) The steep-angle wire rope core conveyor belt is a fixed machine, requiring minimal installation space. Except for the head section, the space required for the middle and tail sections is almost equal to that of a single-hook tandem hoisting shaft. It can be directly modified and installed within the inclined shaft, minimizing mining engineering work. 2) It requires less equipment maintenance and has a low accident rate. The inherent advantages of fixed machinery significantly reduce equipment maintenance and repair compared to tandem hoisting, resulting in virtually zero production accidents. Since there are no personnel working around the vehicles, personal safety is guaranteed. 3) Because the steel wire rope core belt uses steel wire rope as the traction mechanism and load-bearing body, tension is transmitted rapidly, startup is smooth without surges, and transport distances can reach thousands of meters. The continuous ring transport method of the belt conveyor solves the bottleneck impact of intermittent tandem hoisting on coal mine production. It can fully meet all aspects of mine hoisting requirements. Take the Meihe Coal Mine No. 3 of Liaoyuan Mining Group as an example. In 1992, the minehead production system was upgraded, and the coal face adopted low-level top coal caving with fully mechanized supports, resulting in a significant increase in coal production, more than doubling. The mine's designed annual production of 450,000 tons was revised to 900,000 tons. The increase in production made the hoisting system even more unable to meet production needs, creating a bottleneck where production was determined by the hoisting system. To reverse this passive transportation situation and ensure the effective development of mine production... From July to September 1992, the bureau and mine upgraded the hoisting system of the No. 3 well. The main hoisting system adopted the STJ800/2×220Q steep-angle belt conveyor manufactured by Harbin Coal Machinery Plant. The steel wire rope core belt is 800mm wide and the belt strength is 2000kg/cm. The belt conveyor is 659 meters long, the belt loop is 1400 meters long, and the belt joint adopts a hot vulcanization single-stage full tower. The main indicators after replacement are calculated as follows: I. Original conditions: Conveying length L = 570 meters Conveyor installation angle α = 23 degrees Belt weight per meter qd = 45 kg/m Maximum particle size transverse dimension amax = 300 mm Belt width B = 800 mm Belt running speed V = 2.0 m/s Cargo repose angle 30° Overall well productivity A1 (Annual output 900,000 tons, 300 working days, 3 shifts, 6 hours per shift) 1. Verification of belt width B Verify whether a belt with a width of B = 800 mm can meet the particle size requirements of raw coal. B ≥ 2 amax + 200 mm ＝ 2 × 300 + 200 ＝ 800 (mm) That is, a belt with a width of B = 800 mm can meet the cargo requirement of a maximum particle size of 300 mm. 2. Calculation of Transport Volume Q: Q = KB²VRC Where: B – Belt width (m) B = 800 mm = 0.8 m Q – Transport volume (t/h) V – Belt speed (m/s) V = 2.0 m/s R – Bulk density of cargo (t/m³) Take R = 1.0 t/m³ K – Cargo section coefficient, based on a cargo angle of repose of 30°, K = 458 C – Conveyor inclination coefficient, based on a conveyor angle of 23 degrees, C = 0.9 Substituting the parameters into the above formula: Q = KB²VRC = 458 × 0.8 × 2 × 2 × 1.0 × 0.9 = 527.62 t/h From the calculation, Q > A. The transport volume of an 800 mm belt conveyor can fully meet the needs of an annual production of 900,000 tons, and leaves sufficient margin for expanded reproduction. II. Belt Strength Calculation m: Where: m – Safety factor, minimum safety factor requirement is greater than 7. B - Belt width (cm) B = 80cm Gx - Belt strength (kg/cm) Gx = 2000 kg/cm Smax - Maximum static tension of the belt (kg) Calculation diagram of maximum static tension Smax of the belt is as follows: 1. Calculation of belt running resistance 1) Calculation of resistance of heavy section: Resistance of section 2-3 F2-3 F2-3 = (q0 + qd + qg') L2-3 W'cos23° + (q0 + qz) L2-3sin23° Where: q0 - Cargo weight per meter of belt (kg/m) A - Transportation productivity (tons/hour) Considering production potential, take A = 1.25A1 = 1.25 × 167 = 209 Tons/hour: L2-3 - Heavy load length (m): L2-3 = 570 m; qd - Weight of conveyor belt per meter (kg/m): qd = 45 kg/m; qg' - Weight of the rotating part of the upper idler roller per meter: Gg' - Weight of the rotating part of each set of upper idler rollers: Gg' = 11 kg; Lg' - Spacing between upper idler rollers (meters): Lg' = 1.2 m; W' - Resistance coefficient of the trough idler roller: W' = 0.05 (from data). F2-3 = (29.02 + 45 + 9.17) × 570 × 0.05cos23° + (29.02 + 45) × 570sin23° = 18667.93 kg 2) Calculation of resistance in the empty section 4-5 Section resistance F4-5 Calculated by straight line F4-5 = (qd + qg")L4-5W" Where: qg" - weight of the rotating part of the lower idler roller converted to per meter length Gg" - weight of the rotating part of each group of lower idler rollers Gg" = 12 kg Lg" - distance between lower idler rollers (meters) Lg" = 3 m Therefore: L4-5 ≈ 10 m W" - Resistance section of the conveyor belt running on the lower idler roller. According to the data, W" = 0.025. Therefore: F[sub]4-5[/sub] = (45+4)×10×0.025＝12.25kg Resistance of section 6-7 F[sub]6-7[/sub] F[sub]6-7[/sub] = (q[sub]d[/sub]+q[sub]g'"[/sub]) L[sub]6-7[/sub]W'" Where: q[sub]g'"[/sub] - Weight of the rotating part of the lower idler roller per square meter of section 6-7 G[sub]g'"[/sub] - Weight of the rotating part of each group of lower idler rollers G[sub]g'"[/sub]＝12 kg L[sub]g'"[/sub] - Spacing between these lower idler rollers L[sub]g'"[/sub]＝1.2 m W'" - Resistance coefficient of the conveyor belt on the lower idler roller. From the table, W'" = 0.025. F[sub]6-7[/sub] = (45+10)×9×0.025 = 12.375 kg. The resistance of section 8-9 is the frictional resistance between the belt and the roller. F[sub]8-9[/sub] = q[sub]d[/sub]L[sub]8-9[/sub]μ. Where: μ - friction coefficient between the conveyor belt and the roller, μ is taken as 0.3. L[sub]8-9[/sub] = 1.5 m. Therefore, F[sub]8-9[/sub] = 45×1.5×0.3 = 20.25 kg. Resistance of section 1-9: F[sub]1-9[/sub] = (q[sub]d[/sub] + q[sub]g"[/sub]) L[sub]1-9[/sub] W"cos23°-qdL1-9sin23° =（45+4）570×0.025cos23°－45×570sin23° =-9379.51kg Belt tension calculation: Based on the total sag requirement, the minimum tension S2 is calculated. S2＝5（q0+qd）Lg'cos23° =5×（29.02+45）×1.2cos23° =408.81 kg Where: K－roller resistance coefficient K＝1.06 S3=S2+F2-3 =408.81+ 18667.93＝19076.74 kg S[sub]4[/sub]=KS[sub]3[/sub]=1.06×19076.74=20221.34 kg S[sub]5[/sub]=S[sub]4[/sub]+F[sub]4-5[/sub]=20221.34+12.25=20233.59 kg S[sub]6[/sub]=K[sup]2[/sup]×S[sub]3[/sub]=1.06[sup]2[/sup]×19076.74＝21434.63 kg S[sub]7[/sub]=S[sub]6[/sub]+F[sub]6-7[/sub]=21434.63+12.375=21447.00 kg S₉ = S₁ - F₁ - 9₉ = 385.67 - (-9084.55) = 9470.22 kg S₈ = S₉ + F₈ - 9₉ = 9470.22 + 20.25 = 9490.47 kg The maximum static tension of the conveyor belt is S₇ = 21447 kg. Substituting S_max = S₇ = 21447 into the calculation, the conveyor belt strength meets the requirements. Through the above calculations, the steep-angle belt conveyor far exceeds the capacity of the tandem hoisting system in terms of both conveying capacity and equipment strength, and can meet the needs of the mine's continuous development. Practice has also proven this. The Meihe Coal Mine No. 3 of Liaoyuan Mining Group has seen a steady increase in production and output over the past ten years through renovation. Compared to before the renovation, there has been a significant increase in both output and overall efficiency. See the table below: The successful renovation of the inclined shaft conveyor belt has brought significant economic benefits to the enterprise. Following the renovation of the No. 3 shaft, Liaoyuan Mining Group successively renovated the main hoisting shafts of the No. 2 and No. 4 shafts of Meihe Coal Mine, comprehensively improving the overall production capacity of Meihe Coal Mine. Conclusion The renovation of the inclined shaft hoisting system using an inclined shaft conveyor belt has completely eliminated the constraints of the old hoisting method on coal production, giving the mine production a broad space for development. The effectiveness of the renovation of the inclined shaft hoisting system at Meihe Coal Mine of Liaoyuan Mining Group provides a reliable basis for the renovation of hoisting systems in developing mines. In the future development of the coal industry, the inclined shaft conveyor belt will gradually replace the inclined shaft hoisting system and become the mainstream of inclined shaft hoisting. References Zhang Guozhu, "Mining Transportation Machinery", Coal Industry Press, 1979.1. Original text: On the Renovation of Inclined Shaft Hoisting System Using an Inclined Shaft Conveyor Belt.