Analysis of the Current Situation of Belt Conveyor Machinery In the continuous transportation of modern bulk materials, belt conveyors are the main transportation equipment with a wide range of applications. They have the advantages of low transportation costs, large capacity, no terrain restrictions, and easy maintenance. They are increasingly playing an important role in mining, building materials, chemical, port, grain, electricity, coal and other industrial and mining enterprises. With the rapid development of the national economy, new requirements have been put forward for the transportation of bulk materials, namely long-distance, large capacity (high belt speed and large belt competition), and large inclination angle transportation of materials, while proposing pollution-free and environmentally friendly transportation of bulk materials.
       Since the 1980s, belt conveyors in China have made great progress. In the 1990s, soft start and braking devices, as well as electronic control devices with PLC control as the core, have been successfully developed for large angle up and down belt conveyors, bendable belt conveyors, long-distance, high-capacity, multi-point drive belt conveyors and their key technologies and components.
一、 Large inclination downward belt conveyor
      The downward inclination angle of a general belt conveyor is not less than -17 °. When the angle is less than -17 °, the material on the conveyor belt is prone to sliding downward and serious rolling phenomenon occurs. In order to solve the problem of large angle conveying of ordinary conveyor belts, universal belt conveyors need to be improved through technology, and the main technical measures taken include the following three aspects:
     1. Require the driving device to have a brake with adjustable braking force at any time to ensure controllable starting and stopping braking, greatly reducing the impact on materials. Generally, an electromechanical integrated self cooling disc brake device is used; This brake has the characteristics of simple structure, easy installation and debugging, safe and reliable operation, and extremely low investment and maintenance costs. Especially when the system suddenly loses power, it can ensure balanced, safe, and reliable implementation of parking braking.
      2. The rollers of the conveyor adopt deep groove roller groups, which can greatly increase the angle of downward or upward conveying. The deep groove roller group consists of four identical rollers, divided into two in front and two in the back, forming a circular groove. This is beneficial for the conveyor belt to form a groove and greatly improves the additional friction force of the conveyor belt on coal.
       During design, deep groove roller sets with different groove angles should be arranged according to different conveying angles.
     3. The special control technology drive device and deep groove roller group of the inclined downward belt conveyor are the basis for ensuring reliable downward transportation of materials without rolling or sliding; However, the smooth start and stop operation of belt conveyors cannot be achieved without the reasonable control of the electrical system.
      The control characteristics of a large angle downward belt conveyor are significantly different from those of an upward and horizontal belt conveyor, mainly reflected in the following aspects.
     ⑴ Synchronous pressing control of motor: When the conveyor belt starts the belt conveyor with full material, it cannot be directly powered to start the motor. If it starts too quickly, the material may slide or roll, so in this case, the conveyor is started by the sliding force of the material. As the brake is gradually released, the conveyor belt drives the motor to rotate, and the rotational speed is detected by a speed sensor; When the speed reaches the synchronous operating speed of the motor, the PLC controls the motor to automatically power on and start, thereby enabling the motor to operate in a normal power generation state.
     ⑵ Synchronous cut-off control of motor: When the conveyor is stopped under load, the motor cannot be directly cut off, otherwise it is easy to cause runaway and serious accidents. To this end, apply braking force to the conveyor first when stopping; When the rotation speed of the motor is detected to have decreased to its synchronous speed, the motor should be powered off again. This way, when applying braking force to slow down, the braking force of the motor can be fully utilized, making parking smoother.
    ⑶ Direct motor start control: When the conveyor belt is unloaded or lightly loaded and the brake is gradually released, the conveyor cannot start automatically. At this time, according to the speed measurement device, if the conveyor is in a zero speed state or the starting speed is too slow, the motor needs to be started directly before loading the conveyor.
      ⑷ Overspeed protection control during operation: When the conveyor belt operates normally at a large angle, it is in a generating state. According to the mechanical characteristic curve of the squirrel cage three-phase asynchronous motor, when the load torque exceeds the maximum generating braking torque Mm of the motor, the motor speed will further increase, while the braking force will sharply decrease, resulting in serious overspeed phenomenon. Therefore, during control, it is required that the speed of the motor should not exceed the critical speed nm under extreme power limitation. When the motor speed rises to a certain value, the electrical detection and control system controls the electro-hydraulic pressure regulating device and disc brake in the hydraulic circuit to implement closed-loop braking control of the conveyor, while reducing the amount of material fed to lower the motor speed and restore normal operation.
   
二、 Large inclination upward belt conveyor
       The universal belt conveyor achieves reliable upward transportation of materials at large angles through technological improvements. It adopts the same form of deep groove roller group as downward transportation, but its driving and control technology is different from downward transportation.
      1. Drive device: Start the motor with no load to reduce the impact on electrical and mechanical systems; Enable the driving device to provide adjustable, smooth, and impact free starting torque; It has good matching characteristics with the electric motor and fully utilizes the maximum torque of the motor during starting; Under the drive of multiple electric motors, power balance can be achieved among them; It can achieve stepless speed regulation of the conveyor to meet different work needs; When the conveyor is overloaded, automatic overload protection can be achieved, for which a special soft start device is required.
      2. Soft start technology is indispensable for large inclination angle and long-distance belt conveyors. It requires the belt conveyor to start smoothly and without impact. At present, speed regulating hydraulic couplings, electrical frequency converters, CST drive devices, and liquid viscous soft start devices are mainly used. The variable speed hydraulic coupling is generally only used for belt conveyors with small and medium power and short haul distance; For downward belt conveyors, variable speed hydraulic couplings cannot be used, and a two quadrant frequency converter must be used. The soft start performance of CST drive device is superior, but it requires high capital, high maintenance cost, and high oil quality. Similarly, CST drive devices cannot be used for downward belt conveyors; The liquid viscous soft starting device is a widely used soft starting device in China, which can be suitable for driving a variety of belt conveyors.

三、 There are several types of curved belt conveyors: ① flat curved belt conveyor; ② Fixed slope turning belt conveyor; Concave slope turning belt conveyor; ④ Convex slope turning belt conveyor. Among them, flat curved belt conveyors are more common.
     1. Design System of Flat Curved Belt Conveyor
      (1) The basic measures to achieve turning.
       Make the roller at the turning point have an installation support angle j. It is formed by moving the inner end of the roller towards the direction of the conveyor belt at the turning point. The smaller the value of j, the more advantageous it is for the operation of the conveyor belt. Generally, based on experience, j is taken as 0.5 °; The major groove angle j0 is the angle formed by the axis of the side roller and the axis of the middle flat roller. The larger the j0, not only does it reduce the turning radius, but it also enables the conveyor belt to have automatic centering adjustment capability.
       (2) Additional measures.
      The elevation angle g of the inner curve is formed, and the larger the g, the smaller the turning radius. However, if it is too large, the material will roll outward. Theoretical and practical evidence shows that g is appropriate; For the return air branch using a single roller group, apply pressure rollers on the conveyor belt between the two return rollers.
     （3）emergency measure.
      Install vertical rollers on the inside and outside of the conveyor belt at the turning point. This is a backup measure to prevent belt deviation.
     （4）Measures taken when turning difficult.
     Using line friction drive to reduce turning radius; Return to the empty branch pressure roller.
       2、Determination of curvature radius at turning points
      （1）Determine the curvature radius based on the law of force balance. The fundamental reason for deviation lies in the imbalance of forces. Based on the balance equation of various forces at the turning point, the minimum turning radius that satisfies the mechanical equilibrium conditions can be derived.
      （2）Determine the curvature radius based on the allowable stress of the conveyor belt. At the turning point, the outer edge of the conveyor belt is relatively stretched, while the inner edge is relatively compressed. Therefore, it is necessary to ensure that the stress on the outer edge of the conveyor belt does not exceed the allowable stress, and to meet the minimum turning radius R2 that satisfies this condition. According to the calculation of R3, if the turning radius is too small, it is possible for the conveyor belt on the outer roller to float and leave the roller.

四、long distance belt conveyer 
     Long distance belt conveyors are common in ground conveying systems and usually fluctuate with terrain. Therefore, the conveying route may have both upward and downward sections, as well as horizontal sections, making the working conditions complex. Therefore, a comprehensive analysis must be conducted when designing such belt conveyor systems.
　(Selected from the internet)