Compared with automobile transportation, long-distance high-power belt conveyor has low investment and maintenance cost. At present, it is widely used in mining, port, building materials and other industries. Compared with foreign mechanical industrial powers, there are still some gaps in the design, production and other key technologies of long-distance and high-power belt conveyor in China. In order to prevent belt slipping and improve the friction of conveyor drum, belt conveyor is generally equipped with tensioning device. The research and application of tensioning device in China started late and lacks experience in theoretical design and production practice. Therefore, it is of great significance to study the tensioning device and its control system of belt conveyor.
Overview of belt conveyor tensioning device
Belt conveyor tensioning device is a device integrating mechanical technology, hydraulic technology and automatic control technology. In the early stage of design, its layout, installation, structure and working principle need to be fully considered.
By consulting the relevant literature and technical data of belt conveyor, combined with the experience in operation and maintenance, the following basic principles should be considered when arranging the tensioning device: ① The tensioning device should be close to the driving device to ensure that the belt tension near the driving device remains unchanged, because the tensioning device will be affected by acceleration when it is arranged away from the driving device, Therefore, the minimum tension near the driving device cannot be met; ② The tensioning device is best arranged at the place with the minimum belt tension or loose edge; ③ The length of the belt joint shall be taken into account when determining the tensioning stroke, and various operating conditions of the conveyor shall be taken into account when determining the tension.
Under the influence of long distance, large traffic volume and different working conditions, the installation position of tensioning device is particularly important. For example, when starting and braking the motor, the ideal process should be a smooth and slow acceleration process. If the tensioning device cannot dynamically adjust the tension of the belt according to the speed change of the motor, the belt is very easy to deform and affect the stability of the equipment. Figure 1 shows the installation position of the tensioning device of the belt conveyor. Since the slope of the belt conveyor exceeds 5% and the transportation distance exceeds 300 m, the tensioning device is installed on the no-load side of the driving pulley, which has the best effect of reducing the tension change with the driving pulley.
The belt conveyor tensioning device studied in this paper mainly includes three parts: mechanical part, hydraulic part and electric control part. The mechanical part mainly includes winch, tensioning oil cylinder, track, pulley, steel wire rope, etc. The hydraulic part includes accumulator, stop valve, pressure relay, overflow valve and quantitative pump. The electric control part includes sensor and electric control box.
The tension of the belt is collected by the tension sensor installed on the steel wire rope, and then compared with the given tension. The voltage signal processed by the voltage comparison circuit is sent to the controller after pulse frequency processing. The controller comprehensively judges the pulse frequency signal and the working state of the belt conveyor and sends out the control signal. The control signal drives the forward and reverse rotation or braking of the motor through the relay and magnetic starter. When the motor rotates forward, the oil cylinder will be tensioned and the tension will increase; When the motor reverses, the tension cylinder retracts and the tension decreases.
Analysis of hydraulic system of tensioning device
structure and working principle
In the start-up stage and stable operation stage of belt conveyor, the control mode of tensioning force is different. In the start-up stage, the solenoid valve is opened. When the hydraulic oil in the oil pump enters, the electric control box sends the motor start signal; the quantitative pump is driven by the motor to fill the front chamber with hydraulic oil, so as to generate pressure on the piston. The overflow valve is used to limit the upper limit of tension, and the accumulator is used to buffer the fluctuation of belt tension and absorb the loose edge elongation caused by external interference. In the operation stage, the oil pump motor does not work, and the tension of the device is controlled by the electronic control system. The electronic control system judges the required tension at this time through the data collected by the tension sensor, so as to control the action of the hydraulic system to produce the given tension; the function of the pressure relay is to ensure that the tension is within the control range, and the pressure relay can control the solenoid valve and then control the hydraulic circuit. When the pressure exceeds the upper limit, the pressure relay will close the oil pump motor, The tension decreases. When the pressure is lower than the lower limit, the pressure relay opens the oil pump motor and the tension increases.
Connection mode of hydraulic system
The connection of the hydraulic system adopts high-pressure rubber hose, which is a special pipeline for conveying liquid with certain temperature and pressure. The hydraulic pump station is respectively connected with the energy storage station and the rod cavity joint seat of the oil cylinder through a long rubber pipe and a short rubber pipe, and then connected to the rod cavity joint seat through another rubber pipe, so that the connection between the hydraulic pump station and the energy storage station and the oil cylinder is completed. The hydraulic pump station is connected with the motor oil drain port through a long rubber hose. The winch and the hydraulic pump station are connected with two long rubber hoses respectively. One is connected with the “winch forward rotation” interface and the other is connected with the winch reverse rotation interface.
Selection of main components
Hydraulic cylinder is an actuator that converts hydraulic energy into mechanical energy. Its performance directly determines the quality and service life of the tensioning device. There are many applications of various types of valves in the hydraulic system, such as hydraulic control one-way valve, electromagnetic overflow valve, three position four-way electromagnetic directional valve, unloading overflow valve, etc. they all play their respective roles in different occasions, and they should be selected according to different working characteristics. In addition to the hydraulic cylinder and valve, the key components of the hydraulic system include motor, pump and tension sensor.
At present, the dynamic response of the automatic tensioning device of the hydraulic winch of the domestic belt conveyor is poor, and the belt tension cannot be adjusted in time, which is easy to cause the belt to be too tight or too loose, and the belt will be broken in serious cases. The tensioning device studied in this paper shows excellent performance in constant tension control. The tension on the belt can be adjusted in time with the change of the running state or load of the belt conveyor, so as to avoid the occurrence of belt slip.