Detailed explanation and selection of Three major devices of belt conveyors-driving, tensioning and bend devices

Drive device

The driving device of the belt conveyor is composed of a motor, a coupling or a hydraulic coupler, a reducer, a transmission roller, etc. The belt conveyor with an inclined section should also be equipped with a brake or a backstop as required. The function of the driving device is to transmit the gravitational force to the conveyor belt through friction by the driving pulley to make it move and transport the goods.

Most belt conveyors are driven by a single pulley, but as the transportation volume and distance increase continuously, the traction transmitted by the driving pulley is required to increase correspondingly, so double pulley and multi-pulley driving have appeared. Each drive pulley can be equipped with one or two drive units, and the end of the drive pulley shaft is connected with the drive unit by a coupling.

The drive pulley generally adopts the Y series cage motor, which has the advantages of small size, low cost, reliable work, and easy to realize automatic control. When the power is small (≤37kW), it can be directly driven by the flexible coupling; when the power is large (45-315kW), it can be equipped with a hydraulic coupling to make the start-up smooth. In the case of high power (220-800kW), a wound motor can be used, which is easy to control, so that the long-distance belt conveyor starts smoothly, and solves the power balance problem of multi-pulley driving.

In addition to cylindrical gear transmission, the reducer of modern large belt conveyors often uses conical gear reducers in order to reduce the lateral size of the conveyor driving device. For the mobile belt conveyor, in order to reduce its own weight, the transmission device mostly adopts belt, chain or first-stage open gear transmission. In addition, cycloid pin gear reducer or electric drum pulley can be used.

The electric pulley puts the motor and the deceleration device in the transmission pulley, so it has a compact structure, light weight, easy layout, safe operation, and is suitable for humid and corrosive working conditions. The disadvantage is that the heat dissipation condition of the motor is not good, and the maintenance is inconvenient.

The drive pulley transmits traction by means of the friction between its surface and the conveyor belt. There are two types of drive pulley: smooth surface and rubber surface. The rubber surface includes flat rubber surface, chevron rubber surface (suitable for one-way operation), diamond pattern rubber surface (suitable for two-way operation), etc.

Adopting the rubber surface, especially the patterned types, can increase the coefficient of friction, and the patterned rubber surface also has a certain effect on preventing the conveyor belt from deviating. The smooth pulley should be used when the power is not high and the environmental humidity is low; when the environment is humid, the power is high, and it is easy to slip, the pulley with rubber lagging sheet should be used.

When the conveyor belt goes around the pulley, it will cause fatigue damage due to bending. Therefore, the diameter of the drive pulley cannot be too small. The diameter specifications of the transmission pulley are 500, 630, 800, 1000mm, etc., which can be selected according to the belt width.

 Tensioning device

The function of the tensioning device is to maintain the necessary initial tension of the conveyor belt to avoid slipping on the driving pulley, and to ensure that the sag of the conveyor belt between the two supporting pulleys is within the specified range. Tensioning devices mainly include screw type, trolley weight type and vertical weight type.

1) The screw-type tensioning device uses manpower to rotate the screw to adjust the tension of the conveyor belt. Its structure is simple and compact, but the tension force is not easy to grasp, and the tension force cannot be kept constant during the working process. Generally used on conveyors with a length of less than 100m and low power, the tensioning stroke can be selected according to 1%-1.5% of the captain.

2) The trolley heavy hammer tensioning device has an overall size, a large area, and a large mass. It is suitable for conveyors with large length and power, especially on inclined conveyors.

3) The vertical weight-type tensioning device can use the space position under the conveyor corridor and be arranged in the place where the tension of the lower branch belt is least, thus reducing the weight of heavy hammer. The disadvantage is will increase the number of reversing pulley, increase the number of bending of the conveyor belt, and the material is easy to fall between the conveyor belt and the pulley and damage the conveyor belt.

Redirection bend device

Belt conveyors change the direction  with bend pulley or redirection idlers.

The reversing bend pulley can be used to change the direction of the conveyor belt at 180°, 90° or <45°. The bend pulley or the vertical heavy hammer tension pulley generally arranged at the tail changes the direction of the conveyor belt by 180°, the pulley above the vertical heavy hammer tension device changes the direction of 90°, and the direction below 45° is generally used to increase the conveyor belt. The wrap angle between the drive pulleys.

The diameter of the bend pulley is 250, 315, 400, 500, 630, 800, 1000mm, etc., which can be matched with the diameter of the driving pulley when selected. When the direction is changed to 180°, its diameter can be one gear smaller than the diameter of the transmission pulley. When it is changed to 90° or 45°, it can be appropriately reduced by 1-2 gears as the change direction angle decreases.

The reversing idlers are a number of supporting rollers arranged along the arc of the required radius. It is used where the curvature radius of the conveyor belt is larger, or is used in the trough-shaped roller section, where the conveyor belt is thrown at the redirection can maintain trough-shaped cross-section.

When the conveyor belt passes through the convex arc section, the elongation of both sides of the conveyor belt is greater than the center due to the influence of the roller groove angle. In order to reduce the tape stress, the radius of curvature of the convex arc section should be as large as possible, generally the elongation rate of the fabric core belt is 0.8%.