15 reasons and adjustment methods for conveyor belt deviation

The fundamental reason for conveyor belt deviation is that the resultant force of the external force on the belt in the belt width direction is not zero, or the tensile stress perpendicular to the belt width direction is uneven, which causes the roller or drum to produce a component force to one side of the belt's reaction force, and the belt deviates to one side under the action of this component force. Common deviation phenomena are as follows.

1. Analysis of the causes of belt deviation

01 The center of the head, tail, and middle frame are not in a straight line, causing the belt to deviate.

This situation is usually caused by installation. Because the centers of these three are not in a straight line, the longitudinal center line of the belt is not perpendicular to the axis of the roller, causing the belt conveyor to deviate during operation.

02 The incorrect installation position of the roller causes the belt to deviate at the roller.

A belt conveyor has multiple rollers, and the installation positions of all rollers must be guaranteed to be perpendicular to the center line of the belt and parallel to the horizontal plane. If the installation level of the roller is not enough, the roller moves axially, or one end of the roller is in front and the other end is behind, so that the installation position of the roller is not perpendicular to the longitudinal center line of the belt, or the axis of the roller is not parallel to the horizontal plane, the resultant force of the external force acting on the belt in the width direction of the belt will not be zero, and the belt will deviate in the direction indicated by the resultant force.

03 The conveyor belt joint is not straight, causing the middle part of the conveyor belt to deviate.

Commonly used belt joints are mechanical joints and vulcanized joints. Regardless of the method, the joints are required to be flat. If the joints are not straight, the tension on both sides of the belt will be inconsistent, causing deviation during operation. The deviation caused by the misaligned belt joint is that the belt will deviate wherever the belt joint runs.

04 The belt deviates due to the misalignment of the roller frame or the loosening of the bolts fixing the roller frame.

When installing the belt conveyor, the symmetry of the center line of the roller group to the center line of the conveyor frame shall not be greater than 3.0mm, and the upper surface of the roller should be on the same horizontal plane or inclined plane. If the installation error of the roller group is too large or the fastening bolts are loose, it will cause the conveyor belt to deviate.

05 The belt deviates due to damage to the conveyor belt.

The conveyor belt is easily damaged during operation. When the degree of damage on both sides of the center line of the conveyor belt is different, the elongation rate on both sides often changes. When the elongation rate on both sides differs greatly, resulting in inconsistent elongation of the belt on both sides, it is easy to cause the belt to deviate.

06 Belt deviation caused by material unloading point not being in the middle of the conveyor belt.

When the material unloading point is not in the middle of the belt, the force on the belt is unevenly distributed along both sides of the longitudinal center line due to the eccentric load. When the difference between the two is large, it will directly cause the conveyor belt to deviate during operation. If the conveyor belt does not deviate when it is unloaded, but always deviates to one side when it is heavily loaded, it means that the conveyor belt has been eccentrically loaded. At this time, the position of the receiving hopper or conveyor should be adjusted to make the conveyor belt evenly loaded to prevent it from deviating.

07 Belt deviation caused by material discharge impact.

When the material falls on the belt, the gravity and inertia of the material will impact the belt, which may cause the belt to deviate.

08 Belt deviation caused by material accumulation on the roller and idler.

For materials with a certain viscosity such as iron powder, they will stick to the roller and the roller unevenly after being scattered, making the roller or the idler partially uneven, and deviating due to uneven tension. The phenomenon of scattered materials is more serious after deviation, causing a vicious cycle. The probability of this failure is higher in humid weather and seaport operations. Therefore, the belt cleaner must ensure normal operation.

09 The belt deviation caused by the inaccurate installation angle of the idler.

If the error between the center line of the load-bearing belt conveyor and the installation position of the idler is large, the belt will be subjected to lateral force during operation, causing the belt to deviate to one side in the load-bearing section. If the installation position of the redirection roller and the idler group is not correct, then, whether it is the return section or the load-bearing section, the deviation will be lighter as it moves forward, and it will gradually return to the center line of the frame. However, if the driving roller is tilted, the deviation phenomenon will become more and more serious.

10 Belt deviation caused by unqualified belt quality.

The density of the belt core is uneven, and the force along the belt width is uneven. Under the action of tension, the elongation of the belt during operation is inconsistent, causing the belt to deviate. If the uneven density of the belt is caused by a system failure of the production equipment, with a certain regularity, the direction of deviation will also show a certain regularity.

11 Belt deviation caused by installation and debugging errors of the belt tensioning device.

Due to the unskilled operation, lack of responsibility, and lax acceptance of the operators during the installation and debugging process, the belt tensioning device does not work properly, and the tensioning degree and uneven force on both sides of the belt cause the belt to deviate.

12 Long-term use leads to aging and deformation, causing the belt to deviate.

After a cycle of use, the belt will relax, resulting in uneven stress distribution in the belt, thereby increasing the chance of belt deviation.

13 Belt deviation caused by frame tilt.

If the center line of the frame is skewed and the left and right sides of the frame are tilted horizontally, the belt may be subjected to a certain lateral tension, pulling the belt to one side.

14 Belt deviation caused by severe equipment vibration.

During the operation of the belt, the violent vibration of the belt conveyor equipment will also cause the belt to deviate, especially the radial runout of the roller will cause the belt to deviate most obviously.

15 The belt deviates due to the small curvature radius of the concave section belt conveyor.

For a belt conveyor designed with a concave section, if the curvature radius of the concave section is too small, if there is no material on the belt at the start, the belt will bounce up in the concave section, and the belt will be blown off in strong winds.

2. Adjustment measures for belt deviation

Based on the above analysis of the reasons for belt deviation of the belt conveyor, the following corresponding measures are taken.

1) Adjust the head, tail and middle frame of the belt conveyor so that the centers of the three are on the same straight line.

2) Adjust the installation position of the roller so that the axis of the roller is perpendicular to the longitudinal center line of the belt and parallel to the horizontal plane. Taking the first roller as an example, if the belt deviates to which side of the bearing seat, move the bearing seat on that side to the running direction of the belt, or move the bearing seat on the other side to the opposite direction of the running. However, it should be noted that the actual offset between the center line of the roller and the center line of the belt must be determined before adjustment to ensure the correct position of the roller after adjustment.

3) Cut off the irregular belt joints and redo the belt joints. Make the joints straight, and the straightness tolerance value over a length of 10m is not more than 20mm. In addition, the nailed belt buckles are preferably segmented along the length of the grooved rollers to ensure the groove performance at the belt joints, prevent and reduce the breakage of the pins, and avoid accidents of tearing the tape.

4) If the deviation is caused by the misalignment of the roller frame, the roller frame on the side of the deviation can be moved a little in the direction of the belt forward. Generally, moving a few rollers can correct the deviation. If the deviation is serious, the roller frame needs to be recalibrated to control the horizontal error of the roller group within the allowable deviation. If the belt deviation is caused by the loose bolts fixing the roller frame, the loose bolts can be re-tightened to solve it.

5) It can be solved by strengthening the inspection and maintenance of the belt and repairing or replacing the damaged belt in time.

6) Adjust the position of the unloading point so that it is located in the middle of the belt.

7) Use a guide plate with a reasonable structure to avoid direct discharge of large objects or large heights. You can also install several groups of buffer rollers under the discharge port.

8) Remove the sticky materials on the surface of the roller or roller to eliminate them. At the same time, the empty section spring cleaner should be adjusted. The contact length between the cleaner and the conveyor belt in the direction of the roller axis should be greater than 85% of the belt width to ensure that the material is removed at any time.

9) Adjust the roller group to the correct position. When the belt in the middle part of the belt conveyor deviates, the mounting holes on both sides of the roller bracket can be modified and processed to make it a longer hole. When the belt deviates to the left, the left side of the roller group moves forward in the direction of the belt running, or the right side moves backward; when the belt deviates to the right, the right side of the roller group moves forward in the direction of the belt running, or the left side moves backward.

10) Users should choose manufacturers with good reputation and rich production experience, and equipped with perfect technical service personnel, who can solve users' usage problems in time and implement the three guarantees service of good products.

11) When installing the tensioning device, the center line of the belt conveyor and the roller axis of the tensioning device should be vertical. Operators should strictly follow the installation requirements and do debugging work.

12) The belt conveyor should be inspected and repaired after a period of use, and the belt should be replaced in time if it is aging and deformed.

13) Correct the skewed frame. The skew of the frame includes the skewness of the center line of the frame and the high and low tilt of the two sides of the frame. The problem can only be fundamentally solved by reinstalling the frame to ensure that the center line of the frame and the two sides of the frame are flat.

14) Find out the cause of vibration and solve it in time.

15) It is best to add a belt pressure wheel at the concave section of the belt conveyor to avoid the belt from bouncing or being blown off by the wind. In the design stage, a larger concave section curvature radius should be used as much as possible to avoid such a situation.

During the operation of the belt conveyor, you should always pay attention to the deviation of the belt, correctly determine the cause of the deviation and take appropriate elimination measures in time to ensure the safe, efficient and stable operation of the belt conveyor. If conditions and capabilities are met, you can use an anti-deviation switch, or use the travel switch to design a safety protection alarm device to fundamentally eliminate the belt deviation fault, prevent leakage and abnormal damage to the equipment, and ensure the production efficiency of the equipment.