Belt conveyors are commonly used material transportation equipment in current beneficiation plants, with the conveyor belt playing a vital role as the carrying and transporting device. When a belt conveyor operates normally, the conveyor belt forms a closed-loop, with the upper and lower belts running at a uniform speed, their centerlines parallel to each other, and the deviation of the belt direction maintained within a specified range.
During the beneficiation process, belt deviation is a common issue encountered with belt conveyor systems, where the centerline of the belt deviates from the centerline of the conveyor, leaning to one side during operation. There are various reasons causing belt deviation during the operation of belt conveyors, such as improper drum installation or material adhesion, improper or material-adhered idler frames, loose belt tension, uneven ore distribution, and vibration during operation.
Analysis of the Causes of Belt Deviation in Belt Conveyors
- Belt deviation caused by the centers of the head, tail, and intermediate frames not being in a straight line.This situation is typically caused by installation issues. When the centers of these three components are not aligned in a straight line, it results in the longitudinal centerline of the belt not being perpendicular to the axis of the drum, causing the belt to deviate during operation.
- Belt deviation caused by improper drum installation position.A belt conveyor has multiple drums, and all drum installation positions must ensure they are perpendicular to the centerline of the belt and parallel to the horizontal plane. If the drum’s installation is not sufficiently horizontal, it may result in axial movement of the drum or one end of the drum being ahead of the other, causing the installation position of the drum to be non-perpendicular to the longitudinal centerline of the belt or the axis of the drum not parallel to the horizontal plane. Consequently, the resultant force acting on the belt in the width direction is not zero, causing the belt to deviate in the direction of the resultant force.
- Belt deviation caused by improper belt jointing, resulting in deviation in the middle of the conveyor belt.Common belt joints include mechanical joints and vulcanized joints. Regardless of the method used, a smooth joint is required. Improper joints may result in uneven tension on both sides of the belt, leading to deviation during operation. The deviation caused by improper belt joints occurs wherever the joint is located.
- Belt deviation caused by improper idler frame installation or loosening of bolts fixing the idler frame.During installation, the symmetry of the idler roller group centerline to the conveyor frame centerline must not exceed 3.0mm, and the upper surface of the idler roller should be on the same horizontal plane or inclined plane. Excessive installation error or loosening of fastening bolts may cause belt deviation.
- Belt deviation caused by belt damage.Belts are susceptible to damage during operation. When the degree of damage on both sides of the belt’s centerline differs, the elongation rates on both sides often change. Significant differences in elongation rates between the two sides may lead to inconsistent elongation of the two sides of the belt, causing belt deviation.
- Belt deviation caused by loading impact.When material falls onto the belt, the gravitational and inertial forces of the material can impact the belt, potentially causing belt deviation.
- Belt deviation caused by material accumulation on drums and idler rollers.For materials with certain adhesiveness, such as iron powder, uneven adhesion to idler rollers and drums after scattering may occur. This unevenness may cause local irregularities on the idler rollers or drums, resulting in uneven tension and subsequent belt deviation. Material scattering becomes more severe after deviation, creating a vicious cycle. This type of fault is more likely to occur in humid weather and harbor operations, necessitating proper functioning of belt cleaners.
- Belt deviation caused by insufficiently accurate installation angle of idler rollers.If there is a significant error between the centerline of the belt-carrying machine and the installation position of the idler roller, the belt may experience lateral force during operation, causing the belt to deviate to one side in the carrying section. If the deviation is caused by improper installation of the reversing drum or idler roller group, the deviation will be lighter the further it is from the starting point, gradually returning to the centerline of the frame. However, if the deviation is caused by the tilting of the driving drum, the deviation will become more severe.
- Belt deviation caused by tilting of the frame.If the centerline of the frame is skewed, or if the frame is tilted horizontally on both sides, it may cause the belt to be subjected to a certain lateral tensile force, pulling the belt to one side.
- Belt deviation caused by installation and adjustment errors of the belt tensioning device.Due to reasons such as inexperienced technicians, lack of responsibility, and lax acceptance standards during installation and commissioning, the belt tensioning device may not function properly, causing uneven tension on both sides of the belt and resulting in belt deviation.
- Belt deviation caused by severe equipment vibration.During belt operation, severe vibration of the belt conveyor equipment can also cause belt deviation, especially when there is radial movement of idler rollers, resulting in the most noticeable belt deviation.
Adjustment Measures for Belt Deviation Issues
Based on the analysis of the causes of belt deviation in belt conveyors, the following corresponding measures can be taken:
- Adjust the head, tail, and intermediate frames of the belt conveyor to align their centers on the same straight line.
- Adjust the installation position of the drums to ensure that the axis of the drums is perpendicular to the longitudinal centerline of the belt and parallel to the horizontal plane. Taking the first drum as an example, if the belt deviates towards one side of the bearing seat, move the bearing seat on that side in the direction of belt operation, or move the bearing seat on the other side in the opposite direction of operation. However, it is important to determine the actual offset between the centerline of the drum and the centerline of the belt before adjustment to ensure the correct position of the drum after adjustment.
- Cut off improper belt joints and redo the belt joints. Ensure that the joint is straight, with a straightness tolerance of no more than 20mm over a length of 10m. Additionally, it is recommended to segment the nailed belt buckle according to the length of the trough idler to ensure the troughing performance of the belt joint, prevent and reduce the risk of pin breakage, and avoid belt tearing accidents.
- For belt deviation caused by improper idler frame installation, move the idler frame on the side of deviation slightly forward in the direction of the belt, generally moving a few idler rollers can correct the deviation. In case of severe deviation, the idler frame needs to be re-calibrated to control the levelness error of the idler roller group within the allowable deviation. If the deviation is caused by the loosening of bolts fixing the fixed idler frame, tightening the loosened bolts can solve the problem.
- Strengthen inspection and maintenance of the belt, and timely repair or replace damaged belts.
- Adjust the position of the discharge point to be in the middle of the belt.
- Remove adhered materials from the surface of drums or idler rollers. Also, adjust the tension of the spring cleaner for the empty section to ensure that the cleaner has a contact length with the conveyor belt in the direction of the roller axis greater than 85% of the belt width, to ensure timely removal of materials.
- Adjust the idler roller group to the correct position. When the middle part of the belt conveyor belt deviates, the mounting holes on both sides of the idler support can be modified to become longer. When the belt deviates to the left, the left side of the idler roller group should be moved forward in the direction of belt operation or backward on the right side; when the belt deviates to the right, the right side of the idler roller group should be moved forward in the direction of belt operation or backward on the left side.
- Correct the skewed frame. Frame skew includes skew of the frame centerline and uneven height on both sides of the frame. It can only be fundamentally resolved by reinstalling the frame to ensure the centerline of the frame and the evenness of both sides of the frame.
- During the installation of tensioning devices, the centerline of the belt conveyor should be perpendicular to the axis of the tensioning device’s drum. Operators should strictly follow the installation requirements and carry out debugging work.
- Identify and resolve vibration causes in a timely manner.
Conclusion
In conclusion, during the operation of belt conveyors, attention should be paid to the phenomenon of belt deviation. Correctly identify the causes of deviation and take appropriate measures in a timely manner to ensure the safe, efficient, and stable operation of belt conveyors.
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