15 Causes and Adjustment Methods for Belt Conveyor Misalignment

The fundamental cause of belt misalignment is that the resultant force acting on the belt in the width direction is not zero, or the tensile stress perpendicular to the belt width is uneven. This causes idlers or pulleys to exert a lateral force on the belt, leading to deviation. Common misalignment phenomena are listed below.

1. Cause Analysis of Belt Misalignment

01). Misaligned Head, Tail, and Center Frame: Caused by installation errors. Their centers not being collinear makes the belt's longitudinal centerline non-perpendicular to the pulley axis, causing misalignment.

02). Incorrect Pulley Installation: All pulleys must be perpendicular to the belt's centerline and parallel to the horizontal plane. Incorrect installation (tilt, axial movement) creates a non-zero lateral force, pulling the belt to one side.

03). Improper Belt Splicing: Mechanical or vulcanized splices must be straight. An uneven splice creates uneven tension across the belt width, causing misalignment at the splice point as it travels.

04). Crooked Idler Frame or Loose Bolts: Idler group centerlines must align with the frame centerline (deviation ≤ 3.0mm), and idler surfaces must be level. Large installation errors or loose bolts cause misalignment.

05). Damaged Conveyor Belt: Uneven damage across the belt's width causes different elongation rates under tension, leading to misalignment.

06). Off-Center Loading: If material isn't loaded centrally, uneven load distribution creates a lateral force. If the belt tracks true empty but misaligns loaded, it indicates biased loading. Adjust the chute or feeder position.

07). Impact from Feeding Material: The gravity and inertia of falling material can impact the belt, potentially causing deviation.

08). Material Buildup on Pulleys/Idlers: Sticky materials (e.g., iron ore fines) can build up unevenly on pulleys/idlers, creating an irregular surface and uneven tension, leading to misalignment. This worsens with spillage. Common in humid conditions or ports. Ensure scrapers work correctly.

09). Incorrect Idler Installation Angle: Significant error between the conveyor centerline and idler installation angle applies a lateral force, causing misalignment in the carrying run. For return idlers or bend pulleys, misalignment often self-corrects. For drive pulleys, it worsens.

10). Substandard Belt Quality: Uneven carcass density across the width causes uneven elongation under tension, leading to misalignment. If the density issue is systematic, the misalignment direction may be predictable.

11). Take-up Unit Installation/Debugging Errors: Improper installation/adjustment by unskilled personnel can result in uneven belt tension across the width, causing misalignment.

12). Aging and Deformation: Belts relax over time, creating uneven internal stress distribution and increasing misalignment risk.

13). Inclined Conveyor Frame: A slanted frame centerline or uneven frame level applies a constant side pull, dragging the belt to one side.

14). Severe Equipment Vibration: Intense conveyor vibration, especially from idler radial runout, can cause belt misalignment.

15). Small Curvature Radius in Concave Section: If the concave vertical curve radius is too small, an empty belt may lift off the idlers during start-up and be blown off-track by wind.

2. Adjustment Measures for Belt Misalignment

Based on the above analysis, implement these corresponding measures.

01). Adjust the head, tail, and center frame to be collinear.

02). Adjust pulleys to be perpendicular to the belt's longitudinal centerline and level. Example: For a head pulley, move the bearing housing on the side the belt is moving towards in the belt's direction of travel, or move the opposite housing in the opposite direction. Determine the actual offset first.

03). Cut out and re-splice improper joints. Ensure the splice is straight (straightness tolerance ≤ 20mm over 10m). Use staggered splices matching troughing idler length for better troughing and to prevent pin breakage/tearing.

04). For misaligned idler frames, move the idler stands on the side the belt is moving towards slightly in the belt's direction. Usually, adjusting a few idlers suffices. For severe cases, re-align the entire idler frame within tolerance. Tighten loose bolts.

05). Strengthen belt inspection/maintenance. Repair or replace damaged belts promptly.

06). Adjust the loading point to be central on the belt.

07). Use properly designed guide chutes to prevent large lumps or high drop heights. Install impact idlers at the loading point.

08). Remove built-up material from pulleys and idlers. Adjust the return belt scraper; its contact length should be >85% of the belt width.

09). Re-align idler groups to the correct position. For mid-section misalignment, modify the idler stand mounting holes into elongated slots. If the belt moves left, move the left side of the idler group forward (direction of travel) or the right side backward, and vice versa.

10). Choose reputable manufacturers with experience and good technical support, offering reliable after-sales service.

11). During take-up installation, ensure the conveyor centerline is perpendicular to the take-up pulley axis. Follow installation requirements strictly and perform debugging.

12). Perform regular maintenance. Replace belts that are aged or deformed.

13). Correct skewed frames (centerline misalignment or uneven levels). This requires re-installing the frame to ensure its centerline is straight and sides are level.

14). Identify and resolve the root cause of vibration.

15). Add hold-down rolls in concave sections to prevent belt lift-off. Use the largest possible concave curve radius during design.

Monitor belt alignment frequently during operation. Correctly identify the cause and take appropriate measures promptly to ensure safe, efficient, and stable operation. Where possible, use belt misalignment switches or design safety alarm systems using limit switches to prevent spillage, abnormal equipment wear, and maintain productivity.