Diagnosing and Troubleshooting Belt Tracking Problems on Belt Conveyors: A Guide for Maintenance Technicians

1. Problem description & scope of application

These instructions cover the systematic diagnosis and elimination of belt tracking problems (mistracking) in belt conveyor systems. Belt tracking problems manifest themselves as the conveyor belt deviating from the center line of the system, which can lead to edge damage to the belt, loss of material, premature wear of components, increased power consumption and, in extreme cases, to system downtime. The diagnostic steps described here are applicable to all common belt conveyor systems used in bulk and piece goods conveying technology in the DACH manufacturing industry in accordance with DIN 22101.

Severity classification of tape tracking problems:

• Critical: Immediate deviation of more than 10% of the belt width, loss of material in critical areas, contact of the belt with the system structure, potential belt damage or safety risk. Requires immediate action.
• Major: Consistent deviation of 5-10% of the belt width, slight loss of material, increased and uneven wear of pulleys or belts. Requires planning to resolve immediately.
• Minor: Occasional deviation of less than 5% of the bandwidth, no loss of material, no immediate risk of damage. Requires monitoring and root cause analysis at next scheduled maintenance.

2. Safety instructions

WARNING! Working on belt conveyor systems involves significant risks due to moving parts, trapped energy and falling materials. Failure to follow these safety instructions could result in serious injury or death.

• LOTO (Lockout/Tagout): Before any diagnostic or maintenance work begins, the belt conveyor system must be completely disconnected from the power supply and secured against being switched on again in accordance with EN ISO 14118 (Safety of Machines - Avoiding Unexpected Start-Up).
• Personal protective equipment (PPE): Always wear the prescribed PPE, in particular safety shoes with toe protection (EN ISO 20345), protective gloves (EN 388), safety helmet (EN 397) and safety glasses (EN 166).
• Residual energy: Conveyor belts can store considerable mechanical tension. Particular caution is required when inspecting or processing belt tensioning systems. Never enter the danger area under a tensioned belt.
• Material accumulations: Material accumulations under the system or on the belt can represent dangerous tripping hazards or lead to sudden belt movements. Such accumulations must be removed before work begins.
• Motion test: During diagnostic work that requires short-term operation of the system, it must be ensured that there are no people in the danger area. All protective devices must be in place or exemptions must be available.

3. Diagnostic tools required

The following tools are essential for a precise root cause analysis of belt tracking problems:

4. Checklist for initial assessment

Before starting the detailed diagnosis, a careful initial assessment is crucial in order to understand the context of the problem and obtain initial indications of the cause:

5. Systematic diagnosis – flowchart

Follow this structured approach to isolate the cause of the tape run problem:

1. General belt running test (system in operation, under observation, in compliance with all safety regulations):
   • IF Belt deviates consistently to one side:
     1. Check longitudinal alignment of the entire system:
        • IF Belt deviates to the same side on the upper and lower belts:
          • Probable cause: Main rollers (head, foot, drive rollers) not aligned transversely to the conveying direction.
          • Go to 5.2 (Major Role Alignment).
        • IF Belt deviates to one side on the upper belt and to the other side on the lower belt:
          • Probable cause: Structural distortion of the frame or uneven loading, belt tension problem.
          • Go to 5.3 (Frame twist and belt tension).
   • IF Belt only deviates at the top belt:
     1. Check loading point:
        • IF Loading is eccentric or not centered:
          • Probable cause: Uneven material loading.
          • Go to 5.4 (Loading Point Problems).
        • IF Conveyed material collects on belt guides or impact plates:
          • Probable cause: Clogged or incorrectly adjusted belt guides/scrapers.
          • Go to 5.4 (Loading Point Problems).
     2. Check idlers:
        • IF Idlers blocked on one side, stiff or worn:
          • Probable cause: Defective idlers.
          • Go to 5.5 (carrier and support rollers).
        • IF Carrier roller frame crooked or not at an angle to the conveying direction:
          • Probable cause: Misaligned carrier roller frames.
          • Go to 5.5 (carrier and support rollers).
   • IF Belt only deviates at the Bottom belt (return):
     1. Check support rollers:
        • IF Support rollers blocked, stiff or worn on one side:
          • Probable cause: Defective support rollers.
          • Go to 5.5 (carrier and support rollers).
        • IF Material sticks to the belt and collects on the support rollers:
          • Probable cause: Insufficient belt cleanliness, material adhesion.
          • Go to 5.6 (Material adhesion and wipers).
   • IF Belt deviates on a specific main role (e.g. head, foot, deflection pulley):
     1. Check the alignment of the specific pulley:
        • IF pulley is not aligned transversely to the conveying direction:
          • Probable Cause: Incorrect alignment of the roller.
          • Go to 5.2 (Major Role Alignment).
        • IF Roll is contaminated or has accumulation of material (crown formation):
          • Probable cause: Material accumulation on the roll.
          • Go to 5.6 (Material adhesion and wipers).
   • IF Gurt wandert zufällig oder schlägt:
     1. Prüfe Gurtspannung:
        • IF Gurtspannung außerhalb des Toleranzbereichs (zu hoch/zu niedrig):
          • Wahrscheinliche Ursache: Falsche Gurtspannung.
          • Go to 5.3 (belt tension).
     2. Check belt edges for damage/deformation:
        • IF Edges damaged or unevenly worn:
          • Probable cause: Belt edges damaged.
          • Go to 5.7 (Webbing and Splice Defects).

6. Error-cause matrix

This matrix summarizes the most common symptoms, likely causes, and associated diagnostic tests:

7. Root cause analysis for each error

A deeper understanding of the causes is essential for their permanent elimination:

7.1 Misalignment of head, foot or idler pulleys

• Why it happens: Lead roles define the basic tape run. Incorrect angular alignment with the conveying direction will result in the belt constantly being pulled to one side. Causes can include assembly errors, foundation settlement, collisions or improper maintenance.
• How to confirm: Use a laser alignment system. Measure the parallelism of the roller axes to the conveying direction and the angular deviation of the rollers to one another. A deviation of more than 0.1 mm/m across the roll width is critical. Also check the alignment of the drive roller to the transmission and motor according to VDI 2060 (vibration diagnosis).
• Damage if not repaired: Permanent edge wear of the belt, increased bearing load and premature failure of bearings and seals in the rollers, increased energy consumption due to friction, structural damage to the system frame due to constant belt contact.

7.2 Uneven material loading

• Why it happens: If material is not loaded centrally and evenly onto the belt, one-sided pressure occurs. The belt responds by deviating to the more lightly loaded side to compensate for the force imbalance. This can be caused by incorrectly positioned feed hoppers, uneven material feeding, or inadequate flapper guidance.
• How to confirm: Observe the loading point during operation. Visualize the material flow and, if necessary, measure the thickness of the material layer across the belt running direction. A deviation of the material center from the belt center by more than 5% of the belt width is unacceptable.
• Damage if not repaired: Constant belt running, increased wear on belt edges and guides, loss of material due to overflow, damage to side seals and impact plates.

7.3 Insufficient belt tension

• Why it happens: Correct belt tension is crucial for the transmission of drive power and stable belt running. Too little tension leads to slippage on the drive rollers and uncontrolled belt fluttering and wandering. Too high a tension can overload the belt and bearings.
• How to confirm: Measure the belt tension with an acoustic belt tension meter or via the position of the tension carriage on a known belt type. The tension should be within the tolerances specified by the belt manufacturer, typically such that the belt stretch during operation is 1.5% to 2.5% of the belt length. According to DIN 22101, the minimum pretension must prevent the belt from slipping.
• Damage if not rectified: Increased slip leads to belt and drum wear, uncontrolled belt running, damage to the belt edges, unstable operation. If the tension is too high: premature aging and cracking of the belt, bearing damage, increased load on the drive train.

7.4 Defective or blocked carrying and support rollers

• Why it happens: Seized, stiff, crookedly mounted or unevenly worn idler and support rollers create one-sided resistance or a steering force that deflects the belt from the centerline. Accumulation of material on the rollers can also cause one-sided crown formation.
• How to confirm: Check each roller visually and manually for free rotation (by tapping lightly when the system is stationary). Pay attention to noise, heat development (with IR thermometer, above 60°C critical) or accumulation of material. Measuring the longitudinal and lateral inclination of the roller frames with an inclinometer or laser is also critical.
• Damage if not repaired: Local belt wear, fraying of the belt, increased energy consumption, damage to the belt frame due to contact, risk of belt breakage when clamping.

7.5 Belt and splice defects

• Why it happens: A poorly executed or damaged splice (e.g. not cut square, uneven thickness) or a belt with uneven thickness, damage or deformation can behave like a one-sided steering force and cause the belt to run off.
• How to confirm: Inspect the entire belt and especially all splices for damage, cracks, uneven thickness or deformation. Use a caliper to check the thickness of the strap and splice. Deviations in splice thickness of more than ± 1 mm or in belt thickness of ± 0.5 mm (manufacturer tolerance) can be problematic.
• Damage if not repaired: Permanent belt running, premature belt wear, risk of belt breakage at the splice point, loss of material.

8. Step-by-step correction procedure

Once the cause has been identified, the following corrective actions should be taken:

8.1 Elimination of roller misalignments (head, foot, idler rollers)

1. SAFETY NOTE: Disconnect and secure the system according to LOTO.
2. Clean the areas around the roller bearings and attachment points.
3. Use the laser alignment system to determine the actual position of the roll relative to the conveying direction and neighboring rolls.
4. Loosen the bearing or roller frame mounting screws.
5. Carefully adjust the roller until the optimal alignment (angular deviation < 0.1 mm/m) is achieved. Always start at the submission page and work your way towards the task.
6. Tighten the fastening screws with the specified torque (according to the manufacturer's instructions, e.g. 120 Nm for M16 roller bearing screws).
7. Carry out a functional test (short test run under observation, all protective devices in place).
8. Perform a final laser measurement to verify correct alignment.

8.2 Correction of material loading

1. SAFETY NOTE: Disconnect and secure the system according to LOTO. Be careful of accumulations of material.
2. Identify the cause of the eccentric loading (e.g. incorrect position of the feed hopper, lateral material feed).
3. Adjust or modify the feed hopper to ensure central and consistent feeding of material onto the belt.
4. Check the adjustment and condition of the flappers. Make sure they center the material and don't create any bottlenecks. The distance between the impact plate and the belt should be approx. 10-15 mm.
5. Check the function and setting of bulk material distributors or dosing devices, if any.
6. Carry out a test run and observe the loading point. Make fine adjustments if necessary.

8.3 Adjusting the belt tension

1. SAFETY NOTE: Disconnect and secure the system according to LOTO. Be particularly careful with clamping systems with weights or hydraulics!
2. Determine the target tension according to the belt manufacturer's instructions or the system manual.
3. Measure the current belt tension with an acoustic tension meter.
4. Adjust the tension:
   • For screw tensioning systems: Tighten the tensioning screws evenly on both sides.
   • For weight tension systems: Check the correct weighting.
   • For hydraulic/pneumatic clamping systems: Adjust the hydraulic/pneumatic pressure according to specifications (e.g. 6 bar for pneumatic clamping cylinders).
5. Make sure that the tension carriage is perpendicular to the conveying direction and can move freely.
6. Measure the tension again and verify that it is within the tolerance range (e.g. 2% belt stretch).
7. Carry out a test run and observe the belt movement.

8.4 Maintenance/replacement of carrying and support rollers

1. SAFETY NOTE: Disconnect and secure the system according to LOTO.
2. Identify any broken, stiff, or misaligned rollers.
3. Clean the area around the rollers.
4. Completely replace damaged or stiff rollers. Use rollers according to DIN 22112 with the same specifications as the original rollers.
5. Check the longitudinal and transverse inclination of the roller frames. Adjust these using an inclinometer or laser so that they are horizontal (deviation < 0.2°) and perpendicular to the conveying direction.
6. Make sure that the roller axes are perpendicular to the conveying direction. A deviation of < 0.2° should be aimed for here.
7. Carry out a functional test (short test run under observation).

8.5 Repair of belt and splice defects

1. SAFETY NOTE: Disconnect and secure the system according to LOTO. Be careful with sharp tools and hot vulcanizing equipment.
2. Assess the damage to the strap or splice.
   • Small damage (up to 50 mm): Repair by cold hardening or hot vulcanization according to DIN 22129 (repair of conveyor belts).
   • Major damage, permanent deformation or splice defects: Requires a new splice or replacement of the belt part.
3. Carry out a proper splice repair or new production in accordance with the belt manufacturer's instructions and DIN 22126 (conveyor belts with textile tension members - splice connections). Make sure the splice ends are exactly square and centered to each other.
4. After repair, check the strap thickness and splice thickness to ensure uniformity.
5. Carry out a test run.

9. Preventive measures

In order to minimize belt tracking problems in the long term, the following preventative strategies must be implemented:

10. Spare Parts & Components

The availability of the right spare parts is crucial for quick and effective maintenance. The following components are typically affected:

Further spare parts and detailed specifications can be found in our comprehensive e-catalogue: www.unitecd.com/e-catalog/

11. References

• DIN 22101: Belt conveyors for bulk goods – calculation and design
• DIN 22102: Conveyor belts with textile tension members for belt conveyors – dimensions, requirements
• DIN 22112: Support rollers for belt conveyors – dimensions, requirements
• DIN 22126: Conveyor belts with textile tension beams - splice connections
• DIN 22129: Repair of conveyor belts
• VDI 2060: Vibration diagnosis on machines
• VDI 3832: Measuring mechanical vibrations - vibration intensity of non-rotating components on machines with lifting or pendulum movements
• ISO 10816-3: Mechanical vibration – Evaluation of machine vibration by measurements on non-rotating parts – Part 3: Industrial machines with nominal power above 15 kW and nominal speeds between 120 r/min and 15 000 r/min when measured in situ
• EN ISO 14118: Safety of machines – avoiding unexpected startups
• EN 388: Protective gloves against mechanical risks
• EN 397: Industrial safety helmets
• EN 166: Personal eye protection requirements
• EN ISO 20345: Personal protective equipment – safety shoes