Diagnosis and Resolution of Belt Conveyor Misalignment: Technical Guide for Maintenance

1. Description of the Problem and Scope of Application

This technical guide addresses belt conveyor mistracking, a common but critical malfunction that can lead to unplanned production downtime, premature component wear, and safety hazards. Symptoms include lateral deviation of the belt from the central axis of the conveyor, rubbing against the structure, spillage of material, and damage to the edges of the belt. This guide covers belt conveyors used in demanding industrial environments, typical of the aerospace and energy sectors, where reliability and compliance with standards (NF EN 620, NF EN ISO 12100) are essential.

Severity Classification:

• Critical: Severe misalignment resulting in permanent contact of the belt with the structure, belt tears, major spillage, or emergency shutdown. Requires immediate intervention.
• Major: Intermittent or moderate misalignment, causing visible belt edge wear, significant material buildup, or requiring frequent adjustments. Requires rapid remediation planning.
• Minor: Occasional slight misalignment with no immediate impact on production or tape integrity, but indicative of an underlying problem. Requires monitoring and correction during next scheduled maintenance.

2. Safety Precautions

⚠ CRITICAL SECURITY WARNING ⚠

Before any intervention on the conveyor, it is imperative to strictly respect the Lockout and Unlocking procedures (Lockout/Tagout, LOTO) in accordance with the NF standard EN 1037. Ensure that all sources of energy (electrical, hydraulic, pneumatic, mechanical) are cut off, isolated and checked before approaching the moving areas of the conveyor. Energy stored in counterweights, tensioners or hydraulic systems must be released or secured. Always wear the appropriate Personal Protective Equipment (PPE): safety helmet (NF EN 397), protective glasses (NF EN 166), protective gloves (NF EN 388), safety shoes (NF EN ISO 20345) and high visibility work clothing. The risk of entanglement by the pinch points between the belt and the drums/rollers is high. Never work alone.

3. Required Diagnostic Tools

4. Initial Assessment Checklist

Before initiating a thorough diagnosis, it is essential to gather critical information about the conveyor's operating conditions and failure history. This step helps guide the diagnosis and avoid unnecessary investigations.

5. Systematic Diagnostic Flowchart

1. Tape offset observed while running:
   1. Locate the offset zone:
   • Constant offset at a specific location: Examine adjacent components (rollers, drums, scrapers) in this area.
   • Random or full-length offset: Suggests an overall problem (tension, structure, splices).
   2. Check loading point:
   • Is the material centered on the tape?
   • Are the baffles/troughs symmetrical and properly adjusted?
   • If not: Adjust the loading point for optimal centering (Tolerance: +/- 10% of the strip width).
   3. Inspect the condition of the tape:
   • Presence of damage (tears, cuts on the edges)?
   • Is the thickness of the strip uniform across its width? (Use thickness gauge, variation < 0.5 mm on the width).
   • Are the joints (splices) straight and the same thickness as the strip? (Use straight edge, misalignment < 2 mm over 2 m).
   • If damage/irregularities: Repair or replace the strip / redo the splice.
   4. Check the belt tension:
   • Use a tensiometer or dynamometer to measure the return tension.
   • Comparison with OEM specification (Example: 400-600 N/cm bandwidth for medium duty).
   • If incorrect tension: Adjust the tension system (counterweight, tensioner screw) according to specifications.
   5. Examination of drums (head, tail, return, tension):
   • Are the drums clean and free of material buildup?
   • Is the drum covering in good condition? Excessive or asymmetrical wear? (Variation in coating thickness < 1 mm).
   • Are they perpendicular to the longitudinal axis of the conveyor? (Measurement with a tape measure between the bearings, tolerance < 2 mm over 1m).
   • Is their horizontality correct? (Bubble level, tolerance < 0.5 mm/m).
   • If an anomaly: Clean, repair or replace the covering. Adjust the drum alignment.
   6. Roll examination (support, return, centers):
   • Rollers clogged or blocked? (Manual free rotation).
   • Worn or damaged rollers (deformation, noisy bearings)? (Visual inspection, listening, thermal camera > 50°C).
   • Are the roller frames correctly leveled and squared to the frame? (Bubble level, tape measure, tolerance < 1 mm/m of misalignment).
   • Are the rollers correctly installed (centering roller inclination)?
   • If an anomaly: Clean, unblock, replace the rollers or bearings. Adjust or repair frames.
   7. Checking the conveyor frame:
   • Is the structure straight, level and free of distortion? (Laser level over the entire length).
   • Is the foundation stable? (Visual inspection of cracks, sagging).
   • If deformation or instability: Consult a structural engineer for repair.

6. Cause-Effect Matrix of Failures

7. Root Cause Analysis for Each Failure

7.1 Eccentric Loading

Explanation: Non-uniform or offset loading applies uneven force to the belt, pushing it sideways. This is common when loading chutes are poorly designed, worn, clogged, or the material discharge speed does not match the belt speed, causing buildup.

Confirmation: Observe the loading point during operation. Use a camera to record the distribution of material on the tape. Measure the position of the center of gravity of the load relative to the center of the belt. A deviation of more than 10% of the band width is critical.

Unresolved damage: Accelerated belt edge wear, material spillage, damage to centering rollers, and potential for emergency stops if offset activates safety sensors.

7.2 Improper Alignment of Rollers and Frames

Explanation: Individual rollers inclined to the perpendicular of the belt, or unleveled/squared roller frames, act as "steers" forcing the belt to shift. This may be due to incorrect initial assembly, deformation of the frame, impacts, or asymmetrical soiling.

Confirmation: Use a precision spirit level on each roller and a measuring laser to check the squareness of the frames in relation to the frame. The parallelism tolerance of the rollers in relation to the axis of the drums must not exceed 1 mm per meter of belt width. An angular deviation of more than 0.5 degrees is significant.

Unresolved damage:Asymmetrical belt wear, increased energy consumption due to friction, premature failure of roller bearings and, ultimately, belt tearing.

7.3 Misaligned or Damaged Drums

Explanation: The drums (head, tail, return, tension) play an essential role in guiding the belt. If a drum is not perpendicular to the longitudinal axis of the conveyor or if its coating is worn asymmetrically, it will cause a constant offset of the belt. Buildup of material on a drum can also create a “false” cone, causing offset.

Confirmation: Measure the squareness of the drum bearings in relation to the frame (difference between the diagonals of the drum faces and the conveyor axis must be < 2 mm over 1m). Visually inspect coatings for wear or fouling. Use a vibrometer to detect dynamic imbalances or bearing defects (RMS speed value > 4.5 mm/s class 2 EN ISO 10816-3).

Unresolved damage: Excessive belt fatigue, rapid failure of drum bearings, belt tears, risk of jamming and fire (ATEX if explosive environment).

7.4 Inappropriate Band Tension

Explanation: Too little tension does not allow the belt to follow its path correctly, increasing the risk of slipping on the motor drums and shifting. Excessive tension places unnecessary strain on the belt and bearings, potentially causing permanent deformation of the belt and rollers.

Confirmation: Use a dynamometer or belt tension meter at the measurement point specified by the conveyor manufacturer. Compare the measured value with the range recommended by the OEM (Example: for a textile belt, recommended tension 10-12 N/mm width, i.e. for a 1000 mm belt, 10-12 kN).

Unresolved damage: Belt slippage (wear of the drums and belt), erratic offset, bearing overload, irreversible stretching of the belt, and possible splice breakages.

7.5 Faulty or Damaged Splice

Explanation: A poorly made junction (splice), not perpendicular to the axis of the strip, or damaged (delamination, tearing) creates an asymmetry of tension or rigidity which shifts the strip each time the splice passes.

Confirmation: Stop the conveyor and inspect each splice. Check the perpendicularity of the splice in relation to the edges of the strip (deviation < 2 mm over 2 m length). Check the thickness of the splice (must not exceed the thickness of the strip by more than 10%). Visually look for signs of delamination, cracks or damage.

Unresolved damage: Localized wear on the rollers and drums, cyclical offset, risk of belt breakage leading to a major stoppage and significant material damage.

8. Step-by-Step Resolution Procedures

8.1 Correction of Eccentric Loading

1. ⚠ SAFETY: Lock out the conveyor (LOTO).

2. Adjust the position and angle of the loading chutes to center the material on the belt. Use adjustable baffles if necessary.
3. Install steeply inclined centering rollers (35-45°) just after the loading point to help stabilize the belt under load.
4. Check the height of fall of the material. Reduce it if possible to minimize impact and lateral dispersion.
5. Check the alignment of the chute wear plates, replace them if they are worn asymmetrically.
6. Verification: Start the conveyor empty then under progressive load. Observe the stability of the belt at the loading point. The offset must be corrected or significantly reduced.

8.2 Realignment of Rollers and Frames

1. ⚠ SAFETY: Lock out the conveyor (LOTO).

2. Thoroughly clean all rollers and their supports.
3. Identify rollers misaligned or damaged from previous tests.
4. For misaligned rollers:
   • Loosen the roller frame mounting bolts or individual supports.
   • Use a spirit level or laser level to ensure that the axis of the roller is perpendicular to the axis of the belt (parallelism tolerance < 1 mm/m).
   • Adjust the adjustment screws or insert shims to correct the inclination.
   • Tighten all bolts to the torque specified by the manufacturer (often between 50-80 Nm for M12 bolts).
5. For damaged rollers: Replace them with UNITEC rollers of equivalent specification (NF EN 14973).
6. Check: Start the conveyor empty. Observe the passage of the belt over the adjusted rollers. The band must maintain stable centering.

8.3 Drum Alignment and Repair

1. ⚠ SAFETY: Lock out the conveyor (LOTO).

2. Thoroughly clean the drums and the surrounding area.
3. Squaring measurement:
   • Measure the distance between the center of each drum bearing and a fixed reference point on the frame, on each side. Adjust the bearing until the distances are equal (tolerance < 2 mm).
   • Check the horizontality of the drum axis with a precision level (tolerance < 0.5 mm/m).
4. Covering Repair/Replacement:
   • If the coating is worn or damaged asymmetrically, replace it. Prefer a rubber coating with chevron grooves for the motor drums and smooth for the return/delivery drums.
   • Ensure that the new coating is evenly applied and of the same thickness over the entire surface.
5. Check: Start the conveyor empty and observe the entry and exit of the belt at the drum. The band must be stable and centered.

8.4 Adjusting the Belt Tension

1. ⚠ SAFETY: Lock out the conveyor (LOTO).

2. Identify the type of tensioning system (screw, counterweight, hydraulic).
3. Measure the current belt tension with a belt tension meter or dynamometer at the reference point.
4. Adjust the tension system gradually, in small increments, checking the tension after each adjustment.
5. Ideal tension: The belt must be sufficiently taut to prevent slipping without being excessively stressed. Refer to the manufacturer's service manual for specific values ​​(Example: 400-600 N/cm for general applications).
6. Ensure that both sides of the tensioning system (if applicable, e.g. tensioning screw) are adjusted equally to maintain parallelism.
7. Check: Start the conveyor empty. Observe the absence of slipping when starting and stable centering of the belt. Gradually increase the load and re-check.

8.5 Repair of Faulty Splices

1. ⚠ SAFETY: Lock out the conveyor (LOTO). Make sure the splice is accessible safely.

2. If the splice is damaged, make a new splice in accordance with the tape manufacturer's recommendations and the standards in force (NF ISO 7622-1/2 for vulcanized splices, NF ISO 15236 for mechanical splices).
3. Use tools specific to the splicing method (vulcanization kit, presses, cutting tools).
4. Ensure that the new splice is perfectly perpendicular to the edges of the strip and that its thickness is uniform.
5. Check: Start the conveyor empty and observe the behavior of the splice. It must pass smoothly over the rollers and drums without causing offset.

9. Preventive Measures

10. Spare Parts and Components

To ensure rapid response and minimize downtime, it is essential to have critical spare parts on hand. UNITEC-D GmbH offers a complete range of CE certified conveyor components.

For all your spare parts requirements, please view our comprehensive e-catalog: www.unitecd.com/e-catalog/

11. References

• NF EN ISO 12100: Safety of machines – General design principles – Risk assessment and risk reduction.
• NF EN 620: Continuous handling equipment and systems – Safety and EMC requirements for belt conveyors.
• NF EN ISO 10816-3: Measurement and evaluation of mechanical vibrations of machines – Evaluation of machine vibrations on site.
• NF EN 1037: Machine safety – Prevention of accidental start-up.
• NF EN 14973: Conveyor belts – Safety requirements for conveyor belts for continuous handling equipment.
• NF ISO 7622-1/2: Conveyor belts – Vulcanized junctions of conveyor belts – Part 1: Methods of testing longitudinal tensile properties; Part 2: Method of testing longitudinal tensile properties of repair joints.
• NF ISO 15236: Multi-layer textile conveyor belts – Test methods for mechanical joints.
• Conveyor Manufacturers (OEM) Technical and Maintenance Manuals.
• Associated UNITEC-D maintenance guides: “Precise Shaft Alignment”, “Industrial Bearing Diagnosis”.