Maintenance Guides 1 min read

Chain Conveyor Diagnosis and Troubleshooting: A Step-by-Step Technical Guide

Technical analysis: Troubleshooting chain conveyor jamming and overload: chain elongation, sprocket wear, lubrication fa

Chain Conveyor Diagnosis and Troubleshooting: A Step-by-Step Technical Guide

1. Problem Description and Area of Application

This manual is intended for senior engineers, technicians, and mechanics of Ukrainian industry enterprises (metallurgy, cement industry, energy, agro-industrial complex) operating chain conveyors with plate, scraper, and bucket type. The purpose of the document is to provide a clear algorithm for fault searching during sudden stops, relay protection tripping of electric motors or presence of non-characteristic impact loads and noise in the drive station.

Failure Criticality Classification for Chain Conveyor Systems: Critical (CAT-1) — complete chain jamming, chain breakage, gear wheel tooth damage or reducer damage. Causes an emergency stop of the production line. Major (CAT-2) — progressive chain elongation, tooth skipping (chattering), material buildup in the scraper pocket, local bearing unit overheating (above 75°C). Minor (CAT-3) — increased noise from guides, slight lubricant leakage through reducer seals, periodic vibration within 2.8–4.5 mm/s.

2. Precautionary Measures (Safety Techniques)

DANGER! STORED ENERGY AND UNEXPECTED STARTUP.
Before performing any diagnostic or maintenance work on the chain conveyor, perform a full Lockout/Tagout (LOTO) procedure in accordance with occupational safety standards and ISO 14118:
1. Completely turn off the main switch of the drive motor and lock it with a padlock.
2. Remove voltage from the control circuits and frequency converters.
3. Block mechanical energy: if the conveyor is installed on an incline or loaded with process material, install mechanical stops (chain catchers) to prevent reverse rotation due to gravitational force.
4. Check for absence of residual energy using a digital multimeter (zero potential at the motor terminals).
5. Personal protective equipment (PPE): safety helmet, side-shielded goggles, noise-reducing earplugs, heat-resistant gloves (when working with heated components), protective footwear with a steel toe.

3. Required diagnostic tools

Tool Name Specification / Model Measurement range Purpose in diagnostics
Digital multimeter True RMS (CAT III 1000V / CAT IV 600V) 0 – 1000 A (with current clamps), 0 – 600 V AC/DC Measurement of starting and running current of an electric motor
Vibrometer / Vibration analyzer Spectral Analyzer (ISO 10816 / 20816) 10 Hz – 10 kHz, 0.1 – 100 mm/s Roller bearing condition monitoring, gear mesh analysis, imbalance
Thermovisor (Thermal imager) IR camera with resolution of 160x120 -20°C ... +350°C (accuracy ±2°C) Detection of bearing overheating, gearboxes and chain friction points
Laser leveling system Optical Shaft Alignment Tool Up to 10 m, resolution 0.001 mm Alignment Check of the Drive and Driven Shaft of the Conveyor
Vernier Caliper / Plug Gauge Mechanical or digital (DIN 862) 0 – 300 mm, accuracy 0.01 mm Measurement of gear tooth wear and chain pitch length
Ultrasonic flaw detector Portable (for non-destructive testing) 0.5 – 10 MHz Crack detection on rollers, sprockets and welded joints

4. Check-list of initial assessment (before starting diagnostics)

Observation Parameter What to check and fix Norm / Permissible Value Alarm Value
Operating current of the motor ($I_{раб}$) Compare with the nominal current according to the passport ($I_{ном}$) $I_{раб} \le 0.85 \times I_{ном}$ $I_{раб} > 1.15 \times I_{ном}$ (overload)
Temperature of bearing housings Take readings with a thermal imager or contact thermometer $T \le 65^\circ{\text{C}}$ $T > 75^\circ{\text{C}}$ (or increase of 20°C above normal)
Vibration level of the reducer housing and bearings Measure RMS vibration velocity (10–1000 Hz) $V_{rms} \le 2.8$ mm/s (ISO 10816-3, class II) $V_{rms} > 4.5$ mm/s (critical threshold)
Presence of external noises Stethoscope audio control in star zone and groove areas Quiet uniform gear noise Impact, screech, pulsating metallic noise
Lubrication system status Check the oil level in the reducer, condition of the chain lubricators Level in the inspection window in the middle Below minimum, approved lubrication, absence of oil
Technological loading Material feed history, presence of moisture, rancidity Stable supply according to the line passport Impact overload, foreign object ingress

5. Systematic Diagnostic Block Diagram

  1. Symptom A: Sudden conveyor stop or tripping of thermal relay/engine protection circuit breaker.
    • Check the electrical circuits and reducer condition.
      • IF the reducer shaft rotates manually (when disengaged or engine is off) THEN the problem is in the electric motor or short circuit. Check the windings with a multimeter and megohmmeter.
      • IF the reducer shaft is seized or difficult to rotate THEN check the mechanical part of the conveyor.
    • Check for chain jamming in the trough.
      • IF the chain is jammed due to foreign object intrusion or material buildup THEN perform trough cleaning (see section 8).
      • IF foreign objects are not present THEN check the chain extension and star wheel tooth wear (Go to Symptom B).
  2. Symptom B: Continuous jerking, knocking, chain skipping on the drive sprocket (chattering).
    • Measure the chain pitch with a vernier caliper over a section of 10 links and compare it with the nominal value ($P_0$).
      • IF chain elongation $\Delta L > 2.0\%$ of the nominal length THEN the chain is critically worn at the pivot joints. Replacement or removal of worn links (if allowed by the tensioning device) is required.
      • IF elongation within the allowable limit ($\Delta L \le 1.5\%$) THEN check the chain tension and wear of the driven sprocket (Go to Symptom B).
  3. Symptom B: Bearing unit overheating and increased motor current consumption without jamming.
    • Check the lubrication condition and chain tension.
      • IF chain tension is too high (deflection of upper/lower branch is less than normal) THEN reduce the tensioner bolt/tensioner weight force.
        • IF chain tension is normal, but lubrication is absent or contaminated THEN clean the unit, renew the grease (according to ISO 12925-1 for gearboxes or NLGI 2 for bearings).

6. Symptom - Cause Matrix

Symptom Likely causes (sorted by probability) Diagnostic test Expected result upon confirmation of the cause
1. Shafting and shear pin failure 1. Foreign metal object entering the working trough.
2. Deterioration and over-wetting of the product.
3. Skew of the drive chain.		 Visual inspection of the trough from the inside, checking the geometry of the guides. Detection of burrs on the casing walls, dents on the scraper, jammed object.
2. Chain Skipping on the Sprocket 1. Tooth wear (tooth profile wear).
2. Chain pitch elongation due to bushing/pin wear.
3. Insufficient chain tension.		 Measurement of the gear tooth thickness and chain pitch with vernier caliper/template. Reduction of the star gear tooth thickness > 10% or elongation of the chain > 2%.
3. Shaft rotation and load pulsation 1. Insufficient lubrication of chain joints (dry friction in pins).
2. Deformation of individual plates or scrapers.
3. Jamming of support rollers (for plate-type conveyors).		 Thermal imaging inspection of joints, manual rotation check of rollers. Local hot spots on hinges ($T > 70^\circ{\text{C}}$), jammed rollers.
4. Overload of the motor ($I > 1.2 I_{ном}$) 1. Adhesion of the conveyed material to the bottom and sides of the trough.
2. Chain slippage.
3. Internal friction in the reducer (bearing damage).		 Current measurement with clamp meters, vibration check of the reducer, measurement of the gap under the scrapers. High level of vibration on the output shaft of the reducer ($V_{rms} > 5.0$ mm/s), clearance less than normal.

7. Root Cause Analysis

7.1. Chain Elongation

Why it occurs: Chain elongation is not the result of steel stretching in the elastic deformation zone. It is a result of abrasive wear of friction surfaces in the pivot connections (pin bushing or shaft hole). Operating conditions in the Ukrainian industry (cement dust, abrasive ore, grain dust with humidity) accelerate this process 3–5 times in the absence of effective protection and lubrication.

Як підтвердити: Виміряйте довжину контрольної ділянки з 20 кроків ланцюга під натягом (прикладіть зусилля, що становить приблизно 10% від розривного навантаження ланцюга). Порівняйте з паспортним значенням. Якщо відхилення перевищує 1.5–2.0%, ланцюг вичерпав свій ресурс за геометрією зачеплення.

Наслідки: Неправильне входження зубів зірочки в западини ланцюга. Зростання динамічних навантажень, зрізання зубів зірочки, утворення задирів, обрив ланцюга під час пуску.

7.2. Star Wheel Wear (Sprocket Wear)

Why it occurs: The star wheel and chain work in pair. If the chain elongates, the chain pitch no longer corresponds to the sprocket pitch. The load begins to be transmitted not over the entire tooth surface, but on one or two end teeth. This leads to tooth profile cutting («hook-like» wear).

Як підтвердити: Візуальний огляд та вимірювання шаблоном профілю зуба. Наявність виражених канавок від валиків ланцюга на робочій поверхні зуба та асиметричне стоншення зуба більше ніж на 10-12% від початкового розміру.

Наслідки: Проскакування ланцюга, зрив зубів, інтенсивний шум та вібрація, аварійний зупин обладнання з пошкодженням прилеглих конструкцій.

7.3. Lubrication Failure (Lubrication Failure)

Why it occurs: Use of lubricating materials not suitable for the ambient conditions (for example, using mineral-based grease in high temperature or dusty conditions, leading to grease carbonization and conversion into an abrasive paste).

Як підтвердити: Аналіз стану змащувального матеріалу в точках тертя. Наявність затверділих відкладень, чорного кольору та металевої стружки в пробі мастила. Вимірювання температури пірометром ($T > 75^\circ ext{C}$).

Наслідки: Сухе тертя, задир поверхонь ковзання, заклинювання осей ланцюга, різке зростання споживання електроенергії, вихід з ладу двигуна через перевантаження.

7.4. Material Buildup (Material Buildup)

Why it occurs: Transporting wet, sticky or hot bulk materials (clay, wet coal, compound feed, cement raw material), which get stuck in the gaps between the scrapers and the walls/bottom of the trough, as well as adhere to the return branch on the non-working surfaces of the stars.

How to confirm: Visual inspection through access hatches when the conveyor is stopped (strictly according to the LOTO procedure!). Presence of compacted material layers with a thickness of at least 5 mm on the bottom of the trough.

Наслідки: Збільшення опору переміщенню ланцюга, стирання скребків, перевантаження приводу, деформація металоконструкції конвеєра.

8. Step-by-step Troubleshooting Procedures (Resolution Procedures)

8.1. Replacement or Adjustment of the Drive Chain Length

  1. Perform the procedure LOTO (section 2). Secure the chain branches with mechanical stops to prevent their accidental displacement.
  2. Release the tensioning device (screw or spring-hydraulic jacks) to the maximum stroke length.
  3. Locate the detachable coupling (or pin) of the chain. Remove the retaining pins / disassemble the bolted connection.
  4. Option A (Shortened): If the chain has extended slightly and the slack of the tensioning device is exhausted, remove 2 or 4 links (even number) and connect the chain with a new connecting link (according to DIN 8167 / ISO 1977).
  5. Variant B (Full Replacement): If the wear of the pins is critical (elongation > 2%), remove the old chain and tension the new chain using the old one (winch pulling method).
  6. Adjust the chain tension: the sag of the free branch of the lower belt should be 1.0–1.5% of the boundary distance between the centers of the sprockets (according to the recommendations ISO 4190). Tighten the tension bolt lock nuts with the torque according to the bolt strength class (for example, for M24 class 8.8 — torque 650 N·m).
  7. Perform a test run on no load for 30 minutes. Monitor current and vibration.

    8. 8.2. Removal and Replacement of Worn-Out Stars

    1. Perform the procedure LOTO. Remove the drive protective covers.
    2. Release the chain tension to reduce the load on the sprocket.
    3. Remove the drive or driven shaft from the bearing units (if the construction is disassemblable) or loosen the bolts securing the segmented star wheel to the hub.
    4. Using a hydraulic remover, remove the keyway coupling from the conical/cylindrical mounting seat.
    5. Clean the shaft seat, check it for microcracks and scoring (use magnetic particle inspection or liquid for non-destructive testing).
    6. Install a new star wheel UNITEC, aligning the keyway. When using interference fit, use an induction heater to a temperature not exceeding 120°C.
    7. Check the alignment of the shafts using a laser alignment tool (permissible parallel misalignment — not more than 0.15 mm, angular — not more than 0.05 mm/m).
    8. Install protective covers, perform a test run.

      9. 8.3. Lubrication system restoration and cleaning of units

      1. Perform the procedure LOTO.
      2. Perform an inspection of the centralized or point lubrication system of the chain (automatic lubricators, nozzles).
      3. Clean the chain joints with an industrial solvent under pressure to remove abrasive dust and old greased lubricant.
      4. Fill the units with new high-temperature synthetic lubricant (viscosity class ISO VG 220/460 for reducers or lubricant with solid additives based on molybdenum disulfide $MoS_2$ for chain joints).
      5. Check the operation of the chain return side scraper brushes, adjust the gap between the cleaning plate and the chain (recommended gap 1.0 – 1.5 mm).

      9. Preventive Measures (Prevention Matrix)

      Primary Cause Preventive strategy Monitoring method Recommended interval
      Chain extension Tension control, timely lubrication update of joints. Chain pitch measurement with a template. Every 500 hours of operation
      Star ratings Use of tempered stars made of induction-hardened steel (HRC 45–50). Visual inspection of the gear tooth profile. Every 1000 hours of operation
      Lubrication Errors Installation of automatic lubricators with oil selection according to Ukrainian climatic conditions (from -30°C to +40°C). Pressure control in lubrication main lines, oil sample analysis. Monthly / Quarterly
      Material coating Installation of polyurethane linings on trough walls, mounting of vibrators on discharge hoppers. Current consumption monitoring of the motor (warning signal when current increases by 10%). Continuous monitoring (SCADA)

      10. Spare Parts and Components UNITEC-D

      Description of the part Specification / Standard When to replace Category UNITEC
      Drive chain ISO 1977 / DIN 8167 (step 80–250 mm, high shear load) When the step is extended > 2.0% or cracks are present in the plates Chains and drives
      Drive and Tension Stars High-frequency tempered teeth (HRC 48-52), steel 40Х / 35ХГСА Tooth profile deviation > 10%, presence of deep grooves Stars and Gears
      Ball bearing units (housing) SNL / UCP series with Taconite seals for dusty environments Temperature > 75°C, vibration $V_{rms} > 4.5$ mm/s Bearings and housings
      Scraper and trough lining Abrasion-resistant steel HBW 400 / high molecular polyethylene PE-UHMW Reduction of scraper thickness by 30%, damage to supports Conveyor Components
      Synthetic Lubricants ISO VG 320 / NLGI 2 with MoS₂ additives for extreme loads According to the schedule of planned technical maintenance Industrial Chemistry and Lubricants

      For selecting exact equivalents of spare parts for your equipment and placing an order, visit the official electronic catalog UNITEC-D: https://www.unitecd.com/e-catalog/.

      11. Normative References

      • ISO 1977 / DIN 8167: Chain Drives - Plastic Bushed and Roller Chains. Technical Specifications.
      • ISO 10816 / ISO 20816: Vibration Condition Monitoring of Industrial Equipment.
      • ISO 14118: Machine Safety. Prevention of Unexpected Start-up (Lockout/Tagout).
      • DSТU EN 60204-1: Machinery safety. Electrical equipment of machines and mechanisms. Part 1. General requirements.
      • DSSTU EN ISO 12100: Machine Safety. General Principles of Design. Risk Assessment and Risk Reduction.

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