1. Introduction
During operation of the main conveyor belt at the mining and processing plant, the shift crew recorded a critical shift of the belt to the right on the loading branch. The deviation of the belt axis exceeded 75 mm from the nominal position at a belt width of 1200 mm. This resulted in significant damage to the belt edge against the metal structure of the stationary frame and the emergency stop line. Previous inspections indicated an increased level of vibration on the drive drum and a specific noise in the loading unit area. As the chief engineer of UNITEC-D GmbH, I conducted a detailed technical investigation to determine the underlying causes of the destabilization of the belt movement trajectory.
2. Component Overview and Operating Conditions
Conveyor system operates in 24/7 mode, transporting abrasive iron ore with a bulk density of 1.8 t/m³. High-precision units according to specification Parker PCG/10/SI/G5x0,4-PCG are installed in the tensioning and drive unit, ensuring stable tension and torque transmission. Working parameters of the unit:
- Speed of the belt: 2,5 m/s.
- Nominal tension of the belt: 45 kN.
- Ambient temperature: from -20 °C to +40 °C (winter starts at -15 °C).
- Angle of upper roller bearings: 35°.
- Standardized bearing unit life (L10h): 40 000 hours.
Operating conditions are classified as heavy according to ISO 50102: high humidity, presence of fine dispersed ore dust and constant alternating dynamic loads.
3. Failure Evidence
Visual and instrumental inspection revealed the following anomalies:
- The right edge wear of the belt over a length of 42 meters amounted to up to 35% of the initial thickness.
- Radial runout measurement of the drive drum using a dial indicator showed a deviation of 1.8 mm (with a tolerance of ISO 10816-3 not exceeding 0.5 mm).
- Analysis of vibration in vertical and horizontal planes on bearing housings showed peak vibration velocity values of 11.2 mm/s (equipment condition category according to ISO 10816-3: "Unacceptable").
- Uneven tension of the right and left branches of the tensioning station hydraulic cylinders was 14% against the allowable difference of 3%.
- The temperature of the bearing unit Parker PCG/10/SI/G5x0,4-PCG reached 78 °C, which is 30 °C above the steady-state condition.
4. Root Cause Analysis
To determine the sequence of events leading to the accident, the Ishikawa diagram method and the 5 Whys analysis were used. The main hypotheses were focused on mechanical deformation of frames, wear of bearings, and disruption of load symmetry.
- Why has the belt shifted to the right? Due to uneven distribution of lateral tension forces and lateral displacement of the load's center of gravity.
- Why did the lateral imbalance occur? Due to the displacement of the rotation axis of the roller bearing series and the eccentricity of the tensioning drum.
- Why did the drum eccentricity occur? Due to bearing binding in the Parker PCG/10/SI/G5x0,4-PCG housing, resulting from thermal expansion and ingress of abrasive dust.
- Why did dust get into the bearing? Due to the destruction of the contact seals during the winter period under temperature fluctuations.
- Why did the seal fail? Due to the absence of scheduled lubrication with grease according to the maintenance schedule and vibration resonance.
5. Defined Root Causes
| Primary Cause | Probability (%) | Verification Evidence |
|---|---|---|
| Non-rotating roller bearing (attack angle disturbed) | 40% | Wear marks on brackets, axis deviation of 2.5° |
| Failure of Parker PCG/10/SI/G5x0.4-PCG bearing unit | 30% | Temperature exceedance (78 °C), vibration 11,2 mm/s |
| Eccentricity and wear of the drum lining | 20% | Radial runout 1,8 mm, uneven contact trace with the belt |
| Eccentric loading of ore through a displaced trough | 10% | Visual inspection of the material on the belt: 30% more mass on the right side |
6. Corrective Actions
To restore the functionality of the conveyor and prevent recurring failures, a complex of thermal and constructive measures has been developed:
- Urgent repair: Replace the worn-out bearing unit with a new original Parker PCG/10/SI/G5x0,4-PCG set according to the manufacturer's instructions. Perform balancing and adjustment of the drive and tension drums' positions with an alignment accuracy of no worse than 0.2 mm per 1 m of length.
- Довгострокова профілактика: Встановити автоматичні центрувальні ролик-опори з інтервалом у 50 метрів на навантажувальній та холостій гілках. Відрегулювати геометрію завантажувальної воронки для забезпечення симетричного розподілу матеріалу. Перевести систему змащування на автоматичний режим дозування мастила за стандартами ISO 6743-9.
7. Quick Diagnostic Card (for mechanic tablet)
Використовуйте цей чек-лист під час щотижневого обходу конвеєрної лінії.
- [ ] Check the visual condition of the edge of the belt (absence of delamination and breaks).
- [ ] Measure the temperature of the bearing housings with a pyrometer (values must not exceed 65 °C).
- [ ] Carry out an express measurement of the general vibration level on the drive block (alarm threshold: 4,5 mm/s).
- [ ] Assess the condition of bearing unit seals for oil leakage or contamination by ore dust.
- [ ] Check the free rotation of empty roller bearings manually (absence of binding and foreign noises).
- [ ] Measure the tension level of the belt according to the hydrostation scale (pressure deviation < 3%).
- [ ] Check the verticality and horizontality of the roller bearing axes with a laser level.
- [ ] Remove material buildup from the drive and tension drums.
8. Prevention Strategy
To achieve an MTBF level of more than 15 000 hours, the following maintenance standards must be implemented:
- Condition Monitoring: Install continuous vibration sensors and thermal imaging tags on Parker PCG/10/SI/G5x0,4-PCG units, with data output to the workshop's ASTPC system.
- Maintenance intervals: Perform full geodetic alignment of the conveyor metal structures every 6 months. Lubrication work should be carried out every 500 hours of operation using high-temperature grease in accordance with DIN 51825 (KP2N-20).
- Зберігання ЗЧ: Утримувати аварійний запас критичних компонентів (підшипники, ущільнення, ролик-опори) на регіональному складі для оперативного доступу.
9. Conclusion
Analysis showed that the belt slippage was caused by a combination of factors: loss of rotational accuracy due to degradation of the Parker PCG/10/SI/G5x0,4-PCG bearing and distortion of the roller support geometry. Adherence to the alignment schedule and timely replacement of worn components guarantee uninterrupted equipment operation. For selection of original parts and certified components, go to UNITEC-D E-Catalog.
10. References
- ISO 10816-3: Mechanical vibration — Evaluation of machine vibration by measurements on non-rotating parts.
- ISO 50102: Continuous mechanical handling equipment — Safety and EMC requirements.
- DSTU EN 620:2019: Continuous Action Conveyors. Safety and Electromagnetic Compatibility Requirements for Systems for the Transportation of Bulk Materials.
- Parker Hannifin: Technical Manual for Linear Motion and Transmission Components PCG Series.
- SKF Maintenance Handbook: Best Practices for Conveyor Bearing Lubrication and Alignment.
