1. Introduction: Initial Failure Symptom

Overheating of drive belts is a critical symptom of failure in rotating mechanical systems. Observed frequently in the aerospace and energy industries, it can lead to unplanned production shutdowns, catastrophic damage to adjacent equipment, and increased risks to personnel safety. A 30-minute shutdown on an aeronautical production line can result in a loss of €5,000, while in the energy sector, the unavailability of an alternator can cost up to €20,000 per hour. The European directive 2006/42/CE (Machines Directive) and the NF EN ISO 13849-1 standard require high reliability of components for the safety of machines. Belt failure can compromise these requirements.

2. Component Overview: SKF FY65TF Belts and Bearing

Drive belts are fundamental parts of drive systems, transferring power from a motor to a load. They are designed to operate within specific temperature ranges, typically between -30°C and +70°C. Exceeding these limits, particularly above 80°C on the surface, accelerates degradation of the elastomeric material, significantly reducing the belt's rated life (MTBF) of 10,000 to 20,000 hours by 50% for every 15°C increment above its maximum operating temperature. The bearing, here an SKF FY65TF, supports the transmission shafts and is directly impacted by the stresses exerted by the belt. This type of rolling bearing, often pre-lubricated, is designed for moderate radial and axial loads. Its failure due to excessive internal friction can generate heat transferred to the belt system.

3. Evidence of Failure: Technical Observations

Identifying belt overheating is based on multiple observations and quantifiable measurements:

Visual Inspection: Presence of cracks on the surface of the belt, hardening of the material (glaze), detachment of the layers, or deposit of black powder (particles of worn rubber) around the pulleys and the protective casing. These signs indicate thermal degradation.
Thermal Measurements: Using a thermographic camera (e.g. Flir T640) or handheld infrared thermometer to detect abnormal hot spots. A belt surface temperature above 80°C is a clear indicator of overheating. Bearings (SKF FY65TF) may also show high temperatures, exceeding 90°C, indicating internal friction.
Vibration Analysis: A vibration analyzer (for example, Emerson CSI 2140) can reveal specific frequencies. A total RMS vibration amplitude greater than 4.5 mm/s (according to ISO 10816-3 for average industrial machines) is critical. Harmonics at 1x or 2x shaft rotational speed, with predominant axial components, suggest misalignment. Bearing fault frequencies (BPFI, BPFO, FTF, BSF) indicate degradation of the SKF FY65TF bearing.
Tension Measurement: An electronic or sonic tension meter (for example, Gates Sonic Tension Meter) can measure belt tension. A deviation of more than ±10% from the manufacturer's recommended voltage is an indication of incorrect voltage.
Auditory Observation: Abnormal grinding or whistling noises may indicate belt slippage.

4. Investigation of Root Causes: Systematic Approach

The investigation into the root causes of belt overheating must be systematic and factual, based on recognized methods such as the “5 Whys” and the principles of analysis of failure modes, their effects and their criticality (FMEA, NF standard EN 60812). The process begins by collecting all evidence of failure, followed by an analysis of operating conditions, maintenance histories and technical specifications. A diagnostic flowchart can guide this investigation, eliminating less likely causes.

5. Root Causes Identified

Five common causes are predominant in cases of overheating belts:

Pulley Misalignment: Most common cause (40% probability). Parallel or angular misalignment (typically greater than 0.5mm/100mm shaft distance) between pulleys results in uneven belt wear, increased lateral friction and excessive heat generation. Evidence includes asymmetric belt wear and excessive radial and axial vibration at 1x and 2x RPM.
Incorrect Belt Tension: (25% probability)

Tension too low: The belt slips on the grooves of the pulley, generating friction by surface friction and therefore heat. Slippage may be audible.
Tension too high: Imposes excessive load on the belt and bearings (including SKF FY65TF), increasing internal friction of the belt and bearing material, leading to overheating. A belt tension of 280 N where 220 N is required for an SPB type belt can reduce its life by 30%.

System Overload: (15% probability) The drive system transmits more power (kW) than the belts are designed for. This increases the mechanical stress, the internal friction of the belt strands and the temperature. Observing abnormally high power consumption of the drive motor is an indicator.
Inappropriate Belt Selection: (10% probability) Use of a belt of type, material or profile not suitable for the operating conditions (high ambient temperature, presence of oil/chemicals, ATEX environment requiring antistatic belts EN 13398, or transmissible load). A standard belt can overheat quickly in an environment where a high performance or oil resistant belt would be required.
Bearing Failure (SKF FY65TF): (10% probability) An SKF FY65TF bearing damaged by insufficient lubrication, contamination, corrosion or internal wear (bearing fatigue) generates excessive friction. This heat travels along the shaft and is transmitted to the pulley, then to the belt. A bearing surface temperature exceeding 95°C is a warning signal, often preceding failure. Vibration signatures characteristic of bearing defects are detectable.

6. Corrective Actions

For each root cause, immediate and preventive actions are required:

Pulley Misalignment:
- Immediate Action: Stop the machine, loosen the anchors, precisely realign the pulleys using a laser alignment tool (e.g. SKF TKSA 41 or Easy-Laser XT280) with a maximum tolerance of 0.2 mm/100 mm.
- Long-term prevention: Integrate laser alignment into annual preventive maintenance procedures. Install pre-calculated adjustment shims if the anchors do not allow fine adjustment.
Incorrect Belt Tension:
- Immediate Action: Adjust the belt tension to the value specified by the manufacturer using a sonic tension meter. For example, for an SPB 2500 belt, the initial tension must be 250 N/mm and the operating tension 220 N/mm.
- Long-term prevention: Training of staff in the correct use of the blood pressure monitor. Checking and adjusting the voltage after the first 24 hours of operation (break-in), then at regular intervals (monthly or quarterly depending on the application).
System Overload:
- Immediate Action: Reduce the load applied to the system if possible. Check machine compliance with design specifications.
- Long-term prevention: Re-evaluate the design of the drive system, potentially increasing the number of belts, using larger belts, or installing a motor of adequate power. Set up monitoring of the motor's electrical consumption.
Inappropriate Belt Selection:
- Immediate Action: Replace the belt with an appropriate model (for example, ribbed or toothed belt for better heat dissipation, or polyurethane belt for chemical resistance). Refer to the EN ISO 15236 standard for choice.
- Long-term prevention: Standardize the belt selection process based on environmental conditions and service loads. Update spare parts databases.
Bearing failure (SKF FY65TF):
- Immediate action: Stop the machine and replace the SKF FY65TF bearing. Check lubrication and sealing when installing the new bearing.
- Long-term prevention: Optimize the lubrication program according to the manufacturer's recommendations and oil analysis. Implement vibration and bearing temperature monitoring. Use appropriate installation tools (induction heater, hydraulic mounting kits) to avoid damage to the new bearing.

7. Quick Diagnostic Checklist for Technicians

This checklist is designed for tablet use and allows technicians to quickly diagnose belt overheating on site:

General Visual Inspection: Examine the belt and pulleys. Are there signs of cracking, asymmetrical wear, glazing, or rubber debris? (Photo required if anomalies).
Surface Temperature Measurement: Use an IR thermometer to measure the temperature of the belt and bearings (including SKF FY65TF). A temperature > 80°C (belt) or > 90°C (bearing) is a red alert signal.
Checking Pulley Alignment: Use a visual or laser alignment tool. Is the misalignment apparent or measurable (tolerance > 0.2 mm/100 mm)?
Belt Tension Measurement: Apply a sonic tension meter. Does the measured voltage match the manufacturer's specifications (±10%)?
Belt Type Check: Does the belt type (e.g. profile, material) comply with the equipment specifications and environmental conditions (EN ISO 15236)?
Listen for Abnormal Noises: Are there any squealing, whistling or grinding noises coming from the transmission?
System Load Check: Estimate if the machine is under an unusually high load or if blockages are present. Check the motor current if possible.
Bearing Lubrication Status (SKF FY65TF): Are the bearings properly lubricated? Are there signs of grease leaks or contamination?
Checking Protections: Are the protections in place and intact? Are there any obstructions to the flow of cooling air?
Maintenance History: View the maintenance log: when was the last check/replacement?

8. Prevention Strategy

An effective prevention strategy combines preventive and predictive maintenance, as well as design improvements:

Planned Preventative Maintenance: Establish intervals for replacing belts and checking bearings according to manufacturers' recommendations and the NF standard EN 15341 on maintenance performance indicators. This includes regular tension monitoring (monthly or quarterly), alignment (annual) and bearing lubrication (frequency adapted to speed and environment).
Condition Monitoring: Deploy online sensors for continuous monitoring of vibration (ISO 10816) and temperature of bearings and belts. Increasing trends in temperatures or vibration levels (especially frequency bands associated with bearing faults or misalignment) are “red flags” that allow intervention before failure.
Design Improvements: When designing or retrofitting, choose high-performance belts (e.g., synchronous belts to eliminate slip, or low-heat generation belts), properly size transmissions for maximum operating power, and specify heavy-duty bearings with reliable lubrication systems. Integrate more tolerant or self-aligning alignment systems.
Staff Training: Regularly train technicians in best practices for installing, tensioning and aligning belts, in accordance with AFNOR standards on technical skills.

9. Conclusion

Overheating of transmission belts is a complex problem whose resolution requires a rigorous technical approach. By understanding root causes, applying systematic investigation methods, and implementing targeted corrective and preventive actions, operators can improve the reliability of their equipment and reduce maintenance costs. Careful attention to component selection, installation accuracy and continuous monitoring is essential. For the replacement of belts, pulleys, or SKF FY65TF bearings, as well as for alignment and tensioning tools, the choice of certified and standard-compliant components is imperative.

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10. References

NF EN ISO 10816-3: Mechanical vibrations – Evaluation of machine vibrations by measurements on non-rotating parts – Part 3: Industrial machines with a nominal power greater than 15 kW and a nominal speed between 120 rpm and 15,000 rpm when they are rigidly coupled to the foundation.
EN ISO 15236: V-belts and ribbed belts – Determination of lengths and widths and tolerances.
NF E 25-500: Mechanical transmissions – V-belts.
NF EN 13398: V-belts – Recommendations for installation, adjustment, maintenance and safety.
NF EN 60812: System reliability analysis techniques – Failure modes and effects analysis procedure (FMEA).
NF EN ISO 13849-1: Safety of machines – Parts of control systems linked to safety – Part 1: General design principles.
ISO 18436-2: Machine condition monitoring and diagnosis – Personnel qualification and assessment requirements – Part 2: Vibration analysis.