Understanding the Hidden Interactions Between Load, Tension, Friction, and Heat Dissipation

In many cable factories, coiling machine motor heating is treated as a maintenance problem. In reality, it’s a system problem involving mechanical load, machine alignment, thermal pathways, VFD control logic, workspace conditions, tension feedback, and winding parameters.
This article breaks down motor heating at the root-cause level — what is happening inside the motor, why the load curve increases, and what factory engineers can do to stabilize continuous production.

1. Understanding Why the Motor Heats: The Physics Behind It

Cable coiling machines generally use induction motors or servo motors. Both rely on electromagnetic flux to generate torque. Heating occurs mainly from:

• Copper loss (I²R loss): Caused by overcurrent from excessive load
• Iron loss: Caused by high-frequency switching or unstable VFD output
• Mechanical loss: Caused by bearings, misalignment, belt tension
• Cooling inefficiency: Insufficient airflow or blocked ventilation

When the motor temperature rises beyond 80–100°C (depending on insulation class), torque output drops and resistance increases — increasing heating further. This creates a closed-loop thermal runaway effect if not corrected.

2. Load-Sourced Heating: Why the Coiling Section Is Often Underestimated

The coiling machine is the final machine in the line, but it compensates for everything upstream:

• slight diameter variation

• poor tension from payoff

• unstable extrusion speed

• taping line friction

• variation in cable stiffness

All of these push the coiling motor into higher torque zones.

2.1 Coil Diameter Growth = Nonlinear Torque Increase

Torque demand rises exponentially as OD increases because the cable load shifts outward, creating a larger moment arm.
If your motor heats only during the second half of the coil, this is the cause.

2.2 Cable Stiffness → Immediate Torque Jump

If material is XLPE, TPU, or irradiated material, stiffness increases back-force.
When stiffness increases by 10–15%, motor current can rise 20–30%.

2.3 Incorrect Full-Coil Mass Calculation

Many factories calculate coil weight incorrectly, especially with multi-core cables.
A 1.5 kg underestimation can push the motor past rated torque during acceleration.

3. Mechanical Resistance: The Silent Motor-Killer

Mechanical resistance is the No.1 technical cause of unexplained heating.
Most common:

3.1 Shaft Misalignment (0.2–0.6 mm offset is enough)

Misalignment between motor shaft → gearbox → spindle causes continuous radial loading on bearings.

Symptoms:

• Motor heating with normal current

• Slight vibration or humming

• Higher temperature on the non-drive end

Fix:
Use laser alignment or dial indicator, not visual alignment.

3.2 Bearing Preload Due to Improper Installation

If a bearing is over-tightened or installed off-center, preload increases friction.
This alone can make a motor run 15–20°C hotter.

3.3 Belt Tension Too High

A common error in Chinese factories: tightening belts until “they feel strong.”
High belt tension adds constant torque resistance even at no load.

4. Electrical Causes: Why Many Factories Blame Motors Incorrectly

Motor heating often originates in the VFD, not the motor.

4.1 Excessive Carrier Frequency

High carrier frequency → high switching losses → high motor temperature.
Many VFDs are shipped with defaults far above what cable coilers need.

Fix:
Set carrier freq to 2–6 kHz depending on noise & motor spec.

4.2 Unstable Output Frequency

If VFD output oscillates due to poor PID tuning (especially when linked with dancer feedback), the motor runs under micro-acceleration cycles → heating rises sharply.

4.3 Under-Voltage Operation

A motor running at 210–220 V (on a 380/400V three-phase system) produces less torque → draws more current → heats rapidly.

5. Thermal Path Failure: The Motor Cannot Get Rid of Heat

Even without excessive torque, heat can accumulate.

5.1 Fan Airflow Blockage

Dust + PVC powder = insulation layer
Cooling efficiency drops by 30–60%.

5.2 Ambient Workshop Temperature

Extruder zones raise the floor temperature.
If the machine sits near an extruder head (50–60°C ambient), the motor cannot dissipate heat fast enough.

5.3 Incorrect Motor Placement

If the machine frame blocks rear ventilation, airflow forms a recirculation loop → heat cycles back into the motor.

6. Interaction with Tension Feedback (Critical but Ignored)

Tension systems (dancer arm, magnetic brake, servo payoff) control upstream load.
When tension is too high or too sensitive, the coiling machine overworks.

6.1 High PID Sensitivity

If dancer PID is too aggressive → coiling motor continuously micro-adjusts → temperature spikes.

6.2 Brake on Payoff is Over-Tight

A single tight brake increases coiling motor torque by 20–40%.

6.3 Cable Friction in Guide Rollers

Old rollers = rubber aging = increased friction → more motor load.

7. Diagnostic Method: Factory-Applicable, Fast, Accurate

A proper diagnostic workflow prevents guesswork:

Step 1 — Take Motor Current Reading

Compare with motor nameplate.
If current is normal but heating is high → mechanical or cooling issue.
If current is high → load or tension problem.

Step 2 — Run No-Load Test

Disconnect cable.
If motor still heats → mechanical or VFD problem.
If motor stays cool → tension or cable stiffness issue.

Step 3 — Thermal Imaging

Check temperature distribution:

• Uniform heating → electrical

• One-side heating → bearing or shaft

• Fan side hotter → airflow issue

Step 4 — Tension Audit

Lower tension by 10%.
If motor temperature drops significantly → tension system oversensitive.

Step 5 — Check Full Coil Torque Curve

If heating rises dramatically after coil reaches 70% OD → torque miscalculation.

8. Practical Engineering Fixes (Real Factory Solutions)

8.1 Recalculate the Maximum Coil Load

Verify:

• Cable OD

• Density

• Length

• Material stiffness

• Spool weight

Many “motor heating issues” disappear after recalculating load.

8.2 Adjust VFD Settings

Recommended:

• Carrier frequency: 3–4 kHz

• Acceleration time: 3–5 seconds

• Overcurrent limit: 110–120%

• Torque boost: OFF unless necessary

8.3 Reduce Internal Resistance

• Replace bearings (even small wear causes large friction)

• Re-align motor + gearbox

• Re-tension drive belts

• Lubricate spindles & guide rollers

8.4 Redesign Airflow

• Install forced-air duct behind motor

• Add cooling fan on the machine frame

• Redirect heat away from extruder zones

A 10–12°C temperature drop is common after airflow improvements.

8.5 Optimize Tension Control

• Reduce PID sensitivity

• Lower dancer arm weight

• Replace worn magnetic brakes

• Add low-friction rollers

• Tune synchronization speed

9. When to Replace the Motor

Replacement is necessary when:

• Insulation resistance < 1 MΩ

• Temperature rises over 70°C at no-load

• Rotor imbalance is detected

• Copper discoloration indicates thermal history

Investing in an IE3 motor can reduce heating and energy consumption.

10. Conclusion

Coiling machine motor heating is rarely caused by one issue.
It is a system-level interaction between torque demand, tension control, mechanical alignment, VFD logic, and cooling efficiency.

Factories that treat the issue purely as a “motor repair problem” never solve it.
Factories that analyze load → mechanical → electrical → thermal paths eliminate the issue permanently