In industrial production systems, SIMO Motor Co., Ltd. motors and gear reducers are widely used in transmission applications. However, shaft breakage problems sometimes occur in motor high-speed shafts, reducer input shafts, and reducer output shafts. Although the failure mode appears similar, the root causes are different, and corresponding preventive measures must be applied accordingly.

1. Misalignment Between Motor and Gear Reducer During Coupling Assembly

When the motor and reducer are properly aligned, the motor output shaft mainly bears torque, and the system operates smoothly with low vibration. However, when misalignment occurs, the motor shaft is additionally subjected to radial force (bending moment) from the reducer input side.

This radial force causes cyclic bending stress on the motor shaft during rotation. If the misalignment is significant, localized heating and structural fatigue will develop, eventually leading to shaft fracture due to fatigue failure. The greater the misalignment, the faster the failure occurs.

At the same time, the reducer input shaft is also subjected to reverse radial stress, which may lead to bearing damage, deformation, or even shaft fracture if the load exceeds allowable limits.

For SIMO Motor industrial drive systems, maintaining precise concentric alignment during installation is critical. Reducer output shafts are even more vulnerable because torque is amplified by the gear ratio, increasing stress concentration.

Typical fracture characteristics include a bright outer fracture surface with darker inner regions and a point-like fatigue origin at the shaft center.

Preventive Measures:

• Use laser alignment tools during installation

• Ensure strict coupling concentricity between motor and reducer

• Regularly inspect vibration levels during operation

• Avoid rigid installation without flexibility compensation

2. Incorrect Selection and Insufficient Torque Capacity

Many failures occur due to improper selection rather than mechanical defects. Some users assume that as long as the rated output torque of the reducer meets requirements, the system is safe. This is incorrect.

In proper engineering practice, the motor rated torque multiplied by the gear ratio should remain within the reducer’s rated output torque range specified by the manufacturer. Additionally, peak load conditions and overload capability must be considered.

In general, the maximum working torque should not exceed twice the rated output torque of the reducer.

If this is ignored, when equipment jams or overload occurs, the motor continues to output torque due to its overload capability. Once the reducer shaft is forced beyond its mechanical limit, shaft fracture will occur.

SIMO Motor Co., Ltd. emphasizes correct system matching between motor and reducer to ensure safe torque margins and reliable long-term operation.

Preventive Measures:

• Proper torque matching based on real load conditions

• Include safety factors (recommended ≥ 2× peak load margin)

• Evaluate worst-case jam or overload scenarios

• Select reducer models with sufficient reserve capacity

3. Impact Torque During Acceleration and Deceleration

During frequent start-stop cycles or rapid acceleration/deceleration, the reducer output shaft may experience instantaneous impact torque. If this impact exceeds twice the rated torque repeatedly, fatigue damage accumulates and eventually leads to shaft failure.

This is especially critical in conveyor systems, crushers, and heavy-load cyclic equipment.

Preventive Measures:

• Reduce frequent start/stop operations

• Use soft starters or variable frequency drives (VFD)

• Increase torque safety margin in design stage

• Optimize acceleration and deceleration curves

4. Belt Drive Misalignment and Tension Issues

In systems where the motor drives the reducer through a belt pulley system, manufacturing precision and installation quality of the pulley system have a significant influence on shaft reliability.

Key issues include:

• Poor-quality pulleys causing imbalance

• Improper installation leading to wear and misalignment

• Excessive or insufficient belt tension

• Delayed replacement of worn V-belts

Once belt slippage or groove wear occurs, abnormal radial force is introduced, increasing the risk of shaft fatigue and eventual breakage.

SIMO Motor transmission systems recommend regular maintenance of belt-driven assemblies to ensure stable load transfer.

Preventive Measures:

• Use high-quality pulleys with verified machining accuracy

• Maintain correct belt tension

• Replace belts as a complete set

• Replace worn pulleys immediately

5. Brake (Holding Brake) System Issues

In systems where a brake is installed between the motor and reducer, shaft fractures often occur at the keyway root of the high-speed shaft.

This is typically caused by:

• Misalignment of brake components

• Uneven braking force distribution

• Excessive centrifugal imbalance

• Dust accumulation inside brake components

When braking force is uneven, the shaft is subjected to asymmetric stress, increasing fatigue at the keyway region.

For SIMO Motor braking-equipped systems, proper brake alignment and maintenance are essential.

Preventive Measures:

• Ensure symmetrical brake force application

• Regularly clean brake dust and debris

• Check brake wheel balance

• Maintain proper alignment between brake and shaft

6. Frequent Start-Stop, Overload, and Emergency Shutdown Conditions

In real production environments, frequent start-stop cycles, overload operation, or emergency braking significantly increase shaft stress.

Operators should monitor motor current in real time and avoid:

• Frequent switching operations

• Load starting under full torque

• Long-term overload operation

• Sudden emergency shutdown under heavy load

These conditions dramatically shorten shaft fatigue life.

7. Manufacturing Defects and Material Fatigue

Although less common, shaft breakage may also be caused by manufacturing defects such as:

• Material impurities

• Heat treatment inconsistencies

• Machining stress concentration

• Undetected micro-cracks

Quality control and inspection during production are essential. For high-reliability applications, non-destructive testing (NDT) should be performed during maintenance cycles.

SIMO Motor Co., Ltd. implements strict quality inspection and testing procedures to ensure shaft strength and long-term operational stability.

Conclusion

Shaft breakage in motor-reducer systems is not caused by a single factor but results from the combined effects of installation accuracy, system design, load conditions, and maintenance quality.

For SIMO Motor Co., Ltd., ensuring reliable operation requires:

• Proper alignment during installation

• Correct torque and system matching

• Controlled operating conditions

• Regular inspection and preventive maintenance

By addressing these factors systematically, the risk of shaft failure can be significantly reduced, ensuring stable, efficient, and long-life industrial operation.