The root cause of coupling failures often lies in improper selection rather than material quality.  

I. Coupling Function

Couplings are designed to compensate misalignment(parallel, angular, axial) and dampen shock/vibration. Failures occur when couplings are improperly selected for:  

- Misaligned motor/pump/fan shafts  

- Heavy shock loads (e.g., crushers, presses)  

- Thermal expansion-induced shaft displacement  

II. Failure Modes & Solutions

1. Torque Capacity Oversight

Failure:Bolt holes/keyways shear.  

Cause:Rated torque < actual peak torque (especially start-up torque).  

Solution:Select couplings with rated torque > maximum torque × service factor.  

2. Misalignment Compensation Deficiency

Failure:Elastomer wear or metal fatigue.  

Cause:Insufficient misalignment tolerance for system deviations.  

Solution:Choose couplings with adequate compensation (e.g., jaw couplings for angular misalignment, diaphragm couplings for parallel/axial).  

3. Shock/Vibration Neglect

Failure:Brittle fracture of components.  

Cause:Rigid couplings used in high-impact applications.  

Solution:Deploy elastic couplings (e.g., elastomeric jaw, tyre couplings) to absorb shocks.  

4. Environmental Incompatibility

Failure:Corrosion, aging, or thermal deformation.  

Cause: Material mismatch (e.g., rubber in high-temperature environments).  

Solution: Use specialized materials (stainless steel for corrosion, metallic diaphragms for heat).  

III. 4-Step Selection Process

Step 1: Define Requirements

- Calculate theoretical torque: \( T = \frac{9550 \times P}{n} \) (kW, rpm).  

- Apply service factor** (start-up/overload conditions) for design torque.  

- Verify shaft dimensions (diameter, keyway) and space constraints.  

Step 2: Analyze Operating Conditions

- Quantify misalignment (parallel, angular, axial).  

- Assess load characteristics: steady (pumps) vs. shock (presses).  

- Evaluate environment: temperature, chemicals, dust.  

- Identify special needs: zero backlash, insulation, maintenance-free.  

Step 3: Coupling Type Selection  

- High precision/rigidity: Diaphragm or disc couplings.  

- Moderate misalignment/shocks: Elastomeric jaw/spider couplings.  

- Severe impacts: Tyre or grid couplings.  

- Servo systems: Bellows couplings for zero backlash.  

Step 4: Finalize Specifications

- Select a model with:  

  - Rated torque > design torque.  

  - Misalignment tolerance > actual system deviation.  

  - Maximum speed > operating RPM.  

  - Dimensional compatibility (bore, length, OD).  

By addressing torque, misalignment, environment, and load dynamics, coupling failures can be systematically eliminated.