Manufacturing Technology of Suspension & Tension Clamps

Manufacturing Technology of Suspension & Tension Clamps

Suspension and tension clamps are critical power line fittings used in overhead transmission systems to support conductors and transfer mechanical loads to insulator strings or towers. Suspension clamps mainly carry vertical loads, while tension clamps withstand high axial tensile forces at dead-end, angle, or terminal towers. Their manufacturing technology directly determines mechanical reliability, fatigue resistance, and long-term operational safety.

1. Overview of Suspension and Tension Clamps

1.1 Suspension Clamps

Used to hang conductors on straight-line towers, they must:

• Support vertical load of conductors

• Allow limited swing and movement

• Reduce stress concentration on conductors

1.2 Tension Clamps

Used in dead-end and angle towers, they must:

• Bear full conductor tension

• Ensure no slippage under maximum load

• Maintain long-term mechanical stability

2. Main Manufacturing Processes

Suspension and tension clamps are mainly produced using three processes:

• Casting (gravity casting or sand casting)

• Forging

• Aluminum die casting (for lightweight fittings)

Each process is selected based on strength, cost, and application requirements.

3. Raw Material Selection

3.1 Aluminum Alloy (Common for Suspension Clamps)

• Lightweight

• Good corrosion resistance

• Suitable for moderate mechanical loads

Common grades:

• ADC12

• A356 aluminum alloy

3.2 Ductile Iron / Cast Steel (Common for Tension Clamps)

• High tensile strength

• Excellent fatigue resistance

• Suitable for high-load applications

3.3 Forged Steel (High-End Applications)

• Highest mechanical strength

• Superior fatigue performance

• Used in critical high-voltage lines

4. Manufacturing Process of Suspension Clamps

4.1 Mold Design and Preparation

• Precision mold design based on conductor diameter

• Optimization of stress distribution areas

• Consideration of vibration and swing movement

4.2 Casting or Die Casting

• Molten aluminum is poured into molds or injected under pressure

• Controlled cooling to prevent internal defects

Key requirements:

• No porosity

• No shrinkage cavities

• Uniform grain structure

4.3 Machining Process

• CNC machining for dimensional accuracy

• Surface finishing of conductor groove

• Ensures smooth contact surface to avoid conductor damage

4.4 Surface Treatment

• Anodizing or passivation for corrosion resistance

• Deburring to eliminate sharp edges

• Optional coating for harsh environments

5. Manufacturing Process of Tension Clamps

5.1 Forging or Casting

Tension clamps require higher strength:

• Hot forging improves grain structure

• Sand casting used for complex shapes

• Precision forging for high-voltage systems

5.2 Heat Treatment

Heat treatment enhances mechanical properties:

• Normalizing

• Quenching and tempering

• Stress relief treatment

Purpose:

• Improve strength

• Enhance fatigue resistance

• Reduce internal stress

5.3 Machining and Assembly

• Precision machining of conductor grooves

• Thread cutting for bolts and connectors

• Assembly of wedge or bolted structures

5.4 Surface Protection

• Hot-dip galvanizing (steel parts)

• Zinc coating or anti-corrosion paint

• Aluminum surface passivation

6. Key Manufacturing Technologies

6.1 Precision Mold Design

• Ensures correct conductor fit

• Reduces stress concentration

• Improves fatigue performance

6.2 Controlled Solidification Technology

• Prevents shrinkage and porosity

• Improves microstructure density

• Enhances mechanical strength

6.3 CNC Precision Machining

• Ensures groove accuracy

• Improves conductor-clamp contact performance

• Reduces wear and vibration damage

6.4 Surface Finishing Technology

• Polishing of conductor grooves

• Burr removal

• Smooth transition edges to avoid conductor damage

7. Quality Control in Manufacturing

7.1 Dimensional Inspection

• Groove diameter accuracy

• Bolt hole alignment

• Assembly tolerance control

7.2 Mechanical Testing

• Tensile load test

• Slip resistance test

• Fatigue vibration test

7.3 Metallurgical Testing

• Grain structure analysis

• Hardness testing

• Defect detection (porosity, cracks)

7.4 Coating Inspection

• Galvanizing thickness measurement

• Adhesion test

• Corrosion resistance test

8. Performance Requirements

Suspension and tension clamps must meet:

• High mechanical strength

• Excellent fatigue resistance

• Stable conductor grip force

• No conductor damage under load

• Long-term corrosion resistance

9. Common Manufacturing Defects

• Porosity or shrinkage in castings

• Uneven galvanizing coating

• Improper groove machining leading to conductor damage

• Insufficient heat treatment causing weak strength

• Surface cracks from poor cooling control

10. Application Considerations

10.1 Suspension Clamps

• Used in straight-line towers

• Require flexibility and swing allowance

• Focus on vibration resistance

10.2 Tension Clamps

• Used in angle or terminal towers

• Must withstand full conductor tension

• Focus on slip resistance and structural strength

Conclusion

The manufacturing technology of suspension and tension clamps combines material engineering, precision casting or forging, heat treatment, CNC machining, and surface protection technologies. Suspension clamps emphasize flexibility and vibration resistance, while tension clamps prioritize high strength and anti-slip performance. Strict quality control throughout the production process ensures reliable operation of overhead transmission systems under complex mechanical and environmental conditions.

References

1. IEC 61284 – Overhead lines requirements for fittings

2. IEC 60372 – Locking devices for overhead line fittings

3. IEC 60826 – Design criteria for overhead transmission lines

4. ISO 1461 – Hot-dip galvanized coatings on steel products

5. IEEE Std 524 – Installation of overhead line conductors

6. CIGRÉ Technical Brochures on line hardware manufacturing technology