Hot-Wound Springs

Definition: Hot-wound springs are helical springs formed at high temperatures (typically above the material’s recrystallization temperature), primarily used for heavy-load, high-impact, or extreme environment applications.

1. Hot-Wound vs Cold-Wound Springs

Comparison	Hot-Wound Springs	Cold-Wound Springs
Forming Temp.	High temperature (~900°C+)	Room temperature
Material	Large-diameter bars (Φ>16mm)	Steel wire (Φ<16mm)
Applications	Heavy machinery, railways, mining, defense	Electronics, vehicle suspensions, small mechanisms
Strength	Higher (due to stress relief)	Relatively lower
Surface Finish	Requires post-treatment (e.g., shot peening)	Smooth, ready-to-use

       2.Manufacturing Process

      •Material Heating: Spring steel bars (e.g., 60Si2MnA, 55CrSi) are heated to austenitizing temperature (~850–950°C).

      •Hot Coiling: Formed into a helix shape using a coiling machine while red-hot.

      •Quenching + Tempering: Rapid cooling (quenching) followed by medium-temperature tempering for elasticity and toughness.

      •Surface Treatment: Shot peening, anti-corrosion coatings (e.g., zinc plating, epoxy).

3. Key Features

• High Load Capacity: Suitable for static or low-frequency heavy loads (e.g., railway buffer springs).
• Fatigue Resistance: Hot-working refines grain structure for extended service life.
• Size Flexibility: Can produce extra-large diameters (e.g., Φ200mm+) or custom shapes.

4. Typical Applications

• Rail Transport: Train bogie suspension springs, coupler systems.
• Construction Machinery: Excavator and crane suspension systems.
• Defense Equipment: Tank track buffers, artillery recoil mechanisms.
• Energy Sector: Wind turbine pitch control springs.

5. Key Selection Parameters

• Material: 60Si2MnA (common), 55CrSi (heat-resistant), 50CrVA (high fatigue strength).
• Operating Temp.: High-temp environments require heat-resistant alloys (e.g., Inconel 718).
• Load Type: Impact loads demand high toughness; static loads prioritize stiffness.
• Corrosion Resistance: Coatings (e.g., Dacromet) for humid/corrosive environments.

6. Common Issues & Solutions

• Issue 1: Post-Coiling Deformation
  Cause: Uneven cooling or residual stress.
  Solution: Optimize quenching and tempering processes.
• Issue 2: Premature Fracture
  Cause: Material defects or surface cracks.
  Solution: Enhance non-destructive testing (e.g., magnetic particle inspection) and shot peening.
• Issue 3: Insufficient Stiffness
  Cause: Over-tempering reduces hardness.
  Solution: Adjust heat treatment parameters.

7. Precautions

• Avoid Cold Adjustment: Do not forcibly correct hot-wound springs post-forming to prevent brittleness.
• Routine Maintenance: Inspect for cracks or deformation under heavy loads.
• Custom Designs: Validate stress distribution via finite element analysis (FEA).

Shuangyuan produce hot coil spring with wire diameter from 20mm to 60mm.