Long Bar Induction Heat Treatment Machine / Furnace / Equipment

1. Core Definition & System Composition

Long bar induction heat treatment equipment adopts medium/high frequency induction heating for metal long bars (round/square bar), applied to forging heating, quenching & tempering, normalizing, annealing and metal melting. The core is IGBT medium frequency power supply (300Hz–10kHz), different from high frequency power supply (>100kHz) for surface hardening.

1.1 Four Core System Components

• Medium Frequency Melting Power Supply: Convert 50/60Hz AC to medium frequency AC via IGBT inversion; power range 200–3000kW.

• Induction Coil: Made of oxygen-free copper tube with water cooling to generate alternating magnetic field; multi-section spiral coil customized for long bar length.

• Load Matching Unit: Resonant capacitor + matching transformer for impedance matching; power factor ≥ 0.95.

• Cooling & Mechanical System: Closed-loop water cooling for power supply, coil and workpiece + automatic feeding & rotating structure to ensure uniform heating of long bars.

1.2 Working Principle

2. Key Technical Parameters for Power Supply Selection

2.1 Power Calculation

• m: bar weight (kg)

• c: specific heat capacity (steel: 0.48kJ/kg·℃)

• Δt: temperature rise (℃)

• t: heating time (h)

• η: thermal efficiency (induction heating: 0.9–0.95)

2.2 Frequency Selection (Skin Effect Depth)

The larger the bar diameter, the lower the matching frequency.

2.3 Power Supply Topology

• Parallel Resonant (Mainstream): Single unit power up to 3000kW, easy parallel expansion, 100% startup success, adaptive load change; first choice for long bar melting.

• Series Resonant: Suitable for power below 500kW, difficult parallel connection, mainly for small bar surface heat treatment.

3. Common Technical Q&A & Solutions

Q1: Uneven heating, overheated surface & unpenetrated core

• Reduce frequency to increase skin depth;

• Keep uniform coil-bar gap 5–10mm and good concentricity;

• Adopt variable frequency feeding with speed fluctuation < ±1%;

• Coil length ≥ 1.2 times of heating section length.

Q2: Startup failure & frequent overcurrent protection

• Match resonant capacity within ±5% deviation;

• Insulation withstand voltage test for induction coil;

• Control inlet water temperature <30℃, water pressure 0.2–0.4MPa;

• Replace aging IGBT modules.

Q3: Low power output & slow melting

• Optimize transformer ratio and capacitor matching to reach power factor ≥0.95;

• Properly raise output voltage;

• Increase coil turns to reduce copper loss;

• Place raw materials evenly for good magnetic coupling.

Q4: Uneven hardness & large deformation after tempering

• Multi-section coil zoning temperature control, temperature deviation < ±20℃;

• Uniform quenching water spray ring, bar rotating speed 5–10r/min;

• Precise tempering temperature control ±10℃.

Q5: High energy consumption & low efficiency

• Keep equipment working under resonant state; efficiency ≥97%;

• Adopt T2 high-purity copper tube for induction coil;

• Use closed circulating water cooling with heat exchanger;

• Upgrade digital IGBT module for old equipment.

4. Selection & Installation Guidelines

1. Select power with 1.2–1.5 times safety margin according to bar size, target temperature and heating cycle.

2. Match frequency by bar diameter: larger diameter with lower frequency.

3. Induction coil adopts T2 copper tube with water cooling, uniform gap and matched turns.

4. Install power cabinet in well-ventilated environment below 40℃, keep coil-to-power distance within 5m to reduce line loss.

   long bar & rod induction quenching and tempering production line 
   

   
   

5. Summary

Long bar induction heat treatment & melting system relies on digital IGBT medium frequency power supply + matched induction coil + precise temperature control. The key points are reasonable power & frequency selection, resonant load matching, coil optimization and qualified cooling system, ensuring stable operation, uniform heating and low energy consumption.