Medium-Frequency Heater: A High-Efficiency Core Equipment in Heat Treatment Processes
In the field of metal heat treatment, the uniformity of heating, precision of temperature, and energy utilization directly determine the final performance of workpieces. Medium-frequency heaters (usually operating at a frequency of 1-10kHz), with their unique electromagnetic induction heating principle, have become an ideal choice for heat treatment processes such as quenching, tempering, annealing, and normalizing. They are particularly suitable for batch processing of precision parts like gears, bearings, and shafts, significantly improving product quality stability and production efficiency.
| Model |
60KW Induction Preheating PWHT Machine |
| Input Voltage |
3 Phase 380V, 50HZ |
| Output Frequency |
5KHZ ~ 30KHZ |
| Output Power |
60 KW |
| Input Current |
0-90A |
| Cooling Type |
Air cooling |
| Heating Temperature |
Preheat 0 - 350 C |
| Temperature Control |
1 Channel or 4 Channel |
| Heating Pipe size |
Dia: 50 -1000 mm |
| Heating Coil |
Induction Coil, Heating Blanket, Clamp Induction Coil |
| Extend cable |
1-20 meter |
| Heating Blanket |
Induction heating blanket, High temperature tube |
| Alarm |
Over Voltage, Over Current, Over Temperature and so on |
Core Advantages Adapted to Heat Treatment Processes
The technical characteristics of medium-frequency heaters are highly compatible with the requirements of heat treatment processes, demonstrating multiple advantages:
1. Precise Temperature Control to Ensure Performance Consistency
Heat treatment is extremely sensitive to temperature (e.g., a quenching temperature deviation of ±5ºC may lead to unqualified hardness). Medium-frequency heaters achieve precise control through the following designs:
- Closed-loop temperature control system: Equipped with high-precision thermocouples (temperature measurement range 0-1200ºC) and PID algorithms, the temperature control accuracy can reach ±3ºC, and some high-end models can even achieve ±1ºC. For example, when quenching 40Cr steel, it can stably maintain the austenitizing temperature of 850ºC, ensuring uniform grain refinement.
- Zoned heating capability: Through customized induction coils (such as annular coils and profile-following coils), specific areas of the workpiece (e.g., gear tooth surfaces, bearing raceways) can be directionally heated to achieve "local heat treatment". For instance, in the surface quenching of automobile transmission gears, only the tooth parts are heated to 900ºC, while the tooth roots and hubs remain at a lower temperature to avoid damaging the overall performance.
2. Rapid Heating to Reduce Oxidation and Decarburization
Medium-frequency induction heating uses electromagnetic eddy currents to make the workpiece heat itself, with a heating rate of 10-50ºC/second, far exceeding that of box furnaces (0.5-2ºC/second). This feature brings significant advantages:
- Shortened high-temperature residence time: The residence time of workpieces in the austenitizing temperature range (e.g., 800-1000ºC) can be reduced by more than 50%, minimizing oxide scale formation (oxidation loss rate ≤0.3%) and decarburization layer thickness (≤0.02mm). It is especially suitable for materials with strict surface quality requirements such as bearing steel (e.g., GCr15).
- Improved production efficiency: Taking the quenching of a φ50mm shaft part as an example, medium-frequency heating can reach the quenching temperature in only 30 seconds, while a traditional box furnace takes 15 minutes, increasing the single-shift production capacity by more than 20 times.
3. Uniform Heating to Reduce Workpiece Deformation
The penetration depth of medium-frequency current (1-10mm) can be precisely controlled by adjusting the frequency. Combined with optimized coil design, it achieves uniform temperature distribution across the workpiece cross-section:
- Small radial temperature difference: When heating a stepped shaft with an aspect ratio of 5:1, the temperature difference between segments is ≤10ºC, avoiding bending deformation caused by thermal stress (deformation ≤0.1mm/m).
- Adaptation to complex shapes: For irregular parts (e.g., camshafts, spline shafts), segmented coils or rotational heating methods can be used to ensure no heating dead zones in grooves, edges, and corners. For example, the hardness uniformity of the cam surface during camshaft quenching can reach HRC±2.
Typical Application Scenarios
Medium-frequency heaters have mature applications in various processes of heat treatment:
1. Quenching Process
- Surface quenching: The surface layer of parts such as gears and drive shafts is induction-heated (850-950ºC) and then rapidly cooled (water or oil cooling), increasing the surface hardness to HRC55-62 while keeping the core tough. For example, surface quenching of excavator track pins can improve wear resistance while preventing fracture.
- Whole quenching: Small workpieces (e.g., bolts, cutting tools) are entirely heated for quenching. By controlling the cooling rate, a uniform martensitic structure is obtained, such as the quenching of 8.8-grade high-strength bolts.
2. Tempering and Annealing
- Tempering treatment: Quenched workpieces are heated to 200-600ºC (adjusted as required) and held at temperature to eliminate internal stress and stabilize dimensions. For example, spring steel is tempered at 350ºC after quenching to achieve a "balance between strength and toughness".
- Annealing softening: Cold-rolled steel plates and cold-drawn steel wires undergo recrystallization annealing. Medium-frequency heating to 650-750ºC followed by slow cooling reduces hardness (e.g., reducing the hardness of cold-rolled steel plates from HB180 to HB100), facilitating subsequent stamping.
3. Normalizing and Aging
- Normalizing treatment: Castings (e.g., gray cast iron cylinder blocks) are heated to 850-920ºC, held, and then air-cooled to refine grains, homogenize structures, and improve machinability.
- Aluminum alloy aging: Aluminum alloys (e.g., 6061) are heated to 120-180ºC and held to enhance strength through the precipitation of strengthening phases (e.g., increasing strength from 110MPa to 240MPa). The uniformity of medium-frequency heating avoids performance fluctuations caused by temperature differences in traditional aging furnaces.
Equipment Characteristics and Technical Parameters
- Core configuration: Including medium-frequency power supply (50-500kW), induction coil (temperature resistance ≥1000ºC), cooling system (water-cooled/air-cooled), and temperature control system (PLC + touch screen).
- Intelligent functions: Support storage of over 100 heat treatment process parameters, enabling fully automatic "heating-holding-cooling" processes, equipped with infrared temperature monitoring and abnormal alarms (e.g., over-temperature, water shortage).
- Energy-saving and environmental protection: Thermal efficiency reaches 70-85%, saving more than 40% energy compared to gas furnaces, with no smoke emissions, meeting environmental protection requirements (e.g., NOx emissions ≤50mg/m³).
Medium-frequency heaters have reshaped the efficiency and quality standards of heat treatment processes through technological innovation. Their advantages in precise temperature control, rapid response, energy conservation, and environmental protection make them indispensable key equipment in modern metal processing. Especially in automotive manufacturing, engineering machinery, and precision instruments, they provide reliable guarantees for mass production of high-performance parts.
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