High-frequency induction heating technology has been around for several decades. This method offers numerous advantages, including fast heating speed, energy efficiency, consistent quality, reduced oxidation and decarburization, minimal workpiece deformation, low pollution, simple processes, and ease of automation. This article explores high-frequency resistance induction heating quenching technology, its implementation methods, and its applications in the automotive industry.
**Principle and Characteristics of High-Frequency Resistance Induction Heating**
In recent years, both domestically and internationally, induction heating technology has made significant progress in improving product quality, optimizing material usage, reducing production costs, and enhancing equipment performance. It is now widely used across various industries. However, traditional high-frequency induction heating is a basic form of this technique. The core principles behind it are electromagnetic induction effects—such as the skin effect, proximity effect, and ring effect—and heat conduction. For inner-hole components, traditional methods often suffer from low heating efficiency and difficulty in controlling the depth of the hardened layer.
High-frequency resistance induction heating was first introduced in the U.S. in the early 1980s and was initially applied to the inner walls of car engine cylinder liners. Compared to conventional high-frequency induction heating, this technique allows for more concentrated surface current, higher current density, and faster heating speeds. It can achieve much higher power density, enabling efficient surface heat treatment with a hardened layer located between the two electrodes beneath the sensor. The high-frequency resistance-inductive local heating system is simple to operate and similar to traditional induction heating. Standard high-frequency furnaces can be easily modified into localized heating devices. Additionally, the sensor can be designed in curved or complex shapes, making it suitable for hardening irregular or complex parts. Some quenching processes even eliminate the need for a special cooling medium, using self-cooling and self-tempering after quenching, which reduces distortion and simplifies the overall process.
**Applications**
1. **High-Frequency Quenching of Automobile Steering Racks**
The rack and pinion steering system is widely used in modern vehicles due to its simple structure, lightweight design, and high transmission efficiency. The steering rack is a critical safety component, requiring high wear resistance and fatigue strength. Traditionally, it was made from carburized alloy steels like 15Cr or 20Cr, but this method involved high heat treatment costs, difficult calibration, and poor working conditions. Today, materials such as 35Cr, 45Cr, 40Cr, or 38Cr are used with high-frequency resistance induction heating to harden the teeth of the rack. The process involves local quenching of the tooth surface at an angle of 180° ± 20°, achieving a surface hardness of 48–55 HRC. The setup includes clamping cylinders, copper electrodes, inductors, and cooling systems. The entire process is automated via PLC, with heating times around 4 seconds and total cycle times under 20 seconds. The result is minimal distortion, uniform hardness, and excellent working conditions.
2. **High-Frequency Quenching of Valve Sleeve Inner Holes**
Valve sleeves, typically made of 45 steel, require inner hole quenching with a hardened layer depth of 0.5–1.8 mm and a surface hardness of 50–60 HRC. Traditional methods face challenges such as slow heating, coil overheating, positioning difficulties, uneven hardening, and surface discoloration. With high-frequency resistance induction heating, a 75 kW power supply heats the inner hole in about 1 second, producing uniform hardness and minimal deformation. The setup includes copper electrodes, sensors, and insulators, allowing precise control over the heating and cooling process.
**Key Notes on the High-Frequency Resistance Induction Hardening Process**
- Electrodes are made of copper-chromium alloys for better durability and must be cooled during operation.
- The shape of the inductor and its distance from the workpiece significantly affect the hardened layer’s depth and distribution.
- Self-tempering can be achieved by adjusting heating and cooling parameters.
- Clamping force should be just enough to ensure good contact between the workpiece and electrode.
- Existing high-frequency equipment can be adapted with special fixtures for localized heating, offering great flexibility and potential for future development.
Galvanized Wire
Galvanized Wire: Galvanized wire refers to a type of wire that has been coated with a layer of zinc to enhance its corrosion resistance. The process of galvanization involves immersing the wire in a bath of molten zinc or applying a zinc coating through electroplating. Galvanized wire is commonly made from carbon steel wire and is used in a wide range of applications, including fencing, construction, agriculture, and crafts. The zinc coating provides protection against rust and extends the lifespan of the wire.
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Galvanized Steel Wire: Galvanized steel wire refers to a type of steel wire that has undergone the galvanizing process. It is made from carbon steel wire that has been coated with a layer of zinc to protect it from corrosion. Galvanized steel wire is widely used in various applications, including fencing, construction, electrical wiring, and manufacturing. The galvanized coating provides excellent rust resistance, making the wire suitable for both indoor and outdoor environments.
These different types of galvanized wires, including galvanized wire, galvanized steel wire netting, galvanized binding wire, and galvanized steel wire, offer enhanced corrosion resistance and durability. The specific choice depends on the intended application, required strength, and environmental conditions.
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