**Induction Heating Power Supply**
The induction heating power supply is known for its high efficiency and rapid heating capabilities, making it an environmentally friendly solution for processing metal materials. It is widely used in various industrial applications such as thermal treatment, heat treatment, assembly, welding, smelting, and more. The system consists of two main components: the AC power source, also known as the variable frequency power supply, which provides energy, and the induction coil, which performs electromagnetic induction to transfer energy to the workpiece.
**Induction Heating Power Technology**
Induction heating inverters are typically categorized into parallel and series types. A series inverter behaves like a low-impedance voltage source. When multiple voltage sources are connected in parallel, mismatches in amplitude, phase, or frequency can cause large circulating currents, leading to uneven current distribution among devices. This makes parallel operation challenging. However, a DC large reactor at the input of the inverter can act as a current buffer, allowing time for current correction between units, enabling multi-machine parallel operation. This design is commonly used in transistorized high-frequency and super-audio systems due to its modularity and scalability.
The load in induction heating systems varies greatly, and the inverter and load form an integrated system. Matching transformers are used to connect the power supply with the sensor. These transformers are continuously being optimized for better performance. In some cases, passive components are replaced in the circuit topology to eliminate the need for a transformer, resulting in more efficient and cost-effective matching solutions.
China produces a wide range of induction heating power supplies using thyristors, transistors, and vacuum tubes. Thyristor-based systems have been in use for many years, while IGBT-based units are becoming more popular due to their user-friendly features and higher efficiency. Although IGBT systems are more expensive, they are gradually replacing traditional tube-based high-frequency power supplies. Portable, small-scale high-frequency power supplies are widely used in China due to their affordability and convenience, even entering international markets.
**Annealing and Tempering Applications**
Annealing involves heating a workpiece to a specific temperature, holding it for a period based on material and size, and then cooling it slowly to achieve equilibrium in the internal structure. This process improves machinability and prepares the material for further treatments like quenching.
Using induction heating instead of gas or furnace preheating offers several advantages. It allows direct thermal conduction, minimizing heat loss and improving production efficiency and product quality. Precise temperature control reduces welding temperatures, slowing the cooling rate and decreasing the risk of cold cracking and hardening. Additionally, it eliminates exposure to hot gases, enhancing the working environment and reducing fire hazards.
**Characteristics and Applications of High-Frequency Induction Heating Power Supply**
Induction heating equipment offers numerous benefits, including minimal workpiece deformation, low power consumption, pollution-free operation, fast heating speeds, and reduced surface oxidation. It allows precise control over the hardened layer depth and is easily integrated into production lines, enabling automation and improved efficiency. The hardened layer typically has a fine martensite structure, offering high hardness, strength, and toughness. After surface quenching, the workpiece gains compressive stress, increasing resistance to fatigue and breakage.
However, induction heating systems are more complex than flame quenching methods and may not be ideal for irregularly shaped parts. They are widely used for surface hardening of gears, shafts, crankshafts, and other components to improve wear resistance and fatigue life. For example, car half-shafts treated with induction heating can withstand up to 10 times more fatigue cycles under design loads compared to conventional quenching.
Induction heating is suitable for medium-carbon steels, but special low-hardenability steels have been developed for specific applications. High-carbon steels and cast iron can also be quenched using this method, with water or polymer solutions commonly used as quenching media.
The equipment for induction heat treatment includes a power supply, quenching machine, and sensor. The power supply generates alternating current at a suitable frequency, while the quenching machine positions the workpiece and controls movement. Specialized quenching machines are used for mass production of complex parts.
To ensure effective heat treatment, the sensor must be designed according to the workpiece’s shape and requirements. Common sensors include external, internal, flat, universal, and composite types, each tailored for different applications.
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