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Compared to aluminum-alloy furnace bodies, steel-shell furnaces have the following advantages. Therefore, whenever conditions permit, steel-shell furnaces should be chosen whenever possible:

1) Possesses high overall mechanical performance and is suitable for the manufacture of large-tonnage furnaces.

2) Because the magnetic yoke reduces magnetic leakage and the silicon steel sheet can increase the magnetic permeability, thereby enhancing the magnetic field strength, steel-shell furnaces achieve significant energy savings. During the smelting process, they can save up to 10% of electricity.

3) The sensor’s circumference is equipped with a magnetic yoke that occupies 60% of the total cross-sectional area in the radial direction. This design ensures stability, thereby enhancing the sensor’s rigidity and preventing crucible rupture caused by variations in force and thermal changes, as well as mitigating the occurrence of inductance and furnace leakage accidents.

4) The outlet holes are at the same height, making it easy to pour out water.

In summary, there are several energy-saving methods for steel-shell furnaces:

1) Use high-end configurations to reduce equivalent resistance; adopt high-infeed voltage technology to lower current and minimize energy loss during the conversion of electrical energy into heat.

2) Choose a steel-shell furnace with a yoke to reduce magnetic flux leakage.

3) Increase power density, appropriately raise the operating frequency, and adopt a new digital-chip-based constant-power control circuit to achieve rapid melting and minimize heat loss.

China’s medium- and high-frequency power supplies for induction heating in energy-saving steel-shell furnaces have been applied in welding, quenching, smelting, heat preservation, and thermal insulation processes across industries including metallurgy, power generation, petroleum, chemical engineering, and electronics. The current state of their development can be summarized as follows:

1) Induction heating medium-frequency power supplies based primarily on thyristors now cover all operating frequency ranges below 8 kHz. Their single-unit power ratings are 50 kW, 160 kW, 250 kW, 500 kW, 1,000 kW, 2,000 kW, 2,500 kW, and 3,000 kW, with operating frequencies of 400 Hz, 1 kHz, 2.5 kHz, 4 kHz, and 8 kHz.

2) In energy-saving medium-frequency power supplies for electric furnaces, the triggering of three-phase fully controlled rectifier bridges has moved away from the multi-board structure composed of discrete components. Nowadays, most designs feature a single large board that integrates pulse generation, protection, power amplification, and pulse shaping functions—including pulse generation, power amplifiers for the inverter bridge, and regulators.

3) The generation of thyristor trigger pulses for the three-phase rectifier bridge in medium-frequency power supplies has gradually shifted from using synchronous transformers and phase-sequence control modes that required on-site adjustments to employing phase-adaptive triggering without the need for a synchronous transformer.

4) The startup methods for medium-frequency power supplies in thyristor-based energy-saving electric furnaces have evolved from impact startup, zero-voltage startup, and internal/external bridge conversion startup to frequency-sweep startup. Control technology has also advanced from voltage-based or step-down regulation to closed-loop current regulation and then to constant-power control, resulting in improved medium-frequency power control performance and higher operational efficiency.