I. Project Background and Equipment Specifications

This case study involves a medium frequency induction melting furnace, model WDL-KGPS-1000, with a rated capacity of 1 ton and a maximum capacity of 1.2 tons, designed for aluminum melting applications. The equipment employs medium frequency induction heating and is equipped with a hydraulic tilting system for molten aluminum discharge. The electrical system is configured for a 380V/50Hz three-phase power supply, with a three-phase six-pulse rectifier and a parallel-connected inverter.

Compared to the 0.8-ton furnace in the previous case, this equipment features a furnace body designed for a maximum capacity of 1.2 tons, with the power supply rated power increased to 600 kW while maintaining the same output frequency of 1000 Hz. This configuration – with power slightly exceeding the furnace's rated demand – provides a margin for enhanced melting rates.

II. KGPS Medium Frequency Power Supply System

The power supply system adopts the KGPS thyristor-based medium frequency power supply, with a rated power of 600 kW, a medium frequency output voltage of 1500 volts, and an output frequency of 1000 Hz. The power factor exceeds 0.9, and the startup success rate is 100%. The rectifier section is a three-phase full-controlled bridge, with the control circuit employing an eighth-generation digital circuit board architecture.

Core control functions include constant power control, swept-frequency zero-pressure soft start, and dual closed-loop voltage-current feedback. The swept-frequency zero-pressure startup means the system automatically scans from high frequency downward during startup, establishing medium frequency oscillation upon finding the load resonant point – an approach that avoids the sensitivity to load parameter variations inherent in traditional separate-excitation startup methods.

The protection system encompasses overcurrent, overvoltage, undercurrent, undervoltage, water loss, and phase-loss conditions. When any protection parameter exceeds the set threshold, the system automatically blocks pulse output and disconnects the main circuit power. The power supply cabinet includes full voltage, current, and power readings along with status indicators.

The capacitor cabinet provides medium frequency parallel compensation, reducing reactive power transmission losses on the distribution lines and improving the system power factor. The capacitor bank capacity is matched to the resonant frequency of the induction coil, ensuring operation near the resonant point under rated conditions.

III. Induction Coil Design and Magnetic Yoke Shielding

The induction coil is the core energy conversion component, constructed from T2 copper with a wall thickness of 5 mm. When energized, the coil generates a 1000 Hz alternating magnetic field that induces eddy currents in the metal charge within the furnace hearth, generating heat. The coil design is based on electromagnetic field principles and verified through dedicated computer software, with the deviation between actual operating power and design power controlled within 5%.

Turn-to-turn insulation is processed using advanced insulation techniques, with dedicated clamping technology reducing axial vibration of the coil. The coil inner wall is sprayed with imported high-temperature-resistant insulating materials, and a furnace lining leakage alarm system is installed – when molten aluminum seeps into the coil layer, the alarm system detects it early and signals the condition, preventing furnace breakout incidents.

A refractory coating of 10 to 15 mm thickness is applied to the inner surface of the coil. This coating serves two functions: facilitating furnace lining construction and preventing thermal deformation of the lining that would affect service life.

The magnetic yokes are of crescent profile construction, laminated from cold-rolled silicon steel sheets and clamped with stainless steel splints. The contact surface between the yoke and the coil outer surface is curved, providing face contact rather than line contact, achieving better clamping efficiency and reduced magnetic flux leakage. The silicon steel sheets are reinforced with dedicated splints rather than through-bolts, maximizing the effective magnetic area and reducing localized heating. The magnetic yokes simultaneously shield magnetic flux leakage, prevent furnace body heating, and support and secure the induction coil.

IV. Hydraulic Tilting System

Furnace tilting is driven by a hydraulic system with two cylinders arranged on both sides of the furnace body for lifting, with furnace return accomplished by gravity. The hydraulic station is equipped with dual motors and dual pumps – one in service and one on standby, with automatic switching capability. The fuel tank is fully enclosed and welded to prevent hydraulic oil leakage.

The tilting angle range is 0 to 95 degrees, with smooth operation without shock or creeping, adjustable speed, and the ability to hold at any position. Tilt operation is controlled via manual valves, suitable for casting processes requiring precise control of molten aluminum pouring volume.

V. Furnace Body Structure

The furnace shell adopts a steel-frame structure, comprising a fixed mounting base and a tilting furnace body, with the overall frame configuration ensuring rigidity. The hearth diameter-to-height ratio has been optimized through computer analysis – an increased ratio improves the natural power factor and enhances electrical efficiency.

The furnace body is designed with a 3000 kg lining capacity for melting 1000 kg of aluminum, meaning the hearth volume has a significant margin relative to the rated capacity, facilitating charging operations and reducing spillage risk.

VI. Graphite Crucible and Water Cooling System

The crucible is of graphite construction, with a recommended service life of 4 to 6 months, depending on operating conditions including charging method, melting temperature maintenance range, and dross removal frequency.

The water-cooled cables are constructed from TU1 multi-strand oxygen-free copper wire, sheathed in high-strength fire-resistant rubber tubing, with cold-formed connectors. The power supply side requires a cooling water flow rate of no less than 12 m³/h, while the furnace body side requires no less than 22 m³/h. The outlet water temperature on the power supply side must not exceed 35°C, and on the furnace body side must not exceed 45°C, with inlet water pressure maintained between 0.15 and 0.35 MPa. The water cooling system is equipped with a closed cooling tower, water tanks, and a control cabinet, forming an independent circulating cooling loop.