Steel-shell furnace

Furnace Series
The furnace body is the component in the system that performs work. Depending on the material of the furnace shell, it is divided into two types: steel-shell and aluminum-shell furnaces. Aluminum-shell furnaces have a relatively simple structure, consisting of only two main parts: the induction coil and the furnace body itself. Due to their structural instability, the Foundry Association now strictly prohibits the use of aluminum-shell furnaces. Therefore, our products primarily feature steel-shell furnaces.

Working principle:

The basic principle of the induction furnace is a type of air-core transformer. The induction coil serves as the primary winding of the transformer, while the various charge materials in the crucible act as the secondary winding. When a medium-frequency current (200–8,000 Hz) flows through the primary winding, magnetic field lines are generated under the influence of the electromagnetic field, cutting across the secondary winding (the charge materials). This induces an electromotive force in the charge materials and generates eddy currents on surfaces perpendicular to the axis of the induction coil, thereby causing the charge materials themselves to heat up and melt.

 

Product advantages:

1. High safety: The steel-shell furnace uses a hydraulic tilting mechanism, ensuring safety and reliability.

2. Energy Saving and Consumption Reduction: The steel-shell furnace employs a magnetic yoke. This magnetic yoke, made of silicon steel sheets, shields and redirects the magnetic flux lines generated by the induction coil, thereby reducing magnetic leakage, improving thermal efficiency, increasing production output, and enabling energy savings of 5% to 8%.

3. Long service life: From a usage perspective, the average service life of a typical medium-frequency furnace with a steel shell is around ten years. Due to reduced magnetic leakage, furnaces with steel shells have a significantly longer equipment lifespan.

When a medium-frequency current (200–8,000 Hz) passes through the primary coil, magnetic flux lines are generated under the influence of the electromagnetic field, cutting across the secondary coil (the charge material). This induces an electromotive force in the charge material and sets up eddy currents on surfaces perpendicular to the axis of the induction coil, thereby causing the charge material itself to heat up and melt.

 

Steel-shell furnace composition:

Induction coil, magnetic yoke, steel structure, hydraulic system, hydraulic cylinder, hydraulic power unit, furnace lining ejection system, furnace leakage alarm system, cyclonic dust collection hood

The cyclonic dust hood boasts exceptional dust-collection performance, occupies less space, can be tilted forward and backward, and can also be paused at any position. The cyclonic dust hood prevents the furnace lid from overheating operators during front-opening operations. Moreover, this dust hood can effectively collect dust during the spheroidizing process in front of the furnace—something that conventional dust hoods simply cannot achieve.

The key component—the magnetic yoke—is made of high-permeability, grain-oriented silicon steel sheets with a thickness of 0.2–0.3 mm. It is manufactured using fully CNC machining equipment, ensuring high precision. The manufacturing process employs a special W-shaped structure that eliminates local overheating, resulting in low noise and minimal losses. The use of the magnetic shroud effectively forces the magnetic fields generated during the electric furnace’s operation to be collected and uniformly released back into the furnace chamber, thereby reducing magnetic leakage, saving energy, and significantly lowering operational noise, thus safeguarding the health of personnel.

 

Induction Coil Design Features

By employing special flat copper tubes and an auxiliary water-cooling process, and using TU1 oxygen-free copper as the material, we have completely addressed the technical challenges posed by the skin effect and the circular-ring effect of current. This significantly reduces electrical losses generated by medium-frequency currents within the induction coil, resulting in an 8% to 10% improvement in overall system efficiency compared to conventional coils.

Lining top-ejection system

It is used for tilting the furnace to pour out the molten metal, as well as for opening and closing the furnace lid. To ensure reliable operation, the hydraulic station of the electric furnace should be equipped with two main pumps of identical specifications. A throttling valve must be installed at the inlet end of the tilting furnace’s hydraulic cylinder to prevent the furnace body from suddenly dropping in case of a pressure loss in the hydraulic system.

In the event of a prolonged power outage in the grid, the molten metal inside the electric furnace may cool and solidify. This could damage the furnace lining. Moreover, attempting to melt the solidified metal by running the electric furnace itself would be extremely dangerous. Therefore, the electric furnace’s hydraulic system should be equipped with an emergency system. When the grid power is interrupted, this emergency system can be used, if necessary, to pour out the molten metal from the furnace, thereby preventing it from solidifying inside the furnace.

Furnace Leakage Alarm System

Operating principle: The power supply is stepped down by a transformer, rectified using a bridge rectifier, and then filtered by capacitors to produce a safe, low-voltage DC output U. This voltage is applied across two electrodes via a current-limiting resistor. Under normal conditions, the furnace lining has high resistance, and the ammeter indicates a small current range. However, as the furnace lining thins, its resistance decreases, causing the current to increase. When the furnace lining becomes severely thin or develops a leak, the current reading on the meter rises significantly, triggering the pre-set operational amplifier to activate. This in turn causes the transistor to turn on, energizing the relay at the collector terminal. The relay’s contacts simultaneously sound an alarm bell and send a signal to the intermediate-frequency power supply control board, causing it to shut down. Two potentiometers are used to set the specific current-range limits displayed on the ammeter.

 

The application of the furnace lining inspection device requires the installation of a bottom electrode. A low-voltage DC voltage U is applied between the stainless steel mesh located between the induction coil sealant and the furnace lining, and the bottom electrode. When the furnace lining is in good condition, its resistance is high and the current flowing through it is very small; consequently, the corresponding parameters displayed on the device’s screen (or meter) are relatively low. However, if the furnace lining exhibits low resistance—caused, for example, by thinning of the lining or extensive leakage of molten metal—the current will increase dramatically, leading to significantly higher readings on the device’s screen (or meter). If these readings exceed the alarm threshold set by the user, the alarm system will activate and sound an alert. Additionally, this signal can also trigger the variable-frequency drive to shut down the furnace—whether or not to link these actions is at the user’s discretion.