Medium-frequency furnace

Furnace Series
Medium-frequency furnace 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. Due to their structural instability, the Foundry Association now strictly prohibits their use. 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. The medium-frequency furnace boasts high safety: The steel-shell furnace uses hydraulic tilting, ensuring safety and reliability.

2. Energy Saving and Consumption Reduction in Medium-Frequency Furnaces: Steel-shell furnaces employ magnetic yokes. These magnetic yokes, made of silicon steel sheets, shield and redirect 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. Medium-frequency furnaces have a long service life: From an operational perspective, the average service life of a typical steel-shell medium-frequency furnace is around ten years. Due to their minimal magnetic leakage, steel-shell furnaces enjoy a significantly extended 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. The medium-frequency furnace dust hood effectively captures 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. In the medium-frequency furnace process, a special W-shaped structure is employed, which eliminates local overheating, results in low noise levels, and minimizes energy 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 consumption, and significantly lowering operational noise, thus safeguarding the health of personnel.

 

Induction Coil Design Features

The medium-frequency furnace employs special flat copper tubes and an auxiliary water-cooling system. The material used is TU1 oxygen-free copper, which completely addresses the skin effect and proximity effect issues associated with current flow. This significantly reduces electrical losses generated by the medium-frequency current within the induction coil, resulting in an 8% to 10% improvement in overall system efficiency compared to conventional coils.

Medium-frequency furnace 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 due to a loss of pressure 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.

Medium-frequency furnace Furnace Leakage Alarm System

Working principle of the intermediate-frequency furnace: 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 relatively 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 ammeter 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 range within which the ammeter displays readings.

 

The installation of a lining inspection device for medium-frequency furnaces requires the mounting 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, resulting in a very small current flow and relatively low readings on the device’s display (or meter). However, if the furnace lining exhibits low resistance—caused, for instance, 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 display (or meter). If these readings exceed the alarm threshold set by the user, the alarm system will activate and sound an alert. Additionally, this alarm 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.

 

Characteristics of medium-frequency furnaces:

1. Superior working environment, improved worker conditions and company image, zero pollution, low energy consumption.

Compared to coal-fired furnaces, induction heating furnaces eliminate the need for workers to endure the scorching heat and smoke from coal furnaces under the blazing sun. Moreover, induction heating meets all the environmental standards set by regulatory authorities, helping to enhance the company’s external image and align with future trends in the forging industry. Induction heating is an energy-efficient heating method among electric furnaces; it consumes less than 360 kilowatt-hours per ton of forgings when heating from room temperature up to 1,100°C.

2. The medium-frequency furnace provides uniform heating with minimal temperature difference between the core and the surface, and boasts high temperature-control accuracy.

Induction heating generates heat internally within the workpiece itself, ensuring uniform heating and minimizing temperature differences between the core and surface. By employing a temperature-control system, precise temperature regulation can be achieved, thereby improving product quality and increasing the pass rate.

3. Characteristics of the medium-frequency furnace

A melting speed, energy-saving effect, reduced combustion, and lower energy consumption.

B features self-mixing functionality, uniform melt temperature, and homogeneous metal composition.

C electric heating has a good working environment.

D has excellent startup performance; with the furnace empty, the entire blast furnace can achieve a 100% startup rate.

4. Other characteristics of the medium-frequency furnace

The medium-frequency heating device is a new-generation metal heating equipment that features small size, light weight, high efficiency, excellent thermal processing quality, and significant environmental benefits—quickly replacing coal furnaces, gas furnaces, fuel-fired furnaces, and conventional resistance furnaces.