What Is An Intermediate Frequency Induction Melting Furnace? What Are The Characteristics?

  Medium frequency induction melting furnace operating frequency between 50HZ-10KHz, need frequency converter for frequency modulation. Intermediate frequency induction melting furnace has more advantages than industrial frequency induction melting furnace due to its high electrical and thermal efficiency, short melting time, less power consumption, less occupation of land, lower investment, flexible production, and easy implementation of process automation. It is suitable for smelting all kinds of cast iron, especially alloy cast iron, nodular cast iron, and vermicular cast iron, and has strong adaptability to charge. The variety and lumpiness of charge can be changed in a wide range. Intermediate frequency induction melting furnace has the advantages that other cast iron smelting furnaces do not have, which makes it get remarkable development in recent years and is widely used in cast iron production.

IF induction melting furnace

1. SCR inverter

  The development of an intermediate frequency induction melting furnace benefits from the use of an SCR converter. The frequency converter electronically converts the three-phase ALTERNATING current frequency to the desired frequency through a dc intermediate loop with an efficiency of 95 to 98 percent. The new generation of frequency converter USES digital control electronic circuit to provide various control and protection functions for the frequency converter. The rated power of frequency converter used in intermediate frequency induction melting furnace is constantly improved. The frequency converter of 9000kW is connected to the furnace of 12T, and the melting rate of molten iron is 18t/h. By increasing the power density of the intermediate frequency induction melting furnace to 1000kW/ t, the melting period can be shortened to 35min. The melting rate of induction melting furnace varies with the capacity of the furnace. The melting rate of molten iron in an intermediate frequency induction melting furnace is 0.14-35t/h. For example, the melting rate of 2-2.38t/h can be obtained by using a 2T capacity furnace, and 18-21t/ h can be achieved by using a 12T capacity furnace. The melting rate of the cold material using power frequency induction melting furnace is 0.75t/ h for 115T furnace, 1.5t/ h for 3T furnace, 2.5t/ h for 5T furnace and 4t/h for 10T furnace. Visible medium frequency induction furnace melting rate is greater than the power frequency induction melting furnace, it is a when choosing cast iron smelting production equipment with the small generation, using a smaller capacity of medium frequency induction melting furnace instead of large capacity of power frequency induction melting furnace, both reduced the area, and reduce the investment, and ensures the continuous supply of iron liquid, for continuous operation, production capacity of large cast-iron manufacturers. If the medium frequency induction melting furnace is used for molten iron smelting in continuous casting and centrifugal casting ductile iron pipe, it can replace the cupola, or it can be combined with the blast furnace and the cupola, the production capacity will be fully developed.

  The electric and thermal efficiency of intermediate frequency induction melting furnace is high, which not only improves the melting rate and shorts the melting time but also reduces the unit power consumption. Compared with the power frequency induction melting furnace, its power consumption can be reduced from 700kW∙h/ T to 515-580kW∙h/ t. The relevant data show that the unit power consumption of the medium-frequency induction melting furnace is 580kW∙h/ t at cold start-up, 505-545kW ∙h/t at hot furnace operation, and only 494kW∙h/t at continuous feeding operation.

2. Furnace structure

  With the continuous improvement of power density of medium-frequency induction melting furnace, the requirements for furnace safety, lining life and noise are higher and higher, the rationality of furnace body structure is also more and more people pay attention to, among which the heavy steel shell furnace has strong durability, high efficiency and productivity, low noise, easy maintenance and repair and many other advantages. The heavy steel shell furnace is different from the frame furnace. It has a high-strength ring steel shell with several large inspection openings. When the furnace is running, the inspection opening is closed and each inspection opening can be opened during inspection. The inner structure of the heavy steel shell furnace is strong, which can avoid the deformation caused by pouring iron from the pouring furnace and prolong the lining life. And because the enclosed solid steel case and its interior can add sound-absorbing isolation material, the working noise is greatly reduced. The strong steel case also effectively protects the induction coil from the risk of metal spatters, providing maximum safety during operation of the furnace. In order to effectively heat insulation and improve the lining life, the heavy steel shell furnace is also equipped with cooling rings at the top and bottom respectively, playing a role of uniform lining temperature and reducing thermal expansion. Low energy consumption, high strength stainless steel cooling ring, greatly improve furnace efficiency.

  The heavy steel shell furnace not only has a strong steel shell but also has a thick-walled tube structure coil specially designed for induction melting furnace. The coil conversion efficiency is the highest and the resistance is the lowest by choosing the right distance between turns of the induction coil. On the one hand, the induction coil of the thick-walled tube has a large current-carrying area and uniform wall thickness, so it is not easy to cause damage caused by arc and expansion. On the other hand, the coil USES a special support system, each turn is firmly locked, good rigidity, reduces the vibration caused by electromagnetic force, greatly prolongs the service life of the furnace lining. In addition, the induction coil is surrounded by 59% magnetic yoke, effectively changing the distribution of the magnetic field; At the same time, the isolation cushion reduces noise and vibration and increases the efficiency of the yoke. The heavy steel shell furnace also adopts the extended coil design with induction coil extending beyond the bottom of the furnace lining, so that the charge load from the top to the bottom of the furnace body is coupled with the magnetic field very uniformly, which improves the energy conversion efficiency and reduces the influence of stirring force caused by the magnetic field on the bottom of the furnace lining.

3. Production

  Intermediate frequency induction melting furnace has greater flexibility in production arrangement and melting operation. The power frequency induction melting furnace requires continuous operation and the molten iron in each furnace should not be emptied, because the intermittent work increases the cold start, which not only increases the melting time and energy consumption, but also the starting block must be used every time. Medium frequency induction melting furnace used in intermittent time, do not need to start the piece of cold start, can be carried out on iron liquid can also be empty from the furnace, replace the burden is very convenient, and to achieve in a short period of time material replacement, facilitate production organization arrangement, the main bear some non-standard equipment for the manufacture of and demand for large castings, small batch and many varieties, a repair workshop production of iron and steel metallurgy industry has created favorable conditions.

4. Slag removal and furnace repair

  If induction melting furnace productivity is high, the melting period can be shortened to about 35min, in order to maximize the use of the furnace power, must be as fast as possible slag removal. Using a skimmer or manual slag removal, the effect is poor, long time, poor working conditions. For this reason, the method of pouring slag after furnace is put forward, that is, pouring slag after furnace body is tilted 20 ~ 25°, and pouring slag into transport vehicle through the groove behind top of furnace body. This method is fast and convenient. Intermediate frequency induction melting furnace must be repaired after one furnace service. In order to shorten the stop time of replacing lining refractory, it is necessary to adopt the mechanization method, vibration furnace building machine and lining pushing machine to become the main accessories of large medium frequency induction melting furnace. The furnace lining pusher can be pushed out when the furnace lining refractories are not completely cooled, which further reduces the furnace repair time and improves the working environment.

5. Dual power supply

  A breakthrough in intermediate frequency induction melting furnace is to use a set of power supply system to supply power to two furnaces, realizing the working system of no production interval operation. It has been proved in practice that the total effective power of induction melting furnace is usually not fully utilized during the melting period, and the power must be reduced or cut off in the determination of liquid iron temperature, sampling, slag removal, iron production, especially in the case of pouring. If the casting time is long and the utilization rate is only about 50%, the rated power of the power supply equipment must be 118 times the utilization rate of 90% in order to achieve the required productivity. In order to solve this problem, a dual power supply system was developed successfully. The system USES two identical commutators and capacitor Banks, one for each furnace, but each is powered by a common rectifier and transformer. Each converter can be individually controlled and the total effective power can be allocated to two furnaces in an arbitrary ratio. The system can be used to melt molten iron in another furnace with the exception of providing sufficient power for the insulation of one furnace. This kind of power supply can be used to send electricity to two furnaces at the same time, which completely avoids switching switches or adding another set of power supply. It is not necessary to switch the power supply to the heat preservation furnace in the melting process in order to maintain the necessary pouring temperature, thus realizing the functions of melting and heat preservation. When one furnace is in the state of maintenance, the power supply can be isolated from the furnace and only supply power to another furnace, which also increases the safety.

6. Degree of automation

  Intermediate frequency induction melting furnace adopts a computer control system with a high degree of automation. The high power intermediate frequency induction melting furnace has a short melting period and a high overheating rate. Only by using a computer control system can the potential of the equipment be brought into full play and effective protection be provided to the plant and operators. At present, the large intermediate frequency induction melting furnace has been equipped with a relatively complete computer-aided monitoring and control system, whose main functions include:

(1) When the iron liquid in the furnace crucible reaches the pre-programmed temperature, ensure the automatic reduction of furnace power;

(2) Monitor, calculate and control the temperature of molten iron;

(3) Provide automatic sintering procedures for new linings;

(4) Determine the amount of C, Si, and other added elements that meet the requirements of the iron solution;

(5) It has an automatic cold starting device.

The smelting management system provides diagnostic results and various information about the power supply and furnace operation process through an easy-to-read display screen.If the alarm system is started in an abnormal state, the SMM system will provide the problem and can store the fault information for troubleshooting, or it can be connected to a printer for printing. Through the smelting management system, various diagnostic information can be obtained and a series of other functions can be performed.

7. Endnotes

  The development of an intermediate frequency induction furnace and its advantages have injected new vigor into casting production. Intermediate frequency furnace has the advantages of small size, lightweight, high efficiency, and favorable environment, making it quickly replace the coal-burning furnace, gas furnace, oil furnace, and ordinary resistance furnace is a new generation of metal heating equipment.