The development of medium frequency furnaces is very rapid, and the development of power frequency induction furnaces to large capacity has basically stopped. The development of medium frequency furnaces is remarkable. The reasons are as follows:
1, static frequency converter
The development of the intermediate frequency furnace benefits from the use of static frequency converters. Compared with magnetic frequency converters, the efficiency of these inverters is as high as 95% to 98%. The rated power of the inverter used as the induction furnace is continuously increasing. Recently, the 9000 kW inverter has been put into production, and it is connected to a furnace with a capacity of 12t. The productivity of molten iron can reach 18 t/h; the power density of the medium frequency induction furnace is The ton melting capacity is increased to 1000 kW, which shortens the melting period to 35 minutes. The melting rate of the induction furnace varies with the capacity of the furnace. Generally, the melting rate of the cast iron in the medium frequency induction furnace is 0.4 to 35 t/h. For example, using a 2t capacity furnace, a melting rate of 2 to 2.38 t/h can be obtained, and a 12 t furnace can achieve a melting rate of 18 to 21 t/h; while a power frequency induction furnace is used to melt the melting rate of the cold material, The 1.5t furnace is 0.75t/h, the 3t furnace is 1.5t/h, the 5t furnace is 2.5t/h, and the 10t furnace is only 4t/h. It can be seen that the melting rate of the medium frequency induction furnace far exceeds the power frequency induction furnace, which can be used to replace the larger capacity power frequency induction furnace with a smaller capacity medium frequency induction furnace when selecting the cast iron production melting equipment. Condition, the medium frequency furnace replaces the power frequency furnace, which not only reduces the land use, but also reduces the investment, and also ensures the continuous supply of molten iron. It is very beneficial for the continuous operation and the production of cast iron with large production capacity. The medium frequency induction furnace is used for the smelting of molten iron produced by continuous casting or centrifugal casting of ductile iron pipe, and it can be used to replace the cupola or double with the blast furnace and the cupola, and its production capacity can be fully utilized. For example, there is a manufacturer of centrifugal ductile iron pipes in China, which uses a 10t medium frequency induction furnace and a blast furnace double process to raise the temperature and adjust the composition of the molten iron, and heat the stored blast furnace molten iron from 1300 °C to 1520 °C. It takes 27 minutes. The furnace frequency is 100-200 Hz and the power is 2500 kW.
The medium frequency induction furnace has high electrical efficiency and thermal efficiency, which not only increases the melting rate, shortens the melting time, but also reduces the unit power consumption. Compared with the power frequency induction furnace, the power consumption can be reduced from 700kW.h/t to 515-580 kW.h/t. The relevant data show that the unit power consumption is about 582 kW.t/h when the medium frequency induction furnace is cold-started, and the unit power consumption is 505-545kW when the medium-temperature induction furnace is cold-started, considering the energy loss required for melting and overheating of the slag. h/t, if continuous feeding operation, the unit power consumption is only 494kW.h/t.
2, production flexibility
The intermediate frequency furnace has greater flexibility in production scheduling and greater flexibility in the melting operation. For power frequency induction furnaces, continuous operation is required continuously, because intermittently increases cold start, cold start not only increases melting time and energy consumption, but also requires a starting block every time. When the medium frequency induction furnace is used for a short time, the cold start can be performed without using the starter block. It is very convenient to replace the charge, and the iron liquid can be completely emptied, which can realize material replacement in a short time, which is favorable for production organization. This brings favorable conditions for single-piece small batch production. For example, the industrial machine repair factory in the iron and steel metallurgical enterprise mainly undertakes the production of spare parts, spare parts and large consumable parts required by the iron and steel enterprises, and undertakes the manufacture of some non-standard equipments, and most of them are single-piece small-volume production, with more varieties. , material requirements often change. In this respect, the production flexibility of the medium frequency induction furnace makes up for the shortage of the power frequency induction furnace and other melting furnaces.
3, furnace structure
With the continuous improvement of the power density of the medium frequency induction furnace, the requirements for the safe operation of the furnace, the improvement of the life of the lining and the reduction of noise are becoming higher and higher, and the rationality of the structure of the furnace is becoming more and more important. Steel shell furnaces have many advantages such as high durability, high efficiency, high productivity, low noise, and easy maintenance.
Unlike the frame furnace, the heavy-duty steel shell furnace is a high-strength ring-shaped steel shell with a plurality of large inspection ports. When the furnace is running, the inspection port is closed, and each inspection port can be opened during maintenance. The internal structure of the heavy-duty steel shell furnace is strong, which can avoid the deformation caused by the inclined iron casting, prolong the life of the lining, and the working noise is greatly reduced due to the closed strong furnace shell and the interior of the sound-absorbing insulation material. The sturdy steel shell also effectively protects the induction coil from the risk of splashing metal, giving the furnace maximum safety during operation. In order to effectively insulate and improve the life of the lining, the heavy-duty steel shell furnace is also provided with a cooling ring at the top and the bottom respectively, which serves to uniform the lining temperature and reduce the thermal expansion. Low energy, high strength stainless steel cooling ring greatly improves furnace efficiency.
The heavy-duty steel shell furnace not only has a strong steel shell, but also designs a thick-walled tube structure coil specially designed for induction melting, and the coil has the highest conversion efficiency and the smallest resistance by correctly selecting the inter-turn distance of the induction coil. On the one hand, the thick-walled induction coil has a large current-carrying cross section, uniform wall thickness, and is less prone to damage caused by arcing and expansion. On the other hand, the coil adopts a special support system, and each one is firmly locked and has good rigidity. The vibration caused by the electromagnetic force is reduced, and the service life of the lining is greatly prolonged. In addition, the induction coil is covered with a 50% yoke, which effectively changes the distribution of the magnetic field. The isolation of the cushion also reduces noise and vibration, increasing the efficiency of the yoke. The heavy-duty steel shell furnace also adopts an elongated coil design in which the induction coil extends and exceeds the furnace substrate portion, so that the coupling between the charge and the magnetic field from the top to the bottom of the furnace body is very uniform, the energy conversion efficiency is improved, and the stirring due to the magnetic field is also reduced. The effect of force on the bottom lining
Detailed Analysis and Development of Intermediate Frequency Furnace