JPS633005B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a preheating melting method for reducing power consumption and increasing efficiency in an air furnace. Prior Art Conventionally, power consumption in electric furnaces has been saved by scrap preheating, and production capacity has been improved by increasing the capacity of transformers and promoting melting by burner auxiliary combustion. Preheating methods can be divided into in-furnace preheating methods and outside-furnace preheating methods.
An outside-furnace preheating method in which preheating is performed using a dedicated preheating device such as 23677 is well known. This outside-furnace preheating method uses a preheating container such as a basket.
A raw material 2 such as scrap or ferroalloy is charged into the inside of the material, and high-temperature gas from a combustor 3 or high-temperature exhaust gas generated in a melting furnace (not shown) is introduced into the raw material through an introduction pipe 4. It circulates and preheats. The disadvantages of this method are that a special preheating container is required, that heat loss occurs when the preheated raw material is transferred to the melting furnace, and that the preheating effect is low;
Due to handling problems, it was not possible to preheat to a high temperature. On the other hand, with the in-furnace preheating method such as the one used in Tokuko Sho 56-26686, preheating and melting are performed in the same furnace, so there is no need for a dedicated preheating container, and there is no transfer of raw materials after preheating, so there is no heat loss. Although it has advantages such as being able to perform highly efficient preheating and being able to preheat to high temperatures, it has the disadvantages that the preheating uses a burner, which causes severe oxidation of the raw material, and that the exhaust hole position is limited to above the sill level. , high-temperature gas easily blows through a part of the raw material to the exhaust hole (causing a short pass) or flows along the inner surface of the furnace (causing a wall effect), resulting in low preheating efficiency, and when a water-cooled panel (WCP) is applied. In particular, this wall effect tends to cause heat loss in the preheated gas, which has disadvantages such as a decrease in thermal efficiency. Regarding the improvement of production capacity, the melting time can be shortened by increasing the transformer capacity, but since the power off time does not decrease proportionally, the production capacity does not increase in proportion to the transformer capacity. Furthermore, although melting promotion by burner auxiliary combustion can be used for ordinary steel, unresolved problems remain, such as that it is difficult to apply to special steel where oxidation of valuable metals is a problem. Purpose of the Invention The present invention was made in order to solve the above-mentioned difficulties, and its purpose is to reduce the electric power consumption, electrode consumption and refractory consumption in electric furnaces, and to dramatically improve the melting capacity. It is something to do. Structure and operation of the invention The electric furnace of the present invention is a one-power-source, two-furnace system, and preheating and melting are alternately repeated. Preheating of the raw material is carried out using a boring hole, which is characterized by providing at least one vertical hole reaching the bottom of the furnace in the center of the raw material charged into the electric furnace, and introducing high-temperature gas into the inside of the hole through a combustion tube. It uses a preheating method to perform highly efficient preheating. A detailed explanation will be given below with reference to the drawings. In FIGS. 2 and 3, the electric furnace has two furnaces, furnace A and furnace B, and while furnace A is melting with electricity, furnace B is in a preheating state. The electrode power supply device 5 and the preheating furnace cover 6 are common to the A furnace and the B furnace, and are interchangeable. That is, while the furnace A completes melting and taps steel, the preheating furnace lid 6 is moved by the cart 14. And it is waiting at a position between furnaces A and B.
Further, the electrode power supply device 5, which had been set in the furnace A, rotates and moves onto the furnace B, which had been preheating up to that point, and starts melting. On the other hand, the furnace A that has finished tapping steel is repaired and material is charged (the vertical hole is mechanically opened during material charging), and the waiting preheating furnace lid 6 is carried by the cart 14 and is set on the top and preheating begins. Furnace A below
Preheating and melting is repeated alternately in furnace B and furnace B. In the furnace B during preheating, at least one vertical hole 7 reaching the bottom of the furnace is bored in the center of the charged raw material 2. The lower surface of the combustion tube 8 attached to the lower part of the combustor 3 is placed in contact with the periphery of the vertical hole 7 . A preheating furnace lid 6 is installed on top of the furnace body, and an exhaust hole 9 is provided in a part of the preheating furnace lid 6, and a combustor 3 is provided in the center. is movable in the vertical direction.
High-temperature gas generated in the lower combustion tube 8 of the combustor 3 is ejected into the vertical hole 7. At this time, since the lower surface of the combustion tube 8 is in contact with the periphery of the vertical hole 7, the high-temperature gas is introduced into the vertical hole 7 without directly blowing through to the exhaust hole 9. As shown by the arrow in the figure, the high-temperature gas flows from the void in the inner surface 10 of the vertical hole 7 through the void in the raw material 2 toward the furnace wall or toward the furnace top, and is exhausted to the outside of the furnace through the exhaust hole 9. Ru. And furnace body 1
The flow of high temperature gas along the inner surface of 3, the so-called wall effect, hardly occurs. The vertical hole 7 can be opened either mechanically or by using an electrode 11 by applying electricity when charging the raw material. In addition, since the combustion tube 8 is movable in the vertical direction, even if the height of the raw material 2 changes during preheating, no gap is created between the raw material 2 and the lower end of the combustion tube 8, so that high-temperature gas can be removed. It is possible to prevent blow-through to the exhaust hole 9, allow almost the entire amount of high-temperature gas to flow into the raw material, and prevent deterioration of preheating efficiency. Note that by charging the raw material 2 in layers, the high-temperature gas blown into the vertical holes 7 flows through the raw material toward the furnace wall, thereby uniformly preheating the raw material, thereby further increasing the preheating efficiency. Example Using the apparatus shown in FIG. 2, preheating of raw materials in one electric furnace and arc melting of the preheated raw materials in the other electric furnace were alternately repeated under the conditions shown in Table 1. Table 2 shows the effects of this example compared to a comparative example in which no preheating was performed.

【table】

[Table] Effects of the Invention The present invention uses a one-power, two-furnace system that alternately repeats preheating and melting.
The off time) is shortened and sufficient transformer capacity can be generated, dramatically increasing production capacity. On the other hand, preheating is performed by a borehole preheating method in which a vertical hole is made in the center of the raw material inserted into the furnace, reaching the bottom of the furnace, and hot gas is blown into the raw material with a combustion tube in contact with the periphery of the hole. By adopting this method, high-temperature gas flows throughout the raw material from the center to the furnace wall, and from the bottom to the top of the furnace, making it fireproof even for materials with high packing density that would be difficult for high-temperature gas to pass through with conventional preheating methods. There is little heat loss to objects and water-cooled panels, and highly efficient preheating is possible even in furnaces that use water-cooled panels. In addition, since the combustion tube provides sufficient space on the inlet side for high-temperature gas, the combustion flame does not directly contact the raw material, reducing the heat load on the raw material, suppressing material oxidation, and oxidation loss of valuable metals. It is possible to prevent this. Therefore, high-temperature gas can be used as a preheating gas and highly efficient preheating can be performed up to high temperatures, making it possible to significantly reduce electric power consumption, electrode consumption, and refractory consumption, as well as shorten melting time. In addition, the raw materials are not limited to ordinary steel, and raw materials containing metals that are susceptible to oxidation (Cr, Si, Mn, Al etc.) can also be preheated to high temperatures. Despite the in-furnace preheating method, the equipment is inexpensive because exhaust is carried out through the furnace lid, so there is no need to provide an exhaust hole in the furnace body.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a conventional outside-furnace preheating method, Fig. 2 a and b are side views showing melting and preheating states of the electric furnace in the present invention, and Fig. 3 is a plan view of the electric furnace in the present invention. be. 1... preheating container, 2... raw material, 3... combustor,
4...Introduction pipe, 5...Electrode power feeding device, 6...Furnace lid for preheating, 7...Vertical hole, 8...Combustion cylinder, 9...Exhaust hole, 10...Inner surface of vertical hole, 11... electrode, 1
2... Molten steel, 13... Furnace body, 14... Moving cart for preheating furnace lid, 15... Electric run.

Claims (1)

[Claims] 1 In a method where the electric furnace has one power source and two furnaces, and preheating and melting are repeated alternately, one electric furnace melts the raw material, and the other electric furnace has a combustion tube attached to the bottom and is heated vertically. A movable combustor is attached to the preheating furnace lid, and the lower part of the combustion tube is in contact with the periphery of the vertical hole of the raw material that is charged into the furnace and has a vertical hole that reaches the bottom of the furnace. A preheating melting method using an electric furnace, characterized in that the raw material is preheated by introducing high temperature gas into the vertical hole.