JPS6053085B2 - Method for manufacturing cast iron using reduced iron as raw material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an energy-saving and resource-saving method for producing cast iron using reduced iron as a raw material.

Making steel and castings using reduced iron is far more energy and resource efficient than making pig iron, which is made by reducing and melting iron ore in a blast furnace. For this reason, research is being conducted in various places to utilize this reduced iron not only as a raw material for steelmaking, but also as a raw material for casting. However, when an induction electric furnace, which is widely used as a conventional cast iron melting furnace, is used, a large amount of unreduced oxides and other substances contained in reduced iron are generated as slag, which damages the furnace wall and Many drawbacks have been pointed out, such as the fact that they interfere with the addition of alloys, elements, or carburizers into the molten metal.

In addition, in the cupola, reduced iron is generally a small lump with a diameter of 10 to 20 wL, and even briquettes made by the fluidized bed method form a pillow shape of about 50 x 70 x 10 Tm, and when charged in large quantities, it becomes small particles. The resistance inside the furnace increases, making work difficult.
Therefore, a melting furnace and operating method suitable for this property are required. In the basic research conducted by the inventors,
a) The results of elucidating the behavior of reduced iron when it is brought into contact with various atmospheres and solid carbon materials and held at high temperatures, and when it is melted, namely: Co) Air, CO.

As a result of holding and melting experiments in a solid state at 1000° C. in various atmospheres and in contact with solid carbon materials such as coke and graphite lumps, the following findings were obtained. (1) Co
In a reducing gas atmosphere such as gas, even when a solid state is maintained at 1000° C., carbonization easily progresses from the surface and the amount of carbon content increases.

(2) Air, CO.

In an oxidizing atmosphere consisting mainly of gas, oxidation progresses from the surface, and a thick oxide layer can be seen on the outer periphery when viewed in cross section. (
3) When the reduced iron was brought into contact with a solid carbon material, an oxide film was formed on the surface of the reduced iron when the contact time was short or the particle size of the solid carbon material was large.

(4) Sufficient contact with solid carbon material and melting is 1400
Melting was completed by heating to about ℃. This means that at high temperatures of 1000°C or higher, decharring from solid carbon materials was carried out very easily even in the solid state, and that unreduced oxides contained in reduced iron were also reduced. It also became clear. The results of examining the properties of cast iron obtained by melting b reduced iron in pig iron or cast iron scrap in an induction electric furnace by changing the blending amount to 20, 40, and 60% are as follows: (1) Contained components It has become clear that the contents of phosphorus and sulfur, especially sulfur, rapidly decrease with the addition of reduced iron, making it easy to obtain low-sulfur cast iron.

(2) As a result of adjusting the amounts of carbon, silicon, and manganese, which most affect mechanical properties, and making the final components the same amounts, the results were as follows:
It was found that increasing the amount of reduced iron added improves the tensile strength.

As a result of the above basic research, we have completed research on a good method for manufacturing cast iron using reduced iron as a raw material using the method of the present invention.

That is, taking into full consideration the results of the above basic research, a vertical shaft furnace structure is appropriate as a 1-reduced iron melting furnace for the reasons described below.

2 It is necessary to maintain a fairly reducing atmosphere inside the furnace, so
A solid carbon material is filled in the hearth, and the solid carbon material is low-sulfur coke, graphite ingots are used if necessary, and two reactions are carried out in the furnace: air is blown from near the bottom of the hearth, and the heating and heating required for Iji are carried out. Return. Measures the return of original iron.

3. In order to facilitate the melting of reduced iron, it is necessary to proceed with decarburization even in the solid state to lower the melting point. For this reason, the solid carbon material and the reduced iron must be in sufficient contact even in the solid state. It is essential.

To achieve this purpose, the above. When the hearth is filled with carbon material and the raw materials are charged into the melting furnace, reduced iron and carbon material are sufficiently mixed in advance and charged. As mentioned above, reduced iron, the raw material, generally has a small particle size, and in a conventional melting furnace, the wind pressure increases abnormally. to be set in position.

5 Because the exhaust gas taken out from the furnace contains a large amount of CO gas and is at a high temperature, it is passed through a heat exchanger, and before exchanging heat with this heat exchanger, secondary air is pumped into the bottom of the heat exchanger. A combustion chamber is provided for feeding and secondary combustion of this CO gas,
Preheat the incoming air using the surplus of this exhaust gas and combustion heat.

6 Silicon and manganese are less abundant than pig iron, so to replenish them, it is possible to add a device to inject metallic silicon powder and metallic manganese powder into the furnace.

7. As mentioned above, since the raw materials are small particles, it is possible to install a device that allows continuous charging so that the resistance inside the furnace does not temporarily increase due to intermittent charging.

The following points must be considered when operating the improved device based on the above conclusions.

That is, in order to avoid infiltration of sulfur from the solid carbon material charged in the bottom of the furnace and the solid carbon material mixed and charged with the raw material reduced iron, at least 11 of these solid carbon materials are made of electrode graphite.

When the reduced iron as a raw material undergoes sufficient carbon absorption in solid form, the melting temperature decreases and it melts at a relatively low temperature, making it easier to operate the furnace. Mix well and charge.

The manufacturing method of cast iron using reduced iron as a raw material, which is carried out by such operations and the above-mentioned carefully considered equipment, is characterized by a shape that is difficult to handle from the viewpoint of raw material, that is, reduced iron, which is weaker than blast furnace pig iron. (while covering the shortcomings of) It takes advantage of its large surface area to easily absorb carbon in the solid phase, lowering the melting temperature and making furnace operation easier, and its small size enhances this effect. In order to avoid ventilation resistance in the half-sided furnace, exhaust gas is taken out from a relatively low part of the furnace, and by taking advantage of the large amount of CO gas, secondary combustion is added to heat the incoming air to increase thermal efficiency. Instead, it has many features such as being able to advantageously use fine coke, which has a small commercial value, and electrode graphite scrap as a solid carbon material to be mixed with the raw material reduced iron, and making it easy to adjust the quality of the hot water. This is a method of manufacturing castings. Next, an example of a furnace used in the method of the present invention is illustrated. 1 is a melting furnace with a vertical shaft furnace structure used in the method;
The raw material charged from the furnace 1 descends through the exhaust gas outlet 6 and melts red hot below, and is taken out from the tap 3 as hot water.

The high-temperature exhaust gas containing a large amount of CO gas is taken out from the exhaust gas outlet 6 located at a relatively low position in the melting furnace, and is ignited by the ignition burner 10 by air introduced from the secondary combustion air hole 11. , the temperature is further raised by secondary combustion, and the radiant heat exchanger 7 heats the air that is sent in from the cold air inlet 9 and descends to become hot air.The air is then passed from the hot air outlet 8 through the air pipe 5 , is fed into the furnace through the tuyere 4. On the other hand, the exhaust gas that has been cooled after the heat exchange is introduced from the exhaust gas outlet 12 into a portion of the exhaust gas that has been heated and ascended in the raw material tank in the furnace, and is led to the upper chimney. Note that 13 indicates the ground line, and 14 indicates the second floor surface. Using the shaft furnace shown in the figure, electrode graphite (low sulfur coke) was used as a solid carbon material with a low sulfur content of 0.05% or less in the hearth (the part from the tuyere surface to twice the height of the furnace inner diameter). A raw material made by mixing reduced iron and a low sulfur solid carbon material (as the low sulfur solid carbon material, electrode graphite or low sulfur coke with a sulfur content of 0.05% or less is used) A mixture containing approximately 5 to 20% of the iron weight) was charged from the charging port 2 of the shaft furnace, and the operation was started. The solid carbon material with a low sulfur content filled in the hearth and the electrode graphite with a low sulfur content mixed in the raw materials react with oxygen in the hot air introduced from the part near the bottom of the hearth as follows. As a result, the inside of the furnace became a reducing atmosphere, carburization of solid reduced iron started at around 1000°C, the melting point lowered, and it was completely melted at 1400°C.

According to the conventional method, it takes at least 1600℃ to completely melt the pig iron.
It took more than that.

In addition, by lowering the exhaust gas outlet, the blowing resistance inside the furnace was lowered, and sufficient operation was possible.

Moreover, the amount of CO gas in the exhaust gas obtained from the exhaust gas outlet increases, increasing the preheating temperature of the blast air in the heat exchanger section to 50%.
It was possible to raise the temperature to 0°C. As explained above, the present invention uses a vertical shaft furnace, and provides an inlet for air heated by heat exchange using the exhaust gas of the shaft furnace in a portion close to the inside of the furnace.
The exhaust gas is taken out from a relatively low part of the furnace, and the raw materials are mixed in advance and charged while maintaining sufficient contact between the reduced iron and the blended carbon material. Since low sulfur cast iron is obtained by filling the solid carbon material with a low sulfur content of 0.5% or less, there is an advantage that low sulfur cast iron can be obtained in a manner that saves energy and resources compared to conventional methods.

That is, the solid carbon material filled in the hearth can maintain a highly reducing atmosphere inside the furnace, and by mixing the solid carbon material with reduced iron and charging it into the furnace, the above-mentioned Combined with the reducing atmosphere inside the furnace, it promotes charring into the solid reduced iron, lowering the melting point and speeding up melting. Moreover, the exhaust gas outlet is located at a relatively low position in the shaft furnace. Because the air is taken out, the air blowing resistance inside the furnace can be lowered, and since this exhaust gas contains a large amount of CO gas, this exhaust gas can be used to heat-exchange and preheat the incoming air. By preheating the incoming air to a high temperature and using low-sulfur content electrode graphite or low-sulfur coke as solid carbon materials, we can produce low-sulfur, high-quality cast iron that is energy-saving, resource-saving, and inexpensive. This is what you can get.

[Brief explanation of the drawing]

The figure is a partially vertical, overall elevational view of the melting furnace used in the method of the present application. 1...Melting furnace, 2...Charging port, 3...
...Tayer, 4...Tuyere, 5...
Blower pipe, 6... Exhaust gas outlet, 7...
Radiant heat exchanger, 10...Ignition burner, 11...
...Secondary combustion air hole.

Claims (1)

[Claims] 1 A vertical shaft furnace is used, and an air inlet is installed near the bottom of the furnace to heat the air by heat exchange using the exhaust gas from the shaft furnace, and the exhaust gas is taken out from a relatively low part of the furnace. In addition, the raw materials are mixed in advance and charged while maintaining sufficient contact between the reduced iron and the blended carbon material, and the hearth is filled with solid carbon material with a low sulfur content of 0.05% or less. A method for manufacturing cast iron using reduced iron as a raw material, which is characterized by obtaining low-sulfur cast iron.