JP2795527B2 - Cast iron manufacturing method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for producing molten iron from a blast furnace or other ironmaking furnaces to produce cast iron with excellent appearance. Things.

[Prior art] When casting hot metal from a blast furnace or other ironmaking furnaces and casting hot metal to produce a casting pig iron, the length of the strand of the cast iron machine is reduced due to problems in equipment costs and installation space. Then, a large amount of water is sprinkled and cooled to the temperature required for demolding.
On the other hand, it is also known that sprinkling and cooling before the surface layer of the hot metal in the mold completely solidifies impairs the external shape. As an invention relating to this, there is Japanese Patent Application Laid-Open No. 61-159245, "Method for Manufacturing Cast Iron". This method divides watering into spray watering and large watering. However, although the above method is effective for low Si pig, productivity is reduced for high Si pig.

[Problems to be Solved by the Invention] When a casting pig iron is manufactured in a casting machine, in order to cool to a temperature at which the mold can be released in the demolding section, the molten iron injected into the mold is subjected to air Cooling, spray water cooling, water cooling. At that time, when water cooling is performed while the surface of the pig iron is not completely solidified, cooling water accumulated on the surface of the skin of the pig iron enters through cracks on the surface of the skin, and comes into contact with the hot metal to vaporize,
The thinned skin is ruptured, and the thin skin and a part of the hot metal are scattered, so that the appearance of the solidified pig iron is significantly deteriorated. FIG. 3 schematically shows the situation.
In the figure, 10 is a mold, 11 is cooling water, 12 is a solidified portion, and 13 is an unsolidified portion.

It was also found that this phenomenon was particularly noticeable in high Si pig iron. To avoid this, there is no other method than air cooling until the surface layer of the hot metal in the mold is completely solidified, followed by water spray cooling. That is, in order to secure the time required for air cooling, there is a problem in that productivity is reduced due to a reduction in mold conveyor speed.

[Means for Solving the Problems] The present invention relates to a process for performing air cooling, spray water spray cooling, water spray cooling during casting of pig iron for casting from a blast furnace or another ironmaking furnace, before water cooling. It is a method for producing cast iron, characterized in that the superheat of the hot metal surface in the mold is set to 50 ° C. or lower, by pre-cooling the hot metal temperature before pouring into the mold, so that the hot metal surface in the mold before water cooling is cooled. A method for producing cast iron, characterized in that the superheat is reduced to 50 ° C. or lower, and the superheat of the hot metal surface layer in the mold before spraying and cooling with a large amount of water with a droplet diameter of 20 μm or less is sprayed and cooled. A method for producing cast iron, characterized in that the temperature is set to 50 ° C. or lower.

[Operation] Hereinafter, the present invention will be specifically described with reference to the drawings.

Fig. 1 shows the outline of the equipment of the cast iron machine. Hot metal from a blast furnace or another iron making furnace is transported to a casting machine by a mixed iron wheel or a hot metal ladle 2. The hot metal that has arrived at the cast iron machine from the mixed iron wheel or the hot metal ladle 2 is poured into the mold 5 continuously arranged on the mold conveyor 1 via the moving gutter 3, the fixed gutter and the branch gutter 4. . Hot metal after pouring is cooled and solidified to form a product having a certain shape.
The hot metal and the pig iron in the mold 5 are first air-cooled according to the movement of the mold conveyor, and then soft-cooled by the spray water cooling 6 to solidify the surface layer of the hot metal in the mold 5. Next, it is cooled strongly by a large amount of water spraying 7 to a temperature at which the mold can be removed.

The cooled pig iron is naturally dropped by its own weight, removed from the mold 5 in the process of changing the upper surface of the mold 5 from upward to downward in the removing section 8, and is transferred by the apron conveyor 9. At that time, if the pig iron is incompletely solidified due to insufficient cooling, when the pig iron breaks or cracks, the unsolidified hot metal inside the pig iron is released to the outside, causing equipment trouble and product failure. ,
Cooling and solidification control of pig iron is very important.

However, as described above, when water spray cooling is performed in a state in which the surface layer of the hot metal in the mold 5 is not completely solidified, the appearance of the manufactured pig iron deteriorates.

The present inventors, the difference between the solidification temperature of the hot metal injected into the mold 5 and the hot metal surface layer temperature in the mold 5 immediately before water spray cooling,
When the so-called superheat was measured, as shown in Fig. 2 showing the relationship between the cast iron temperature and the appearance of the shape due to the difference in the superheat at the start of watering, a cast iron having a general composition was cast at a temperature of 1350 ° C. In the range of 11450 ° C., when the superheat was 50 ° C. or less, it was confirmed that the appearance shape defect of the pig iron did not occur. Table 1 shows typical test conditions in FIG.

Thus, the present invention, during the casting of cast iron from a blast furnace or other ironmaking furnace, in the process of performing air cooling, spray water cooling, water cooling, the hot metal surface in the mold before water cooling. Superheat is to be reduced to 50 ° C or less.

As a specific means of reducing the superheat of the hot metal surface layer in the mold before water spray cooling to 50 ° C. or lower, for example, a coolant such as a pig iron is put into a hot metal in a hot metal wheel or a hot metal pot 2. A method of controlling the hot metal temperature in a set temperature range in consideration of a transportation time, a casing that brings air cooling action together with dust collection to a moving gutter 3, a fixed gutter, and a branch gutter 4 through which the hot metal before being injected into the mold 5 (see FIG. (Not shown), and a method of forcibly cooling the hot metal to be injected and a combination thereof.

The above-described method of cooling the hot metal temperature before injection to a predetermined temperature can be effectively applied to, for example, low Si pigs with Si: 2.0% or less, but high methods with Si: 2.0% or more. Since the solidification temperature of Si pig is low, there are cases where it cannot be cooled to a predetermined temperature.

Thus, in the present invention, water is atomized with a gas to form a droplet having a diameter of 20 μm.
m is sprayed and cooled using air water of m or less to solidify the skin of the hot metal in the mold 5 before spray cooling. This air-water cooling uses very fine spray particles of 20 μm or less to collide with the object to be cooled by the force of air, and utilizes the sensible heat accompanying the evaporation of water particles. Since the cooling ability equivalent to the spray watering by the spray can be obtained, there is no infiltration of the cooling water into the pig iron.

[Examples] Table 2 shows the results of a cooling test using a conventional spray nozzle and a steam-water nozzle according to the present invention. Table 3 shows the hot metal components and operating conditions at that time. The start of cooling was 7.6 m from the injection position, and the cooling length was 9.5 m. The outer shape of the pig iron was sampled and visually evaluated before hot cold watering.

As a result, in the spray type, there was a phenomenon in which cooling water accumulated on the surface of the pig iron, and the appearance was poor. In the case of the air-water type spray particle size of 20 μm or less, there was no phenomenon that cooling water accumulated on the surface of the pig iron, and the appearance was good.

Table 4 shows the results when the air-water nozzle is applied to the conventional spray watering zone. The cooling start position is 18m from the injection position, and the nozzle used is the same as the test product in Table 2 and the water pressure is
0.5, and the air pressure was set to 2.5 kg / cm ² . As a result, there was no defect rate at the same production volume as before the countermeasures were implemented.

[Effects of the Invention] By setting the superheat of the hot metal (mold pig) surface in the mold before sprinkling cooling by a cast iron machine to 50 ° C or less, there is a remarkable effect that there is no appearance defect of the pig iron.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic explanatory diagram of a casting machine, and FIG. 2 is a diagram illustrating a relationship between a casting iron temperature and a difference in superficial shape due to a difference in superheat at the start of watering (cast iron temperature and FIG. 3 is a model diagram of the occurrence of a shape defect, showing the appearance shape due to the difference in superheat on the surface of the pig iron. DESCRIPTION OF SYMBOLS 1 ... Mold conveyor 2 ... Molten iron or hot metal pot 3 ... Movable gutter, 4 ... Fixed gutter and branch gutter 5 ... Mold 6 ... Spray watering header 7 ... Sprinkling header, 8 ... Mold 9: Apron conveyor 10: Mold, 11: Cooling water 12: Solidified part, 13: Unsolidified part

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukimasa Abe 5-3 Tokai-cho, Tokai-shi, Aichi Prefecture Nippon Steel Corporation Nagoya Works (56) References JP-A-2-175048 (JP, A) 57-33090 (JP, B2) (58) Field surveyed (Int. Cl. ⁶ , DB name) B22D 3/00-5/04

Claims (3)

(57) [Claims] (1) In the process of performing air cooling, spray water cooling, and water cooling when casting pig iron from a blast furnace or another iron making furnace, the superheat of the hot metal surface layer in the mold before water cooling is performed. The method for producing cast iron, wherein the temperature is set to 50 ° C. or less. 2. In the process of performing air cooling, spray water cooling, and water cooling when casting pig iron from a blast furnace or another iron making furnace, the hot metal temperature before pouring into a mold is previously cooled. A superheat of the surface layer of the hot metal in the mold before water spray cooling is reduced to 50 ° C. or less. 3. The process of performing air cooling, spray water cooling, and water cooling when casting pig iron from a blast furnace or another iron making furnace, using steam having a droplet diameter of 20 μm or less. A method for producing cast iron, characterized in that superheat of the surface layer of hot metal in a mold before spray cooling is reduced to 50 ° C. or lower by spray water spray cooling.