JPS59104249A - Casting method of hollow steel ingot and core for casting - Google Patents

Abstract

PURPOSE:To enable free control of a final solidification position with a large-sized hollow steel ingot as well in a device for producing the hollow steel ingot with inside and outside double connecting cores packed therein with refractories by shifting the indirect cooling of the cores to direct cooling upon thickening of a solidified shell. CONSTITUTION:An assembled core 7 which is cylindrical over the entire part and is packed therein with castable refractories 6 is installed in the cavity between an annular or cylindrical casting mold 3 formed of iron on a molding board and inside and outside cylinders 4, 5 which are formed of inside and outside, relatively thin-walled double iron pipes and are disposed concentrically in the inside central part of said mold. A header 9 for injecting a cooling medium provided with many injection ports 8 opening toward the inside periphery of the core in the central part thereof is provided in an upright attitude through the molding board. A molten steel 10 is charged, by bottom pouring, into the part between the mold 3 and the core 7, and the medium is injected through the ports 8 to the cylinder 4 during the charging and during the initial stage of solidification, thereby cooling indirectly the steel 10. When the strength of the solidified shell on the inside surface of the steel 10 attains the level substantially equal to the static pressure of the molten steel, the cylinder 4 is removed upward by a handle 15, then the refractories 6 flow out and the cylinder 5 is directly cooled by the medium from the ports 8.

Description

DETAILED DESCRIPTION OF THE INVENTION A1 Technical field to which the invention relates The present invention relates to a method for casting hollow steel ingots and a casting core thereof, and in particular to a method for determining the final solidification position, which is a problem when casting large hollow steel ingots. It is an object of the present invention to make it possible to advantageously manufacture hollow steel materials having sound internal properties through free control.

Description of the Prior Art, its Problems, and Purpose of the Invention In general, in order to produce hollow forging materials in the form of cylinders or rings for applications such as pressure vessels, it is difficult to use the forging process from old solid steel ingots. In addition to processes such as drilling and expanding holes, there are also methods that use metal cores to produce hollow steel ingots during the ingot making process. The cooling surface area is generally 8 on the outer and inner surfaces.
9, especially when considering the ratio of heat extraction surface area to the stacking of hollow steel ingots to be solidified, it is 5 to 1.
The anisotropy is so significant that cooling of the inner surface becomes extremely insufficient.

In this respect, in conventional methods such as simple air cooling for metal plate cores, there is a risk of melting and damage to the metal plate core itself, and if a thick plate is used, the core side of the hollow steel block However, there are many problems in strengthening and promoting heat removal to accelerate the solidification rate from the inner surface of the hollow steel ingot, and therefore, in practical terms, the final solidification position is on the side of the assembled core. Therefore, the goal is to reach only about 20 to 30% of the wall thickness of the hollow steel ingot, but due to the training effect including effective crimp crimping, the target range is as much as 50% of the wall thickness of the hollow steel ingot. However, the control of the final solidification position had to be completely different.

Therefore, the applicant previously proposed in Japanese Patent Publication No. 56-18587 a mold device for producing a hollow 1Iilj ingot using a double inner and outer connecting core filled with refractories. , Since indirect cooling is applied to the above-mentioned connecting core through a refractory, in order to achieve the above-mentioned goal of determining the final solidification position, many considerations must be made to operational factors depending on the wall thickness of the hollow steel ingot. required.

The inventors went a step further and completely prevented the thickening of the solidified shell by directing the growth of the solidified shell by indirect cooling in much the same manner as described above, only during the pre-casting period when it must counteract the static pressure of the molten steel. Focusing on the transition to direct cooling, we have conducted fire experiments and studies, and have advantageously solved the drawbacks and problems mentioned above.
Development regarding the production of advantageous hollow steel ingots that not only have excellent inner surface properties, but also allow the final solidification position to be freely controlled in accordance with the above goals, even for large hollow steel ingots of, for example, 100 tons or more. I was able to achieve results.

C0 Structure of the Invention This invention has an annular or cylindrical iron mold placed on a mold surface plate, and an irregularly shaped iron mold in a gap between two relatively thin-walled iron pipes arranged concentrically at the inner center of the mold. A generally cylindrical assembly core filled with a refractory and sandwiched therein is installed, and a ladder is placed between the mold and the assembly core for a cooling medium having a dense opening through the center hole of the mold surface plate. During the initial stage of solidification following the completion of the above injection, the assembled core is indirectly cooled through the monolithic refractory by the injection of cooling medium discharged from the injection port into the fluid iron pipe located inside the core. According to the growth of the solidified shell, only the iron pipe located inward was removed upward, and at the same time, the monolithic refractory was removed through the center hole of the mold surface plate and was positioned outside the assembled core. The solution to the above problem is to directly cool the inner surface of the iron pipe by injecting a cooling medium from a fluid injection port, and to control the final solidification position of the hollow steel ingot by selecting the injection flow rate of the cooling medium. In addition, relatively thin-walled iron pipes with two inner and outer layers are arranged concentrically in the inner center of an annular or cylindrical iron mold on a mold surface plate, and a monolithic refractory is placed in the gap between these iron pipes. It is an assembly core for casting steel ingots, which has a cylindrical shape as a whole and is filled with the inside of the assembly core, and the ladder is inserted into the cooling medium in an upright position passing through the center hole of the mold surface plate, and is concentric with the assembly core. casting of a hollow steel ingot, in which the assembled core has a hanger on the top of the iron pipe located inside the core, which is useful for removing the monolithic refractory from the central hole of the mold surface plate; It is proposed that the core be used for the effective implementation of the above method.

In this invention, during and immediately after the conventional molten steel pouring operation as the first step in the casting process of a hollow steel ingot, a cooling medium, such as a compressed Provide indirect cooling by releasing from the ladder to pressurization with a gas or cold water injection port to prevent the growth of the solidified shell resulting therefrom;
In the second step, only the iron pipe located inside the assembly core (hereinafter referred to as the inner tube) is lifted upwards and pulled out and removed. At the same time, the monolithic refractories of the assembly core are flowed out and removed, and then the assembly core is removed. By applying direct cooling to the inner periphery of the iron pipe (hereinafter referred to as the outer tube) located outside the core, and adjusting the cooling medium injection flow rate to enhance the heat removal from the core side, the molten steel can be extracted from the inner surface. The final solidification position of the hollow steel ingot is controlled by adjusting the heat rate so that it is comparable to that from the outside surface, resulting in particularly excellent surface texture as well as inner surface texture, making it easy to corrugate during forging after casting. It is crimped to easily ensure sound internal performance, and can be manufactured without any problems even in large hollow steel ingots.

This invention will be specifically explained with reference to FIGS. 1 and 2.

Figure 1 shows the cooling process of the hollow steel ingot during or immediately after pouring molten steel as the first step, and Figure 2 shows the cooling process of the hollow steel ingot as the second step in which the cylinder of the assembly core is removed and the monolithic refractory is assembled. The process of directly cooling the inner surface of the outer cylinder of the assembled core by removing the outflow is shown.

In Fig. 1, for example, upper and lower mold surface plates 1,
An annular or cylindrical iron mold 8 is placed on the inner and outer cylinders 4 and 5, and an irregularly shaped iron mold 8 is placed in the gap between the inner and outer cylinders 4 and 5. A cylindrical assembly core 7 filled with a refractory 6 is installed, and a large number of injection ports 8 opening facing the inner circumference are installed in the center of the assembly core 7 in the height direction and A large number of cooling medium injection headers 9 provided in the circumferential direction are installed especially on the mold surface plate 1.
The molten steel 1 is placed in an upright position passing through the central hole of the mold 1.
0 is poured between the mold 8 and the assembled core 7.

During this injection and the subsequent initial stage of solidification, compressed gas 12 or cooling water 18, for example, is injected into the inner cylinder 4 of the assembly core 7 from the injection port 8.
Since the inner surface of the molten steel is indirectly cooled through the molten steel, this indirect cooling is useful for preventing deterioration of the inner surface quality and cracking of the inner periphery of the hollow steel ingot due to excessive rapid cooling, without causing melt damage to the outer cylinder 5. Note that 14 is a runner refractory.

Of course, when pouring this molten steel, it is necessary to take precautions to prevent molten steel from leaking in the gap between the lower end of the assembly core 7 and the upper surface plate 1, etc. For the above-mentioned first stage of indirect cooling, it is preferable to use compressed gas, which is useful for avoiding accidents such as steam explosions due to reactions between cooling water and leaking steel, rather than using cooling water.

The reason for filling and sandwiching the monolithic refractory material 6 between the outer cylinders 4 and 5 in the assembled core 7 is because there are concerns when directly cooling a steel plate core such as only the outer cylinder 5. In addition to avoiding the disadvantages of cracking and melting of the outer cylinder 5, especially in the case of water cooling, it is possible to avoid the above-mentioned accidents, especially when water cooling is performed. This is to advantageously allow thermal contraction on the inner surface of the hollow steel ingot by making the iron plate relatively thin, thereby effectively preventing the occurrence of inner surface cracks.

Next, as the solidified shell grows on the inner surface of the molten steel, when the strength of the solidified shell sufficiently rivals the static pressure of the molten steel,
In the second step, the inner cylinder 4 of the assembly core 7 is removed upward by a crane or the like via a hanger 15 provided at the top thereof. At the same time, the monolithic refractory filled and held between the outer cylinders 4 and 5 of the assembled core 7 loses its inner periphery support, and as shown in FIG. The water is removed and collected in the duct 17.

During this time, the outer cylinder 5 is directly cooled by the cooling medium ejected in a spray form through the injection port 8, so the cooling rate from the inner surface of the molten steel 10 is extremely increased as will be described later with reference to FIG. Although we are concerned about the use of water 18, we can appropriately control the final solidification position of the hollow steel ingot by adjusting the water droplet.

The steam generated at this time can be discharged from the system by installing a hood 18, for example, after the inner cylinder 4 is removed, and excess cooling water can be recovered from the duct 17.

Further, the monolithic refractory 6 needs to be able to be easily flowed down and removed after the assembly core 70 and cylinder 4 are removed, and it is preferable to use a monolithic refractory that easily sinters, such as chromite sand. Of course, its recovery and reuse is advantageous.

FIG. 8 shows an example of the results obtained by calculating the progress of solidification from the inner and outer surfaces of a hollow steel ingot in the casting method according to the present invention using an electronic computer using the differential method. - Also, Table 1 shows typical values of the calculation conditions in this case.

Table 1 Temperature of initial molten metal: 1550°C Emissivity of metal mold: ε=0.8 Surface heat transfer coefficient: Natural convection Emissivity of outer surface of steel ingot: ε=0.8 Souffle cooling water: 10077 m ”・min Monolithic refractory: Chromite sand (thickness 50mrrL)
Steel ingot shape Inner diameter = 80oφrrLrn Outer diameter:
2800φmm Inner and outer tube: Made of iron plate (thickness 15 mm) Molten steel in the iron mold a is solidified at the inner and outer tubes at the $1 stage because the refractory is sandwiched between the inner and outer tubes of the assembly core. As shown in Fig. 8, at point A, which is considerably lower than that on the outer surface, but reaches a predetermined thickness or more due to the growth of the solidified shell on the inner surface of the molten steel, the inner cylinder of the assembly core is removed upward in the second step, and at the same time the thickness is removed. The inner surface of the outer cylinder was directly cooled with spray cooling water while the shaped refractory was removed downward. Although there is a slight cooling delay compared to the outer surface of the molten steel, the solidification rate on the inner surface increases extremely, and the calculation results show that the final solidification position is approximately 45% of the wall thickness than the inner surface of the hollow steel ingot. .

Example inner diameter '100mmφ, outer diameter 2800mrr+φ, 100
tons of hollow steel ingots were cast according to the invention. The composition of the molten steel is shown in Table 2, and the casting equipment conditions and casting conditions are shown in Table 8.

Table 2 Table 8 Initial jAA temperature of molten steel: 1548℃ Mold outer cylinder steel plate thickness 211mm Mold inner cylinder steel plate thickness 211mm Monolithic refractory: Chromite sand (thickness 85rrLr
rL) 9 m3/h, time 240 minutes) Injection nozzle: Full cone nozzle 8-4 t/mln No. of injection ports m: 8 ft+i/rr12 As a result, casting work can be carried out safely and final solidification of hollow steel ingots. The position was also almost near the center of the wall thickness.

E. Effects According to the present invention, the molten steel injected into the casting space formed on the mold platen between the annular or cylindrical iron mold and the assembly core located at the inner center of the mold is cooled. The process is divided into a first stage and a second stage before and after the growth of the solidified shell, and in the first stage, indirect cooling with a core structure that can sufficiently cure the growth of the solidified shell allows relatively thin assembly. The outer shell is used to effectively absorb the shrinkage caused by the growth of the solidified shell without causing melt damage, and effectively prevent inner cracking, and direct cooling in the second stage allows the final solidification position of the molten steel to be adjusted. By making it possible to make a wide range of adjustments so that the thickness of the hollow steel ingot reaches approximately the center of the wall thickness, it is possible to effectively improve the internal and external properties as well as the internal properties.

Moreover, appropriate improvements in the core structure that can be adapted to the development of each of the cooling stages described above can be realized, and the implementation of the method of the present invention can be facilitated.

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views schematically showing the process of manufacturing a hollow steel ingot according to the present invention, and Figure 8 shows the progress of solidification from the inner and outer surfaces of the hollow steel ingot using a computer using the differential method. This is the explanatory chart I found. 8... Mold, 4... Cylinder of assembly core, 5... Outer cylinder of assembly core, 6... Monolithic refractory, 7... Assembly core, 8... Injection port, 9...Header for cooling medium injection, 10... Molten steel, 15... Hanging hand. Patent applicant: Kawasaki Steel Corporation

Claims (1)

[Scope of Claims] L An annular or cylindrical iron mold on a mold surface plate, and a monolithic refractory in the gap between two relatively thin-walled iron pipes arranged concentrically at the inner center of the mold. A cylindrical assembling core filled with and sandwiched together is installed, and a ladder is installed through the center hole of the mold surface plate to produce a hollow steel ingot in which molten steel is injected between the mold and the assembling core. In the initial stage of solidification following the completion of the above-mentioned injection, indirect cooling is performed from the middle set via the missing refractory, and as the solidified shell grows, only the inner iron pipe is removed upwards, and at the same time the insufficient refractory is removed. The material is removed by flowing down through the center hole of the mold surface plate, and the inner surface of the iron pipe located outside the assembled core is directly cooled by the injection of cooling medium from the fluid injection port. A method for casting a hollow steel ingot, characterized in that the final solidification position of the hollow steel ingot is controlled by selecting the injection flow rate. An entire structure in which two relatively thin-walled iron pipes, an inner and outer layer, are arranged concentrically in the center of an annular or cylindrical iron mold on a mold surface plate, and the void between these iron pipes is filled with monolithic refractories. This is an assembly core for casting hollow steel ingots in which a cylindrical shape is combined with a ladder, and the ladder is placed concentrically with the assembly core in an upright position passing through the center hole of the mold surface plate to the cooling medium,
A core for casting a hollow steel ingot, in which the assembled core has a hanger on the top of the iron pipe located inside the core to help remove the missing refractory from the center hole of the mold surface plate. .