JPS6349582B2 - - Google Patents

Description

[Detailed description of the invention]

B. Technical field to which the invention pertains The present invention relates to a method for manufacturing hollow steel ingots, and in particular, to freely control the final solidification position, which is a problem when casting large hollow steel ingots, to produce hollow steel materials with sound internal properties. The aim is to make it possible to manufacture it advantageously. B. Prior art, its problems, and purpose of the invention In general, in order to manufacture hollow forging material in the shape of a cylinder or ring for use in pressure vessels, etc., it is difficult to make a forging process from an old solid steel ingot. drilling·
In addition to processes such as hole expansion, methods are already known in which metal cores are used to produce hollow steel ingots during the ingot making process. Generally speaking, the surface area of the outer surface and the inner surface differs significantly by about 3:1, and especially when considering the ratio of heat removal surface area to the weight of the hollow steel ingot to be solidified, it differs significantly by about 5:1. Cooling of the inner surface becomes significantly insufficient. In this respect, if the conventional metal plate core is simply air cooled, there is a risk that the metal plate core itself will be damaged by melting, and if a thick wall plate is used, the core side of the hollow steel block will There are many problems in strengthening and promoting heat removal to speed up the solidification rate from the inner surface of the hollow steel ingot because it is accompanied by disadvantages such as the occurrence of cracks on a certain inner surface.Therefore, in practice, the final solidification position is from the assembled core side. However, due to the effectiveness of the forging process, including effective crimp bonding, the target can reach up to 50% of the wall thickness of the hollow steel ingot. However, the control of the final solidification position was inevitably insufficient. Therefore, the applicant previously proposed in Japanese Patent Publication No. 56-13537 a mold device for manufacturing hollow steel ingots using a double inner and outer connecting core filled with refractories. Since indirect cooling is applied to the core through the refractory, in order to achieve the goal of determining the final solidification position as described above, it is necessary to take into account many operational factors depending on the wall thickness of the hollow steel ingot. did. The inventors went one step further and guided the growth of the solidified shell through indirect cooling, similar to the above, only during the pre-casting period when it must compete with the static pressure of molten steel, and then directly cooled the solidified shell after its thickening. We conducted experiments and studies with a focus on transitioning to
Development results related to 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 according to the above goals, even for large hollow steel ingots weighing more than 100 tons. I was able to give you C. Structure of the Invention This invention provides an annular or cylindrical iron mold on a mold surface plate, and a monolithic refractory in the space between two relatively thin-walled iron pipes arranged concentrically at the inner center of the mold. In manufacturing a hollow steel ingot, a cylindrical assembly core filled with materials and sandwiched together is installed, and molten steel is injected between the mold and the assembly core. A coolant header having a number of fluid injection ports opening through the center hole of the mold platen is disposed through the central hole of the mold platen so that the assembled core is positioned inside thereof during the initial stage of solidification following completion of the above-mentioned injection. By injecting the cooling medium from the fluid injection port, the iron pipes are cooled indirectly through the monolithic refractories, and as the solidified shell grows, only the iron pipes located inward are removed upward, and at the same time, the iron pipes located inside are removed upward. The shaped refractory 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. The solution to the above problem is to control the final solidification position of the hollow steel ingot by selecting the injection flow rate. 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 indirect cooling by discharge from a pressurized header with gas or cold water injection ports;
To prevent the growth of the solidified shell derived from this, 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, and the amorphous waterproof material of the assembly core is removed. After removing the outflow, we directly cool the inner periphery of the iron pipe (hereinafter referred to as the outer tube) located outside the assembled core, and increase the heat removal from the core side by selecting the cooling medium injection flow rate. By making adjustments, the heat removal rate on the inner surface of the molten steel is made comparable to that from the outer surface, and the final solidification position of the hollow steel ingot is controlled, resulting in particularly excellent surface and inner surface properties, making it possible to cast. In the subsequent forging process, the zaku is easily crimped, ensuring sound internal performance, and it is possible to manufacture large hollow steel ingots without any problems. This invention will be specifically explained with reference to FIGS. 1 and 2. Figure 1 shows the cooling process of a hollow steel ingot that is performed during or immediately after pouring molten steel as the first step.
In addition, Figure 2 shows the second step of removing the inner cylinder of the assembled core and removing the monolithic refractory from flowing out from the center hole of the mold surface plate to provide direct cooling to the inner surface of the outer cylinder of the assembled core. Indicated. In Fig. 1, for example, an annular or cylindrical iron mold 3 is arranged concentrically at its inner center, and an inner and outer cylinder made of two relatively thin-walled iron pipes is placed in the gap between the inner and outer cylinders 4 and 5. Installed together with a cylindrical assembly core 7 filled with a shaped refractory 6 and sandwiched therein, the lower two-tiered mold surface plates 1 and 2 have a central hole that communicates with the inside of the assembly core 7. 16 will be provided. A coolant injection header 9 is provided with a large number of injection ports 8 in the height direction and circumferential direction that open facing the inner periphery of the inner cylinder 4 through the central hole 16.
is arranged concentrically with the assembly core 7 in an upright position passing through the center hole 16 of the mold surface plates 1 and 2, and the molten steel 10 is passed through the introduction passage 11 provided in the mold surface plates 1 and 2. Assemble molten steel 10 with mold 3 and core 7
Perform a bottom pour injection in between. During this injection and the initial stage of solidification that follows, the assembly core 7 is moved against the injection port 8 against its inner cylinder 4.
For example, compressed gas 12 or cooling water 13 is injected from the assembly core 7 to indirectly cool the inner surface of the molten steel. This indirect cooling is useful for preventing deterioration of the inner surface properties and cracking of the inner periphery of the hollow steel ingot due to excessive rapid cooling, without causing melting damage to the outer cylinder 5. Note 14
is a runner refractory. Of course, when pouring this molten steel, consideration must be given 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.
With emphasis on safety in the unlikely event that
For indirect cooling of the stages, it is preferable to use compressed gas, which is useful to avoid 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 to avoid concerns when directly cooling a steel plate core such as the outer cylinder 5 only. In addition to avoiding the disadvantages of cracking and melting of the core, especially when water cooling is performed, it is possible to avoid the above-mentioned accidents, especially when water cooling is performed, and to ensure the rigidity of the core with the inner tube 4 through the monolithic refractory, while the outer tube 5 is 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 reaches a point where it sufficiently rivals the static pressure of the molten steel, in the second step, the inner cylinder 4 of the assembly core 7 is attached to a suspension provided at the top. It is removed upward using a crane or the like using hands 15. 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. It 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. water 13
There is no need to worry about using it, and the final solidification position of the hollow steel ingot can be appropriately controlled by adjusting the amount of water. 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. Moreover, the monolithic refractory 6 is the inner cylinder 4 of the assembly core 7.
It is necessary that the refractory can be easily flowed down and removed after removal of the refractory, and it is preferable to use a monolithic refractory that does not undergo sintering, such as chromite sand, and of course, it is advantageous to recover and reuse it. FIG. 3 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. Table 1 shows representative values of calculation conditions in this case. Table 1 Temperature of initial molten metal: 1550℃ Emissivity of metal mold: ε=0.8 Surface heat transfer coefficient: Natural convection Emissivity of outer surface of steel ingot: ε=0.8 Amount of spray cooling water: 100/m ² min Monolithic refractory: Chromite sand (thickness 50mm) Steel ingot shape Inner diameter: 800φmm Outer diameter: 2800φmm Inner and outer cylinders: Made of iron plate (thickness 15mm) Molten steel in the iron mold 3 is transferred to the inside of the assembly core in the first stage. Since the refractory is sandwiched between the outer cylinders, the solidification rate on the inner surface is much lower than that on the outer surface, as shown in Figure 3, but it reaches a predetermined thickness or more due to the growth of the solidified shell on the inner surface of the molten steel. At point A, in the second step, the inner cylinder of the assembled core was removed upward, and at the same time, the monolithic refractory was flowed down and removed, and the inner surface of the outer cylinder was directly cooled with spray cooling water. Although there is a slight cooling delay compared to the outer surface of the molten steel, the solidification rate on the inner surface is extremely increased, 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. . D. Example A 100-ton hollow steel ingot with an inner diameter of 700 mmφ and an outer diameter of 2300 mmφ was cast according to the present invention. The composition of the molten steel is shown in Table 2, and the casting equipment conditions and casting conditions are shown in Table 3.

[Table] Table 3 Molten steel initial temperature: 1548℃ Mold outer cylinder steel plate thickness: 11mm Mold inner cylinder steel plate thickness: 11mm Monolithic refractory: chromite sand (thickness 35mm) 1st stage cooling medium: Air (gas pressure: 5.5 atm, Flow rate: 20m ³ /h, time 150 minutes) Second stage cooling medium: Water (water pressure: 4.5 atm, flow rate;
^9m3 /h, time 240 minutes) Injection nozzle: Full cone nozzle 3-4/min Number of injection ports: 8/ ^m2 Thickness of solidified shell when switching after indirect cooling (estimated): 135
mm Final solidification position of hollow steel ingot: 45-48% from the inner surface As a result, casting work can be performed safely,
The final solidification position of the hollow steel ingot was also approximately near the center of thickness. E. Effects According to this invention, an annular or cylindrical iron mold;
The cooling process of the molten steel injected into the casting space formed on the mold surface plate between the assembly core located in the inner center part is divided into the first stage and the second stage before and after the growth of the solidified shell. In the previous stage, indirect cooling with a core structure that can sufficiently cure the growth of the solidified shell allows the use of a relatively thin assembled skin to allow the growth of the solidified shell to occur without the risk of melting and damage. The shrinkage is properly absorbed to effectively prevent internal cracking, and the final solidification position of the molten steel is adjusted to approximately the center of the wall thickness of the central steel ingot through direct cooling in the second stage. Make it possible,
It is possible to effectively improve the internal and external properties as well as the internal properties.

[Brief explanation of drawings]

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 3 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. 1, 2... Surface plate for mold, 3... Mold, 4... Inner 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, 11 ... Inlet passage, 12 ... Compressed gas, 13 ...
...cooling water, 14... runner refractory, 15... hanging hand,
16...Central hole.

Claims (1)

[Claims] 1 An annular or cylindrical iron mold is placed on a mold surface plate, and a monolithic refractory is filled and held in the space between two relatively thin-walled iron pipes arranged concentrically at the inner center of the mold. In manufacturing a hollow steel ingot, a generally cylindrical assembly core is installed and molten steel is injected between the mold and the assembly core. A cooling medium header having a fluid injection port is installed through the central hole of the mold surface plate to inject fluid into the iron pipe located inside the assembled core during the initial stage of solidification following completion of the above injection. By injecting the cooling medium from the injection port, indirect cooling is performed through the monolithic refractory, and as the solidified shell grows, only the inner iron pipe is thrown upward, and at the same time, the monolithic refractory is cast. 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, and the injection flow rate of the cooling medium is selected. A method for casting a hollow steel ingot, characterized by controlling the final solidification position of the hollow steel ingot.