JPS5877744A - Production of hollow cast ingot - Google Patents

Abstract

PURPOSE:To produce a hollow cast of good quality without wasting unsolidified steel by increasing the gaseous pressure on the surface of the molten steel in a mold at the point of the time when the solidified shell of a prescribed thickness is formed after charging of the molten steel into the mold and forcing and discharging the unsolidified steel into an intermediate vessel. CONSTITUTION:A nozzle 4A of a ladle 4 is opened and molten steel 8 is charged through an intermediate vessel 6 into a mold 2. Upon completion of the charging, the molten steel 8 in the mold 2 begins to solidify from the mold wall, and after a specified time, the molten steel forms a solidified shell 30 of a prescribed thickness. Thereupon the pressure in a top cover 18 is increased to force and discharge the unsolidified steel 8 in the mold 2 into the vessel 6 so as to leave no molten steel 8 in the mold 2; thereafter a sliding gate 14 is closed. An oil hydraulic cylinder 24 is driven to draw a hollow solidified shell 30 from the inside of the mold 2, whereby a hollow steel ingot is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a hollow steel ingot, and particularly to a method for manufacturing a hollow steel ingot that can be easily mass-produced.

Conventionally, hollow steel ingots have been manufactured by a centrifugal casting method or a core method. Centrifugal casting is a method in which molten steel is injected into a cylindrical mold, the cylindrical mold is rotated at high speed, and a hollow body is manufactured using centrifugal force. is separated and a dense and sound casting is obtained.
It has the advantage of high casting yield because it does not require a boiler or sprue. This method is suitable for manufacturing thin-walled hollow bodies, but in the case of thick-walled bodies, segregation is promoted and the deviation of the concentration distribution in the thickness direction becomes large, causing quality problems.

Moreover, the equipment cost is high, and there is a drawback that a large amount of equipment cost is required to install casting equipment suitable for a large smelting furnace where the amount of melting per time is 100 or more.

Compared to the centrifugal casting method, the core method is more suitable for manufacturing thick-walled hollow bodies. A rotating water-cooled core is installed in the center of the mold, and molten steel is supplied between the mold and the core, and a solidified shell in contact with the core is used. After the core has grown to a certain extent, the core is raised continuously and pulled out.Furthermore, a metal plate core with a circular or irregular horizontal cross section is installed in the center of the mold, and the inside of the metal plate core is removed. There are four methods in which the solidification conditions are adjusted by making the tube hollow and cooling the inside with water, blowing cooling gas, or filling the tube with a radiant heat absorber.

These core methods have problems such as the complexity of core manufacturing and installation, poor surface quality of the hollow steel ingot, and cracks on the inner surface, and have drawbacks that make it difficult to say that it is a practical method suitable for mass production. .

Furthermore, the principle that a hollow steel ingot can be easily obtained by discharging the unsolidified molten steel from a lump in the middle of solidification is well known, but in rounding, the effective use of unsolidified molten steel cannot be achieved without the use of special equipment. Manufacturing hollow steel ingots by the discharge method could not become a practical method.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for manufacturing a hollow steel ingot that does not use a core and can effectively utilize unsolidified molten steel.

The gist of the present invention is as follows.

Specifically, there is a step in which molten steel is poured from an intermediate container containing molten steel from a ladle into a mold by a bottom pouring method through a runner, and when a solidified shell of a predetermined thickness is generated in the mold, A hollow steel ingot characterized by comprising the steps of pressurizing the molten steel surface with gas and pumping and discharging the unsolidified molten steel into the intermediate container, and pulling the formed hollow solidified shell upward. This is a manufacturing method.

Details and embodiments of the invention will now be described with reference to the accompanying drawings. First, the apparatus used to carry out the present invention will be described. A bottom pouring method is used to manufacture the hollow steel ingot according to the present invention, and an intermediate container 6 is provided between the mold 2 and the ladle 4 to temporarily store the molten steel 8 from the ladle 4. The intermediate container 6 and the mold 2 are communicated with each other by a runner 12 made of fireproof cylindrical bricks 10, as in the usual bottom pouring method, and a sliding gate 14 is provided at the lower exit side of the intermediate container 6 to allow the molten steel 8 to flow. injection can be controlled arbitrarily.

The method for manufacturing a hollow steel ingot according to the present invention is as summarized above.
After pouring the molten steel 8 into the mold 2, when a solidified shell of a predetermined thickness is generated, the gas pressure on the surface of the molten steel in the mold 2 is increased and the unsolidified molten steel is forced into the intermediate container 6 and discharged. Since this method was adopted, an upper lid 18 with a closed chamber structure is provided on the upper part of the mold 2 via a sealing material 16 such as an O-ring, and the upper lid 1
8 is provided with an inlet pipe 20 and an exhaust pipe 22 for pressurizing gas, and is also provided with a control valve for controlling the gas pressure during pressurization.

Furthermore, a hydraulic cylinder 24 is provided in the upper part of the upper cover 18, and its piston 26 extends downward within the upper cover 18 and is connected to a hollow solidified shell extraction device 28.

Next, a method for manufacturing a hollow block according to the present invention which utilizes the above-mentioned apparatus will be explained. That is, first, the hydraulic cylinder 24
The piston 26 is extended and a holding fitting 29 is attached to the hollow solidified shell extracting device 28 at its tip, and the lower end of the holding fitting 29 hangs down to a position where it is fully injected into the bath ms.

In this case, the pressure within the top 418 may be atmospheric pressure.

After completing the maintenance of the above-mentioned equipment, the
The nozzle 4A is opened and the molten steel 8 is injected into the mold 2 through the intermediate container 6. In this case, the sliding gate 14 is left open, and when the level of the molten steel 8 in the mold 2 reaches a predetermined level, the injection of the molten steel 8 from the pot 4 is stopped, or the sliding gate 1 is closed. As a result, the injection of molten steel 8 into the mold 2 is stopped. Since the level of the molten steel 8 in the mold 2 is the same as the level in the intermediate container 6, the expected level in the casting #12 can be known by marking the inner wall of the intermediate container 6 in advance.

When the injection of molten steel 8 is completed, the molten steel 8 in the mold 2 starts solidifying from the mold wall, and after a certain period of time, a solidified shell 30 of a predetermined thickness is formed.
can be obtained. The thickness of the solidified shell 30 can be determined from the temperature of the molten steel 8 at the time of pouring the molten steel and the elapsed time from the completion of pouring.

The upper lid 18 is installed in anticipation of the point in time when the solidified shell 30 reaches a predetermined thickness.
The unsolidified molten steel 8 in the mold 2 is transferred to the intermediate container 6 by increasing the pressure inside.
After the molten steel 8 is pumped and discharged so that at least no molten steel 8 remains in the mold 2, the sliding gate 14 is closed.

At this point, the holding fitting 29 attached to the hollow solidified shell drawing device 28 is completely welded to the upper end of the formed hollow solidified shell 30, so the hydraulic cylinder 24 is driven to remove the mold.
The hollow solidified shell 30 can be pulled out from within. In order to facilitate the drawing out of the hollow solidified shell 30, it is preferable to use a wide-top mold for the mold 2, and it is also preferable to use a copper water-cooled mold that is machined and has no irregularities on its inner surface. The middle nitrogen solidified fi 30 can be easily taken out by releasing the connection of the upper lid 18 to the mold 2.

When the drawing out of the hollow solidified shell 30 is completed, a new holding fitting 29 is attached to the hollow solidified shell drawing device 28, the mold device is maintained, and the molten steel 8 corresponding to the hollow lump produced from the hollow solidified shell 30 is manufactured from the hollow solidified shell 30. By replenishing the intermediate container 6 and repeating the above operations, hollow steel ingots can be manufactured intermittently.

In addition, in the actual leprosy of the present invention, the upper lid 18 and the mold 20 are
It is preferable to use 0S/G made of heat-resistant rubber as the sol material 16 to keep the contact area with ll1 airtight.

Furthermore, in order to continuously produce a large number of hollow bodies whose solidified shell thickness is as constant as possible, it is necessary to maintain the thermal conditions of the mold 2 constant throughout the operation.

For this purpose, it is necessary that the accumulation of heat in the mold 2 is small, and it is preferable to water-cool a mold made of copper with excellent heat conductivity using a water-cooling jacket 32.

EXAMPLE The production of a hollow cylindrical steel ingot with a diameter of 300 m and a wall thickness of 60-1 and a length of 2 m will be explained with reference to the accompanying drawings.

A cylindrical mold 2 with a lower inner diameter of 300111+, an upper inner diameter of 340 m, and a length of 2500 m was stood on a cast iron surface plate 34, and a runner 12 was made with fire-resistant cylindrical bricks 10. Intermediate container 6
A sliding gate 14 was provided at the connection between the runner 12 and the runner 12 to control the injection of molten steel into the mold 2 and the injection speed. A water cooling jacket 32 was provided on the outer surface of the copper mold 2 to provide a water cooling structure.

Using the above apparatus, the chemical composition is C: 0.13,
8i: 0.25 s, Mn: 0.78%, P: 0.0
Molten steel 8 of 18, s: o, oos, At: 0.035 was injected from the ladle 4 into the intermediate container 6, and then the sliding gate 14 was opened and the molten steel was poured into the mold 2. A cushion fitting 29 attached to a hollow solidified shell drawing device 28 was previously suspended from the upper part of the mold 2. It took about 30 seconds to inject a predetermined amount of molten steel into mold 2. 2
After leaving it still for 40 seconds, pressurizing Ar gas was introduced into the upper lid 18,
The gas pressure was set to 2.7 atmospheres in absolute terms, and the unsolidified molten steel 8 was pumped and discharged into the intermediate container 6. Immediately thereafter, the hydraulic cylinder 24 was operated to pull the solidified shell 30 upward. After drawing is completed, the control pulp of the gas exhaust pipe 22 in the upper lid 18 is opened to return the pressure in the mold 2 to atmospheric pressure, and the intermediate container 6 is
The molten steel inside was reinjected into @type 2. At the same time, the upper lid 1
8 and the pulled-out hollow solidified shell 3o are removed from above the mold 2,
Another separately prepared upper cover 18 and a pulling device 26 were set on the upper surface of the mold 2.

The above operation was repeated 9 times to produce 9 hollow steel ingots. Through this operation, molten steel 8 was replenished from the ladle 4 to the intermediate container 6 at appropriate times, and the molten steel level in the intermediate container 6 was maintained almost constant. did.

The obtained hollow steel ingots, excluding the first steel ingot, have an average inner thickness of 6
A hollow steel ingot with a substantially uniform wall thickness ranging from 57 to 64 cm was obtained.

- Surface defects were observed with the naked eye on the surface and inner surface of the ingot, but there were no defects such as cracks, and a hollow steel ingot of satisfactory quality was obtained.

As is clear from the above embodiments, the present invention produces a hollow steel ingot of good quality without wasting unsolidified molten steel by pumping and discharging unsolidified molten steel into an intermediate container using high-pressure gas. I was able to do that.

[Brief explanation of drawings]

The accompanying drawing is a schematic sectional view of a casting apparatus showing an embodiment of the present invention. 2... Mold 4... Ladle 6... Intermediate container 8... Molten steel 30... Solidified shell agent Takeo Nakaji

Claims (1)

[Claims] (1) A step in which molten steel is poured from an intermediate container containing molten steel from a ladle into a mold by a bottom pouring method through a runner, and when a solidified shell of a predetermined thickness is generated in the mold. A hollow steel molding method comprising the steps of pressurizing the molten steel surface in the mold with gas and pumping and discharging the unsolidified molten steel into the intermediate container, and pulling the formed hollow solidified shell upward. Method of manufacturing steel ingots.