JPS63238948A - Method and apparatus for continuously casting hollow cast billet - Google Patents

Abstract

PURPOSE:To smoothen casting surface of inner peripheral face and to obtain a hollow cast billet having uniform structure by holding coaxially a forcedly cooled core in inside of a forcedly cooled cylindrical mold, impressing gas pressure in inner peripheral face of poured molten metal between the mold and the core, forming annular space and casting. CONSTITUTION:At the upper end face of the core 16, a header 18 penetrating a cooling water introducing pipe 17 is fixed coaxially with the core 16. The lower face of the header 18 horizontally hangs over the upper end of the core 16 to outside, to form an overhang part 23. At contacting part of the upper end of the core 16 with the lower end of the header 18, the slit 24 is formed and in the slit 24, the pressurized gas is supplied from an introducing pipe 25 and gas pressure is impressed on the inner peripheral face of the molten metal at lower part of the overhang part 23. Further, a pressurized oil is supplied from an introducing pipe 26 and seeps through fine hole 26a of the core 16 to uniformly wet the outer peripheral face. Therefore, the contact of molten metal with the outer peripheral face of the core 16 is prevented and also thermal flow rate into the core 16 is reduced, and friction between the core 16 and the cast billet is reduced.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method and apparatus for continuous casting of hollow metal ingots, and more specifically, the present invention relates to a continuous casting method and apparatus for hollow metal ingots, and more specifically, the inner circumferential surface thereof has a smooth casting surface and there is little reverse segregation layer. The present invention relates to a method for continuously casting hollow ingots and an apparatus for carrying out the method.

(Prior art) In addition to its own uses, metal pipes or long hollow members have
For example, it is essential as a material for various cylindrical products such as vehicle wheel rims and compressor cylinders. Manufactured by casting method. As a material for plastic working such as ring rolling or forging, a hollow ingot produced by continuous casting is suitable because it does not have a directional fiber structure, has a homogeneous and fine casting structure, and is low cost.

Continuous casting of hollow ingots is generally carried out by holding a core coaxially inside a forced-cooled cylindrical mold, and continuously injecting molten metal into an annular space between the mold and the core. A hollow solidified shell is formed within the mold, and then cooling water is directly sprayed outside the mold to cool and solidify the inside, and the formed hollow ingot is drawn out under control of the casting speed. .

In the above continuous casting method, there is a so-called float method in which a refractory float is floated above the surface of the molten metal in a forced-cooled cylindrical mold to control the amount of poured metal, and a relatively deep insulating refractory is placed in the upper part of the forced-cooled mold. Generally, the so-called hot top method is applied, in which molten metal receiving tanks are connected together and the molten metal surface in the receiving tank is at the same level as the hot water supply trough. Also,
Some casting methods have also been implemented that do not use a mold, but instead use electromagnetic force to directly inject water into the molten metal held in a columnar shape to solidify it. Regardless of which method is used, commercially, a large number of molds are installed in a row and multiple casting is performed.

The conventional method of casting hollow ingots using the above-mentioned continuous casting method is characterized by the structure of the core, and can be broadly classified into:
(4) A method of using an uncooled core made of refractory material, (2) A method of using a forced cooling core, (C) A method of using a core to which electromagnetic force is applied are known.

As for the method belonging to (4) above, (1) In the float method, a long preformed air permeable gypsum plaster split core is used, and the core is cast in by pouring the metal between it and a forced cooling mold. A method in which a solidified long ingot is taken out and then the core is disassembled and removed (Japanese Patent Publication No. 35-1106). (2) In the float method, a refractory core that is difficult to get wet with molten metal is placed at a predetermined level in a cooling mold. Method of maintaining
72725).

Methods belonging to 03) above include (3) a method of casting while applying vibration to the core using an electromagnetic vibrator, etc. (Japanese Patent Application Laid-open No. 127548/1983); (4) a method of casting using a rotating core; A method of providing a vertically long slit for supplying lubricating oil on the outer peripheral surface of the (Japanese Patent Application Laid-Open No. 14944/1983), and (5) a method of using a refractory material core with a cooling pipe embedded therein (
! ¥j Kaisho 57-181759).

Furthermore, in the above (0), (6) an inductor is disposed inside the water-cooled core, and the inner peripheral surface of the molten metal is formed by the generated electromagnetic force, and the molten metal is directly cooled with water without contacting the core. Method of
etc. are known.

(Problems to be Solved by the Invention) The quality required for hollow ingots, especially hollow ingots as materials for plastic working such as forging, ring rolling, and swaging, is a smooth casting surface on the inner circumferential surface of the hollow, and the opposite quality. It has a fine homogeneous structure with little segregation. Furthermore, in the case of hollow billets, the roundness of the hollow part and the uniformity of the wall thickness are important quality measures. If these qualities are not met, it will be necessary to cut and remove a large amount of the inner circumferential surface during plastic working. In that case, it is necessary to manufacture a thick hollow ingot in advance according to the planned cutting depth, and the cutting cost increases, and the melt loss of cutting waste is also large, resulting in a large increase in cost. Particularly in the case of a long ingot having a small-diameter hollow portion, the cutting operation itself of the hollow inner circumferential surface is difficult, and productivity is inevitably reduced.

The conventional continuous casting method of hollow ingots mentioned above also has an advantage.

- It is difficult to industrially and stably produce hollow ingots that satisfactorily satisfy the above-mentioned quality. In methods (1) and (2) above, since the core does not have a cooling function, there is a large difference in solidification conditions between the inner and outer circumference of the ingot, making it impossible to obtain a homogeneous structure, and the casting speed In addition to the low surface resistance, the cast surface on the inner surface is also smooth. Other drawbacks include (1), which involves a consumable core, which increases costs, and (2), which makes stable operation difficult due to the tendency for hot water to leak from the core.

Although the method (3) has the effect of reducing entrainment of the surface oxide film, it tends to break the thin solidified shell and cause leakage, and it is difficult to form a smooth casting surface. In the method (4) above,
When tightening a water-cooled core due to solidification and contraction of molten metal, the force avoidance means are not operated consistently, making it difficult to rotate the core stably and making it difficult to achieve an effect. In method (5) above, the temperature of the core is controlled by burying a cooling pipe through which air, etc. flows inside the refractory core, but the solidification of the inner and outer peripheries of the ingot is Methods (1) and (2) have similar drawbacks in that there is a large difference in conditions. Although the method (6) above has the effect of reducing surface defects and reverse segregation in the ingot, it requires high equipment costs for generating an electromagnetic field, limits the mold array spacing in multiple casting, and reduces ingot surface defects. It has drawbacks such as a decrease in roundness. Furthermore, since a space is required to incorporate the inductor inside the core, it is difficult to miniaturize the core, and it cannot be adopted for manufacturing an ingot having a small diameter hollow portion.

The present invention has been made in view of the above circumstances, and its purpose is to have a smooth casting surface, especially the casting surface on the inner circumferential surface of the hollow part, and a homogeneous and fine structure throughout with few reverse segregation layers. Developed a method for stable and efficient continuous casting of hollow metal ingots with high roundness and uniform wall thickness, especially hollow ingots of light metals such as aluminum and magnesium, and equipment suitable for carrying out the process. It is to be.

(Means for Solving the Problems) In order to solve the above problems, the present inventors have conducted various studies and found that it is possible to apply the above float method, hot top method, or direct pouring method using a spout. I have found a way.

That is, the first invention includes a forcedly cooled cylindrical mold;
The molten metal, which is continuously injected into the annular space between the core, which is held coaxially inside the mold and is forcibly cooled, is cooled by contacting the mold and the core. solidified,
In the continuous casting method of the formed hollow ingot, gas is introduced into the outer peripheral surface of the core, and gas pressure is applied to the inner peripheral surface of the molten metal held in the hollow columnar shape to form an annular void. This is a continuous casting method characterized by casting.

A second invention is a continuous casting apparatus suitable for carrying out the method of the first invention, which includes a forcedly cooled cylindrical mold and a forcedly cooled medium held coaxially inside the cylindrical mold. In a continuous casting apparatus for hollow ingots, the outer circumferential surface of the area of the core in contact with the molten metal protrudes evenly in the horizontal outward direction during casting to form an overhang part,
It is characterized in that an opening communicating with a gas supply source is provided on the outer peripheral surface of the core below the overhang portion.

The hollow ingots to which the present invention is applied are mainly cylindrical hollow ingots (so-called hollow billets) that serve as materials for various ring-shaped or cylindrical products, but the present invention is also applicable to prismatic hollow ingots. I can do it.

The annular gap to which gas pressure is applied is formed so as to prevent the contact from above to below the position where the molten metal contacts the outer peripheral surface of the cooling core and begins to form a solidified shell. As a means of forming an annular gap in which gas pressure is applied to such a region, the uppermost outer circumferential surface of the cooling core is evenly extended in the horizontal direction to form an overhang, and the overhang is directed downward. The method is to introduce pressurized gas.

The gas can be introduced through any route as long as it is directed downward from the overhang. The gas introduction openings are fine gaps or fine pores defined to prevent molten metal from entering. Various embodiments of these introduction openings can be mentioned. For example, in a so-called hot-top structure in which a columnar or cylindrical fireproof insulator is connected to the top end surface of a cooling core, the lower end surface of the outer periphery of the fireproof insulator protrudes outward from the top end surface of the cooling core and overhangs the top end surface of the cooling core. forming a hang part, and providing a gas introduction slit in the connecting part;
A gas introduction path provided inside the fireproof heat insulating body is connected to and communicated with the slit. As yet another example, the outer circumferential surface of the cooling core below the overhang may be made of a breathable refractory material connected and communicating with the gas introduction path. In the above, as the fireproof heat insulator, a material that is difficult to wet with molten metal, such as aluminum, which is well known under trade names such as marinite and fiber flux, is preferably used. In addition, the above-mentioned breathable refractory material is preferably a material that has high thermal conductivity, is difficult to get wet with molten metal, and is difficult for molten metal to penetrate into minute pores, such as ceramics such as porous graphite, porous silicon nitride-bonded silicon carbide, or heat-resistant materials. Sintered metals are suitable for this purpose.

The gas introduced as described above forms a reservoir under the overhang of the upper part of the cooling core, and further forms an annular gap between the outer circumferential surface of the cooling core and the molten metal below the overhang. When the above-mentioned overhang portion is not provided, the introduced gas floats in the molten metal without stopping, bubbles out from the upper surface of the molten metal, and does not form an annular gap.

The size of the above-mentioned overhang, that is, the extent to which the outer peripheral surface of the core protrudes outward, is selected in advance through experiments based on the type of metal and alloy, the shape and dimensions of the ingot, the casting speed, the height of the molten metal and forced cooling mold, etc. However, for example, in a cylindrical hollow ingot made of aluminum or magnesium-based alloy and having an inner diameter of 20 to 100 mm, the tan is 1.5 tan or more, preferably 3.
0 mm or more, and below this lower limit, it is difficult to stably maintain the annular gap to which gas pressure is applied, and the pounding surface of the obtained ingot is also poor.

Although there is no particular upper limit, an overhang of 15w+m or more is meaningless.

The gas pressure to be applied to the annular gap is close to a value equivalent to the hydrostatic pressure of the molten metal at the level of the annular gap below the overhang, and its upper limit is such that the gas overflows onto the overhang and rises above the surface of the molten metal. The lower limit is determined by the pressure at which no bubbling occurs, and the lower limit is determined by the pressure at which an annular void is formed that can substantially reduce the contact area between the outer peripheral surface of the cooling core and the molten metal.

The annular gap formed by the introduced gas is not airtight, and the excess gas to which gas pressure is applied flows downward through the fine gap at the contact interface between the outer peripheral surface of the cooling core and the thin solidified shell of the molten metal. I will do it. There is experimental evidence that suggests that these minute gaps are formed in a pulsating manner in the circumferential direction due to the balance between contraction as the molten metal cools and expansion due to molten metal pressure. Therefore, in order to maintain an annular gap with a predetermined gas pressure applied under certain casting conditions,
It is necessary to maintain a more or less constant gas flow rate.

The gas introduced above is preferably one that is inert to the molten metal.
For example, in aluminum-based alloys, argon, nitrogen, etc.
In magnesium-based alloys, argon, boron tetrafluoride, etc. are used, and according to the experimental confirmation by the present inventors, air, nitrogen, and pyrolysis gases and steam of lubricating oil have unexpected effects on these alloys. It is also important to bring about favorable results.

When the influence of the oxygen concentration in these gases was investigated, it was found that gases or vapors containing 40 volumes of oxygen or less are preferably used for these light metals or their alloys.

The outer circumferential surface of the cooling core forms a lubricating interface similar to that in conventional continuous casting, and prevents the molten metal from seizing on the outer circumferential surface of the core. Such a lubricating interface is formed by a well-known method such as wetting the core by continuously or semi-continuously supplying liquid lubricating oil, or constructing the core with a self-lubricating heat-resistant material such as graphite or boron nitride.

(Function) In the method of the present invention, gas is introduced into the outer peripheral surface of the forcedly cooled core, and gas pressure is applied to the inner peripheral surface of the molten metal held in the shape of a hollow column, thereby forming an annular void. and cast.

Such an annular gap prevents the molten metal from coming into contact with the outer peripheral surface of the forced cooling core, reduces the contact area around the entire circumference, and moves the contact position downward. This reduces the heat flow to the cooling core on the inner circumferential surface of the molten metal held in a hollow column, and also reduces the heat flow between the core and the ingot (semi-solidified, solidified).
Reduces friction with the Therefore, the casting surface of the inner circumferential surface of the hollow ingot obtained is smooth, and the metal structure immediately below the casting surface has few reverse segregation layers, resulting in a co-uniform structure of the inner and outer layers.

(Example) The present invention will be described in detail below with reference to the drawings, but the present invention is not limited thereto.

Embodiment 1 FIG. 1 is a longitudinal sectional view showing an example of an apparatus in which the method according to the present invention is applied to a hot top method. To summarize the device shown in the figure, Japanese Patent No. 1007387 (Japanese Patent Publication No. 54-42847
The gas pressurized hot top continuous casting equipment shown in
This is a device equipped with a core for carrying out the present invention, and is intended to obtain a hollow ingot with an excellent smooth cast surface on both the inner and outer circumferential surfaces.

The cylindrical mold 1 made of a highly thermally conductive and heat-resistant material such as metal or graphite has an appropriate shape that defines the outer peripheral contour of the hollow ingot 15, for example, a circular cross section in the case of a cylindrical ingot. It surrounds the space in which the mass 15 is formed.

The mold 1 has a cavity into which a forced cooling medium, for example water 4, flows from the water supply pipe 3, thereby being forcedly cooled. A molten metal receiving tank 2 made of a refractory heat insulating material (trade name: Marinite) is coaxially and fixedly connected to the upper end surface of the mold 1.

The lower end surface of the inner circumference of the molten metal receiving tank 2 extends horizontally evenly inward from the inner circumferential surface of the mold l to form an overhang portion 5. A minute slit 6 is formed toward the inside at the part where the upper end surface of the mold 1 and the lower end surface of the molten metal receiving tank 2 contact, and pressurized gas is supplied to the slit 6 from the introduction lower, and the overhang part 5 is Gas is introduced downward. In addition, pressurized liquid lubricating oil is supplied from the inlet 8, and the mold 1
It flows out towards the inner peripheral surface.

The molten metal 9 is poured into the molten metal receiving tank 2 through the supply port 10 and reaches a molten metal level 11 . The molten metal 9 comes into contact with the cooled inner peripheral surface of the mold 1, is cooled, and begins to solidify. This solidification starting point is pushed down by an annular gap to which a gas pressure created by gas flowing below the overhang portion 5 is applied. The gap is formed so as to extend downward from just below the overhang portion 5 along the inner circumferential surface of the mold 1, and prevents contact between the molten metal and the inner circumferential surface of the mold.

The solidified ingot 15 is supported by a lower mold 13 placed on a table 12 that is supported by a hydraulic mechanism so as to be able to rise and fall, and is directly injected with secondary cooling water 14'i from a slit directed inward from the lower end of the mold 1. It descends while being cooled. When the ingot reaches a predetermined length, the pouring into the molten metal receiving tank 2 and the lowering of the lower mold tape 12 are stopped, the mold is moved, and the table 12 is raised to take out the ingot 15. .

In FIG. 1, a forcedly cooled core 16 is coaxially held inside a forcedly cooled cylindrical mold 1. The core 16
is made of the same material as the cylindrical mold 1, and has an appropriate shape that defines the inner peripheral contour of the hollow ingot, for example, in the case of a cylindrical ingot, it has a cylindrical shape, and the hollow part 19 of the ingot 15 is It occupies the space formed. The outer circumferential surface 168' of the core 16 is inclined inward as shown in the figure to cope with solidification shrinkage of the molten metal. A support tube 17 is integrally attached to the core 16 and extends vertically upward. The support tube 17 is movable up and down or supported at a predetermined position by a support mechanism (not shown) to regulate the vertical and horizontal positions of the core. In this embodiment, as shown in FIG.
The level of the upper end of the core 16 is made to match the level of the upper end of the cylindrical mold 1. However, depending on the type of metal, the dimensions of the hollow ingot, the thermal equilibrium conditions of the device, etc., the level of the core 16 relative to the cylindrical mold 1 may be appropriately selected to be above or below.

The lower end of the support tube 17 opens into the cavity 21 of the core 16, and after cooling water is supplied from the upper part 20 of the support tube 17 and cools the core, a slit is opened outward from the periphery of the lower end of the core. The secondary cooling water 22 is injected from the cooling water.

A header 18 made of a cylindrical fireproof heat insulating material (trade name: Marinite) is coaxially and fixedly connected to the upper end surface of the core 16, passing through the support tube 17 vertically. Although the header was made of the same material as the molten metal receiving tank 2, the two may be made of different materials. The outer peripheral lower end surface of the header 18 extends horizontally and uniformly outward from the upper end outer peripheral surface of the core 16 to form an overhang portion 23 . A fine slit 2 is formed uniformly outward at the portion where the upper end surface of the core 16 and the lower end surface of the header 18 touch.
4 is formed, and pressurized gas is supplied to the slit 24 from an introduction pipe 25 disposed through the ladder 18, and gas pressure is applied toward the inner circumferential surface of the molten metal below the overhang portion 23. be done. Further, pressurized lubricating oil is supplied from the lubricant introduction pipe 26, and leaks out toward the vertical outer circumferential surface of the core 16 through the fine holes 26a formed radially toward the outer circumferential surface near the upper end of the core. Wet the outer circumferential surface uniformly.

Figure 2 is an enlarged view of the main parts of the core in Figure 1, with (,) in the figure.
is a longitudinal cross-sectional view, and a cross-sectional view taken along the line AA' in (a) is shown in (b) of the figure. The lower end surface of the header 18 and the core 16
O-rings 28 and 29 are provided at the joints on the upper end surface at positions surrounding the gas introduction pipe 25 and the lubricating oil introduction pipe 26, respectively.
An O-ring 30 is also interposed along the inside of the gas distribution groove 31 to prevent these fluids from leaking at the joint.

The pressurized gas is introduced from the gas introduction pipe 25 through the annular gas distribution groove 31 formed at a position close to the outer periphery of the upper end surface of the core, through the slit 24 and below the overhang 23, and is introduced into the molten metal inner peripheral surface at this position. An annular space 23a is formed to which gas pressure is applied. Then, the gas from the spikes flows downward through the minute gaps between the outer peripheral surface of the core and the thin, fluctuating solidified shell of the molten metal, which does not yet have rigidity.

The lubricating oil fills an annular distribution groove 26b formed inside the outer periphery of the core from the introduction pipe 26, leaks out from the radial micropores 26a, and wets the outer periphery of the core. The lubricating oil used may be, but is not limited to, natural vegetable oils such as castor oil, peanut oil, rapeseed oil, or synthetic lubricating oils alone or in combination.

Embodiment 2 The apparatus shown in FIG. 3 is an example of application of the present invention in continuous casting by the float method. The cylindrical mold 1 is forcibly cooled by cooling water flowing in from the water supply pipe 3.
A cylindrical core 16 is held coaxially inside the cylindrical core 16 . The core 16 is forcibly cooled by cooling water flowing in from the water supply pipe 17. The core 16 and the top of the mold l are on the same level, and the molten metal 10 in the dandysh 27
flows through the lower end of the pouring frame 10, the spout 28, and between the mold 1 and the core 16 via the float 29'ff:.

The float 29 regulates the mold self-molten metal surface 110 level. A thin plate ring 23b with a uniform width extends outward from the outer peripheral surface of the core near the level at which the molten metal starts to solidify.
An overhang portion 23 is formed. Thin ring 2
The outer peripheral surface of the core immediately above and above 3a is surrounded by a fireproof heat insulating fell 2a for relaxing cooling. Nakako 16
The outer circumferential surface of the overhang portion 23 and the lower portion thereof is formed into an inverted conical inclined wall surface having a dimension corresponding to the solidification shrinkage in the axial direction of the ingot.

A conduit 25 penetrating into the interior of the core 16 from above is for introducing pressurized gas, and a conduit 26 is for introducing liquid lubricant. These introduction pipes are connected to respective distribution grooves having a structure similar to that shown in FIG. 2 of Embodiment 1, and from there, pressurized gas passes through each slit toward the overhang portion 23a directly below the core outer circumferential surface. Lubricant is supplied towards the Pressurized gas or lubricant is supplied in the same manner as in Example 1 via a fluid pressure and flow rate adjustment mechanism (not shown).

Embodiment 3 The apparatus shown in FIG. 4 is used as a core in the hot top method of Embodiment 1. A header 18 made of a fireproof heat insulating material is fixed to the upper part of the forcedly cooled core 16, with its lower end surface uniformly extending outward from the outer peripheral surface of the top of the core 16 to form an overhang part 23. connected.

A thermally conductive and breathable refractory ring 32 is fitted into the outer periphery of the core 16, and the joint between the ring and the core is tightly sealed by O-rings 32a and 32b. An annular groove 33 is provided on the ring side of the joint, and the groove 33 is connected to the lubricant introduction pipe 26 passing through the header 18 to supply pressurized lubricant to lubricate the outer peripheral surface of the ring 32. Oil leaches out. As the above-mentioned breathable fireproof material, porous lead dot material (for example, commercially available Union Carbide gAT
J) Alternatively, a powdered metal sintered body can be applied, but the pore size is so small that the molten metal cannot penetrate.

On the other hand, a metal spacer 34 is fitted into the lower end of the header 18 as shown in the figure to improve airtightness. Pressurized gas introduction pipe 2 passing through header 18 and spacer 34
5 is provided, and an annular groove portion 35 provided in the spacer
connected to one corner of the

Slits 24 are provided radially from the annular groove toward the overhang 23 to form a gas passage. The O-ring 29 prevents the introduced gas from leaking.

In the above, the longitudinal direction of the groove portion 33 in the breathable refractory material.

The position in the direction includes a level corresponding to the contact area between the molten metal and the refractory material, and is preferably provided in a band shape at a level close to the overhang part 23.

The outer peripheral surface of the ring 32 made of breathable fireproof material is as described in Example 1,
Similar to 2, it is desirable to incline into an inverted conical shape in consideration of solidification shrinkage of the molten metal. Further, a pipe 36 coaxially provided inside the cooling water introduction pipe 17 passing through the header 18 is open to the atmosphere at the upper part (not shown), and the lower end is connected to the core 16'! ! - It is open through and serves to maintain the pressure in the internal space 37 of the hollow ingot 15 at atmospheric pressure, but is not essential.

Embodiment 4 The apparatus shown in FIG. 5 is another embodiment of Embodiment 3, and is suitably used as a core in the hot top method as shown in FIG.

A thermally conductive and breathable refractory ring 32 similar to that in the third embodiment is fitted into the outer circumference of the cooling core 16. A flange portion 38 uniformly extends outward from the upper portion of the ring 32 to form an overhang portion 23 . A fireproof and insulating header 1.8 is fixedly connected to the flange and the top of the cooling core, and these joints are filled with O-rings 38a, 38b to prevent leakage of gas and lubricating oil. The lubricating oil is supplied through an introduction pipe 26 that passes through the header.
It is led into the core body and connected from there to a band-shaped annular groove 39 provided inside the refractory ring 32. The annular groove 39 is formed radially outward toward the position where the molten metal contacts the outer circumferential surface of the refractory ring 32 and directly below the overhang 23 above the contact point, and the lubricating oil fills this annular groove and is heated there. It penetrates into the refractory ring and wets its outer surface.

On the other hand, the gas is introduced into the core body through an inlet pipe 25 passing through the header, connected to one end of a horizontal annular groove 40 provided in the flange part of the refractory ring near the overhang part 230, and from there Gas is pumped through the ring and directly below the overhang 23. This forms a gas pressure application space 23a.

Embodiment 5 The device shown in FIG. 6 is a vertical cross-sectional view of the device used as the core of the pot top method of Embodiment 1. The upper part of the core 16 is fitted, and the lower peripheral edge of the header has a descending part 42 that covers the upper outer peripheral edge of the core 16, and the bottom surface of the descending part 42 is aligned outwardly from the outer peripheral surface of the core 16. The overhang part 23 is formed by projecting out like this.

The lower end of the lubricating oil introduction pipe 26 that passes through the header 18 and goes downward connects to an annular groove 26bK in the core 16, passes through a radial capillary tube 26m, and opens into the outer peripheral surface of the core 16. to wet the outer peripheral surface of the cooling core. Further, the lower end of the pressurized gas introduction pipe 25 that passes through the header 18 and goes downward is connected to the annular groove 31 in the core 16, and then passes through the fine slit 24 and then connects to the outer peripheral surface of the core and the header 1.
The fine sinter 24ai on the inner circumferential surface of the descending portion 42 of No. 8 is opened directly below the overhang 23, and a gas pressure-applied nitrogen gap 23a is formed in the molten metal at that position, thereby causing contact between the molten metal and the forced cooling core surface. The area has been reduced.

FIG. 7 is a partial vertical cross-sectional perspective view of FIG.
The passage of the gas passing through the slit 24 is free from clogging and is highly effective.

(Comparative Example) Comparative Example 1 A hot top type continuous casting apparatus shown in FIG. hang 2
Continuous casting was performed without forming an annular gap to which gas pressure was applied directly below No. 3.

Comparative Example 2 A float-type continuous casting apparatus shown in FIG. 3 was used, but the core was formed from a columnar fireproof heat insulating material (trade name: Marinite), and therefore was not forcedly cooled. The lubricant is
Continuous casting was performed by feeding the core through a fine slit on the upper outer circumferential surface of the core.

The results of Examples 1 to 5 and Comparative Examples 1 to 2 are shown in Table 1. The casting speed was determined to be the best speed while keeping the alloy type, cooling conditions, etc. constant, and the values shown in the table are the casting speeds. Although air was used as the gas in both cases, the results were the same as in the preliminary tests for argon and nitrogen.

Regarding the stability at the start of continuous casting, all methods of the present invention were extremely stable, and casting could be performed stably without any trouble. However, in the comparative example, troubles occurred such as a break out at the start, and the ingot burned into the core and did not descend and casting was stopped. The casting surface of the inner peripheral surface of the ingot was an extremely uniform and smooth surface in all of the Examples. On the other hand, in the comparative example, more or less burned skin (vertical streaks) occurred due to periodic re-melting and contact with the core mold.
This phenomenon was more common in Comparative Example 1 than Comparative Example 2, and the casting surface cracked in the circumferential direction.

The thickness of the segregation layer directly under the casting surface is as shown in the values in Table 1 (75 to 95 μm in the examples, 45 μm in the comparative examples).
There was a large difference of 0.1500 μm.

Figure 8 shows a microstructure photograph of the inner peripheral surface layer of the ingot (Example 1)
and Fig. 9 (Comparative Example 1) shows that the thickness of the reverse segregation layer near the casting surface and the uniformity of the structure of the Example are clearly superior to those of the Comparative Example. It will be done.

In addition, the roundness of the hollow part of the ingot and the uneven thickness of the ingot of the example were both significantly superior to those of the comparative example.

(Effects) As described above, according to the continuous casting method and apparatus for hollow ingots of the present invention, the obtained ingot has an extremely smooth casting surface on the inner peripheral surface of the hollow part, and the ingot structure near the casting surface is reversed. The segregation layer is thin and the structure is uniform, and the inner periphery of the hollow part is highly circular and the wall thickness is uniform.

Therefore, as a material for plastic working such as casting, ring rolling, swaging, etc., the inner circumferential surface of the hollow portion can be removed thinly, and there is little cutting waste, so metal loss is small and cutting time can be shortened. Further, the method and apparatus of the present invention cause fewer troubles in the casting process, and therefore are extremely useful industrially as they improve yields.

[Brief explanation of the drawing]

Figures 1 and 2 (a) and (b) are drawings of the apparatus of Example 1 in which the present invention is applied to the hot top casting method, where Figure 1 is an overall longitudinal sectional view and Figure 2 (a) 2 is a longitudinal section of the main part of the core, and FIG. 2) is a plan view of the core. FIG. 3 is an overall vertical sectional view of an apparatus according to a second embodiment in which the present invention is applied to a float casting method. Figures 4 and 5 show examples 3 and 4 of the present invention in which a breathable refractory ring is fitted to the outer peripheral surface of the cooling core.
FIG. FIG. 6 is a longitudinal cross-sectional view of a core of Example 5 in which the present invention is applied to the hollow shell casting method. FIG. 7 is a vertical cross-sectional perspective view of the core shown in FIG. FIG. 8 is a microstructure photograph of the inner peripheral surface layer of an aluminum alloy (JIS 5052) hollow ingot manufactured according to the present invention (Example 1), and FIG. 9 is a photograph of the same type of alloy manufactured according to Comparative Example 1. This is a microstructure photograph of the inner peripheral surface layer of a hollow ingot. 9. Molten metal, 15. Hollow ingot, 16. Forced cooled core, 17. Cooling water introduction pipe to the core.
18... Header made of fireproof insulation material, 22... Secondary cooling water from core, 23... Overhang, 23a...
- Between the gas pressure application and nitrogen immediately below the overhang, 25...pressurized gas introduction pipe to the core, 26...lubricating oil introduction pipe to the core, 32...breathable fireproof material ring. Figure 6 Figure 7

Claims (1)

[Claims] 1. Continuously injected into an annular space between a forcedly cooled cylindrical mold and a forcedly cooled core held coaxially inside the mold and held in a hollow column shape. A method for continuous casting of a hollow ingot, including a step in which the molten metal is cooled and solidified by the mold and the core, and the formed hollow ingot is continuously taken out from below the mold, Continuous casting of a hollow ingot, characterized in that gas is introduced into the outer peripheral surface of the core and gas pressure is applied to the inner peripheral surface of the molten metal held in the shape of a hollow column, thereby forming an annular gap and casting. Method. 2. The gas is one or more of air, nitrogen, an inert gas, a pyrolysis gas with an oxygen content of 40% by volume or less, and steam. The method for continuous casting of a hollow ingot according to item 1. 3. The upper limit of the gas pressure is determined depending on the hydrostatic pressure at the level of the molten metal in the annular space, and the contact area between the outer peripheral surface of the core and the molten metal is substantially reduced. The continuous casting method for hollow ingots according to claim 1, characterized in that a lower limit thereof is determined. 4. In a continuous hollow ingot casting device consisting of a forcedly cooled cylindrical mold and a forcedly cooled core held coaxially inside the mold, the area of the core that comes into contact with molten metal during casting. The outer circumferential surface extends horizontally outward evenly to form an overhang part,
A continuous casting apparatus for a hollow ingot, characterized in that an opening communicating with a gas supply source is provided on the outer peripheral surface of the core below the overhang part. 5. The continuous casting apparatus for hollow ingots according to claim 4, wherein the overhang portion is formed by an extension of the outer peripheral surface of the forcedly cooled core itself. 6. The overhang portion connects a columnar or cylindrical refractory insulator on the upper end surface of the forcibly cooled core, and the lower end surface of the outer periphery of the refractory insulator connects to the upper end surface of the forcibly cooled core. 5. The continuous casting device for hollow ingots according to claim 4, wherein the device is formed so as to extend outward from the end surface. 7. The opening is a slit formed at the joint between the upper end surface of the strongly cooled core and the lower end surface of the refractory object, and the slit is defined so that the molten metal does not enter the gap. 5. The continuous casting apparatus for hollow ingots according to claim 4, characterized in that the device is connected to a gas supply source. 8. The opening is characterized in that the outer circumferential surface of the core below the overhang portion is made of an air-permeable refractory material that communicates with a gas supply source and prevents the molten metal from entering. A continuous casting device for hollow ingots according to scope 4.