JPH0673717B2 - Hollow billet casting method - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for casting a hollow billet, and particularly to continuous casting of a long hollow billet in which the inner wall surface of the hollow billet is smooth and no cracks occur in the inner wall surface of the hollow billet. Regarding the method.

2. Description of the Related Art A continuous casting method for hollow billets using a water-cooled core or a core in which a graphite mold is directly arranged on the water-cooled core is known.

In such a method, since the molten metal is forcibly cooled by the water-cooled core or the graphite mold directly arranged in the water-cooled core, cracks parallel to the casting direction are generated on the inner wall surface of the hollow part of the hollow billet, or The once solidified portion becomes an adiabatic state due to the air gap, is redissolved and the surface becomes uneven, and there is a drawback that a smooth inner wall portion cannot be obtained.

The present inventors have formed a cast surface of a core by graphite or a carbonaceous material in order to eliminate the above-mentioned defects, and a cast surface member formed of such a material is used as a water-cooled mold provided in the core. A casting method has been proposed in which a hollow billet is cast using a core in which the above-mentioned cast surface body is not forcedly cooled, without being mounted via a heat insulating material or using such a water-cooled mold (Japanese Patent Laid-open No. Sho-61-200). 61-135452 gazette, Shokai 60-4693
(See publication 7).

When the hollow billet is cast by using the non-forced cooling type core as described above, the molten metal on the casting surface of the core may be forcibly and rapidly cooled by the core. Since there are no cracks parallel to the casting direction on the inner wall surface of the hollow billet, and there is no reheating action of the ingot due to the formation of the so-called air gap, the surface irregularities due to remelting of the solidified portion It is possible to obtain a hollow billet in which the inner wall surface of the hollow portion is smooth without causing

However, in the casting method using such a non-forced cooling type core, when a plurality of long hollow billets having a casting length of about 5-6 m are cast, the casting length is set to some of them. From 2 to 3m, the length of the inner wall is 2 to 10
It was found that a right-angle crack was generated in the casting direction of 0 mm, and when observing the core cast from the hollow billet with such a right-angle crack, remarkable adhesion of molten metal was observed on the cast surface of the core. As a result, there is a new problem that the molten metal adhering to the cast surface may cause the above-mentioned right-angled crack.

To further explain such a phenomenon based on the findings of the present inventors, the cast surface at the solidification start point of the molten metal, its action depending on the composition of the molten metal, the material of the cast surface member, the surface state of the cast surface, etc. Although the magnitude of the force is different, the action force that the molten metal tries to adhere to the cast surface works.

However, since the cooling rate at the solidification start point of the molten metal that is in contact with the cast surface of the core that is forcibly cooled is high,
Since a strong solidified layer larger than the above-mentioned acting force is immediately formed on the inner wall surface of the hollow billet, the deposit adhered to the cast surface is discharged downward together with the cast body, but is not forcedly cooled. The cooling rate at the solidification start point of the molten metal in contact with the cast surface of the non-forced cooling type core is slow, and the strength of the solidification part at the early stage of solidification is small. It is easier to win, and the amount of molten metal that adheres to the cast surface tends to increase. When the amount of such adhesion exceeds a certain limit amount, the strength of the solidified portion in the early stage of solidification cannot fully oppose the shearing force generated between the cast body and the cast body which is guided downward.
It is considered that, because it adheres to the casting surface, it separates from the cast body that is led out downward, and cracks that are perpendicular to the casting direction occur.

In particular, such a phenomenon remarkably occurs in aluminum, magnesium or alloys thereof.

As a result of various studies by the present inventors to prevent the above-mentioned right-angled cracks generated on the inner wall surface of the hollow part of the hollow billet, the inventors have found that at the solidification start point during casting with respect to the acting force of the molten metal on the cast surface. It has been found that the atmosphere in which the gas flows is greatly affected, and by making this atmosphere an inert gas or enriched with an inert gas, the above-mentioned action force can be made extremely small, and The present invention has been completed by finding that the amount of kimono generated can be made as small as possible, and as a result, the above-described right-angle cracks can be prevented from occurring on the inner wall surface of the hollow portion of the hollow billet.

Therefore, an object of the present invention is to provide a novel casting method in which not only cracks parallel to the casting direction do not occur even if the inner wall surface of the hollow part of the hollow billet is smooth, and cracks perpendicular to the casting direction do not easily occur. Is to provide.

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention provides a core including a cast surface member made of graphite or a carbonaceous material inside a hollow portion of a mold having upper and lower ends opened and in a non-forced cooling state. In the method for casting a hollow billet, wherein the solidification start point of the molten metal is cast and led out while maintaining the solidification start point of the molten metal on the casting surface of the casting surface member substantially constant, It is characterized in that an inert gas is supplied to the portion to form an inert gas or an atmosphere enriched with the inert gas, and casting is performed.

Here, in order to supply the inert gas to the hollow part of the hollow billet, not only the inert gas is supplied, but the gas body such as air is enriched with the inert gas, and this gas is used. It is also possible to supply an inert gas.

In the present invention, it is advantageous that the inert gas enrichment ratio of the inert gas enriched atmosphere in the hollow portion of the hollow billet is 80% by volume or more with respect to 20% by volume of air.

Further, in the present invention, the supply of the inert gas introduced into the hollow portion of the hollow billet, the lower end of the hollow billet reaches the water surface in the pit, the hollow billet, the core and the water surface in the pit. After the space bounded by is closed, it can be stopped before the difference between the closed space and the external pressure exceeds the hydrostatic pressure of the molten metal.

Furthermore, in the present invention, the core is provided with an exhaust hole for discharging the atmosphere in the hollow part of the hollow billet, and a support pipe for the inert gas is provided in a support of the core or the hollow billet, It is also possible to continuously supply the inert gas into the hollow portion at a flow rate such that the pressure difference between the hollow portion of the billet and the outside air does not exceed the hydrostatic pressure of the molten metal.

As described above, in the present invention, the starting point of molten metal solidification on the cast surface of the cast surface member made of graphite or carbonaceous material (which becomes a linear shape surrounding the cast surface member) which is not subjected to forced cooling is set to an inert gas. Alternatively, by forming an atmosphere enriched with an inert gas, a long hollow billet with a smooth inner wall surface of the hollow billet and a casting length of 2 to 3 m or more is formed on the inner wall surface of the hollow portion in the casting direction. It is possible to cast a hollow billet in a state where it is difficult to generate a right-angled crack.

By the way, the above-mentioned cracks perpendicular to the casting direction are aluminum, magnesium, when a non-forced cooling type core is used,
Or, it occurs remarkably in those alloys, and for casting using such a molten metal, if the amount of inert gas enrichment is increased even if it is small, the effect of preventing right-angle cracking is not Although it is recognized, the enriched amount is
By making the amount 80% by volume or more with respect to 20% by volume, the above-mentioned effect of preventing the right-angled crack becomes remarkable.

Also, in addition to electrolytic metal, as a result of various molten metal treatments for the purpose of refining the solidification structure of the molten metal, or descaling, degassing, and preventing the oxidation of magnesium, Na and Be may be contained, but when such a Na or Be is contained, it promotes the action force of the molten metal to adhere to the cast surface of the cast surface member, so Na,
For a molten metal containing a metal such as Be that is more easily oxidized than aluminum or magnesium, it is desirable to use a gas in which the above-mentioned amount of enriched inert gas is more than 80% by volume.

The above-mentioned inert gas is aluminum or magnesium,
Any gas that is inert to metals such as sodium and beryllium may be used, and for example, argon gas, nitrogen gas, carbon dioxide gas, etc. can be used.

Hereinafter, the method of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view of a mold device used for casting a hollow billet, and reference numeral 1 is a cylindrical water-cooled mold with open upper and lower ends,
20 is placed in the hollow part of the water-cooled mold 1,
The core device 2 supported by the support rod 15 attached to the core is a core water-cooled mold having a circular cross-section in the direction perpendicular to the casting direction, and the heat insulating material 3 surrounds the upper outer peripheral surface thereof. Reference numeral 4 is a cast surface member made of graphite or a carbonaceous material arranged so as to surround the outer peripheral surface of the lower portion of the heat insulating material 3, and is configured so as not to be forcibly cooled by the core water-cooled mold 2.
It is arranged at a position where the solidification start point of the molten metal (indicated by reference numeral 28 in FIG. 2) comes in the steady state. The solidification starting point 28 is the casting surface of the casting surface member 4 (reference numeral 25 in FIG. 2).
In order to position it above, the casting conditions are set in advance by preliminary experiments, or the depth of the solidification starting point 28 from the molten metal surface 6 after casting is measured by the usual method, and this depth is the casting value. If it is off the surface, it can be easily positioned on the casting surface by adjusting the casting conditions such as the amount of cooling water and the casting speed.

Reference numeral 32 is a pedestal for the molten metal, which is located at a position where the lower end of an annular casting path 21 bounded by the core device 20 and the water cooling mold 1 is closed at the beginning of casting, and the molten metal is injected into the casting path 21 to After being cooled by the cooling unit 5 exposed to the outside of the lower end of the core water-cooled mold 2 and solidification progresses, the above-described pedestal 32 is sequentially lowered downward to continuously perform casting.
Reference numerals 7 and 7 ′ are cooling water discharged from the slits below the water-cooled mold 1 and the core water-cooled mold 2. Reference numeral 9 denotes an inert gas supply pipe, which is movable in the vertical direction together with the pedestal 32, and by this supply pipe, the hollow portion of the hollow billet (second
The gas is introduced into the inside of the hollow portion 11
The inside is filled with the inert gas or the atmosphere enriched with the inert gas. Reference numeral 23 denotes a molten metal level controller for the molten metal 27 injected into the casting passage 21, which is composed of a dip tube 22 and a float 8. The flow direction of the inert gas is indicated by reference numeral 10.

FIG. 2 shows a hollow billet using the core device 20 shown in FIG.
It is explanatory drawing which shows the steady state at the time of casting 12 and 24 shows the solidification start line of a molten metal, and the solidification start point 28 on the core side exists on the casting surface 25 of the casting surface member 4.

Reference numeral 13 denotes the water surface of the cooling water in the pit, and the hollow portion 11 of the hollow billet 12 is closed by the core device 20, the hollow billet 12, and the water surface 13 'in the hollow portion of the hollow billet 12. The inert gas is supplied into the hollow portion 11 of the hollow billet 12 through the supply pipe 9 at the start of casting, and the upper end of the pedestal 32 or the lower end of the hollow billet 12 reaches the water surface 13 in the pit and the hollow portion of the hollow billet 12 is reached. Hollow part before 11 is sealed
The air in 11 is made an inert gas or an atmosphere enriched with the inert gas. When the airtight state is reached, the gas supply is stopped and the samurai casting is continued. Since the inside of the hollow portion 11 is in a sealed state, the atmosphere of the gas supplied is maintained until the end of casting. As a result, the vicinity of the solidification start point on the cast surface is in the supplied inert gas or the atmosphere enriched with the inert gas, and the action force of the molten metal working on the cast surface 25 is reduced,
The amount of the deposits on the cast surface 25 is reduced, and the above-mentioned cracks perpendicular to the casting direction are prevented from occurring.
The supply of the gas can be continued until the water surface 13 'in the hollow portion 11 is slightly lowered and becomes slightly positive pressure. However, the difference between the pressure in the hollow portion 11 and the external pressure is the static of the molten metal. When the water pressure is exceeded, the gas in the hollow portion 11 blows upward in the casting passage 21 and hinders normal casting, so the value of the positive pressure in the hollow portion 11 must be kept below the hydrostatic pressure of the molten metal.

That is, the above-mentioned relation is expressed by an equation, ΔHρ _M > Δhρ _W, where ΔH is the depth of the molten metal shown in FIG. 2, Δh is the difference between the water surface 13 in the pit and the water surface 13 ′ in the hollow portion 11, ρ _M is the specific gravity of the molten metal, and ρ _W is the specific gravity of the cooling water in the pit.

FIG. 3 shows another core device 26 which does not use a core water-cooled mold. Reference numeral 3 ′ is made of a heat insulating material, and a support rod 15 attached to the water-cooled mold 1 serves to fix the hollow part of the water-cooled mold 1. The core is supported inside, and the molten metal receiving tank is on the top of this core 3 '.
29 is formed, and the melt level controller 23 can be arranged in the melt receiving tank 29. Reference numeral 16 denotes an atmosphere discharge hole in the hollow portion 11 of the hollow billet 12, which discharges the above-mentioned inert gas introduced into the hollow portion 11. By providing such a discharge hole 16, the gas introduced from the supply pipe 9 fills the hollow portion 11 and is then discharged to the outside from the discharge hole 16, so that the gas is continuously supplied until the end of casting. You can do it. Of course, even when such a device is used, it is necessary to maintain the pressure in the hollow portion 11 in the above-mentioned relationship.
There is an advantage that the control range of the supply gas amount can be expanded as compared with the case of using the device shown in the figure.

FIG. 4 shows another core device including a core mold 3 ″ provided with a discharge hole 16 for the atmosphere in the hollow portion 11 and a gas supply pipe 9 ′ in the core device.
Shows 30. By thus providing the core tube 30 with the supply pipe 9 ', the effect of simplifying the structure of the entire apparatus can be obtained.

FIG. 5 shows another embodiment of the core device including the core mold 3 made of graphite or carbonaceous material without heat insulating material. The core device 3 includes a gas supply pipe 9'and a discharge hole 16. In order to use the non-forced cooling type, the thickness of the peripheral wall of the core 3 is a hollow member. Since it does not require a complicated combination structure with a heat insulating material like the core device shown in FIGS. 2, 3, and 4, it has an advantage that the device can be easily manufactured.

The apparatus described above is an apparatus disclosed for explaining the method of the present invention, and is not intended to limit the present invention, and can be applied to a hollow billet having an irregular cross section such as an ellipse or a square.
In short, it is understood from the above description that the cast surface member of the core is constituted by a non-forced cooling type, and further, it may be provided with an inert gas supply means or such a supply means and a gas discharge means. This is where you can do it. However, the devices disclosed above each have advantageous features, and it is desirable to use these disclosed devices in performing the method of the present invention.

The above-mentioned graphite or carbonaceous material forming the cast face body is artificial graphite or natural graphite, or amorphous carbon molded and cured with a binder, and the cast face body molded with such a material is SiC, Si ₃ When ceramics such as N ₄ is used as the cast surface member, it has better thermal shock resistance than these ceramic members and can smooth the casting surface, which is desirable in operation.

Further, in the present invention, the surface of the cast surface member formed of graphite or a carbonaceous material is polished and then coated with powder of boron nitride powder, carbon powder, carbon black, molybdenum disulfide, etc., or wax. It is also possible to apply it by mixing it with the like, and by doing so, the effect of improving the lubricity and making the casting surface of the casting more beautiful can be obtained.

As the heat insulating material, Recepal (trade name) manufactured by Asahi Asbestos Co., Lumiboard (trade name) manufactured by Nichias, Mass Rock manufactured by Toshiba Monoflux Co., Ltd., or comparison. Flux paper (trade name) having a thin thickness can be used, but the invention is not limited to these. However, these are desirable because they have excellent heat insulating properties.

Examples of the Invention Example 1 Using the mold apparatus shown in FIG. 3, 12 pieces of this apparatus were placed in a water cooling jacket (not shown) through which cooling water passed, and casting was performed. The mold equipment had the dimensions shown below.

Inner diameter of water-cooled mold 1 270 mm φ Depth of water-cooled mold 1 80 mm Material of cast surface body 4 Graphite (buffed surface) Height of cast surface body 4 40 mm Thickness of casting path in cast surface body 4 30 mm Cast surface portion The height of the molten metal receiving part above the body 4 is 60mm. The heat insulating material that constitutes the core. RECEPAR (Asahi Asbestos Co., Ltd.) The inner diameter of the gas discharge hole 16 provided in the core is 10mmφ. The graphite core that constitutes the cast surface body. Was buffed and heated to about 200 ° C., and an aqua duck (with a product name interval) was sprayed on this as a release agent, dried, and then cast.

A5454 alloy (composition: Mg2.8%, M
n 0.5%, Cr 0.15%, the balance of Al) with or without Na or Be cast.

Simultaneously with the start of casting, argon gas was continuously supplied from the supply pipe 9 at a rate of 7 / min per one casting mold device, and the casting for the metal was completed.

The casting conditions are shown below.

Casting temperature 680-700 ° C Casting speed 150 mm / min Cooling water amount 100 / min / Mold Casting length 6 m The hollow inner wall surface of the hollow billet cast under these conditions was visually observed. The results are shown in Table 1. The hollow billet does not cause cracks parallel to the casting direction as in the past,
Moreover, the inner wall surface of the hollow part of the hollow billet was smooth.

Example 2 Using the casting mold device shown in FIG. 1, four casting devices were placed in a water cooling jacket (not shown) through which cooling water was passed. The mold equipment had the dimensions shown below.

Inner diameter of water-cooled mold 1 489mm φ Depth of water-cooled mold 1 80mm Material of cast face body 4 Graphite (buffed surface) Height of cast face body 4 40mm Thickness of casting path in cast face body 4 86mm Cast face portion Insulation material above the body 4 height 80mm Insulation material that constitutes the core Recepal (Asahi Asbestos Co., Ltd.) No discharge holes in the core The graphite core that composes such cast surface body is buffed to approx. It was heated to 200 ° C, sprayed with Aquadac (trade name) as a release agent, dried, and then manufactured. The alloy used was A60611 alloy (composition: Mg1.0%, Si0.67%, Fe0.18
%, Cu 0.35%, Cr 0.12%, Al balance), argon gas is supplied to the casting channel at the same time as hot water is supplied at a rate of 15 / min per casting mold device, and the lower end of the ingot reaches the water surface in the pit. At that time, the one in which the supply of the argon gas was stopped and the one in which the argon gas was not supplied during the casting were cast and compared.

The casting conditions are shown below.

Casting temperature 680-700 ° C Casting speed 70 mm / min Cooling water amount 100 / min / Mold Casting length 4.7 m The inner wall surface of the hollow part of the hollow billet cast under these conditions was visually observed. As a result, the inner surface of the hollow billet supplied with argon gas did not cause any cracking defects at right angles to the casting direction, whereas those not supplied with argon gas caused the defects of right angle cracking to four billets. occured. As in the conventional case, the hollow billet did not cause cracks parallel to the casting direction, and the inner wall surface of the hollow part of the hollow billet was smooth.

From the above results, when the method of the present invention is used, not only cracks parallel to the casting direction do not occur as in the conventional case, but also the hollow inner wall surface of the hollow part of the billet is smooth, and it is perpendicular to the casting direction. It can be seen that no cracks occurred.

EFFECTS OF THE INVENTION As described above, according to the method of the present invention, not only does the conventional cracks parallel to the casting direction do not occur on the inner wall surface of the hollow billet, but the hollow billet has a smooth inner wall surface. It can be seen that an excellent effect is obtained in which cracks in the direction perpendicular to the surface are not generated.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a desirable apparatus for carrying out the method of the present invention at the beginning of casting. FIG. 2 is a sectional view showing a steady state of the apparatus of FIG. 1 after the start of casting. FIG. 3 is a sectional view showing a modified embodiment of the apparatus shown in FIG. 1 which does not use a core water-cooled mold. FIG. 4 is a cross-sectional view showing still another modified embodiment of the apparatus shown in FIG. FIG. 5 is a sectional view showing another embodiment of the apparatus of FIG. 1 which does not use a heat insulating material. 1 ... Water-cooled mold with open upper and lower ends 2 ... Core water-cooled mold 3, 3 "... Heat insulating material 3 '... Core made of heat insulating material 3 ... Core of graphite or carbonaceous material 4 ... Cast surface body 6 …… Molten surface 7,7 ′ …… Cooling water 8 …… Float 9,9 ′ …… Inert gas supply pipe 10 …… Inert gas flow direction 11 …… Hollow part of hollow billet 12… … Hollow billet 13 …… Water surface in pit 13 ′ …… Water surface in hollow part 15 …… Support rod 16 …… Discharge hole 20 …… Core device 21 …… Casting path 22 …… Dip tube 23 …… Molten surface Controller 25 …… Cast surface 26 …… Core device 27 …… Molten metal 28 …… Solidification starting point 29 …… Molten metal receiving tank 32 …… Cage stand

Claims (4)

[Claims] 1. A core containing a cast face body made of graphite or a carbonaceous material and in a non-forced cooling state is disposed inside the hollow part of the mold with the upper and lower ends opened, and the solidification starting point of the molten metal is In a method for casting a hollow billet, in which a hollow billet is cast and led out while being kept substantially constant on the cast surface of the cast surface member, an inert gas is supplied to the hollow portion of the hollow billet to make it inert. A semi-continuous casting method for hollow billets, which comprises casting in an atmosphere enriched with an active gas or an inert gas. 2. The inert gas-enriched atmosphere in the hollow part of the hollow billet is characterized in that the enrichment ratio of the inert gas is 80% by volume or more with respect to 20% by volume of air. The method for casting a hollow billet according to item 1. 3. The supply of the inert gas introduced into the hollow part of the hollow billet is such that the lower end of the hollow billet reaches the water surface in the pit and is bounded by the hollow billet, the core and the water surface in the pit. After the space to be sealed is in a sealed state, it is stopped before the difference (Δh · ρ _W ) between the sealed space and the external pressure exceeds the hydrostatic pressure (ΔH · ρ _M ) of the molten metal. The method for casting a hollow billet according to any one of the first and second aspects. 4. Inside the hollow part of the hollow billet, the core is provided with an exhaust hole for discharging the atmosphere in the hollow part of the hollow billet, and the pedestal of the core or the hollow billet provided with the inert gas supply pipe. 3. The inert gas is continuously supplied into the hollow portion at a flow rate such that the pressure difference between the molten metal and the outside air does not exceed the hydrostatic pressure of the molten metal, according to claim 1 or 2. The method for casting a hollow billet according to any one of claims 1.