US20040226681A1

US20040226681A1 - Apparatus for manufacturing magnesium-alloy plate by wheel-band continuous casting, and manufacturing method thereof

Info

Publication number: US20040226681A1
Application number: US10/655,058
Authority: US
Inventors: Bong-Sun You; Ha-Sik Kim; Byung-Gi Moon; Won-Wook Park
Original assignee: Korea Institute of Machinery and Materials KIMM
Current assignee: Korea Institute of Machinery and Materials KIMM
Priority date: 2003-05-13
Filing date: 2003-09-04
Publication date: 2004-11-18
Also published as: KR20040097705A; KR100537429B1

Abstract

A magnesium-alloy plate manufactured by completely melting a magnesium-alloy material received in a hermetic type melting furnace; transferring the molten magnesium-alloy into a hermetic type heat insulation furnace through a hermetic type transfer runner; discharging the molten magnesium-alloy received in the heat insulation furnace into a recessed portion of a casting wheel through a casting runner, to which a mixed gas containing SF₆is injected by ignition-suppression gas injection tubes; and continuously casting the molten magnesium-alloy entered into the recessed portion of the casting wheel into a magnesium-alloy plate using a casting band circulating around the casting wheel while coming into contact with an upper portion of the recessed portion.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method for manufacturing a magnesium-alloy plate by wheel-band continuous casting, and more particularly to a plate manufacturing apparatus and method using wheel-band continuous casting, which can safely manufacture a magnesium-alloy plate directly from highly ignitable molten magnesium-alloy.

2. Description of the Related Art

As well known to those skilled in the art, a magnesium-alloy plate is generally manufactured to have a thin strip shape using hot and warm rolling processes. The manufactured magnesium-alloy plate is used for fabrication of a cellular phone case or notebook computer case with desired shape.

The conventional magnesium-alloy plate of such a thin strip shape is manufactured by casting molten magnesium-alloy into a large size of a billet by vertical or horizontal continuous casting and then extruding and rolling the large billet. In this case, however, since the used magnesium-alloy is highly ignitable upon exposure to the atmosphere in its molten state, the large billet has to be manufactured within a hermetic type apparatus configured to prevent contact between the molten magnesium alloy and the atmosphere and then processed to have a desired plate shape.

Such a conventional method for manufacturing the magnesium-alloy plate, therefore, has many technical restrictions because it requires a large scale casting apparatus, and the casting apparatus is also configured to completely prevent contact between the atmosphere and the molten magnesium-alloy. Further, the conventional method has a weak point that its casting velocity is too slow.

Furthermore, in order to process the manufactured large billet to a desired shape of plate, an additional post-treatment of the billet is required. This additional post-treatment results in several problems including increase in manufacturing cost and deterioration in productivity.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an apparatus and method for manufacturing a magnesium-alloy plate by wheel-band continuous casting, which continuously cast a magnesium-alloy plate directly from molten magnesium-alloy using a casting wheel, which is processed at the surface thereof to conform to a sectional shape of the plate to be manufactured, and a casting band circulating in contact with the casting wheel, thereby considerably eliminating inter-stage shaping processes and consequently maximizing productivity.

In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of an apparatus for manufacturing a magnesium-alloy plate by wheel-band continuous casting comprising: a hermetic type melting furnace for heating and melting magnesium-alloy received therein; a hermetic type heat insulation furnace; a hermetic type transfer runner extending from a lower portion of the melting furnace to an upper portion of the heat insulation furnace; a casting runner installed at a lower portion of the heat insulation furnace so as to discharge molten magnesium-alloy; ignition-suppression gas injection tubes installed above the casting runner; a casting wheel formed at its surface with a recessed portion to continuously cast the molten magnesium-alloy supplied from the casting runner; a casting band circulating around the casting wheel while coming into contact with an upper portion of the recessed portion formed at the casting wheel; a lower guide roll installed just below the casting wheel to come into contact with the casting wheel while interposing the casting band therebetween; a band tension roll for adjusting a tension of the casting band while guiding the casting band; and a band press roll installed just above the casting wheel so as to adjust a press force of the casting band.

Preferably, according to the present invention, the casting wheel may comprise a cooling jacket of a water-cooled type, which is installed inside the casting wheel for enabling self-cooling of the casting wheel.

Preferably, according to the present invention, the casting band may be cooled by a plurality of gas injectors installed to cool a portion thereof coming into contact with the casting wheel.

In accordance with another aspect of the present invention, the above and other objects can be accomplished by the provision of a method for manufacturing a magnesium-alloy plate by wheel-band continuous casting comprising the steps of: a) completely melting a magnesium-alloy material received in a hermetic type melting furnace; b) transferring the molten magnesium-alloy into a hermetic type heat insulation furnace through a hermetic type transfer runner; c) discharging the molten magnesium-alloy received in the heat insulation furnace into a recessed portion of a casting wheel through a casting runner, to which a mixed gas containing SF ₆is injected by ignition-suppression gas injection tubes; d) continuously casting the molten magnesium-alloy entered into the recessed portion of the casting wheel into a magnesium-alloy plate using a casting band circulating around the casting wheel while coming into contact with an upper portion of the recessed portion; and e) discharging the continuously cast magnesium-alloy plate from a lower side of the casting wheel coming into contact with a lower guide roll installed just therebelow while interposing the casting band therebetween.

Preferably, according to the present invention, the mixed gas containing SF ₆, injected through the ignition-suppression gas injection tubes, consists of CO₂, air and maximally 1 percent of SF₆.

Preferably, according to the present invention, the step d) is carried out at a casting velocity from 2 m/min to 25 m/min.

Preferably, according to the present invention, wherein the step d) further includes the step d-1) of cooling the casting band using inert gas injected from a plurality of gas injectors installed above the casting wheel.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: [0016]
FIG. 1 is a perspective view illustrating the whole construction of an apparatus for manufacturing a magnesium-alloy plate and shapes by wheel-band continuous casting in accordance with the present invention; [0017]
FIG. 2 is a schematic view illustrating the whole construction of the apparatus for manufacturing a magnesium-alloy plate and shapes by wheel-band continuous casting in accordance with the present invention; [0018]
FIGS. 3A and 3B are a perspective view and a partial sectional view, respectively, illustrating a casting wheel as one component of the apparatus for manufacturing a magnesium-alloy plate and shapes by wheel-band continuous casting in accordance with the present invention; [0019]
FIG. 4 is an enlarged view illustrating ignition-suppression gas injection tubes as one component of the apparatus for manufacturing a magnesium-alloy plate and shapes by wheel-band continuous casting in accordance with the present invention; and [0020]
FIGS. 5A and 5B are pictures illustrating a magnesium-alloy plate obtained by the apparatus and method for manufacturing a magnesium-alloy plate and shapes by wheel-band continuous casting in accordance with the present invention.[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective view illustrating the whole construction of an apparatus for manufacturing a magnesium-alloy plate and shapes by wheel-band continuous casting in accordance with the present invention. FIG. 2 is a schematic view illustrating the whole construction of the apparatus for manufacturing a magnesium-alloy plate and shapes by wheel-band continuous casting in accordance with the present invention. [0022]
As shown in FIGS. 1 and 2, an apparatus of the present invention is provided at an entrance thereto with a [0023] melting furnace 1 for heating and melting magnesium-alloy received therein.
The [0024] melting furnace 1 may be constructed as an electric furnace using heating elements or high frequency induction furnace. The melting furnace 1 is a hermetic type furnace configured in such a fashion that a steel crucible is located inside thereof, so as to prevent contact between the atmosphere and molten metal therein.
The hermetic [0025] type melting furnace 1 is installed with a transfer runner 2 adjacent to the bottom thereof. The transfer runner 2 extends outward from the interior of the melting furnace 1 to provide a transfer passage of the molten magnesium-alloy from the melting furnace 1. The transfer runner 2 is also manufactured as a hermetic type runner capable of preventing contact between the atmosphere and molten magnesium-alloy passing therethrough.
The hermetic [0026] type transfer runner 2 is preferably formed with a middle valve 2 a, so as to selectively intercept the feeding of the molten magnesium-alloy if any emergency situation, such as ignition of the molten magnesium-alloy, occurs.
The hermetic [0027] type transfer runner 2 constructed as mentioned above is connected to a heat insulation furnace 3 located therebelow. The heat insulation furnace 3 is also formed as a hermetic type furnace capable of preventing contact between the atmosphere and the molten magnesium-alloy received therein.
The molten magnesium-alloy is transferred into the hermetic type [0028] heat insulation furnace 3, and again discharged along a casting runner 4, which extends outward at its one end from the interior of the heat insulation furnace 3 adjacent to the bottom thereof.
The [0029] casting runner 4 is coupled at the other end thereof to a casting wheel 6 so that the end is positioned just at or near the top portion of the casting wheel 6. At the upper side of a certain region of the casting wheel 6, into which the molten magnesium-alloy discharged from the casting runner 4 is entered, a group of ignition-suppression gas injection tubes 5 is arranged in multiple rows. These ignition-suppression gas injection tubes 5 blow a mixed gas of SF₆and CO₂, designated as reference numeral 5 a (shown in FIG. 4) and capable of restricting the ignition of the molten magnesium-alloy, thereby preventing contact between the atmosphere and the molten magnesium-alloy discharged from the casting runner 4.
After being transferred along the [0030] casting runner 4 constructed as mentioned above, the molten magnesium-alloy is entered into a recessed portion 6 a of the casting wheel 6. The entered molten magnesium-alloy is continuously cast by the casting wheel 6 and a casting band 7 surrounding the outer circumference of the casting wheel 6 until it is discharged from the lower side of the casting wheel 6. The casting wheel 6 is driven by directly receiving a driving force transmitted through a timing belt connected to an electric motor (not shown).
FIGS. 3A and 3B are a perspective view and a partial sectional view, respectively, illustrating the [0031] casting wheel 6 as one component of the apparatus for manufacturing a magnesium-alloy plate and shapes by wheel-band continuous casting in accordance with the present invention.
The [0032] casting wheel 6, as shown in FIGS. 3A and 3B, has to be cooled to solidify the molten magnesium-alloy. Conventionally, the casting wheel takes a cooling method of a generic spray manner. That is, the conventional casting wheel is configured in such a fashion that the inner surface thereof is exposed to enable molten alloy to be directly cooled by cooling water. This cooling method of the casting wheel, however, carries a hazard of an explosion due to hydrogen gas generated while the molten magnesium-alloy is in contact with the cooling water. Therefore, in accordance with the present invention, the casting wheel 6 comprises a perfectly hermetic type cooling jacket 6 b inside thereof, thereby allowing the molten magnesium-alloy entering into the casting wheel 6 to be cooled by the cooling water circulating through the cooling jacket 6 b. For the supply and drainage of the cooling water into and from the cooling jacket 6 b, pipes 6 c are installed to a wheel shaft so that they do not interfere with the rotation of the casting wheel 6.
As mentioned above, the cooling of the molten magnesium-alloy, received in the [0033] recessed portion 6 a of the casting wheel 6, is achieved by the cooling water circulating through the cooling jacket 6 b provided inside the casting wheel 6. In addition, by the casting band 7 circulating along the outer circumference of the casting wheel 6 while being in contact with the casting wheel 6, the upside of the molten magnesium-alloy is additionally cooled. The casting band 7 also serves to control the shape of a plate to be formed from the molten magnesium-alloy.
Considering the circulation of the [0034] casting band 7, it circulates at the same linear velocity as the casting wheel 6 while coming into contact with the upper surface of the recessed portion 6 a formed at the casting wheel 6. In order to prevent the casting band 7 from separating from the casting wheel 6 during the circulation thereof, a lower guide roll 8, a band tension roll 9 and an upper guide roll 11 are provided. These rolls 8, 9 and 11 are formed at their surfaces with grooves, respectively, in order to guide the casting band 7 more stably.
Referring to the [0035] lower guide roll 8 and band tension roll 9 in detail, first the lower guide roll 8 is located just below the casting wheel 6 to come into contact with the casting wheel 6 while interposing the casting band 7 therebetween.
The [0036] band tension roll 9 functions to adjust a tensile force applied to the casting band 7 while guiding the casting band 7. That is, such a tensile force applied to the casting band 7 is adjusted by a tension adjustment cylinder 9 a of the band tension roll 9, which is axially coupled to a bracket 9 b for fixing a rotating shaft of the band tension roll 9.
The apparatus of the present invention is further provided with a [0037] band press roll 10. The band press roll 10 is installed just above the casing wheel 6 to apply a press force to the casting band 7 for allowing the casting band 7 circulating around the casting wheel 6 to come into close contact with the casting wheel 6. The press force of the band press roll 10 is adjusted by a press force adjustment cylinder 10 a thereof, which is axially coupled to a bracket 10 b fixed at a rotating shaft of the band press roll 10.
According to the present invention, for the cooling of the molten magnesium-alloy being continuously cast by the [0038] casting band 7 inside the casting wheel 6, the casting wheel 6 is provided above the rear side thereof with a plurality of gas injectors 12 arranged at regular distances, in addition to the cooling jacket 6 b contained inside the casting wheel 6 in a hermetic manner as stated above.
That is, whereas the existing facility provided for cooling the [0039] casting band 7 takes a cooling water spray manner, since the present invention must completely prevent any contact between the molten magnesium-alloy and cooling water, such a plurality of the gas injectors 12 are installed above the rear side of the casting wheel 6 so as to inject inert gas and compressed gas.
Especially, in the case of an existing continuous casting apparatus adopting a Properzi method, a casting band thereof horizontally extends as a guide roll is disposed in parallel to an advancing direction of a casting material. On the other hand, in accordance with the present invention, the [0040] upper guide roll 11 and band tension roll 9 are installed above both sides of the casting wheel 6, and the lower guide roll 8 is installed below the casting wheel 6. This arrangement of the guide rolls 8 and 11 and band tension roll 9 prevents the casting band 7 from interfering with the advancement of the solidified magnesium-alloy plate, thereby minimizing the generation of any defects due to the deformation of the casting material.
FIG. 4 is an enlarged view illustrating ignition-suppression gas injection tubes as one component of the apparatus for manufacturing a magnesium-alloy plate and shapes using wheel-band continuous casting in accordance with the present invention. FIG. 4 shows a state wherein the molten magnesium-alloy, designated as [0041] reference numeral 14, is guided into the recessed portion 6 a of the casting wheel 6 through the casting runner 4 and a molten magnesium-alloy injection plate 4 b, thereby being continuously cast while receiving the mixed gas from the ignition-suppression gas injection tubes 5 at the upper side thereof. The mixed gas consists of CO₂and maximally 1 percent of SF₆.
The molten magnesium-[0042] alloy 14 guided into the casting wheel 6 is cooled and solidified by virtue of the cooling capability of the casting wheel 6 and the gas injectors 12 installed at the rear side of the casting band 7 for blowing cooling gas, thereby being continuously cast into a plate.
Now, the operation of the present invention is explained through a preferred example. [0043]

EXAMPLE

AZ31(Mg—Al—Zn) material as a kind of processing magnesium-alloy was cut and inserted into the [0044] melting furnace 1, thereby being converted to a molten state therein. The obtained molten magnesium-alloy was maintained at a temperature of 730 degrees for about 20 minutes for the stabilization thereof. After that, by opening the middle valve 2 a provided at the transfer runner 2 extending outward from the melting furnace 1, the molten magnesium-alloy was transferred along the transfer runner 2 to be received in the heat insulation furnace 3.
The molten magnesium-alloy received in the [0045] heat insulation furnace 3 was again transferred along the casting runner 4 by opening the middle valve 4 a provided at the casting runner 4 extending outwardly from the heat insulation furnace 3 adjacent thereto, thereby being guided into the casting wheel 6 through the molten magnesium-alloy injection plate 4 b.
The guided molten magnesium-alloy was entered into a space defined by the [0046] casting band 7 coming into close contact with the recessed portion 6 a formed at the casting wheel 6. In this state, in order to prevent contact between the atmosphere and the molten magnesium-alloy entering into the recessed portion 6 a of the casting wheel 6, the ignition-suppression gas injection tubes 5 installed just above the molten magnesium-alloy injection plate 4 b blew the mixed gas 5 a, consisting of CO₂, air and about 1 percent of SF₆, toward the casting wheel 6 from the upper side of the molten magnesium-alloy injection plate 4 b.
Such a supply of the [0047] mixed gas 5 a containing SF₆serves to prevent contact between the atmosphere and molten magnesium-alloy, and to allow the molten magnesium-alloy to be more smoothly supplied from the molten magnesium-alloy injection plate 4 b to the recessed portion 6 a of the casting wheel 6.
This is possible because SF[0048] ₆gas is about five times heavier than the atmosphere. By virtue of such a property of SF₆gas, the mixed gas containing SF₆can effectively prevent contact between the atmosphere and the molten magnesium-alloy entering into the recessed portion 6 a of the casting wheel 6. However, the content of SF₆gas is preferably not more than 1 percent in the mixed gas because it is very expensive and toxic.
In the above example of the present invention, the recessed [0049] portion 6 a of the casting wheel 6 was formed to have a width of 50 mm and a depth of 5 mm, a certain high temperature lubricating agent was applied to the casting wheel 6 and casting band 7 to allow the casting band 7 to smoothly circulate while coming into contact with the casting wheel 6 and other rolls 8, 9, 10 and 11.
The molten magnesium-alloy supplied into the [0050] casting wheel 6 was primarily cooled by the cooling water circulating through the cooling jacket 6 b contained in a hermetic manner within the casting wheel 6, and then secondarily cooled by inert and compressed gas blown from the plural gas injectors 12 installed above the rear side of the casting wheel 6, namely, at a portion where the casting wheel 6 and casting band 7 come into close contact with each other.
A magnesium-alloy plate obtained by the continuous casting as stated above, designated as [0051] reference numeral 13, was stably discharged from the lower side of the casting wheel 6.
According to the apparatus of the present invention, even if the [0052] casting band 7 thereof is loosened fter the apparatus is repeatedly used for the manufacture of magnesium-alloy plates, the tensile force of the casting band 7 can be adjusted by manipulating the tension adjustment cylinder 9 a fixed at the bracket 9 b provided at the rotating shaft of the band tension roll 9.
In addition, even if the press force of the [0053] casting band 7 coming into contact with the recessed portion 6 a of the casting wheel 6 is increased or reduced, thereby causing deterioration of casting ability, the apparatus of the present invention is designed to maximize the casting ability thereof by adjusting the press force adjustment cylinder 10 a fixed at the bracket 10 b provided at the rotating shaft of the band press roll 10 located just above the casting wheel 6.
FIGS. 5A and 5B are pictures illustrating the magnesium-alloy plate manufactured using the apparatus and method for manufacturing a magnesium-alloy plate and shapes by wheel-band continuous casting in accordance with the present invention. [0054]
As shown in FIGS. 5A and 5B, in accordance with the example of the present invention, the [0055] casting wheel 6, which was manufactured to have the recessed portion 6 a in 5-100 mm deep and 20-500 mm wide, was used to continuously cast a magnesium-alloy plate. As a result of several continuous cast experiments performed by mounting the casting wheel 6 constructed as stated above in the apparatus of the present invention, it was noted that an optimal casting ability is achieved if a continuous casting velocity is not more than 25 m/min.
That is, if the continuous casting velocity exceeds 25 m/min, a large amount of casting defects, such as air gaps or cracks, are generated at the manufactured magnesium-alloy plate. These defective magnesium-alloy plates cannot be used in after-treatment processes. [0056]
As apparent from the above description, the present invention provides a continuous casting apparatus of a wheel-band type, which is configured to continuously cast a magnesium-alloy plate directly from molten magnesium-alloy, being highly ignitable and explosive on exposure to the atmosphere. According to the present invention, a casting velocity thereof can be considerably improved, in comparison with a conventional method for manufacturing a plate by processing a large billet. Further, according to the present invention, since the plate is directly manufactured from the molten magnesium-alloy without a separate processing step, it is possible to reduce a manufacturing cost as well as increase a productivity thereof. [0057]
Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. [0058]

Claims

1. An apparatus for manufacturing a magnesium-alloy plate by wheel-band continuous casting comprising:

a hermetic type melting furnace for heating and melting magnesium-alloy received therein;

a hermetic type heat insulation furnace;

a hermetic type transfer runner extending from a lower portion of the melting furnace to an upper portion of the heat insulation furnace;

a casting runner installed at a lower portion of the heat insulation furnace so as to discharge molten magnesium-alloy;

ignition-suppression gas injection tubes installed above the casting runner;

a casting wheel formed at its surface with a recessed portion to continuously cast the molten magnesium-alloy supplied from the casting runner;

a casting band circulating around the casting wheel while coming into contact with an upper portion of the recessed portion formed at the casting wheel;

a lower guide roll installed just below the casting wheel to come into contact with the casting wheel while interposing the casting band therebetween;

a band tension roll for adjusting a tension of the casting band while guiding the casting band; and

a band press roll installed just above the casting wheel so as to adjust a press force of the casting band.

2. The apparatus as set forth in claim 1, wherein the casting wheel comprises a cooling jacket of a water-cooled type, which is installed inside the casting wheel for enabling self-cooling of the casting wheel.

3. The apparatus as set forth in claim 1, wherein the casting band is cooled by a plurality of gas injectors installed to cool a portion thereof coming into contact with the casting wheel.

4. A method for manufacturing a magnesium-alloy plate by wheel-band continuous casting comprising the steps of:

a) completely melting a magnesium-alloy material received in a hermetic type melting furnace;

b) transferring the molten magnesium-alloy into a hermetic type heat insulation furnace through a hermetic type transfer runner;

c) discharging the molten magnesium-alloy received in the heat insulation furnace into a recessed portion of a casting wheel through a casting runner, to which a mixed gas containing SF₆is injected by ignition-suppression gas injection tubes;

d) continuously casting the molten magnesium-alloy entered into the recessed portion of the casting wheel into a magnesium-alloy plate using a casting band circulating around the casting wheel while coming into contact with an upper portion of the recessed portion; and

e) discharging the continuously cast magnesium-alloy plate from a lower side of the casting wheel coming into contact with a lower guide roll installed just therebelow while interposing the casting band therebetween.

5. The method as set forth in claim 4, wherein the mixed gas containing SF₆, injected through the ignition-suppression gas injection tubes, consists of CO₂, air and maximally 1 percent of SF₆.

6. The method as set forth in claim 4, wherein the step d) is carried out at a casting velocity from 2 m/min to 25 m/min.

7. The method as set forth in claim 4, wherein the step d) further includes the step d-1) of cooling the casting band using inert gas injected from a plurality of gas injectors installed above the casting wheel.