The present invention relates to a pulling-up-type continuous casting method.
Patent Literature 1 proposed a free casting method as a revolutionary pulling-up-type continuous casting method that does not requires any mold. As shown in Patent Literature 1, after a starter is submerged into the surface of a melted metal (molten metal) (i.e., molten-metal surface), the starter is pulled up, so that some of the molten metal follows the starter and is drawn by the starter by the surface film of the molten metal and/or the surface tension. Note that it is possible to continuously cast a cast-metal article having a desired cross-sectional shape by drawing the molten metal and cooling the drawn molten metal through a shape defining member disposed in the vicinity of the molten-metal surface.
In the ordinary continuous casting method, the shape in the longitudinal direction as well as the shape in cross section is defined by the mold. In the continuous casting method, in particular, since the solidified metal (i.e., cast-metal article) needs to pass through inside the mold, the cast-metal article has a shape extending on a straight-line in the longitudinal direction.
In contrast to this, the shape defining member used in the free casting method defines only the cross-sectional shape of the cast-metal article, while it does not define the shape in the longitudinal direction. Further, since the shape defining member can be moved in the direction parallel to the molten-metal surface (i.e., in the horizontal direction), cast-metal articles having various shapes in the longitudinal direction can be produced. For example, Patent Literature 1 discloses a hollow cast-metal article (i.e., a pipe) having a zigzag shape or a helical shape in the longitudinal direction rather than the straight-line shape.
Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2012-61518
The present inventors have found the following problem.
In the free casting method disclosed in Patent Literature 1, a cooling gas is blown on cast metal following the starter immediately after the cast metal is solidified and the molten metal is thereby indirectly cooled. It should be noted that the casting process needs to be advanced in a state where the speed at which the solidification advances from the top toward the bottom of the cast metal (hereinafter called a “solidifying speed”) is substantially equal to the pulling-up speed. For example, if only the pulling-up speed is increased while maintaining the cooling power for the pulled-up molten metal unchanged (i.e., while maintaining the solidifying speed unchanged), the solidification interface rises and hence the pulled-up molten metal is torn apart. That is, if the cooling power is determined, an appropriate pulling-up speed corresponding to that cooling power is determined. Note that to increase the pulling-up speed and thereby improve productivity, the above-described cooling power needs to be increased.
At the start of casting, the starter is accelerated from a standstill state to a desired pulling-up speed (i.e., the above-described appropriate pulling-up speed corresponding to the cooling power). However, there has been a problem that if the acceleration for the pulling-up operation is too high, the molten metal pulled-up by the starter is torn apart before the pulling-up speed of the starter reaches the desired pulling-up speed, thus making the casting itself impossible. Further, there is another problem that if the acceleration for the pulling-up operation is lowered in order to prevent the molten metal from being torn apart due to the acceleration, it takes time before the pulling-up speed of the starter reaches the desired pulling-up speed, thus deteriorating productivity.
The present invention has been made in view of the above-described problems, and an object thereof is to provide a pulling-up-type continuous casting method that has excellent productivity while preventing the pulled-up molten metal from being torn apart during the acceleration.
A pulling-up-type continuous casting method according to an aspect of the present invention is
a pulling-up-type continuous casing method for pulling up molten metal held in a holding furnace by using a starter, in which
when the starter is accelerated to a predetermined pulling-up speed at a start of casting, the pulling-up-type continuous casting method includes:
a first acceleration section in which the starter is accelerated from a standstill state to a first speed at a first acceleration;
a second acceleration section in which the starter is accelerated from the first speed to a second speed at a second acceleration; and
a constant speed section in which the starter is pulled up at the first speed, the constant speed section being positioned between the first and second acceleration sections.
This configuration can provide a pulling-up-type continuous casting method that has excellent productivity while preventing the pulled-up molten metal from being torn apart during the acceleration.
The first acceleration is preferably an acceleration that will cause a tearing in the molten metal pulled-up by the starter before the pulling-up speed of the starter reaches the predetermined pulling-up speed if the starter is continuously accelerated from the standstill state at that acceleration, and the second acceleration is preferably an acceleration that will cause a tearing in the molten metal pulled-up by the starter before the pulling-up speed of the starter reaches the predetermined pulling-up speed if the starter is continuously accelerated from the standstill state at that acceleration. It is possible to improve productivity even further.
Further, the first and second accelerations are preferably equal to each other. In this case, each of the first and second accelerations is particularly preferably a maximum acceleration that a pulling-up machine that pulls up the starter can deliver.
Further, the pulling-up-type continuous casting method may further include a third acceleration section in which the starter is accelerated from the second speed to a third speed at a third acceleration, and a constant speed section in which the starter is pulled up at the second speed, the constant speed section being positioned between the second and third acceleration sections.
Alternatively, the second acceleration may be higher than the first acceleration. In this case, the second acceleration is preferably a maximum acceleration that a pulling-up machine that pulls up the starter can deliver.
According to the present invention, it is possible to provide a pulling-up-type continuous casting method that has excellent productivity while preventing the pulled-up molten metal from being torn apart during the acceleration.
Specific exemplary embodiments to which the present invention is applied are explained hereinafter in detail with reference to the drawings. However, the present invention is not limited to exemplary embodiments shown below. Further, the following descriptions and the drawings are simplified as appropriate for clarifying the explanation.
Firstly, a free casting apparatus (pulling-up-type continuous casting apparatus) according to a first exemplary embodiment is explained with reference to
The molten-metal holding furnace 101 contains molten metal M1 such as aluminum or its alloy, and maintains the molten metal M1 at a predetermined temperature at which the molten metal M1 has fluidity. In the example shown in
The shape defining member 102 is made of ceramic or stainless steel, for example, and disposed near the molten-metal surface. In the example shown in
Note that the xyz-coordinate system shown in
As shown in
The support rod 104 supports the shape defining member 102.
The support rod 104 is connected to the actuator 105. By the actuator 105, the shape defining member 102 can be moved in the up/down direction (vertical direction) and in the horizontal direction through the support rod 104. With this configuration, it is possible to move the shape defining member 102 downward as the molten-metal surface is lowered due to the advance of the casting process. Further, since the shape defining member 102 can be moved in the horizontal direction, the shape in the longitudinal direction of the cast metal M3 can be changed.
The cooling gas nozzle (cooling unit) 106 is cooling means for blowing a cooling gas (such as air, nitrogen, and argon) supplied from a cooling gas supply unit (not shown) on the cast metal M3 and thereby cooling the cast metal M3. The position of the solidification interface SIF can be lowered by increasing the flow rate of the cooling gas and can be raised by reducing the flow rate of the cooling gas. Note that although it is not shown in the figure, the cooling gas nozzle (cooling unit) 106 can also be moved in the horizontal direction and in the vertical direction in accordance with the movement of the shape defining member 102.
By cooling the cast metal M3 by the cooling gas while pulling up the cast metal M3 by using the pulling-up machine 108 connected to the starter ST, the held molten metal M2 located in the vicinity of the solidification interface SIF is successively solidified, and the cast metal M3 is thereby formed. The position of the solidification interface SIF can be raised by increasing the pulling-up speed of the pulling-up machine 108 and can be lowered by reducing the pulling-up speed.
Next, a free casting method according to a first exemplary embodiment is explained with reference to
Firstly, the starter ST is lowered and made to pass through the molten-metal passage section 103 of the shape defining member 102, and the tip of the starter ST is submerged into the molten metal M1.
Next, the starter ST starts to be pulled up at a predetermined speed. Note that even when the starter ST is pulled away from the molten-metal surface, the molten metal M1 follows the starter ST and is pulled up from the molten-metal surface by the surface film, the surface tension, and the like, thus forming the held molten metal M2. As shown in
Next, since the starter ST is cooled by the cooling gas blown from the cooling gas nozzle 106, the held molten metal M2 successively solidifies from its upper side toward its lower side. As a result, the cast metal M3 grows.
It should be noted that at the start of the casting, the pulling-up speed is accelerated (i.e., increased) from a standstill state to a desired pulling-up speed (i.e., an appropriate pulling-up speed corresponding to cooling power by the cooling gas nozzle 106). One of the features of the free casting method according to the first exemplary embodiment lies in the pulling-up speed acceleration method at the start of the casting. The pulling-up speed acceleration method at the start of the casting is explained hereinafter with reference to
Further, in
Therefore, in the free casting method according to the first exemplary embodiment, a constant-speed operation section is provided between acceleration operation sections in order to improve productivity while preventing the held molten metal M2 from being torn apart. Specifically, in
After the pulling-up speed is kept at the speed V11 for a predetermined period, the pulling-up operation is switched from the constant-speed operation to the acceleration operation in which the starter is accelerated at the acceleration a1 again. By providing the constant-speed operation section and thereby lowering the position of the solidification interface SIF, the tearing of the held molten metal M2, which would otherwise occur at the speed V1, can be prevented after the acceleration operation in which the starter is accelerated at the acceleration a1 is resumed. The acceleration in this acceleration operation section does not necessarily have to be equal to the acceleration in the previous acceleration operation section. However, the accelerations in both of the acceleration operation sections are preferably higher than the acceleration a2 in view of the resulting improvement in productivity. In other words, in view of the resulting improvement in the productivity, the acceleration in the acceleration operation section is preferably an acceleration that will cause a tearing in the held molten metal M2 before the pulling-up speed reaches the maximum pulling-up speed Vmax if the starter is continuously accelerated from the standstill state at that acceleration.
Further, in the example shown in
Further, productivity can be improved by reducing the length of each constant-speed operation section. On the other hand, if the constant-speed operation section is too short, the position of the solidification interface SW is not sufficiently lowered in the constant-speed operation section. As a result, a tearing is likely to occur in the held molten metal M2 when the pulling-up operation is switched to the acceleration operation.
Further, in the free casting method according to the first exemplary embodiment, the starter is accelerated at an acceleration that is higher than the acceleration a2 at which no tearing occurs in the held molten metal M2 even when the starter is continuously accelerated at that acceleration. Therefore, as shown in
Next, a free casting method according to a modified example 1 of the first exemplary embodiment is explained with reference to
Therefore, in the free casting method according to the modified example 1 of the first exemplary embodiment, the pulling-up operation is switched to the constant-speed operation at the point when the pulling-up speed reaches a speed V21 that is higher than the speed V1 and lower than the speed V2. That is, in the example shown in
Next, a free casting method according to a modified example 2 of the first exemplary embodiment is explained with reference to
As has been explained above, in the free casting method according to the first exemplary embodiment, a constant-speed operation section(s) is provided between acceleration operations at the start of the casting. This can prevent the held molten metal M2 from being torn apart even when the starter is accelerated at an acceleration that will cause a tearing in the held molten metal M2 if the starter is continuously accelerated at that acceleration. Further, the pulling-up speed can be increased to the maximum pulling-up speed Vmax in a shorter time period than the time period that is required in the related art. Therefore, productivity is excellent.
Next, a free casting apparatus according to a second exemplary embodiment is explained with reference to
The shape defining member 102 according to the first exemplary embodiment shown in
As shown in
Further, as shown in
The shape defining plates 102a and 102b are disposed in such a manner that they are in contact with the top sides of the shape defining plates 102c and 102d.
Next, a driving mechanism for the shape defining plate 102a is explained with reference to
As shown in
Further, as shown in
As has been explained above, in the free casting apparatus according to the second exemplary embodiment, the shape of the molten-metal passage section 103 can be changed. Therefore, the cross-sectional shape of the cast metal M3 can be changed during the casting process.
Further, control may be performed so that the shape of the molten-metal passage section 103 is reduced in size in the acceleration operation section at the start of the casting. The tearing in the held molten metal M2 can be prevented or reduced even further by reducing the mass of the held molten metal M2.
Note that the present invention is not limited to the above-described exemplary embodiments, and various modifications can be made without departing the spirit and scope of the present invention.
For example, the present invention can be applied to a pulling-up-type continuous casting method in which the shape defining member 102 is not used, provided that the molten metal is pulled up by using a starter ST in the pulling-up-type continuous casting method.
This application is based upon and claims the benefit of priority from Japanese patent application No. 2013-158202, filed on Jul. 30, 2013, the disclosure of which is incorporated herein in its entirety by reference.
Number | Date | Country | Kind |
---|---|---|---|
2013-158202 | Jul 2013 | JP | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/JP2014/003010 | 6/5/2014 | WO | 00 |