JP2009090322A - Continuous casting machine and continuous casting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous casting machine which can attain both reduction of inclusions in a continuous casting product and flow control of a spout by a stopper. <P>SOLUTION: A cover jig 11 of a proper size is arranged at a proper position where a Karman's vortex is generated at a downstream side of the stopper 2 in a trough 6, by which even if the Karman's vortex is generated, it does not result in the harmful Karman's vortex which includes an oxide film of a molten metal surface, and various kinds of non-metallic inclusions floating in molten metal. As a result, it is prevented that the molten metal oxide film and the inclusions existing on the molten metal surface of the trough 6 are drawn into the spout 10, and that the inclusions are mixed in a final product by a negative pressure effect produced by inflow of the high-speed molten metal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a continuous casting apparatus and a continuous casting method for controlling a molten metal surface in continuous casting of a non-ferrous metal, particularly aluminum, particularly a stopper / float control when pouring from a trough to a mold.

  As a casting method for aluminum plates or aluminum alloy plates used in automobiles and household appliances, continuous casting is performed by continuously pulling the molten metal injected into the ladle or melting furnace or holding furnace to the lower part by a dummy bar through a trough. Continuous casting using an apparatus is performed.

   In this continuous casting, as a method of controlling the flow rate when the molten metal is introduced from the trough into the mold as the ingot descends, as shown in FIG. 17, the control method (FIG. 17 (a)) using the spout 100 / float 101, There is a control method using the stopper 102 and the float 103 (FIG. 17B) (Light Metal Basic Technology Course Fifth Edition (Japan Society of Light Metals: August 2006, continuous casting of aluminum, FIG. 12)).

  The control method using the stopper 102 and the float 103 has a quality problem that the molten metal poured into the float part is likely to entrain oxide when it gets into the float part. It was necessary to make it smaller. For this reason, when manufacturing a large slab, the control method by the stopper 102 and the float 103 is mainly used.

In the control method using the stopper 102 and the float 103, the molten metal amount is controlled by adjusting the opening degree by the stopper 102 processed into a columnar shape in a state where the molten metal having a predetermined depth is accumulated in the trough 104.
However, the molten metal in the trough 104 flows even when the molten metal of a predetermined depth is accumulated, and therefore, the molten liquid downstream of the stopper 102 has a flow when the flowing liquid is blocked by a cylindrical object. In addition, Karman vortices generated on the downstream side are generated, and the Karman vortices sometimes involve oxides on the surface of the melt. The oxides involved were scattered inside the ingot and became inclusions in the final product, causing deterioration of product characteristics.

  This Karman vortex is normally generated on the downstream side in the flow direction when the molten metal surface depth is small, and when the Karman vortex reaches the spout, an oxide film on the surface of the molten metal is engulfed as an inclusion. Therefore, as a countermeasure, it is necessary to prevent the generation of Karman vortex and the entrainment of the oxide film due to this by maintaining a predetermined amount of the molten metal surface depth.

  However, even if it is easy to maintain a predetermined amount of the molten metal surface depth in the steady state, it is possible for the operator to maintain the molten metal surface depth in the unsteady state (at the start or at the end) at the predetermined depth. It was necessary to be ready to operate with constant monitoring, and the load on the workers was heavy.

  In Patent Document 1, a stopper body that opens and closes a molten metal outlet formed on the bottom surface of the trough by a vertical movement is rotatably supported, and a stirring blade is attached to the downstream portion, and the molten metal follows the stopper body by the rotation of the stopper body. There has been disclosed a long stopper for continuous casting that can generate an upward flow and prevent inclusions on the surface of the Dandy surface due to the upward flow around the long stopper even when the height of the surface of the tundish decreases.

JP 2002-11565 A

However, the measure of Patent Document 1 is to stir the molten metal, and the continuous casting apparatus for that purpose is intricately complicated and increased in cost, and adverse effects due to adding dynamic energy by stirring to the molten metal are expected. .
Therefore, a means for preventing Karman vortices generated on the downstream side when the stopper is blocked by a cylindrical object by making it an integral streamline is also conceivable. However, it is expensive to process the stopper shape into a streamline shape, and there are drawbacks such as easy breakage in handling.

  The present invention has been made in view of the above-described problems in the prior art, and an object of the present invention is to provide a continuous casting apparatus and a continuous casting method capable of achieving both reduction of inclusions in a continuously cast product and control of a stopper / spout flow rate.

  The inventors of the present invention examine in detail the Karman vortex generation location and entrainment situation that occurs on the downstream side of the molten metal flow direction in the trough of the cylindrical stopper, and by providing a cover jig that covers the molten metal surface, It has been clarified that the generation of Karman vortex can be suppressed and the entrainment of oxide film on the surface of the melt and various non-metallic inclusions floating in the melt can be suppressed.

That is, the continuous casting apparatus of the present invention includes a trough to which molten metal from a ladle, a melting furnace or a holding furnace is supplied, a spout having a molten metal injection hole disposed between the trough and the mold, and a molten metal injection hole. It has a stopper that attaches and detaches to the opening and closes and opens to control the amount of molten metal passing through the spout, and a cover jig that covers at least the molten metal surface on the downstream side of the stopper is arranged along the molten metal flow direction in the trough. Features.

Further, the continuous casting method of the present invention supplies molten metal from a ladle, a melting furnace or a holding furnace to a trough, and attaches / detaches a stopper to a molten metal injection hole of a spout disposed between the trough and the mold, thereby passing the spout through molten metal. The amount is controlled, and at least the downstream molten metal surface of the stopper is covered with a cover jig along the molten metal flow direction in the trough.

The cover jig is preferably arranged so as to cover a region defined by the following formulas (i) and (ii).
(I) Distance L in the melt flow direction from the center of the stopper having a diameter of 2r
r <L ≦ 2r
(Ii) Distance w from the center of the stopper having a diameter of 2r in the direction perpendicular to the molten metal flow direction
-0.5r≤w≤0.5r (provided that the center of the stopper is 0, one direction is positive, and the opposite direction is negative)

  The cover jig is preferably made of a material that does not react with molten metal.

  The molten metal may be aluminum or an aluminum alloy.

[Action]
According to the continuous casting apparatus and continuous casting method of the present invention, inclusion of inclusions can be achieved by setting the depth of the molten metal surface to a predetermined depth or more by disposing a cover jig that covers at least the downstream molten metal surface of the stopper. Not only in a steady state to be suppressed, but also in an unsteady state such as at the start and end of casting when the molten metal surface depth is less than 150 mm where the Karman vortex is noticeably generated downstream in the flow direction when the molten metal surface depth is small In addition, the generation of Karman vortices reaching the spout inlet from the hot water surface on the trough can be suppressed, and the Kalman vortices can reach the spout and prevent the oxide film on the surface of the molten metal from being involved as inclusions.

  According to the continuous casting apparatus and the continuous casting method of the present invention, the entrainment of the oxide film can be suppressed, so that the ingot quality is improved and the product quality after processing is also improved.

Hereinafter, the best mode for carrying out the continuous casting apparatus of the present invention will be described in detail.
As shown in FIG. 1, in the continuous casting apparatus 5 of the present invention, the molten metal is first supplied to the trough 6 from a ladle (not shown), a melting furnace or a holding furnace.

Next, the molten metal that has contacted the water-cooled mold 7 immediately below the trough 6 at the exit of the trough 6 is rapidly solidified, and the tip of the solidified slab 8 is pulled out by a dummy bar (not shown), and the slab 8 is pulled out by a dummy bar. Is continuously drawn through the mold 7 while solidifying. A spout 10 having an injection hole 9 is disposed between the trough 6 and the mold 7, and the amount of molten metal passing through the spout 10 is controlled by the stopper 2.
In the continuous casting apparatus 5 of this embodiment, the stopper 2 has a circular cross section, and the cover jig 11 is disposed so as to cover the molten metal surface on the downstream side of the stopper 2 along the molten metal flow direction in the trough 6. .

  As shown in FIG. 2, coupled with the negative pressure effect due to the high-speed molten metal flowing into the spout 10 triggered by the generation of Karman vortex 3 behind the cylindrical stopper 2 in the direction perpendicular to the fluid flow in the fluid flow 1. Karman vortex 4 is generated, and the molten oxide film and inclusions present on the trough surface 1a are drawn into the spout 10 and inclusions are mixed into the final product.

  The location where the Karman vortex 3 is generated depends on the molten metal flow velocity, the molten metal surface height, and the diameter of the cylindrical stopper. As a result of the examination by the inventors, the occurrence location of harmful Karman vortex 3 that entraps various nonmetallic inclusions floating in the oxide film on the molten metal surface or the molten metal is proportional to the diameter of the stopper 2. By covering the surface of the molten metal in a specific region corresponding to the diameter with the cover jig 11, it is possible to prevent the oxide film and the non-metallic inclusions from being involved.

This harmful area is most prominent in the area α shown in FIG. 3. This area α is an area defined by the following equations (i) and (ii) on the downstream side of the stopper 2 when the stopper diameter is 2r. there were.
(I) Distance L from the center of the stopper 2 in the molten metal flow direction
r <L ≦ 2r
(Ii) The distance w from the center of the stopper 2 in the direction perpendicular to the molten metal flow direction
−0.5r ≦ w ≦ 0.5r

In addition, an oxide film is rarely involved by Karman vortices generated in the region β shown in FIG. This region β is a region defined by the following equations (iii) and (iv) on the downstream side of the stopper 2 when the stopper diameter is 2r.
(Iii) Distance L from the center of the stopper 2 in the molten metal flow direction
r <L <3r
(Iv) The distance w from the center of the stopper 2 in the direction perpendicular to the molten metal flow direction
-R ≦ w ≦ r

From the above examination, the stopper 2 used in the continuous casting apparatus and continuous casting method of the present invention has a circular cross section, and covers at least the downstream molten metal surface of the stopper 2 having a diameter of 2r along the molten metal flow direction in the trough 6. Similarly, the cover jig 11 is arranged. The cover jig 11 is disposed so as to cover the region α.

About the fixing method of the cover jig 11, the aspect shown, for example in FIG. 4 is employable. In the embodiment shown in FIG. 4, a long iron plate 13 having a triangular or U-shaped locking recess 12 is provided downstream of the trough 6 on the stopper 2 so that the locking recess 12 opens toward the upstream side. To place. On the other hand, a round bar 14 is attached to the cover jig 11 in an upright central portion so that the round bar 14 of the cover jig 11 is inserted into the locking recess 12 from the upstream side of the opening of the locking recess 12 of the long iron plate 13. The cover jig 11 is arranged so that is inserted.
In addition to this, a dustproof trough cover (not shown) having a triangular or U-shaped locking recess 12 is arranged on the trough 6, and a round bar 14 attached to the center of the cover jig is connected to the triangular or U-shaped trough cover. It can also arrange | position so that the latching recessed part 12 may be entered.

The shape of the cover jig 11 is most preferably a streamlined shape that flows in the molten metal flow direction. However, in consideration of ease of processing and handling, it may be a pseudo-streamline shape, a circular shape, or a quadrangular shape. Alternatively, the cover jig 11 may have a shape that covers the periphery of the stopper 2 by penetrating a circular hole into which the stopper 2 can be inserted in advance and fitting the stopper 2.

The material of the cover jig 11 is preferably lighter than the molten metal density so long as it does not react with the molten metal or change in temperature at the molten metal and can float on the molten metal surface. For example, a commercially available refractory that does not react with molten metal. Can be used.
Moreover, the refractory material which is the boat-shaped shape which made the center part the concave shape, and is heavier than a molten metal density can also be used.
Specifically, the cover jig 11 is made of calcium silicate refractories, SiC refractories, silicon nitride refractories, alumina refractories, SiO2 refractories, graphite, etc. for molten aluminum. In addition, an appropriate material can be selected and used properly according to the type of molten metal.

  The molten metal to be cast can be aluminum or an aluminum alloy.

  As described above, the cover jig 11 having an appropriate size is disposed at an appropriate position at a position where the Karman vortex is generated on the downstream side of the stopper 2 in the trough 6, so that the surface of the molten metal is oxidized even if Karman vortex is generated. It does not lead to harmful Karman vortices that involve various non-metallic inclusions floating in the film or molten metal.

As a result, the molten oxide film and inclusions present on the surface of the trough 6 are drawn into the spout 10 due to the negative pressure effect caused by the high speed molten metal flowing in, and inclusions are prevented from being mixed into the final product.

FIG. 5 schematically shows an installation mode of the cover jig 11 in the continuous casting apparatus according to the embodiment of the present invention.
In this embodiment, the cover jig 11 has a circular shape as viewed from above, and the arrangement position with respect to the stopper 2 is the downstream side of the molten metal flow of the stopper 2. In addition, the area of the molten metal surface coating region on the downstream side of the stopper 2 is about 1.7, where the region α is 1.

FIG. 6 shows how the cover jig 11 is installed in a continuous casting apparatus according to another embodiment of the present invention.
In this embodiment, the cover jig 11 has a quadrangular shape as viewed from the upper surface, and the arrangement position with respect to the stopper 2 is the downstream side of the molten metal flow of the stopper 2. Further, the area of the molten metal surface coating region on the downstream side of the stopper 2 is about 1.2, where the region α is 1.

FIG. 7 shows how the cover jig 11 is installed in a continuous casting apparatus according to still another embodiment of the present invention.
In this embodiment, the shape of the cover jig 11 viewed from the upper surface is pseudo-streamline, and the arrangement position with respect to the stopper 2 is the downstream side of the molten metal flow of the stopper 2. In addition, the area of the molten metal surface coating region downstream of the stopper 2 is about 2.5, where the region α is 1.

FIG. 8 shows an aspect of installation of the cover jig 11 in the continuous casting apparatus according to another embodiment of the present invention.
In this embodiment, the cover jig 11 has a circular shape viewed from the upper surface, and the arrangement position based on the stopper 2 is the periphery of the stopper 2. In addition, the area of the molten metal surface coating region on the downstream side of the stopper 2 exceeds 5 with the region α being 1.

FIG. 9 shows how the cover jig 11 is installed in a continuous casting apparatus according to still another embodiment of the present invention.
In this embodiment, the shape of the cover jig 11 viewed from the upper surface is an ellipse, and the arrangement position based on the stopper 2 is the periphery of the stopper 2. In addition, the area of the molten metal surface coating region on the downstream side of the stopper 2 exceeds 5 with the region α being 1.

FIG. 10 shows how the cover jig 11 is installed in a continuous casting apparatus according to still another embodiment of the present invention.
In this embodiment, the cover jig 11 has a rhombus shape as viewed from above, and the arrangement position with respect to the stopper 2 is the periphery of the stopper 2. In addition, the area of the molten metal surface coating region on the downstream side of the stopper 2 exceeds 5 with the region α being 1.

FIG. 11 shows a continuous casting apparatus according to still another embodiment of the present invention.
In each of the above-described embodiments, the flow control is performed at the inlet of the spout 10, whereas in this embodiment, the cover jig 11 is installed downstream of the stopper 2 in the flow control at the outlet of the spout 10. An aspect is shown.
In this embodiment, similarly to each of the above-described embodiments, the cover jig 11 having an appropriate size is disposed at an appropriate position at a position where the Karman vortex is generated on the downstream side of the stopper 2 in the trough 6. 2, the generation of Karman vortex flow (Kalman flow) is suppressed, and the molten oxide film and inclusions existing on the molten metal surface of the trough 6 are prevented from being drawn into the spout 10 and an appropriate stopper / spout flow rate. Control is performed.

Example Using the continuous casting apparatus according to the embodiment of the present invention shown in FIGS. 3 to 10, as an example of the continuous casting method of the present invention, an ingot (400 mm thickness × 1600 mm width) of 5182 alloy was used with a continuous casting machine. Casted. At this time, the hot water surface depth in the trough 6 was 130 mm. A U-shaped groove was formed in the trough dustproof cover arranged on the downstream side of the stopper (diameter 50 mmφ), and the molten metal surface cover jig 11 was inserted into the U-shaped groove to fix the position.
After casting, the bottom 300 mm and the head 200 mm are cut, then the long side surface is shaved 10 mm on one side, and after soaking, cold rolling is performed after hot rolling to obtain a 1.6 mm thick plate. . A 30 cm × 30 cm sample was cut from the coil plate, and heated at 450 ° C. × 1 H in a steam atmosphere to investigate the number of blister defects.
In addition, the other conditions were the same as in the example, and the continuous casting method of each comparative example shown below was performed, and the number of defects was investigated in the same manner as in the example. Table 1 shows the results of the above examples and comparative examples.

FIG. 12 shows Comparative Example 1 and was cast without using the cover jig 11.
FIG. 13 shows Comparative Example 2 in which a circular cover jig 11 was placed on the downstream side of the stopper 2 at a position outside the region α, and casting was performed.
FIG. 14 shows Comparative Example 3 in which a circular cover jig 11 was cast on the downstream side of the stopper 2 assuming that the area of the molten metal surface coating area was about 0.2 with the area α being 1.
FIG. 15 shows Comparative Example 4 in which a triangular cover jig 11 was cast on the downstream side of the stopper 2 with the area of the molten metal surface coating area being about 0.35, where the area α was 1.
FIG. 16 shows Comparative Example 5 in which a circular cover jig 11 was cast around the stopper 2 assuming that the area of the molten metal surface coating area was about 0.2 with the area α being 1 as described above.

As shown in Table 1, in each example, the number of inclusions (the number of blister defects / 900 cm ² ) is 0, whereas in each comparative example, the number of inclusions (the number of blister defects / 900 cm ² ) is around 20. In addition, according to the continuous casting method of the present invention, it is recognized that the oxide film can be prevented from being involved, and the ingot quality is remarkably improved.

It is a schematic diagram of the continuous casting apparatus concerning embodiment of this invention. (A) Explanatory drawing which shows the Kalman flow around the stopper observed in the water model experiment. (B) It is explanatory drawing which shows the Karman vortex grown from the Karman flow. It is a partial expansion schematic diagram of the continuous casting apparatus concerning embodiment of this invention. It is the other partial expansion schematic diagram of the continuous casting apparatus concerning embodiment of this invention. It is a partial expansion schematic diagram of the continuous casting apparatus concerning other embodiment of this invention. It is the elements on larger scale of the continuous casting apparatus concerning other embodiment of this invention. It is the elements on larger scale of the continuous casting apparatus concerning other embodiment of this invention. It is the elements on larger scale of the continuous casting apparatus concerning other embodiment of this invention. It is the elements on larger scale of the continuous casting apparatus concerning other embodiment of this invention. It is the elements on larger scale of the continuous casting apparatus concerning other embodiment of this invention. It is the elements on larger scale of the continuous casting apparatus concerning other embodiment of this invention. It is the partial expansion schematic diagram of the continuous casting apparatus used for the continuous casting performed as the comparative example of this invention. It is the elements on larger scale of the continuous casting apparatus used for the continuous casting performed as another comparative example of this invention. It is the elements on larger scale of the continuous casting apparatus used for the continuous casting performed as another comparative example of this invention. It is the elements on larger scale of the continuous casting apparatus used for the continuous casting performed as another comparative example of this invention. It is the elements on larger scale of the continuous casting apparatus used for the continuous casting performed as another comparative example of this invention. With respect to the molten metal flow rate control method in continuous casting using a continuous casting apparatus, (a) shows a control method using a spout / float, and (b) shows a control method using a stopper / float.

Explanation of symbols

2 ... stopper, 6 ... trough, 10 ... spout, 9 ... injection hole, 11 ... cover jig.

Claims (8)

The trough to which the molten metal from the ladle, the melting furnace or the holding furnace is supplied, the spout having the molten metal injection hole disposed between the trough and the mold, and the opening and closing of the molten metal injection hole is attached and closed. And a stopper for controlling the amount of molten metal passing through the spout in the process, and a cover jig for covering at least the molten metal surface on the downstream side of the stopper is arranged along the molten metal flow direction in the trough. . The continuous casting apparatus according to claim 1, wherein the cover jig is disposed so as to cover a region defined by the following formulas (i) and (ii).
(I) Distance L in the melt flow direction from the center of the stopper having a diameter of 2r
r <L ≦ 2r
(Ii) Distance w from the center of the stopper having a diameter of 2r in the direction perpendicular to the molten metal flow direction
-0.5r≤w≤0.5r (provided that the center of the stopper is 0, one direction is positive, and the opposite direction is negative) The continuous casting apparatus according to claim 1, wherein the cover jig is manufactured using a material that does not react with molten metal. The continuous casting apparatus according to any one of claims 1 to 3, wherein the molten metal is aluminum or an aluminum alloy. In the process of supplying molten metal from a ladle, melting furnace or holding furnace to the trough, and closing / opening the opening by attaching a stopper to the opening of the molten metal injection hole of the spout arranged between the trough and the mold. A continuous casting method characterized by controlling the amount of molten metal passing and covering at least the downstream molten metal surface of the stopper with a cover jig along the direction of molten metal flow in the trough. The continuous casting method according to claim 5, wherein the cover jig is disposed so as to cover a region defined by the following formulas (i) and (ii).
(I) Distance L in the melt flow direction from the center of the stopper having a diameter of 2r
r <L ≦ 2r
(Ii) Distance w from the center of the stopper having a diameter of 2r in the direction perpendicular to the molten metal flow direction
-0.5r≤w≤0.5r (provided that the center of the stopper is 0, one direction is positive, and the opposite direction is negative) The continuous casting method according to claim 5 or 6, wherein the cover jig is manufactured using a material that does not react with molten metal. The continuous casting method according to any one of claims 5 to 7, wherein the molten metal is aluminum or an aluminum alloy.

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