JPH0461734B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is an aluminum alloy casting method in which a pair of rolls are arranged at an appropriate length interval, and molten aluminum alloy is supplied between the rolls to cast an aluminum alloy plate. The present invention relates to a twin roll casting method, and in particular to a twin roll casting method for aluminum alloys suitable for casting plates made of aluminum alloys having a wide solidification range, such as Al-Mg alloys containing 3% by weight or more of Mg.

[Conventional technology]

Twin-roll casting machines are used to obtain wide sheet aluminum or aluminum alloy plates. This casting machine consists of a melting furnace for melting raw materials, a gutter for transferring molten metal, a casting nozzle, and a pair of rotating rolls (twin rolls) arranged vertically at an appropriate distance. ing.

In this twin roll type casting machine, first,
Aluminum or aluminum alloy raw material is melted in a melting furnace. Next, this molten metal is supplied to a casting nozzle via a refractory gutter. The casting nozzle has its tip disposed near the gap between the twin rolls, and discharges the molten metal between the twin rolls. The twin rolls are cooled by cooling water flowing inside them, and the molten metal is supplied between the twin rolls, cooled by the twin rolls, and solidified into a flat plate shape. In this way, aluminum or aluminum alloy cast plates are continuously cast. The obtained cast plate is rolled to a predetermined thickness and used for various purposes.

Conventionally, in the twin roll casting method, the ratio between the width and thickness of the aluminum or aluminum alloy plate to be cast is extremely large, resulting in various non-uniformities in the width direction of the resulting aluminum or aluminum alloy plate. This causes defects in the cast plate (H. Westengen and K. Nes “Twin
roll casting of aluminum”Light Metals
1984 pp.1111-1127 A Publication of The
Metallurgical Society of AIME).

Various improvement measures have been proposed to suppress these defects. For example, in order to prevent defects caused by gas generated in the molten metal, the twin rolls are arranged so that their opposing directions are inclined from the vertical direction, so that the aluminum or aluminum alloy plate after casting is tilted from the horizontal direction. A casting machine configured so that the casting is carried out upwards was proposed (Special Public Interest Publication in 1973-
No. 15968), which ensures that there are no defects.
It has been reported that 1100, 2014, 5005, 5052 and 3003 aluminum alloy plates can be cast. Also,
We also proposed a technology that uses a casting nozzle that equalizes the flow velocity of the melt over the entire width of the twin rolls, thereby preventing the occurrence of defects (Japanese Patent Application Laid-Open No. 1456/1983).
has been done.

[Problem to be solved by the invention]

However, as mentioned above, various proposals have been made to eliminate defects in aluminum or aluminum alloy cast sheets cast by twin rolls, but it is impossible to completely eliminate streak defects extending in the casting direction of the cast sheet. Have difficulty. This streak defect occurs frequently in the twin-roll casting method, especially in Al
-Since this occurs with remarkable frequency in Mg-based alloys, improvement is desired.

The present invention has been made in view of such problems, and an object of the present invention is to provide a twin-roll casting method for aluminum alloys that can avoid defects such as streak defects that occur during casting.

[Means to solve the problem]

In the twin-roll casting method for aluminum alloy according to the present invention, molten aluminum alloy is discharged from the tip of a casting nozzle between a pair of rotating rolls, and the molten metal is solidified between the rolls to continuously form an aluminum alloy plate. When the discharge port at the tip of the casting nozzle is divided into 10 equal parts in the width direction, the average flow velocity of the molten metal in the two blocks in the center is the molten metal in each of the two blocks at both ends in the width direction. It is characterized by being 5% or more faster than the average flow velocity.

[Effect]

Conventionally, in order to prevent the occurrence of streak defects, a method has been proposed in which gas is removed by upward casting for defects caused by gas in the molten metal, as described above, and for other defects. For example, a method has been proposed in which defects are prevented by making the flow velocity of the molten metal discharged from the nozzle tip uniform across the width of the nozzle. That is, in the past, the causes of defects were eliminated by the above-mentioned method based on the recognition that the quality of aluminum or aluminum alloy cast plates could be improved by ensuring the uniformity of the molten metal inside the casting nozzle. The focus is on that.

However, as a result of intensive experimental research by the inventors of the present application in order to improve the quality of cast sheets, it was found that due to the rolling effect of the twin rolls, the solute elements in the molten metal are locally concentrated in the center of the sheet during solidification (center line segregation). As a result of this concentration phenomenon, a concentrated area and bubbles are generated in the center of the cast plate in the thickness direction, and various defects occur in the cast plate due to this concentrated area and bubbles, and this is simply due to upward casting. It was also found that uniform flow casting could not solve the problem.

In particular, it is generally known that defects are likely to occur when a cast plate is manufactured using a twin roll casting machine from a molten metal of an alloy having a wide solidification range, such as an Al-Mg alloy. This is because the higher the Mg content in the alloy, the deeper the molten metal part (sump) between the casting nozzle tip and the solid-liquid interface becomes, resulting in a phenomenon of concentration of solute elements such as Mg. This is because the phenomenon of discharge becomes more likely to occur. Therefore, streak defects caused by the gas present in the molten metal inevitably occur as a result of this discharge phenomenon in the case of alloy systems with a wide solidification range.

In normal engineering production, the amount of gas in molten aluminum alloy is controlled to 0.20cc/100g or less. However, this value far exceeds the solid solubility limit of gas during solidification of the molten metal. Therefore, even if the amount of gas in the molten metal is regulated in this way, if continuous operation is performed for a long time (one hour or more), bubbles will be generated as the molten metal solidifies as a result of the above-mentioned concentration phenomenon. Therefore, although the above-mentioned conventional method (Japanese Patent Publication No. 15968/1983) is effective against large bubbles that suddenly occur, it has no effect on defects caused by gases generated from the molten metal itself. It's not something you have.

Defects in aluminum alloy cast plates caused by gas are formed when minute air bubbles are ejected from the molten metal due to the concentration phenomenon and are gradually incorporated into the cast plate. It is conceivable to reduce the gas content in a certain molten metal. However, this method is impossible to actually realize due to equilibrium with atmospheric pressure. For this reason, since microbubbles are always generated within the sump, a means for removing these microbubbles is essential.
To achieve this, instead of forming a uniform parallel flow at the tip of the nozzle (Japanese Unexamined Patent Publication No. 1456/1983), it is necessary to form a flow component of the molten metal from the center in the width direction of the plate toward the ends within the sump. It is necessary to push out the microbubbles to the sides in the width direction of the zamp.

In the present invention, the flow velocity of the molten metal at the center in the width direction at the tip of the casting nozzle is 5% or more faster than the flow velocity of the molten metal at the ends, so a flow component from the center to the ends occurs in the sump. do. As a result, microbubbles are pushed out to the sides of the sump, and a phenomenon in which the solute is locally unevenly distributed can be avoided.
Therefore, generation of streak defects and other defects can be avoided. In addition, in this specification, the widthwise central portion of the casting nozzle tip refers to the widthwise center portion of the nozzle tip where the molten metal discharge port is located in the width direction.
When divided into 10 equal parts, the two blocks in the center are the two blocks, and the ends are the two blocks at both ends in the width direction.

〔Example〕

Figure 1a is a plan sectional view showing a casting nozzle used in the embodiment method of the present invention, and Figure 1b is Figure 1a.
A vertical cross-sectional view taken along line A-A of Figure 1c is Figure 1a
A vertical cross-sectional view taken along line B-B of , Figure 1 d is the same as Figure 1 a
FIG.

The distribution box 1 has a flat box-like shape, and a molten metal inlet 2 is opened in the wall surface on the base end side. Further, a horizontal slit extending from one longitudinal edge to the other edge is opened in the wall surface on the tip side opposite to this wall surface. Furthermore, a rectangular buffer plate 3 is disposed within the distribution box 1 so as to be in contact with the top and side walls of the box 1.

On the wall surface of the distal end side of the distribution box 1 where the slit is provided, there is a nozzle tip 5 in the shape of a flat rectangular cylinder having a hole that aligns with the slit.
is connected. The internal space of this nozzle tip 5 has a constant thickness and a width that increases toward the tip end side. In the hole of the nozzle tip 5, a tear drop 7 for controlling the flow direction of the molten metal in the nozzle tip 5 and a spacer 8 for maintaining the shape of the hole in a predetermined shape are provided. This teardrop 7 is nozzle tip 5
The flow at the center of the nozzle tip 5 advances at an almost direct angle to the tip edge of the nozzle tip 5, and the flow at the end of the nozzle tip 5 proceeds at a large angle to the tip edge.

When the molten metal is twin-roll cast using the casting nozzle configured as described above, the molten metal flowing into the distribution box 1 through the molten metal inlet 2 flows into the buffer plate 3 as shown by the arrow.
The water passes under the nozzle tip 5 and is supplied to the nozzle tip 5.
At this time, the molten metal hits the buffer plate 3 and flows in the width direction thereof, and is also supplied to the side ends of the nozzle tip 5. After passing through the buffer plate 3, this molten metal flows linearly through the nozzle tip 5 toward its tip, and is discharged from the tip between the twin rolls.

In this case, the molten metal enters the inside of the distribution box 1 from the molten metal inlet section 2 at the center in the width direction, hits the buffer plate 3, and a part of it spreads in the width direction of the box 1, causing the buffer plate to rise. 3 and is supplied to the nozzle tip 5. Therefore, the flow rate of the molten metal supplied from the distribution box 1 to the nozzle tip 5 is faster at the center in the width direction and relatively slower at both ends in the width direction. Therefore, the flow velocity of the molten metal at the center in the width direction at the tip of the nozzle is faster than the flow velocity of the molten metal at both ends. In other words, the flow rate of the molten metal at the tip of the casting nozzle is highest at the center and decreases at both ends. Therefore, a flow component of the molten metal is formed in the sump between the tip of the casting nozzle and the solid-liquid interface from the center to the end in the width direction of the plate. Therefore, the flow of the molten metal suppresses the concentration phenomenon of solute elements, and the flow also quickly discharges air bubbles and the like to the sides in the width direction of the plate.
As a result, defects such as streak defects can be avoided in the cast plate obtained by solidification.

In order to confirm this effect, a water model experiment was conducted as follows. That is, the tip of the casting nozzle described above is divided into 10 regions in the width direction, a container is attached to each region, water is passed through at a flow rate of 29 l/min instead of molten metal, and the water is collected in the container at a predetermined time. The amount of liquid released was measured. Then, the flow velocity of the liquid in each region was calculated. FIG. 2 is a graph showing the molten metal flow velocity distribution at the nozzle tip, with the horizontal axis representing the position of the nozzle tip and the vertical axis representing the flow rate per cm. As is clear from FIG. 2, the flow velocity of the molten metal at the center in the width direction at the tip of this casting nozzle is more than 10% faster than at the ends.

This casting nozzle was actually installed in a twin roll casting machine, and an aluminum alloy plate containing 5% by weight of Mg was cast. The thickness of this cast plate is 7 mm, and the plate width is approximately 900 mm. In this case, defects caused by gas sometimes occurred in the early stage of casting, but
This defect could be removed by continuous operation for about a minute.

3a shows a casting nozzle in which the shape of the buffer plate 3a is changed so that the flow velocity of the molten metal at the center of the nozzle tip is slower than at both ends, in order to compare with the above-mentioned embodiment. 3b is a longitudinal sectional view taken along the line D--D in FIG. 3a, and FIG. 3c is a longitudinal sectional view taken along the line E--E in FIG. 3a.

This casting nozzle has approximately the same structure as the nozzle shown in FIGS.
Only the shape of a is different. That is, the buffer plate 3a has a rectangular shape, and there are 3
The through holes 4 are opened at appropriate length intervals. This buffer plate 3a is supported by the upper and lower walls of the distribution box 1.

When the molten metal is twin-roll cast using this casting nozzle, the molten metal that has flowed into the box 1 through the molten metal inlet 2 is transferred to the sides of both ends of the buffer plate 3a and through the flow holes as shown by the arrows. 4 and is supplied to the nozzle tip 5.

FIG. 4a is a schematic plan view showing the flow of molten metal inside the nozzle tip 5, and FIG. 4b is a schematic side view showing the buffer plate 3a. In this casting nozzle, 20l/
When the same amount of water is supplied, the molten metal forms a flow as shown by the arrow in the figure in the nozzle tip 5.

Next, an aluminum alloy plate containing 4% by weight of Mg was cast using a twin roll casting machine equipped with this casting nozzle. The thickness of this cast plate is 6
mm, and the plate width is approximately 900 mm. FIG. 5 is a schematic diagram showing the result of observing the temperature distribution of the cast plate immediately after casting carried out from the twin rolls using a thermoviewer. As is clear from FIG. 5, the central part of the cast plate immediately after casting is at a high temperature, and this central part in the width direction is the final solidified part. As described above, if non-uniform parts exist in the cast plate, there is a possibility that bubble defects caused by gas in the molten metal and casting cracks caused by internal strain in the final solidified part occur.

FIG. 6a is also a plan sectional view showing a casting nozzle configured so that the flow velocity of the molten metal at the center part at the nozzle tip is slower than at both ends by adjusting the shape of the buffer plate 3b. b is F in Figure 6a
- Longitudinal cross-sectional view taken along line F, Figure 6c is G of Figure 6a
- Longitudinal cross-sectional view taken along line G, Figure 6 d is H of Figure 6 a.
FIG. 6e is a longitudinal sectional view taken along line -H in FIG. 6a.

This casting nozzle differs from the nozzles shown in FIGS. 1a to 1d in that the shape of the buffer plate 3b is different. That is, the buffer plate 3b used in this casting nozzle is connected to the top and bottom walls of the distribution box 1 at the center, and the width of the side portions becomes narrower toward the ends. The molten metal passes under both sides of the buffer plate 1 and is supplied to the nozzle tip 5, as shown by arrows in FIGS. 6a to 6d.

FIG. 7 is a graph showing the molten metal flow velocity distribution at the tip of this casting nozzle, measured in the same manner as in the previous example. As is clear from this figure, the speed at the middle part of the tip of this casting nozzle is extremely slow compared to the end part.

An aluminum alloy plate containing 3.5% by weight of Mg was manufactured using a twin roll casting machine equipped with this casting nozzle. The thickness of this alloy plate is 5mm,
The board width is approximately 900mm. As a result, streak defects caused by the gas were generated, and these defects could not be removed even after continuous operation for a long time.

FIG. 8a is a plan sectional view showing a casting nozzle configured so that the shape of the buffer plate 3c is adjusted so that the flow velocity of the molten metal at the nozzle tip is uniform across the width, and FIG. 8b is the same. FIG. 3 is a plan view showing the buffer plate 3c.

In this casting nozzle, a guide plate 9 is provided in the distribution box and the nozzle tip 5a, so that molten metal is supplied from the distribution box only to the center in the width direction of the nozzle tip 5a. That is, the molten metal flows only in the area sandwiched between the guide plates 9 and flows from the distribution box to the nozzle tip 5a.
It is introduced into the interior from the center in the width direction. Further, in this example, no teardrop is provided in the nozzle tip 5a.

FIG. 9 is a graph showing the flow velocity distribution at the tip of this casting nozzle, measured in the same manner as in the previous example. As is clear from this figure, the flow rate at the tip of this casting nozzle is approximately uniform across the width.

An aluminum alloy plate was cast using a twin roll casting machine equipped with this casting nozzle. As a result, a streak-like defect caused by the gas occurred in the center of the cast plate in the width direction, and this defect could not be removed even after long-term operation.

FIG. 10a is a plan sectional view showing a nozzle tip of a casting nozzle configured so that the shape of the buffer plate 3d is changed so that the flow velocity of molten metal at the center of the nozzle tip is slower than at both tips; 10
FIG. b is a plan view showing the buffer plate 3d.

This nozzle chip 5b has a shape different from that of the nozzle chip used in the previous embodiment, and the hole in the nozzle chip 5b is formed into a rectangular shape in plan view. Further, a slit 10 extending in the longitudinal direction is opened in the center of the buffer plate 3d.

FIG. 11 is a graph showing the flow velocity distribution at the tip of this casting nozzle, measured in the same manner as in the previous example. However, the flow rate of water flowing through the casting nozzle was 50 l/min. As is clear from FIG. 11, since the flow velocity distribution has a tendency opposite to that of the method of this embodiment shown in FIG. 2, the occurrence of streak defects could not be prevented even in the casting using the actual machine.

As mentioned above, in the example in which the flow velocity of the molten metal at the center of the casting nozzle tip is 5% or more higher than that at the end to perform twin roll casting, defects such as streak defects are prevented from occurring. I was able to do that. on the other hand,
Both the cast plate that was cast with twin rolls with the flow velocity of the molten metal at the nozzle tip uniform across the width and the cast plate that was cast with twin rolls with the flow velocity of the central part of the nozzle tip slower than those at both ends. A streak defect had occurred.

Various methods can be considered to control the flow velocity of the molten metal in the width direction, but as in the above embodiment (Fig. 1), the shape of the buffer plate in the distribution box may be adjusted. The method is preferred. In addition to this, it is possible to control the flow rate by changing the shape (for example, length) of the teardrop, but this method would be impractical because the nozzle would become too large. Furthermore, controlling the flow by teardrops is not preferable because it tends to cause turbulence and causes entrainment of oxides. Therefore, it is preferable to use the tear drop to obtain a rectifying effect as in this embodiment.

〔Effect of the invention〕

As explained above, according to the present invention, the flow velocity of the molten metal at the center in the width direction at the tip of the casting nozzle is 5% or more faster than at the ends, so that the flow from the center to the ends at the thump is It is formed. Therefore, since air bubbles and the like are removed from the sides of the bump, an extremely high-quality cast aluminum alloy sheet in which streak defects are avoided can be obtained.

[Brief explanation of the drawing]

Figure 1a is a plan sectional view showing a casting nozzle used in the embodiment method of the present invention, and Figure 1b is Figure 1a.
A vertical cross-sectional view taken along line A-A of Figure 1c is Figure 1a
A vertical cross-sectional view taken along line B-B of , Figure 1 d is the same as Figure 1 a
Fig. 2 is a graph showing the molten metal flow velocity distribution at the nozzle tip, and Fig. 3 a shows a longitudinal cross-sectional view taken along line C-C of the nozzle. A plan sectional view showing a casting nozzle configured to
A vertical cross-sectional view taken along line D-D of Figure 3c is Figure 3a
FIG. 4a is a schematic plan view of the nozzle tip, and FIG. 4b is a schematic side view of the buffer plate.
Figure 5 is a schematic diagram showing the results of observing the temperature distribution of the cast plate immediately after casting using a thermoviewer, Figure 6a
6 is a plan sectional view showing a casting nozzle configured such that the flow velocity of molten metal at the center of the nozzle tip is slower than at both ends, and FIG.
A vertical cross-sectional view taken along line F, Figure 6c is G- in Figure 6a.
A vertical cross-sectional view taken along line G, FIG. 6 d is H- in FIG. 6 a.
A vertical cross-sectional view taken along line H, Figure 6e is - of Figure 6a.
A vertical cross-sectional view drawn by a line, FIG. 7 is a graph showing the molten metal flow velocity distribution at the tip of the nozzle, and FIG. 8 a
is a plan cross-sectional view showing a casting nozzle configured so that the flow velocity of molten metal at the nozzle tip is uniform across the width, FIG. 8b is a plan view showing the buffer plate, and FIG. 9 is the same. A graph showing the molten metal flow velocity distribution at the nozzle tip, FIG. 10a is a planar cross-section showing the nozzle tip of a casting nozzle configured such that the molten metal flow velocity at the center of the nozzle tip is slower than at both ends. Figure 10b is a plan view showing the buffer plate,
FIG. 11 is a graph showing the molten metal flow velocity distribution at the tip of the nozzle. 1; distribution box, 2; molten metal inlet, 3, 3a, 3b, 3c, 3d; buffer plate, 4; communication hole, 5, 5a, 5b; nozzle tip, 7; tear drop, 8; spacer,
9; Guide plate, 10; Slit.

Claims (1)

[Claims] 1 The process includes discharging molten aluminum alloy from the tip of a casting nozzle between a pair of rotating rolls and solidifying the molten metal between the rolls to continuously cast an aluminum alloy plate; When the discharge port of the section is divided into 10 equal parts in the width direction, the average flow velocity of the molten metal in the two blocks in the center is 5% or more faster than the average flow velocity of the molten metal in each of the two blocks at both ends in the width direction. A twin-roll casting method for aluminum alloy, characterized by: