JPH07115131B2 - Twin roll casting machine - Google Patents

Description

TECHNICAL FIELD The present invention relates to a twin roll type casting apparatus for casting and rolling a thin plate of an aluminum alloy or the like directly from a molten metal. More specifically, it has a cooling ability of a casting roll. An improved twin roll casting machine.

[Prior Art] In a twin-roll casting apparatus, a pair of rolls whose inner surfaces are water-cooled are arranged at appropriate intervals, and a molten metal is supplied through the nozzles between the rolls. Then, this molten metal is cooled by a roll to be solidified and rolled to directly produce a thin plate of an aluminum alloy.

[Problems to be Solved by the Invention] However, when an aluminum alloy cast plate is manufactured by a twin roll method, for example, center segregation occurs in an Al-Mg alloy or the like, and this casting defect is caused by a casting speed. It is known that the higher the speed, the more noticeable it becomes. [“Center Line Segregation in Twin Roll Cast Al
uminum Alloy Siab "Light Metals1982, Publication of
The Metallurgical Society of AIME (pages 873 to 888)
page)].

Besides the center segregation, defects such as level line and surface line pattern exist in the cast plate manufactured by the twin roll casting apparatus.

Conventionally, among these defects, especially center segregation always occurs when an Al-Mg alloy having a wide solidification temperature range is cast by twin roll casting. This is for the following reason. That is, even in a normal thick-walled ingot, concentration segregation of solute elements occurs in the final solidified portion, but particularly in the case of casting by the twin roll method, before solidification is completed, unsolidified molten metal is contained inside. Since rolling is applied to the cast plate in the state, the concentration segregation portion just before the completion of solidification is pushed backward, and the concentration segregation of solute elements becomes extremely remarkable.
As a result, extreme concentration segregation occurs in the central portion of the plate thickness, and center segregation defects occur. This was conventionally thought to occur essentially in the twin roll casting technique.

The present invention has been made in view of such problems,
An object of the present invention is to provide a twin roll type casting device capable of reducing center segregation of an aluminum alloy cast plate to a level at which there is substantially no problem.

[Means for Solving the Problems] In the twin-roll casting apparatus according to the present invention, a pair of rolls whose inner surfaces are water-cooled are arranged at appropriate length intervals.
In the twin roll type casting apparatus in which the molten metal is supplied between the rolls and the molten metal is cooled and solidified by the rolls, the roll has a shell thickness of 35 mm or more and 60 mm or less.

[Operation] In the present invention, since the molten metal is cooled by contacting with a pair of rolls having a shell thickness of 35 to 60 mm, the molten metal is cooled with extremely high efficiency by the roll having the optimum heat capacity in terms of cooling efficiency of the molten metal. It For this reason, the center portion of the cast plate is also rapidly cooled and solidified, so that center segregation is reduced.

[Embodiment] An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a sectional view showing a molten metal injecting section of a twin roll type casting apparatus according to an embodiment of the present invention. A pair of rolls 1,
2 are arranged so that their axial directions are parallel to each other and are vertically opposed to each other with an appropriate length interval. The rolls 1 and 2 have a cylindrical shape having a constant shell thickness t, and a cooling member 3 through which cooling water flows is fixed to the inner peripheral surface thereof. By passing the cooling water through the cooling member 3, the rolls 1, 2
The shell is cooled.

The rolls 1 and 2 are driven to rotate in the direction of the arrow.
A cylindrical nozzle 4 is arranged at a position upstream of the rotational direction of 1 and 2. The nozzle 4 is connected to a molten metal supply source such as a molten metal ladle, and a molten aluminum alloy 5 is injected into the gap between the rolls 1 and 2 through the nozzle 4.

The molten metal 5 is cooled by the rolls 1 and 2 and solidified to obtain a cast plate 7. A solid-liquid coexisting phase 6 exists between the molten metal 5 and the rolls 1, 2 or the cast plate 7.

The present invention is characterized in that the shell thickness of the rolls 1 and 2 is set to 35 to 60 mm in the twin roll type casting apparatus configured as described above.

The reason will be described below. For alloys with a wide solidification temperature range such as Al-Mg alloys, concentration segregation is likely to occur in the central part. However, even in such an alloy, concentration segregation can be prevented by making the cooling rate extremely fast. Therefore, even in the twin roll casting method, the molten aluminum alloy 5 is cooled by the contact between the casting rolls 1 and 2, so that a copper shell is used for the casting rolls 1 and 2 for the purpose of increasing the cooling rate. Attempts were made to lower the temperature of the cooling water flowing through the rolls. However, conventionally, the center segregation cannot be reduced by any of the methods.

The inventors of the present application have obtained the following findings as a result of various experimental studies to investigate the cause.

That is, thermal diffusion (cooling) during solidification of molten aluminum alloy
The rate-determining process was conventionally thought to be between the cooling water and the roll shell, but the inventors of the present application have found that the heat transfer between the molten metal and the roll shell does not solidify between the cooling water and the shell. I came up with the idea that the heat diffusion of time is controlled.

When a low-thickness roll is used and low-temperature cooling water is flowed, the shell itself is cooled well during non-casting when the molten metal is not supplied. For this reason, when the molten aluminum alloy comes into contact with the roll, its surface layer rapidly solidifies, but since the shell of the roll is thin and has a small heat capacity, the surface of the roll shell is easily heated to 100 ° C. or higher, A water vapor film is formed at the interface between the shell and the cooling water, and the two are in a heat insulating state. Therefore, in this case, the central portion of the cast plate in the plate thickness direction is in a state similar to that of slow cooling, and the concentration segregation becomes extremely severe.

On the other hand, when the thick shell is used, the cooling capacity of the shell by the cooling water is small, but the heat capacity of the shell itself is large, so that the solidification is completed before the adiabatic state by the steam film is reached. Therefore, by using a roll having a large shell thickness, it is possible to solidify the central portion of the plate thickness at a high cooling rate.

The inventors of the present application have completed the present invention from this viewpoint. As described above, the shell thickness is set to 35 mm or more in order to secure the heat capacity of the shell sufficient to cool the cast plate to the central portion in the plate thickness direction at a high cooling rate. If the shell thickness is less than 35 mm, the water vapor film between the shell and the molten aluminum alloy tends to be adiabatic, and the center segregation becomes remarkable. Therefore, the shell thickness must be 35 mm or more.

The upper limit of shell thickness is 60 mm. When the shell thickness exceeds 60 mm, on the contrary, the heat capacity is too large, and the cooling member 3 on the inner surface of the shell causes The effect of cooling does not reach the outer surface of the shell, and the shell surface (outer surface) is not sufficiently cooled. As a result, the solidification of the surface of the cast plate 7 is delayed and the surface quality is degraded. Therefore, the shell thickness of the roll must be 60 mm or less. In order to more strictly control the cooling rate of the molten aluminum alloy and the cooling conditions of the shell, it is desirable that the shell thickness is 40 mm or more and 50 mm or less.

The material of the shell preferably has a large specific heat so as to have a large heat capacity. Further, since the twin roll type casting equipment is equipment which rolls 1 and 2 also have a function of rolling the cast plate 7, the roll shell needs to have a hardness that can withstand such rolling of the cast plate. Is. For this reason, it is desirable to use heat resistant steel or the like for the roll shell. Regarding the cooling time, it is desirable to take 1.5 minutes or more for a roll having a diameter of about 90 cm. In the case of the shell thickness specified in the above range, it is within the range of the casting conditions of a normal aluminum alloy cast plate (about 80 to
There is no problem with the cooling time at 180 cm / min roll peripheral speed).

Hereinafter, the result of actually manufacturing a cast plate using the casting roll of the casting apparatus according to the embodiment of the present invention will be described.

Using heat-resistant special steel, diameter is about 900mm, thickness is 25mm, 4
A shell processed to have a size of 5 mm, 55 mm, and 70 mm was shrink-fitted to a core having a structure in which cooling water circulates to obtain a roll. Then, using this roll, Al-4 wt% Mg
A cast alloy plate was cast. The thickness of the cast plate is 6mm,
The roll peripheral speed is 100 cm / min. Further, cooling water having a water temperature of 30 ° C. was caused to flow at a flow rate of 300 l / min. The roll was not spray-coated with the lubricant.

The relationship between the center segregation state and surface quality of the cast plate thus produced and the roll shell thickness is shown in Table 1 below.

However, the evaluation of the center segregation, polishing the cross section of the casting plate along the casting direction, after etching with a phosphoric acid solution, measuring the length of the center segregation, the area per 100mm of the casting plate as the inspection area When the total length of segregation is 50 mm or more, ×,
The case of 20 mm or more and less than 50 mm is indicated by △, and the case of less than 20 mm is indicated by ○.

In addition, the surface quality is expressed as × when there are many spot defects on the surface of the cast plate, Δ when there are spot defects and ◯ when there is no surface defect.

The stain defects are segregation of about 1 to 5 cm extending in the casting direction, and in severe cases, cracks. From Table 1, the shell thickness within the range specified in the present invention (45 mm, 55 m
It is clear that when a roll having m) is used, the internal quality such as center segregation and the surface quality are extremely excellent.

[Effects of the Invention] According to the present invention, since the shell thickness is 35 to 60 mm, an appropriate heat capacity can be obtained, the center of the cast plate can be cooled at a high cooling rate, and the center segregation can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing a molten metal injection part of a casting apparatus according to an embodiment of the present invention. 1,2; roll, 4; nozzle, 5; molten metal, 7; casting plate

Claims (1)

[Claims] 1. A twin-roll casting method in which a pair of rolls, the inner surface of which is water-cooled, are arranged at appropriate intervals to each other, a molten metal is supplied between the rolls, and the molten metal is cooled and solidified by the rolls. In the equipment, the roll has a shell thickness of 35 mm or more
Twin roll type casting equipment, which is less than 60mm.