JPH04274841A - Method for continuous production of half-solidified metal and stirrer - Google Patents

Abstract

PURPOSE:To accelerate the discharge of a half-solidified metallic slurry by utilizing the centrifugal head by the rotating flow of a stirrer through a discharge port provided on the side wall at the bottom end of a stirring tank. CONSTITUTION:A molten metal 9 is continuously supplied into a molten metal receiving port and is introduced through a molten metal receiving tank into a stirring space 8 of the stirring tank 2. The molten metal 9 is cooled by coming into contact with the stirring and cooling part of the stirrer 3. The molten metal is simultaneously subjected to stirring by the high speed rotation of the stirrer 3 and while the half-solidified slurry is formed, the molten metal 9 flows down and is continuously discharged from the discharge port 4 on the side wall in the bottom of the stirring tank 2. The discharge of the half-solidified slurry is accelerated by the centrifugal head generated by the rotating flow of the half-solidified metallic slurry arising from the rotation of the stirrer 3 through the discharge port 4 provided on the side wall at the bottom end of the stirring tank 2 at this time.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a method of continuously producing a solid-liquid metal mixture (hereinafter referred to as semi-solid metal for simplicity) in which non-dendritic primary crystals are dispersed in a metal melt using a mechanical stirring means. The present invention relates to a method for manufacturing semi-solid metal that can realize smooth discharge of the semi-solid metal, and a stirring bar useful for advantageously promoting the discharge.

0002

[Prior Art] As disclosed in Japanese Patent Publication No. 56-20944, an apparatus for continuously producing semi-solid metal is used to maintain molten metal supplied to a heat-retaining tank at a constant temperature while producing a cylindrical metal. A mechanically stirred metal is introduced into the gap between the stirrer rotating at high speed in a cooling stirring tank, and is made into a semi-solid state by adding stirring action under appropriate cooling action, and is continuously discharged as semi-solid metal from a nozzle at the bottom. Things are common. Further, in prior art such as Japanese Patent Application No. 63-238788, it has been proposed to use a water-cooled stirrer in order to enhance the cooling effect.

0003

[Problem to be Solved by the Invention] This semi-solid metal is produced by appropriately stirring a molten metal (generally an alloy) while cooling it to remove the dendrites that are forming in the molten metal, so that the branches disappear. It is formed by reducing or converting it into a rounded shape. The finer the particles of non-dendritic primary crystals in semi-solid metals, the better their properties. Therefore, strong cooling is required when producing semi-solid metals. On the other hand, semi-solid metals with strong cooling and high solid phase ratio , has a problem in that it has a very high apparent viscosity and is difficult to flow and continuous discharge is difficult.

In the continuous semi-solid metal manufacturing method,
The amount of discharge determines the solid phase ratio of semi-solid metal, which in turn affects the discharge characteristics, and controlling the amount of discharge is essential to stably produce semi-solid metal under certain conditions. This is the condition.

[0005] The higher the solid fraction, the higher the apparent viscosity of the semi-solid metal. For example, when the solid fraction (fs) exceeds 60%, there is a characteristic that there is almost no fluidity, and it is especially difficult to reduce the cooling rate by strong cooling. If the temperature is increased too quickly, there is a problem that the apparent viscosity increases significantly and fluidity is lost even at a lower solid phase ratio.

[0006] When the apparent viscosity increases and the fluidity deteriorates, the amount of discharge decreases due to the increase in viscous resistance in a simple nozzle discharge method, which in turn causes an increase in the solid fraction, which further reduces the discharge. Another problem is that a vicious cycle occurs in which the amount decreases, making continuous discharge difficult.

[0007] Therefore, in conventional devices, a method is adopted in which the nozzle is provided with a means for adjusting the aperture area (for example, a slide nozzle or a stopper) to control the discharge amount. For viscous and condensable fluids,
The controllability was poor, the discharge amount was not stable, the properties of the semi-solid metal were unstable, and the system often ended up clogging, making it impractical.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, it is an object of the present invention to provide an alternative method to nozzle discharge using gravity discharge. In the mechanical stirring method for producing semi-solid metal, a stirrer rotates at high speed in the stirring gap in order to apply an appropriate stirring effect to the molten material, and as a result, the molten material and the semi-solid metal being formed in the stirring gap also rotate at high speed. The centrifugal head acts in the radial direction as it rotates. This is also one of the reasons why it is difficult to discharge semi-solid metal from the discharge nozzle installed at the center of the rotation axis of the stirrer.
In the present invention, this centrifugal force head is effectively utilized,
A discharge hole is provided in the side wall of the lower end of the stirring tank to promote discharge, and the opening degree of the discharge hole can be adjusted, and the number of revolutions of the stirrer can be adjusted to control the discharge amount. It is.

[0009] This invention utilizes a stirrer that rotates at high speed, a stirring tank that accommodates the stirrer, and a cooling means provided on the outer surface of the stirrer and/or the inner surface of the stirring tank. In this method, molten metal introduced into a narrow annular gap formed between the two is strongly cooled and stirred to produce a semi-solid metal slurry. A method for producing semi-solid metal, characterized in that the discharge of semi-solid metal slurry is promoted by using a centrifugal force head generated by rotational flow of semi-solid metal slurry as a stirrer rotates, and the stirring bar changes its rotational speed. Therefore, it is more desirable to control the discharge amount of semi-solid metal and the solid phase ratio.Furthermore, to promote discharge of this semi-solid metal slurry, a narrow annular gap is provided between the stirring tank and its inner surface. It is useful to use a plurality of machined grooves or blade plates arranged radially in a radial direction on the bottom surface of the tip of the stirrer.

FIG. 1 shows a cross-sectional view of an example of a continuous semi-solid metal manufacturing equipment using a mechanical stirring method suitable for carrying out the method of the present invention, and FIG. 2 shows a cross-sectional view of its discharge hole.

In the place shown in FIG. 1, 1 is a receiving tank;
2 is a stirring tank, and 3 is a stirrer. The receiving tank 1 is a container lined with a heat insulating material such as a refractory material, and has a heat insulating structure by preheating it to a sufficient temperature, and is provided with a receiving port 1' in one part, and is tightly attached to the upper end of the stirring tank 2. has been done. Similar to the receiving tank 1, the stirring tank 2 is a cylindrical container lined with a heat insulating material such as a refractory material, and has a stirring gap 8 formed between it and the stirring cooling part 3a of the stirrer 3. Molten metal 9 is introduced, and a semi-solid metal slurry 9' is produced by cooling and stirring.

A discharge hole 4 is provided in the bottom side wall of the stirring tank 2.
The slide gate 5 has a structure in which the discharge area 4' can be adjusted.

Further, a discharge chute 6 for guiding the discharged semi-solid metal slurry 9' is installed below the discharge hole 4. Next, although not shown, the stirring bar 3 has a water-cooled structure, and includes a stirring cooling part 3a, a tip part 3b, and a drive shaft 3c.
The part immersed in the molten metal is protected by a refractory material. The stirring cooling part 3a is a part that forms a stirring gap 8 with the inner surface of the stirring tank 2, and has a structure that allows strong cooling with a water-cooled wall. The tip portion 3b is made of ceramics, and its bottom surface is provided with radial grooves or blades 3d to promote discharge of centrifugal force. This stirrer 3 is connected to a drive device by a drive shaft 3c and rotates at high speed as shown by arrow 7.

Although not shown, the inner peripheral surface of the stirring tank 2 may be made into a water-cooled wall instead of the water-cooled wall of the stirrer 3, or both may be made into water-cooled walls.

[0015]

[Operation] Molten metal 9 is continuously supplied to the inlet 1',
The molten metal is introduced into the stirring gap 8 of the stirring tank 2 through the receiving tank 1 . In the stirring gap 8, the molten metal flows through the stirring cooling section 3a of the stirrer 3.
The semi-solid metal slurry 9 is cooled by being in contact with the metal slurry 9, and at the same time receives a stirring action due to the high speed rotation of the stirrer 3.
' is formed and flows down, and is continuously discharged from the discharge hole 4 in the bottom side wall of the stirring tank 2.

At this time, the semi-solid slurry is discharged through the opening of the discharge hole 4 provided in the side wall of the lower end of the stirring tank 2 by the centrifugal force head caused by the rotational flow of the semi-solid metal slurry as the stirrer 3 rotates. promoted.

That is, the discharge amount (Q) of the semi-solid metal slurry 9' from the discharge hole 4 is determined by the discharge cross-sectional area 4' being (A), the gravity head being (Hg), and the centrifugal force head being (Hc).
), the following equation (1) is obtained.

[Chemical formula 1] is determined as follows. k; Flow rate coefficient Here, the centrifugal force head (Hc) has a rotation radius of the stirrer 3 in the cross section of the discharge hole as Rm, and a rotation speed of the stirrer 3 as Nr.
．． p. If m, Hc = (πRm N)2/1800
×g --- (2) The higher the rotation speed (N), the higher the gravity head (H
The ratio of the centrifugal force head (Hc) to g) increases, making it possible to control the discharge amount by changing the rotation speed (N) of the stirrer 3 while maintaining the discharge cross-sectional area 4' at (A). It is in. Furthermore, the higher the rotational speed (N) of the stirrer 3, the greater the effect of promoting discharge by the centrifugal force head, which is very advantageous for discharging semi-solid metals with a high solid fraction and high viscosity. Stable continuous discharge is possible.

A stirring tank having a stirring bar with a radius Rm of 100 mm was actually manufactured, and it was filled with a solid-liquid mixed solution corresponding to a solid phase ratio of 0.2 so that the gravity head Hg was 400 mm. Cross-sectional area A provided on the lower end side wall of stirring tank 2
Figure 3 shows the experimental results of examining the discharge amount (Q) characteristics from a discharge hole with a diameter of 4 cm2.

From FIG. 3, it can be seen that the rotation speed (N) of the stirrer is 200
r. p. Up to 20 m, the influence of the centrifugal force head (Hc) is small and the discharge amount (Q) does not increase much.
0 r. p. m or more, the centrifugal force head (Hc)
As the rotation speed increases, the discharge amount increases almost linearly, and therefore, by changing the rotation speed of the stirrer 3, the discharge amount can be controlled.

[0020]

[Example] Based on the above results, the lower diameter is 180 mm,
In a semi-solid metal manufacturing apparatus using a water-cooled stirrer 3 having a conical cooling surface with an upper diameter of 280 mm and a discharge hole of 5 mm x 8 mm in the lower end side wall of the stirring tank 2, an experiment for manufacturing semi-solid metal of Al alloy was carried out. When I went there, I found that the stirrer rotation speed was
200-500r. p. By varying the m in the range, the semi-solid metal discharge rate can be increased from 20 to 50 l/min.
It was possible to control within the range of . In this case, the semi-solid metal slurry 9' changes due to the change in stirring effect due to the difference in rotation speed.
There was no difference in structure and quality, and it was recognized that it was very effective in controlling the solid phase ratio.

[0021]

[Effects of the Invention] According to the present invention, (1) It is easy to discharge semi-solid metals with a high solid phase ratio and high viscosity (2)
) By adjusting the rotation speed of the stirrer, it is possible to reliably control the amount of discharge. (3) If the amount of discharge can be reliably controlled, it is possible to control the discharge solid phase rate, and stable operation is possible. (4) If the problem of discharge is solved, great effects are expected, such as a very simple structure for the mechanical device.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of cooling stirring equipment suitable for carrying out the present invention.

FIG. 2 is a cross-sectional view of the discharge hole.

FIG. 3 is a graph showing experimental results.

[Explanation of symbols]

1　Hot water tank 1′　　Receiving spout 2 Stirring tank 3 Stirrer 3a　　Agitation cooling section 3b Tip 3c Drive shaft 4 Discharge hole 4'　Discharge cross section 5　Sliding gate 6 Discharge chute

Claims (3)

[Claims] Claim 1: A stirrer that rotates at high speed, a stirring tank that houses the stirrer, and a cooling means provided on the outer surface of the stirrer and/or the inner surface of the stirring tank. In this method, a semi-solid metal slurry is produced by strongly cooling and stirring the molten metal introduced into a narrow annular gap formed in the stirring tank. A method for producing a semi-solid metal, characterized in that discharge of the semi-solid metal slurry is promoted using a centrifugal force head caused by the rotational flow of the semi-solid metal slurry as the semi-solid metal slurry rotates. 2. The method for producing semi-solid metal according to claim 1, wherein the amount of semi-solid metal discharged and the solid phase ratio are controlled by changing the rotational speed of the stirrer. 3. A stirrer housed in a stirring tank with a narrow annular gap separated from the inner surface of the stirrer, the stirrer having a plurality of machined grooves or blades arranged radially in the radial direction on the bottom surface of the tip of the stirrer. A stirrer characterized by being equipped with.