JPH0344428A - Apparatus for continuously producing semi-solidified metal - Google Patents

Abstract

PURPOSE:To prevent involution of gas into semi-solidified metal by arranging a molten metal receiving vessel on gap between stirrer and inner face of the vessel to form molten metal basin and setting a cylindrical sleeve submerged into the molten metal basin. CONSTITUTION:The molten metal 14 is poured into the molten metal receiving vessel 1 and introduced into the gap 6 between stirring vessel 2 and the stirrer 4 and continuously discharged from a discharging nozzle 3 under condition of the semi-solidified metal. The heat resistant cylindrical sleeve 8 having the inside diameter smaller than the outside diameter of the stirrer 4 independently arbiratily liftable is submerged concentrically with the stirrer into the molten metal basin in the molten metal receiving vessel 1 to prevent the involution of gas. As the inside diameter of cyliNdrical sleeve 8 is larger than diameter of stirrer submerged shaft 4a to form the suitable gap so that flowing resistance does not become large and selected to be smaller than the diameter of stirrer 4, even in the case of developing whirlpool recessing 16 in the molten metal 14', the molten metal does not reach stirring gap 6.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a solid-liquid metal mixture (simply referred to as a semi-solid metal for simplicity) in which non-dendritic primary crystals are dispersed in a metal melt.
The purpose of this paper is to propose an apparatus for continuously producing semi-solid metal of high quality, particularly preventing gas entrainment.

(Prior art) As disclosed in Japanese Patent Publication No. 56-20944, an apparatus for continuously producing semi-solid metal is known to maintain molten metal supplied to a heat-retaining tank at a constant temperature while producing a cylindrical shape. The basic method is to introduce the metal into a gap between it and a stirrer that rotates at high speed in a cooling stirring tank, and apply strong stirring action under appropriate cooling action to make it into a semi-solid state, and then continuously discharge it as semi-solid metal from a nozzle at the bottom. The structure is known.

In this case, semi-solid metals are produced by violently stirring the molten metal (generally an alloy) while cooling it, so that the dendrites that are forming in the molten metal disappear or shrink, becoming rounded. It is formed by converting it into a different form.

The finer the particles of non-dendritic primary crystals in semi-solid metals, the better their properties. Therefore, strong cooling effects and strong stirring effects are essential conditions for semi-solid metal manufacturing equipment. In order to obtain the stirring effect, conventional devices require high-speed rotation of the stirrer immersed in the molten metal, but as the stirrer rotates, the molten metal also rotates, and due to the centrifugal acceleration acting on it,
Vortex depressions occur on the liquid surface, making it easy for gas to get caught up in the semi-solid metal, making it impossible to manufacture products of very good quality under atmospheric pressure.

(Problems to be Solved by the Invention) As mentioned above, in the conventional semi-solid metal manufacturing equipment, the stirring bar is immersed in the molten metal and rotated at high speed to provide an intense stirring effect. As the shaft rotates, the solution surface also rotates, and as a result of centrifugal acceleration, a large vortex depression is generated on the solution surface, causing gas to be drawn into the solution.

Semi-solid metal has a very high viscosity, so once gas is involved, it becomes difficult to float and separate from the semi-solid metal, and it remains as bubbles in the semi-solid metal, resulting in quality problems. It becomes a big problem.

In other words, it is important to prevent the vortex depressions from reaching the cooling stirring section, but in order to minimize the vortex depressions that occur in conventional equipment, it is necessary to limit the rotational speed or raise the temperature of the solution part. Even if such considerations were taken, this resulted in significant constraints on the performance and structure of the device, and was not satisfactory.

It is therefore an object of the present invention to provide an apparatus for continuously producing semi-solid metal, in which entrainment of gas into the semi-solid metal under high speed rotation of the stirrer can be advantageously avoided.

(Means for Solving the Problems) The present invention has a stirrer that rotates at high speed, introduces molten metal into a narrow gap formed between the outer surface of the stirrer and the inner surface of the tank, and produces strong cooling and intense stirring effects. This is an apparatus for producing semi-solid metal by a method, in which a receiving tank is provided above the stirring gap to prevent gas from being entrained in the semi-solid metal to form a pool of molten metal, and the interior of the pool of molten metal is For stirring, an independent cylindrical sleeve made of heat-resistant metal or ceramic, whose inner diameter is sufficiently large for the diameter of the driving shaft of the immersed part of the stirrer and smaller than the outer diameter of the stirrer, is detachably attached to the receiving tank. This is an apparatus for continuously producing semi-solid metal, characterized by a immersion arrangement concentric with the shaft.

Here, the size of the vortex depression in the liquid surface in the pool of molten metal due to the rotation of the stirrer is determined by the rotational speed Ω of the stirrer, the shaft diameter 2r of the immersion part, and the inner diameter 2r+ of the receiving tank. The conditions for reaching the stirrer are determined by the correlation between the inner diameter 2rz of the molten metal tank and the outer diameter 2r3 of the stirrer.
If r2<r, no matter how fast the stirrer rotates, the vortex indentation will not reach the side of the stirrer. By immersing the metal into a pool of molten metal in the receiving tank, it was possible to completely prevent gas entrainment due to the rotation of the stirrer.

This cylindrical sleeve is removably fixed to the receiving tank, and when the stirrer is moved up and down, the fixing device is removed so that it can be moved up and down in the same way as the stirrer.

First, the structure, operation, and problems of a conventional continuous semi-solid metal manufacturing apparatus will be explained with reference to FIGS. 2 and 3.

The apparatus for continuously producing semi-solid metal is composed of a receiving tank 1, a stirring tank 2, and a stirring bar 4, as shown in FIG.

The receiving tank l has a receiving port 1a for continuously receiving molten metal as shown by an arrow 14, and the molten metal 14 is passed through the communicating hole 1 from there.
b and supplied to the stirring tank 2.

The stirring tank 2 has suitable cooling means on its wall and is provided with a discharge nozzle 3 at its bottom.

The stirrer 4 is connected to a drive shaft 5 and rotates at high speed in the stirring tank 2 in the direction of an arrow 12, and intensely stirs the molten metal in the gap 6 between the stirrer 4 and the stirring tank 2 while giving strong cooling to the molten metal. The semi-solid metal is brought into a semi-solid state, and the semi-solid metal is discharged from the discharge nozzle 3 by the arrow 15.
It has a structure that discharges water continuously.

In this case, the stirring bar 4 needs to be removed upward from the stirring tank 2 and the receiving tank 1 in order to prevent condensation accidents and for maintenance and inspection, and is designed to be able to move up and down as desired along the arrow 13.

The biggest problem with such a device is that since the stirrer 4 is immersed in the molten metal, the molten metal is also dragged and rotated by the rotation of the immersion shaft 4a, and due to centrifugal acceleration,
A vortex depression 16 is generated, which causes the immersion shaft 4 to
Gas entrainment occurs along a.

If this vortex dent 16 is small and gas entrainment occurs only in the molten metal, the gas becomes bubbles and floats and separates, but when the vortex dent 16 reaches the stirring gap 6, the gas is trapped in the semi-solid metal. Air bubbles become trapped and cause quality defects.

This relationship will be explained in detail with reference to FIG.

In the receiving tank 1 and the stirring tank 2, the stirring bar 4 has an angular velocity of Ω.
Assuming that it rotates at rad/sec, the molten metal 14'' in the receiving tank 1 rotates with the rotation of the immersion shaft 4a of the stirrer 4, and as mentioned above, the vortex depression 16 is generated due to centrifugal acceleration. It is.

The depth of the vortex indentation at point A along the axis in this case (h
) is a function of Ωr and β=r H/ r z,
It is expressed by the following formula.

From the flow analysis in the concentric double cylinder, it can be seen that as the angular velocity (Ω) of the stirrer 4 increases, the depth (h) of the vortex depression also increases, and the gas entrainment along the axis of the immersion shaft 4a becomes deeper. Go.

Generally, the radius (r3) of the stirrer 4 is larger than the radius (rl) of the immersion shaft 4a, so the depth of the vortex depression (h
) is also temporarily stopped at the upper end surface of the stirrer 4, but as the rotation speed increases further, the vortex dent 16 exceeds the upper end point (point P) of the stirrer 4 and reaches the stirring gap 6.
′ is reached, air bubbles become trapped in the semi-solid metal and remain in the product.

The vortex depression caused by this high-speed rotation is very large, and under normal design conditions, it is difficult to prevent gas entrainment, which has become a major problem.

However, the inner diameter 2r of the receiving tank 1 is the outer diameter 2r of the stirrer 4.
If the vortex indentation 16 is selected to be smaller than t, no matter how high the stirrer 4 rotates and the calculated vortex indentation depth (h) becomes infinite, the vortex indentation 16 will reach the upper end of the stirrer 4 (P ) and reach the stirring gap 6 to entrain the gas into the semi-solid metal. However, in the actual device,
Since the stirrer 4 cannot be pulled out upwardly, it is impossible to employ such a structure.

Therefore, in the present invention, the inner diameter of the receiving tank l is 2r.

The present invention proposes a practical device in which gas entrainment is completely prevented by making the outer diameter of the stirrer 4 smaller than 2rz, and there is no problem in raising and lowering the stirrer.

In FIG. 1, the device of the present invention has a receiving tank 1, similar to the conventional device.
, a stirring tank 2 and a stirring bar 4.

Molten metal 14 is continuously supplied to the receiving port 1a, flows into the receiving tank 1 through the communication hole 1b, and is introduced into the gap 6 between the stirring tank 2 and the stirrer 4 which is rotating at high speed.

The molten metal is strongly cooled by the cooling means provided in the stirring tank 2 or the stirring bar 4, and a strong stirring effect is applied to it to make it into a semi-solidified state, which is then discharged from the discharge nozzle 3 provided at the bottom of the stirring tank in the direction of the arrow 15. This process continuously produces semi-solid metal.

The stirrer 4 is connected to a drive electric motor (not shown) via an immersion shaft 4a and a drive shaft 5, enabling high-speed rotation as shown by arrow 12, and the entire drive system is installed on an elevating frame 7. It is possible to move up and down together with the stirrer 4 as shown by the arrow 13.

In such an apparatus, a cylindrical sleeve 8 having an inner diameter smaller than the outer diameter of the stirrer 4 and useful for preventing gas entrainment is immersed in a pool of molten metal in the receiving tank 1.

This cylindrical sleeve 8 has a mounting bracket on its upper part, and can be fixed to the receiving tank 1 by inserting a mounting pin 10 through a mounting lever 9. Also,
The cylindrical sleeve 8 is connected to the elevating frame 7 via a lifting chain 11, or is provided with its own elevating means, so that it can be moved up and down as desired by removing the fixing bottle 1O.

The material of the cylindrical sleeve 8 is made of a heat-resistant metal, a highly heat-resistant refractory material, or a ceramic, depending on the metal to be handled.

(Function) The molten metal 14' in the receiving tank 1 rotates and flows in the gap between the immersion shaft 4a and the inner surface of the cylindrical sleeve 8 due to the high speed rotation of the stirrer 4, generating a vortex depression 16. The exterior and uke? In the gap between JH110, it is almost stationary.

The inner diameter of the cylindrical sleeve 8 is larger than the diameter of the stirring immersion shaft 4a, with an appropriate gap to prevent the flow resistance from becoming too large, and is also smaller than the diameter of the stirrer 4, so that the vortex depression 16 is prevented. Even if it occurs, it stops at the upper end surface of the stirring bar 4 and does not reach the stirring gap 6.

Therefore, no matter how high the stirrer 4 rotates, gas entrainment will not occur in the semi-solid metal. Moreover, it can be moved up and down by removing the attachment bottle at any time as needed, and does not interfere with the work of lifting and lowering the stirrer 4.

(Example) As a specific example, the inner diameter of the receiving tank is 500M, and the outer diameter of the stirrer is 2.
In an apparatus that uses a stirrer with an immersion part shaft diameter of 180 mm and operates with a stirring gap of 10 mm, the inner diameter is 270 mm,
Immerse a cylindrical sleeve with an outer diameter of 370M to prevent gas entrainment,
We created an experimental device to observe vortex indentation and gas entrainment at various rotational speeds of the stirrer, and confirmed the effect of preventing gas entrainment.

(Effect of the invention) From the above, the present invention is a semi-solid metal! ! In production equipment, it is possible to prevent gas entrainment and produce sound semi-solid metal, as well as to obtain sufficient stirring effects, and there are no problems in operation, maintenance, and inspection. It is very useful in practice.

[Brief explanation of drawings]

FIG. 1 is an overall view of the device of the present invention, FIG. 2 is an overall view of a conventional device, and FIG. 3 is an explanatory diagram showing the principle of generation of vortex depression and gas entrainment. 1... Receiving tank 1b... Communication hole 3... Discharge nozzle 4a... Stirrer immersion shaft 6... Stirring gap 8... Cylindrical sleeve 10... Mounting bin 1a... Receptacle 2... Stirring tank 4... Stirrer 5... Drive shaft 7... Lifting frame 9... Mounting lever 11... Lifting chain

Claims (1)

[Claims] 1. This device has a stirrer that rotates at high speed, introduces molten metal into a narrow gap formed between the outer surface of the stirrer and the inner surface of the tank, and produces semi-solid metal by strong cooling and intense stirring effect. A molten metal reservoir is provided above the stirring gap to prevent gas from entering the semi-solid metal. An independent cylindrical sleeve made of heat-resistant metal or ceramic that is sufficiently large for the shaft diameter and smaller than the outside diameter of the stirrer is immersed and placed concentrically with the stirring shaft so that it can be attached to and removed from the receiving tank. An apparatus for continuously producing semi-solid metal, characterized by: