JPH06297097A - Production of half solidified metal - Google Patents

Abstract

PURPOSE:To continuously and stably produce the half solidified metal by preventing the excessive growth of a solidified shell by the heat extracting heat flow flux of a cooling plate and the shearing strain rate of a solid-liquid boundary, thereby preventing an increase in the torque of a stirrer at the time of cooling molten metal under rotation of this stirrer. CONSTITUTION:The half solidified metal is produced by cooling the molten metal injected into a cylindrical cooling vessel having the cooling plate from the upper part of this vessel under rotation of the stirrer. The excessive growth of the solidified shell is prevented by the heat extracting heat flow flux of the cooling plate and the shearing strain rate of the solid-liquid boundary, by which the increase in the torque of the stirrer is prevented. The relation between the heat extracting heat flow flux of the cooling plate and the shearing strain rate of the solid-liquid boundary satisfies the inequality. The inequality gamma>12.9(m<2>/kcal).q, where gamma: the shearing strain rate (s<-1>) of the solid-liquid boundary, q: the heat extracting heat flow flux (kcal/m<2>.s) of the cooling liquid. As a result, the increase in the torque generated in the stirrer is prevented and the half solidified metal having fine primary crystal grains and high solid phase rate is continuously and stably produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention continuously stabilizes a slurry-like solid-liquid metal mixture (hereinafter simply referred to as semi-solidified metal) in which a non-dendritic primary crystal is dispersed in a metal (generally an alloy) liquid. It proposes a method for producing a semi-solid metal produced by the above method.

The semi-solidified metal can be processed into materials having good internal quality, a downstream processing step, that is, a rheoform directly processed into a product, or a solidified metal once solidified and then reheated to a semi-molten state for processing. Stable industrial production of semi-solidified metal from its usefulness, such as enabling substantial reduction of processing energy by realizing near net shape in thixocasting, casting, etc. and the possibility of developing new materials Development of technology is desired.

[0003]

2. Description of the Related Art A means for continuously producing semi-solidified metal is disclosed in, for example, Japanese Patent Publication No. Sho 56-20944 (apparatus for continuously forming an alloy containing non-dendritic primary crystal solids). As shown in the figure, the molten metal at a constant temperature is introduced into the gap between the inner surface of the cylindrical cooling tank and the stirrer rotating at high speed, cooled while applying a strong stirring action, and the resulting semi-solid metal is cooled from its bottom. A mechanical stirring method (hereinafter referred to as a stirrer rotation method) of continuously discharging is known. Also,
As a stirring method, a method using electromagnetic force (hereinafter referred to as electromagnetic stirring method) is also well known.

As another means, the molten metal is supplied to a gap between a single roll having heat removal ability and rotating around the horizontal axis and a fixed wall formed of a concave curved surface along the outer circumference of the roll, and the roll is rotated. Means for producing semi-solidified metal by the generated shear strain of the solid-liquid interface (hereinafter referred to as a single roll method) is disclosed in JP-A-3-142040 (method and apparatus for continuously producing semi-solidified metal) and JP-A-3-14240. No. 4-238645 (method and apparatus for producing semi-solidified metal).

In any of these means, the solid phase particles in the semi-solidified metal are agitated while cooling the molten metal, whereby the branches of the dendritic primary crystals that are being formed in the melt disappear or shrink. Then, it is formed by being converted into a rounded form. It is said that the finer the non-dendritic primary crystal particles and the higher the solid fraction of the semi-solidified metal, the better the quality characteristics of the product obtained from the semi-solidified metal. The higher the cooling rate, the finer the particles.

For this reason, an apparatus capable of performing strong cooling is required as an apparatus for producing semi-solidified metal, but it is subjected to intense cooling to produce fine primary crystal grains and semi-solidified metal with a high solid fraction. In this case, the apparent viscosity becomes large, so that the fluidity becomes very poor, and it becomes difficult to continuously and stably discharge the semi-solidified metal having a high solid fraction.

When the above-mentioned means are examined from the viewpoint of the discharging ability of the semi-solidified metal, in the single roll method, the discharge of the generated semi-solidified metal is promoted by the rotation of the roll, and the solidified shell attached to the surface of the roll is scraper. Since it is scraped off with, even if the solid phase ratio of the semi-solidified metal to be discharged is large, there are few obstructive factors for discharging, and the discharging ability is very excellent. However, in the stirrer rotation method and the electromagnetic stirring method, in the cooling tank, since the supplied molten metal is rotated and stirred with the center of the cooling tank as the rotation axis, the pressure on the wall surface of the cooling tank due to centrifugal force increases, On the contrary, it reduces the discharge capacity. Therefore, in the stirrer rotation method and the electromagnetic stirring method, establishment of a technique for increasing the discharge capacity of semi-solidified metal becomes a particularly important issue.

On the other hand, in the stirrer rotation method and the electromagnetic stirring method, if the discharge capacity can be increased, the manufactured semi-solidified metal is passed through a nozzle or directly extruded into a round cross section or a square cross section. Enables direct processing of high solid fraction semi-solidified metal (Reoform),
It is a very excellent means for shaping semi-solidified metal, such as billet processing.

From this point of view, the stirrer rotation method is used as a means for improving the ability to discharge semi-solidified metal, as disclosed by Japanese Patent Laid-Open No. 4-124231 (semi-solidified metal production apparatus) by the inventor of the present invention. We proposed a device that uses a spiral screw-shaped stirrer and forcibly feeds the semi-solidified metal generated in the cooling tank downward, but there is still room for improvement as it is industrialized. ing.

[0010]

Under the circumstances as described above, the inventors of the present invention further conducted experiments on the stirrer rotation method, and as a result, in the conventional means, even if a paddle is adopted as the stirrer, a spiral screw is used. Even if adopted, the torque of the stirrer increases due to the growth of the solidified shell generated on the inner surface of the cooling tank with the lapse of time after the start of semi-solid metal discharge, and this increase in torque hinders the continuous discharge of semi-solid metal. We came to discover that it would be a factor.

Therefore, in order to take advantage of the excellent features of the stirrer rotation method, it is necessary to prevent the excessive growth of the solidified shell and prevent the torque generated in the stirrer from rising and continuously discharge semi-solidified metal. Establishing becomes an important issue to be solved.
In view of the above, an object of the present invention is to propose a method for producing semi-solidified metal by the stirrer rotation method, which can advantageously solve such problems and continuously and stably discharge semi-solidified metal.

[0012]

In order to solve the above-mentioned problems, the inventors have studied the torque increasing mechanism of the stirrer and achieved the present invention. That is, the gist of the present invention is as follows.

In a method for producing a semi-solid metal, in which a molten metal poured from an upper portion of a cylindrical cooling tank having a cooling plate is cooled while a stirrer is rotated, a heat removal heat flux of the cooling plate and a shear at a solid-liquid interface are used. A method for producing semi-solidified metal, characterized by preventing excessive growth of a solidified shell and preventing an increase in torque of a stirrer by a strain rate.

The method for producing a semi-solid metal according to the item [1], wherein the relationship between the heat removal heat flux of the cooling plate and the shear strain rate at the solid-liquid interface satisfies the following expression (1). [Note] γ> 12.9 (m ² / Kcal) · q ----- (1) where γ: Shear strain rate of solid-liquid interface (s ^-1 ) q: Heat removal heat flux of cooling plate (Kcal / m ² · s)

The method for producing a semi-solidified metal according to the item 1), wherein the thickness of the solidified shell growing on the inner surface of the cooling plate is limited according to the value of the set clearance between the cooling plate and the stirrer.

The semi-solid metal according to any one of claims 1, 2 and 3 is characterized in that a stirrer provided with a spiral screw groove at the tip is adopted to accelerate the discharge of the semi-solidified metal while preventing an increase in torque. Manufacturing method of solidified metal.

[0017]

The present invention will be described in detail below based on the experimental results.
The semi-solidified metal manufacturing apparatus shown in FIG. 1, that is, the hot water receiving tank 5, the cooling tank 6, the holding tank 7, the discharge amount control nozzle 12, and the stirrer 10 rotating about the center of the cooling plate 8 of the cooling tank 6 and the torque meter 3 thereof. The influence of the heat removal heat flux (heat removal rate) of the cooling plate 8 of the cooling tank 6 and the shear strain rate of the solid-liquid interface on the torque increase of the stirrer 10 is injected by the molten metal 1 by an experimental apparatus mainly composed of An experiment was conducted by changing the gap distance (set clearance) between the cooling plate 8 and the stirrer 10, which was set in advance.

First, the solid phase ratio of the semi-solidified metal to be discharged is 0.15, and the set clearance is 7, 10 and 15 m.
FIG. 2 shows changes with time in the torque generated in the stirrer 10 when the value is changed to m. The control of the solid phase ratio of the semi-solidified metal discharged in the above was performed by adjusting the retention time of the poured molten metal 1 in the cooling tank 6 by the discharge amount control nozzle 12. As the stirrer 10, a paddle type shown in FIG. 3A was adopted.

3A and 3B are explanatory views showing the shape of the stirrer, wherein FIG. 3A is a paddle type stirrer, and FIG. 3B is a paddle / screw composite type in which a spiral screw is attached to the tip of the paddle. It is a stirrer.

As shown in FIG. 2, the set clearance is 1
In the case of 0 mm or less, the torque of the stirrer 10 increases as time passes, while the set clearance is set to 15 m.
When it was set to m, it was revealed that the torque of the stirrer 10 did not increase and the semi-solidified metal could be continuously discharged. If the set clearance is large in the above, the shell thickness that can grow in the clearance on the inner surface of the cooling plate 8 becomes thick, which means that the heat removal rate when the solidified shell approaches the stirrer becomes small. .

Next, in FIG. 4, the solid phase ratio of the discharged semi-solidified metal is 0.45, and the set clearances are 15 and 2.
It is a graph which shows the time-dependent change of the torque which occurs in stirrer 10 when it changes to 3 mm.

It should be noted that when the solid phase ratio of the semi-solidified metal to be discharged is increased, the discharging capacity is lowered, but in this experiment, as shown in FIG.
A paddle / screw composite type stirrer 10 shown in (b) is used to discharge semi-solidified metal having a solid fraction of 0.45.
When discharging the semi-solidified metal having a large solid fraction, it is extremely effective to improve the discharging ability of the semi-solidified metal by the stirrer 10.

As is clear from FIG. 4, when the set clearance is 15 mm, the torque of the stirrer 10 increases with the passage of time, whereas the set clearance is 23 m.
By setting to m, the torque of the stirrer 10 did not increase and the semi-solidified metal could be continuously discharged. As described above, even when the solid fraction is increased, increasing the set clearance can prevent the increase in torque.

In the above, the reason why the torque increase of the stirrer 10 can be prevented by increasing the set clearance (thickening the thickness of the solidified shell growing on the inner surface of the peripheral wall 8 of the cooling tank 6 without increasing the torque of the stirrer 10) Indicates that the severe shear strain at the solid-liquid interface generated by the high-speed rotation of the stirrer 10 gradually increases with the growth of the solidified shell generated on the inner surface of the cooling plate 8 as shown by the following formula (2) ( The clearance with the stirrer 10, that is, the clearance S becomes smaller), and as a result, the stirrer 1
The rotation speed of 0 increases the fragmentation rate of the solidified shell gradually, while the growth rate of the solidified shell decreases with the growth of the solidified shell. This is probably because there is a condition that makes

[Note] γ = 2 · r ₁ · r ₂ · Ω / (r ₂ ² −r ₁ ² ) −− (2) r ₂ = S + r ₁ where γ: solid-liquid interface shear strain rate (s ^-1 ) r ₁ : Stirrer radius (m) r ₂ : Cooling tank (cooling plate) inner diameter (m) Ω: Stirrer angular velocity (rad / s) S: Clearance (m)

Therefore, the increase in the torque generated in the stirrer due to the increase in the set clearance can be prevented because the heat removal rate of the cooling plate 8 and the shear strain rate of the solid-liquid interface are optimized, and the excessive growth of the solidified shell is caused. Probably because it was prevented. This means that the increase in torque generated in the stirrer 10
This means that it can be prevented by adjusting the melt cooling conditions such as the material and thickness of the cooling plate 8 of the cooling tank 6 and the thickness of the solidified shell and the shear strain rate at the solid-liquid interface.

Therefore, as a result of further experimentation, the heat removal rate of the cooling plate 8 and the shear strain rate of the solid-liquid interface are calculated, and based on these calculation results, the cooling plate 8 capable of preventing the torque increase. The relationship between the heat removal rate and the shear strain rate at the solid-liquid interface is shown in FIG.

In the above, the heat removal rate of the cooling plate 8 is calculated from the temperature gradient measured by the thermocouple embedded in the cooling plate 8 and the heat transfer coefficient of the material of the cooling plate 8, and the molten metal 1 injected It was also calculated and confirmed from the temperature drop in the cooling tank 6, the growth behavior of the solidified shell, and the cooling surface area of the cooling plate 8. The shear strain rate at the solid-liquid interface was calculated from the above equation (2) using the device shape, the rotation speed of the stirrer 10 and the clearance S. The clearance S at which the torque started to increase was about 0.8 mm according to the tracer addition test.

The straight line in FIG. 5 thus obtained is a boundary line which can prevent the torque of the stirrer 10 from rising, and the shear strain of the solid-liquid interface required for stopping the growth of the solidified shell according to the respective heat removal rates. The lower limit of the speed is shown, and the straight line is expressed by the following equation (3). [Note] γ = 1.29 (m ² / Kcal) · q ----- (3) where γ: Shear strain rate of solid-liquid interface (s ^-1 ) q: Heat removal rate of cooling plate 8 (heat removal Heat flux) (Kcal / m
²・ s)

Therefore, the growth of the solidified shell when operating in the high shear strain rate region where the torque of the stirrer 10 shown in FIG. 5 does not increase is the reduction of the solidified shell growth rate and the shear strain rate due to the growth of the solidified shell. The increase causes a stop before reaching the boundary line, and the clearance at that time becomes a value larger than 0.8 mm. The above is
It means that the torque increase of the stirrer 10 can be prevented by limiting the thickness of the solidified shell generated and grown on the inner surface of the cooling plate 8 by the set clearance so that the clearance becomes 0.8 mm or more.

As described above, in the production of semi-solidified metal by the stirrer rotation method, the shear strain rate of the solid-liquid interface corresponding to the heat removal rate of the cooling plate 8 is adopted, and the stirrer shown in FIG. In the region where the torque does not increase in 10, that is, the formula (1) is satisfied, and further, the thickness of the solidified shell formed on the inner surface of the cooling plate 8 is limited according to the value of the set clearance. It is possible to prevent the excessive growth of the solidified shell to prevent an increase in the torque of the stirrer 10, and to easily increase the heat removal rate to continuously produce fine primary crystal grains and semi-solidified metal with a high solid fraction. Can handle.

[0032]

【Example】

Example 1 An explanatory view of a semi-solid metal manufacturing apparatus in which an experiment was carried out is shown in FIG. The main configuration of this device includes a hot water receiving tank 5, a cooling tank 6 having a cooling plate 8, a holding tank 7, a stirrer 10, a discharge amount control nozzle 12 (sliding nozzle), and a torque meter 3. In addition, in FIG. 1, 1 is a molten metal, 2 is a stirring motor, 4 is a tundish, 9 is a cooling spray of the cooling plate 8, and 11 is each heater of the hot water receiving tank 5 and the holding tank 7.

The paddle type shown in FIG. 3 (a) is used as the stirrer 10, the semi-solidified metal is produced by the above apparatus, the hot water receiving tank 5 and the holding tank 7 are controlled by the respective heaters 11, and the discharge amount is controlled. After sufficiently preheating the working nozzle 12 with a burner (not shown), the molten metal 1 adjusted to an appropriate temperature is injected from above the device through the tundish 4 to remove heat from the cooling plate 8 of the cooling tank 6 and stir it. The semi-solid metal is generated by stirring by rotating the child 10, and the solid phase ratio of the semi-solid metal discharged is adjusted by controlling the residence time in the cooling tank 6 by the discharge amount control nozzle 12, and discharged. It was carried out by discharging the semi-solidified metal having a desired solid fraction from the amount control nozzle 12.

In the experiment, an Al-10 mass% Cu alloy was used, and the solid phase ratio of the discharged semi-solidified metal was 0.15.
The set clearance, that is, the gap between the cooling plate 8 of the cooling tank 6 and the stirrer 10 was changed to 7, 10 and 15 mm, and the change with time of the torque generated in the stirrer 10 was measured by the torque meter 3. The results are summarized in FIG.

FIG. 2 shows the stirrer 1 in the case where the solid phase ratio of the discharged semi-solidified metal is 0.15 and the set clearance is changed.
8 is a graph showing a change with time of the torque generated at 0 from the start of discharging. It should be noted that the torque generated in the stirrer 10 in FIG. 2 excludes the torque initially generated due to mechanical loss or the like.

As is clear from FIG. 2, the time-dependent change in the torque increase generated in the stirrer 10 varies depending on the set clearance, and there is no increase in the torque generated in the stirrer 10 by setting the set clearance to 15 mm. The semi-solid metal having a solid phase ratio of 0.15 could be continuously discharged.

Example 2 A semi-solid metal was prepared by using the semi-solid metal production apparatus shown in FIG. 1 in the same manner as in Example 1 except that the paddle-screw composite type shown in FIG. Manufactured. In this experiment, the solid phase ratio of the semi-solidified metal discharged using the same alloy as in Example 1 was set to 0.45, the set clearance was changed to 15 and 23 mm, and the change with time of the torque generated in the stirrer 10 was changed. It was measured. These results are summarized in FIG.

FIG. 4 shows the stirrer 1 in the case where the solid phase ratio of the discharged semi-solidified metal is 0.45 and the set clearance is changed.
8 is a graph showing a change with time of the torque generated at 0 from the start of discharging. Note that the torque generated in the stirrer 10 is the torque generated in the initial stage due to mechanical loss or the like as in FIG.

As shown in FIG. 4, even when the solid phase ratio of the discharged semi-solidified metal is 0.45, the stirrer is increased by increasing the set clearance (23 mm) as in the case of the solid phase ratio of 0.15. It was possible to prevent an increase in the torque generated in No. 10 and to continuously discharge the semi-solidified metal having a solid fraction of 0.45.

However, when the solid phase ratio is 0.45, the set clearance that can prevent the torque from increasing is larger than when the solid phase ratio is 0.15. It is considered that the reason for this is that the growth rate of the solidified shell formed on the cooling plate 8 is increased due to the increase of the solid phase ratio.

Example 3 Using the paddle type and the paddle-screw composite type shown in FIGS. 3A and 3B for the stirrer 10, the semi-solid metal production shown in FIG. An experiment was conducted using the device.

This experiment was conducted in accordance with JIS H-5202 AC.
4C, JIS H-5302 ADC12 and JIS
It was performed using three kinds of Al alloys such as H-4000 2024.

The heat removal rate of the cooling plate 8 of the cooling tank 6 is adjusted by changing the set clearance, the amount of cooling water, and the material of the cooling plate 8, and the heat removal rate is the thermocouple embedded in the cooling plate 8. It was calculated from the temperature gradient and the heat transfer coefficient measured by. The shear strain rate at the solid-liquid interface is 10
It adjusted by the number of rotations of and calculated by the said Formula (2). FIG. 5 shows the relationship between the heat removal rate of the cooling plate 8 and the shear strain rate at the solid-liquid interface that can prevent the torque generated in the stirrer 10 from increasing based on the above calculation results.

As is clear from this figure, the increase in the torque generated in the stirrer 10 depends on the heat removal rate of the cooling plate 8, the shear strain rate at the solid-liquid interface, and the increase in the torque shown in FIG. This can be prevented by selecting a range that can be prevented, that is, a range that satisfies the relationship of the above formula (1). Therefore, if operating under the above conditions, the torque of the stirrer 10 does not increase,
The semi-solid metal can be continuously and stably produced.

[0045]

According to the present invention, when a semi-solidified metal is produced by the stirrer rotation method, the shear strain rate of the solid-liquid interface is adjusted according to the heat removal rate (heat removal heat flux) per unit area of the cooling tank cooling plate. By optimizing the increase in torque generated in the stirrer, fine primary crystal grains, high solid fraction semi-solidified metal can be continuously and stably produced,

According to the present invention, a rheoform for directly processing a semi-solidified metal into a product, a thixocast for solidifying the semi-solidified metal and then reheating it into a semi-molten state, and a near net shape in casting, etc. By realizing the above, it is possible to greatly reduce the processing energy, and it is possible to develop new materials that make the best use of the characteristics of semi-solidified metal.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a semi-solidified metal manufacturing apparatus used in an experiment.

FIG. 2 is a graph showing the change over time from the start of discharge of the torque generated in the stirrer when the solid phase ratio of the discharged semi-solidified metal is 0.15 and the set clearance is changed.

FIG. 3 is an explanatory diagram showing the shape of a stirrer used in an experiment. (A) is an explanatory view of a paddle type stirrer. (B) is an explanatory view of a paddle / screw composite stirrer in which a helix screw is attached to the tip of the paddle.

FIG. 4 is a graph showing a change over time from the start of discharge of torque generated in a stirrer when the solid phase ratio of discharged semi-solidified metal is 0.45 and the set clearance is changed.

FIG. 5 is a graph showing a relationship between a heat removal rate of a cooling plate and a shear strain rate capable of preventing a torque increase of a stirrer.

[Explanation of Codes] 1 Molten Metal 2 Stirring Motor 3 Torque Meter 4 Tundish 5 Hot Water Tank 6 Cooling Tank 7 Holding Tank 8 Cooling Plate 9 Cooling Spray 10 Stirrer 11 Heater 12 Emission Control Nozzle

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[Procedure amendment]

[Submission date] June 14, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction content]

[Note] γ = 2 · r ₁ · r ₃ · Ω / (r ₂ ² −r ₁ ² ) −−− (2) r ₃ = r ₂ −d = S + r ₁ where γ: solid-liquid interface Shear strain rate (s ^-1 ) r ₁ : Stirrer radius (m) r ₂ : Cooling tank radius (m) Ω: Stirrer angular velocity (rad / s) S: Clearance (m) r ₃ : Molten metal in cooling tank Radius (m) d: Solidified shell thickness (m) ─────────────────────────────────────── ───────────────

[Procedure amendment]

[Submission date] June 24, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction content]

[Note] γ = 2 · r ₁ · r ₃ · Ω / (r ₃ ² −r ₁ ² ) −−− (2) r ₃ = r ₂ −d = S + r ₁ where γ: solid-liquid interface Shear strain rate (s ^-1 ) r ₁ : Stirrer radius (m) r ₂ : Cooling tank radius (m) Ω: Stirrer angular velocity (rad / s) S: Clearance (m) r ₃ : Molten metal in cooling tank Radius (m) d: Solidified shell thickness (m)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyoshi Takahashi, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Stock Company Rheotec (72) Akihiko Namba 1, Kawasaki-cho, Chuo-ku, Chiba Stock Company In rheotech

Claims (4)

[Claims] 1. A method for producing a semi-solid metal in which a molten metal poured from an upper portion of a cylindrical cooling tank having a cooling plate is cooled while a stirrer is rotated, wherein a heat removal heat flux of the cooling plate and a solid-liquid interface are provided. A method for producing semi-solidified metal, characterized in that it prevents excessive growth of the solidified shell and prevents the torque of the stirrer from rising due to the shear strain rate of. 2. The method for producing a semi-solid metal according to claim 1, wherein the relationship between the heat removal heat flux of the cooling plate and the shear strain rate at the solid-liquid interface satisfies the following formula (1). [Note] γ> 12.9 (m ² / Kcal) · q ----- (1) where γ: Shear strain rate of solid-liquid interface (s ^-1 ) q: Heat removal heat flux of cooling plate (Kcal / m ² · s) 3. The method for producing a semi-solidified metal according to claim 1, wherein the thickness of the solidified shell growing on the inner surface of the cooling plate is limited according to the value of the clearance set between the cooling plate and the stirrer. 4. A stirrer having a spiral screw groove at its tip is used to prevent the rise of torque and accelerate the discharge of semi-solidified metal.
Or the method for producing a semi-solid metal according to item 3.