JP2984065B2 - Method and apparatus for producing semi-solid metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for stably and continuously producing a solid-liquid metal mixture in which non-dendritic primary crystals are dispersed in a metal melt (hereinafter simply referred to as semi-solid metal). The present invention relates to an apparatus used to carry out the method.

[0002] A semi-solid metal is agitated vigorously while cooling a molten metal (generally an alloy) to form dendrites which are being formed in the melt, with the branches disappearing or shrinking and rounded. And mixed with a metal melt in a dispersed manner.

[0003]

2. Description of the Related Art As a method for continuously producing semi-solid metal, for example, as disclosed in Japanese Patent Publication No. 56-20944, high-speed rotation of a stirrer is carried out in a cylindrical cooling and stirring tank. Vigorously agitate while cooling by cooling to change the dendrites that are forming in the molten metal into rounded forms with their branches disappearing or shrinking, dispersing them and mixing them in the metal melt It is well known that the slurry-like semi-solidified metal is continuously discharged from a bottom nozzle of a cooling and stirring tank. However, in this method, the molten metal is introduced into a gap between a stirring rotor having a vertical rotating shaft rotating at high speed and a concentric cylindrical cooling and stirring tank, and a suitable cooling and strong stirring action is applied to the molten metal in the tank to perform a half-turn. It is solidified and continuously discharged as semi-solid metal from the nozzle below, but the cooling rate is limited to 2 ° C / s or less in order to prevent clogging of gaps due to the formation and growth of solidified shells on the cooling surface There were also difficulties in controlling the speed.

[0004]

In order to improve the controllability of discharging semi-solid metal, a stirrer consisting of a cylindrical body rotating around a horizontal axis and a concave curved surface along the outer periphery of the cylindrical body of the stirrer are first described. The raw material molten metal is continuously supplied toward the gap formed between the cooling wall and the cooling wall, and dendrites generated in the gap are crushed by the shearing force based on the rotation of the stirring rotor. Applicant's research and development of a semi-solid metal production method (Japanese Patent Application No. 1-279959) characterized by making fine non-dendritic crystals and thus promoting continuous discharge of semi-solid metal from below the gap In this method, it is easy to give a sufficient cooling rate and stirring effect by selecting the diameter and rotation speed of the stirrer. , Rotating the stirrer in the direction of discharging the semi-solid metal In this case, it is possible to discharge the high-viscosity semi-solid metal having a higher solid fraction because it can promote the discharge flow. The solidification shell forms and grows, which narrows the gap through which the semi-solid metal passes, which may cause a decrease in the discharge rate or blockage of the gap, and the heat removal / cooling rate associated with an increase in heat transfer resistance due to the formation of the solidification shell. However, problems such as a decrease in the quality of the semi-solid metal having a stable quality and operation over a long period of time still remain.

In general, the quality such as the crystal grain size of a semi-solid metal is determined by the cooling rate during its production or the rate of increase of the solid phase ratio per unit time in a coexisting state of solid and liquid (hereinafter simply referred to as solidification rate). It is well known that it is greatly affected by the average value of the change in velocity per unit distance of the fluid which is influenced by the stirring speed (for simplicity, simply referred to as the shear strain rate), the solid fraction, and the like.

It is needless to say that in order to continuously discharge semi-solid metal having poor fluidity stably from the manufacturing apparatus, it is necessary to secure a stable cross-sectional area of the discharge port. Even in a semi-solid metal manufacturing device that combines a fixed cylindrical cylinder with a fixed wall, in order to stably produce and discharge semi-solid metal of a predetermined quality continuously for a long time, solidification in a cooling and stirring tank section is required. It is necessary to prevent shell formation and growth, and to stabilize the heat removal / solidification rate, shear rate, solid fraction, and discharge rate.

[0007] The inventors studied the factors that affect the crystal grains, solid fraction, and discharge rate of the semi-solid metal discharged from the above-mentioned semi-solid metal production apparatus, and stably and continuously discharge the target semi-solid metal. With this in mind, the research and development was advanced, and the present invention was reached.

[0008]

In general, the apparent viscosity, which is an index of the fluidity of a semi-solid metal, is determined by the degree of suspension in a melt, that is, the solid fraction, as shown in FIG. It is greatly affected by the rate of solidification and the rate of shear strain. In other words, the higher the solid fraction, the higher the viscosity, and there is an upper limit solid fraction that can flow, but this limit solid fraction is higher as the solidification rate during semi-solid metal production is higher, and the shear strain rate is lower. It turns out that it gets smaller. Therefore, the solidification rate or viscosity of the semi-solid metal that can be discharged from the solidification rate and shear strain rate of the device characteristics of the semi-solid metal production apparatus, the discharge rate, the shape of the discharge port, etc. are naturally determined, and therefore, The semi-solid metal having a solid phase ratio or viscosity that can be discharged cannot be discharged.However, the present invention increases the solid phase ratio or viscosity that can be discharged and semi-solidified at a predetermined solidification rate or solid phase ratio. It is an object of the present invention to provide a method for producing a semi-solid metal capable of continuously discharging metal stably for a long period of time and an apparatus for producing a semi-solid metal used for carrying out the invention.

The inventors have studied various solidification rates, stirring conditions,
An experiment was conducted on the production of semi-solid metal in the form of slurry under the discharge condition. As a result of the elucidation, the above problem was solved by selecting the heat removal method of the cooling and stirring part so as to enable stable discharge, and furthermore, by using a jig to remove the solidified shell generated on the heat removal surface Can be advantageously solved. That is, in the method of the present invention, the molten metal is continuously fed into a gap formed between a stirrer formed of a cylindrical body rotating around a horizontal axis and a fixed wall formed of a concave curved surface along the outer periphery of the cylindrical body of the stirrer. To produce a semi-solid metal in which fine non-dendritic primary crystals are suspended by shearing force based on rotation of a stirrer while causing solidification by forced cooling in the gap. In the semi-solid metal manufacturing method of continuously discharging, the forced cooling is performed by removing heat from the cylindrical body of the stirrer, and the concave curved surface of the fixed wall is insulated. It is more advantageous to scrape off the solidified shell solidified and adhered to the peripheral surface of the cylindrical body of the stirrer at the discharge port where the semi-solid metal is continuously discharged from below the gap. And the device of the present invention rotates about a horizontal axis. A stirrer consisting of a cylindrical drum that,
The stirrer has a concave surface along the peripheral surface of the cylindrical body, and the concave surface has a fixed wall having a gap formed between the concave surface and the cylindrical body peripheral surface. The molten metal is continuously supplied to the gap. Of the semi-solid metal which is crushed by the shearing force based on the rotation of the stirrer to crush the dendrites formed in the molten metal and disperse the particles of the crushed pieces as a semi-causing metal from the gap while dispersing the particles in the melt In the manufacturing apparatus, the semi-solid metal manufacturing apparatus, wherein the cylindrical body of the stirrer is formed of a cooling surface that controls heat removal from the molten metal, while the concave curved surface of the fixed wall is formed of an abandoned surface. It is more preferable that a jig for separating the solidified shell which is solidified and attached to the cylindrical body of the child facing the cylindrical body is arranged on the exit side of the gap.

FIG. 2 illustrates the structure of a semi-solid metal manufacturing apparatus used for carrying out the method of the present invention. In FIG. 2, 1 is a stirrer, 2 is a fixed wall, 3 is a refractory side wall, and 4 is a refractory. Inner wall 5 is a peeling jig, and 6 is an adjusting drive for fixed wall 2, 7
Is a slab, 8 is a solidified shell, 9 is a molten metal, 10 is a semi-solidified metal,
11 is an outlet, 12 is a cooling water system, 13 is a heater for heating, 14
Is a ladle, 15 is an injection nozzle, 16 is a forming roll, 17 is a thermocouple, and 18 is an adjustment driving device for the peeling jig 5.

In the illustrated example, the refractory inner wall 4 is
A concave curved surface of the fixed wall 2 is formed along the outer peripheral surface of the cylindrical body of the above, and serves as a heat insulating surface of the fixed wall 2.

[0012]

[Function] In a device using a stirrer with a fixed wall and a horizontal rotating shaft, the heat transfer analysis and the formation of solidified shell during cooling and agitation in the continuous production of semi-solid metal were investigated. It is evident that some fixed walls and rotors have solidified or semi-solidified shells on both cooling surfaces, which can lead to fluctuations in the solidification rate and discharge cross-section of the semi-solid metal, causing the grain size to change. It was found that the ratio greatly affected the solid phase ratio and the discharge rate.

That is, when solidified shells or semi-solidified shells are formed on the cooling surface, they become heat transfer resistances, thereby removing heat, lowering the cooling rate, causing fluctuations in crystal grain size, and reducing the cross-sectional area of the discharge port. Due to the decrease, the discharge rate is reduced or the blockage is caused, so that stable production of semi-solid metal having a predetermined crystal grain size and solid fraction and stable discharge at a predetermined discharge rate are impossible.

Therefore, the solidification rate, shear strain rate, discharge solid phase ratio and discharge rate of the semi-solid metal of the semi-solid metal production apparatus are accurately and stably controlled to continuously discharge as a predetermined semi-solid metal. For this purpose, it is necessary to stabilize the heat removal amount and the discharge speed during the cooling and stirring of the molten metal.

That is, it is necessary to prevent the thickness of the solidified shell formed on the cooling surface from excessively growing and to keep the thickness constant, and to prevent the outlet of the semi-solid metal from shrinking or closing due to the growth of the solidified shell. is there.

Therefore, the fixed wall is made of a heat insulating material or a heat insulating structure so that no solidified shell or semi-solidified shell is formed on the fixed wall, and the cooling and heat removing function is exclusively provided only by the stirrer. The solidified shell formed on the shell surface is cut and peeled by a cutting tool in the form of a bite facing the shell surface on the outlet side of the outlet, so that the cooling heat removal conditions and the outlet cross-sectional area are always constant. Was found to be kept.

As already mentioned with reference to FIG. 1, the fluidity of the semi-solid metal during cooling and stirring deteriorates as the solid phase ratio increases, and the discharge speed decreases even with the same opening of the discharge port.
In order to ensure a predetermined discharge speed, it is necessary to increase the cross-sectional area of the discharge port, that is, the distance between the fixed wall of the discharge port and the stirrer, depending on the solid phase ratio of the semi-solid metal.

Therefore, based on the temperature measurement value of the discharged semi-solid metal by the thermocouple installed at the discharge port, the discharged solid phase ratio is converted based on the equilibrium diagram, and at the same time, the load torque of the stirrer is simultaneously converted to the driving device. The discharge rate is measured by a torque detector (not shown) installed in the apparatus, and the rotation speed of a forming roll or a load cell (not shown) attached to a semi-solid metal receiving vessel is measured. Is to move the fixed wall in the radial direction of the stirrer according to the torque value and the discharge speed, and adjust the clearance between the fixed wall at the discharge port and the rotor to an opening that provides the predetermined solid fraction and discharge speed. Accordingly, the semi-solid metal having a predetermined solid fraction can be stably and continuously discharged at a predetermined discharge rate.

Thus, the above problems are solved, troubles such as clogging of the semi-solid metal can be avoided, and the operation is facilitated, so that the target semi-solid metal can be continuously and stably produced. Was.

Next, the operation of the apparatus for producing semi-solid metal according to the present invention will be described in more detail with reference to FIG. The apparatus of the present invention comprises a stirrer 1 having a cylindrical body rotatable around a horizontal axis having an internal cooling function, a fixed wall 2 made of a heat insulating material or a heat insulating structure having a refractory inner wall 4 lined as shown in the drawing. The refractory side wall 3 which serves to store the molten metal, the peeling jig 5 which cuts and removes the solidified or semi-solidified shell 8 which adheres and solidifies around the stirrer 1 at the discharge port 11, It mainly comprises an adjusting drive device 6 for the fixed wall 2 which changes the gap size.

Although not shown, the stirrer 1 is rotated by a drive source that is operatively connected to its rotating shaft, and the refractory inner wall 4 of the fixed wall 2 is rotated.
A stirrer effect is given to the semi-solid metal being cooled in the gap between the stirrer 1 and the primary crystal particles having a fine non-dendritic shape. The diameter of the stirrer 1 is determined by the amount of discharged semi-solid metal and the cooling capacity. The stirrer 1 is internally connected to a cooling water system to cool the molten metal 11 between the stirrer 1 and the fixed wall 2 and directly perform forced cooling to a semi-solid metal.

At the discharge port 11 for discharging the semi-solid metal 12, a solidified shell or semi-solidified shell 8 solidified and adhered around the rotating stirrer 1 by means of a cutting tool 5 made of heat-resistant tool steel or the like. To facilitate separation and discharge of the discharged semi-solid metal from the stirrer 1. The refractory side wall 3 forms a molten metal reservoir for allowing a variation in the injection amount of the injected molten metal 11 and also has a refractory inner wall 4 so as to prevent leakage of the molten metal on both sides of the stirrer 1.
The stirrer 1 is in close contact with the fixed wall 2 and has a sliding structure with both end surfaces of the stirrer 1.

The molten metal 11 transported in the ladle 14 is supplied to the gap between the stirrer 1 and the fixed wall 2 through the injection nozzle 15. The supplied molten metal 11 is given a strong shearing force by the stirrer 1 while the temperature is lowered by the heat removal from the water-cooled stirrer 1, and a slurry-like semi-solidified metal in which fine non-resinous crystals are suspended. It is discharged from outlet 9 as 12.

At this time, based on the temperature measurement value of the discharged semi-solid metal by the thermocouple 17 installed at the discharge port, the discharged solid phase ratio is calculated based on the equilibrium diagram, and preferably, the stirrer 1 is fixed at the same time. By detecting the load torque rotated at the speed by a torque detector, and calculating the discharge speed of the discharged semi-solid metal, for example, by measuring the rotational speed of the forming roll,
The fixed wall 2 is moved and adjusted in the radial direction of the stirrer 1 by operating a hydraulic or electric driving device or the like via an indicator and a controller according to the solid phase ratio, the load torque value and the discharge speed, and fixed. The gap between the wall 2 and the stirrer 1 is adjusted to an optimum gap for the semi-solid metal 12 to pass.

By doing so, the semi-solid metal having a fixed solid fraction can be discharged at a stable discharge speed, and blockage in the apparatus can be avoided. It is desirable to install a heater 13 on the fixed wall 2 in order to enhance its heat insulating effect.
It is also possible to adjust the discharge solid phase ratio by the heater 13.

In order to protect the surface of the stirrer 1 which comes into contact with the molten metal 11, a part of the solidified shell 8 attached to the rotor 1 can be left. It is desirable to provide a driving device 18 for adjusting the distance from the device 1.

At this time, the rotation of the stirrer 1 is controlled by the semi-solid metal.
While rotating so as to promote the discharge flow of 12, the solidified shell and semi-solid metal adhered to the periphery of the stirrer 1 are separated and discharged by the separation jig 5, and the surface condition of the stirrer 1 and the cross section of the discharge port are always the same. Since the state is maintained, the heat removal conditions and the discharge speed are uniform, and the continuous and more stable discharge of the semi-solid metal with high viscosity becomes possible.

By fixing a separation jig 5 for cutting and removing the solidified shell of the molten metal which solidifies and adheres to the cooling surface of the stirrer 1 at a distance of preferably 2 mm or less from the cooling surface of the cylindrical body, the solidification is performed. Leaving a part of the adhered solidified shell as a self-coating of the metal solidified shell on the surface of the stirrer 1 prevents damage due to reaction with the molten metal or semi-solidified metal and extends the life of the stirrer 1. Can be measured.

[0029]

EXAMPLE 1 A semi-solid metal manufacturing apparatus having a gap of 5 mm at the discharge port between the refractory inner wall 4 of the fixed wall 2 and the stirrer 1 at the discharge port shown in FIG. A molten alloy of Cu alloy is poured, and while stirring a stirrer 1 having an outer diameter of 400 mm at 250 rpm (shear strain rate = 530 / s), cooling is performed under the condition that the average solidification rate during solidification becomes 3.0% · s ⁻¹ , The temperature of the semi-solid metal flowing out from the outlet 11 at the bottom of the apparatus was continuously measured by the thermocouple 17, and the solid phase ratio converted from the temperature based on the equilibrium diagram, 25% of the semi-solid metal was discharged. As a result, a semi-solid metal was continuously and stably produced, and the metal was discharged without stagnation of the flow.

Embodiment 2 A semi-solid metal producing apparatus in which the distance between the refractory inner wall 4 of the fixed wall 2 and the stirrer at the discharge port 11 shown in FIG. And stir bar 1
While rotating at 0 rpm (shear strain rate = 319 / s), cooling is performed under the condition that the average solidification rate during solidification is 0.45% · s ^−1, and the separation jig 5 and the stirrer 1 for cutting and removing the solidified shell are removed. Self-coating of 1mm solidified shell on the rotor surface with a 1mm gap between the rotors resulted in stable production of a semisolid metal with a solid phase ratio of 32% by temperature conversion of the semisolid metal at the outlet 11 at the bottom of the device. The discharge was successful.

FIG. 3 shows the change in the solid fraction and the discharge rate over time during the production of the semi-solid metal of Example 1 according to the present invention in comparison with a comparative example. In the example of the present invention, the solid phase ratio and the discharge speed are stable, but in the comparative example, the discharge is stopped due to fluctuations in the solid phase ratio and the discharge speed and clogging in the tank.

[0032]

The method of producing a semi-solid metal according to the present invention has the following effects. (1) Operation with strong cooling and operation with an optimum minimum gap from the stirrer effect and stable operation surface become possible, so that the cooling rate can be increased to 3 ° C / s or more, and fine non-dendritic , And semi-solid metal having excellent characteristics can be produced. Particularly, since strong cooling is possible, the production capacity is large and practical.

(2) Since the stirring is performed with the optimum minimum gap, a sufficient stirring effect can be obtained even if the rotation speed is lower than in the prior art, and the danger of gas entrainment accompanying high-speed rotation can be obtained.
And all problems on the structure, strength and safety aspects of the device are solved.

(3) Since the operation can be performed while maintaining the optimum minimum gap and the optimum cooling rate, the quality of the semi-solid metal is stabilized.

(4) It is possible to cope with the formation of a solidified shell due to excessive heat removal in an unsteady state at the start of the operation, which facilitates the operation. Further, even during long-time continuous operation, there is no accident such as fusing or clogging of semi-solid metal in the apparatus, and stable operation is possible.

(5) In the case where a semi-solid metal is supplied to a twin-roll caster for casting, the semi-solid metal can be uniformly supplied in the width direction of the stirrer. Can be manufactured.

(6) The self-coating of the solidified shell can be performed on the surface of the stirrer under severe operating conditions, so that the life of the stirrer can be extended and the flexibility of selecting the stirrer material can be increased.

(7) Even a semi-solid metal continuous production apparatus with a high solidification rate, which has a poor fluidity and tends to be clogged in the apparatus, can be produced stably and continuously and can be discharged. Therefore, the semi-solid metal is discharged from the semi-solid metal manufacturing apparatus, and there is no accident such as blockage in the apparatus with respect to transfer to the subsequent apparatus or the discharge and transfer to the holding apparatus in the next process, the casting machine and the processing apparatus, Stable operation is possible.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a solid fraction of a semi-solid metal and an apparent viscosity.

FIG. 2 is an explanatory view showing a semi-solid metal continuous production apparatus used in an embodiment of the present invention.

FIG. 3 is a graph showing a relationship between a solidification rate and a shear strain rate with respect to a discharge elapsed time, a discharge rate, and a discharged solid fraction in Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stirrer 2 Fixed wall 3 Refractory side wall 4 Refractory inner wall 5 Peeling jig 6 Fixed wall adjusting drive 7 Cast piece 8 Solidified shell 9 Molten metal 10 Semi-solid metal 11 Outlet 12 Cooling water system 13 Heater 14 Ladle 15 Injection nozzle 16 Forming roll 17 Thermocouple 18 ... Driving device for peeling jig

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B22D 11/00 B22D 11/04 314 B22D 11/06 310 B22D 11/10

Claims (4)

(57) [Claims] 1. A molten metal is continuously supplied to a gap formed between a stirrer having a cylindrical body rotating around a horizontal axis and a fixed wall having a concave curved surface along the outer periphery of the cylindrical body of the stirrer. Then, a semi-solid metal in which fine non-dendritic primary crystals are suspended is produced by shearing force based on rotation of the stirrer while solidifying by forced cooling in the gap, and the solid is continuously formed from below the gap. Wherein the forced cooling is carried out by removing heat from the cylindrical body of the stirrer, and the concave curved surface of the fixed wall is insulated. 2. A solidification shell solidified and adhered to a peripheral surface of a cylindrical body of a stirrer is scraped off by a peeling jig at an outlet for continuously discharging the semi-solidified metal from below the gap. A method for producing a semi-solid metal according to claim 1. 3. A stirrer comprising a cylindrical body rotating around a horizontal axis, and a concave surface along the peripheral surface of the cylindrical body of the stirrer, wherein the concave surface is provided between the concave surface and the cylindrical body peripheral surface. It has a fixed wall with a gap, and continuously supplies molten metal to this gap to crush dendrites generated in the molten metal by shearing force based on the rotation of the stirrer, and to melt particles of the crushed pieces. In a semi-solid metal producing apparatus for discharging as a semi-solid metal from the gaps while dispersing the molten metal in the body, the cylindrical body of the stirrer comprises a cooling surface for controlling heat removal from the molten metal, while a concave curved surface of the fixed wall. Is an apparatus for producing semi-solid metal, which consists of heat insulating surfaces. 4. The semi-solid metal according to claim 3, wherein a jig for separating a solidified shell attached to the cylindrical body of the stirrer facing the cylindrical body of the stirrer is disposed on the exit side of the gap. Manufacturing equipment.