JPH07115123B2 - Method and apparatus for continuously producing semi-solid metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is a solid-liquid metal mixture in which non-dendritic primary crystals are dispersed in a metal melt (for simplicity, simply referred to as semi-solid metal). ) And a device therefor for continuously producing a).

Semi-solid metal is a dendritic crystal that is being formed in the melt by vigorously stirring molten metal (generally an alloy) while cooling it.
The branches are eliminated or shrunk, crushed into a rounded shape, separated, and mixed with the metal melt.

This semi-solid metal is superior in characteristics as the non-dendritic primary crystal grains in the metal melt are finer, for example, in the casting operation and the quality of the cast product in the downstream elevation where the semi-solid metal is used. Therefore, in the production of semi-solidified metal, the stirring effect is so strong that dendrites disappear or shrink, and they are crushed and separated into fine non-dendritic crystals in a rounded form.

 Strong cooling effect that can make the cooling rate as high as possible.

The following two conditions are essential.

(Prior Art) Japanese Patent Publication No. 56-20944 discloses an apparatus for continuously producing semi-solid metal, but still has various drawbacks.

That is, this device supplies molten metal to a heat-retaining tank and, while maintaining it at a constant temperature, introduces it into a gap between a stirring rotor having a vertical rotating shaft that rotates at high speed and a concentric cylindrical cooling stirring tank,
In this tank, appropriate cooling and strong stirring action are applied to make a semi-solidified state, and the semi-solidified metal is continuously discharged from the lower nozzle, but this device is industrially limited due to structural restrictions. On a large scale, the cooling rate remains below 1 ° C / sec, the stirring strength also requires a maximum shear strain rate of 450 sec ^-1, and there is a difficulty in temperature control. I couldn't do it.

(Problems to be Solved by the Invention) The problems found by the inventors regarding the above-mentioned conventional techniques are as follows.

In order to enhance the stirring effect, it is effective to increase the rotation speed of the stirring rotor or to reduce the gap between the cooling stirring tank and the stirring rotor, but increase the rotation speed of the stirring rotor. That is, the tendency of the melt to separate from the stirring rotor due to centrifugal force increases, the risk of gas entrapment increases, and there is a limit due to structural strength restrictions.

On the other hand, if the gap is made small, the solidification shell is likely to be formed and the viscous resistance is increased.

If you use strong cooling means to increase the cooling speed,
A solidification shell is formed on the cooling cotton, which causes fusion with the stirring rotor and renders it inoperable.

During unsteady heat transfer such as at the start of operation, temperature control is difficult, and excessive cooling may cause fusion on the stirring rotor, making stable operation difficult.

When discharging semi-solidified metal under gravity, the force that allows the semi-solidified metal to pass through the gap between the cooling and stirring tank and the stirring rotor is only the pressure due to gravity, and the solid phase ratio of the semi-solidified metal increases and the viscosity increases. If it does, it cannot be discharged.

As described above, the present invention aims to effectively solve various problems remaining in the conventional technique, and enhances the stirring effect in order to produce a semi-solid metal having excellent quality.

 To increase the cooling rate.

In addition, it should be possible to continuously and easily discharge a homogeneous semi-solid metal that is free from gas entrainment.

The present invention has been achieved through development and research with the priority items such as.

(Means for Solving the Problems) Generally, the stirring effect is proportional to the rotation speed of the stirring rotor, but the larger the diameter of the stirring rotor, the smaller the gap between the cooling wall and the stirring rotor. In addition, in addition to obtaining a sufficient stirring effect without requiring high-speed rotation, in the conventional technique, the gap between the cooling wall and the stirring rotor cannot be arbitrarily controlled during operation, and, Focusing on the fact that the force of discharging semi-solidified metal is only gravity, the invention was completed.

That is, in the prior art, while the rotating shaft uses the stirring rotor whose vertical axis is the vertical axis, in the present invention, the horizontal axis stirring rotor is used, and the gist thereof is as follows. .

1. The raw material molten metal is continuously supplied to the gap formed between the stirring rotor composed of the horizontal axis rotating cylinder and the cooling wall composed of the concave curved surface along the circumference of the stirring rotor. The dendrites generated in the gap are crushed by a shearing force based on the rotation of the stirring rotor, and are continuously discharged from below the gap as non-dendritic primary crystals having fine particles. Method for producing semi-solid metal.

2. In an apparatus for producing semi-solidified metal in a gap formed between a stirring rotor made of a rotating cylinder and a cooling wall having a concave curved surface along the circumference of the stirring rotor, the stirring rotor is used. An apparatus for producing semi-solidified metal, wherein the axis of rotation of the is the horizontal axis.

The above method is preferably carried out so as to optimally adjust the gap by detecting the load torque of the stirring rotor,
In the above device, a torque detector is provided on the rotating shaft of the stirring rotor to adjust the clearance between the stirring rotor and the cooling wall. In any case, it is preferable to heat the molten metal from the rotor side.

(Operation) Since the rotation axis of the stirring rotor including the rotating cylinder is the horizontal axis, it is easy to increase the diameter of the stirring rotor. By increasing the diameter, the rotation of the stirring rotor is increased. It is possible to give a strong stirring effect without increasing the number at a high speed, and since the area for cooling the molten metal can be increased, rapid cooling is also possible. Therefore, sufficient cooling and stirring effects can be provided while adjusting and maintaining the optimum gap for discharging the semi-solidified metal.

Further, the discharging force of the semi-solidified metal is not only gravity, but the rotation of the stirring rotor is rotated so as to promote the flow of the semi-solidified metal. Highly viscous semi-solidified metal with high solid fraction can be discharged. Therefore, it is easy to start operations,
Problems such as blockage of semi-solid metal can be avoided and stable steady operation can be achieved.

Furthermore, when supplying and casting the semi-solidified metal to a twin roll casting machine in the next step, in the conventional apparatus, it was very difficult to uniformly supply the semi-solidified metal between the rolls, but according to the present invention, Since the discharged semi-solidified metal is uniform in the longitudinal direction, it is possible to easily perform casting with a twin roll casting machine.

Next, a specific configuration of the semi-solidified metal producing apparatus according to the present invention will be described with reference to FIG.

The apparatus of the present invention comprises a stirring rotor 1 having a horizontal axis rotating cylinder,
Cooling jacket 2 having a cooling wall 2 ', refractory 3 for molten metal reservoir, side support refractory 4, discharge refractory 5,
It comprises a drive mechanism 6 for adjusting the gap between the cooling wall 2'and the stirring rotor 1 and a rotation driving mechanism 7 for the stirring rotor.

The stirring rotor 1 is rotated by a driving mechanism 7 to give a stirring effect to the semi-solidified metal being cooled and to uniformly disperse fine non-dendritic primary crystal grains. This stirring rotor 1
The diameter of is determined from the amount of semi-solid metal discharged and the cooling capacity. Normally, the outer surface of the stirring rotor 1 is coated with a refractory material so as to have a heat insulating structure. However, when the cooling rate of the semi-solidified metal is increased, an internally cooled metallic stirring rotor can be used.

The cooling jacket 2 having the cooling wall 2 ′ has cooling water inside.
In order to forcibly cool the molten metal to the semi-solidification temperature by flowing 10 and to adjust the gap between the stirring rotor 1 and the cooling wall of the cooling jacket 2, the hydraulic pressure that can move in the radial direction of the stirring rotor 1 is used. It is connected to the drive mechanism 6.

The refractory wall 3 above the cooling jacket 2 is filled with injected molten metal 8
It is used to form a molten metal reservoir to cover the variation of the injection amount of the. The side-supporting refractory wall 4 used to prevent molten metal from leaking from the side surface is in close contact with the side surface of the cooling jacket 2 and has a sliding structure with the stirring rotor with a very small gap. .

The refractory 5 in the discharge part is composed of a front wall 5 ′ and a rear wall 5 ″ along the longitudinal direction of the stirring rotor 1 to uniformly discharge the semi-solid metal in the longitudinal direction of the stirring rotor 1. Used for.

Now, the molten metal carried in the ladle is fed through the injection nozzle into the gap between the stirring rotor and the cooling wall. The molten metal supplied is given a strong shearing force by the stirring rotor while the temperature drops due to heat removal from the water-cooled cooling wall,
The semi-solid metal is uniformly discharged from the discharge nozzle in the longitudinal direction. At this time, by rotating the rotation of the stirring rotor so as to promote the flow of the semi-solidified metal (direction of arrow A in FIG. 1), the discharging force by this rotation is added to the discharging force by gravity, so that high viscosity is obtained. The semi-solidified metal can be easily discharged.

The stirring rotor rotates at a constant speed, and its load torque is detected by a torque detector, and the cooling jacket is moved in the radial direction of the stirring rotor by operating the hydraulic unit and hydraulic cylinder via the support gauge and controller. The gap between the cooling wall and the stirring rotor is adjusted to the optimum passage gap for the semi-solidified metal. By doing this,
It is possible to discharge semi-solidified metal having a constant viscosity, and it is possible to avoid clogging of the semi-solidified metal in the device due to rapid changes in cooling conditions.

The behavior occurring in the cooling and stirring tank constituted by the cooling wall and the stirring rotor will be described with reference to FIG. In the present invention, in order to increase the cooling rate as much as possible, a copper plate 2'is used for the cooling wall of the cooling jacket 2 and rapid cooling can be achieved by passing cooling water at high speed to the back surface thereof. The molten metal 8 that enters the gap between the cooling wall 2'and the stirring rotor 1 comes into direct contact with the cooling wall 2'and is forcibly cooled to form a solidified shell 9. This solidified shell 9 The thickness d is determined by the balance between the cooling capacity and the stirring effect, and is extremely unstable during operation, and tends to be thick at the start.

On the other hand, the stirring effect provided by the rotation of the stirring rotor 1 is proportional to the peripheral speed of the stirring rotor and inversely proportional to the clearance, and is generally expressed as a function of shear strain rate.

The rotation speed of the stirring rotor is 10 m / s at the peripheral speed due to the entrainment of gas by centrifugal force and the structural strength of the device.
The above is generally difficult, and high-speed rotation is not preferable in terms of safety. Therefore, in order to give a sufficient stirring effect, it is most practical to maintain an appropriate molten metal gap (in FIG. 2, meaning gap (c) on apparatus-thickness (d) of solidified shell). Is the way.

By the way, when the solidified shell 9 is formed to have a thickness (d) by performing strong cooling, the actual clearance becomes narrower (cd) than the clearance (c) on the apparatus. If this gap is very unstable and becomes too narrow, the viscosity of the semi-solidified metal will increase and excessive torque will be generated in the stirring rotor, which may cause fusion between the stirring rotor and the semi-solidified metal. There is. Therefore, in the past, the clearance (c) was selected to be large in view of safety in design, so that a sufficient stirring effect could not be provided.

On the other hand, in the present invention, since the cooling jacket 2 is movable in the radial direction of the stirring rotor and the clearance (c) can be controlled arbitrarily, a sufficient stirring effect can be provided. Is.

(Example) An example in which a semi-solid metal is manufactured according to the present invention and continuously cast by a twin roll casting machine is illustrated in FIG.

The molten metal in the ladle is 500 mm in radius and 1 in length with the injection nozzle.
It is supplied to a gap of about 10 mm between the stirring rotor consisting of a 000 mm cylinder and the cooling wall made of copper (changed by detecting the load torque of the stirring rotor), and by the stirring rotor rotating at 100 rpm.
A shear strain rate of 190 sec ^-1 is applied, and cooling of the copper cooling wall ejects semi-solidified metal with a solid fraction of 0.3. On the other hand, the discharged semi-solidified metal was cast by a twin roll casting machine with a roll radius of 300 mm and a length of 700 mm, and a slab with a plate thickness of 3 mm and a width of 500 mm could be manufactured.

FIG. 4 shows the effect obtained by controlling the gap between the stirring rotor and the cooling wall. The dotted line in the figure shows the fluctuation of the load torque applied to the stirring rotor and the discharge speed of the semi-solidified metal when the gap is not controlled and is kept constant at 10 mm. The load torque fluctuates due to the temperature fluctuation of the supplied molten metal and the heat removal fluctuation of the cooling wall, and finally the load torque increases and it becomes impossible to discharge. On the other hand, as indicated by the solid line, if the method of detecting the load torque of the stirring rotor, which is a feature of the present invention, and controlling the gap is adopted, the load torque is maintained substantially constant during operation, and the solid phase ratio is 0.3. The semi-solidified metal is constantly discharged.

(Effects of the Invention) The method and apparatus for producing semi-solidified metal according to the present invention exert the effects listed below.

(1) The operation with strong cooling and the operation with the optimum minimum gap from the viewpoint of stirring effect and stable operation are possible, so that the cooling rate can be increased to 10 ° C / sec or more and fine non-dendritic It is possible to produce a semi-solidified metal having excellent properties, which is composed of primary crystal particles that exhibit the following characteristics. Particularly, strong cooling is possible, which increases the production capacity and is practical.

(2) Since the stirring is performed in the optimum minimum clearance, a sufficient stirring effect can be obtained even if the rotation speed is slower than that of the prior art, and there is a risk of gas entrainment due to high speed rotation, and the structure and strength of the device. And all safety issues are resolved.

(3) Since the operation can be performed while maintaining the optimum minimum gap, the quality of the semi-solidified metal is stable.

(4) It is possible to cope with the formation of excessive solidification shell at the start, and the operation can be started easily. In addition, even when operating continuously for a long time, the operation is performed while controlling the load torque to be constant, so there is no accident such as blockage of semi-solidified metal in the equipment or fusion to the stirring rotor, and stable operation is possible. is there.

(5) In the case of supplying and casting semi-solidified metal to a twin roll casting machine, there is not much restriction in the longitudinal direction of the stirring rotor, and the semi-solidified metal can be uniformly supplied in the longitudinal direction. It is possible to manufacture a thin plate that is homogeneous and has excellent characteristics.

[Brief description of drawings]

FIG. 1 is an overall explanatory view showing the structure of the present invention in a cross section of the main part, FIG. 2 is an enlarged view showing the action of a cooling and stirring part according to the present invention, and FIG. 3 is an embodiment of the present invention. It is sectional drawing shown. FIG. 4 is a diagram showing the effect when the clearance is controlled so that the load torque of the stirring rotor during operation is constant. The symbols shown in FIGS. 1 to 3 are as follows. 1 ... Stirring rotor, 2 ... Cooling jacket 2 '... Cooling wall 3 ... Molten metal reservoir refractory wall 4 ... Molten metal reservoir side refractory wall 5 (5', 5 ") Refractory wall for discharge nozzle 6 …… Hydraulic cylinder for gap adjustment 7 …… Stirring rotor drive 8 …… Supply molten metal, 8 ′ …… Melted metal in ladle 9 …… Solidification shell, 10 …… Semi-solidification Metal 11 …… Cooling water, 12 …… Ladle 13 …… Twin roll caster, 14 …… Slab A …… Rotating direction of stirring rotor c …… Gap between cooling wall and stirring rotor d… ... Thickness of solidified shell

Claims (5)

[Claims] 1. A molten metal as a raw material is continuously directed toward a gap formed between a stirring rotor having a horizontal axis rotating cylinder and a cooling wall having a concave curved surface along the circumference of the stirring rotor. The dendritic crystals generated in the gap are crushed by the shearing force based on the rotation of the stirring rotor, and are continuously discharged from below the gap as non-dendritic primary crystals with fine particles. A method for producing a semi-solidified metal characterized. 2. The method for producing a semi-solid metal according to claim 1, wherein the gap is optimally adjusted by detecting the load torque of the stirring rotor. 3. An apparatus for producing semi-solidified metal in an apparatus for producing semi-solidified metal in a gap formed between a stirring rotor composed of a rotating cylinder and a cooling wall composed of a concave curved surface along the circumference of the stirring rotor. An apparatus for producing semi-solidified metal, wherein the axis of rotation of the rotor for use is the horizontal axis. 4. The torque detector is provided on the rotary shaft of the stirring rotor, and the gap between the stirring rotor and the cooling wall is adjusted by the torque detector. Manufacturing equipment for semi-solidified metal. 5. The semisolid metal according to claim 3 or 4, wherein the inside of the stirring rotor has a cooling structure, and the molten metal is removed from the side of the stirring rotor. Manufacturing equipment.