JP2735843B2 - Apparatus for continuous production of semi-solid metal - Google Patents

Description

The present invention relates to a method for continuously producing a solid-liquid metal mixture in which non-dendritic primary crystals are dispersed in a metal melt (referred to as semi-solid metal for simplicity). The present invention relates to an apparatus for manufacturing.

(Conventional technology) As for an apparatus for continuously producing semi-solid metal, as disclosed in Japanese Patent Publication No. 56-20944, while maintaining molten metal supplied to a heat retaining tank at a constant temperature, a cylindrical shape is obtained. Guided to the gap with the high-speed rotating stirrer in the cooling stirring tank,
A vigorous stirring action is applied under an appropriate cooling action to form a semi-solid state, and the metal is continuously discharged as a semi-solid metal from a nozzle at the bottom.

This semi-solid metal transforms dendrites, which are being formed in the melt by vigorous stirring while cooling the molten metal (generally an alloy), into a rounded form with its branches disappearing or shrinking. It is formed by doing.

The non-dendritic primary crystals in the semi-solid metal have better characteristics as the particle size is smaller. Therefore, as a device for producing a semi-solid metal, a strong cooling effect that allows the cooling rate to be as high as possible.

A strong stirring effect to the extent that dendrites can be converted to non-dendrites in a rounded form by eliminating or shrinking the branches.

These two conditions are indispensable, but various disadvantages still remain in the conventional semi-solid metal production apparatus described above for such conditions.

(Problems to be Solved by the Invention) The apparatus described in the above-mentioned Japanese Patent Publication No. 56-20944 has a cooling rate of 1 ° C./sec or less and a stirring strength of about 450 sce ⁻¹ at maximum in shear strain rate due to structural restrictions. In addition, there was a problem in temperature control, and in practice, very good results were not obtained. The problems that the inventors have investigated and found about this are as listed below.

(1) If a strong cooling means is used to increase the cooling rate, a solidified shell is formed on the cooling surface, causing sticking of the stirrer and making operation impossible.

(2) In order to enhance the stirring effect, it is effective to increase the rotation speed of the stirrer or to reduce the gap between the cooling stirrer and the stirrer. The centrifugal force increases the tendency to move away from the stirrer, increasing the risk of entrainment of the gas and limiting the structural strength, while reducing the gap results in the formation of a solidified shell and winning. For practical reasons, it cannot be made very small because of the increase in viscous resistance.

(3) At the time of unsteady heat transfer, such as at the start of operation, there is a possibility that the stirrer sticks due to excessive cooling, and it is difficult to start the operation stably at high temperature, and it is difficult to control the temperature.

(Means for Solving the Problems) Generally, the stirring effect is proportional to the number of revolutions of the stirrer. However, if the rotation gap of the stirrer is small, a sufficient stirring effect can be obtained without requiring much high-speed rotation. In addition, the development of the invention was repeated, focusing on the fact that the problem raised above was mainly due to the fact that the rotation gap of the stirrer could not be arbitrarily controlled during operation. lead.

The present invention has a molten metal tank provided with cooling means on the bottom peripheral wall, and a stirrer rotating at the center of the bottom peripheral wall,
In a device for continuously producing semi-solid metal by supplying a cooling metal while supplying molten metal to the gap between the bottom peripheral wall and the stirrer, the bottom peripheral wall has a concave conical surface and the corresponding stirrer has a convex conical surface. The cooling stirrer is formed by a Taber ring-shaped gap formed by the above, and the stirrer is provided with an elevating / lowering position adjusting device for the molten metal tank, whereby the gap with the cooling stirrer can be controlled. And a device for continuously producing semi-solid metal.

Here, the cone apex angle forming the tapered annular gap of the cooling agitation zone is in the range of 30 ° to 120 °, and the stirrer has a torque detector in its rotary drive system, via an indicator and a controller. It is further useful to enable control of the adjustment of the position of the stirrer up and down by the adjustment output according to the variation of the load torque.

In the present invention, the so-called cooling / stirring surface of the molten metal and the corresponding stirrer are all conical surfaces, and the gap of the cooling stir zone can be arbitrarily controlled by raising and lowering the stirrer. It is more preferable to automatically control the gap by measuring the viscous resistance torque.

Thus, it is possible to take a strong cooling means for the cooling / stirring tank, and even if the solidified shell is formed on a scale, it is possible to provide a sufficient stirring effect while maintaining an optimum gap, thereby enabling high-speed rotation. In addition to being unnecessary, the start of operation is easy, and the self-coating state can be easily realized even during regular operation, and there is no contamination by the refractory material.

The specific structure of the present invention will be described below with reference to FIG.

The apparatus for producing semi-solid metal according to the present invention comprises a heat retaining tank 1, a cooling and stirring tank 3, a discharge device 5, a stirrer 9, and a drive mechanism 10 to 14 for the stirrer 9. The heat retaining tank 1 is a container of a molten metal lined with a refractory material, an induction heating coil is provided on the outer periphery thereof, and the electric power 23 is supplied to heat the molten metal 20 in the heat retaining tank 1 to maintain the temperature at a constant temperature. . The cooling and stirring tank 3 connected to the bottom of the heat retaining tank 1 has an inner surface having a particularly inverted conical shape. A water cooling jacket 4 is formed around the cooling and stirring tank 3, and the cooling water 22 is passed through to directly perform forced cooling. . Therefore, the heat retaining tank 1 and the cooling / stirring tank 3 as a whole are nothing but molten metal tanks provided with cooling means on the bottom peripheral wall.

The discharge unit 5 is connected to the bottom of the cooling and stirring tank 3,
Is provided with an electric heater 6, which is supplied with electric power 23 to always maintain the heat retention state, to prevent solidification of the semi-solid metal passing through the discharge section 5, and to reduce the discharge amount by the slide gate valve 7 attached to the discharge section 5. Control.

The upper part of the heat retaining tank 1 is covered with a furnace lid 8 provided with an inlet 8 'for molten metal raw material. Although not shown, the temperature of the heat retaining tank 1 can be adjusted by blowing inert gas or the like.

On the other hand, the stirrer 9 has an inverted conical stirring surface corresponding to the cooling stirrer 3, and this stirrer 9 is installed at the center of the cooling stirrer 3, via the drive shaft 10 and the deceleration support device 11. , Electric motor 14
Thus, it is possible to rotate in the direction of arrow 24 at a predetermined rotation speed.

The deceleration support device 11 and the electric motor 14 are connected to a torque detector 12
And more preferably by a torque limiting joint 13 so that the rotation of the electric motor 14 is continued even if the stirrer 9 stops.

The drive mechanisms 10 to 13 of the stirrer 9 are installed as a whole on an elevating pedestal 15, thereby moving the stirrer 9 up and down as indicated by a double-headed arrow 25. The lifting platform 15 is supported by guide rolls 16 and connected to a hydraulic cylinder 17 for lifting. With the operation of a pressure 28 ′ from a hydraulic unit 28, the lifting platform 15 moves up and down along the arrow 25 using the guide roll 11 as a guide. The position can also be controlled.

(Operation) The molten metal 19 that has been put into the ladle 18 and transported is supplied from the charging port 8 ′ into the heat insulation tank 1.

The molten metal 20 is kept at a constant temperature in the heat retaining tank 1 and flows into the cooling and stirring tank 3.

In the cooling and stirring tank 3, the concave conical surface and the stirrer 9
In the cooling and stirring zone 29 formed of a tapered annular gap formed by the convex conical surface of the metal, the stirring effect is exerted by the rotation of the stirrer 9 as indicated by the arrow 24 under the strong cooling effect of the water cooling jacket 4 and the semi-solid metal Get. The semi-solid metal is continuously discharged from the slide gate valve 7 as shown by an arrow 21.

In this case, the stirrer 9 rotates at a constant speed, and the load torque is detected by the torque detector 12, through the indicator 26 and the controller 27, and by the operation of the hydraulic unit 28 and the lifting / lowering hydraulic cylinder 17, the stirrer 9 is rotated. Adjust the vertical position of 9,
The cooling stirrer 29 is controlled to the optimum state. Even if a thick solidified shell is generated in the cooling stirrer 29 due to excessive cooling and excessive torque is generated, the stirrer 9 is stopped by the torque limiting joint 13. Regardless, since the electric motor 14 is not stopped, the operation can be immediately resumed by slightly widening the gap between the cooling and stirring zones 29.

 FIG. 2 shows the behavior that occurs in the cooling and stirring tank 3.

In the present invention, in order to increase the cooling rate as much as possible, a copper plate 4 'is used for the cooling surface of the water-cooling jacket 4, and the strong cooling can be achieved by allowing the cooling water 22 to flow at high speed to the back surface.

The molten metal that enters the gap between the cooling plate 4 'and the stirrer 9 directly contacts the cooling plate 4' and is forcibly cooled to form a solidified shell 30. The degree (d) is determined by the balance between the cooling capacity and the stirring effect, and in any case, is very unstable during operation, and tends to be thicker, especially at the start. Next, the stirring effect given by the rotation of the stirrer 9 is proportional to the peripheral speed of the stirrer and inversely proportional to the gap, and is generally expressed as a function of the shear strain rate. The rotational speed is generally difficult at a peripheral speed of 10 m / s or more because of the savings in centrifugal force, gas entrainment, and structural strength of the device, and high-speed rotation is not preferable from the viewpoint of safety. Therefore, maintaining a proper gap is the most practical method for providing a sufficient stirring effect.

However, when the solidified shell 30 is formed with a thickness d by performing strong cooling, the actual gap becomes (cd) with respect to the gap (c) on the apparatus. Even if this gap is very unstable, if it is too small, an excessive torque is generated and there is a risk of sticking due to solidification. Since a large safe gap C 'is selected in design, sufficient stirring effect is obtained. Could not give.

In the present invention, the cooling stir zone 29 forms a tapered ring with a vertex angle 2θ, so that the stirrer 9 is moved by the stroke S
When raised as shown in Fig. 25, the radial gap becomes C '= C +
Sin increases to θ. That is, the gap can be controlled.

In general, a stable cooling stir zone is most ideally based on a cylindrical surface, which provides a sufficient stirring area by adjusting the length of the cylinder while keeping the stirring effect constant, that is, while keeping the turning radius constant. Because. On the other hand, if a conical surface is adopted, the gap can be adjusted arbitrarily as described above.However, if a sufficient stirring area is to be obtained, the radius of rotation will vary greatly, and the stirring effect will be constant. Disappears.

Therefore, in order to obtain a stirring effect as stable as possible when a conical stirrer is employed, a cooling stir zone 29 having a large rotating radius and a short axial length is provided. Here the apex angle 2θ of the conical surface is 30 ° ~ 120
The range of ゜ is suitable.

Note that, in the present invention, the stirring tank and the stirrer having an inverted conical surface have been described, but the combination of the stirrer and the stirrer having a regular conical surface can also adjust the gap by raising and lowering the stirrer. Naturally, it is included in the scope of the present invention.

(Embodiment) FIG. 3 shows a plurality of cooling / stirring tanks 202 provided at the bottom of a tundish 201 which is an intermediate container of molten metal according to the present invention.
And a stirrer 207 are provided, and a semi-solid metal 213 manufactured independently is supplied to each of the molds 211 to continuously manufacture a semi-solid metal billet 216.
The tundish 201 is a container lined with a refractory material, and a predetermined number of cooling and stirring tanks 202 can be attached to the bottom thereof.
The cooling and stirring tank 202 forms an inverted conical surface on its inner surface, and most of the cooling and stirring tank 202 is a water-cooling jacket 203, and forced cooling can be performed by passing cooling water 214. A discharge part 204 and a slide gate valve 206 are attached to the bottom of the cooling and stirring tank 202, and a power 215 is supplied to the electric heater 205 to heat the electric heater 205.
The produced semi-solid metal 213 is continuously discharged while preventing solidification.

On the other hand, a stirrer 207 having an inverted conical surface corresponding to the cooling stirrer tank 202 is connected to a driving device by a driving shaft 208, and is indicated by an arrow.
Rotation and elevation / position control as indicated by an arrow 210 shown in 209 are possible. The molten metal 212 in the dundish 201 is maintained at a constant temperature range, flows into a tapered annular gap or cooling / stirring zone between the cooling / stirring tank 202 and the stirrer 207 at the bottom, and flows into the water cooling jacket 203. Is cooled to a semi-solid state by both effects of rotation of the stirrer 207, and is continuously discharged through the discharge unit 204 and the slide gate valve 206.

The semi-solid metal 213 continuously discharged from each cooling and stirring device is directly supplied to the corresponding continuous casting mold 211 to produce the product billet 216.

In this case, the stirrer 207 moves up and down as described above, and can be controlled so as to appropriately maintain the gap between the cooling surface and the stirrer.

The production capacity of the apparatus of the present invention depends on the physical properties of the target metal and the target solid fraction (the ratio of solidified crystals present in the melt), but is determined by the cooling / stirring area and is sufficient for the conventional continuous casting technology. It is applicable and greatly helps to improve the quality of conventional castings and reduce the thermal load on equipment. Further, by simply changing the mold 211, it can be sufficiently applied to a general casting process.

(Effect of the Invention) The semi-solid metal manufacturing apparatus embodying the present invention exhibits the following effects.

(1) Since the operation can be performed with an appropriate minimum gap by strong cooling, the cooling rate can be increased to 10 ° C / sec or more, and a semi-solid metal having excellent characteristics with fine primary crystal grains can be manufactured. In particular, since it can be cooled strongly, the production capacity is large and practical.

(2) Since the stirring is performed with an appropriate minimum gap, a sufficient stirring effect can be obtained even if the rotation speed is lower than half that of the conventional one, and the risk of gas entrainment accompanying high speed rotation and All problems related to the structure, strength and safety of the device design are solved.

(3) The quality of the semi-solid metal is stable because it can be operated while maintaining an appropriate minimum gap.

(4) It is possible to cope with the formation of an excessively solidified shell at the start, and it is easy to start a lesson. In addition, even during long-time continuous operation, operation is performed while monitoring fluctuations in torque, so that stable operation can be performed without any accident.

[Brief description of the drawings]

FIG. 1 is an overall explanatory view showing a configuration of the present invention in a cross section of a main part, FIG. 2 is an enlarged view showing an operation in a cooling and stirring zone according to the present invention, and FIG. 3 is an embodiment of the present invention. FIG. DESCRIPTION OF SYMBOLS 1 ... Insulated tank, 2 ... Induction heating coil 3 ... Cooling and stirring tank, 4 ... Water cooling jacket 5 ... Ejector, 6 ... Electric heater 7 ... Slide gate valve, 8 ... Lid 8 '... Inlet, 9 Stirrer 10 Drive shaft 11, Deceleration support device 12 Torque detector 13, Torque limiting joint 14 Motor, 15 Lifting platform 16 Guide roll, 17 … Hydraulic cylinder for lifting 18… Ladle, 26… Torque indicator 27… Controller, 28… Hydraulic unit

Claims (3)

(57) [Claims] 1. A bath of a molten metal having cooling means provided on a bottom peripheral wall, and a stirrer rotating at the center of the bottom peripheral wall,
In an apparatus for continuously producing semi-solid metal by supplying a cooling and stirring effect while supplying molten metal to the gap between the bottom peripheral wall and the stirrer, the bottom peripheral wall has a concave conical surface, and the corresponding stirrer has a convex conical surface. A stirrer is provided with a cooling / stirring zone comprising a gap formed in the shape of a ring, and a stirrer is provided with an elevating / lowering position adjusting device for the molten metal tank, whereby the gap in the cooling stirrer can be controlled. An apparatus for continuously producing semi-solid metal, comprising: 2. The apparatus according to claim 1, wherein the conical apex angle forming the tapered annular gap of the cooling stirring zone is in the range of 30 ° to 120 °. 3. The stirrer has a torque detector in its rotary drive system, and it is possible to control the adjustment of the position of the stirrer up and down by an adjustment output according to a change in load torque via an indicator and a controller. An apparatus according to claim 1.