JPH07100589A - Production of half-solidified metal without deteriorated quality by stirrer rotating method and apparatus therefor - Google Patents

Abstract

PURPOSE:To prevent the attenuation of cooling capacity of a cooling plate and to produce a half-solidified metal having high quality by cutting and successively removing the solidified shell grown on the cooling surface of the cooling plate in a cooling stirring vessel of the rotation of a stirrer with scraper tip arranged on the stirrer surface. CONSTITUTION:The scraper tip 23 is fitted to the outer periphery of screw thread part 22 into equal divisions on the outer periphery and arranged so as to be able to cut the solidified shell grown on the inner surface over the whole length of the height direction of the cooling plate 6. Molten metal is cooled while rotating the stirrer 4 with the scraper tip 23 in the cooling stirring vessel 5, and the discharging speed is adjusted by operating the opening degree of a slide valve 13 and controlled so that the solid phase ratio in the discharged half-solidified metal becomes the constant. By this method, the high quality half-solidified metal containing fine primary crystal grain can stably be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slurry-like solid in which non-dendritic primary crystals are dispersed in a metal (generally an alloy) liquid.
With regard to the production of a liquid metal mixture (hereinafter simply referred to as a semi-solidified metal), a method and an apparatus for producing a high-quality semi-solidified metal containing fine primary crystals without quality deterioration by a stirrer rotation method are proposed.

[0002]

2. Description of the Related Art A means for continuously producing a semi-solid 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 described above, 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, and cooled with a strong stirring action, and the obtained semi-solid metal is A mechanical stirring method (hereinafter referred to as a stirrer rotation method) of continuously discharging from the bottom is known.

As a stirring method, a method using electromagnetic force (hereinafter referred to as electromagnetic stirring method) is also well known.

Further, as another means, the molten metal is supplied to a gap between a single roll (stirrer) having heat removal ability and rotating around a horizontal axis, and a fixed plate having a concave curved surface along the outer circumference of the roll. Japanese Laid-Open Patent Publication No. Hei 4 (1999) -4 means for producing semi-solidified metal by shear strain of the solid-liquid interface generated by rotation of the roll while causing solidification by forced cooling.
-238645 (a method and an apparatus for producing semi-solidified metal) is proposed and disclosed.

In any of these means, the solid-phase particles in the semi-solidified metal are vigorously stirred while cooling the molten metal, whereby the branches of the dendritic primary crystals that are being formed in the melt disappear or shrink. It is formed by converting it into a slightly rounded form.

It is said that the finer the non-dendritic primary crystal grains and the higher the solid fraction of the semi-solidified metal, the more excellent the quality characteristics of the product obtained from the semi-solidified metal. The size becomes finer as the cooling rate due to the cooling capacity increases.

For this reason, an apparatus having excellent cooling capacity is required as an apparatus for producing semi-solidified metal, but in the case of producing semi-solidified metal with fine primary crystal grains and high solid fraction by intense cooling. However, since the apparent viscosity is not so large, the fluidity is remarkably deteriorated, and it becomes particularly difficult to stably and continuously discharge the semi-solidified metal having a high solid fraction.

Examining the above-mentioned means from the viewpoints of the discharging ability and cooling ability of the semi-solidified metal, the single roll method is
The rotation of the roll accelerates the discharge of the generated semi-solidified metal, and the solidified shell adhering to the roll surface is scraped off by the scraper, so even if the solid-phase ratio of the discharged semi-solidified metal is large, there are few obstruction factors for the discharge. In addition, since there are few factors that reduce the cooling capacity due to the growth of the solidified shell, this method is very excellent in discharging capacity and cooling capacity.

However, in the stirrer rotation method and the electromagnetic stirrer method, in order to stir the supplied molten metal in the cooling tank by rotating around the center of the cooling tank as a rotation axis, the number of rotations of the stirrer is increased to increase the strength. The more the agitation is attempted, the more the pressure on the wall surface of the cooling tank due to the centrifugal force is increased, and the discharge capacity is decreased. Even if a cooling plate with a high cooling capacity is used, the growth suppression effect of the solidified shell generated on the cooling surface is only due to the shear strain of the solid-liquid interface due to stirring, so the effect of suppressing the growth of the solidified shell cannot be expected so much. As a result, the cooling capacity is attenuated due to the growth of the solidified shell. Therefore, in the stirrer rotation method and the electromagnetic stirring method, the establishment of a technology for suppressing the growth of the solidified shell on the cooling surface becomes a particularly important issue, along with the probability of the technology for increasing the discharge capacity of semi-solidified metal.

On the other hand, in the stirrer rotation method and the electromagnetic stirring method, if the discharge capacity and the cooling capacity can be increased, a semi-solidified metal containing fine primary crystal grains is passed through a nozzle or directly rounded. It is a very excellent means to shape fine primary crystal grains and semi-solidified metal with a high solid fraction by enabling continuous casting into a shape such as a square cross section.

From such a point of view, in the stirrer rotation method, as a means for improving the ability to discharge semi-solidified metal, the inventor of the present invention previously disclosed in Japanese Patent Laid-Open No. 4-124231 (semi-solidified metal manufacturing apparatus) with a screw on the surface. An apparatus has been proposed and disclosed in which a stirrer having a groove is used and means for forcibly feeding the semi-solidified metal generated in the cooling stirring tank downward is introduced. However, the technology for suppressing the growth of the solidified shell on the cooling surface has not yet been established, and the cooling capacity of the cooling plate of the cooling and stirring tank declines with the growth of the solidified shell, and the primary crystal grains of the semi-solidified metal obtained are coarse. However, there remains a problem that the quality is deteriorated.

[0012]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention is a stirrer rotation method using a stirrer having a thread groove on the surface thereof, which can suppress the deterioration of quality that advantageously suppresses a solidified shell growing on a cooling surface. An object of the present invention is to propose a manufacturing method and an apparatus for obtaining a high quality semi-solidified metal.

[0013]

As a result of various studies and studies on the above-mentioned method for suppressing the growth of a solidified shell, the inventors have found an effective method for cutting and removing the solidified shell, and achieved the present invention. That is, the gist of the present invention is as follows. The molten metal supplied from above a cooling and stirring tank having a cylindrical cooling plate is stirred by rotation of an agitator having a thread groove on the surface at the center of the cooling tank under cooling to suspend non-dendritic crystals with fine particles. In the method for producing a semi-solid metal which is a turbid solid-liquid mixed phase metal slurry and is discharged from a lower outlet, a solidified shell that grows on a cooling plate cooling surface is provided by a scraper tip provided on the outer circumference of the screw thread of the stirrer. It is a method for producing a semi-solid metal without quality deterioration by a stirrer rotation method, which is characterized in that the cooling capacity of a cooling plate is prevented from being attenuated sequentially by cutting and removing based on the rotation of the stirrer. In a semi-solid metal manufacturing apparatus comprising a cooling and stirring tank having a cylindrical cooling plate, a stirring bar having a thread groove on the surface rotating at the center of the cooling stirring tank, and a discharge port below the cooling stirring tank A large number of scraper chips for solidifying shell cutting that grow on the cooling plate cooling surface are arranged on the outer peripheral portion of the threads of the child, and a large number of the scraper chips are arranged.
It is an apparatus for producing semi-solid metal without quality deterioration by the stirrer rotation method, which is arranged in the number of evenly distributed distributions on the circumference corresponding to the value exceeding the ratio of the thread pitch to the scraper chip width.

[0014]

The background of the present invention and its operation will be described below. Under the circumstances as described above, the inventors further conducted an experimental study on a stirrer rotation method using a stirrer having a thread groove on the surface, and as a result, even if the rotation speed of the stirrer was increased, the solid-liquid The shear strain rate of the interface alone is not sufficient to suppress the growth of the solidified shell generated on the cooling surface of the cooling stirring tank, and the growth of the solidified shell becomes remarkable when a cooling plate with a high heat removal rate is used for strong cooling. As a result, the heat removal rate decreases and the cooling capacity decreases, and conversely, with a cooling plate with a heat removal rate that does not cause the growth of the solidification shell, the cooling capacity is small from the beginning and high quality semi-solidified metal is produced. We came to discover that we could not obtain it.

As a method for suppressing the growth of the solidified shell, it is effective to add a means for forcibly scraping off the solidified shell in addition to the shear strain of the solid-liquid interface due to the rotation of the stirrer. It was clarified that it is most effective to give the stirrer a scraper function and to remove the solidified shell by rotating the stirrer.

Therefore, according to the present invention, when the semi-solidified metal is produced by the stirrer rotating method using the stirrer having the thread groove on the surface, the molten metal supplied from above the cooling stirrer having the cylindrical cooling plate is cooled. When cooling while stirring with a stirrer in the stirrer, the stirrer is equipped with a scraper function. The action of forcibly scraping off the growing solidified shell is added.

As a result, it is possible to prevent the heat removal rate of the cooling plate from being lowered due to the growth of the solidified shell, that is, the decrease of the cooling capacity, and it is possible to manufacture the semi-solidified metal while maintaining the high cooling capacity. It will be possible to manufacture high quality semi-solidified metal with fine primary grains.

In the above-mentioned scraper provided in the stirrer, a large number of cutting bite-shaped scraper chips are arranged on the outer peripheral portion of the screw thread of the stirrer, and the arrangement is a value exceeding the ratio of the screw thread pitch to the scraper chip width. The solidified shell that grows on the cooling plate cooling surface due to the rotation of the stirrer is cut sequentially by the scraper tip provided on the stirrer over the entire surface. By being removed, the thickness of the solidified shell can be kept substantially constant, and the cooling capacity of the cold plate will be kept substantially constant.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an example of a semi-solid metal manufacturing apparatus suitable for the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram of a semi-solid metal manufacturing apparatus by a stirrer rotation method using a stirrer having a thread groove on the surface. In FIG. 1, 1 is an immersion nozzle, 2 is a tundish, and 3 is a hot water tank. Reference numeral 5 is a cooling and stirring tank, and the cylindrical cooling plate 6 is water-cooled by cooling water through a cooling water inlet 7 and a cooling water outlet 8. An agitator 4 having a thread groove on the surface is inserted in the center of the cooling and agitating tank 5, and the dipping nozzle 1 from the ladle (not shown),
The molten metal supplied through the tundish 2 and the hot water receiving tank 3 is stirred by the rotation of the stirrer 4 and a discharging force is given to the semi-solidified metal produced, and the semi-solidified metal is the nozzle of the discharging tank 11. It is discharged through 12 and the slide valve 13. Further, 9 and 10 are temperature sensors at the cooling water inlet 7 and the outlet 8, and 14 and 15 are heaters for the hot water receiving tank 3 and the discharging tank 11, respectively.

The semi-solidified metal production apparatus according to the present invention is the stirrer 4 of the apparatus having the structure shown in FIG.
On the outer periphery of the screw thread, a large number of scraper chips for sequentially cutting and removing the solidified shell growing on the cooling plate 6 can be cut over the entire height of the cooling plate 6, that is, the ratio of the thread pitch to the scraper chip width can be adjusted. The number of equal divisions on the circumference corresponding to the value exceeding the number is arranged. An example of the stirrer is shown in FIGS. 2 (a) and 2 (b).

FIG. 2 (a) is an explanatory view of the front of the stirrer having a large number of scrapers arranged on the outer peripheral thread portion according to the present invention, and FIG. 2 (b) is an explanatory view of the upper surface of (a). In FIG. 2, 21 is a shaft, 22 is a thread portion (screw pitch: 4
5mm) and 23 are scraper chips (chip width: 20m
m), and the scraper chips 23 are attached to the outer circumference of the threaded portion 22 at eight positions so as to be equally divided on the circumference (center angle is 45 °), and over the entire height of the cooling plate 6, It is arranged so that the solidified shell that grows can be cut on its inner surface. Further, the gap between the blade edge of the scraper chip 23 and the cooling plate 6 depends on the type of semi-solidified metal to be manufactured,
It may be appropriately determined according to the heat removal rate required by the characteristics.

Next, as a conforming example of the present invention, a semi-solid metal is manufactured by the semi-solid metal manufacturing apparatus of FIG. 1 equipped with a stirrer having the scraper chip shown in FIG.

The production of the semi-solid metal is carried out by pouring an Al-7mass% Si alloy molten metal adjusted to an appropriate temperature from a ladle into a tundish 2 through a dipping nozzle 1 to form a tundish 2 and a hot water tank 3. It is poured into a cooling and stirring tank 5 having a Cu cooling plate through the inside, and is cooled while being stirred by the rotation of the stirrer 4 with a scraper tip in this cooling and stirring tank 5, and the opening degree of the slide valve 13 is operated. The discharging rate was adjusted so that the solid phase ratio of the semi-solidified metal discharged was controlled to be constant at 0.3.

In the above, the cooling water amount of the cooling stirring tank 5 is
The speed of the stirrer 4 was set to 500 l / min and 1000 rpm. The main body of the cooling and stirring tank 5, the stirrer 4, and the scraper chip 23 were made of SUS410.

Further, as a comparative example, a semi-solid metal was manufactured by the same method using a stirrer without a scraper tip.

When the respective semi-solidified metals were produced in this way, changes in the heat removal rate of the cooling plate 6 with the lapse of time during operation and the average grain size of the discharged primary crystal grains of the semi-solidified metal were investigated. did.

Here, the heat removal rate is obtained by calculation from the temperature difference between the water temperatures measured by the cooling water temperature sensors 9 and 10, and the average grain size of the primary crystal grains of the semi-solidified metal is the discharged semi-solidified metal. Was investigated on a rapidly cooled sample.

The results of these investigations are shown in FIGS. 3 and 4. FIG. 3 is a graph showing changes in the heat removal rate of the cooling plate with the lapse of time from the start of pouring. As is clear from this figure, in the comparative example, the decrease in the heat removal rate due to the growth of the solidified shell over time is remarkable, but in the compatible example, the solidified shell is sequentially scraped off by the scraper tip at the growth stage, The heat removal rate is stably maintained at a high level.

FIG. 4 is a graph showing changes in the average particle size of the discharged semi-solidified metal with the lapse of time from the start of pouring. As is clear from this figure, in the comparative example, the average primary crystal grain size increases with the decrease of the heat removal rate with the passage of time, but in the conforming example, the primary crystal grain size is maintained small, It shows that high quality semi-solidified metal can be obtained without quality deterioration.

[0030]

According to the present invention, when a semi-solidified metal is produced by a stirrer rotating method using a stirrer having a thread groove on the surface, the growth of a solidified shell formed on a cooling plate of a cooling stirring tank is forcibly cut and removed. However, it is intended to prevent a decrease in heat removal rate due to the growth of solidified shell, and according to the present invention, it is possible to stably produce a high quality semi-solidified metal containing fine primary crystal grains. Therefore, it is possible to improve the quality characteristics of products manufactured from this semi-solid metal.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a semi-solid metal manufacturing apparatus by a stirrer rotation method using a stirrer having a thread groove on the surface.

FIG. 2 (a) is an explanatory view of the front of the stirrer having a large number of scraper chips arranged on the outer peripheral thread portion according to the present invention. (b) is an explanatory view of the upper surface of (a).

FIG. 3 is a graph showing changes in the heat removal rate of the cooling plate with the lapse of time from the start of pouring.

FIG. 4 is a graph showing changes in the average particle size of discharged semi-solidified metal with the lapse of time from the start of pouring.

[Explanation of symbols]

 1 Immersion Nozzle 2 Tundish 3 Hot Water Tank 4 Stirrer 5 Cooling Stirring Tank 6 Cooling Plate 7 Cooling Water Inlet 8 Cooling Water Outlet 9 Temperature Sensor (For Inlet Cooling Water) 10 Temperature Sensor (For Outlet Cooling Water) 11 Discharge Tank 12 Nozzle 13 Slide valve 14 Heater (for hot water tank) 15 Heater (for discharge tank) 21 Shaft 22 Thread portion 23 Scraper tip

 ─────────────────────────────────────────────────── ─── 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 (2)

[Claims] 1. A molten metal supplied from above a cooling and stirring tank having a cylindrical cooling plate is stirred by rotation of an agitator having a thread groove on the surface thereof at the center of the cooling tank while cooling to obtain fine particles. A solid-liquid mixed-phase metal slurry in which dendrites are suspended and discharged from the lower outlet in the method for producing semi-solidified metal. A method for producing a semi-solid metal without quality deterioration by a stirrer rotation method, which comprises sequentially cutting and removing the stirrer with a tip based on the rotation of the stirrer to prevent the cooling ability of a cooling plate from being attenuated. 2. A semi-solidified metal comprising a cooling and stirring tank having a cylindrical cooling plate, a stirring bar having a thread groove on the surface rotating at the center of the cooling stirring tank, and a discharge port below the cooling stirring tank. In the manufacturing apparatus, a large number of scraper chips for solidifying shell growth that grows on the cooling plate cooling surface are arranged on the outer periphery of the threads of the stirrer. An apparatus for producing semi-solidified metal that does not deteriorate in quality by the stirrer rotation method and is arranged in a number of evenly divided distributions on the circumference corresponding to a value that exceeds the magnification for.