JP2004066238A - Rotator for stirring molten metal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotator for stirring molten metal with which the development of the fracture or crack of a stirring disk is prevented by improving the conventional rotator for stirring the molten metal and also bubbles can be dispersed more uniformly. <P>SOLUTION: The ceramics-made stirring disk is fixed to a shaft having a gas supplying path in the inside. The lower end part of the shaft is protruded to the lower side from the bottom surface of the stirring disk and is closed. A plurality of gas exhausting holes are arranged on the side surface near the lower end part of the shaft. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a rotating body for stirring a molten metal which releases an inert gas such as nitrogen or argon gas into a molten metal such as aluminum in a bubble state to remove impurities such as a gas such as hydrogen and oxides in the molten metal. .
[0002]
[Prior art]
In a molten metal such as aluminum or aluminum alloy, an inert gas such as nitrogen or argon gas is bubbled in the molten metal while stirring the molten metal to float and remove impurities and hydrogen gas in the molten metal. A rotary body for agitating a molten metal is used, which makes the particles finer and disperses them uniformly in the molten metal.
[0003]
For example, Japanese Patent Publication No. 61-40737 discloses that a rotating body (stirring disk) for atomizing and dispersing bubbles is attached to the lower end of a vertical rotating shaft (shaft) having a gas supply passage therein, and the lower end of the gas supply passage rotates. A plurality of grooves are radially provided on the bottom surface of the rotating body from the opening of the gas supply path to the periphery on the bottom surface of the rotating body, and the lower end rotates between the openings of the grooves on the circumferential surface of the rotating body. A molten metal stirring rotator having a recess opened at the periphery of the bottom surface of the body is described.
[0004]
Japanese Patent Application Laid-Open No. 7-55365 discloses that a stirring disk made of ceramics is fixed to a shaft having a gas supply passage therein, and an opening for blowing an inert gas is provided in a tubular shape below the bottom surface of the stirring disk. A rotating body for agitating a molten metal in which a plurality of grooves from the opening of the gas supply path to the periphery are radially provided on the bottom surface of the stirring disk.
[0005]
According to JP-A-7-55365, the gas blown into the molten metal rises toward the bottom surface of the stirring disk together with the flow of the molten metal affected by the rotation of the stirring disk. During this time, the gas is heated by the molten metal and, when it reaches the bottom surface of the stirring disk, no longer rapidly cools the stirring disk. For this reason, a large thermal stress due to a temperature difference between the upper surface side and the bottom surface side of the stirring disk does not occur, and the generation of cracks and cracks can be prevented.
[0006]
[Problems to be solved by the invention]
The rotating body for stirring a molten metal disclosed in Japanese Patent Application Laid-Open No. 7-55365 has an advantage that cracks and cracks of the stirring disk can be prevented. It tends to be layered while rising toward the bottom surface, and there is room for improvement in dispersing the bubbles more evenly.
[0007]
Accordingly, an object of the present invention is to improve a conventional rotating body for stirring a molten metal, to prevent generation of cracks and cracks in a stirring disk, and to provide a rotating body for stirring a molten metal capable of dispersing air bubbles more uniformly. To provide.
[0008]
[Means for Solving the Problems]
In the rotating body for stirring molten metal of the present invention, a ceramic stirring disk is fixed to a shaft having a gas supply passage therein, and a lower end portion of the shaft is protruded below a bottom surface of the stirring disk. And a plurality of gas discharge holes provided on a side surface near the lower end of the shaft.
[0009]
[Action]
The present invention does not discharge air bubbles directly below the opening of the gas supply path as in the related art, but closes the lower end of the shaft and forms a plurality of gas discharge holes on the side surface near the lower end of the shaft. In order to provide a plurality of gas discharge holes at equal intervals in the circumferential direction, preferably on the side surface near the lower end of the shaft, air bubbles are discharged in the circumferential direction of the shaft and rise toward the bottom surface of the stirring disk. During this process, the particles are uniformly dispersed without being deviated in layers.
[0010]
In addition, since the lower end of the shaft protrudes below the bottom surface of the stirring disk, while the released bubbles rise toward the bottom surface of the stirring disk, the bubbles are heated by the molten metal, and When reaching the bottom, the stirring disk is no longer quenched. For this reason, a large thermal stress due to a temperature difference between the upper surface side and the bottom surface side of the stirring disk does not occur, and generation of cracks and cracks can be prevented.
[0011]
Further, in the molten metal stirring rotating body of the present invention, similarly to the conventional technique, it is preferable to radially provide a plurality of grooves from the central portion to the peripheral edge on the bottom surface of the stirring disk in order to improve the bubble miniaturization action. .
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a longitudinal sectional view showing an embodiment of a rotating body for stirring molten metal of the present invention. FIG. 2 is a bottom view thereof. 1 and 2, the molten metal stirring rotor 1 of the present invention comprises a shaft 2 and a stirring disk 3 such that the lower end 23 of the hollow tubular shaft 2 projects below the bottom surface 31 of the stirring disk 3. Is fixed. The male screw formed above the lower end 23 of the shaft 2 and the female screw formed in the center hole of the stirring disk 3 were fixed by screwing.
[0013]
The shaft 2 is made of a silicon nitride-based ceramics sintered body, and has a hollow gas supply path 21 for supplying an inert gas such as nitrogen or argon gas into the inside thereof. The shaft 2 has its lower end 23 closed, and eight gas discharge holes 25 are provided on the side surface 24 near the lower end 23 of the shaft 2 at intervals of 45 degrees in the circumferential direction. An inert gas is supplied from the gas supply path 21 to the bottom surface 31 of the stirring disk 3 via each gas discharge hole 25.
[0014]
The stirring disk 3 is made of a silicon nitride-based ceramics sintered body similarly to the shaft 2, and has eight protrusions 32 protruding in the radial direction on the outer periphery thereof at intervals of 45 degrees in the circumferential direction. In addition, the protrusion 32 is inclined such that the front surface in the rotation direction faces diagonally upward and the rear surface in the rotation direction faces diagonally downward. Accordingly, the lift force acts on the molten metal by the pressing force on the front surface, and the pressing force also acts on the molten metal by the suction force on the rear surface. Therefore, the generation of a vortex on the surface of the molten metal is prevented.
[0015]
The upper surface 33 of the stirring disk 3 is gradually reduced in thickness from the central hole toward the peripheral edge portion 34 to secure the necessary strength at a screwing portion of the central hole with the shaft 2. It was formed thin so as not to be damaged by thermal stress.
[0016]
On the bottom surface 31 of the stirring disk 3, a plurality of grooves 35 are formed radially from the central portion of the stirring disk 3 located at a position close to the gas discharge holes 25 of the gas supply passage 21 to the peripheral edge portion 34.
[0017]
In the present invention, since the stirring disk 3 is particularly required to have erosion resistance, it is necessary to form the stirring disk 3 from ceramics. The shaft 2 is desirably formed of ceramics, but may be formed of other materials. Further, the front surface and the rear surface in the rotation direction of the protrusion 32 may not be inclined, and the stirring disk 3 is not limited to the shape of the embodiment.
[0018]
Here, the rotating body for stirring the molten metal of the example of the present invention was manufactured as follows. First, 2.8% by volume of magnesium oxide powder having an average particle diameter of 0.2 μm and 0.2 μm of aluminum oxide powder having an average particle diameter of 0.2 μm were added to silicon nitride powder having an average particle diameter of 0.5 μm as a sintering aid. 0.4% by volume of yttrium oxide powder having an average particle size of 2.0 μm and a volume of 08% by volume were added, an appropriate amount of a dispersant was added, and the mixture was ground and mixed in ethanol. Then, after vacuum drying, the mixture was granulated through a sieve, filled in a rubber mold, and subjected to cold isostatic pressing (CIP) by hydrostatic pressure to produce a molded body to be a stirring disk and a shaft. These compacts were fired in a nitrogen gas atmosphere at 1750 ° C. and 9 atm for 5 hours to obtain a stirring disk and a shaft of the present invention comprising a silicon nitride ceramic sintered body.
[0019]
In addition, in order to examine the following characteristics, from the obtained silicon nitride-based ceramics sintered body, a test piece for measuring the density and thermal conductivity of 10 mm in diameter × 3 mm in thickness, and 3 mm in length × 4 mm in width × 40 mm in length Four-point bending test pieces were collected. The density was determined from the results of dimensional measurement and weight measurement using a micrometer. The thermal conductivity was determined by measuring the specific heat and the thermal diffusivity at room temperature by a laser flash method and calculating the thermal conductivity. The four-point bending strength was measured at room temperature in accordance with JIS R1606. As a result, the silicon nitride ceramic sintered body of the example of the present invention had a density of 99.2%, a thermal conductivity at room temperature of 85 W / (m · K), and a four-point bending strength at room temperature of 720 MPa.
[0020]
The ceramic forming the stirring disk and the shaft of the present invention is preferably a silicon nitride ceramic. In particular, the silicon nitride-based ceramics sintered body preferably has a thermal conductivity of 60 W / (m · K) or more at room temperature. By increasing the thermal conductivity, heat can be quickly transferred from the surface of the rotating body for stirring the molten metal to the inside when immersing in the molten metal. Cracks can be prevented. Further, it is desirable that the silicon nitride-based ceramics sintered body has a four-point bending strength at room temperature of 600 MPa or more so as to sufficiently withstand mechanical stress and impact during use.
[0021]
The rotating body for stirring the molten metal according to the embodiment of the present invention thus constructed is immersed in the molten aluminum at 680 ° C., and the shaft is rotated at a high speed by the driving device. When subjected to rotary stirring to suspend the impurities and the like, the effect of finely dispersing bubbles was sufficiently obtained. In addition, almost no erosion by the molten aluminum was observed, and no cracks or cracks occurred due to thermal stress during use.
[0022]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the rotating body for agitating a molten metal of this invention, while being able to prevent generation | occurrence | production of a crack and a crack of an agitating disk, a bubble can be disperse | distributed more uniformly than before.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing an embodiment of a rotating body for stirring a molten metal of the present invention.
FIG. 2 is a bottom view showing an embodiment of a rotating body for stirring molten metal of the present invention.
[Explanation of symbols]
1 rotating body for stirring molten metal, 2 shaft, 3 stirring disk,
21 gas supply path, 23 lower end, 24 side surface, 25 gas discharge hole,
31 bottom surface, 32 protrusion, 33 top surface, 34 peripheral portion, 35 groove

Claims (1)

A stirring disk made of ceramics is fixed to a shaft having a gas supply passage therein, and the lower end of the shaft is projected below the bottom surface of the stirring disk to close the lower end of the shaft and the lower end of the shaft. A rotating body for stirring molten metal, wherein a plurality of gas discharge holes are provided on a side surface in the vicinity.

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