JP4123740B2 - Molten metal processing equipment - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an apparatus for removing dissolved gas and non-metallic inclusion particles in molten metal by blowing an inert gas or the like.
[0002]
[Prior art]
Since the dissolved gas and inclusions contained in the molten metal cause defects, the dissolved gas and inclusions in the molten metal are removed before casting.
For example, when casting aluminum or an aluminum alloy, in order to remove non-metallic inclusions such as hydrogen gas and oxides contained in the molten metal, an inert gas or the like is blown to remove the inert gas or the like. A molten metal treatment for removing dissolved gas and non-metallic inclusions is performed by attaching dissolved gas and non-metallic inclusions to the bubbles. In particular, with the recent improvement in required casting quality, it has become necessary to remove contained gases and non-metallic inclusions at levels not previously considered as problems.
[0003]
In order to efficiently remove dissolved gas and non-metallic inclusions, it is necessary to increase the surface area of the bubbles. In order to increase the surface area of the bubbles as much as possible, it is necessary to disperse the bubbles as finely as possible.
A conventional molten metal processing apparatus includes a vertical rotation shaft having a gas ventilation path disposed in a molten metal holding tank and extending in the axial direction inside, a gas rotation path provided at a tip of the vertical rotation shaft, and the gas ventilation path on a bottom surface or a side surface. It consists of a rotating body provided with a connected gas outlet. In order to finely disperse the bubbles injected into the molten metal, the shape of the rotating body is devised or the rotational speed of the rotating shaft is further increased.
[0004]
[Problems to be solved by the invention]
However, if the rotating shaft is rotated at a high speed, a vortex is generated in the molten metal around the rotating shaft, and dissolved gas and non-metallic inclusions floating on the surface of the molten metal are entrained. It cannot be increased.
As a method of preventing the vortex from being generated in the molten metal, there is a method of providing a baffle plate on the side wall or the like of the molten metal treatment tank. However, if the baffle plate is provided, a portion where the blown bubbles do not reach the molten metal is formed. In addition, the baffle plate and the swirling flow of the molten metal collide, and the molten metal surface undulates, increasing the amount of surface oxidation.
The present invention has been devised to solve such a problem, and an object thereof is to provide a molten metal processing apparatus in which vortices are not generated even when a rotating body is rotated at a high speed.
[0005]
[Means for Solving the Problems]
In order to achieve the object, the molten metal processing apparatus of the present invention has a molten metal holding tank, a vertical rotating shaft that is disposed in the molten metal holding tank and has a gas vent passage extending axially therein, and the vertical rotating shaft. A rotating body provided at a tip of the gas outlet and provided with a gas blowout opening connected to the gas ventilation path on either or both of the bottom surface and the side surface, and covering the vertical rotating shaft and the rotating body at the tip of the rotating shaft. A non-rotating swirl flow generation prevention cover is also provided.
[0006]
[Simulation experiment]
First, in order to know the process that hinders the removal effect of hydrogen gas and non-metallic inclusions, and to know the vortex generation prevention effect of the non-rotating swirl flow prevention cover, a water model that is easy to observe is adopted instead of molten aluminum did.
An experiment was conducted by putting water into a transparent PVC treatment tank having an inner diameter of 700 mm, which is similar to the molten metal tank 2, to a depth of 700 mm. In addition, a fine plastic resin piece (5 × 10 × 1 mm) 6 having a specific gravity similar to that of water was imitated as an oxide film and was mixed in water.
[0007]
In order to generate bubbles, a rotating body 4 made of graphite and having an outer diameter of 75 mm and a rotating blade 4 having an outer diameter of 230 mm and a thickness of 60 mm integrated at the lower end thereof was used. In addition, a hollow (inner diameter: 10 mm) inert gas entry hole is penetrated in the central portion of the rotating shaft 4, and the lower surface of the rotating blade has a width of 30 mm and a depth of 10 mm toward the outer periphery. The processing grooves are provided radially at six locations from the center toward the outer periphery.
Such a rotating body 4 is immersed in water at a depth of 500 mm for the rotating shaft and 50 mm for the rotating blade and 550 mm as a whole, and the Ar gas amount is kept constant at 20 L / min while changing the rotation speed. Blowing, vortex generation and water behavior were observed.
[0008]
The swirl flow prevention cover consists of a transparent PVC round pipe-shaped body part with an inner diameter of 80 mm and an outer diameter of 100 mm, which can be varied in immersion depth, and an additional PVC-made cover part covering the rotating blades as necessary. The attachment is fixed to the non-rotating part of the processing apparatus main body.
[0009]
The installation depth of the swirl flow generation prevention cover was changed, and the rotation speed of the rotating body 4 was varied between 0 and 500 rpm, and the vortex generation state and water behavior were observed.
FIG. 3 shows the relationship between the rotational speed and the vortex flow. In the figure, (a) is a conventional method without a swirl flow generation prevention cover, (b) is a cover up to a position of 50 mm from the water surface, (c) and (d) are also covered up to 200 mm and 500 mm, Furthermore, (e) covers the rotating body 4.
[0010]
As can be seen from the figure, the depth of the vortex formed near the surface of the rotating shaft increases substantially in proportion to the rotational speed. However, in the case of the conventional method, for example, the vortex depth at 500 rpm was 20 mm, but in the method of the present invention provided with the swirl flow generation prevention cover, each experimental example was 5 mm or less, which The prevention effect was confirmed.
Further, at this time, the swirl flow generation prevention cover is more effective as the immersion depth is deeper, and is particularly effective when covering the rotating body that generates bubbles.
[0011]
In the case of the conventional method, the pseudo inclusions assumed in the oxide film adhering to the bubbles swirl in synchronism with water and then float once, but after that, they are caught in the vortex generated near the water surface of the rotating shaft, and again, It was confirmed that it was returned to the water.
On the other hand, in the case of the method of the present invention in which the swirl flow generation prevention cover is used and the vortex flow is hardly generated, the water flow such as the swirl flow and the vortex flow is retained in the swirl flow generation prevention cover. Most of the water in the outside treatment tank did not flow.
It was observed that the gas blown out from the rotator 4 became turbulent and attached to the pseudo inclusions while being rubbed against the fine bubbles and floated.
Of course, it was not observed that the pseudo-inclusion plastic piece that once floated returned to the water again.
[0012]
【Example】
Example 1
Based on the knowledge obtained in the water model experiment, the installation effect of the swirl flow prevention cover mainly confirming the removal of hydrogen gas and oxide film in the molten aluminum alloy was confirmed.
As shown in FIG. 4, a cast iron crucible having an inner diameter of 700 mm and a depth of 700 mm and having a heat retaining function is charged with 620 kg of an Si-containing Al-Si alloy molten metal having a Si content of 6.5 to 7.5 mass% (by the way, the molten metal). The depth is about 700 mm.) The molten metal temperature was kept at 730 ° C. As the rotating body, the same material and shape as those used in the water model experiment were used, and Ar gas was supplied at 20 liters / minute while rotating uniformly at a rotational speed of 400 rpm at a depth of 550 mm from the molten metal surface. The molten aluminum alloy was treated by blowing.
[0013]
A swirl flow prevention cover made of graphite with a thickness of 10 mm is prepared with various inner diameters to ensure a predetermined gap width composed of the inner periphery of the swirl flow generation prevention cover and the outer periphery of the rotating shaft. did. On the other hand, the immersion depth of the swirl flow generation prevention cover is movable so that it can be adjusted to an arbitrary length.
First, in this example, the swirl flow generation prevention cover indicated by 8 in FIG. 4 was attached at a distance of 10 mm from the rotating shaft 3 while changing the immersion depth, and a gas blowing process was performed.
[0014]
After the treatment, the hydrogen gas content in the molten aluminum alloy and the amount of oxide formed on the surface were measured and compared with the results of the treatment before, after the treatment, and the conventional method.
The analysis after the treatment was carried out after removing the treatment device from the cast iron crucible, and after gently stirring for 3 minutes, taking a sample, and as an analysis means, the amount of hydrogen gas was calculated using the Lansley method. In addition, the Olin-Frit test method was used for the amount of oxide film representing inclusions. The result is shown in FIG.
[0015]
Example 2
The swirl flow generation prevention cover indicated by 8 in FIG. 4 is attached by changing the distance between the rotating shaft and the swirl flow generation prevention cover by unifying the immersion depth to 250 mm and performing the gas blowing process under the same conditions as in the first embodiment. Went. Thereafter, in the same manner as in Example 1, the hydrogen gas content and the surface oxide amount in the molten aluminum alloy were measured.
The result is shown in FIG.
[0016]
As can be seen from the results shown in FIGS. 5 and 6, the hydrogen gas content in the molten aluminum alloy is reduced to half or less in both the conventional method and the method of the present invention after the treatment, compared to before the treatment. Yes. Due to the installation of the swirl flow generation prevention cover, the hydrogen gas content is reduced as compared with the prior art, and in order to enhance the installation effect of the swirl flow generation prevention cover, it is preferable to cover the rotating shaft deeper, It is preferable to install with a small distance from the rotating shaft.
[0017]
The amount of oxide film in the molten aluminum alloy after molten metal treatment is larger than that before treatment in the conventional method, whereas in the case of the method of the present invention, a significant improvement effect is confirmed under any condition setting. It was.
And the installation effect of installation of the swirl | flow generation | occurrence | production prevention cover regarding the amount of oxide films becomes so high that the immersion depth of this cover is deepened, and becomes remarkable by covering even a rotary body. In addition, regarding the amount of the oxide film, it is preferable to install it with a small distance from the rotating shaft.
In addition, the phenomenon that the amount of oxide film increased by the conventional method than before treatment is that the oxide film originally on the molten metal surface is caught in the swirling flow of molten aluminum accompanying the rotation of the treatment device, and enters the molten metal, This is probably because the oxide film newly formed on the molten metal surface was rewound by eddy current.
[0018]
【The invention's effect】
As described above, a vertical rotation shaft having a gas ventilation path extending in the axial direction inside, and a gas blower provided at the tip of the vertical rotation shaft and connected to the gas ventilation path on either the bottom surface or the side surface. When processing the molten metal by rotating the rotating body provided with the outlet in the molten metal, the vertical rotating shaft is covered with a non-rotating swirl flow prevention cover, thereby generating swirl vortex in the molten metal. Therefore, it is possible to provide a molten metal processing apparatus capable of preventing, efficiently removing contained gases and non-metallic inclusions and preventing oxidation of the molten metal itself, and can contribute particularly to the improvement of quality of aluminum alloys and the like.
[Brief description of the drawings]
[Fig. 1] Conventional molten metal processing equipment [Fig. 2] Water model experimental device [Fig. 3] Graph showing the eddy current generation state by water model experiment [Fig. 4] Conceptual diagram of molten metal processing device of the present invention [Fig. Graph showing changes in hydrogen gas content and oxide film formation amount in the molten metal depending on the immersion depth of the flow prevention cover [Fig. 6] Hydrogen gas in the molten metal due to the difference in the distance from the rotating shaft of the swirl prevention cover Graph showing changes in content and oxide film formation amount [Explanation of symbols]
1: molten metal, 2: molten metal tank, 3: rotating shaft, 4: rotating body,
5: Gas outlet, 6: Plastic piece, 7: Motor,
8: Swirl flow prevention cover

Claims (1)

A molten metal holding tank, a vertical rotating shaft that is disposed in the molten metal holding tank and has a gas vent passage extending in the axial direction therein, and provided at the tip of the vertical rotating shaft and on either or both of the bottom surface and the side surface comprising: the rotating body in which the gas vent passage and continuous gas outlet is provided, a non-rotating swirling flow prevention cover covering also the rotating body of the rotating shaft tip covers the vertical shaft Molten metal processing equipment.

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