JP2021159984A - Molten metal holding furnace for low-pressure casting - Google Patents

Abstract

To provide a molten metal holding furnace for low pressure casting capable of preventing or suppressing air bubbles generated from a refractory material constituting a molten metal storage container from flowing in through a lower end opening of a stoke.SOLUTION: A molten metal holding furnace for low pressure casting has: a furnace body comprising a molten metal storage container 10 and a stoke 3 for connecting a molten metal M inside the molten metal storage container to a cavity of a mold; and pressurized gas supply means for supplying pressurized gas to an internal space in the molten metal storage container 10. The molten metal holding furnace for low pressure casting has a bubble guide member 20 which is arranged to face a lower end opening of the stoke 3 and whose outer edge 20a is located outside the lower end opening position of the stoke 3. The bubble guide member 20 has a contact lower surface 20b whose lower surface at least in a peripheral part thereof comes into contact with the molten metal M, and the contact lower surface 20b is provided with a guide part having an inclination that rises toward the outer edge 20a.SELECTED DRAWING: Figure 2

Description

The present invention relates to a molten metal holding furnace for low pressure casting. In particular, the present invention relates to a molten metal holding furnace for low-pressure casting, which is suitable for a low-pressure casting method in which a molten metal of aluminum, an aluminum alloy, a non-ferrous metal, or the like is injected into a mold at a low speed and a low pressure to form a cast product.

Low-pressure casting methods for obtaining castings such as aluminum, aluminum alloys and non-ferrous metals are known.
In this low-pressure casting method, air, dry air, or a gas such as an inert gas such as argon or nitrogen is held by pressurizing and supplying it to a holding furnace containing the molten metal at a low pressure of 0.01 to 0.2 MPa. The molten metal in the furnace (melted metal storage container) is filled into the cavity of the mold.
When the solidification of the filled molten metal is completed, the pressure in the holding furnace is released, the mold is removed, and the cast product is extruded.

Generally, this type of low-pressure casting molten metal holding furnace is provided with a molten metal storage container made of a breathable refractory material such as a standard refractory or an amorphous refractory. As a result, the following phenomenon occurs.

That is, in the process of supplying a pressurized gas (hereinafter, also referred to as a pressurized gas), pressure is applied to the inside of a breathable refractory material such as a standard refractory or an irregular refractory constituting the molten metal storage container. The gas invades and is once held inside the refractory material.
After that, in the process of stopping the supply of the pressurized gas and exhausting it from the holding furnace (releasing the pressurization), when the pressure in the molten metal storage container becomes almost the same as the atmospheric pressure, the inner surface of the molten metal storage container The gas that has entered the refractory material from the inner bottom surface (hearth) becomes bubbles and is released into the molten metal. At that time, the bubbles rise while oxidizing the surrounding molten metal, and flow into the stalk (hot water supply pipe) together with the oxide. Bubbles and oxides that have flowed into the stalk flow into the mold cavity from the outlet when the pressurized gas is supplied to the holding furnace again, and are hard spots (existing inside the product) in the cast product. It has been a cause of deterioration of product quality, such as the generation of hard foreign substances. The phenomenon of oxidizing the molten metal is particularly remarkable when the supplied pressurized gas is air.

As a remedy for this, in Patent Document 1, a non-breathable air bubble blocking member having a size larger than the lower end opening of the stalk is arranged at a position facing the lower end opening of the stalk in the hearth of the molten metal storage container. By doing so, it is disclosed that air bubbles from the hearth surface are prevented from entering the lower end opening of the stalk.

Similarly, as shown in Patent Document 2, the present inventor also arranges a plate-shaped member made of a material having a lower porosity than the molten metal storage container so as to be substantially directly below the lower end opening of the stalk. , Disclosed to prevent the inflow of air bubbles into the molten metal injected from the stalk into the mold.

JP-A-2018-12131 Japanese Unexamined Patent Publication No. 2018-94622

However, as in Patent Document 1, when a non-breathable air bubble blocking member having a size larger than the lower end opening of the stalk is arranged, making it into a desired flat plate shape and size causes distortion during firing. Easy to manufacture and difficult to manufacture. Moreover, even if it can be manufactured, there is a problem in terms of economy such as a high unit price due to a low yield.

Further, the present inventors, as in Patent Document 2, even if a plate-shaped member made of a refractory material having a low porosity is arranged, bubbles and oxides generated may be generated from the lower end opening of the stalk depending on the movement of the molten metal. We obtained the knowledge that there are still problems that may flow in.
Further, in Patent Document 1, it is naturally expected that there will remain a problem that generated bubbles and oxides may flow in from the lower end opening of the stalk depending on the movement of the molten metal.

Therefore, a main subject of the present invention is to provide a molten metal holding furnace for low-pressure casting that can prevent or suppress the inflow of bubbles and oxides generated from the refractory material constituting the molten metal storage container from the lower end opening of the stalk. To do.

Aspects according to the present invention that solve the above problems are as follows.

<First aspect>
A furnace body equipped with a molten metal storage container and a stalk that connects the molten metal inside the container and the cavity of the mold.
A pressurized gas supply means for supplying a pressurized gas to the internal space inside the molten metal storage container, and
It is a molten metal holding furnace for low-pressure casting with
It has a bubble guiding member which is arranged to face the lower end opening of the stalk and whose outer edge is located outward from the lower end opening position of the stalk.
The bubble induction member has a contact lower surface in which the lower surface at least in the peripheral portion thereof comes into contact with the molten metal.
The lower surface of the contact is provided with a guide portion having an inclination that rises toward the outer edge.
A molten metal holding furnace for low-pressure casting.

<Second aspect>
A furnace body equipped with a molten metal storage container and a stalk that connects the molten metal inside the container and the cavity of the mold.
A pressurized gas supply means for supplying a pressurized gas to the internal space inside the molten metal storage container, and
It is a molten metal holding furnace for low-pressure casting with
It has a bubble guiding member which is arranged to face the lower end opening of the stalk and whose outer edge is located outward from the lower end opening position of the stalk.
The bubble induction member has at least a first member and a second member, and the lower surface of at least the peripheral portion of the second member has a contact lower surface that comes into contact with the molten metal.
The lower surface of the contact is provided with a guide portion having an inclination that rises toward the outer edge.
A molten metal holding furnace for low-pressure casting.

According to the present invention, it is possible to prevent or suppress the inflow of air bubbles and oxides generated from the refractory material constituting the molten metal storage container from the lower end opening of the stalk.

It is a schematic sectional view of the molten metal holding furnace for low pressure casting. The first embodiment is shown, in which (a) is a sectional view of a main part and (b) is a bottom view of a bubble guiding member. The second embodiment is shown, in which (a) is a cross-sectional view of a main part and (b) is a bottom view of a bubble guiding member. A third embodiment is shown, in which FIG. 3A is a cross-sectional view of a main part and FIG. 3B is a bottom view of a bubble guiding member. A fourth embodiment is shown, in which (a) is a cross-sectional view of a main part and (b) is a bottom view of a bubble guiding member. A fifth embodiment is shown, in which FIG. 5A is a cross-sectional view of a main part and FIG. 5B is a bottom view of a bubble guiding member. A sixth embodiment is shown, in which FIG. 6A is a cross-sectional view of a main part and FIG. 6B is a bottom view of a bubble guiding member. A seventh embodiment is shown, in which FIG. 7A is a cross-sectional view of a main part and FIG. 7B is a bottom view of a bubble guiding member.

Hereinafter, embodiments of the present invention will be described.

The molten metal holding furnace 1 shown in FIG. 1 is a one-chamber type molten metal holding furnace for low-pressure casting that also serves as a molten metal holding chamber and a pressurizing chamber, and includes a molten metal storage container 10 for storing the molten metal. The container layer 11, the fireproof layer 12, and the heat insulating layer 13 are located in this order from the inside, and the outer wall (iron skin) 14 covers the bottom surface, the side surface, and the upper surface on the outside.

The container layer 11 is formed of a breathable refractory material, such as an alumina-based amorphous refractory. The container layer 11 in the embodiment is formed by mixing, for example, powdered alumina, silicon dioxide, and water in advance, forming the container layer 11 into a predetermined shape, and drying and firing the mixture. The heat insulating layer 13 can be formed by, for example, attaching a refractory cloth to a standard heat insulating body.

The molten metal holding chamber 6, which is the internal space of the molten metal storage container 10, is provided with, for example, a cylindrical stalk 3 having a hot water outlet 2 at the upper portion, and constitutes a furnace main body. Further, the molten metal holding chamber 6 is provided with a tube heater 7 fixed to the side wall portion (details are not shown), and the molten metal M inside can be held within a predetermined temperature range. The molten metal holding chamber 6 is provided with an air supply port 4 and an exhaust port 5 at the upper portion so that pressurized gas can be supplied and exhausted to the inside of the molten metal holding chamber 6.

In the molten metal holding furnace 1, the molten metal M is stored in the molten metal holding chamber 6 in advance.
Air, dry air, or an inert gas such as argon or nitrogen, etc., via the air supply port 4 by a pressurized gas supply means (not shown) that supplies the pressurized gas to the internal space inside the molten metal storage container 10. Pressurized gas is sent into the molten metal holding chamber 6. At this time, since the container layer 11 of the molten metal storage container 10 is formed of a breathable refractory material such as an amorphous refractory material made of alumina, silicon dioxide, etc., the inside of the refractory material constituting the molten metal storage container 10 Pressurized gas may enter the container.

The liquid level of the molten metal M is pressurized by the pressurized gas sent into the molten metal holding chamber 6, and the molten metal M rises in the stalk 3 and enters the cavity of the casting die (not shown) through the hot water outlet 2. It is press-fitted.

After the casting is completed, the supply of the pressurized gas from the air supply port 4 is stopped, and the pressurized gas in the molten metal holding chamber 6 is exhausted from the exhaust port 5. In the step of releasing the pressure, when the pressure is released at once and becomes almost the same as the atmospheric pressure, the pressure is invaded and held in the container layer 11, the refractory layer 12 and / or the heat insulating layer 13 in the molten metal storage container 10. The pressurized gas that has been used is released as bubbles from the container layer 11.

As described above, the bubbles accompanying the release of the pressurized gas rise while oxidizing the surrounding molten metal, and flow into the stalk 3 together with the oxide. The bubbles and oxides that have flowed into the stalk 3 flow into the mold cavity (not shown) from the outlet 2 when the pressurized gas is supplied into the molten metal holding furnace 1 again, and are cast. It has been a cause of deterioration of product quality, such as causing hard spots (hard foreign substances existing inside the product) on the product.

Various embodiments have been proposed to prevent or suppress this.

As shown in FIG. 1, the present invention is provided in a furnace main body including a molten metal storage container 10, a molten metal M inside the molten metal storage container 10, and a stalk 3 for connecting a cavity of a mold, and an internal space inside the molten metal storage container 10. The present invention relates to a molten metal holding furnace for low-pressure casting having a pressurized gas supply means for supplying the pressurized gas.

In the first embodiment, as shown in FIG. 2, the bubble guiding member 20 is arranged so as to face the lower end opening of the stalk 3 and the outer edge 20a is located outside the lower end opening position of the stalk 3. The bubble guiding member 20 has a contact lower surface 20b whose lower surface at least in its peripheral portion contacts the molten metal M, and the contact lower surface 20b includes a guiding portion having an inclination that rises toward the outer edge 20a.

The bubble guiding member 20 of the first embodiment is, for example, an inverted conical trapezoid formed in a disk shape and whose contact lower surface 20b is inclined toward a peripheral edge (outer edge 20a).
The contact lower surface 20b may not be a uniform inclined surface as shown in the figure, but may be a curved surface such as an arc.

As the bubble induction member according to the present invention, a material that is breathable, a material that has a lower porosity than the container layer 11, a non-breathable material, or the like can be used, and the material is not limited for the following reasons. ..

That is, according to the first embodiment, if the bubble release position due to the release of the pressurized gas is located outside the outer edge 20a of the bubble guiding member 20, the bubble rises as it is, so that the stalk 3 It is possible to avoid the opening at the lower end of the stalk 3 and prevent bubbles and oxides from flowing into the stalk 3.
Further, even if the bubble release position due to the release of the pressurized gas is inward from the outer edge 20a of the bubble guiding member 20, the bubbles and oxides are guided along the contact lower surface 20b and the peripheral edge (outer edge 20a). Since it rises from the outside of the peripheral edge (outer edge 20a) toward, the lower end opening of the stalk 3 is avoided, and bubbles and oxides can be prevented from flowing into the stalk 3.

By using the bubble guiding member having the guiding portion of the embodiment, there are the following advantages as compared with the form without the guiding portion shown in Patent Document 1.
Even if the release of bubbles from the container layer 11 due to the release of the pressurized gas is at a position including the lower end opening of the stalk 3, the lower surface 20b of the contact serves as a bubble induction portion, and the rise of bubbles and oxides is on the periphery ( Since it is outside the outer edge 20a), the lower end opening of the stalk 3 is avoided, and bubbles and oxides can be prevented from flowing into the stalk 3.

Then, in particular, bubbles and oxides come to store kinetic energy having a horizontal vector in the process of being induced (rised) along the contact lower surface 20b, and do not rise as it is from the peripheral edge (outer edge 20a). As schematically shown in FIG. 2, the air is discharged to the outside from the peripheral edge (outer edge 20a), so that the effect of avoiding the lower end opening of the stalk 3 is high.

In the second embodiment shown in FIG. 3, the annular grooves 20b1 and 20b2 are formed on the contact lower surface of the bubble guiding member 20A, and the entire surface is inclined upward toward the peripheral edge (outer edge 20a). Bubbles and oxides that have entered the annular grooves 20b1 and 20b2 accumulate and become saturated, and when they flow out from the annular grooves 20b1 and 20b2, they become large as kinetic energy having a horizontal vector and move outward in the radial direction. Is smooth.
Further, an appropriate support column portion 23 can be formed in the vicinity of the outer edge 20a.

In the third embodiment shown in FIG. 4, the contact lower surface 20b of the bubble guiding member 20B straddles the axis of the stalk 3 and has an ascending inclined surface from one side toward the other outer edge 20a.
Although the bubble guiding member 20B in the illustrated example is square in a plan view, it may have another shape such as a circle or an ellipse. The support pillar portion 23 is formed.

In the fourth embodiment shown in FIG. 5, a groove 20 g is formed on the lower surface of the bubble induction member 20C, and the groove 20 g straddles the axis of the stalk 3 and inclines upward from one to the other outer edge 20a. This is an example in which a contact lower surface 20b for guidance is formed by using a surface.
In this embodiment, there is an advantage that bubbles and oxides cannot move in the vertical direction of FIG. 5 (b) due to both walls of the groove 20 g, and are guided exclusively to the left of FIG. 5 (b).
In FIG. 5, a plurality of grooves 20g are formed to form a plurality of contact lower surfaces 20b for guidance, but only one groove 20g is formed and only one contact lower surface 20b for guidance is formed. You may.

Although the bubble guiding member in the above example is composed of a single member, it is possible to form a bubble guiding member having a guiding portion by a plurality of members, for example, two members as in the fifth embodiment of FIG. can.
For example, corresponding to the stalk 3, the bubble induction member 20 is composed of the first member 21 located in the central portion and the second member 22 located in the peripheral portion, and at least the periphery of the second member 22. The lower surface of the portion has a contact lower surface 20b that comes into contact with the molten metal, and the contact lower surface 20b is provided with an induction portion that has an inclination that rises toward the outer edge 20a.
Further, the first member 21 and the second member 22 may be the same member or may be different members. For example, the first member 21 may be a breathable material and the second member 22 may be a material having a lower porosity than the container layer 11, or the first member 21 may be a breathable material and a second member. 22 may be a non-breathable material. Furthermore, both the first member 21 and the second member 22 may be made of a breathable material. That is, any combination of a breathable material, a material having a porosity lower than that of the container layer 11, and a non-breathable material may be used.
Examples of the breathable material include silicon carbide, low cement refractory, silicon carbide refractory, high alumina refractory, silicon nitride-bonded silicon carbide refractory, and zirconia refractory. In particular, low cement refractories and silicon nitride-bonded silicon carbide refractories are desirable. Furthermore, it may be the same as the breathable refractory material for molding the container layer 11.
Examples of the material having a porosity lower than that of the container layer 11 include porous ceramics, for example, porous alumina ceramics and porous silicon carbide ceramics.
Examples of the non-breathable material include fine ceramics, for example, silicon nitride fine ceramics and the like.
Also in this form, the shape in a plan view is not limited.

The bubble guiding member is installed on the surface of the container layer 11, and as in the sixth embodiment shown in FIG. 7, a recess 11a is formed in the container layer 11, and the bubble guiding member 20D is provided in the recess 11a. It is almost the same surface as the surface of the container layer 11.
In the sixth embodiment shown in FIG. 7, a groove 20 g is formed on the lower surface of the bubble induction member 20D, and the groove 20 g forms the axis of the stalk 3 as in the fourth embodiment shown in FIG. This is an example in which a contact lower surface 20b for guidance is formed by straddling and forming an ascending inclined surface from one side toward the other outer edge 20a.

Further, as in the seventh embodiment shown in FIG. 8, the bubble guiding member is installed on the container layer 11 surface as in the fourth embodiment shown in FIG. 5, and the sixth embodiment shown in FIG. It is also possible to set the intermediate position between the surface of the container layer 11 and the form having substantially the same surface as in the embodiment of the above.

As described above, the bubble induction member may be a breathable material. Examples of the breathable material suitable for the bubble induction member include silicon carbide, low cement refractory, silicon carbide refractory, high alumina refractory, silicon nitride-bonded silicon carbide refractory, and zirconia refractory. In particular, low cement refractories and silicon nitride-bonded silicon carbide refractories are desirable. Furthermore, it may be the same as the breathable refractory material for molding the container layer 11. Since the bubbles released from the container layer 11 are generated when the pressure is released at once and become substantially the same as the atmospheric pressure, the diameter of the bubbles is larger than the pores of the container layer 11.
Therefore, for example, even if the bubble guiding member is formed of the refractory material forming the container layer 11, the bubbles in contact with the contact lower surface 20b do not penetrate the bubble guiding member.
Therefore, as long as the form is such that bubbles are induced, it is not necessary to select a special material, and a refractory material in the technical field of this type of molten metal can be used.

The inclination angle of the contact lower surface with respect to the horizontal plane (inclination angle θ is shown only in FIG. 5) is preferably 1 to 45 degrees, particularly 1 to 10 degrees. If it is less than 1 degree, the effect of inducing bubbles and oxides is not sufficient, and if it exceeds 45 degrees, bubbles and oxides do not escape from the outer edge 20a to the outside and rise from the outer edge 20a as it is, sometimes. The molten metal will be fluidized, and from these viewpoints, the effect of suppressing the inflow into the lower end opening of the stalk will be insufficient.

Further, the bubbles and oxides in contact with the contact lower surface 20b may be hindered from moving due to friction due to the unevenness on the surface of the contact lower surface 20b, and may be difficult to be guided. A glass-based coating material may be applied, and if there is a groove on the contact lower surface 20b, the glass-based coating material may be applied in advance only to the groove.

The above embodiments have been described as applying the present invention to a one-chamber type molten metal holding furnace for low-pressure casting that also serves as a molten metal holding chamber and a pressurizing chamber, but the present invention is limited to the one-chamber type. However, it is applicable to all low-pressure casting molten metal holding furnaces provided with a molten metal holding chamber and a pressure chamber, such as a two-chamber type molten metal holding furnace consisting of a molten metal holding chamber and a pressure chamber. Furthermore, it applies to at least all low-pressure casting molten metal holding furnaces equipped with a pressurizing chamber.

On the other hand, the bubble induction member is arranged so as to face the lower end opening of the stalk. That is, when the lower end opening of the stalk is projected downward, the bubble guiding member is provided on the hearth of the molten metal storage container at a part of the lower position where the outer edge of the bubble guiding member can cover the projection. Is.
Here, the “on the hearth portion” may be in contact with the “surface of the hearth portion”, or may be separated from the “surface of the hearth portion” by being supported by, for example, a support member. ..
Further, when the bubble guiding member is composed of a plurality of members, the outer edge of the member constituting the peripheral portion of the bubble guiding member may cover the lower end opening projection of the stalk.

The molten metal may be aluminum, an aluminum alloy, or another metal molten metal. Also, those skilled in the art will appreciate that the above embodiments can be modified in various ways.

1 ... molten metal holding furnace, 3 ... stalk, 10 ... molten metal storage container, 11 ... container layer, 11a ... recess, 12 ... refractory layer, 13 ... heat insulating layer, 20, 20A, 20B, 20C, 20D, 20E ... bubble induction member , 20a ... outer edge, 20b ... contact bottom surface, 20g ... groove, 21 ... first member, 22 ... second member, M ... molten metal, B ... air bubbles or oxides.

Claims (8)

A furnace body equipped with a molten metal storage container and a stalk that connects the molten metal inside the container and the cavity of the mold.
A pressurized gas supply means for supplying a pressurized gas to the internal space inside the molten metal storage container, and
It is a molten metal holding furnace for low-pressure casting with
It has a bubble guiding member which is arranged to face the lower end opening of the stalk and whose outer edge is located outward from the lower end opening position of the stalk.
The bubble induction member has a contact lower surface in which the lower surface at least in the peripheral portion thereof comes into contact with the molten metal.
The lower surface of the contact is provided with a guide portion having an inclination that rises toward the outer edge.
A molten metal holding furnace for low-pressure casting. A furnace body equipped with a molten metal storage container and a stalk that connects the molten metal inside the container and the cavity of the mold.
A pressurized gas supply means for supplying a pressurized gas to the internal space inside the molten metal storage container, and
It is a molten metal holding furnace for low-pressure casting with
It has a bubble guiding member which is arranged to face the lower end opening of the stalk and whose outer edge is located outward from the lower end opening position of the stalk.
The bubble induction member has at least a first member and a second member, and the lower surface of at least the peripheral portion of the second member has a contact lower surface that comes into contact with the molten metal.
The lower surface of the contact is provided with a guide portion having an inclination that rises toward the outer edge.
A molten metal holding furnace for low-pressure casting. The molten metal holding furnace for low-pressure casting according to claim 1 or 2, wherein the bubble induction member is made of a breathable material. The molten metal holding furnace for low-pressure casting according to claim 1 or 2, wherein the bubble induction member is made of a breathable material having a low porosity that constitutes the molten metal storage container. The molten metal holding furnace for low-pressure casting according to claim 1 or 2, wherein the induction portion has an inclination that rises from the central portion of the bubble induction member toward the peripheral portion thereof. The molten metal holding for low-pressure casting according to claim 1 or 2, wherein the induction portion extends from one side in the horizontal direction of the bubble induction member to the other side, and the extending edge on the other side forms the outer edge. Furnace. The molten metal holding furnace for low-pressure casting according to claim 5, wherein the induction portion is formed by a groove that opens downward, and the groove bottom has an inclination that rises toward the outer edge. The molten metal holding furnace for low-pressure casting according to claim 2, wherein the first member and the second member are made of different materials.

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