JP2008164249A - Melting and retaining furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a melting and retaining furnace capable of effectively applying molten metal stirring force when using a permanent magnet type molten metal stirring device. <P>SOLUTION: In the melting and retaining furnace 1, the permanent magnet type molten metal stirring device 10 is arranged below a hearth member 2. The hearth member 2 has a structure comprised by laminating a silicon nitride sheet with relatively superior high temperature strength than an inner side refractory material layer 23, and outer side refractory material layers 21, 2 comprised of at least one type of a silicon carbide sheet on top faces and bottom faces of one layer or plural layers of the inner side refractory material layer 23. Or, an opening is provided on a bottom plate 3 of the melting and retaining furnace to suppress magnetic force shielding of a permanent magnet of the molten metal stirring device 10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a melting / holding furnace used as a melting furnace for metals such as aluminum, and more particularly to a melting / holding furnace in which a permanent magnet for stirring molten metal is disposed below.

  For example, in a melting / holding furnace for holding molten aluminum, an agitator for stirring the molten metal is generally provided in order to save energy and prevent variation in component analysis values. As a method for stirring the molten metal, various methods have been devised and implemented, such as mechanical stirring, stirring by introducing gas into the molten metal, utilization of suction and discharge by a vacuum pump, and application of magnetic force by an electromagnetic stirring device.

  Each method is characterized by effects, equipment costs, running costs, safety and workability.

  Therefore, recently, a permanent magnet-type molten metal stirring device has been proposed that has a low equipment cost, is surprisingly compact, is easy to control and maintain, and has a very low running cost (see, for example, Patent Document 1). ).

  However, in the permanent magnet type, the strength of the magnet at the time of equipment design determines the stirring capacity, and the magnetic force of the magnet is fixed and cannot be changed during operation. In addition to this, it is necessary to devise the melting / holding furnace side.

In order to obtain sufficient stirring force by the permanent magnet type (a) The distance between the magnet and the molten metal should be as close as possible.

(B) It is desirable that there is no magnetic shielding material such as a magnetic material between the magnet and the molten metal.
JP-A-10-146650

However, in conventional melting and holding furnaces for metals such as aluminum,
-The hearth member that forms the bottom of the holding furnace is composed of several hundreds of millimeters of refractory material and heat insulating material.
The bottom surface of the hearth member is covered with a bottom plate made of an iron-based material such as an iron plate (SUS in the case of electromagnetic stirring).
The structure is such that the magnetic force is shielded. For this reason, the molten metal stirring force by a permanent magnet could not fully be acted on.

  The present invention has been made in view of such a technical background, and when a permanent magnet type molten metal stirring device is used, a melting and holding furnace capable of effectively acting the molten metal stirring force. For the purpose of provision.

In order to sufficiently obtain the stirring force of the permanent magnet type molten metal stirring apparatus, the present inventors make the distance between the magnet and the molten metal as close as possible,
-There should be no magnetic shielding such as magnetic material between the magnet and the molten metal.
As a result of diligent research on the structure of melting and holding furnaces that enable this, the conventional common refractory structure was overturned, and a new refractory structure was invented.

 In addition, attention was paid to the holding furnace structure itself, and the problem was solved by using it in combination with the above refractory material structure.

That is, the said subject is solved by the following means.
(1) A melting / holding furnace in which a permanent magnet type molten metal stirring device is disposed below a hearth member constituting the bottom of the holding furnace, wherein the hearth member is an inner refractory material having one or more layers. A structure in which an outer refractory material layer composed of at least one of a silicon nitride plate and a silicon carbide plate having relatively higher high-temperature strength than the inner refractory material layer is laminated on the upper and lower surfaces of the layer. A melting / holding furnace.
(2) A melting / holding furnace in which a bottom plate made of an iron-based material is arranged on the bottom surface of a hearth member constituting the bottom of the holding furnace, and a permanent magnet type molten metal stirring device is arranged below the bottom plate, The melting / holding furnace, wherein the bottom plate is provided with an opening at a position above the molten metal stirring device, and the hearth member is exposed through the opening.
(3) A melting and holding furnace in which the bottom surface of the hearth member constituting the bottom of the holding furnace is covered with a bottom plate made of an iron-based material, and a permanent magnet type molten metal stirring device is disposed below the bottom plate, The hearth member is composed of at least one of a silicon nitride plate and a silicon carbide plate which are relatively superior in high-temperature strength to the upper and lower surfaces of one or more inner refractory material layers than the inner refractory material layer. The outer refractory material layer is laminated, and the bottom plate is provided with an opening at a position above the molten metal stirring device, and the hearth member is exposed through the opening. A melting and holding furnace characterized by having
(4) The melting / holding furnace according to item 1 or 3, wherein the inner refractory material layer is composed of at least one of high alumina brick, alumina cement castable, chamotte brick, lightweight heat insulating castable, and heat insulating board.
(5) The melting / holding furnace according to item 2 or 3, wherein the opening ratio of the opening is 30% or more.
(6) The melting / holding furnace according to any one of items 1 to 3, wherein a cooling medium is supplied to a gap between the molten metal stirring device.

  According to the invention described in the preceding item (1), the hearth member is formed on the upper surface and the lower surface of one or a plurality of inner refractory material layers, and has a relatively high temperature strength compared to the inner refractory material layer. Since the outer refractory material layer composed of at least one of a plate and a silicon carbide plate is laminated, the thickness can be reduced without reducing the fire resistance of the hearth member. Therefore, the distance between the molten metal stirring device of the permanent magnet type and the molten metal can be shortened, and the magnetic force acting on the molten metal by the permanent magnet can be increased.

  According to the invention described in the preceding item (2), the bottom plate made of iron-based material is disposed on the bottom surface of the hearth member, and the bottom plate is provided with an opening at a position above the molten metal stirring device, and the opening is Therefore, the magnetic force acting on the molten metal is suppressed from being shielded by the bottom plate by the permanent magnet of the molten metal stirring device, and a large magnetic force can be applied to the molten metal.

  According to the invention described in item (3), a large magnetic force can be applied to the molten metal due to the presence of both the structure of the hearth member and the opening of the bottom plate.

  According to the invention described in item (4), at least one of high alumina brick, alumina cement castable, chamotte brick, lightweight insulating castable, and insulating board can be used as the inner refractory material layer.

  According to the invention described in item (5) above, since the opening ratio of the opening of the bottom plate is 30% or more, a large magnetic force can be reliably applied to the molten metal.

  According to the invention described in the preceding item (6), since the cooling medium is supplied to the gap between the molten metal stirring device, the high temperature deterioration of the permanent magnet of the molten metal stirring device due to the temperature rise of the hearth member can be suppressed. At the same time, the distance between the molten metal stirring device and the bottom plate can be shortened, and a larger magnetic force can be applied to the molten metal.

  FIG. 1 is a longitudinal sectional view showing a schematic configuration of an aluminum melting / holding furnace according to an embodiment of the present invention, and FIG. 2 is a bottom view.

  The inventors first scrutinized how much stirring force can be obtained by the permanent magnet type aluminum molten metal stirring device 10 using a commercially available Nd-Fe magnet that can obtain high magnetic force, and stirring force. The requirements for maximizing are summarized.

as a result,
(A) The distance from the upper surface (permanent magnet surface) of the permanent magnet type aluminum stirring device 10 to the molten aluminum (molten metal) 20 is set to 400 mm or less.
(B) The distance from the upper surface of the permanent magnet type aluminum melt stirring apparatus 10 to the hearth member 2 constituting the bottom of the holding furnace 1 is set to 50 mm or less.

(C) It is better that there is no bottom plate made of an iron-based material that covers the lower surface of the hearth member 2 in a portion corresponding to an area where a magnetic force that causes stirring is crossed.
The conclusion was obtained.

  However, as described in the background art section, a conventional holding furnace has a structure that obstructs them. Therefore, we first focused on the refractory structure of the furnace.

  The hearth member 2 in a conventional general furnace is constructed with fire bricks and castables having high fire resistance as the first layer from the molten aluminum side. The thickness of brick is about 230mm, and it can be 300 ~ 400mm by castable construction. In addition, the second layer is made of brick or castable having an appropriate fire resistance and heat insulation, although its fire resistance is lower than that of the first layer, and its thickness is set to 100 to 200 mm. Brick or lightweight castable with excellent heat insulation performance is applied to the third layer. The thickness is also 100 to 200 mm.

  As the fourth layer, a 25 to 50 mm heat insulating board having a very good heat insulating property is often adopted. A heat-resistant fiber may be laid between the bottom plate 3 as the casing material below and the heat insulating board (thickness of about 10 mm).

  The bottom plate 3 is made of an iron-based material such as SS steel or SUS steel having a thickness of about 3 to 9 mm.

  With such a configuration, there are many furnaces exceeding 450 mm even if the thickness of the hearth member 2 is thin.

  Moreover, in the furnace using the crucible 4, although the refractory material structure is designed to be thinner than a general reflection furnace, in addition to the similar refractory material structure, the thickness of the crucible 4 itself (about 50 mm) and the crucible base (high It is common to use a fixed base called 30 to 80 mm).

Therefore, in this embodiment, the conventional structure as described above has been fundamentally reviewed. That means
[1] For the uppermost layer on the side of the molten aluminum (molten metal), a refractory having a high fire resistance is used. Moreover, a plate-like refractory material is required instead of a brick-like one.
[2] Below that, refractory materials and heat insulating materials such as high alumina bricks and chamotte bricks are used, but for example, bricks do not use long pieces, but use the short piece side to suppress the thickness. .
[3] A heat insulating board or the like may be used, but in order to suppress the thickness, it is reduced to about half of the conventional one.
[4] If the lowermost layer is left as [2] or [3], there is a high possibility that the brick will collapse or the board will break, making it impossible to maintain the refractory material. Therefore, a plate-like refractory material that is strong and resistant to heat is required for the lowermost layer.

  Therefore, when the design was made in consideration of these comprehensively, it was found that silicon nitride or silicon carbide plate material is suitable for the uppermost layer (molten aluminum side) and the lowermost layer (bottom plate side) of the hearth member 2. I understood. For this reason, the refractory material structure of the hearth member 2 has a structure in which the inner refractory material layer 23 is sandwiched by upper and lower silicon nitride plates or silicon carbide plates as the outer refractory material layers 21 and 22 of about 20 to 60 mm. . However, this sandwich structure only needs to be included in at least a part of the hearth member 2, and it is excluded that another refractory material is disposed further outside the outer refractory material layers 21 and 22 of the sandwich structure. It is not a thing.

  In this structure, the distance from the upper surface (permanent magnet surface) of the permanent magnet type aluminum stirring device 10 to the molten aluminum (molten metal) 20 can be made 400 mm or less.

  Ideally, a refractory material (brick or castable) is 100 mm or less as an inner refractory material layer 23 between upper and lower outer refractory material layers 21 and 22 made of a silicon nitride plate of about 20 to 40 mm. Alternatively, it is preferable that the castable or heat insulating board is sandwiched to 100 mm or less and the total thickness is 250 mm or less.

  In the above structure, the temperature of the bottom surface of the hearth member (the refractory material surface of the lowermost layer) rises to near 150 to 250 ° C., and there is a concern about deterioration of the permanent magnet in the molten metal stirring device 10. It may be difficult to set the distance from the upper surface of the furnace floor to the lower surface of the hearth member 2 to 50 mm or less.

  Therefore, the stirrer 10 and the holding furnace are used for the purpose of preventing the permanent magnet from being deteriorated at a high temperature in combination with the provision of an in-device cooling mechanism for protecting the magnet in the main body of the permanent magnet type aluminum melt stirrer 10. It is recommended that a refrigerant supply means for supplying the refrigerant is provided in the gap with 1.

  The size L of the gap 5 between the stirring device 10 and the bottom plate 3 is 10 to 15 mm, and a cooling medium is passed through the gap 5 to suppress the temperature rise of the permanent magnet. The type of the cooling medium is not particularly defined, but air is sufficient, and the flow rate thereof may be about 6 to 15 L / min.

  Next, an iron plate-like casing material (bottom plate 3) disposed on the lower surface of the hearth member 2 will be described.

  Generally, the holding furnace 1 is manufactured by casing a bottom part and a side part with a plate material made of an iron-based material such as iron or a SUS plate, and assembling a refractory material therein. The crucible furnace further has a crucible 4 disposed therein.

  However, in that structure, a partition wall is provided on the bottom plate 3 of the casing between the permanent magnet type aluminum molten agitator 10 and the hearth member 2 (and thus the molten aluminum 20 located on the upper part thereof). That is, the passage of magnetic force is inhibited by the bottom plate 3.

  In the present embodiment, an opening 6 is formed in the bottom plate 3 as shown in FIG. 2 in the area where the magnetic force causing stirring of the molten metal 20 crosses, in other words, in the upper position of the stirring device 10, and the hearth member 2 By making the surface appear to be exposed, the influence of the magnetic force shielded by the bottom plate 3 is reduced.

  However, simply forming the opening 6 in the bottom plate 3 is expected to cause problems such as insufficient strength as a structure and dropping of the hearth member 2. As a result of repeated investigations on the ratio of the opening 6, an effect of reducing the influence of shielding from the opening ratio of 30% or more was found. The opening ratio is the area of the bottom plate 3 facing the circle formed at the outermost end of the permanent magnet when the permanent magnet of the stirring device 10 rotates (the total area where the magnetic force of the permanent magnet crosses). The ratio of the area which is not shielded by the bottom plate 3 in the area).

  The sandwich-structured hearth member 2 and the opened bottom plate 3 may be provided at the same time, or at least one of them may be provided at the same time. It is possible to increase the part ratio, and ideally, an opening ratio of 60 to 75% can be realized.

  In addition, in order to prevent the hearth member from falling off from the opening 6, a method of reinforcing with a cross plate 31 crossing the opening 6, a method of forming the opening 6 in a slit shape, an original material such as punching metal, etc. The bottom plate 3 may be formed of a plate that is not a continuous body.

  Next, examples of the present invention will be described.

  A crucible-type circular melting / holding furnace 1 as shown in FIG. 1 was manufactured. The crucible 4 was made of graphite.

  Further, for the hearth member 2, the refractory material 24 made of commercial high alumina bricks from the upper layer, the heat insulation material 25 made of commercially available B1 brick, and the inner refractory material layer 23 made of a three-layer structure of the heat insulation board 26 are implemented. In Product Example 1, a sandwich structure sandwiched between upper and lower outer refractory material layers 21 and 22 made of a silicon nitride plate was used. In the product example 2 of the present invention and the comparative product example 1, only the inner refractory material layer 23 is provided without providing the upper and lower outer refractory material layers 21 and 22.

  The bottom plate 3 as a casing located on the lower surface of the hearth member 2 is made of SUS, and in the first and second embodiment examples of the present invention, the opening 6 is provided in the bottom plate 3. In addition, a permanent magnet type molten metal stirring device 10 is disposed below the hearth member 2. Reference numeral 7 shown in FIG. 1 is a support leg for supporting the melting and holding furnace 1.

  In the product example 1 of the present invention, cooling air was supplied to the gap 5 between the molten metal stirring device 10 and the bottom plate 3 at a flow rate of 10 L / min.

  In the melting / holding furnace 1 having the above configuration, the dimensions of each component, the opening ratio of the bottom plate 3, the weight of the molten aluminum 20, etc. are set as shown in Table 1, and the permanent magnet of the molten metal stirring device 10 is rotated at a constant speed. It was rotated with.

  The rotational speed of the molten aluminum 20 at that time was investigated.

  The results are also shown in Table 1.

  As understood from the results of Table 1, in Comparative Product Example 1, the distance between the molten metal stirring device 10 and the molten metal 20 is large, and the magnetic force is shielded by the bottom plate 3 made of SUS without the opening 6. The rotation speed was low.

  On the other hand, in the product example 2 in which the opening 6 is provided in the bottom plate 3, the distance between the molten metal stirring device 10 and the molten metal 20 is the same, but the permanent magnet is shielded by the presence of the opening 6 in the bottom plate 3. Therefore, the melt rotation speed was larger than that of Comparative Product Example 1.

  In the product example 1 in which the upper and lower sides of the inner refractory material layer 23 are covered with silicon nitride plates and the opening 6 is provided in the bottom plate 3, the distance between the molten metal stirring device 10 and the molten metal 20 is short. Since the magnetic force of the permanent magnet is prevented from being shielded by the presence of the opening 6, the melt rotational speed is further increased as compared with the product example 2.

  Further, when the same test was performed by replacing the outer refractory material layers 21 and 22 from the silicon nitride plate to the silicon carbide plate, similar results were obtained.

It is a shield sectional view showing a schematic structure of a melting and holding furnace concerning one embodiment of this invention. FIG. 2 is a bottom view of the melting / holding furnace of FIG. 1.

Explanation of symbols

1 melting / holding furnace 2 hearth member 3 bottom plate 5 gap 6 opening 21, 22 outer refractory material layer 23 inner refractory material layer

Claims (6)

A melting and holding furnace in which a permanent magnet type molten metal stirring device is disposed below a hearth member constituting the bottom of the holding furnace,
The hearth member is composed of at least one of a silicon nitride plate and a silicon carbide plate which are relatively superior in high-temperature strength to the upper and lower surfaces of one or more inner refractory material layers than the inner refractory material layer. A melting / holding furnace having a structure in which an outer refractory material layer is laminated. A melting / holding furnace in which a bottom plate made of an iron-based material is arranged on the lower surface of a hearth member constituting the bottom of the holding furnace, and a permanent magnet type molten metal stirring device is arranged below the bottom plate,
The melting / holding furnace, wherein the bottom plate is provided with an opening at a position above the molten metal stirring device, and the hearth member is exposed through the opening. A melting / holding furnace in which the bottom surface of the hearth member constituting the bottom of the holding furnace is covered with a bottom plate made of an iron-based material, and a permanent magnet type molten metal stirring device is disposed below the bottom plate,
The hearth member is composed of at least one of a silicon nitride plate and a silicon carbide plate which are relatively superior in high-temperature strength to the upper and lower surfaces of one or more inner refractory material layers than the inner refractory material layer. The outer refractory material layer to be laminated,
The melting / holding furnace, wherein the bottom plate is provided with an opening at a position above the molten metal stirring device, and the hearth member is exposed through the opening.   The melting / holding furnace according to claim 1 or 3, wherein the inner refractory material layer is composed of at least one of high alumina brick, alumina cement castable, chamotte brick, lightweight heat insulation castable, and heat insulation board.   The melting / holding furnace according to claim 2 or 3, wherein an opening ratio of the opening is 30% or more.   The melting / holding furnace according to claim 1, wherein a cooling medium is supplied to a gap between the molten metal stirring device.

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