Patent Application
20240019212
The present invention relates to a molten metal furnace for holding a molten metal of, for example, aluminum, aluminum alloys, or non-ferrous metals.
There is conventionally known a melting and holding furnace for melting and holding a molten metal of aluminum, aluminum alloys, non-ferrous metals, or the like (for example, see Patent Publication 1). A furnace body of a common melting and holding furnace is composed of a bottom wall and a peripheral wall or side walls extending vertically from the peripheral edges of the bottom wall. The bottom wall and the side walls generally have, in order from outside inwards, an outer wall made of iron (steel shell) and lining materials, such as a heat insulting layer, a back-up layer, and a refractory layer (referred to also as a refractory product or a refractory material hereinbelow), and a molten metal storage part for holding the molten metal therein is formed inside the refractory layer.
In such a melting and holding furnace, a lining material, in particular the refractory layer to be in contact with a molten metal, is formed of refractory precast blocks, refractory bricks, or castable refractories, or the like. Molten metal has a property of easily permeating the structure of such refractory layer.
For example, it happened that oxides were formed in an aluminum alloy molten metal (referred to also as an aluminum molten metal hereinbelow), prolonged use or drastic temperature change caused easy cracking which damaged the furnace body, the aluminum molten metal permeated the cracking in the refractory layer to cause molten metal leakage, and the aluminum molten metal leaked out of the molten metal storage part.
In order to avoid molten metal leakage, Patent Publication 2 discloses a lining structure for a molten metal holding vessel, wherein the inner surface of a permanent lining is provided with a plurality of dents arranged in a staggered pattern, and covered with a mortar layer having a lower longitudinal elastic modulus. It was demonstrated that, with such a structure, the strain generated on the inner surface of the permanent lining was dispersed to avoid cracking and, even if cracks were formed on the inner surface of the permanent lining, the mortar layer could block the molten metal leakage.
As discussed above, Patent Publication 2 teaches how to avoid molten metal leakage, but is silent about measures for controlling heat radiation from the furnace body.
Heat radiation from the furnace body causes the following problems. It was necessary to continuously operate a heat source, such as an immersion heater or an immersion burner, for holding a molten metal at a certain temperature in the molten metal storage part. However, a conventional furnace body radiates heat, so that the heat source was supplied with energy, such as electric power or gas, more than necessary, which was inefficient. Further, the surface temperature of the furnace body or the ambient temperature around the furnace body tends to rise easily, which may lead to damages to workers, such as burn injury due to contact with the furnace body, or deterioration of the working environment.
Molten metal leakage may actually be coped with by using a refractory material of about 100 mm thick in the refractory layer, but after the lapse of 6 to 8 years from the beginning of use of the furnace, damages by cracking may be found in the furnace body.
Moreover, in continuous operation, where the operation is ceased only twice to four times a year for maintenance, it is extremely difficult to avoid molten metal leakage to outside, and dedication was required to secure safety of workers or deal with disadvantages in operation, such as decrease in heat quantity of molten metal.
It is therefore an object of the present invention to provide a molten metal furnace in which molten metal leakage may be avoided or controlled and heat radiation from the furnace body may be controlled.
Means for solving the above problem is as follows.
A molten metal furnace including:
According to the present invention, molten metal leakage may be avoided or controlled, and heat radiation from the furnace body may be controlled.
Embodiments of the present invention will now be explained below.
As shown in
The lining layers are composed of, for example as shown in
The first lining layer 10 constitutes a surface to be in contact with the molten metal M, such as of aluminum or alloys thereof, and is composed of a refractory material. The refractory material may be, for example, a low-cement castable mainly composed of aluminum oxide (Al2O3), which is adjusted in water content to 10% or lower for construction, and then dried to have a density of 2500 to 3500 kg/m3. The second lining layer 20, the third lining layer 30, and the like, will be discussed later.
The molten metal furnace may be any of various structures. The furnace of the structure shown in
The furnace has a tap port 2 in the upper portion thereof, which is composed of a cylindrical stalk 3. The furnace has an air supply port 4 and an air discharge port 5 provided in the upper portion thereof, which allow supply/discharge of pressurized gas into/out of the molten metal holding chamber.
By means of a pressure device, not shown, pressurized gas, such as dry air or inert gas, e.g., argon or nitrogen, is fed through the air supply port 4 into the molten metal holding chamber. The pressurized gas fed into the molten metal holding chamber presses the molten metal surface, causing the molten metal to rise upward through the stalk 3 and be pressed into the cavity of a casting mold, not shown, through the tap port 2.
After completion of the casting, the supply of the pressurized gas through the air supply port 4 is ceased, and the pressurized gas in the molten metal holding chamber is discharged through the air discharge port 5.
In this kind of molten metal furnace, as discussed above and shown in the schematic view of
For addressing such problems, in the embodiment shown in
The sealing material 50 may preferably be in the form of a sheet, in particular with a thickness of 2 to 10 mm.
The sealing material 50 may particularly preferably be a woven sheet of at least either of ceramic fibers and bio-soluble ceramic fibers, and at least either of glass fibers and stainless steel fibers.
The bio-soluble ceramic fibers used in the present invention is selected from the fibers classified in Category 0 (exempt substances) in the “EU Directive 97/69/EC” regulation. Such a fiber needs to be a fiber whose safety is verified based on Nota Q “criteria for bio-soluble fibers” by any of the following four animal experiments, or a fiber in which a numerical value obtained by subtracting a value twice the standard deviation from the length weighted geometric average diameter exceeds 6 μm, based on Nota R “criteria for non-inhalable fibers”.
The bio-soluble ceramic fibers with the confirmed safety as discussed above may be used without any particular limitation on their production process, chemical composition, average fiber diameter, or average fiber length and, for example, bio-soluble rock wool may be used.
Those containing over 18 mass % oxides of alkali metals or alkaline earth metals (Na2O, K2O, CaO, MgO, BaO, or the like) may be used.
Silica-magnesia-calcia alkaline earth silicate wool or the like may be used.
As ceramic fibers, there are known amorphous refractory ceramic fibers (abbreviated as RCF hereinbelow) mostly for use at a regular use temperature of 1400° C. or lower, which are artificial mineral fibers mainly composed of alumina (Al2O3) and silica (SiO2), and crystalline alumina ceramic fibers used at temperatures higher than 1400° C. These RCF and crystalline ceramic fibers are widely different in production method, performance, and cost, and used differently according to the respective characteristics.
Molten metal, in particular a molten metal of aluminum or an aluminum alloy, reaches a temperature as high as 700° C. or higher. In this regard, the at least either of the ceramic fibers and bio-soluble ceramic fibers are preferably reinforced with the at least either of the glass fibers and stainless steel fibers.
In particular, in view of heat resistance, it is preferred to reinforce at least with stainless steel fibers.
The sealing material 50 may take a sheet shape, in particular with a thickness of 2 to 10 mm, by weaving fiber threads (fibers or strands). The weaving may be, for example, plain weave as shown in
As shown in
As shown in
Further, as shown in
According to the present invention, it suffices that the sealing material 50 is provided along at least two boundaries present in the range between the first lining layer 10 and the outer wall 1. For example, as shown in
Further, as shown in
The sealing material 50, which has been provided between the adjacent lining layers as discussed above, may emit a burnt odor, when the molten metal M is first introduced into the molten metal storage part and the heat thereof is transferred via the first lining layer 10 to the sealing material 50. For the purpose of controlling this odor, the sealing material 50 may be fired in advance.
Conventionally, in coping with the molten metal leakage, a major focus has been on selection of material of the first lining layer. However, cracking of the first lining layer 10 cannot be avoided and is likely, and the risk of molten metal leakage through the cracking remains.
The present inventor has reached the present invention without focusing on the selection of material of the first lining layer 10, but on the premise of the cracking in the first lining layer 10.
Even if the molten metal leakage through the cracking occurs, molten metal leakage to the outer wall may be blocked, which is the ultimate goal, through minimization of amount of leakage, reduction of heat radiation outside the furnace, or directional control of leakage to avoid permeation up to the outer wall. Further, heat radiation from the furnace may be controlled.
Use of a sealing material, in particular a heat resistant (refractory) sealing material, according to the present invention provides the following advantages:
In general, leaked molten metal moves downwards by gravity along and between the adjacent lining layers and, when reaches a horizontally-extending lining layer located closer to the outer wall, spreads in the horizontal direction. Depending on circumstances, the horizontally-extending lining layer located closer to the outer wall may be cracked, and the molten metal leakage may spread through the cracking by gravity, so that the direction of leakage cannot be predicted.
The sealing material 50 according to the present invention provided between the adjacent lining layers hinders downward movement by gravity of the leaked molten metal along and between the adjacent lining layers (i.e., the rate of downward movement may be regulated), with the sealing material 50 acting as a resistance. Then, the leaked molten metal is dispersed while flowing along the woven fibers of the sealing material 50, so that the heat quantity (heat capacity per unit area) of the leaked molten metal is lowered. In addition, since the first sealing material 50A and the lining layer located on the side of the first sealing material 50A closer to the molten metal storage part 6 are made of different materials, heat conduction from the lining layer to the first sealing material 50A may be limited. As a result, the molten metal leaking out to the lining layer located on the side of the first sealing material 50A closer to the outer wall 1 may be significantly reduced. Depending on the size of the cracking, the amount of molten metal leakage may vary, but by providing a second sealing material 50B along any of the boundaries present in the range between the outer wall 1 and the lining layer located on the side of the first sealing material 50A closer to the outer wall 1, reduction of heat radiation outside the furnace (as the second sealing material 50B and the lining layer located on the side of the second sealing material 50B closer to the molten metal storage part 6, and/or the second sealing material 50B and the lining layer located on the side of the second sealing material 50B closer to the outer wall 1, are made of different materials, heat conduction between the second sealing material 50B and the respective lining layers may be limited), directional control of leakage, and regulation of molten metal permeation up to the outer wall 1 may further be achieved. Further, the plurality of disposed layers of sealing material 50 hinders the molten metal to be brought into direct contact with the lining layer located on the side of the respective layers of the sealing material closer to the outer wall 1, leading to reduced risk of cracking.
As used herein, the directional control of molten metal leakage, when occurred, refers specifically to reduction of the rate of molten metal leakage by narrowing the space between the adjacent lining layers with the sealing material 50 to increase the resistance, and regulation of molten metal permeation up to the outer wall.
A lining layer sandwiched between a plurality of layers of sealing material 50 stacked in the thickness direction, like the second lining layer 20 in the embodiment shown in
Further, the density of the second lining layer 20 in the embodiment shown in
The second lining layer 20 in the embodiment shown in
The second lining layer 20 in the embodiment shown in
Note that a lining layer located outside the outermost sealing material 50 (the second sealing material in the embodiment shown in
Further, in the illustrated embodiments, the number of the lining layers is at most four (up to the fourth lining layer 40, but may be five or more. In that case, the sealing material 50 may be provided inside the fifth or subsequent layer.
The conventional design concept was to combine the second lining layer 20 formed of a refractory material having a density of 1000 to 1500 kg/m3 with the first lining layer 10 formed of a refractory material having a density of 2500 to 3500 kg/m3. This blocked flow of the molten metal leakage or controlled its flow rate even when the first lining layer 10 was cracked, which had a surface in contact with the molten metal M, such as aluminum or an alloy thereof as discussed above. Further, the third lining layer 30 and the fourth lining layer 40 formed of fibers containing at least one of aluminum oxide (Al2O3) and silica (SiO2), or boards containing calcium silicate as a main component and having a density of 150 to 250 kg/m3, or the like, were used to lower the temperature of the leaked molten metal to avoid molten metal leakage outside the furnace.
In contrast, the design concept according to the present invention is to combine the lining layer formed of a thermal insulation board containing at least silicon dioxide (SiO2) and sandwiched between layers of the sealing material 50 with the first lining layer 10 formed of a refractory material having a density of 2500 to 3500 kg/m3. By means of this combination, even when the first lining layer 10 is cracked, which has a surface in contact with the molten metal M, such as aluminum or an alloy thereof as discussed above, the lining layer formed of the thermal insulation board containing at least silicon dioxide (SiO2) and sandwiched between layers of the sealing material 50 blocks flow of the molten metal leakage and, at the same time, hinders heat conduction to the outer side (e.g., to the neighboring layers, such as the third lining layer 30 and the fourth lining layer 40 in the embodiment shown in
In this way, since the lining layer formed of the thermal insulation board containing at least silicon dioxide (SiO2) and sandwiched between layers of the sealing material 50 acts both to block flow of the molten metal leakage and to control heat radiation from the furnace body, part of the conventional back-up layers for blocking flow of molten metal leakage may be omitted or reduced in thickness, and the thickness of each lining layer may be reduced from the conventional thickness. Consequently, the molten metal furnace itself may be made smaller. In other words, the size of the molten metal furnace may be made smaller with the same volume of the molten metal storage part as the conventional. Even with the volume of the molten metal storage part somewhat larger than the conventional, the size of the molten metal furnace may be made the same as or smaller than the conventional.
The molten metal may be of aluminum or an aluminum alloy, or any other molten metal.
Note that the technical scope of the present invention is not limited to the embodiments discussed above, and various changes and modifications may be made therein without departing from the spirit and scope of the invention. For example, the molten metal furnace according to the present invention may be applied to a melting and holding furnace, melting furnace, holding furnace, or low-pressure casting furnace.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-051699 | Mar 2021 | NO | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/047181 | 12/21/2021 | WO |
