JPS6357487B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an underheater type low melting point metal molten metal holding furnace used to maintain the temperature of a low melting point metal molten metal such as aluminum or zinc.

In a work system that distributes molten metal from a melting furnace to a holding furnace and injects the molten metal into a mold from this holding furnace, it increases the heat retention capacity of this molten metal holding furnace and reduces the power consumed to maintain it at the required temperature. In addition, the purpose of the present invention is to make improvements such as increasing the amount of molten metal pumped out, and through these improvements, it is possible to improve the efficiency and cost reduction of casting products made of low melting point metals such as aluminum (including alloys). do.

The upper heater type holding furnace, in which the upper lid of the holding furnace is used as the heating part, does not have good heating efficiency for the internal molten metal. For this purpose, a method has been proposed in which the heating element is protected by a protection tube and the molten metal is heated by the heat of the heating element through the protection tube immersed in the molten metal. For example, Japanese Patent Application Publication No. 1983-
This is what you see in 23686. Over the past five years, many ceramic materials that do not easily react with molten metal have become known.
Since it is very easy to change the material of the protection tube in a variety of ways depending on the molten metal, it is necessary to develop a holding furnace structure in order to fully complete an energy-saving type of molten metal holding furnace.

The problems that need to be solved for this purpose are a heating method that generates appropriate heat convection to suppress heat dissipation during replenishment and pumping of molten metal, and suppression of deviations in molten metal composition, and a method of heating that generates appropriate heat convection to suppress the occurrence of deviations in molten metal components, and a method of heating that generates appropriate heat convection during molten metal replenishment and pumping. The goal is to increase
These must be met simultaneously by the developed furnace structure. The present invention has developed a furnace vessel structure that significantly prevents heat dissipation to about one-tenth of that of conventional holding furnaces, and has a pumping rate of over 60%. This is one of the first things to do.

In particular, heat dissipation is improved during replenishment and pumping of molten metal.
The emphasis was on developing a reactor vessel structure to keep it as small as possible.

The basic furnace vessel structure of the present invention suppresses heat dissipation to one-tenth of that of conventional practical holding furnaces. It has a structure with partition walls made of a heat insulating material. In the case of the under-heater type, even if the inside of the furnace is divided by such partition walls, the molten metal will not be heated unevenly and efficient heating can be achieved. In the Atsupah heater type that has been put into practical use, if such a partition is installed inside the furnace, the configuration of the heating element becomes complicated in order to achieve uniform heating distribution, and at the same time, it is not possible to achieve a high level of heating efficiency. As a result of the increased power consumption, such a furnace structure is not practical. The remarkable rationality of this partition wall structure in the furnace, which could not be expected with an upper heater type or high-temperature gas-heated holding furnace, is that the upper furnace lid wall, which is provided above the molten metal surface and can be opened for replenishing and pumping out the molten metal, is On the contrary, it can be placed in the lower part of the molten metal. In other words, one of the rationalities is that the partition wall in the furnace does not affect the heat distribution during heating at all, so the above-mentioned unreasonableness that appeared in conventional holding furnaces does not occur when the partition wall is provided. The second point of rationality is that the heat from the underheater applied to the lower part of the molten metal is directly absorbed by the molten metal and carried by convection, thereby suppressing the expansion of the temperature difference between the lower part of the molten metal and the surface of the molten metal. The ability to hold molten metal, which suppresses the amount of heat lost over a day and night to about 5%, is remarkable and cannot be expected from conventional holding furnaces. In this case, the power consumption can be reduced to about one-tenth of that of a conventional holding furnace, and the improvement effect of the present invention is noteworthy.

The underheater type low melting point metal molten metal holding furnace of the present invention contains 50-99wt% Al ₂ O ₃ and 0.5-50wt%
A molten metal pumping chamber is constructed by integrally molding or assembling at least one partition wall in a furnace vessel that is integrally formed with a castable refractory whose main component is SiO ₂ , and a molten metal transfer chamber is formed at the bottom of the partition wall. one or more protective tubes containing a heating element are disposed at the bottom of the furnace vessel, one sealed end of which is supported without being fixed within the furnace vessel, and the other end is open; is inserted into a through hole provided in the wall of the furnace vessel, and a sloped portion is inserted from the inside to the outside to increase the bonding pressure between them due to the difference between the linear expansion of the heating element and the linear expansion of the wall of the furnace vessel. A seal hole is formed in the peripheral wall of the through hole so as to have a diameter that increases as the diameter increases. An insulating and heat-insulating ceramic tube having a conduction hole extending in the direction is connected to the protective tube, and the heating element housed in the protective tube is electrically connected to an external power source via the ceramic tube. Insulating blankets are layered on the outer periphery of the furnace vessel, the blankets are fixed with exterior materials, and a sealing lid member having an openable and closable pumping lid located above the molten metal pumping chamber is attached to the upper part of the furnace vessel. This is a characteristic feature.

Hereinafter, preferred embodiments of the present invention in molten aluminum will be described with reference to the drawings.

In FIG. 1, a through hole 9 is formed in a furnace wall 3 of a low melting point metal molten metal holding furnace 1. As shown in FIG. The under-heater type holding furnace of this embodiment has a three-layer structure consisting of a furnace shell 4 as an exterior material, a heat insulating material 10, and a castable refractory furnace vessel 3 in order from the outside. Molten aluminum A is placed in a refractory furnace vessel 3. Molten aluminum A is heated by an immersion heater H, which is a heating element protected by a heat-resistant, corrosion-resistant ceramic material. In this example, the immersion heater H is composed of a protective tube 2 and a heating element placed in the protective tube 2. 50~ as castable refractory material for making furnace vessel 3
A composition based on 99.5 wt% Al ₂ O ₃ and 0.5 to 50 wt% SiO ₂ is preferred, and the components may be changed to equivalent components to suit the purpose. Examples of the heating element include a metal wire and a heating element made of silicon carbide, and SiC-based ceramics having excellent heat resistance and corrosion resistance are preferable for the protective tube. When using this SiC material, the necessary electrical resistance is provided between it and the heating element to prevent electrical leakage from the heating element through the protective material.

The sealing lid member 1' includes a molten metal replenishment funnel 14 and a sensor 16. FIG. 2 shows the molten metal pumping part 1d provided in the sealing lid member 1', and the handle 1e is used to draw out the molten metal.
This pumping part 1d is opened and closed. This opening and closing may be done by a sliding method. A molten metal pumping chamber 1a, which will be described later, faces the lower part of the pumping section 1d. The sensor 16 includes an upper limit sensor 16 that detects the upper limit position of the molten metal surface.
b and a lower limit sensor 16 for examining the lower limit position.
In addition to c, there is a temperature sensor 16a for detecting the temperature of the molten metal. In this example, a SiC end-blocking tube 16d is used to specifically protect the temperature sensor 16a, and a lead wire 6' shown in FIG. 4, which will be described later, is used.
For example, 12V between the attached stainless steel ring 6
Apply voltage.

In FIG. 4, the through hole 9 is formed with a tapered threaded portion 9a that opens outward from the bottom of the side wall of the furnace vessel 3. As shown in FIG. The open end 2a of the protective tube 2 is passed through the tapered threaded portion 9a formed as this inclined portion and supported. A sealing material 12 is filled in the gap between the protective tube 2 and the tapered threaded portion 9a.

When the protective tube 2 is made of SiC and the furnace vessel is made of the castable composition of the above example, the coefficient of linear expansion of both is slightly larger in the latter. When the furnace vessel wall 3 linearly expands, the inclined portion of the tapered threaded portion 9a acts to increase the bonding pressure against the sealing material filled in the threaded portion 9a, so that the sealing function works firmly. . Due to the large penetrating power of molten aluminum, zinc, copper, or their alloys,
A sealing means having such a sloped portion works effectively and eliminates the weak points of the underheater. The sealing material mortar is colloidal mortar containing fibers, and the fibers are carbon fibers, alumina-silica ceramic fibers.

One end of the protective tube 2 is an open end 2a, and the other end is a closed end 2b.
A support stand 11 is provided on the inner surface of the bottom of the furnace vessel 3 . The support base 11 and the through hole 9 are located at opposing positions. The end portion 2b of the protective tube 2 is placed on the support stand 11 as a free end without being fixed, allowing movement of the protective tube during thermal expansion and preventing damage to the protective tube. In this example where the sealing hole of the through hole 9 is filled with mortar to cantilever the protective tube 2, since the other end is a free end that is not fixed, there is a risk that the difference in thermal expansion will cause the mortar seal surface to shift. well resolved.

When the castable composition contains Si and the retained molten metal is aluminum, this Si chemically reacts with Al and is consumed. Therefore, the SiO ₂ component is preferably 50wt% or less, for example, 40wt%.
The content of Al ₂ O ₃ is preferably 60 wt% or more. If a BN coat, which is not compatible with Al, is formed on the inner surface of the furnace vessel, the consumption of Si can be considerably suppressed, so a combination of the BN coat in place of composition control is also a preferred method.

Continuing from the through hole 9, a ceramic fiber molded tube 8 having excellent insulating and heat insulating properties and having a through hole 9' is passed through the heat insulating blanket 10. As shown in detail in FIG. 4, one end of the ceramic fiber molded tube 8 is configured to hold down the protective tube 2 and the sealing material 12 with a flange portion 8a. A sensor 6 is attached to the outer periphery of the flange portion 8a. The sensor 6 is for detecting leakage of the molten aluminum A. The sensor 6 is preferably a stainless steel wire or a nichrome wire, and is led to a power source outside the furnace by a lead wire 6'. An alternative implementation method to the above example is to utilize the electric resistance that changes due to short circuit between the wires when the molten metal penetrates into this position. Alternatively, a method of detecting electrical resistance that changes due to a chemical change with the penetrating metal can also be used. Other heat-sensing leak sensors can also be used. Lead wire 6' is guided along ceramic fiber molded tube 8. As described above, when a voltage is applied between the protection tube 16d and the sensor 6, when the molten metal penetrates into the sensor 6 and comes into contact with it, this penetration forms an electric circuit and is immediately detected. In addition, if the protective tube 2 is damaged, the aluminum and the heating resistor will come into contact with each other.
Since the resistance changes significantly, it is recommended to install a control device that detects the change with a detector, sounds a buzzer, and cuts off the power for safe operation.

FIG. 3 illustrates a pumping chamber 1a with a partition wall 13a that maximizes the heating characteristics of the under heater and highly suppresses heat dissipation. The opening 13b is an example of molten metal moving means. Although a T-shaped orthogonal partition wall is shown here, a single partition wall structure or a U-shaped partition wall structure that crosses the furnace vessel 3 in accordance with the shape of the pump outlet can also achieve the purpose of increasing heat retention capacity.
Further, the partition structure can be freely changed depending on the type of partition structure such as an orthogonal cross partition, the capacity of the furnace vessel, the pumping operation frequency, and further the pumping means. In the T-shaped partition wall 13a of this example, there is a molten metal replenishment chamber 1c located below the funnel 14 and a holding chamber 1 located beside it.
b, and the pumping chamber 1a is limited to about 1/4 of the furnace vessel 3. The sensor 16 here hangs into the molten metal in the holding chamber 1b. Under heater H
The molten aluminum supplied to the replenishing chamber 1c moves to the holding chamber 1b and the pumping chamber 1a, as indicated by the arrow, through the moving hole 13b having a larger hole. At this time, the movement of impurities floating on the upper surface can be suppressed, and it has the effect of a filter. In addition, when using the above-mentioned castable composition, the temperature of the molten metal in the pumping chamber 1a is
Since the temperature can be maintained at 714°C, when the upper part of the pumping chamber 1a is opened for pumping, this partition wall has the effect of significantly suppressing heat dissipation from here. The heat of underheating is effectively absorbed into the molten metal from its bottom, and the heat dissipation from above the molten metal surface is controlled to be extremely small by this partition wall. in this way,
The attachment of the sealing lid member 1' is a new and important configuration made possible by the underheating method.

Since the temperature difference between the top surface of the molten metal and its bottom is kept smaller than in conventional holding furnaces, the pumping rate of the molten metal that can be pumped out from the pumping chamber 1a for casting has increased from about 40% in the past to more than 60%. The day and night molten metal holding furnace efficiency is over 95%, which means power consumption can be reduced to less than 1/6 of the conventional external heating type, and temperature control accuracy is ±3.
It became possible to raise the temperature to a high level.

The increased molten metal holding capacity by the partition wall 13a,
A means for replenishing molten metal was also developed for further utilization. The ceramic funnel 14 shown in FIG. 1 has a tapered surface 14a that narrows the inner wall downward, and a ceramic tube 15 integrally molded with a wire gauze built into the lower hole 15a is fitted into the lower hole 15a. This ceramic tube 15, which has sufficient strength and heat resistance against molten metal, can be put to practical use even if the inner diameter is limited to about 30 mm. When the holes are formed in this way, only the molten metal can be replenished into the holding furnace container 3 without passing the slag accompanying the melting furnace. The ability to control impurity contamination to virtually zero is another noteworthy feature of the holding furnace. The generation of dross is also considerably suppressed when compared with conventional holding furnaces.

An example of a holding furnace bottom structure for supporting the furnace vessel 3 is shown in FIG. Bottom support 17 and furnace vessel 3
A large number of ceramic tubes 17a are arranged at appropriate intervals between the bottom part of the ceramic tube and the bottom part of the ceramic tube. and tube 17a
A fiber bulk 17b is filled inside to prevent heat from dissipating due to convection. The bottom structure is provided between multiple layers of insulation blankets, preferably ten or more layers, of insulation material 10 wrapped around the outer circumference of the furnace vessel 3, thereby making it sufficiently stable and sufficiently suppressing the dissipation of heat from the bottom. It is advisable to insert aluminum foil as appropriate. The heat reflective power of AI foil not only suppresses heat convection to ensure heat retention ability, but also effectively prevents the penetration of molten metal into the blanket when it penetrates the blanket. can.

In addition, when using a heating element such as SiC in the protective tube 2 as the heating element H, asbestos, magnesia powder,
It is preferable to fill the tube with ceramic fiber or the like. If the protective tube 2 is cracked, the molten metal that flows out will solidify as it cools down by cutting off the power supply to the under heater H, and this filling will promote self-occlusion and effectively prevent leakage accidents.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of an underheater type aluminum holding furnace showing an example of the present invention, Fig. 2 is a plan view thereof, and Fig. 3 is a cross section taken along line XX in the first drawing showing an example of the partition wall structure at the bottom of the furnace vessel. 4 are partially enlarged cross-sectional views of the tapered threaded portion 9a of FIG. 1, with the periphery omitted to show the tapered threaded portion 9a. DESCRIPTION OF SYMBOLS 1... Holding furnace, 1'... Sealing member, 1a... Pumping chamber, 2... Protection tube, 3... Furnace container, 9... Through hole, 12... Sealing material, 13a... Partition wall, A... …
Molten metal, H...heating element.

Claims (1)

[Claims] 1 At least one partition wall is formed by integral molding or assembly in a furnace vessel that is integrally molded with a castable refractory whose main components are 50 to 99 wt% Al ₂ O ₃ and 0.5 to 50 wt % SiO ₂ to constitute a molten metal pumping chamber, and the partition wall is provided with an opening means for allowing movement of the molten metal,
One or more protective tubes containing a heating element are disposed at the bottom of the furnace vessel, one sealed end of which is supported without being fixed within the furnace vessel, and the other open end of the protective tube is attached to the wall of the furnace vessel. The diameter increases from the inside to the outside of the sloping part that is inserted into the provided through hole and increases the bonding pressure between them due to the difference between the linear expansion of the heating element and the linear expansion of the wall of the furnace vessel. A sealing hole is formed in the peripheral wall of the through hole so that the protective tube is supported by filling a gap between the protective tube and the sloped portion with a sealing material, and the heating element housed in the protective tube and the external A power supply is electrically connected to the reactor vessel, heat insulating blankets are layered around the outer periphery of the furnace vessel, and the blankets are fixed with an exterior material, and a sealing lid member having an openable and closable pumping lid located above the molten metal pumping chamber is installed. An under heater type low melting point metal molten metal holding furnace characterized by being attached to the top of the furnace vessel.