JP7250388B1 - Immersion heater - Google Patents

Abstract

A heating output is increased in an immersion heater that contributes to a reduction in CO2 emissions. A heating heater unit (30) includes a forward heating wire extending from a base end side to a distal end side, a return heating wire connected thereto and returning from the distal end side to the proximal end side, and The heater unit 30 has an outer heating wire 42A located radially outward from the center and an inner heating wire 42B located inside. , the outer diameter of the outer heating wire 42A is smaller than the outer diameter of the inner heating wire 42B; FIG. 6A

Description

The present invention relates to an immersion heater that is used while immersed in molten metal.

In recent years, in order to prevent the emission of greenhouse gases such as CO ₂ that cause global warming, research and development of decarbonization to break away from fossil fuels such as oil and coal are being promoted in various fields. In order to reduce CO ₂ emissions generated by combustion, decarbonization is required.
In the field of heating molten metal such as molten aluminum, conventionally, a heating burner that burns gas or the like has been used as a heating means. , immersion heaters are beginning to be considered.

An immersion heater is a heater that uses electricity inserted into a bottomed protective tube that is installed in a tank or container to heat molten metal (e.g., molten aluminum). It is immersed in the molten metal inside, and the molten metal is directly heated to keep it warm.
This system has high temperature controllability, can improve the quality of the molten metal, and can reduce energy consumption and costs.

The following heaters are known.
Patent Literature 1 describes a set of a plurality of double wire portions each having a folded form of a heating wire that extends from the proximal end toward the distal end, is folded back at the distal end side, and returns to the proximal end side again.

Further, Patent Document 2 describes a plurality of sets of double line portions in which a heating wire on the radially outer side and a heating wire on the inner side of the cross section of the heater are connected in a folded form.
In these documents, it is described that the double line portion formed by folding the heating wire has a U shape.

Japanese Patent No. 4402743 Japanese Utility Model Laid-Open No. 61-113398

Compared to heating burners, heaters that use electricity can further reduce CO ₂ emissions and are superior in terms of dealing with decarbonization.
However, there is a problem that the heating output is small.

A main object of the present invention is to increase the heating output in an immersion heater that contributes to the reduction of CO ₂ emissions.

Modes of means for solving the above problems are as follows.
In an immersion heater having a heater unit,
The heater unit is inserted into a bottomed protective tube and used in a state of being immersed in molten metal,
The heater unit includes a forward heating wire that extends from the proximal side to the distal side, a return heating wire that is connected to this and returns from the distal side to the proximal side,
and a plurality of heater insulators provided at intervals in the longitudinal direction of the heater unit,
Each of the heater insulators has an insertion hole through which the forward heating wire and the return heating wire are individually inserted,
One of the forward heating wire and the return heating wire is located radially outward from the center of the heater unit and constitutes an outer heating wire, and the other heating wire is located from the center of the heater unit. positioned radially inward and constituting an inner heating wire,
The outer diameter of the outer heating wire is smaller than the outer diameter of the inner heating wire,
An immersion heater characterized by:

According to the present invention, the heating output can be increased in the immersion heater that contributes to the reduction of CO ₂ emissions.

BRIEF DESCRIPTION OF THE DRAWINGS It is a top view which shows an example of the immersion-type heating heater of embodiment. It is a top view which shows an example of the heating heater unit of embodiment. It is a front view of a heating heater unit of an embodiment. 4 is a view taken along line 4-4 of FIG. 3; FIG. 4 is a view taken along line 5-5 of FIG. 3; FIG. FIG. 6 is a view taken along line 6-6 of FIG. 3 in a state without a heating wire; FIG. 6 is a view taken along line 6-6 in FIG. 3 in a state where heating wires are present; 4 is a view taken along line 7-7 in FIG. 3; FIG. It is a connection state longitudinal cross-sectional view of a heater insulator. It is a sectional view of a flat insulator. It is a side view of a flat insulator. It is explanatory drawing of a heating wire. It is a perspective view of a crossover. It is a perspective view of a crossover. It is a perspective view of a crossover. It is a photograph of the heater unit used for experiment. It is a photograph of the heater unit used for experiment. It is a photograph of the heater unit used for experiment. It is a photograph of the heater unit used for experiment. FIG. 10 is a partial cross-sectional view of a furnace with a heater installed in an experiment; It is a graph which shows the result of a test example.

Next, the form for implementing this invention is demonstrated. It should be noted that this embodiment is an example of the present invention, and the scope of the present invention is not limited to the scope of the present embodiment, but is clarified only by the description of the claims.

(Embodiment)
The immersion heater 10 has a heater unit 30 .
This heater unit 30 is inserted into the bottomed protective tube 20 and used in a state of being immersed in molten metal (for example, molten aluminum).
The immersion heater 10 has a bottomed protective tube 20 having a circumference and a bottom, and a heater unit 30 inserted into the bottomed protective tube 20 .
The immersion heater 10 is used in a state of being immersed in the metal to be melted in order to heat the molten metal (for example molten aluminum).

The heater unit 30 has a plurality of outgoing heating wires extending from the proximal side to the distal side and a plurality of returning heating wires connected thereto and returning from the distal side to the proximal side. The forward heating wire and the return heating wire are connected (electrically connected) at an appropriate position, for example, the distal end side or the proximal end side of the heater unit 30, and arranged as one long resistance heating wire. there is

A heater insulator 41 is provided to hold the heating wires parallel without shorting.
A plurality of (for example, 15) heater insulators 41 are provided at intervals in the longitudinal direction of the heater unit 30 .

Each of the heater insulators 41 has insertion holes 41A and 41B through which the forward heating wire and the return heating wire are individually inserted.

One of the forward heating wire and the return heating wire is positioned radially outward from the center of the heater unit 30 and constitutes an outer heating wire 42A.

The other heating wire of the forward heating wire and the return heating wire is positioned radially inward from the center of the heater unit 30 and constitutes an inner heating wire 42B.

The outer diameter of the outer heating wire 42A positioned outside the heater unit 30 is formed smaller than the outer diameter of the inner heating wire 42B positioned inside the heater unit 30 .
In other words, the cross-sectional area of the outer heating wire 42A is smaller than the cross-sectional area of the inner heating wire 42B.
FIGS. 6B and 11 exaggerate the size relationship of the outer diameters of the outer heating wire 42A and the inner heating wire 42B.

In the embodiment, the forward heating wire extending from the base end side to the distal end side and the return heating wire extending back from the distal end side to the proximal end side are connected and arranged as one long resistance heating wire. , the amount of heat generated is large with respect to the length of the heater unit 30 .

In addition, since the heater unit 30 has the outer heating wire 42A radially outward from the center of the heater unit 30 and the inner heating wire 42B radially inward, heating is more efficient than when the heating wires are arranged only in the outer peripheral portion of the heater unit 30. The arrangement density of the heating wires per cross-sectional area of the heater unit 30 can be increased.

The mechanical strength of a heating wire having a circular cross section is directly related to the size of the section modulus of the circle. The section modulus Z of a circle has a relationship of Z=πd ³ /32 with the diameter d of the circle.
Therefore, a heating wire having a circular cross section increases in mechanical strength at a rate of the cube as the diameter (outer diameter) of the circle increases.

The electrical resistance of a heating wire with a circular cross section increases as the cross-sectional area of the circle decreases, and increases in inverse proportion to the square of the diameter d of the circle.

However, in the embodiment, the cross-sectional area (outer diameter) of the outer heating wire 42A is smaller than the cross-sectional area (outer diameter) of the inner heating wire 42B.
Therefore, the amount of heat generated by the outer heating wire 42A is greater than that of the inner heating wire 42B. This means that a large amount of heat is generated outside the heater unit 30 and that the heat is efficiently released to the bottomed protective tube 20 . As a result, the molten metal can be efficiently heated (heating output is increased).
On the other hand, it means that a small amount of heat is generated inside. The heat generated on the inside is dissipated to the bottomed protective tube 20 through a large gap between the outer heating wires having a small outer diameter (compared to the gap when the outer heating wire and the inner heating wire have the same outer diameter). Since it is carried out, the amount of heat generation inside is small.

In addition, the mechanical strength of the inner heating wire 42B (for example, bending strength, strain resistance, resistance to disconnection due to heating, etc.) is higher than the mechanical strength of the outer heating wire 42A.
As for the heater unit 30 as a whole, it is necessary that the outer heating wire 42A and the inner heating wire 42B as a whole remain parallel without bending and are held by the heater insulator 41 .
However, in the embodiment, the mechanical strength of the inner heating wire 42B is high and the mechanical strength of the outer heating wire 42A is low.

As described above, in the embodiment, when using the immersion heater that contributes to the reduction of CO ₂ emissions, the outer heating wire 42A and the inner heating wire 42B as a whole are kept parallel without bending, It can be held by the heater insulator 41 and the heating output can be increased.

The ratio of the outer diameter of the outer heating wire 42A/the outer diameter of the inner heating wire 42B is preferably 0.95 to 0.60. More preferably, it can be 0.93 to 0.80.

The forward heating wire and the return heating wire can be directly connected by welding, or can be connected by welding via a short connecting wire (not shown). In the embodiment, as shown in FIGS. 7 and 18, the outer heating wire 42A and the inner heating wire 42B are directly connected by welding.

The insertion hole of the heater insulator 41 has an outer insertion hole 41A located radially outward from the center of the heater unit 30 and an inner insertion hole 41B located inside.
The outer heating wire 42A is inserted through the outer insertion hole 41A, and the inner heating wire 42B is inserted through the inner insertion hole 41B. It is held parallel without

In the embodiment, two or more holes of the heater insulator 41 are formed at annular positions radially outward from the center of the heater unit 30 at intervals in the circumferential direction. It has an insertion hole 41A and two or more inner insertion holes 41B, in the illustrated embodiment, twenty inner insertion holes 41B, which are formed at annular positions radially inward from the center of the heater unit 30 at intervals in the circumferential direction. there is
In addition, as shown in FIG. 6A, center through holes 41C are formed at circumferentially spaced intervals at an annular position in the center of the heater insulator 41 in the radial direction. By forming the central through hole 41C in the heater insulator 41, the heat capacity of the heater insulator 41 can be reduced and heat can be dissipated while the weight of the heater insulator 41 itself is reduced and the strength is maintained. In addition, when it is necessary to maintain the heating output after making the length of the immersion heater 10 shorter than usual, one long resistance heating wire of the heater is connected to the outer insertion hole 41A and the inner insertion hole. The central through-hole 41C can also be used when the 41B alone cannot be inserted (insufficient).

For example, as shown in FIG. 8, the plurality of heater insulators 41 has a center protrusion 41D tapered toward the tip end and a flange 41E projecting radially integrally from one side thereof. A recessed portion 41a extending from 41E to the central protrusion 41D is formed.
The center projection 41D of one heater insulator 41 is fitted into the recess 41a of the heater insulator 41, and the one heater insulator 41 and the other heater insulator 41 are connected.
In the illustrated embodiment, a through hole 41F is formed extending from the flange 41E through the central protrusion 41D, and a recess 41a is formed at the entrance of the through hole 41F.
As will be described later, the heater insulator 41 is often made of ceramics. By forming the through holes 41F in the heater insulator 41, the heat capacity of the heater insulator 41 can be reduced and heat can be dissipated while the strength is maintained by making the thickness of the ceramics uniform. Further, when measuring the temperature inside the immersion heater 10, a thermocouple can be inserted into the through hole 41F.

The outer heating wire 42A and the inner heating wire 42B are connected to each other to form a single heating wire that conducts while repeating a plurality of back and forth.
As shown in FIG. 11, the inner heating wire 42B is longer than the outer heating wire 42A at each end. The inner heating wires 42B at both ends thereof are connected to a power supply (not shown) via the first lead rod 45 and the second lead rod 46 shown in FIGS. 1-3.
The inner heating wire 42B at both ends, the lead rod 45 and the second lead rod 46 can be directly connected by welding, or can be connected by welding with a short connecting wire (not shown) interposed. In the embodiment, as shown in FIG. 16, the inner heating wire 42B at both ends and the lead rod 45 and the second lead rod 46 are connected by welding with a short connecting wire interposed therebetween.

6A, 6B, and 12 to 14, connecting wires 48A, 48B, and 48C are provided so that both ends of the single heating wire are connected to each other. , to a first lead bar 45 and a second lead bar 46 .

Such an immersion heater is installed in a target melting furnace or holding furnace, and is used to heat molten metal (for example, molten aluminum) via a bottomed protective tube 20 .

An appropriate number of flat insulators 43 having the shape shown in FIGS. 9 and 10, for example, are provided at the distal end and the proximal end of the outer heating wire 42A and the inner heating wire 42B. The flat insulator 43 has an outer insertion hole 43A located radially outward from the center of the heater unit 30 and an inner insertion hole 43B located inside.
The outer heating wire 42A is inserted through the outer insertion hole 43A, and the inner heating wire 42B is inserted through the inner insertion hole 43B. It is held parallel without
In the embodiment, the flat insulator 43 at the distal end is one piece, and the flat insulator 43 at the base end is two pairs in FIGS. In the photographs of FIGS. 15 to 17 showing such a heater unit, two pairs of heater units are provided.

A hemit plate 44 is provided for the first lead rod 45 and the second lead rod 46 and fixed by a nut 47 .

The outer heating wire 42A and the inner heating wire 42B can be made of the same material, such as Kanthal (registered trademark) AF (ferritic iron-chromium-aluminum alloy (FeCrAl alloy)). The same applies to the crossover wires 48A, 48B, and 48C.
On the other hand, it is also possible to use a connection made of different materials. Combinations of different materials include combinations of iron-chromium systems (especially iron-chromium-aluminum systems) and nickel-chromium systems.
For example, the inner heating wire 42B is a nickel-chromium-based heating wire (maximum temperature of 1000 to 1150° C.) that suppresses the amount of heat generated, and the outer heating wire 42A is an iron-chromium-aluminum-based heating wire that increases the calorific value (maximum temperature: temperature 1400° C.).

The heater insulator 41 is also called a radiant insulator, and is a non-conductive, fire-resistant and heat-resistant insulator. For example, the heater insulator 41 is made of mullite (3Al ₂ O ₃ .2SiO ₂ (a compound of aluminum oxide and silicon dioxide)), which is a ceramic.
A similar material can be used for the flat insulator 43 as well.

The hemit plate 44 is a high-strength cement-based heat insulating plate that can also be used as, for example, a cement plate for electrical insulation. Since the thermal conductivity is low, it is possible to prevent the release of heat from the base end side to the outside.

As the material of the bottomed protective tube 20, a known inorganic sintered body (for example, made of fine ceramics) can be used so as to have heat resistance.
The shape of the bottomed protective tube 20 is, for example, a substantially cylindrical cylindrical shape, with one end being an open end and the other being a closed bottom.
During use, the heater unit 30 is inserted from the open end of the bottomed protective tube 20 .

The following experiment was conducted in order to confirm the improvement of the heat radiation efficiency to the outside in the immersion heater.
(Experimental example 1)
15 to 18 are photographs of the heater unit that was produced.

The heater unit 30 of Experimental Example 1 is shown in Table 1. The outer diameter of the outer heating wire is 4.5 mm, the outer diameter of the inner heating wire is 5 mm, and the material of each heating wire is manufactured by Kanthal. "Kanthal AF" was used.
The total length of the heater unit 30 was set to 1073.5 mm from the end of the lead rod.
Next, as shown in FIG. 19, the heater unit 30 was assembled in a bottomed protective tube 20 made of fine ceramics having an outer diameter of 155 mm, an inner diameter of 135 mm, and a total length of 830 mm to prepare a heater.

When the heater unit 30 is incorporated into the bottomed protective tube 20, the distance between the outer heating wire of the heater unit 30 and the inner wall of the bottomed protective tube 20 is set to about 5 mm apart, and about 40 mm apart on the top plate side opposite to the furnace bottom side. Further, the space between the hemit plate 44 having a diameter of 105 mm and the disk-shaped flat insulator 43 was filled with glass wool to form a heat insulating layer.

In addition, a K thermocouple inserted into the Tc tube was installed at a position about 550 mm from the hemit plate 44 in the space between the heater unit 30 on the top plate side and the bottomed protective tube 20 . At this time, the distance between the outer heating wire of the heater unit 30 and the K thermocouple was set to about 10 mm.

(Comparative example)
This comparative example is a conventional product, and the outer diameter of each of the outer heating wire and the inner heating wire of the heater unit is the same as 5 mm, each material is Kanthal AF manufactured by Kanthal, and the others are Experimental Example 1. Same specifications as

First, the heater according to Experimental Example 1 was installed in the holding chamber of a holding furnace for two-chamber low-pressure casting (“Two-bath furnace for constant water surface type LP” manufactured by Tounetsu Co., Ltd.).
The holding furnace has a wall height of 800 mm and can accommodate 1,000 kg of molten aluminum. Each heater was installed horizontally at a position where the distance from the furnace bottom to the bottomed protective tube 20 was 100 mm (installed as a so-called horizontal immersion heater).
After that, molten aluminum at about 680° C. was put into the holding furnace to the full amount. Each heater was heated with an output power of 15 kW, and the time from when the temperature of the K thermocouple in the holding chamber reached about 730°C to when the temperature rose to about 800°C was measured.
Similarly, a comparative example was installed in the holding chamber of the two-chamber low-pressure casting holding furnace. Otherwise, the measurement was performed under the same conditions as in Experimental Example 1.

The results of Experimental Example 1 and Comparative Example are summarized in a graph (see FIG. 20).
In Experimental Example 1, the temperature reached 800°C in 240 seconds, but in Comparative Example, the temperature reached about 795°C in 240 seconds, and even if the experiment was continued thereafter, the temperature did not reach 800°C.
That is, it was found that in Experimental Example 1, the heat radiation efficiency to the outside of the heater was improved as compared with the conventional product of Comparative Example.

INDUSTRIAL APPLICABILITY The immersion heater of the present invention can be used, for example, in the field of heating molten metal such as molten aluminum.

DESCRIPTION OF SYMBOLS 10... Immersion-type heating heater 20... Bottomed protective tube 30... Heating heater unit 40... Heating wire 41... Heater insulator 41A... Outer insertion hole 41B... Inner insertion hole 41C... Central projection 41D... Collar portion 42A... Outer heating wire 42B... Inner heating wire 43... Flat insulator 43A... Outer insertion hole 43B... Inner insertion hole 44... Hemit plate 46... Lead rod 48A, 48B, 48C... Crossover wire .

Claims (7)

In an immersion heater having a heater unit,
The heater unit is inserted into a bottomed protective tube and used in a state of being immersed in molten metal,
The heater unit includes a forward heating wire extending from the base end side to the distal end side, a return heating wire connected thereto and returning from the distal end side to the proximal end side,
and a plurality of heater insulators provided at intervals in the longitudinal direction of the heater unit,
Each of the heater insulators has an insertion hole through which the forward heating wire and the return heating wire are individually inserted,
One of the forward heating wire and the return heating wire is located radially outward from the center of the heater unit and constitutes an outer heating wire, and the other heating wire is positioned from the center of the heater unit. positioned radially inward and constituting an inner heating wire,
The outer diameter of the outer heating wire is smaller than the outer diameter of the inner heating wire,
An immersion heater characterized by: 2. The immersion heater according to claim 1, wherein said forward heating wire and said return heating wire are connected by welding directly or with a short connecting wire interposed. The insertion hole of the heater insulator has an outer insertion hole positioned radially outward from the center of the heater unit and an inner insertion hole positioned inside,
The outer heating wire is inserted through the outer insertion hole, and the inner heating wire is inserted through the inner insertion hole,
The immersion heater according to claim 1 or 2. The insertion hole of the heater insulator includes two or more outer insertion holes that are circumferentially spaced apart in an annular position radially outward from the center of the heater unit, and a radial two or more inner through-holes circumferentially spaced at annular positions on the inner side of the direction;
The outer heating wire is inserted through the outer insertion hole, and the inner heating wire is inserted through the inner insertion hole,
The immersion heater according to claim 1 or 2. The insertion hole of the heater insulator has an outer insertion hole on the outer side and an inner insertion hole on the inner side in a radial direction from the center of the heater unit,
In the heater unit, a forward heating wire extending from the proximal end side to the distal end side and a return heating wire returning from the distal end side to the proximal end side are connected to each other. connected to a power source via a lead rod and a second lead rod;
The outer heating wire is inserted through the outer insertion hole, and the inner heating wire is inserted through the inner insertion hole,
The immersion heater according to claim 1 or 2. The plurality of heater insulators each have a central protrusion and a flange integrally projecting radially from one side thereof,
A concave portion extending from the collar portion to the central protrusion is formed,
2. The immersion heater according to claim 1, wherein the central protrusion of one of the heater insulators is fitted into the recess of the other of the heater insulators, and the one heater insulator and the other heater insulator are connected. . 2. The immersion heater according to claim 1, wherein said outer heating wire and said inner heating wire are made of different materials.

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