JPH06129778A - Heating furnace - Google Patents

Abstract

PURPOSE:To provide a heating furnace with a resistance heating element, the life of which can be substantially prolonged by completely suppressing evaporation of graphite from a surface of the heating element. CONSTITUTION:A carbon fiber thread layer 3 comprising a laminate formed by winding of carbon fiber threads, and a sheet-shaped graphite layer 4 comprising a laminate formed by winding of a sheet-shaped graphite cover in this order an outer surface of a cylindrical-shaped resistance heating element 2 which is formed of graphite and has an inlet 9a and an outlet 9b for a thread Y. The insulating members 5 which comprise a compact of boron nitride is provided between the sheet-shaped graphite layer 4 and the resistance heating element 2 on the opposite ends thereof. Accordingly, the insulating members 5 prevent carbon vapor having evaporated from an outer surface of the resistance heating element 2 from leaking outside the element, so that a heating furnace is provided to have a heating element 1, the life of which is substantially prolonged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating furnace for heating a resistance heating element through an electric current, and more particularly, an improvement of a Tamman furnace type heating furnace for high temperature firing of 2500 ° C. or higher using cylindrical graphite for the resistance heating element. Regarding

[0002]

2. Description of the Related Art Conventionally, as a high temperature heating furnace used for firing carbon materials such as carbon fibers and various industrial materials such as ceramic materials, many heatings such as resistance furnaces, induction furnaces, arc furnaces and plasma furnaces have been performed. Although a furnace is used, a heating furnace of a Tammann furnace type (hereinafter referred to as a Tamman heating furnace), which is a resistance furnace using graphite as a resistance heating element, has a relatively simple heating means. Widely used for heat treatment of industrial materials.

Using this Tammann type heating furnace, at least 2
In order to perform high-temperature heating at 000 ° C. or higher, an electric current is passed through a cylindrical resistance heating element made of graphite, and Joule heat generated from the resistance heating element causes the object to be heated to be left stationary or continuously passing through the resistance heating element. However, this heat treatment
Usually, in an inert gas such as nitrogen or argon or under reduced pressure,
Done under vacuum.

The resistance heating element made of this graphite melts even in a high temperature range of 2000 to 3000 ° C., which cannot be practically used in the resistance heating element made of a metal material or a ceramic material.
Since it does not cause decomposition etc., it exhibits its function sufficiently as a resistance heating element and is a relatively inexpensive material, but it gradually wears out and deteriorates when used for a long time at the above-mentioned high temperature.
There was a drawback that continuous use was difficult.

That is, when the resistance heating element is worn or deteriorated and its thickness is reduced, the electric resistance of the portion locally increases and the wear is accelerated at an accelerated rate. Further, the furnace is accompanied by a change in heat generation density. Since it causes a change in the temperature distribution inside, it becomes an obstacle to stabilizing the quality of the baked product. Therefore, the resistance heating element needs to be replaced with a new one over time. For safety, it is necessary to replace the resistance heating element after cooling the furnace, but especially in a large heating furnace, a large amount of time and labor are required for a series of operations such as cooling-disassembly-assembly-reheating. However, as the resistance heating element replacement cycle becomes shorter, not only the material cost of the resistance heating element but also the productivity is significantly impaired and the firing cost is increased.

To solve this problem, Japanese Patent Application Laid-Open No. 58-138981 proposes a heating furnace provided with a resistance heating element having an extended life.

The resistance heating element of this heating furnace is obtained by winding fibrous carbon and film-like or sheet-like carbon or graphite in a bun shape on the outer peripheral surface of a resistance heating element made of a cylindrical carbon material. , Evaporation of graphite from the outer peripheral surface of the resistance heating element,
The abrasion loss is suppressed by these wound layers.

[0008]

However, in the resistance heating element proposed above, the sheet-like carbon or graphite laminated in a bun winding has remarkable anisotropy in thermal and electrical characteristics. Therefore, the evaporation of graphite from the outer surface of the resistance heating element is extremely suppressed, but since both ends of the wound layer are not electrically insulated from the resistance heating element, the carbon evaporated from the resistance heating element is There is a drawback in that the graphite leaks from both ends of the wound layer to the outside from the resistance heating element, and evaporated graphite adheres and deposits in the vicinity of both ends. Therefore, the resistance heating element of the above proposal cannot completely suppress the evaporation of graphite from the surface of the resistance heating element even if the film-shaped or sheet-shaped carbon or graphite is provided, so that the resistance heating element of There was a drawback that the life could not be extended.

The present invention has been made in view of the above circumstances, and is provided with a heating element capable of significantly extending the life of the resistance heating element by significantly suppressing the evaporation and wear of graphite. It is intended to provide a heating furnace.

[0010]

In order to achieve the above object, the present invention comprises a carbon fiber yarn wound and laminated on the outside of a cylindrical resistance heating element made of graphite with both ends open. The heating element comprises a carbon fiber yarn layer and a sheet-like graphite layer formed by winding sheet-like graphite in this order, and an electric current is passed through the resistance heating element of the heating element to generate an internal portion of the resistance heating element. In a heating furnace for heat-treating an object to be heated, at least both ends of the heating element between the sheet-shaped graphite layer and the resistance heating element are sealed with an insulating member made of a boron nitride molded body, To do.

The heating furnace of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a schematic vertical sectional view of an embodiment of a heating furnace according to the present invention.

In the figure, reference numeral 1 is a heating element for heating a yarn Y continuously passing through the inside thereof, and a carbon fiber yarn is wound a plurality of times on the outside of a cylindrical resistance heating element 2 made of graphite. A carbon fiber yarn layer 3 formed by turning and a sheet-like graphite layer 4 formed by winding sheet-like graphite are formed in this order. Further, both end portions between the outer surface of the resistance heating element 2 and the graphite graphite layer 4 are sealed with an insulating member 5 made of a boron nitride molded body. On the outside of the sheet-shaped graphite layer 4, a heat-insulating material 6 for heating the heating element 1, for example, carbonaceous or graphite powder or granular material, or felt-like material is coated with the same width as the sheet-shaped graphite layer 4. The outer side is further covered and protected by the furnace shell 7 made of a thin steel plate. Further, terminal portions 2a and 2b having a larger cross-sectional area than the central portion of the resistance heating element 2 are formed at both ends of the resistance heating element 2, and a current is passed through the resistance heating element 2 at each terminal portion. Electrode 8
Is fixed. The electrode 8 is connected to a low-voltage, high-current power supply unit (not shown), and the resistance heating element generates Joule heat when energized from the power supply unit. That is, since the central cross-sectional area of the resistance heating element 2 is smaller than the cross-sectional area of the terminal portions 2a and 2b, the electric resistance of the central portion becomes high, and the temperature inside the furnace becomes a high temperature of about 2500 to 3000 ° C. The yarn Y is heated. Note that 9a and 9b
Are the inlets and outlets of the yarn Y, respectively, and the ring-shaped members having these inlets and outlets are fixed to the openings of the terminal portions 2a, 2b so that when the yarn Y is heated, an inert gas supply unit (not shown) It also serves as a seal portion for preventing the inert gas supplied inside the resistance heating element from leaking to the outside. As described above, in order to suppress the oxidation and deterioration of the yarn Y and the resistance heating element 2, the heat insulating material 6 inside the resistance heating element 2 and inside the furnace shell 7 is usually filled with an inert gas such as nitrogen or argon. Filled or kept under vacuum.

In the above embodiment, the resistance heating element 2 is used.
In order to exhibit the contradictory characteristics of having sufficient electrical resistance for heat generation and yet withstanding wear due to evaporation of carbon content and maintaining a long life as much as possible, the central part thickness is
It is preferable to be about 5 to 50 mm, 10 to 30 mm
It is more preferable to adjust the degree. The length is not particularly limited. The shape of the terminals 2a and 2b is not a linear object like the yarn Y of the present embodiment but a plate-like object or a rod-like object in the case of batch type heat treatment. Alternatively, a structure may be used in which a blind portion and a flange having an entrance / exit are provided without providing a seal portion.

The carbon fiber yarn layer 3 is, for example, a pitch type,
A general carbon fiber yarn obtained by firing organic fibers such as cellulose or acrylic in an inert gas at 800 ° C. or higher is wound around the resistance heating element a plurality of times, and the laminated thickness is Although it is not generally determined depending on the thickness of the heating element, it is preferably about 5 to 20 mm. It should be noted that usually commercially available carbon fiber yarns are often provided with a sizing agent such as an epoxy type, but since these sizing agents are decomposed and gasified when heated, they contaminate the atmosphere in the furnace. Become. Therefore, it is preferable to remove the sizing agent before forming the wound laminate on the outside of the resistance heating element, and it is more preferable to use the carbon fiber yarn to which the sizing agent is not applied. The fineness of the carbon fiber yarn is not particularly limited, but a fineness of 1000 to 20000 denier is usually used. In any case, since this wound layer is in direct contact with the outside of the resistance heating element 2 for a long time and graphitization proceeds, either a carbonization type or a graphitization type can be used. Although the carbon fiber yarn itself has electrical conductivity, even if it is wound so as to be orthogonal to the axis of the resistance heating element which is a dielectric, the carbon fiber thread layer and the resistance heating element are formed. Since the contact resistance is extremely higher than the electric resistance of the resistance heating element, most of the current flows inside the resistance heating element, so that a good electric insulating layer is formed.

When the carbon fiber yarns are wound and laminated, it is important that they are closely attached to the outside of the resistance heating element 2 and that they are tightly wound so that there is no gap between the yarns. For example, a winder or a lathe is used. Use the carbon fiber while rotating the heating element.
It is preferable to wind and laminate under a constant tension of about 0 to 1000 g. In this case, it is preferable to tightly wind the heating element so that it is substantially perpendicular to the axial direction of the heating element, because evaporation of carbon vapor is suppressed.

The sheet-shaped graphite layer 4 is made of a flexible sheet-shaped material having a thickness of about 0.1 to 1 mm, which is obtained by press-molding expanded graphite. Specific examples thereof are commercially available. "Perm foil" (made by Toyo Tanso Co., Ltd.),
Examples include "Nikafilm" (manufactured by Nippon Carbon Co., Ltd.) and "Grafoil" (manufactured by Union Carbide). The number of laminated sheet graphite layers is 1 in order to prevent carbon vapor leaking from the surface of the carbon fiber yarn layer 3 from escaping to the outside.
The number of layers is less than 2 layers, and preferably 3 to 10 layers. The sheet-like graphite layer may be a laminated sheet obtained by stacking a plurality of single sheet-like materials and solidifying them with a carbon material, or a sheet-like material obtained by making carbon fiber yarns and solidifying them with a carbonaceous binder. . The sheet-like graphite layer has a significant anisotropy in thermal characteristics and electrical characteristics, the thermal conductivity is high in the plane direction, but is low in the direction perpendicular to the plane, that is, the thickness direction,
In addition, the electrical resistivity is low in the plane direction and extremely high in the thickness direction, which is opposite to the thermal conductivity, which is a characteristic suitable as a heating element of a heating furnace.

Any material may be used as the insulating member 5 as long as it has a large electric insulation resistance and can withstand high temperatures. As a concrete example, the insulating member 5 is manufactured by thermochemical deposition method (so-called thermal CVD method) under reduced pressure at high temperature. Commercially available boron nitride compacts and the like may be mentioned. When the above-mentioned boron nitride molded body is used for the insulating member 5, from the viewpoint of sealing the carbon vapor evaporated from the surface of the resistance heating element, a thickness of 1 m is formed on the outer peripheral surface of the resistance heating element by thermochemical deposition.
It is preferably formed into a cylindrical shape having a width of m and a width of 20 mm to 30 mm. Boron nitride can be safely used in an inert gas atmosphere up to about 2800 ° C., which is the heating temperature range of the heating furnace of the present invention, and its electric resistance is 5 × 10 ⁹ Ω · cm at 1000 ° C. Since the resistance heating element made of graphite has a remarkably large value as compared with the electric resistance of 0.0010 to 0.0020 Ω · cm, it can be used as an electric insulating member. As shown in the figure, the insulating member 5 may be provided at least at both ends between the sheet-shaped graphite layer 4 and the resistance heating element 2, and between the insulating member 5 and the sheet-shaped graphite layer 4. Although it does not prevent the carbon fiber yarn layer 3 from intervening, the carbon vapor evaporated from the outer surface of the resistance heating element 2 short-passes from the carbon fiber yarn layer 4 and easily leaks out of the furnace. It is preferable that the fiber yarn layer 3 does not intervene.

In the object to be heated which can be processed in the heating furnace of the present invention described above, as the yarn Y, the same yarn as that forming the carbon fiber yarn layer 3 can be heat-treated. Moreover, as a simple substance, a plate-shaped body, a rod-shaped body, or the like can be heat-treated.

[0020]

According to the heating furnace of the present invention, the carbon fiber yarn layer is
The carbon evaporated from the outer surface of the resistance heating element is blocked, and the partial pressure of the evaporated carbon inside the carbon fiber yarn layer is increased. Further, the sheet-shaped graphite layer reflects radiant heat to the inside due to its anisotropy, and exhibits a heat insulating effect. In this case, at both ends of the resistance heating element, carbon vapor evaporated from the outer surface of the resistance heating element tries to leak to the outside of the resistance heating element, but the insulating member seals the outer surface of the heating element and the sheet graphite layer at this part. Therefore, the leakage is prevented.

Therefore, the heating furnace of the present invention is 2500
Even at a high temperature of ℃ or more, the object to be heated can be continuously heat-treated while the life of the heating element is greatly extended.

[0022]

EXAMPLE In the heating furnace shown in FIG.
Inner diameter 30mm, outer diameter 50mm (wall thickness of the central part 10m
m), a graphite pipe having a length of 1250 mm is used, and a carbon fiber yarn “Torayca” (manufactured by Toray Industries, Inc.) T-1000G × 6 is provided along the outer periphery of the central portion of the pipe at a length of 600 mm.
A no-sizing yarn of K yarn was wound and tightly wound and laminated at a tension of about 250 g so as to be orthogonal to the pipe axis to form a carbon fiber yarn wound layer 3 having a thickness of 5 mm. Then, the insulating member 5 made of a boron nitride molded body is formed on both ends of the carbon fiber yarn winding layer 3.
Sheet-like graphite layer 4 by welding 5 layers of "permafoil" with a thickness of 0.2 mm around the outer peripheral surface of the sheet.
Was formed and bound with the above-mentioned carbon fiber thread to form the heating element 1.

Next, a block made of graphite is placed at the central position of the heating element 1, the electrode 8 is energized, and an argon gas of 99.999% purity is filled from an inert gas filling portion (not shown) to block the block. Was continuously heated while controlling the measurement of the red-hot color with a radiation thermometer installed at one end in the axial direction so that the surface temperature of the product became about 3000 ° C. under normal pressure. When the life until the surface of the heating element 1 was depleted and broken was measured, it was 437 hours (about 18 days).

[0024]

Comparative Example On the other hand, in the heating element 1 of FIG. 1, except that the insulating member 5 does not exist, the heating element under exactly the same conditions as in Example 1 was used, and the life was measured under the same heating conditions. It was 258 hours (about 10.8 days), and it was found that the heating element without the insulating member 5 had a shorter life than the heating element of Example 1.

[0025]

As is apparent from the above description, in the heating furnace of the present invention, the carbon fiber yarn is wound and laminated on the outside of the cylindrical resistance heating element made of graphite with both ends open. And a sheet-shaped graphite layer formed by winding and laminating sheet-shaped graphite in this order.A heating element is formed in this order, and a current is passed through the resistance heating element of the heating element to cover the inside of the resistance heating element. In a heating furnace for heat-treating a heat-treated product, at least both ends between the sheet-shaped graphite layer and the resistance heating element are sealed with an insulating member made of a boron nitride molded body, so carbon vapor evaporated from the outer surface of the resistance heating element. Can be suppressed from leaking from both ends of the resistance heating element to the outside of the resistance heating element, and the life of the heating element can be greatly extended.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of an embodiment of a heating furnace according to the present invention.

[Explanation of symbols]

 1: Heating element 2a, 2b: Terminal part 3: Carbon fiber yarn layer 4: Sheet-shaped graphite layer 5: Insulating member 6: Heat insulating material 7: Furnace shell 8: Electrode 9a: Inlet 9b: Outlet Y: Yarn

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomihiro Ishida 1515 Tsutsui, Matsumae-cho, Iyo-gun, Ehime Prefecture Toray Co., Ltd. Ehime factory

Claims (1)

[Claims] 1. A carbon fiber yarn layer formed by winding and laminating a carbon fiber yarn and a sheet-shaped graphite are laminated on the outside of a cylindrical resistance heating element made of graphite with both ends open. A sheet-like graphite layer composed of a heating element formed in this order,
In a heating furnace for heat-treating an object to be heated inside the resistance heating element by passing an electric current through the resistance heating element of the heating element, at least both ends of the heating element between the sheet graphite layer and the resistance heating element are A heating furnace characterized by being sealed with an insulating member made of a boron nitride molded body.