JPS58138981A - Electric heating furnace - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric heating furnace, such as a Tanman Niura heating furnace, which uses carbon material as a resistance heating element.
This is a high-temperature heating furnace that can be used to smelt various persimmon industrial materials such as carbon materials such as Shishifiber and ceramics. Various types of heating furnaces such as furnaces, induction furnaces, arc furnaces, and plasma furnaces are known, but resistance furnaces, especially Tammann furnace type PA furnaces (hereinafter referred to as Tammann type) that use carbon material as a resistance heating element, are known. Since the heating means is relatively simple, it is widely used as a heating furnace for the above-mentioned industrial materials.

An electric current is passed through the heating element (called the lower heating element) to generate heat using Joule heat, and the object to be heated, which is left stationary or passes continuously inside the tube, is heated and fired, but usually an inert gas such as nitrogen or argon is used. It is carried out in medium or reduced pressure (vacuum), and carbon (graphite) material is generally used as the heating element.

The heating element made of this carbon material is different from the heating element made of metal or ceramic materials, and has a heating element of 2,000 to 3
Even in the high-temperature range of 1,000°C, it does not undergo melting and bicomponent decomposition and performs its function as a heating element, and it is a relatively inexpensive material. It becomes difficult to use.

In other words, when the wall thickness decreases due to wear and tear on the heating element, the electrical resistance of that part increases, causing a change in the temperature distribution in the furnace due to changes in heat generation density, which is an impediment to the quality stability of fired products. For safety reasons, is it necessary to perform this after the furnace has been cooled? 1.1 In large heating furnaces, the series of operations such as cooling, disassembly, assembly, and reheating can be very labor-intensive. As the heating element replacement period becomes shorter, not only the material cost of the heating element increases, but also the productivity is significantly hindered and the firing cost increases.

The present inventors have proposed a heating furnace having five carbonaceous heating elements, which solves this problem and has an extended lifespan.
No. 460, but the present invention was achieved through further research.

A feature of the present invention is the use of a resistance heating element made of lead as described in the claims.

In a heating furnace using a heating element wound with P element iK and rolled threads proposed in the invention of the above-mentioned Special Patent Ill, No. 56-203,460, the life of the heating element is significantly longer than that of conventional heating furnaces. In order to further enhance the effect, the present invention is characterized in that the heating element is wound with not only fibrous carbon but also film or sheet carbon or graphite. .

The reason why the life of the heating element can be extended by winding and laminating fibrous carbon is not necessarily clear, but it is thought that the effect of relaxing the thermal and electrical boundary conditions on the outer surface of the heating element is working effectively. . In particular, under thermal boundary conditions, it is necessary that the wound yarn layer exhibits a sufficient heat insulating effect, and the present %tl+ focuses on this point and makes improvements.

Film-like or sheet-like carbon or graphite is commercially available as "Gura 7 Oil" from Union Carbide Co., Ltd., but these exhibit remarkable anisotropy in thermal properties, and within the plane □ Although the conductivity is high,
It has the characteristic that it is low in the direction perpendicular to the plane. In the present invention, by taking advantage of this feature and stacking the #-shaped carbon together with the winding layer, one
7 (It becomes possible to suppress heat even more effectively.

In particular, at high temperatures of 2000°C or higher, heat transfer is mainly through radiation, and the bv and dissipation of σ heat from the surface of the heating element to the outside world can be further reduced by cutting this radiant heat. Also, by rolling the sheet-like material into a cylindrical shape, it is possible to reflect heat radiation inside and improve the heat insulation effect.

The configuration of the apparatus of the present invention will be explained in 8 below according to the drawings.

FIG. 1 is a side sectional view showing one example of a heating furnace used in the present invention. 1 is a heating element made of carbon material;
The internal space of the heating element must be large enough to accommodate or pass the object to be heated, and it must be maintained at the desired temperature and atmosphere, but the outer surface of the heating element simply transfers heat to the outside world. It is a heat dissipating surface.

Therefore, the heating element 1 is kept warm by covering it with a heat insulating material 2. 3 is an electrode for passing current, and 4 is an entrance/exit seal portion. When heat-treating the object to be heat-treated continuously, it is necessary to provide a gap in the sealing part through which the sample can pass, but in the case of batch-type heat treatment, a 7-lunge structure can be used. The heat insulating material layer 2 inside the outer shell 5 and the inside of the heating element are constantly filled with an inert gas such as nitrogen or argon to prevent oxidative deterioration of the books to be heated and the heating element. , or a felt-like material is used. (2) is a heating element winding layer in which carbon fibers and sheet-like graphite are laminated, and the sheet-like graphite (2) is wound together with carbon fibers. The fibrous carbon and the film or sheet carbon or graphite may be alternately wound in at least two layers, but the invention is not limited thereto.

The carbon N & group used here is made by preparing organic fibers such as pitch, cellulose, and acrylic fibers in an inert gas at 800%
It is a general carbon fiber obtained by firing at temperatures above ℃. In some cases, graphite fibers fired at a temperature of 2000° C. or higher may also be used. In any case, since it is in direct contact with the heating element 1 for a long time, graphitization progresses, so either carbonaceous or graphite can be used. Additionally, commercially available carbon fibers are often coated with sizing agents such as epoxy or polyvinyl alcohol, but these sizing agents decompose and gasify when heated, polluting the atmosphere inside the furnace. I will do it. Therefore, before the object to be heated is actually processed, it is necessary to heat it sufficiently and replace the decomposition gas during that time, and it is preferable to remove it before winding it around the heating element.

Further, the film or sheet-like material used here is preferably a flexible sheet-like material formed by pressure-molding expanded graphite and having a thickness of 01 to 1 m. Alternatively, it may be a laminate sheet in which multiple νI of these single sheets are stacked and hardened with a carbon material, or a sheet-like product made from carbon fibers and bonded with a carbonaceous binder.

If the above-mentioned film or sheet is highly flexible, it can be inserted into the film or sheet and wound into a cylindrical shape when winding the carbon fiber thread. In this case, it is preferable that the innermost layer that comes into direct contact with the heating element is made of carbon fiber, and that carbon fiber is wound around it to a thickness of at least 2 to 5 square meters, and then a sheet is sandwiched between the sheets and a thread is wound around the outside of the carbon fiber. . The reason for this is that if there is a film or sheet-like material in the innermost layer, it is difficult to make uniform contact with the surface of the heating element, and it may actually worsen the boundary conditions between the heating element and the outside world. . Further, the number of sheets to be laminated is not necessarily one, but a plurality of sheets, for example, two to three sheets, may be stacked with carbon fiber layers interposed therebetween.

Example 1 In a Tammann furnace as shown in FIG. 1, a graphite pipe serving as a heating element having an inner diameter of 400, an outer diameter of 70, and a length of 1 m was used. After wrapping carbon fiber 6 trading cards "■ T-300 to a thickness of 4" over 70ffi of the central part of this pipe, cover it with Kurofune sheet and graph oil ■ thickness 0.
A heating element was constructed by wrapping a graph oil sheet by wrapping one layer of 6° carbon fiber and then wrapping the same carbonized thread as above to a thickness of 5 cm.

The furnace was heated under a nitrogen seal with a purity of 99.999% by passing an electric current so that the maximum temperature inside the hollow part of the heating body was 2800°C. Disassemble it after 30 days, peel off the thread and check the condition of the heating element lol! However, the wear and tear was minor.

On the other hand, when a similar test was conducted using only the graphite pipe without winding the carbon fiber yarn, the graphite pipe serving as the heating element broke after 7 days and became unusable. Upon disassembly and inspection, it was confirmed that the graphite on the outer wall of the central part of the pipe had been evaporated and wasted, leading to the breakage.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of the electric heating furnace of the present invention. 1 - heating element, 2 = heat insulating material layer, 3: electrode. 4: Seal part, 5: Outer shell, 6: Heating element winding 7:
Sheet graphite patent applicant Toshi Co., Ltd.

Claims (1)

[Claims] (]) I for electric heating/furnace using carbon material as resistance heating element
JII heat furnace.