Industrial electric heating furnaces – Resistance furnace device – With heating element detail
Patent
1997-10-01
1999-01-26
Hoang, Tu Ba
Industrial electric heating furnaces
Resistance furnace device
With heating element detail
373114, 373117, 373128, 219408, H05B 360
Patent
active
058645764
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an electric furnace which can be used stably even at a high temperature of not lower than 1,400.degree. C. and which is superior in durability.
BACKGROUND ART
Electric furnaces are required to have various performance characteristics such as an ability to rapidly elevate the temperature, superior stability in a high-temperature oxidizing atmosphere, good durability against continuous use at high temperatures and against repeated increase and decrease of temperatures, a long length of soaking zone in a heating chamber, high handleability and the like.
Conventional electric furnaces equipped with resistance heating elements have the structure shown in FIGS. 1A and 1B wherein a plurality of cylindrical heating elements 12 are arranged around a furnace tube 13 used as a heating chamber, and wherein said heating elements are surrounded with a heat-resistant tube 14, heat-insulating layers 15 and 16 and an external casing 17 in this order.
However, the electric furnaces of this structure are adapted to indirectly heat the heating chamber by radiation of Joule heat from the cylindrical heating elements 12, and thus require a number of heating elements 12, involving a drawback of having a complicated structure and a great size as compared with the effective volume of the heating chamber. Such electric furnaces have posed problems such as poor durability due to low heating efficiency. Further, other problems exist in terms of the service life of heating elements and economy, because the constituent materials for electric furnaces have a large heat capacity and great electric power is required for heating to a predetermined temperature and in maintaining the temperature.
DISCLOSURE OF THE INVENTION
A primary object of the present invention is to provide a small-size electric furnace which can be used stably even at a high temperature of not lower than 1,400.degree. C., the furnace being superior in durability and handleability and economically advantageous.
The present inventors conducted extensive research to overcome the foregoing problems and found the following. The inventors used, as a heating element, a hollow lanthanum chromite ceramic element opened at both ends and having the following structure. The hollow ceramic element has terminal portions at both ends, and the terminal portions are larger in the cross-sectional area of the ceramic than a central portion of the element. High-temperature electrodes and metallic lead wires are attached to the terminal portions. When said heating element is used, the heating efficiency can be improved and the resulting electric furnace has a small-size, simplified structure. The electric furnace of specific construction produced using the heating element of said structure is excellent in durability, handleability and the like and economically beneficial. Further, when a lanthanum chromite ceramic having a specific composition and specific properties is used as the material for a heating element, an electric furnace of improved durability can be obtained. Based on these novel findings, the present invention was completed.
The present invention provides an electric furnace comprising: ceramic and opened at both ends; heating element, larger in the cross-sectional area of the ceramic on a plane perpendicular to the longitudinal direction of the element than a central portion of the element, high-temperature electrodes and metallic lead wires being attached to the terminal portions, the portion between the terminal portions being used as a heat-generating portion, and the empty space in the interior of the hollow ceramic member being used as an effective heating chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 (A) is a longitudinal section of a conventional tubular electric furnace.
FIG. 1 (B) is a cross-sectional view of the conventional tubular electric furnace.
FIG. 2 (A) is a longitudinal section of the electric furnace of the present invention.
FIG. 2 (B) is a cross-sectional view of the electric furnace
REFERENCES:
patent: 2121744 (1938-06-01), Ridgway et al.
patent: 3128325 (1964-04-01), Andersen et al.
patent: 4041236 (1977-08-01), Dumont et al.
patent: 4490828 (1984-12-01), Fukuhara et al.
Abe Takeshi
Kawanami Toshio
Nakatani Masanori
Hoang Tu Ba
Nikkato Corp.
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