US3735008A

US3735008A - Electric furnace

Info

Publication number: US3735008A
Application number: US00125986A
Authority: US
Inventors: M Ieda; Y Mizushina; M Shimazaki
Original assignee: Kokusai Electric Corp
Current assignee: Kokusai Electric Corp
Priority date: 1970-03-20
Filing date: 1971-03-19
Publication date: 1973-05-22
Anticipated expiration: 1990-05-22

Abstract

An electrically energizable heating coil having a plurality of convolutions about its longitudinal axis. The coil is kept from deforming by a tubular insulator split longitudinally in a plane corresponding with the longitudinal axis of the coil so that it comprises two half-cylinders. Avoiding deformation allows uniform heat distribution by the coil. The tubular insulator is made of a thermosetting material and has a supporting radial rib axially thereof on one of half-cylinders along the full axial length of the coil. The rib is disposed in a plane normal to the firstmentioned plane so that in a horizontal position of the coil the rib is a principal support for the coil.

Description

ilnited lieda et al.

atent [191 [451 May 22,1973

[541 ELECTRIC FURNACE [73] Assignee: Kokusai Denki Kabushiki Kaisha,

Tokyo-to, Japan [22] Filed: Mar. 19, 1971 [21] Appl. No.: 125,986

[30] Foreign Application Priority Data [56] References Cited UNITED STATES PATENTS 2,688,046 8/1954 Norton, Jr. et a1. ..l3/35 2,880,297 3/1959 Yohe .219/548 3,406,275 10/ 1968 Pedrotti 2,901,521 8/1959 Yoder et al "13/25 Primary ExaminerHarold Broome Attorney-Robert E. Burns and Emmanuel J. Lobato [57] 7 ABSTRACT An electrically energizable heating coil having a plurality of convolutions about its longitudinal axis. The coil is kept from deforming by a tubular insulator split longitudinally in a plane corresponding with the longitudinal axis of the coil so that it comprises two halfcylinders. Avoiding deformation allows uniform heat distribution by the coil. The tubular insulator is made of a thermosetting material and has a supporting radial rib axially thereof on one of half-cylinders along the full axial length of the coil, The rib is disposed in a plane normal to the first-mentioned plane so that in a horizontal position of the coil the rib is a principal support for the coil.

1 Claim, 2 Drawing Figures ELECTRIC FURNACE This invention relates to an electric furnace and, more particularly, to a sorking pit used for homogeneous-heating an object.

In conventional electric furnaces, there are disadvantages such that a heater formed into a coil is softened at a high temperature of about 1,000 to 1,300 C, a supporter (a cylindrical supporter for the coiled heater) is deformed so as to be pressed down at remainder except supporting points due to gravity. Accordingly, homogeneity in the electric furnace is deteriorated. To eliminate this defect, a number of supporting points are necessary. However, a material having sufficient strength at the above mentioned high temperature has such disadvantages as high hardiness and density, large heating loss due to deformation, and ununiform temperature distribution. Moreover, heat insulator blocks are usually heaped up so as to surround the coiled heater to obtain homogeneous heating in the electric furnace. Accordingly, exchange of the heater cannot be readily performed, and the heat insulator blocks are necessary to be disused and exchanged each time.

An object of this invention is to provide an electric furnace capable of eliminating the above defects of the conventional devices.

The principle of this invention will be better understood from the following detailed discussion taken in conjunction with the accompanying drawings, in which the same or equivalent parts are designated by the same reference numerals, characters and symbols, and in which:

FIG. 1 is a cross section view illustrating an embodiment of this invention in which upper parts except a heating coil are lifted by a small distance from lower parts; and

FIG. 2 is a longitudinal sectional view illustrating an embodiment of this invention shown in FIG. 1.

With reference to FIGS. 1 and 2, an embodiment of this invention comprises a heating coil 1 of an alloy wire of aluminum (Al), chromium (Cr), nickel (Ni) and iron (Fe) having a maximum allowable temperature of l,320 C; a supporting tube 2 for the heating coil 1 which is a ceramic tube of high purity divided into an upper part and a lower part; heat-curing

heat insulating materials

3 and 4 of half cylinder, each of which is moulded by an unvoluminous mixture of silicon dioxide (SiO and alumina (A1 having a small specific gravity and by an additional binder for solidity; heat insulating materials 5 of felt-type having the same contents as the

heat insulating materials

3 and 4 without the additional binder; and a pair of cases 6. Moreover, in the embodiment of this invention, a supporting rib (or a supporting bed) 4a extending the axial length of the coil acting as the supporting point is incorporated with the heat insulating material 4 so as to form a single body (i.e.; a heat insulator) to avoide the above mentioned deformation of the heating coil 1 and the cylindrical supporter 2, and the heating coil 1 is sup ported by the cylindrical supporter 2 in the entire length thereof while the cylindrical supporter 2 is supported by the heat insulator (4 and 4a).

As a result of the above construction, deformation of the heat insulator (4 and 4a) can be effectively avoided, so that temperature distribution becomes extremely uniform and heat loss is improved. Moreover, since the remainders except the heating coil 1 are designed so as to be divided into respective upper parts and lower parts as shown, operation of this electric furnace and exchange of the heating coil 1 can be readily performed. Furthermore, since the

heating insulating materials

3, 4, 4a and 5 are not at all damaged in operation and exchange, they can be again employed as they are.

In the above embodiment, the supporting rib 4a (or supporting bed) and the heat insulating material 4 form a single body. However, the heat insulating material 4a may be connected with a half-cylindrical heat insulator similar to the heat insulating material 3.

The heat insulating material 3 may be formed so as to have the same formation as the heat insulating material 4 having a projection similar to the supporting rib 4a.

We claim:

1. A heating coil for use in an electric furnace comprising, an electrically conductive heating coil having a plurality of convolutions about a longitudinal axis, a pair of half-cylinders for supporting the coil longitudinally to avoid deformation thereof in use thereby to maintain heat distribution uniform, and a tubular insulator made of a thermosetting material disposed circumferentially of said half-cylinders and axially thereof to axially support the half-cylinders, said tubular insulator being split longitudinally along a plane corresponding with the longitudinal axis thereby comprising two other half-cylinders, one of said other half-cylinders having a single radial rib integral therewith and extending the axial length of the coil, said rib being disposed in a plane substantially normal to the first-mentioned plane and made of the same thermosetting material as the two other half-cylinders.