JPH05157452A - Electric furnace using both lanthanum chromite and zirconia for heating element - Google Patents

Abstract

PURPOSE:To produce a furnace having a compact structure which makes it unnecessary to take a preheating heater out of the furnace or to use an inner casing. CONSTITUTION:Inside a furnace lanthanum chromite heating elements 12 and zirconia heating elements 11 are arranged alternately and at a specific ratio between the numbers of the heating elements. The lanthanum chromite heating elements 12 are used for preheating and up to a temperature range of 1,500 to 1,800 deg.C and the zirconia heating elements 11 are used for heating in a high temperature range of 1,500 to 1,900 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric furnace in which a lanthanum chromite heating element and a zirconia heating element are commonly used for heating to an extremely high temperature of 1800 ° C. or higher in the atmosphere or an oxidizing atmosphere.

[0002]

2. Description of the Related Art A zirconia heating element rapidly lowers its electric resistance value as the temperature rises, and it is generally 1300 ° C.
Above, it is used as a resistance heating element. A furnace body of a conventional electric furnace using a zirconia heating element is composed of an inner box and an outer box, and a preheating chamber is formed between the inner box and the outer box, and a silicon carbide heating element and molybdenum disulfide are formed in the preheating chamber. A preheating heater composed of a heating element is arranged to heat the inner box, and the temperature at which the zirconia heating element arranged in the inner box can conduct electricity (1300
When the temperature reaches (° C.), the zirconia heating element is energized to heat the temperature in the inner box to a predetermined temperature.

FIG. 3 shows such a conventional ultra-high temperature apparatus, in which a silicon carbide heating element or a molybdenum disulfide heating element is provided in a preheating chamber 5 formed by an alumina heat insulating board 4 forming an outer box and an inner box 3. Preheater 2 consisting of
A zirconia heater 1 is arranged inside. The preheating chamber 5 is heated to about 1300 ° C. by the heater 2. Zirconia is an insulator, but it exhibits conductivity when heated to about 1300 ° C., and when it is energized in this state, it functions as a heating element, and a high temperature of 2000 ° C. or higher can be obtained.

[0004]

However, in the conventional electric furnace, it is necessary to preheat the zirconia heating element to a temperature at which electricity can be applied, and a silicon carbide heating element or disilicide which is generally used as a heating element for preheating. A heating element such as molybdenum
Safe operating temperature limit under oxidizing atmosphere is 1800
It is below ℃. Therefore, the heating element used for preheating has a drawback that it must be taken out when the zirconia heating element reaches a temperature at which it can be energized. Further, the furnace body is composed of an inner box and an outer box, and a preheating heater is arranged in the preheating chamber so that even if the temperature in the furnace of the inner box becomes 1800 ° C or higher, the heating element for preheating becomes 1800 ° C or lower. However, there is a problem in that the outer dimensions of the furnace become large due to the complicated double structure.

The present invention is intended to solve the above-mentioned problems, and it is not necessary to take out a heater for preheating outside the furnace, and an inner box is not necessary, so that a lanthanum chromite heat generation that enables compact manufacture of the furnace is possible. An object is to provide an electric furnace for both a body and a zirconia heating element.

[0006]

A lanthanum chromite heating element and a zirconia heating element common electric furnace of the present invention is a high temperature electric furnace in which a zirconia heating element heats a lanthanum in a furnace after preheating to a predetermined temperature by a preheating heater. A chromite heating element and a zirconia heating element are arranged, and the lanthanum chromite heating element is used as a preheating heater. Further, the present invention is characterized in that the lanthanum chromite heating element and the zirconia heating element are alternately arranged at a predetermined number ratio.

[0007]

According to the present invention, the lanthanum chromite heating element and the zirconia heating element are arranged in the furnace, and the lanthanum chromite heating element is preheated up to 1500 to 1800 ° C.
In a high temperature range of about 900 ° C., heating is performed with a zirconia heating element.
Since the lanthanum chromite heating element is stable at a surface temperature of about 1900 ° C for a long time, it is not necessary to pull it out of the furnace at high temperatures, and it is not necessary to provide an inner box to protect the heating element for preheating. It can be made compact and an economical furnace can be manufactured.

[0008]

Embodiments Embodiments will be described below with reference to the drawings. 1A and 1B are views showing an electric furnace of the present invention. FIG. 1A is a plan sectional view, FIG. 1B is a longitudinal sectional view, and FIG. 1C is a side sectional view. In the figure, 10 is a furnace body, 11 is a zirconia heater, 1
2 is a lanthanum chromite heater, 13 is a zirconia fiber board, 14 is an alumina fiber board, 15
Is a hearth, 16 is a ceiling, and 17 is a side wall.

The furnace body 10 is a zirconia fiber board 1
A furnace body composed of a hearth 15, a side wall 17, and a ceiling 16 composed of 3 is surrounded by an alumina fiber board 14. In the furnace, along the opposing side walls as shown in FIG. 1A, and as shown in FIGS. 1B and 1C, the hearth 15, the ceiling 16, and the alumina fiber board 1 are provided.
The zirconia heaters 11 and the lanthanum chromite heating elements 12 are alternately arranged so as to penetrate through 4.

The zirconia heating element is obtained by adding a small amount of another oxide to zirconium oxide (Zro ₂ ) and sintering it at a high temperature. After manufacturing a zirconia round bar, it is dried and sintered, and the central heating portion is processed and polished by a lathe to finish as a small-diameter heating portion and a large-diameter terminal portion.
Since this zirconia heating element has a low thermal conductivity and a high thermal expansion coefficient, connection with a lead wire for electrical conduction becomes a problem. Therefore, for example, 5 to 80 parts by weight of zirconia fiber and zirconia powder containing a zirconia stabilizer are added. 20-95
A flexible refractory sheet formed by adding 20-50 parts by weight of a flexible binder to 100 parts by weight of an aggregate composed of parts by weight is wound around a terminal portion of a zirconia heating element, Use a sheet with a current-carrying lead wire in contact with the surface of this sheet, or use a magnesia pipe for the current-carrying lead wire so that the lead wire does not melt and evaporate at ultra-high temperatures, resulting in thin wires and breakage. Use the covered one.

The lanthanum chromite heating element 12 is made of Cr ₂
A resistance heating element made of a composite oxide containing LaCrO ₃ as a main component, which was synthesized by heating an equimolar mixture of O ₃ and La ₂ O ₃ at 1300 ° C. or more, and a heating element surface temperature of 1900.
It can be used stably at ℃ for a long time, and is formed into a round bar shape. The specific resistance of this lanthanum chromite can be made smaller than that of zirconia, the conductivity is strongly influenced by the atmosphere, and even when heating in vacuum or an inert gas,
Conductivity is obtained by treating in advance in an oxygen atmosphere.

In such a furnace configuration, the lanthanum chromite heating element 12 is preheated up to a furnace atmosphere temperature of about 1500 to 1800 ° C., and the zirconia heating element 11 is heated in a high temperature range of about 1500 to 1900 ° C. At this time, since the lanthanum chromite heating element 12 can be used for a long time at the surface temperature of 1900 ° C., it is not necessary to take it out of the furnace and an inner box is not required, so that the furnace structure can be made compact.

FIG. 2 is a diagram for explaining an example of the heating rate,
FIG. 2A shows the case where 12 lanthanum chromite heaters are used, and FIG. 2B shows the case according to the present invention where 6 lanthanum chromite heaters and 6 zirconia heaters are used.

When 12 lanthanum chromite heaters are used, as shown in FIG. 2 (a), the temperature is 1800 ° C. in about 6 hours.
The temperature was raised to. In FIG. 2B, the temperature was raised to 1500 ° C. in about 7.5 hours by the six lanthanum chromite heaters, and 1950 ° C. could be achieved in about 10.5 hours by heating with the zirconia heater.

Although the same number of lanthanum chromite heating elements and zirconia heating elements are arranged alternately in the above embodiment, the present invention is not limited to this and the number of lanthanum chromite heating elements and zirconia heating elements is not limited to this. The ratio of 2: 1, 1: 2, etc. may be appropriately changed as necessary.

[0016]

As described above, according to the present invention, the lanthanum chromite heating element is used for preheating, and the zirconia heating element and the zirconia heating element are arranged in the furnace. In addition, since there is no need to provide an inner box to protect the preheating heating element, the furnace structure can be made compact and an economical furnace can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a high temperature furnace of the present invention.

FIG. 2 is a diagram illustrating an example of a temperature rising rate.

FIG. 3 is a diagram illustrating a conventional high temperature furnace.

[Explanation of symbols]

10 ... Furnace body, 11 ... Zirconia heater, 12 ... Lanthanum chromite heater, 13 ... Zirconia fiber board, 14 ... Alumina fiber board, 15 ... Hearth floor, 1
6 ... Ceiling, 17 ... Side wall.

Claims (2)

[Claims] 1. A high temperature electric furnace in which a zirconia heating element is used to preheat a lanthanum chromite heating element after preheating it to a predetermined temperature by a preheating heater. An electric furnace for both lanthanum chromite heating element and zirconia heating element characterized by being used as. 2. The electric furnace according to claim 1, wherein the lanthanum chromite heating element and the zirconia heating element are alternately arranged in a predetermined number ratio.