WO1981003238A1

WO1981003238A1 - Resistant heat generating element and method of manufacturing same

Info

Publication number: WO1981003238A1
Application number: PCT/US1980/000476
Authority: WO
Inventors: J Lee
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-04-30
Filing date: 1980-04-30
Publication date: 1981-11-12
Anticipated expiration: 1982-10-30
Also published as: EP0050612A1

Abstract

Electrically resistant heat generating elements are formed by kneading fine particles of a carbonized plant material that provides electrical insulation below a predetermined temperature and serves as a conductor or a semiconductor above said temperature. The mixture is sintered, cooled and then pulverized.

Description

RESISTANT HEAT GENERATING ELEMENT AND METHOD OF MANUFACTURING SAME

TECHNICAL FIELD

The present invention relates to a heat generating element which depends on electrical contact resistance and to a method of manufacturing such an element.

BACKGROUND OF THE PRIOR ART Conventionally, resistive heat generating elements have been made of carbon particles. These carbon particles have been disadvantageous in that the temperature control is difficult when a space between electrodes is filled with the carbon particles and an electric current is supplied for conduction. An objective of the present invention is to provide a method for manufacturing a heat generating element which is capable of eliminating this disadvantage.

BRIEF SUMMARY OF THE INVENTION The following described the method of the present invention by which a heat generating element results.

The method comprises a first step of carbonizing a plant and pulverizing the carbonized plant to obtain fine particles. A second step is mixing and kneading said fined particles of the carbonized plant with fine particles of a non-organic heat resistant fine material which provides electrical insulation at low temperatures and serves as a conductor or a semi-conductor at high temperatures. A binder is provided which can be carbonized. Sintering of the kneaded lumps then takes place followed by cooling. The lumps are then pulverized.

The non-organic heat resisting material can be a metallic compound such as calcium dihydnogenphosphate, calcium hydrozide, calcium oxide, calcium carbide, calcium silicate, alumina, molten alumina, D soda alumina, alumina white, alumina silicate, alumina oxide, compound silicate, silicon nitride, zeolite, tungsten compounds, boron compounds (for example, borax, boron nitride and boron carbide), zirconium, zirconium oxide, etc. Materials such as calcium, silicic acid and silicon can be oxidized into a suitable metallic compound during the sintering process in an electric furnace or the sintering can be carried out in a carbonizing atmosphere or a nitrifying atmosphere to make these materials a carbide or a nitride. Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. DETAILED DESCRIPTION OF INVENTION

Various embodiments of the present invention are shown below. ExampIe 1 ;

5 parts of plant carbide of 500 mesh grain size and 1 part of silica of 500 mesh garin size are kneaded with the addition of a solution consisting of 0.5 parts of polyvinyl alcohol and 1 part of water. Then lumps of the kneaded materials are sintered in an electric furnace at 1,500°C for an hour and the sintered lumps are pulverized to obtain, after cooling, heat generating elements of 0.1 to 1 mm in size. The results as shown in Table 1 were obtained by filling the electric furnace of 100 mm in length and 50 mm in width and depth with the above-mentioned heat generating elements and supplying an electric power across the electrodes provided at both sides in the lengthwise direction.

In the above experiment, the values of voltage and current in the initial stage were maintained at a fixed level. Since the voltage and current may not be controlled in practice, the initial current value differs with each furnace due to contact resistance of the heat generating element. In the experiment, it was ascertained that the physical characteristics of the heat generating element obtained according to the present invention, due to voltage drop and current increase, were more moderate than conventional carbon particles and the furnace temperature was higher than conventional. Example 2:

One part of calcium trihydrogenphosphate in grain size of less than 500 mesh and 1 part of silica in a grain size of less than 500 mesh are added to 4 parts of charcoal powder in a grain size of less than 500 mesh and this mixture is then mixed with a solution consisting of 0.1 parts of polyvinyl alcohol and 2 parts of water. After molding in lumps and drying, the lumps are sintered at 1,500°C for an hour. The sintered lumps are pulverized after cooling to obtain heat generating elements of 0.1 to 1 mm in size. The heat generating elements are placed in a furnace as described in Example 1 and an electric power is supplied across the graphite electrodes. The following results have been obtained in this manner.

In this example, a constant voltage is supplied for conduction since commercial power is employed. As described above, the initial current value is not constant due to the contact resistance which varies with each furnace.

It was ascertained in this experiment that the physical characteristics pertaining to variations of the current and the temperature of the heat generating elements were of a linear, unlike conventional heat generating elements. Example 3:

Four parts of charcoal particles having a grain size of 500 mesh and 1 part of zirconium having a grain size of 500 mesh are mixed together. This mixture is sintered at 1,800°C for an hour after having been kneaded with a solution consisting of 0.5 parts of polyvinyl alcohol and 2 parts of water. It is then pulverized, after having been cooled, to obtain heat generating elements of 0.5 to 1 mm in size.

The results, as shown in Table 3, were obtained by filling the furnace used in Example 1 with the heat generating elements and supplying the electric power while controlling the voltage along with the lapse of time.

It was ascertained in this experiment that the furnace temperature can be controlled by controlling the voltage value.

The heat generating element obtained by the method according to the present invention has the characteristics described above and, therefore, the following effects can be expected.

The heat generating element obtained comprises carbon particles and non-organic heat resisting material, and this non-organic heat resisting material provides electric insulation until the temperature of the heat generating element reaches the predetermined high temperature value and service as a semi-conductor or a conductor once the temperature reaches the predetermined value.

According, it is considered that, since the calorific value of the heat generating element becomes large in the high temperature region, the rate of increase of the furnace temperature will be larger in the region of high temperatures. Since the resistance of the non-organic heat resisting material is constant, subsequent variation of the resistance of the whole heat generating element will be moderate as compared with the heat generating element. made of only conventional carbon particles.

The heat generating element according to this method contains a non-organic heat resisting material and provides excellent heat retaining characteristics. Therefore, the element can be improved so that furnace temperature rise in the high temperature region is promoted and the voltage and current can be easily controlled since the resistance variation is moderate.

While particular forms of the invention have been illustrated and described, it will also be apparent that various modifications can be made without departing from the spirit and scope of the invention.

Claims

1. A method for manufacturing an electrically resistant heat generating element comprising kneading fine particles of a carbonized plant material and fine particles of a non-organic heat resistant material which provides electrical insulation below a predetermined temperature and serves as a conductor or a semiconductor above said predetermined temperature, sintering lumps obtained from kneading said fine particles, cooling the sintered lumps, and pulverizing them to produce grains of a specified size.

2. The method as claimed in Claim 1, wherein said heat resistant material is a metallic compound.

3. The method as claimed in Claim 1, wherein said heat resistant material is selected from the group consisting of calcium dihydrogenphosphate, calcium hydrogenphosphate, calcium trihydrogenpbosphate, calcium hydrozlde, calcium oxide, calcium carbide, calcium silicate, alumina, molten alumina, D soda alumina, alumina white, alumina silicate, alumina oxide, compound silicate, silicon nitride, zeolite, tungsten compounds, boron compounds, zirconium and zirconium oxide.

4. An electrically resistant heat generating element comprising: a mixture of fine particles of a carbonized plant materials and fine particles of a non-organic heat resistant material which provide electrical insulation below a predetermined temperature and serve as a conductor or a semiconductor above said predetermined temperature.

5. The heat generating element as claimed in Claim 4, wherein said heat resistant material is a metallic compound.

6. The heat generating element as claimed in Claim 4, wherein said heat resistant material is selected from the group consisting of calcium dihydrogenphosphate, calcium hydrogenphosphate, calcium trihydrogenphosphate, calcium hydrozide, calcium oxide, calcium carbide, calcium silicate, alumina, molten alumina, D soda alumina, alumina white, alumina silicate, alumina oxide, compound silicate, silicon nitride, zeolite, tungsten compounds, boron compounds, zirconium, and zirconium oxide.