JPS6252436B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a first insulating layer made of at least one of titanide and carbide around a heating wire disposed in a tubular body made of metal, and The purpose of this invention is to easily obtain a sheathed heater with excellent safety regarding a method for manufacturing a sheathed heater in which a second insulating layer made of an oxide with excellent insulation and thermal conductivity is provided around the do.

A typical sheathed heater is manufactured by inserting a coiled heating wire into a metal pipe, filling it with magnesium oxide powder, and then reducing the diameter by rolling or other means. If a sheathed heater manufactured in this manner and provided with only one insulating layer made of magnesium oxide powder around the heating wire is used for a long period of time, the heating wire will eventually break. When the wire breaks, the broken part becomes incandescent, causing the metal pipe to melt. This phenomenon occurs because the heat of the arc discharge generated at the time of wire breakage melts the magnesium oxide in the vicinity of the wire breakage, making it conductive and allowing the current to continue flowing. Therefore,
To prevent this phenomenon, the inorganic insulating material in the vicinity of the heating wire must either not melt due to the heat of the arc discharge, or must be a material that is a poor conductor of electricity even if it melts. Such inorganic insulators include silicon nitride, boron nitride, aluminum nitride, and silicon carbide, but all of these are inferior to magnesium oxide in thermal conductivity and insulating properties when electricity is applied. Therefore, in order to solve this problem, the heating wire is surrounded with two layers of different types of insulators.
It is desirable to have a structure using carbide and surrounding magnesium oxide, which has excellent thermal conductivity and insulation properties. However, the above-mentioned chitide and carbide powders,
It is difficult to fill the magnesium oxide powder at the same time, and even if it were possible, there is a risk that the two powders would mix. When the two powders are mixed together, magnesium oxide will also be present in the vicinity of the heating wire, causing the aforementioned incandescent heat and melting of the metal pipe when the wire breaks. The double encircling effect is lost.

In order to solve this problem, the present invention makes sure that only the titanide and carbide are present in the area close to the heating wire and are separated from the magnesium oxide on the outside, so that at the end of the service life, The present invention aims to provide a manufacturing method that can easily produce a sheathed heater that disconnects safely, and examples thereof will be described below.

After coiling the heating wire and connecting terminal rods to both ends, a molded body is created by wrapping it in a material that will become the first insulating layer, such as silicon titanide, boron titanide, aluminum titanide, silicon carbide, etc., and then forming a metal pipe. After inserting and fixing into the center of the metal pipe, the gap between the metal pipe and the molded body is filled with magnesium oxide powder that will become the second insulating layer. After filling, the diameter of the metal pipe is reduced by rolling or swaging to prevent powder from spilling from the end.

Here, the molded body may have a helical shape along the heating wire, or a cylindrical shape that includes the entire coiled heating wire. In addition, the thickness of the coating of the heating wire made of titanide or carbide is 0.2 mm or more, and when the molded body is inserted into the metal pipe, the inner wall of the metal pipe is 1 mm or more.
A thickness with some gaps is desirable. If the thickness is less than 0.2 mm, there is a risk that the heat generated when the wire breaks will reach the surrounding magnesium oxide and melt it. Furthermore, when the gap between the metal pipe and the molded body is less than 1 mm, the insulation resistance between the heating wire and the metal pipe decreases, resulting in poor heat conduction. The molded body is produced by forming a green compact of the titanium or carbide powder, or by making the powder into a slurry with a solvent, applying it to a coiled heating wire, and then drying it.

The sheathed heater manufactured as described above was
They are shown in Fig. 2 and Fig. 2, respectively. Figure 1 shows a case in which a coiled heating wire is formed into a helical shape and inserted into a metal pipe, and Figure 2 is manufactured by inserting a spiral shape along a coiled heating wire into a metal pipe. This shows the case where it is inserted and manufactured. In the figure, 1 is a metal pipe, 2 is a coiled heating wire arranged in the center of the metal pipe 1 and terminal rods 3 are connected to both ends, and 4 is a first insulating layer formed around the heating wire 2. , 5 is a second insulating layer formed around the first insulating layer, and 6 is a sealing member that seals both ends of the metal pipe 2.

In a sheathed heater having such a structure, the first insulating layer 4 formed around the heating wire is made of silicon nitride, boron nitride, aluminum nitride, silicon carbide, etc., which becomes a good conductor of electricity due to the heat generated when the wire breaks. Since it is made of a material that does not cause the wire to become energized, it will not continue to be energized even after the wire is disconnected.

As described above, according to the present invention, a molded body in which a heating wire is wrapped with titanide and carbide constituting the first insulating layer is created and inserted into a tubular body made of metal, and then the second insulating layer is formed. The molded body is filled with an oxide with excellent insulation and thermal conductivity, and the diameter of the tubular body is further reduced, and if the heating wire breaks due to this manufacturing method. Since the strongly covalently bonded substances (chitride, carbide) arranged around this heating wire do not become good conductors of electricity even when heated by arc discharge, a second tubular body is formed around the outer periphery of the heating wire. The oxide can be prevented from melting, and as a result,
Melting of the first tubular body on the outermost periphery can also be prevented, and since the second tubular body has good thermal conductivity and high electrical insulation, it is possible to efficiently transfer the heat of the heating wire to the first tubular body, and 1) It is possible to maintain the insulation between the tubular body and the heating wire, and at the same time, it does not lose the good workability that sheathed heaters have.
It has various excellent effects.

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views of sheathed heaters manufactured according to examples of the present invention, in which Figure 1 is manufactured by forming the first insulating layer in a spiral shape along a coiled heating wire. FIG. 2 shows a case in which the first insulating layer is formed to cover the entire heating wire. 1...metal pipe, 2...heating wire, 4...first
Insulator layer, 5... second insulator layer.

Claims (1)

[Claims] 1. A first insulating layer made of at least one of titanide or carbide is provided around a heating wire disposed in a tubular body made of metal, and a layer having insulation and thermal conductivity is provided around this first insulating layer. In a method for manufacturing a sheathed heater provided with a second insulating layer made of a superior oxide, a molded body is prepared in which the heating wire is wrapped with the titanide and carbide constituting the first insulating layer, and the heating wire is made of the metal. and then filling the oxide constituting the second insulating layer around the molded body,
A method for manufacturing a sheathed heater, further comprising reducing the diameter of the tubular body.