JPH08321375A - Manufacture of sheathed heater - Google Patents

Abstract

PURPOSE: To reduce leakage current flowing across a metallic pipe and a heating wire during an operation at a high temperature equal to or higher than 600 deg.C by preliminarily oxidizing the internal surface of the pipe at least to such an extent as the appearance of weak light brown color and, then, inserting or otherwise an internal heating body. CONSTITUTION: The whole internal surface of a sheathing bottomed metallic pipe 1 formed out of stainless steel, iron or the like is sufficiently oxidized preliminarily at least to such an extent as the appearance of weak light brown color. Thus, an oxidized skin layer having a high insulating function at high temperature is formed on the inner surface of the pipe 1. Thereafter, a core insulator 5 with an inner heating wire 8 wound around on the outer surface thereof is housed in the center section of the pipe 1, and a lead pin 7 to be connected to the wire 8 is inserted. Then, space between the pipe 1 and the insulator 5 is filled with a heat resisting insulator 10 such as magnesia. Furthermore, the outer surface of the wire 8 and the pin 7 is preferably oxidized at least to such an extent as the appearance of light brown color preliminarily. Also, a high temperature sintering process in the air or the atmosphere containing oxygen, or the use of chemicals is preferable as the oxidizing method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a sheathed heater, and more particularly to a method for manufacturing a sheathed heater suitable for use at high temperatures.

[0002]

2. Description of the Related Art In a conventional sheath heater manufacturing method, a bottom plate portion 32 is fixed to the bottom surface of a metal pipe 31 made of stainless steel, as shown in FIGS.
The core insulator 33 is housed in the central portion of the metal pipe 31,
A pair of lead pins 34 are inserted into the small holes provided inside the core insulator 33, and an internal coil 35 for heat generation is wound around the core insulator 33, and then the core insulator 33 and the metal pipe 31 are connected to each other. The space between them was filled with the heat-resistant insulator 37, and the sheath heater 30 was formed by reducing the diameter.

[0003]

The sheathed heater is 600
When used at a high temperature of ℃ or higher, the insulation performance of the insulator inside the sheathed heater decreases as the temperature rises, so the leakage current increases as the temperature increases. As a result, a leakage current flows between the metal pipe 31 and the internal coil 35, the breaker (not shown) interposed between the sheathed heater and the power supply is cut off, and the heating work is interrupted. However, if a plurality of sheathed heaters are used at the same time, the worker who is performing the heating work finds a defective sheathed heater with a large leakage current, removes the heater, and replaces it with another heater. After replacing the breaker, the breaker needs to be reloaded, which is a troublesome task.

For this reason, a heating wire and a filler are housed in a pipe whose inner surface is coated with a metal, and the metal is oxidized by heat treatment to consume oxygen in the sheathed heater to maintain a constant oxygen partial pressure. The one designed to prevent the volatilization of heating wire components is disclosed in JP-A-58-157079.
It is shown in the publication. However, the oxygen in the sheathed heater is originally small, and the above method in which the sheathed heater is formed and then heated externally to oxidize the metal is insufficient in the above oxidation, and is oxidized to at least a light brown color. I don't get it. As a result of various experiments and researches, the present inventor has shown that the degree of oxidation is quite small by the method such as the cited example,
It was found that at a high temperature of 600 ° C. or higher, there is no leakage current reduction effect. And, the degree of this oxidation is not enough in the oxidation obtained by simply exposing it to the air, and there is no effect unless it is oxidized to at least a light brown in the color-light brown-brown-black. The inventors of the present invention have found that it is impossible to oxidize to this extent after being incorporated as a sheathed heater, and it is necessary to oxidize in advance before assembling.

[0005]

A method of manufacturing a sheathed heater according to the present invention comprises a step of oxidizing an inner peripheral surface of a metal pipe in advance to at least a light brown color, and an internal heating wire inside the metal pipe. A step of inserting lead pins connected to both ends of the internal heating wire, and a step of filling a heat-resistant insulating material such as magnesia between the metal pipe and the internal heating wire.

Further, the method for manufacturing a sheathed heater of the present invention comprises a step of pre-oxidizing the internal heating wire and the outer peripheral surfaces of the lead pins connected to both ends of the internal heating wire to a degree of at least a light brown color in advance. Is inserted into the metal pipe, and a step of filling a heat resistant insulating material such as magnesia between the metal pipe and the internal heating wire.

Further, in the method for manufacturing a sheathed heater of the present invention, the entire inner peripheral surface of the metal pipe is previously oxidized,
In addition, a step of preliminarily oxidizing the outer peripheral surfaces of the heating wire inserted in the metal pipe and the lead pins connected to both ends of the internal heating wire to at least a light brown color in advance, and the heat generation in the metal pipe. It includes a step of inserting wires and lead pins, and a step of filling a heat resistant insulating material such as magnesia between the metal pipe and the internal heating wire.

The above-mentioned oxidation is performed in a high temperature and high oxygen atmosphere before using the sheathed heater or by using a chemical.

[0009]

1 and 2 show a sheathed heater 12 to which the method of the present invention is applied, wherein 1 is a metal pipe for an outer jacket made of stainless steel, iron, other special heat-resistant steel material, etc. Similarly, a bottom plate portion 2 made of stainless steel, iron, or other special heat-resistant steel material is fixed and formed in a bottomed shape. Further, in the central portion of the metal pipe 1, a core insulator 5 formed by solidifying magnesia or the like is housed, and a pair of lead pins 7 is formed in a small hole 6 formed in the inner longitudinal direction of the core insulator 5. Each of the core heating elements 5 is inserted into the core heating element 5, and an internal heating wire 8 made of a nichrome wire is wound around the core insulator 5, and the internal heating wires 8 and the end portions of the lead pins 7 are electrically connected appropriately to form a heating element 9. There is.
Furthermore, the core insulator 5, the metal pipe 1 and the bottom plate 2
A sheathed heater 12 is formed by filling a heat-resistant insulating material 10 such as magnesia in a space between the sheathed heater 12 and the space.

FIGS. 3 and 4 show another sheath heater 12a to which the method of the present invention is applied. Reference numeral 21 denotes a metal pipe for an outer cover made of stainless steel, iron or other special heat-resistant steel material, and a nichrome wire inside thereof. A coil-shaped internal heating wire 28 made of, and lead pins 27 connected to both ends of the internal heating wire 28 are drawn out from both ends of the metal pipe 21 and placed in a space between the metal pipe 21 and the internal heating wire 28. The sheathed heater 12a is formed by filling a heat resistant insulator 29 such as magnesia.

5 and 6 show still another sheath heater 12b to which the method of the present invention is applied, and the internal heating wire 38 is composed of a straight wire.

Although a metal pipe having a circular cross section is used in each of the sheath heaters, a rectangular cross section, a triangular cross section,
It may have an elliptical cross section or the like.

In the present invention, the metal pipe 1 or 21
In advance, fully oxidize the entire inner peripheral surface of the so that it becomes at least a light brown color. Inside the metal pipe 1 or 21, the internal heating wire 8, 28 or 38 such as a nichrome wire, and both ends of this internal heating wire are The connected lead pin 7 or 27 is inserted, and a heat resistant insulating material such as magnesia is filled between the metal pipe and the internal heating wire.

In another embodiment of the present invention, an internal heating wire 8, 28 or 38 such as a nichrome wire inserted in the metal pipe 1 or 21 and lead pins 7 or 27 connected to both ends of the internal heating wire. The outer peripheral surface of the above is preliminarily sufficiently oxidized to be at least a light brown color, then these are inserted into the metal pipe, and a heat-resistant insulating material 10 such as magnesia filled between the metal pipe and the internal heating wire is used.
Or fill with 29.

In still another embodiment of the present invention, in the above embodiment, the inner peripheral surface of the metal pipe is also previously oxidized.

There are several methods for forming an oxide film layer on a metal pipe or the like, one of which is 30 using an electric furnace or the like in air or in an atmosphere containing oxygen.
It is performed by baking at a high temperature of 0 ° C. to 1300 ° C. for 5 minutes to 10 hours or at a high temperature of 1000 ° C. to 1300 ° C. for 5 minutes to 1 hour.

Another method for forming an oxide film layer on a metal pipe or the like is to oxidize the metal pipe or the like using a known chemical agent such as an oxidizing agent, thereby forming an oxide film layer. .

The oxide film layer referred to here is different from an extremely thin oxide film layer in which stainless steel, nichrome, etc. are normally formed in air, and is the result of being heated at a high temperature in an oxygen atmosphere or treated with a chemical agent. As a result, the oxide film layer becomes thicker,
It means an oxide film layer which is colored and is colored at least light brown among light brown to brown to black.

The oxide film has good insulation performance at high temperatures,
Since the insulation resistance is increased by interposing the metal pipes 1, 21 and the internal heating wires 8, 28, 38, the leakage current generated from the internal heating wires 8, 28, 38 is reduced.

Metal pipe 1 having an oxide film layer on its inner surface
The sheathed heater 12, 1 of the present invention assembled by using 21 or the like
2a and a metal pipe 3 which does not have a conventional oxide film layer 3
When the sheathed heater 30 assembled using 1 is heated to a high temperature of 600 ° C. or higher and used, the former leakage current is
In the latter case, it could be reduced to about 1/3 to 1/10, and the heating work could be performed efficiently.

The advantage of substantially preventing the flow of leakage current by forming the oxide film layer on the inner surfaces of the metal pipes 1 and 21 is not limited to stainless steel pipes, but is made of iron or other special heat-resistant steel. The same applies to the pipe. Also, the leakage current could be similarly reduced in the heater in which the metal pipe was not oxidized and the oxide film layer was attached only to the internal heating wires and the pins.

[0022]

According to the present invention, an oxide film layer having a good insulating property at high temperature is provided on the inner surface of a metal pipe.
When using a sheathed heater at a high temperature of ℃ or higher, by reducing the leakage current that tends to occur between the metal pipe and the internal heating wire, there is almost no possibility that the breaker will break unnecessarily and the electric circuit will be cut off. Instead, it has the advantage that the heating operation can be performed continuously and efficiently.
Further, in the method of the present invention, since the metal pipe or the like is previously oxidized before being incorporated into the sheathed heater, the step of coating the inner surface of the pipe with metal as in the above-mentioned reference is completely unnecessary, which is a great cost advantage. is there.

[Brief description of drawings]

FIG. 1 is a vertical sectional front view of a sheathed heater to which a method of the present invention is applied.

FIG. 2 is a sectional view taken along line 2-2 of FIG.

FIG. 3 is a vertical sectional front view of a sheathed heater according to another embodiment to which the method of the present invention is applied.

FIG. 4 is a sectional view taken along line 4-4 of FIG.

FIG. 5 is a vertical sectional front view of a sheathed heater in still another embodiment to which the method of the present invention is applied.

6 is a sectional view taken along line 6-6 of FIG.

FIG. 7 is a vertical cross-sectional view of a sheathed heater according to a conventional method.

8 is a sectional view taken along line 8-8 of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal pipe 2 Bottom plate part 3 Inner surface 3a Inner surface 5 Core insulator 6 Small hole 7 Lead pin 8 Internal heating wire 9 Heating element 10 Heat-resistant insulator 12 Sheath heater 12a Sheath heater 12b Sheath heater 21 Metal pipe 23 Inner surface 27 Lead pin 28 Internal heating wire 29 Heat resistance Insulator 30 Sheath heater 31 Metal pipe 32 Bottom plate 33 Core insulator 34 Lead pin 35 Internal coil 38 Internal heating wire

Claims (5)

[Claims] 1. A step of pre-oxidizing the inner peripheral surface of a metal pipe sufficiently to at least make it light brown, an internal heating wire and lead pins connected to both ends of the internal heating wire in the metal pipe. A method of manufacturing a sheathed heater, comprising: a step of inserting the sheathed heater; and a step of filling a heat resistant insulating material such as magnesia between the metal pipe and the internal heating wire. 2. A step of sufficiently oxidizing beforehand the outer peripheral surfaces of the internal heating wire and the lead pins connected to both ends of the internal heating wire so that at least a light brown color is obtained, and a step of inserting these into a metal pipe. A method of manufacturing a sheathed heater, comprising a step of filling a heat-resistant insulating material such as magnesia between the metal pipe and the internal heating wire. 3. The entire inner peripheral surface of the metal pipe is previously oxidized, and at least the outer peripheral surfaces of the heating wire inserted into the metal pipe and the lead pins connected to both ends of the internal heating wire are light brown in advance. A step of sufficiently oxidizing so as to give a color, a step of inserting the heating wire and the lead pin into the metal pipe, and a step of filling a heat-resistant insulating material such as magnesia between the metal pipe and the internal heating wire. And a sheathed heater manufacturing method. 4. The method for manufacturing a sheathed heater according to claim 1, wherein the oxidation is performed in a high temperature and high oxygen atmosphere before assembling the sheathed heater. 5. The method for manufacturing a sheathed heater according to claim 1, wherein the oxidation is performed by using a chemical before assembling the sheathed heater.