JPH048904B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a type of sheathed heater impregnated with silicone oil, among sheathed heaters widely used as a heating source.

BACKGROUND ART Conventionally, sheathed heaters have been widely used as a heating source for general cooking appliances such as toaster ovens, microwave ovens, rice cookers, and hot plates.

In general, a sheathed heater consists of inserting a coiled heating wire with terminal rods at both ends into the center of a metal pipe, filling the metal pipe with electrically insulating powder made of fused magnesia powder, and then inserting the metal pipe into the metal pipe. Manufactured by rolling to reduce diameter.

In order to use fused magnesia powder, which is highly hygroscopic, as the electrical insulating powder, the following various methods have been considered.

(1) Seal the mouth of the metal pipe.

(2) Impregnate with silicone oil.

In particular, for method (1), various methods have been considered, such as complete sealing with low melting point glass, simple sealing with silicone resin, epoxy resin, etc.

However, in order to ensure workability and reliability after sealing, two methods in particular have been devised and implemented in method (1).

(1)-1 Insert the packing impregnated with oil and insert the sealing material on the outside to seal it. (Japanese Unexamined Patent Publication No. 50-121346) (1)-2 The mouth of the metal pipe is sealed with the plug, and a low polymerization degree polymer such as silicone grease or silicone oil is applied to the gap between the plug, the metal pipe, and the terminal. Seal with a high viscosity liquid such as (Japanese Unexamined Patent Publication No. 52-6839) Also, in method (2), if left as is, silicone oil may remain at the mouth of the metal pipe.
It is difficult to put it into practical use because it blows out when electricity is applied, so the silicone oil at the mouth of the metal pipe is gelled in advance, and then sealed with silicone resin or the like.

Problems to be Solved by the Invention However, in the method described above, especially (1)
-1 and (1)-2, the electrically insulating powder made of fused magnesia powder is not treated to be water repellent, so in the unlikely event that the sealing structure is defective or the electrically insulating powder is When the packing, plug body, etc. change over time and moisture intrudes, the electrical characteristics deteriorate significantly.

Further, the packing used in 1-1 is a porous material such as asbestos or foamed rubber, which does not have very good heat resistance and may deteriorate during actual use.

On the other hand, in method (2), the gelation operation is complicated, which is a major factor in increasing costs.

For these reasons, a sheathed heater having a sealing structure that is relatively simple and has excellent reliability has been desired.

In view of these problems, it is an object of the present invention to provide a sheathed heater that has high reliability in electrical characteristics and can be manufactured by a relatively simple method.

Means for Solving the Problems In order to solve the above problems, the present invention uses fused magnesia powder impregnated with silicone oil as an electrical insulating powder, and
A silicone oil-impregnated layer made of inorganic fiber paper containing silica or alumina fibers as a main component, and an insulating layer located outside this layer and made of a silicone rubber molded product or a ceramic molded product are formed.

Function Conventionally, the opening of the metal pipe of a sheathed heater has been equipped with a metal pipe for various purposes such as (1) preventing dust from entering, (2) ensuring insulation distance, and (3) ensuring electrical properties by preventing moisture from entering. Sealing is performed.

However, as mentioned in the prior art section, when sealing the mouth of a metal pipe, other methods, except for complete sealing with low-melting glass,
Because the electrical insulating powder is not treated to be water repellent,
If the sealing portion deteriorates over time and moisture intrudes, the electrical characteristics will significantly deteriorate. Furthermore, in the method of impregnating the metal pipe with silicone oil, the silicone oil is not completely impregnated into the electrical insulating powder, and only a small amount remains at the mouth of the metal pipe, making it difficult to seal it easily.

In contrast, according to the present invention, electrical insulating powder is impregnated with silicone oil and treated to make it water repellent, and the silicone oil slightly remaining at the mouth of the metal pipe is replaced by silica or alumina. Since the silicone oil is absorbed by the silicone oil-impregnated layer made of inorganic fiber paper whose main component is fiber, the silicone oil will not blow out when electricity is applied.

Further, on the outside of this silicone oil-impregnated layer, an insulating layer made of a silicone rubber molded body or a ceramic molded body is simply provided in order to prevent dust from entering and ensure an insulation distance, which is very simple.

For these reasons, the method of impregnating silicone oil has traditionally had problems such as (1) blowing out of the silicone oil when using electricity, and (2) complicating the process of sealing the mouth of the metal pipe. In addition to being able to solve problems such as these, it is also possible to ensure reliability that could not be obtained by simply sealing the mouth of the metal pipe.

On the other hand, inorganic fiber paper mainly composed of silica or alumina fibers used as a silicone oil-impregnated layer has excellent heat resistance, absorbs silicone oil remaining at the mouth of metal pipes, and is treated to be water repellent. Therefore, the electrical characteristics are not impaired in this part.

Embodiment Hereinafter, an embodiment of the present invention will be described based on FIGS. 1 to 3.

First, a coiled heating wire 2 with terminal rods 1 on both terminals is inserted into the center of a metal pipe 3, and this metal pipe 3 is filled with electrical insulating powder 4 made of fused magnesia powder. 3 was rolled to reduce its diameter.

Thereafter, after annealing and bending into a predetermined shape, silicone oil was injected from the mouth of the metal pipe 3 to impregnate it into the electrical insulating powder 4. Next, an inorganic fiber paper made of silica-alumina fibers shown in FIG. 1 is inserted into the mouth of the metal pipe 3 to absorb the silicone oil remaining at the mouth of the metal pipe 3, thereby forming a silicone oil-impregnated layer. 5 was formed.

Furthermore, an insulating layer 6 is formed by inserting a ceramic molded body mainly composed of alumina having the shape shown in FIG. 2 on the outside of this silicone oil impregnated layer 5.
The sheathed heater of the present invention shown in FIG. 3 was completed.

In order to evaluate the sheathed heater of the present invention completed in this way, it was left in a humid atmosphere at 40°C and 95% relative humidity for one month, and electricity was applied to evaluate the occurrence of silicone oil blowout, etc. .

After being left in a humid atmosphere for one month, no particular decrease in insulation resistance or withstand voltage was observed. Furthermore, no silicone oil was blown out due to energization. Thus, it showed very excellent characteristics.

In the examples of the present invention, a ceramic molded body was used as the insulating layer, but the invention is not particularly limited to this, and other silicone molded bodies may also be used.

Effects of the Invention As is clear from the above description, according to the present invention, electrofused magnesia powder impregnated with silicone oil is used as the electrical insulating powder, and silica or alumina fiber is the main component at the mouth of the metal pipe. It has a silicone oil-impregnated layer made of inorganic fiber paper and an insulating layer made of silicone rubber molded product or ceramic molded product located outside this layer, so it has high reliability and relatively low electrical properties. It is possible to provide a sheathed heater that can be manufactured by a simple method.

[Brief explanation of drawings]

Fig. 1 is a perspective view of inorganic fiber paper used as a silicone oil impregnated layer in a sheathed heater according to an embodiment of the present invention; Fig. 2 is a perspective view of a ceramic molded body used as an insulating layer in the same embodiment; FIG. 3 is a plan view showing a section of a part of a sheathed heater showing an embodiment of the present invention. 3...metal pipe, 4...electrical insulating powder, 5...
...Silicone oil impregnated layer, 6...Insulating layer.

Claims (1)

[Claims] 1. Electrofused magnesia powder impregnated with silicone oil is used as electrical insulating powder, and a silicone oil-impregnated layer made of inorganic fiber paper mainly composed of silica or alumina fibers is placed at the mouth of the metal pipe, and a silicone oil-impregnated layer is placed on the outside of this layer. 1. A sheathed heater characterized in that an insulating layer made of a silicone rubber molded body or a ceramic molded body is formed.