JPS5917514B2 - sheath heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the insulation resistance characteristics of a sheathed heater due to moisture absorption.

As shown in Fig. 1, a conventional sheathed heater is one in which an electrical insulating material 4 is filled between a metal pipe 1 and a coiled heater 3 to which a terminal bar 2 is welded, and then the diameter of the metal pipe 1 is reduced. be.

Magnesia powder is the most widely used electrically insulating material9, but since magnesia powder is hygroscopic,
It has the disadvantage that it easily absorbs moisture in the indoor atmosphere and deteriorates insulation resistance. Therefore, this magnesia powder is mixed with, for example, silicone resin and then heated to form a silicone resin film on the surface of the magnesia powder.3 By doing so, the surface of the filling material becomes water repellent and absorbs moisture from the outside. There are ways to prevent the deterioration of insulation performance. but,
This method also uses silicone resin as the water repellent agent, so after long-term use or use at abnormally high temperatures, the organic groups contained in the silicone resin decompose or gradually carbonize, forming conductive paths. However, the disadvantage was that the insulation properties tended to deteriorate.

The present invention overcomes these drawbacks, namely, to prevent the insulating properties of the sheathed heater from deteriorating even after long-term use or use at abnormal temperatures, magnesia powder used as an electrical insulating material absorbs moisture. To provide a sheathed heater that has improved properties and does not deteriorate even after long-term use.

Below, based on the drawings showing one embodiment of the present invention, 5 will be explained. In FIG. A terminal bar □ protruding from the pipe 5 is provided. 8 is magnesia powder filled in the metal pipe 5, and a fine powder hydrophobic silica layer 9 is formed on the surface of the filler 8 as shown in FIG.

An example of a manufacturing method for this sheathed heater is shown below.

A heater 6 with terminal rods T attached at both ends is placed in the center of a metal pipe 1 with an outer diameter of 10.5 mm, the lower end of the metal pipe 1 is temporarily sealed, and magnesia powder and 1 wt % hydrophobic silica are thoroughly mixed from the upper end. After that, the outer diameter of the metal pipe 1 is reduced to about 8.0 mm, and the pipe is completed. Such finely powdered hydrophobic silica 9 has a very fine particle size and is a heat-resistant substance that can easily adhere to the periphery of the magnesia powder.

In other words, it is not a resin in which one or more organic groups are bonded to all silicon atoms as in silicone resins such as dimethylsiloxane, but, for example, SiO2 is used as a base material and only some of its oxygen atoms are methyl. It is substituted with a group, etc., and is a fine powder with a particle size of 0.1μ or less. Although the number of organic groups bonded to silicon atoms is small per unit area, since it is a fine powder, it has a large surface area and is a substance that exhibits great hydrophobicity as a fine powder hydrophobic silica layer. Furthermore, since it is a fine powder with a large surface area and high adsorption capacity, if magnesia is crushed during the diameter reduction process of the metal pipe 1 or during the heating and cooling cycle, the fine hydrophobic silica powder will migrate to new magnesia crystal surfaces in the crushed part. It adheres to the surface and maintains water repellency.

As described above, the sheathed heater of the present invention has water repellency because a hydrophobic fine powder silica layer is formed on the surface of the particles of the filling material that insulates and holds the heater and terminals inside the metal pipe, and has water repellency and prevents external moisture. It no longer absorbs moisture easily.
Furthermore, even if magnesia is crushed during the manufacturing process or during the cooling and heating cycle during use, a hydrophobic silica layer is formed on the crushed surface to maintain water repellency and prevent insulation deterioration due to moisture absorption. Furthermore, even if the filler is heated to an abnormally high temperature, hydrophobic fine powder silica has a slower carbonization rate than silicone resin, and since it is an aggregate of small particles of 0.1μ or less, even if it is carbonized, the carbon atoms will not interact with each other. It has features such as poor adhesion and retained electrical insulation properties, and its industrial value is great.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional sheathed heater, FIG. 2 is a cross-sectional view of a sheathed heater according to an embodiment of the present invention, and FIG. 3 is an enlarged view of the essential parts thereof. 5...Metal pipe, 6...Heater
7...Terminal bar, 8...Filling material, 9...
...Silica layer.

Claims (1)

[Claims] 1. In a sheathed heater formed by filling an electrical insulating material such as magnesia powder between a coiled heater equipped with a terminal bar and a metal pipe, and reducing the diameter of the metal pipe,
A sheathed heater characterized in that the magnesia powder and hydrophobic fine powder silica are mixed and filled into the metal pipe.