JPS6112355B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a sheathed heater, and particularly improves the electrical insulation properties of the sheathed heater in high humidity.

[Technical background of the invention and its problems]

Conventional sheathed heaters insert a coiled heating wire with a terminal attached by welding or crimping inside a metal pipe, and a heat-resistant electrical insulator such as magnesia powder is used between the metal pipe and the coiled heating wire. The sheathed heater is filled with a material, and both ends of the sheathed heater are sealed with a sealant such as silicone rubber so that the electrical insulation resistance of the sheathed heater does not decrease even in humid conditions.

Magnesia powder, which is generally used as an electrical insulating material, has an activated surface and therefore has a property of being highly hygroscopic, and when left in the atmosphere, it absorbs moisture from the atmosphere. Therefore, great care must be taken when handling magnesia powder during the sheathed heater manufacturing process, and even if the terminals of the sheathed heater are sealed with silicone rubber, they should not be left in a humid atmosphere for a long time. Due to the moisture permeability of silicone rubber, magnesia absorbed moisture from the atmosphere, lowering the electrical insulation resistance of the sheathed heater.

In addition, as an alternative to the insulation treatment method for sheathed heaters described above, a metal pipe is filled with a mixture of a filling material such as magnesia and a methyl silicone resin, etc. and heated, and the entire heater is insulated. has begun to be adopted.

In addition, after filling a metal pipe with a filler such as magnesia in advance, methyl-based silicone oil or the like is introduced from the sealing part to impregnate the filling.
A common method was to seal the opening.
However, when using methyl silicone resin mixed with the former magnesia powder,
Silicone resin does not harden when heated at a low temperature of 300°C.
Requires high temperatures of ℃ or higher, which impairs workability on heated surfaces. The latter method has the disadvantage that the filler is not uniformly impregnated with silicone oil, resulting in variations in insulation properties, which adversely affects the properties of the sheathed heater.

[Object of the Invention] The present invention improves the above-mentioned drawbacks and maintains a high electrical insulation resistance of the sheathed heater.

[Summary of the invention]

After mixing magnesia powder with reactive silicone oil in which a portion of the methyl groups have been replaced with at least one reactive group among hydrogen, hydroxyl, and vinyl groups, this is cured at room temperature to 150°C corresponding to the above reactive group. The pulverized powder is filled into a metal pipe with a heater wire placed in the center, and then further fired.

[Embodiments of the invention]

An example will be described with reference to the drawings.

The particle size distribution of magnesia powder 1 is 40 to 80 mesh.
40-80% wt, 80-150 mesh 15-30% wt,
150-200 mesh 5-15%wt200-300 mesh 10%wt or less is mixed with 0.2-5%wt reactive silicone oil 2 and cured to form a coating film on the surface of magnesia particles with silicone oil. do.

This reactive silicone oil has a part of methyl group substituted with a reactive group such as hydrogen group, hydroxyl group, vinyl group, etc. Such reactive silicone oil includes methyl/hydrogen group-containing silicone oil, methyl・There are silicone oils containing hydroxyl groups, silicone oils containing methyl vinyl groups, etc.

Furthermore, the oil may contain two or more types of the above-mentioned reactive groups in the same molecule, or a mixture of two or more types of oils may be used. When using such reactive silicone oils, those using conventional methyl silicone resins must be heated to 300°C.
If you do not heat it to a higher temperature, it will harden and not form a coating film on the surface of magnesia powder. However, if you use a material with the above-mentioned reactive group, it will harden at a low temperature of room temperature to 150℃ and will not form a coating on the surface of magnesia powder. A film can be formed. For example, methyl/hydrogen group-containing silicone oil can be cured at 100 to 150°C with a tin/lead catalyst to form a coating, and methyl/hydrogen group-containing silicone oil
Hydroxyl group-containing oil can be cured to form a coating film at room temperature (about 20℃) to 100℃ using a small amount of ethyl silicate and a tin-based catalyst.
Vinyl group-containing oil can be cured at 100 to 150°C by adding an organic peroxide catalyst to form a coating film.

The magnesia powder and reactive silicone oil thus produced are combined into a lump, which is then crushed through a roll or the like into a powder so that it can be tied to the metal pipe 3. This powder is filled between the metal pipe 3 of the sheathed heater and the coiled heater wire 5 attached to the terminal 4 by welding or caulking. After increasing the filling rate of the powder filled in No. 3, it is fired at 200 to 400°C for about 1 to 5 hours. The baked reactive silicone oil is remelted by this baking and penetrates into the surface and between the particles of the magnesia powder, forming magnesia powder so that methyl groups (CH ₃ ) surround the magnesia powder in the sheathed heater. becomes inactive, and the electrical insulation properties of the sheathed heater can always be kept high even in humid conditions.

〔Effect of the invention〕

As described above, according to the present invention, reactive silicone oil is uniformly and firmly coated on the surface of magnesia powder, and is powdered and then filled into a metal pipe and fired. The reactive silicone oil uniformly forms a coating around the magnesia powder, making the magnesia powder inactive, so the electrical insulation properties of the sheathed heater can always be maintained at high levels even in humid conditions. Furthermore, the curing process after mixing magnesia powder and reactive silicone oil can be carried out at a relatively low temperature of room temperature to 150°C, rather than the extremely high temperature of 300°C or more that is required in the past. It is economically advantageous and has the advantage of improving workability on heating surfaces.

[Brief explanation of the drawing]

The figure is a sectional view of a main part of the present invention. 1... Magnesia powder, 2... Reactive silicone oil, 3... Metal pipe, 4... Terminal, 5... Coiled heater wire.

Claims (1)

[Claims] 1. Reactive silicone oil in which a portion of the methyl groups were substituted with at least one reactive group among hydrogen, hydroxyl, and vinyl groups was mixed with magnesia powder, and this was cured at room temperature to 150°C corresponding to the above reactive group. A method for manufacturing a sheathed heater, in which powder obtained by post-pulverization is filled into a metal pipe with a heater wire arranged in the center, and then further fired.