JPS6333272B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sheathed heater constructed by insulating a heat generating wire and a tube with magnesia powder loaded between the tube and the heat generating wire, and to an improvement in a manufacturing method thereof.

A conventional sheathed heater has a heating wire 2 located in the center of a metal pipe 1, as shown in the partial cross-sectional view in the figure.
It has a structure in which the metal pipe 1 and the heating wire 2 are insulated with magnesia powder 3 loaded between them, and the energizing terminals 4 at both ends and the metal pipe 1 are sealed with an airtight sealing material 5. Since the heating wire 2 is not directly exposed to the outside, it is widely used as a heater with high leakage resistance.

However, although magnesia, which is the insulating material used in this heater, has excellent thermal conductivity and electrical insulation properties, it is highly hygroscopic and the electrical insulation properties rapidly deteriorate due to moisture absorption. It has its drawbacks.

Because magnesia has such drawbacks,
Hermetic sealing of the heater ends has become an essential element. However, even if the ends are hermetically sealed using low-melting glass or resin, which has been conventionally done, the former may cause cracks in the glass, and the latter may be difficult to achieve in the long term due to the moisture permeability of the material itself and the interface between the inner wall of the pipe and the resin. This resulted in electrical insulation deterioration, making it difficult to guarantee long-term characteristics.

In order to improve the drawbacks of the moisture-proofing method for magnesia using the hermetic sealing method, magnesia is impregnated with silicone oil, and a coating of magnesium silicate is formed on the surface of the magnesia particles through heat treatment. Prior art techniques to render the powder itself moisture inert have been invented as an effective method for moisture proofing magnesia. Although this method is a unique and highly practical moisture-proofing method, silicone oil alone has poor reactivity with magnesia.
It was difficult to form a film of magnesium silicate sufficient for moisture proofing, and complete moisture proofing could not be guaranteed.

This invention was carried out in order to improve the incompleteness of the above-mentioned prior invention, and by adding an organic titanium compound at the same time as silicone oil, the solid phase reaction of MgO-SiO ₂ was carried out using the three-dimensional reaction of MgO-SiO ₂ -TiO ₂ . The present invention provides a sheathed heater in which magnesia powder is more completely moisture-proofed by forming a film through a solid phase reaction of components, and a method for manufacturing the same.

Examples of the present invention will be described below.

Add 2 c.c. of isobutyl titanate and 4 c.c. of ethyl silicate-based silicone oil to 94 c.c. of butanol to prepare a completely dissolved mixture.
After adding 8g to g and mixing thoroughly,
Dry off the butanol at 150°C to 200°C. Then, using the usual magnesia powder filling method, the space between the metal pipe and the heating wire is filled, the pipe is squeezed to increase the density of the magnesia powder, and then heat treated at 600°C to 800°C to form the pipe. MgO−SiO ₂ −TiO ₂ is removed at the same time as decomposition of isobutyl titanate and silicone oil.
A solid-phase reaction is carried out on the surface of magnesia particles to complete moisture-proofing treatment. The ends of the metal pipes need only be sealed to the extent that the magnesia powder in the pipes does not fall out, and there is no need for conventional hermetic sealing.

In addition, 5 c.c. of isopropyl titanate and 10 c.c. of methyl silicate-based silicone oil were added to 85 c.c. of isopropanol to prepare a completely dissolved mixed solution, and this mixed solution was mixed with fused magnesia powder in the same manner as in the above example. After adding 5g to 100g and thoroughly mixing, the alcohol component is removed by drying at 150°C to 200°C. After that, it is filled between the metal pipe and the heating wire, and after the pipe drawing process is performed to further increase the density of the magnesia powder, it is heated to 600℃~800℃.
After heat treatment at ℃, MgO− is added to the surface of magnesia particles.
The moisture-proofing treatment is completed by forming a solid phase reaction layer of SiO ₂ -TiO ₂ . In this case as well, the ends of the pipe need only be sealed to the extent that the magnesia powder is prevented from falling off, as in the previous embodiment.

In addition to the examples described above, n-propyl titanate, tetrabutyl titanate, tetraacetyl titanate, tetraisopropyl titanate, etc. may be used as organic titanium compounds, and silicone oil is relatively fluid with a viscosity of 100 poise or less. Similar effects can be achieved even in combination with alkyl-based silicone oil, which has a high degree of properties.

In this invention, when the concentration of the organic titanium compound and the silicone oil are less than 0.5% by volume, there is no effect, and when the former is more than 5% by volume, sintering between magnesia particles occurs due to heat treatment, making it unsuitable as a filler for a sheathed heater. . The latter was not effective at less than 1% by volume, and was unsuitable because it could not be filled into metal pipes at more than 10% by volume. Furthermore, when the volume ratio of the organic titanium compound and the silicone oil was increased, a desirable combined effect was exhibited.

As described above, according to the present invention, MgO−
By providing a sheathed heater with a three-component solid-phase reaction layer of SiO ₂ -TiO ₂ and its manufacturing method, a three-component solid-phase reaction layer is formed on the surface of magnesia powder, resulting in moisture resistance. An excellent sheathed heater can be obtained.

[Brief explanation of the drawing]

The figure is a partial sectional view showing a schematic configuration of a sheathed heater. In the figure, 1 is a metal pipe, 2 is a heating wire, 3 is magnesia powder, 4 is a current-carrying terminal, and 5 is an airtight sealing material.

Claims (1)

[Claims] 1. A solid-phase reaction layer of three components of magnesia, silicon oxide, and titanium oxide is formed on the surface of a magnesia powder loaded between a tube and a heating wire inside the tube. Sea heater. 2 Magnesia powder in which an organic silicon compound and an organic titanium compound are mixed is loaded between a tube and a heating wire inside the tube, and then heated to form a mixture of magnesia, silicon oxide, and titanium oxide on the surface of the magnesia powder.
A method for manufacturing a sheathed heater, characterized in that a solid phase reaction layer of components is formed. 3. The method for manufacturing a sheathed heater according to claim 2, wherein the heating is performed at a temperature of 600°C to 800°C. 4 0.5% to 5% by volume of an organic titanium compound,
Claim 1, characterized in that 5 to 10 g of an alcohol solution containing 1 to 10 volume % of an organic silicon compound is added to 100 g of magnesia powder and mixed, and then the alcohol is removed by drying. 2. A method for manufacturing a sheathed heater according to item 2. 5. The method for manufacturing a sheathed heater according to any one of claims 2 to 4, wherein the added capacity of the organic titanium compound is larger than the added capacity of the organic silicon compound. 6. The method for manufacturing a sheathed heater according to any one of claims 2 to 5, wherein the organic silicon compound is an alkyl-based silicone oil having a viscosity of 100 poise or less. 7. Claims characterized in that the organic titanium compound consists of at least one of isobutyl titanate, isopropyl titanate, n-propyl titanate, tetrabutyl titanate, tetraacetyl titanate, and tetraisopropyl titanate. The method for manufacturing a sheathed heater according to any one of Items 2 to 6.