JPS5823714B2 - Manufacturing method of sheathed heater - Google Patents

Description

Detailed Description of the Invention The present invention provides magnesium oxide (M
The present invention relates to processing of electrically insulating heat-resistant material powder such as gO) and a sheathed heater using the same.

Generally, a sheathed heater is equipped with a coiled heating wire 3 to which a terminal bar 2 is connected inside a metal pipe 1 constituting an outer casing, as shown in FIG. It is filling.

Conventionally, magnesium oxide (MgO) has been widely used as the electrically insulating heat-resistant material powder 4, but this magnesium oxide (MgO) is reactive with water, so a sheathed heater using it has moisture resistance. It had some disadvantages.

Therefore, a method of coating the surface of each particle of magnesium oxide (MgO) with silicon has been proposed, but the method lacks specificity.

The present invention has been made in view of the above-mentioned problems, and will be described below based on examples.

That is, in the present invention, the powder of fused magnesia (MgO) is 40 to 80 mesh, 20 to 50 mesh, 80 to 1 mesh.
Powder with particle size composition of 00 mesh is 20 to 40, 100 to 150 mesh is 20 to 40, 150 to 200 mesh is 5 to 15%, and 200 to 325 mesh is 5 to 20. The individual surfaces of the
O) particles and uncoated fused magnesia (MgO) particles having the above particle size structure are mixed and used.

[Example ■]

In the former case described above, the fused magnesia (MgO) is subjected to treatments such as coating, dipping, and mixing with a resin solution having the following composition.

Resin: Methyl silicone resin, silicone oil, methylphenyl silicone oil, silicone varnish, etc.

100-150 parts by weight Toluene: 600-1000 parts by weight P.A. (That's it.

07e/-/Lz) ” ” 0 to 300 parts by weight Parts by weight: Some others 0 At this time, the weight ratio of the resin should be 0.2 to 5 parts, and the resin should be applied uniformly to all particle surfaces. Do so so that it is coated.

After these treatments, drying is performed at 80-150°C for 1-30 minutes, and then as a pretreatment, drying is performed at 1208°C-250°C.
Heat for 10 minutes or more at ℃ range.

(11 hours at 180° C. in one example).

After that, the semi-hardened powder is powdered again and then filled into a pipe 1 made of metal etc. as a sheathed heater.
After that, the diameter is reduced by rolling, swaging, etc.

After that, as a post-treatment, the temperature at which the resin hardens (150
~600°C) heat treatment.

As an example, 4 hours at 150°C → 2 hours at 200°C →
250°G, 2 hours → 320°C, 2 hours → 450
1500C to 600° within 3 minutes
Heat treatment is carried out at least twice in a batch system as described above in the temperature range of C, or at a heating rate of 0.1 °C/min and 10 °C/min in a continuous furnace. Gradually heat and harden.

The key to this curing is drying at 80-150°C to scatter adsorbed water and low-boiling solvents, and during pre-treatment at 120°C-250°C, water (H2O) generated by dehydration condensation in the reaction.
The remaining water (H2O) produced by dehydration condensation and the R-O
Disperses the alcohol content, which is in the shape of an H.

At this time, the reason why the temperature is gradually raised or the heat treatment is performed at least twice is to prevent a large amount of reaction products from being generated at once and carbonizing inside the sheathed heater.

Furthermore, another purpose is to help the silicone resin to be uniformly dispersed on the individual surfaces of the fused magnesia (MgO).

Yet another purpose is the M formed inside the sheathed heater.
g.

It helps fill the voids between particles with resin.

By performing such heat treatment, the solvent content of the silicone resin-containing solution added at the beginning is completely dispersed, and the number of organic groups in the silicone resin is reduced to about 115 to 415 from the initial amount.

Here, unstable organic components are dispersed beforehand, which is extremely important in preventing unstable resin components from being generated when using a sheathed heater. It is valid.

[Example ■]

treated with a solution consisting of the components described in Example I.

Additionally, untreated fused magnesia (MgO) powder is added to the fused magnesia (MgO) powder.

Here, the concentrations in this case are: Resin: 200 to 500 parts by weight of methyl silicone resin, silicone oil, methylphenyl silicone oil, silicone varnish, etc. Toluene: 00 to 1000 parts by weight PA (isopropylene).

Panaud, L.): 100 to 300 parts by weight Catalyst: Some others // The concentration is higher than in Example I.

The ratio of the organic component coated on the surface of the fused magnesia (MgO) is such that the silicone resin is 5 to 10wt% based on the weight of the fused magnesia (MgO).

Thereafter, untreated fused magnesia is added to the fused magnesia (MgO) that has been heat-treated and powdered as described in Example ① at a weight ratio of 50 parts or more. .

After mixing, based on the total fused magnesia (MgO) weight,
The ratio of silicone resin is set to 0.1 to 5%.

Thereafter, heating is further performed at 120° C. to 250° C. for 10 minutes or more, and then, as in Example I, the process of filling → diameter reduction and heat resistance is performed under the same conditions.

In addition, Figure 2 is a diagram comparing the moisture resistance of the present invention according to the above-mentioned method, a pipe filled with only MgO powder, and a pipe simply mixed with MgO powder in a constant temperature and humidity environment. where a is a product of the present invention, b is a product containing only Mgl, and C
is a mixture of MgO and resin.

Also, Figure 3 shows the same person as Hee! This shows the decrease in insulation resistance at the initial stage of energization.

As is clear from the above description, compared to the sheathed heater based on the present invention and the sheathed heater mixed with MgO + silicone resin and heated, it maintains far superior moisture resistance because the coating is uniform and sufficient. .

In addition, by reducing the resin content to 115 to 415 through heat treatment, the unstable resin content is removed, thereby preventing the drop in insulation resistance that occurs in the early stages of heating, which occurs in conventional heaters.

Note that if the resin content becomes 115 or less due to heat treatment, moisture resistance will be lost, and conversely, if the resin content is 415 or more, the resin content will be carbonized by energization and the insulation will deteriorate.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a typical sheathed heater, Figure 2 is a characteristic diagram showing the relationship between the elapsed time and insulation resistance of the inventive product and the conventional product at constant temperature and humidity, and Figure 3 is the initial state of energization. FIG.

Claims (1)

[Scope of Claims] 1. The silicone resin content is reduced to 0.2 by coating, dipping, etc. in a solvent prepared by adding xylene, toluene, or acetone and isopropanol to a methyl-based silicone resin.
Coating is applied to the electrofused magnesia powder so that it has a ratio of ~5, and then it is hardened in the second half, then it is powdered again, filled with it, the diameter is reduced, and then it is heated and cured in a temperature range of 150°C to 600°C. A method for manufacturing a sheathed heater, characterized in that the organic content is reduced to an initial level of 115 to 415. 2. Apply a solvent such as xylene, toluene, or acetone and isopropanol to a methyl-based silicone resin, and reduce the silicone resin content by 5 to 1.
The coated electrofused magnesia powder and the uncoated electrofused magnesia are mixed so that the amount of the silicone resin is 0.2 to 5 parts based on the total magnesia weight. A method for producing a sheathed heater, which comprises filling the heater, reducing the diameter, and then heating and curing it at a temperature range of 150°C to 600°C to reduce the organic content to an initial level of 115 to 415.