JPS645758B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a sheathed heater sealing method for sealing a pipe end opening with glass during manufacture of a sheathed heater.

The conventional glass sealing method for manufacturing a sheathed heater is, for example, as shown in FIG.
A glass sealing material 5, such as a powder of low-melting glass, is put into the opening at the end of the pipe, and then the end of the pipe 1 of the sheathed heater is inserted into a heating furnace 11 in which a heater 10 is disposed inside, as shown in the figure. It was common practice to melt the glass sealing material 5 and remove it from the heating furnace 11 to complete the sealing process.

In such a conventional sealing method, when the end of the pipe 1 is heated to melt the glass sealing material 5, the heat at the end of the pipe 1 is transmitted throughout the pipe, raising the internal temperature of the pipe 1. As a result, the gas inside the pipe expands and a part of it passes through the molten glass sealing material 5 and is released into the atmosphere, so when passing through the glass sealing material 5, an opening for gas passage is created and the sealing This opening remains afterwards, causing a sealing failure. Furthermore, even if the sealing is performed well, the sealing is performed with the gas inside the pipe 1 expanded, so the pressure of the sealed gas inside the pipe 1 after sealing is considerably lower than the atmospheric pressure. It was hot.

The present invention has been made to solve these drawbacks, and provides a method for sealing a sheathed heater with good electrical insulation properties without lowering the pressure of the gas sealed inside the pipe below atmospheric pressure when manufacturing the sheathed heater. The purpose is to

A specific embodiment of the present invention shown in FIG. 2 will be described below. In FIG. 2, a heating coil 2 and a take-out terminal 3 connected to each other are inserted into a pipe 1, and magnesia powder 4 is filled into the end opening of the pipe 1. The sealing material 5 is inserted in the same manner as in the conventional example. Next, the end of the pipe 1 is inserted into a heating device 7 in which heating parts 6, 6' of high-frequency induction heating coils are arranged adjacently in two stages. The heating parts 6 and 6' of this heating device 7 are such that one heating part 6 is located on the main body side slightly away from the end sealing part of the pipe 1 with respect to the other, and the other heating part 6' is It is located at the end sealing section. That is, the heating section 6
is located directly below the heating section 6'. When heating, first, the heating section 6 is operated to heat the portion of the pipe 1 facing the heating section 6. This heating heats the gas near the end inside the pipe 1, expands it, and releases it into the atmosphere through the glass sealing material 5. In this case, since the heating is rapid heating by high-frequency induction, the part of the pipe 1 closer to the main body than the heating part 6 is hardly heated, and the temperature at the end of the pipe 1 is also below the melting point of the glass sealing material 5. The glass sealing material 5 also does not melt and does not prevent the release of the expanded gas. Next, heating of the heating section 6 is stopped, and the heating section 6' is operated to similarly heat the opposite end of the pipe 1, thereby melting the glass sealing material 5 and sealing it. At this time, since the internal expanding gas has already been released near the end of the pipe 1, new gas expansion does not occur near the sealing part, and therefore, the phenomenon of openings in the molten glass sealing material 5 does not occur. Does not occur at all.

As explained above, in the present invention, before heating the glass sealing material at the end of the pipe, the area adjacent to the sealing part on the main body side is locally rapidly heated to release the expanded gas near the sealing part to the atmosphere in advance. After that, the heating of the adjacent part is stopped, the sealing part is heated, and the glass sealing material is melted.Since this is a two-stage heating method, no expanding gas is generated when the glass sealing material is melted, unlike conventional methods. There is no risk of sealing failure due to the occurrence of holes in the sealing part, and the internal pressure after sealing does not drop significantly below atmospheric pressure as in conventional methods, and can be maintained at a pressure almost equal to atmospheric pressure. As a result of being able to make the pressure during use higher than atmospheric pressure, it is possible to obtain a sheathed heater with extremely good electrical insulation properties. Note that the heating sections 6 and 6' do not necessarily need to be divided into two; for example, the heating section 1
This can also be done by moving the heater individually or by moving a sheathed heater. Furthermore, it is preferable to make the heating temperature on the main body side higher than the heating temperature on the end portion, since this can enhance the effect of gas release.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a conventional sheathed heater sealing method, and FIG. 2 is a sectional view showing a sealing method of the present invention. DESCRIPTION OF SYMBOLS 1...Pipe, 2...Heating coil, 3...Takeout terminal, 4...Magnesia, 5...Glass sealing material, 6...Heating part, 7...Heating device. Note that the same parts in the drawings are designated by corresponding symbols.

Claims (1)

[Claims] 1. In a sheathed heater sealing method that seals the end of a sheathed heater in which a heating coil is disposed inside a pipe, and a lead-out terminal and a glass sealing material are disposed at the end, a portion adjacent to the sealing portion on the pipe body side is locally sealed. A method for sealing a sheathed heater, characterized in that the sealing portion is heated by high-frequency induction heating, and then the sealing portion is heated to melt the glass sealing material at the end, thereby sealing the end.