JPS5852313B2 - How to seal a sheathed heater - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for sealing a sheath heater.

Magnesia, which is used for insulation between the protective sheath and the heating coil of a sheath heater, has the disadvantage that when left in the air, it absorbs moisture from the air and its insulation resistance decreases.

In order to prevent the above drawbacks, it is necessary to seal the ends of the protective sheath.

The method is to place a heating wire coil inside a protective sheath, fill it with magnesia, and then drop a sintered ring made by molding and sintering glass powder into the entrance of the protective sheath through the lead wire of the heating element. The heating element is placed in a heating furnace and held at a temperature near the deformation temperature of the sintered body ring, for example, 320° C., and the moisture absorbed by the magnesia is removed.

The temperature of the heating furnace is then adjusted to the melting temperature of the sintered ring, e.g.
The temperature was raised to 80°C and sealed.

When using this method to seal both ends at once by inserting sintered rings into both ends of a U-shaped heating element as shown in Figure 1, the melting temperature of the m-ring When the inside of the heating furnace rises, the sintered ring melts and closes the openings at both ends of the protective sheath.

As a result, the air remaining in the magnesia inside the heating element
It is sealed at the same temperature as the inside of the heating furnace, and air flow is stopped.

Next, by lowering the temperature inside the furnace, the molten sintered body will also harden and the glass sealing will be completed.

At this time, the remaining air inside the heating element is sealed at 480° C., and the heating element is cooled to room temperature.

According to Boyle-Charles' law, the pressure inside the heating element becomes negative when it is cooled to room temperature.

Now, the temperature inside the furnace is 480℃, and the pressure inside the furnace is 1 hla! It can be closed, cooled to room temperature (20°C), and sealed at a pressure lower than atmospheric pressure.

In reality, it will be slightly larger than 0.4 Ay/cm from L', which is not 2 V', but judging from the value of the thermal expansion coefficient, it is not enough to cause a large change, and negative pressure can be avoided. What (・.

If the internal pressure of the completed sheath heater becomes negative as described above, the dielectric strength will be particularly poor.

According to Pa5chen's law, the discharge voltage (■) is determined as a function of the product Pd of the distance d between the electrodes and the gas pressure P.

From this relationship, it is clear that as the internal pressure decreases, the dielectric strength characteristics deteriorate.

Therefore, the completed sheathed heater cannot withstand the voltage of the legally stipulated value and becomes defective.

In order to improve this point, it is necessary to increase the diameter of the protective sheath of the sheathed heater to increase the insulation distance, which is extremely inconvenient.

In order to improve these inconveniences, the present invention is designed to perform sealing on one side at a time, and to quickly sinter the sheathed heater before the entire sheathed heater rises to the melting temperature of the sintered ring during the second sealing. The objective is to melt the solid ring and minimize the reduction in internal pressure after cooling to prevent a decrease in dielectric strength characteristics.

The effects of the present invention will be explained in detail below.

In FIG. 1, 1 is a heating element coil, 2 is a protective sheath made of metal or the like, 3 is magnesia powder, and 4 is a lead wire from the heating coil.

A low melting point glass sealant is attached to one side of the end of the protective sheath 2 shown in FIG.

Figure 2 shows a sintered ring 5 made of glass powder press-molded and sintered at around its softening temperature.The outer diameter is smaller than the inner diameter of the protective sheath 2, and the inner diameter of the ring is the outer diameter of the heating coil lead wire 4. Make it bigger.

FIG. 3 shows the glass sintered ring 5 inserted into one end of the protective sheath 2 by passing the sunrise wire 4 through it.

The product in this state is placed in a heating furnace and heat treated at the temperature shown in FIG. 4 to seal one side of the protective sheath 2.

FIG. 4 shows that a sintered ring 5 made of low melting point glass is coldly dropped into one end of the protective sheath 2, then placed in a heating furnace and heated to a temperature near the deformation temperature of the sintered ring 5, e.g. 320
It is held at ℃, and the magnesia powder 3 is sucked in to remove moisture.

Thereafter, the temperature of the sintered ring 5 in the heating furnace is 48, for example.
After raising the temperature to 0°C and melting it, the temperature inside the furnace was lowered and one end was sealed.

Then, as shown in Figure 5, take out the sheathed heater from the furnace,
After dropping the sintered ring 5 into the other end of the protective sheath 2 through the marking line 4, as shown in FIG.
A sheathed heater is placed in a furnace heated to a melting temperature of, for example, 480° C., and after the sintered ring is melted, it is slowly cooled and sealed.

As described above, after putting the sintered ring 5 into one end of the protective sheath 2 and removing the moisture absorbed by the magnesia powder 3 in the heating furnace, the heating furnace reaches the melting temperature of the sintered ring 5. After being raised, the molten sintered ring 5 is slowly cooled to a temperature at which it solidifies.

After that, the sheathed heater is taken out, the sintered ring 5 is put into the opening at the other end of the protective sheath 2, and then the sintered ring 5 is placed in a heating furnace where it is heated to the melting temperature of the sintered ring 5 or higher. Promptly melt the sintered ring 5,
Both ends are sealed.

In this way, the magnesia powder 3 absorbs temperature in the first sealing process.
After the step of removing the trapped moisture, the temperature of the heating furnace is raised to melt the sintered body ring 5.

Then, the inside of the heating furnace is slowly cooled to complete sealing of one side of the protective sheath 2.

In this -th sealing, there is no drop in internal pressure because the other end is open.

The purpose of the first sealing is to dry the magnesia powder 3 and prepare for the second sealing.

That is, when the inside of the heating furnace is slowly cooled to about 100° C., the sintered ring 5 is immediately taken out of the furnace and dropped into the opening of the protective sheath 2 at the other end, and then the sintered ring 5 is re-cooled. The sintered body ring 5 at the other end is heated to a melting temperature of or slightly higher than +-3 and then placed in a furnace, where the sintered body ring 5 at the other end is melted and slowly cooled.

In order to melt only the sintered ring 5 during the second sealing without raising the temperature of the entire sheathed heater, set the heating furnace to a temperature slightly higher than the melting temperature of the sintered ring 5 in advance. When the sintered body ring 5 is placed inside the sintered body, the sintered body ring 5, which has a much smaller heat capacity than the protective sheath 2 and the magnesia powder 3, melts first.

That is, before the entire sheathed heater is heated, the sintered ring 5 is melted and the opening of the protective sheath 2 is closed.

By doing so, it is possible to close the opening before the remaining air in the magnesia powder 3 is sufficiently heated.

In addition, when heating is performed for the second time, one side is already sealed, so the discharge speed of the remaining air in the magnesia powder 3 to the outside of the sheathed heater due to thermal expansion is much faster than when both sides are opened. Since the L is slow, it is possible to reduce the degree of internal pressure reduction after sealing is completed, and it is possible to obtain an L sheathed heater with good dielectric strength characteristics.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a sheathed heater for explaining the present invention in detail, Fig. 2 is a perspective view of a sintered glass ring used for the sealing opening, and Fig. 3 is a sintered glass ring used for sealing. Fig. 4 is a graph showing the heat treatment temperature when the heater shown in Fig. 3 is placed in a heating furnace and heated, and Fig. 5 is the heat treatment process shown in Fig. 3. 6 is a cross-sectional view showing the sintered glass ring inserted into the opening at the other end of the heater that has been taken out. Figure 6 is a graph showing the heat treatment temperature when the one in Figure 5 is placed in a heating furnace and heated. It is. In the figure, 1 is a heating element coil, 2 is a protective sheath, 3 is magnesia powder, 4 is a grid line, and 5 is a sintered body ring.

Claims (1)

[Claims] 1. A sintered body formed by sintering glass powder near the softening temperature of glass is inserted into the entrance of one end of a protective sheath containing magnesia and a heating element through the sunrise wire of the heating element,
This protective sheath is placed in a heating furnace and held at around the deformation temperature of the glass, then the furnace is heated to the melting temperature of the glass and slowly cooled, and then a glass similar to the above is placed inside the inlet at the other end of the protective sheath. After inserting the sintered body, the protective sheath glass is heated to a temperature slightly higher than the melting temperature L.
- A method for sealing a sheathed heater, which is characterized by sealing both ends of the sheath by placing it in a furnace.