JPS6019119B2 - How to seal the end of a sheathed heater - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a method for sealing the end of a sheathed heater, and its purpose is to reduce the defective rate during the manufacturing process and to obtain a sheathed heater with high dielectric withstand voltage characteristics. .

Conventionally, in a sheathed heater, as shown in Fig. 1, a heating coil 2 with an outlet wire 3 connected to the terminal thereof is inserted into a metal tube 1, after being insulated with magnesia powder 4. The end gate is sealed with low melting point glass 5. Next, a rubber cap 6 is inserted into the outer surface of the end of the metal pipe 1, and an epoxy resin 7 is injected into the cap 6.
The end portion of the terminal and the connection portion between the output wire 3 and the lead wire 8 were buried, and the epoxy resin 7 was heated and hardened, thereby sealing the terminal. In the end structure of the sheathed heater sealed in this way, the low melting point glass 5 that closes the end entrance of the metal pipe 1 has an extremely smooth and glossy surface, and is filled with epoxy resin that is filled and hardened. It has no affinity with, and does not adhere to.

When further heated and cured and returned to room temperature, the epoxy resin 7
Since it has a large coefficient of thermal expansion and a large degree of shrinkage, a small gap is created at the interface with the low melting point glass 5. Since this gap is at a vacuum or a pressure close to it, the discharge characteristics are extremely good. Therefore, the completed sheathed heater had extremely low dielectric withstand voltage characteristics, failed to meet legally stipulated values, and had a high defective rate. This invention should respect this point.By roughening the surface of the low-melting point glass, even if there is a slight gap between the glass and the epoxy resin, the electric discharge will not occur because of the uneven interlocking. The present invention provides a sheathed heater that can improve dielectric strength characteristics.

An embodiment of the present invention will be described in detail below.

In Fig. 2, 1 is a metal pipe, 2 is a heating coil, and 3 is a metal pipe.
is connected to the heating coil 2 by an outlet wire. 4 is magnesia powder, and 5 is low melting point glass, which seals the end opening of the metal/filter.

As shown in 5a, the surface of the glass 5 is roughened by sandblasting or the like. Reference numeral 6 denotes a rubber cap attached to the outer surface of the end of the metal/gupoo, and 7 is epoxy resin, which is injected into the rubber cap 6.

Reference numeral 8 denotes a lead wire, which is connected to the outlet wire, and the connecting portion is located inside the rubber cap 6 and buried in epoxy resin 7.

This is then placed in a heating furnace to harden the epoxy resin 7. By roughening the surface of the low melting point glass 5 as described above, it becomes smooth and loses its luster.

Moreover, since the surface becomes uneven, the surface area increases. Therefore, the affinity with the epoxy resin 7 increases, the bushing property becomes good, the surface area increases, and the adhesive force becomes strong. Therefore, it is difficult to form a gap at the interface between the low melting point glass 5 and the epoxy resin 7 due to shrinkage when the epoxy resin 7 is heated and cured and then returned to room temperature. Even if a gap is created, the low melting point glass 5 and the epoxy resin 7 are interlocked in an uneven manner, resulting in a long discharge path length and poor discharge characteristics. Note that the above-mentioned gap does not occur over the entire surface of the interface, and since it is an extremely small gap, the tips of the convex parts do not come close to each other, and electric field concentration at the tips does not become a problem. do not have. Therefore, the insulation voltage characteristics are high,
It was possible to manufacture a sheathed heater without any defects, and the productivity was greatly improved.It was also possible to obtain a sheathed heater that can be used with peace of mind, which is of great practical value.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a sealed terminal of a sheathed heater according to a conventional method, and FIG. 2 is a sectional view showing a sealed terminal of a sheathed heater according to a method of the present invention. In the figure, 1 is a metal pipe, 2 is a heating coil, 3 is a lead wire, 4
5 is a magnesia powder, 5 is a low melting point glass, 6 is a rubber cap, 7 is an epoxy resin, and 8 is a lead wire. Figure 1 Figure 2

Claims (1)

[Claims] 1. After sealing the end opening of the sheathed heater with low-melting glass, the surface of the glass is roughened into an uneven shape, and then epoxy resin is injected into the cap attached to the end of the metal pipe and cured by heating. A method for sealing the end of a sheathed heater by sealing the end opening of a metal pipe.