JPH0340474B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sheathed heater with an improved lead portion.

For example, in a sheathed heater used under high-temperature conditions, such as a nuclear fuel simulating heater, the lead portion is also exposed to high temperatures, so special consideration must be given to the lead portion.

FIGS. 1 and 2 show the structure of a lead portion in such a cartridge-type sheathed heater, for example. That is, in the figure, 1 is an outer tube, 2 is a heating element forming a double coil provided inside the outer tube 1,
3 is a heat-resistant insulating powder filled in the outer tube 1, 4 is an intermediate conductor made of nickel connected to the end of the heating element 2, and 5 is made of copper for external wiring connection connected to the intermediate conductor 4. It is the lead. Note that the intermediate conductor 4 and the lead 5 are divided into two along the longitudinal direction. Here, the reason why the lead 5 made of copper is used is as follows.
This is to keep the heat generation in the lead 5 small even when a large current is applied. The reason for using the intermediate conductor 4 made of nickel is to prevent the leads 5 from melting since the heat generation temperature of the heating element 2 exceeds the melting point of copper.

In such a structure of the lead part, conventionally, TIG welding (tungsten inert
Welding methods such as gas arc welding) and electron beam welding are used. Therefore, the joint A of the intermediate conductor 4 and the lead 5 joined by welding is
It can be used until the surface temperature of the nearby outer tube reaches around 800℃, but if a large current and high power density are applied and the surface temperature reaches 900℃ or higher, a wire breakage will occur at the joint A. It has the disadvantage of short high temperature life. A life test when the surface temperature was 950°C or higher was conducted using a sheathed heater in which the intermediate conductor 4 and lead 5 were joined by TIG welding, by repeatedly applying current at 85 amperes for 5 minutes.
Connection A broke at the end of the fifth energization. The reason why the high-temperature life of the welded joint A between the intermediate conductor 4 and the lead 5 is short is considered to be due to the following reasons. Welding melts the joint end of the lead 5 and coarsens its copper crystals, reducing its strength. In addition, a copper-nickel alloy is formed at the joint A by the nickel of the intermediate conductor 4 and the copper of the lead 5, causing the joint to deteriorate. The electrical conductivity and thermal conductivity of A change, and the amount of heat generated increases. Therefore, when electricity is repeatedly applied to the joint A, each joint end of the intermediate conductor 4 and the lead 5 deteriorates due to fatigue and breaks, resulting in a disconnection.

The present invention has been made in view of the above circumstances, and provides a sheathed heater that increases the high temperature life of the joint between the intermediate conductor made of nickel and the lead made of copper, and can be used satisfactorily under large current and high power density. It is.

That is, the sheathed heater of the present invention includes an outer tube;
a heating element disposed inside the outer tube; an intermediate conductor made of nickel disposed inside the outer tube and connected to an end of the heating element; A lead made of copper arranged inside the outer tube and joined to the intermediate conductor by soldering; and an insulating powder filled inside the outer tube and embedding at least the joint between the intermediate conductor and the lead. It is characterized by having the following.

Embodiments of the present invention illustrated in the drawings will be described below.

In the sheathed heater of the present invention, as shown in FIG. 1, an intermediate conductor 4 made of nickel is connected to the end of a heating element 2 provided inside an outer tube 1, and a lead 5 made of copper is connected to the intermediate conductor 4. In addition, the joint end of the intermediate conductor 4 and the joint end of the lead 5 are joined by soldering.

FIG. 3 shows an embodiment of the joint A between the intermediate conductor 4 and the lead 5 in the sheathed heater of the present invention. For example, the joining end 4a of the intermediate conductor 4 and the joining end 5a of the lead 5 are cut diagonally so that they can be combined with each other. The joint end 4a of the intermediate conductor 4 and the joint end 5a of the lead 5 are soldered together with a gold solder 6 of BAU-1V type, for example. In this case, since the joint ends 4a and 5a are cut diagonally, the joint cross-sectional area is large.

Here, a life test was conducted on the joint A by brazing the joint end 4a of the intermediate conductor 4 and the joint end 5a of the lead 5. As in the previous test, the outer tube surface temperature was
As a result of repeatedly applying electricity at 85 amperes for 5 minutes at 950°C, the joint A did not break even after applying electricity 15 times. Therefore, it is clearly seen that the soldered joint A has a very long high temperature life.

The high temperature life of the joint A formed by soldering between the intermediate conductor 4 and the lead 5 is considered to be due to the following reasons. Since the melting point of the gold solder 6 is lower than the melting point of copper, the joint ends of the leads 5 made of copper do not melt during soldering, the copper crystals do not become coarse, and the strength does not decrease. Furthermore, since the nickel at the joint end 4a of the intermediate conductor 4 and the copper at the joint end 5a of the lead 5 do not form a copper-nickel alloy due to soldering, the electrical conductivity and thermal conductivity at the joint A are determined by the base metal. It can be maintained the same as that of the intermediate conductor 4 and lead 5, and the amount of heat generated when energized is small. and,
Even if the junction A is repeatedly energized, the intermediate conductor 4
Since the joint end 4a of the lead 5 and the joint end 5a of the lead 5 do not deteriorate due to fatigue and do not break, the joint part A does not break. Furthermore, the solder metal 6 melts once the joint A reaches a temperature of 950°C or higher, but since the heat-resistant insulating powder 3 filled in the outer tube 1 surrounds the solder metal 6, the solder metal 6 cannot be welded. Since the gold solder 6 is held by the insulating powder 3 and does not flow out, it remains in the joint A and is in contact with the joint ends 4a and 5a, allowing current to flow between the intermediate conductor 4 and the lead 5. It is. Therefore, the joint end 4 of the intermediate conductor 4 joined by soldering
The joint A between A and the joint end 5a of the lead has an excellent high-temperature life without breaking even when the surface temperature of the outer tube exceeds 950°C, and can carry large current and high power density. be.

Note that the intermediate conductor 4 and the heating element 2 are joined by brazing or welding as necessary.

A sheathed heater having a lead portion configured in this manner can be effectively applied to those used at high temperatures, such as nuclear fuel simulators.

Note that the brazing material used for soldering the intermediate conductor 4 and the lead 5 may be a gold solder, but a gold solder is most suitable.

As explained above, according to the sheathed heater of the present invention, the joint between the intermediate conductor made of nickel connected to the heating element and the lead made of copper for external wiring connection is joined by soldering, and furthermore, this joint is Since it is embedded in the insulating powder filled in the outer tube,
The junction between the intermediate conductor and the lead has an excellent high-temperature life, and can be used well under high-temperature conditions, as well as at large currents and high power densities.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional side view showing a sheathed heater to which the present invention is applied, FIG. 2 is a sectional view taken along the line shown in FIG. FIG. DESCRIPTION OF SYMBOLS 1... Outer tube, 2... Heating element, 3... Heat resistant insulating powder, 4... Intermediate conductor, 5... Lead, 6... Gold solder, A... Joint part.

Claims (1)

[Scope of Claims] 1. An outer tube, a heating element disposed inside the outer tube, and an intermediate conductor made of nickel disposed inside the outer tube and connected to an end of the heating element. a lead made of copper that is disposed inside the outer tube with a portion protruding outside the outer tube and joined to the intermediate conductor by soldering; and a lead that is filled inside the outer tube and is connected to at least the intermediate conductor A sheathed heater comprising: an insulating powder in which a joint portion with the lead is embedded. 2. The sheathed heater according to claim 1, wherein the soldering is performed using gold solder.