JPH0436019Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an improvement in the sealing structure of a conductor rod in a bushing.

<Prior art and problems> In the pellet type temperature fuse, as shown in Fig. 2, a bushing B' through the fixed contact rod is fixed to one end of the case A', and the contact rod 2' and the bushing are fixed to one end of the case A'.
B' is sealed with an epoxy resin mold 5'.

However, in pellet type temperature fuses, thermal stress (peel stress) occurs at the interface between the mold resin and the contact rod due to frequent heat cycles.
acts repeatedly and the coefficient of thermal expansion of the molding resin is considerably larger than that of the contact rod, so the peeling stress is quite large. That is, if the radius of the contact rod is r, its Young's modulus is E ₁ , its thermal expansion coefficient is α ₁ , the thickness of the molded resin layer is t, its Young's modulus is E ₂ , and its thermal expansion coefficient is α ₂ , then the temperature The above peeling stress P under the increase △T is P=1/r/t1/E ₂ +1/E ₁・(α ₂ −α ₁ )△T...
, and since α ₂ is considerably larger than α ₁ , P is considerably large. Therefore, the interface between the mold resin layer and the contact rod is likely to peel off, and the sealing performance at that interface is unstable.

By the way, there are cases where a plastic covered wire is introduced into a device case and its introduction port is sealed with molded resin.In this case, at the interface between the plastic covered layer and the molded resin layer, the coefficient of thermal expansion of the two is approximately equal. Because they are equal, almost no thermal stress occurs. Regarding the thermal stress between the conductor of the plastic-covered wire and the plastic coating layer, the plastic coating material is softer than the molding resin, and E ₂ in the first equation can be substantially reduced.
It can be made smaller than the thermal stress at the interface between the mold resin layer and the contact rod as shown in the equation. however,
Even in this case, thermal stress acts as an interfacial peeling force, so as the number of heat cycles increases over a long period of time, the sealing performance inevitably deteriorates, and further improvement of the sealing performance is required.

<Purpose of the invention> An object of the invention is to provide a sealing structure for a conductor rod in a bushing that can sufficiently improve the sealing properties of the interface between the mold resin and the contact rod against heat cycles.

<Structure of the invention> The sealing structure of the conductor rod in the bushing according to the invention is such that the conductor rod is passed through the conductor rod through hole of the bushing body, the protrusion of the conductor rod is covered with a heat-shrinkable tube, and the conductor rod is sealed. This structure is characterized by molding resin between the protrusion and the end of the bushing body.

<Explanation of Examples> The present invention will be explained below with reference to the drawings.

In FIG. 1, 1 is the butting body;
For example, it is made of ceramic and has a through hole 2. Reference numeral 3 denotes a conductor rod, which has a contact head at its tip and passes through the through hole of the bushing body. 4
is a heat-shrinkable plastic tube, such as a heat-shrinkable vinyl chloride tube, which is coated on the protruding portion of the conductor rod in a heat-shrinkable state. Therefore, tensile hoop stress remains in the heat-shrinkable tube. 5 is an epoxy resin molded between the protruding portion of the conductor rod and the end of the bushing body. This mold may be provided with the tube protruding.

Compressive stress (tightening stress) acts between the protrusion of the conductor rod and the heat-shrinkable plastic tube due to the shrinkage force of the heat-shrinkable plastic tube. On the other hand, the thermal stress P at the interface between the heat-shrinkable plastic tube and the conductor protrusion due to the temperature increase ΔT is expressed as the Young's modulus of the plastic tube.
As mentioned above, since E ₂ is small, it can be made considerably small, but this thermal stress is a peeling force that tries to separate the interface. However, in the case of the present invention, since the tightening stress (F) can be generated as described above, the stress acting on the interface is F-P, and F increases the heat shrinkage rate of the heat-shrinkable plastic tube. Alternatively, it can be increased by increasing the thickness of the tube, so it is possible to make F-P a positive pressure.

It should be noted that at the interface between the heat-shrinkable plastic tube and the mold layer, the thermal expansion coefficients of the two are almost equal, and almost no thermal stress occurs.
This is clear from the above explanation.

<Effects of the invention> As mentioned above, the sealing structure of the conductor rod in the bushing according to the invention can maintain a constant positive pressure state at the interface between the resin mold layer and the conductor rod despite heat cycles. , the sealing property of the interface can be well guaranteed.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a sealing structure of a conductor rod in a bushing according to the present invention, and FIG. 2 is an explanatory diagram showing a conventional example. In the figure, 1 is the bushing body, 2 is a conductor rod through hole, 3 is a conductor rod, 4 is a heat-shrinkable tube, 5
It is mold resin.

Claims (1)

[Scope of utility model registration request] A bushing characterized by passing a conductor rod through the conductor rod through hole of the bushing body, covering the protrusion of the conductor rod with a heat-shrinkable tube, and molding resin between the conductor rod protrusion and the end of the bushing body. Seal structure of conductor rod.