JPH0834077B2 - Alloy type thermal fuse - Google Patents

Description

The present invention relates to an alloy type thermal fuse.

<Prior Art> In an alloy type thermal fuse, a low melting point fusible metal piece is bridged between a pair of lead conductors, a flux is applied on the low melting point fusible metal piece, and the low melting point fusible applied by the flux is applied. Surround the alloy piece with an insulating case, for example, a ceramic case,
The structure is such that the opening between the case and each lead conductor is sealed with a sealing material, for example, an epoxy resin. If the electrical equipment to be protected generates heat due to overcurrent,
The generated heat melts the low melting point soluble metal piece, and the molten metal is spheroidized due to its surface tension and the interfacial tension between it and the lead conductor. Power is cut off. In this case, the flux prevents oxidation of the low-melting point soluble metal piece, and even if the low-melting point soluble metal piece contains some oxide, the flux exhibits activity under heating and melting, To promote spherical fragmentation of the molten metal. In the absence of flux, an oxide film is generated on the surface of the low melting point fusible metal piece, and this oxide film forms a hard skin that hinders the spherical fragmentation of the molten metal. It is difficult to expect the operation. Thus, the flux is an indispensable component for the operation of the alloy type thermal fuse.

<Problems to be Solved> In the above-mentioned alloy type thermal fuse, if the case is completely filled with flux, a high internal pressure is generated due to thermal expansion of the flux during the heat cycle, which may cause damage to the sealing portion. . Therefore, it is usually necessary to have an air layer in the case. Therefore, the thermal fuse may be used by being attached to a high-potential part of the equipment, for example, a high voltage transformer such as a flyback transformer for TV. Depending on the mounting conditions, the fuse element of the thermal fuse (low melting point soluble Most of the high voltage acts between the metal piece) and the case, resulting in excessive electrical stress on the fuse element surface, especially at the edges, which may cause corona discharge in the space inside the case. In and, carbonization of the flux is forced. When the flux is carbonized in this way, the activity of the above-mentioned flux is remarkably lowered, it is difficult to expect a rapid melting and cutting of the molten metal, and it is difficult to guarantee the smooth operation of the thermal fuse.

An object of the present invention is to prevent corona discharge in the above case when used in a high potential region, to keep the flux in a normal state, and to ensure a smooth operation of the alloy type thermal fuse.

<Means for Solving the Problems> In the alloy type thermal fuse according to the first invention of the present application, a low melting point fusible alloy piece is bridged between a pair of lead conductors, and flux is applied on the low melting point fusible alloy piece. The flux-coated low melting point fusible alloy piece is surrounded by a case in which a conductive layer is fixed on the outside of the insulating case body, and the conductive layer and one of the lead conductors are electrically connected to each other. It is a composition.

In the alloy type thermal fuse according to the second invention of the present application, a low melting point fusible alloy piece is bridged between a pair of lead conductors, flux is applied on the low melting point fusible alloy piece, and the flux coating low melting point fusible The alloy piece is surrounded by an insulating case, a conductive cover is attached on the case, and the cover and one of the lead conductors are electrically connected to each other.

<Description of Embodiments> Hereinafter, embodiments of the present invention will be described with reference to the drawings.

1A is a longitudinal sectional view showing an embodiment of the first invention, and FIG. 1B is a sectional view taken along line bb in FIG. 1A.

In FIGS. 1A and 1B, 11 and 12 are a pair of lead conductors that are parallel to each other, and usually copper wires are used. Two
Is a low melting point fusible metal piece bridged by welding between the lead conductors, and one having a composition corresponding to the operating temperature is selected, for example, Sn-Pb system, Sn-Pb-Bi, Sn-Pb-Cd, Sn-Pb-In,
Sn-Bi-In based alloys can be used. 3 is a flux applied on a low melting point soluble metal piece, which contains rosin as a main component,
Activator as required (eg dimethylamine hydrochloride)
Can be used. Reference numeral 4 denotes a case in which a conductive layer is fixedly provided on the outer side of the main body of the insulating case (hereinafter referred to as an insulating case with a conductive layer), which surrounds the flux-coated low melting point fusible alloy piece, and the opening and lead of the case 4. The space between the conductor and the conductor is sealed with a sealing material such as an epoxy resin.
For the insulating case with a conductive layer, a conductive metal such as brass, copper, aluminum, iron or nickel may be plated on the outer surface of the insulating case body, or a conductive paint may be applied / baked. 6 is one of the conductive layer of the insulating case 4 with a conductive layer and the pair of lead conductors, for example,
It is an electrically conducting portion provided between the wire 11 and 11, and can be welded or soldered with bond wires, or can be applied by soldering, dropping adhesion of a conductive resin, or the like.

FIG. 2 shows another embodiment of the first invention, in which a low melting point fusible alloy piece 2 is bridged by welding between a pair of lead conductors 11, 12 arranged in a straight line, and the low melting point fusible alloy piece 2 is bridged over the low melting point fusible alloy piece. Flux is applied, and then a cylindrical insulating case with a conductive layer 4 is applied.
And the lead conductor 11 is sealed between the respective ends of the case and the lead conductors, and the conductive portion 6 is provided between the lead conductor 11 on one side and the outer conductive layer of the insulating case 4 with a conductive layer. Conducted by. This one lead conductor and the insulating case with a conductive layer 4
Conduction with the outer conductive layer is performed by bending one lead conductor 11 as shown in FIG.
It is also possible to make contact with the conductive layer and solder or weld the contact point.

4A is a vertical sectional view showing an embodiment of the second invention, and FIG. 4B is a sectional view taken along line bb in FIG. 4A.

In FIGS. 4A and 4B, 11 and 12 are lead conductors, 2 is a low melting point metal piece bridged between the lead conductors, 3
Is a flux, and each of the configurations is the same as that of the first invention. Reference numeral 40 denotes an insulating case that surrounds the low melting point fusible metal piece, for example, a ceramics case, and 5 denotes a sealing material that seals between each end of the insulating case and the lead conductor. Reference numeral 42 is a conductive cover attached to the insulating case, for example, a metal cover, which connects the cover 42 and one lead conductor 11 to the conducting portion 6
Conducted by. This conducting portion has the same structure as that described above.

FIG. 5 shows another embodiment of the second invention, in which a cylindrical insulating case, for example, a cylindrical ceramic case is used as the case 40,
A space between each end of the tubular insulating case and each of the lead wires 11 and 12 is sealed with a sealing material 5, and a tubular metal cover 42 having lead wire retaining ears 43 is inserted into the insulating case. Then, bend one of the lead conductors 11 and attach the bent lead conductor 11 to the edge of the ear portion 43.
I am wearing 431.

<Effects of the Invention> The alloy-type thermal fuse according to the present invention is configured as described above, and uses an insulating case with a conductive layer or an insulating case in which a conductive cover is attached to the case. Since the cover and one of the lead conductors are electrically connected and the insulating case and the low melting point fusible metal piece inside the case can be made to have the same potential, it is possible to eliminate the effect of electrical stress on the space inside the case. However, the corona discharge in the case can be avoided and the carbonization due to the flux can be prevented. Therefore, the spheroidizing action of the molten metal (low melting point soluble metal) by the flux can be well ensured, and the smooth operation of the alloy type thermal fuse can be secured. However, since the outer surface of the case is exposed to a high electric potential, it is necessary to reinforce the insulation between the outer surface of the case and the ground potential, but this reinforcing treatment can be easily performed by winding an insulating tape or the like.

In particular, the alloy-type thermal fuse according to the second aspect of the invention can be implemented by inserting a conductive cover on the insulating case of the conventional alloy-type thermal fuse, and can be used in a low-potential region where corona discharge does not pose a problem. There is also an advantage that it can be easily used properly in a high-potential region where the above problem arises.

Further, in any of the alloy type thermal fuses according to the invention, since the inner surface of the case surrounding the low melting point fusible alloy piece is an insulating surface, the low melting point fusible alloy piece is melted into a spherical shape when the thermal fuse is activated. Even if the molten low melting point alloy bridges between the lead conductor (the other lead conductor to the lead conductor electrically connected to the conductive layer or the conductive cover) and the inner surface of the case, it is possible to secure the current interruption and keep the current flowing. Sufficient blocking performance can be maintained.

[Brief description of drawings]

FIG. 1A is an explanatory view showing an embodiment of the first invention, and FIG. 1B.
FIG. 4A is a sectional view taken along the line bb in FIG. 1A, FIGS. 2 and 3 are explanatory views showing another embodiment of the first invention, and FIG.
Is an explanatory view showing one embodiment of the second invention, FIG. 4B is a sectional view taken along line bb in FIG. 4A, and FIG. 5 is an explanatory view showing another embodiment of the second invention. 11,12 ... Lead conductor, 2 ... Low melting point fusible metal piece, 3 ...
… Flux, 4… Insulating case with conductive layer, 40… Insulating case, 42… Conductive cover, 6… Conducting part.

Claims (2)

[Claims] 1. A low melting point fusible alloy piece is bridged between a pair of lead conductors, and flux is applied onto the low melting point fusible alloy piece,
An alloy type characterized in that a flux-coated low melting point fusible alloy piece is surrounded by a case in which a conductive layer is fixedly provided outside the insulating case body, and the conductive layer and one of the lead conductors are electrically connected to each other. Thermal fuse. 2. A low melting point fusible alloy piece is bridged between a pair of lead conductors, and flux is applied onto the low melting point fusible alloy piece.
An alloy-type thermal fuse characterized in that the flux-coated low melting point fusible alloy piece is surrounded by an insulating case, a conductive cover is attached on the case, and the cover and one lead conductor are electrically connected to each other. .