JPH05135649A - Manufacture of thermal fuse - Google Patents

Abstract

PURPOSE:To provide a manufacturing method for thermal fuse which comprises forming of the hermetical seal structure into a double structure in order to shield from an external air the parts accommodated within a metallic casing and thereby enhancing the reliability. CONSTITUTION:An upper end surface and outer peripheral surface of an insulation bushing 8 are covered beforehand by a cap-like packing member 14 made of an insulative and heat-resistance material. Thereafter, the resulting bushing 8 is engaged with an opening end of a metallic casing 1 and a portion 16 of the structure projecting outwardly from the insulation bushing 8 is caulked toward the center axis and thus is secured. Subsequently, a fluid sealing resin 12 is supplied to the upper surface of the insulation bushing 8 to provide a seal, thereby making the seal structure a double structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thermal fuse in which a temperature-sensitive pellet is housed in a cylindrical metal case and sealed with a sealing resin.

[0002]

2. Description of the Related Art As a non-reset type thermal fuse that shuts off an electric circuit when the ambient temperature rises above a certain temperature and maintains the shutoff state of the electric circuit even when the raised ambient temperature falls below a certain temperature. In some cases, a temperature-sensitive pellet made of an insulating organic chemical substance is used as a temperature-sensitive member that melts at a specific temperature.

FIG. 3 is a sectional view showing the structure of a typical thermal fuse of this type. In the figure, reference numeral 1 denotes a cylindrical metal case made of a metal having good conductivity and good heat conductivity such as copper or brass, and a first lead wire 2 made of copper is caulked and fixed to one end thereof. Reference numeral 3 denotes a cylindrical temperature-sensitive pellet made of an insulating chemical substance that melts at a specific temperature, and 4 and 5 average the elasticity of a strong compression spring 6 described later to the temperature-sensitive pellet 3 and a movable contact 7 described later. Is a pressing plate made of copper or the like, 6 is a strong compression spring for closing the circuit, which is interposed between the pressing plates 4 and 5 in a compressed state, and 7 is a silver alloy having good conductivity and an appropriate elastic force. Is a movable contact having a plurality of tongue pieces 7a around it, and each tongue piece 7a is in pressure contact with the inner surface of the metal case 1.

The temperature sensitive pellets 3 or the movable contacts 7 are housed in the metal case 1 in the order described above. Reference numeral 8 denotes an insulating bushing made of ceramic or the like that closes the open end of the metal case 1. The trapezoidal portion 8a has an inner end engaged with a step 1a formed on the metal case 1, and the opening of the metal case 1 is opened. A portion 1b protruding from the end of the insulating bushing 8 is bent toward the central axis to prevent the insulating bushing 8 from moving inward and outward. Reference numeral 9 denotes a second lead wire penetrating the central hole of the insulating bushing 8, which has a fixed contact 10 which contacts the movable contact 7 at its inner end and which is adjacent to the inside and outside of the insulating bushing 8. The enlarged portions 9a and 9b are provided in the portions to prevent the second lead wire 9 from moving outward and inward. A weak compression spring 11 is interposed between the movable contact 7 and the insulating bushing 8 and is in a steady state compressed by the strong compression spring 6. Reference numeral 12 is a sealing resin made of epoxy resin or the like attached to the outer surface of the insulating bushing 8. Reference numeral 13 is an insulating cylinder made of ceramic or the like, which is provided as necessary to increase the creepage distance between the metal case 1 and the second lead wire 9.

In the above structure, the temperature-sensitive pellet 3 is solid at room temperature, and the strong compression spring 6 resists the elastic force of the weak compression spring 11 to press the movable contact 7 against the fixed contact 10 strongly. .. Therefore, in the path of the first lead wire 2-metal case 1-movable contact 7-fixed contact 10-second lead wire 9, both lead wires 2 and 9 are held in a conductive state.

When the ambient temperature abnormally rises and reaches the melting point of the temperature sensitive pellets 3, the temperature sensitive pellets 3 are melted, and therefore the strong compression springs 6 expand and their elastic force disappears. As it extends, the movable contact 7 separates from the fixed contact 10 as shown in FIG. 4, and the lead wires 2 and 9 are brought out of conduction.

By the way, when manufacturing the thermal fuse, the metal case 1 in which the first lead wire 2 is caulked and fixed
Is supported in an upright state with the first lead wire 2 on the lower side, and the temperature sensitive pellet 3, the pressing plate 4, the strong compression spring 6, the pressing plate 5, and the movable contact are opened from the upper end opening in the metal case 1. 7,
The weak compression springs 11 are sequentially inserted. On the other hand, the second lead wire 9 is inserted into the insulating bushing 8 to be integrated,
Following the weak compression spring 11, an insulating bushing 8 is fitted into the opening of the metal case 1, and the portion 16 of the metal case 1 that extends beyond the insulating bushing 8 is caulked toward the central axis to fix the insulating bushing 8. .. Subsequently, as shown in FIG. 5, a fluid sealing resin 12 is supplied to the upper surface of the insulating bushing 8, and the insulating cylindrical body 13 is inserted into the second lead wire 9 before the sealing resin 12 is cured, Sealing resin 12
Press on. Then, the sealing resin 12 rises through the gap between the second lead wire 9 and the insulating cylindrical body 13, and the insulating cylindrical body 13
A part of the thermal fuse is discharged to the upper part of the to obtain a thermal fuse as shown in FIG.

[0008]

By the way, the purpose of the sealing resin 12 is to press the pressing plates 4, 5, the compression springs 6, 11, the movable contacts 7, which are incorporated in the metal case 1.
The purpose is to shield and protect the metal parts such as the fixed contact 10 and the temperature sensitive pellets 3 from the outside air.

That is, under the condition that each of these parts is not hermetically sealed, the metal part is oxidized and electrical reliability cannot be ensured, and the temperature sensitive pellet 3 may absorb moisture depending on its material. Depending on the deliquescence, some show sublimation with a slight temperature rise, and this phenomenon results in no abnormal temperature rise around the thermal fuse.
Further, the temperature fuse malfunctions even though the ambient temperature does not reach the melting point of the temperature sensitive pellet 3.

Therefore, in order to hermetically seal the thermal fuse, as the sealing resin 12, a two-component mixed room temperature curing type epoxy resin, which is usually a mixture of a main component and a curing agent, is used, and reliability such as airtight adhesiveness is obtained. Has been secured for a long time.

However, in the thermal fuse as shown in FIG. 3 used for home electric appliances and industrial products, in addition to the cooling and heating cycle even during normal use, the heat resistance guarantee limit in continuous use of epoxy resin at high temperature use It may be used near the temperature of 150 to 160 ° C., or may be exposed to a temperature below zero when not used.

As a result, if the product is used for a long period of time,
The adhesive surface of the sealing resin 12 and the portion 1b protruding from the insulating bushing 8 at the opening end of the metal case 1 is affected by thermal stress, and finally peeling occurs at this boundary surface, resulting in loss of airtightness and temperature sensing. The pellet 3 is adversely affected, and the thermal fuse malfunctions.

On the other hand, as a result of mechanical stress impairing the airtightness of the sealing resin portion, malfunction may occur even at a relatively early stage when the thermal fuse is used. That is, the thermal fuse is generally attached by bending or cutting the lead wires 2 and 9 when it is attached to a set of home electric appliances or industrial products, and in particular, cutting or bending of the second lead wire 9 is performed. When processing is performed, bending stress is applied to the joint surface of the sealing resin 12 and the portion 1b protruding from the insulating bushing 8 at the opening end of the metal case 1, so that when the stress exceeds the adhesive strength of this portion, the joint surface is Since the exfoliation of the thermal fuse causes the same adverse effect as the result caused by the thermal stress described above, the thermal fuse malfunctions even when there is no abnormal temperature rise in the use atmosphere at a relatively early stage of use. It will cause it.

Therefore, according to the present invention, even if the joint surface of the sealing resin 12 and the portion 1b protruding beyond the insulating bushing 8 at the opening end of the metal case 1 is cracked due to thermal or mechanical stress, it is still airtight. It is an object of the present invention to provide a method for manufacturing a thermal fuse, which maintains its reliability and can secure reliability for a long period of time.

[0015]

According to the present invention, as means for achieving the above object, the outer circumference and outer end surface of a trapezoidal portion of an insulating bushing made of ceramic or the like for closing the open end of a metal case are made of silicone rubber, polyurethane or polypropylene. Provided is a method of manufacturing a thermal fuse, which is covered with an integrally formed cap-shaped packing member made of an insulating and heat-resistant material such as, and is further sealed with an epoxy resin or the like.

[0016]

By interposing a cap-like packing member made of an insulating and heat-resistant material between the opening end of the metal case and the insulating bushing, it is possible to firmly fix it mechanically and maintain airtightness. Further, by sealing with an epoxy resin or the like, the airtightness between the metal case and the insulating bushing can be made a double structure, and the reliability is remarkably improved.

[0017]

FIG. 1 and FIG. 2 show an embodiment according to the present invention.
A description will be given with reference to (a) and (b). However, the parts described in the related art are given the same reference numerals and the description thereof will be omitted.

First, as shown in FIG. 1, a temperature sensitive pellet 3, a pressing plate 4, and a strong plate 4 are placed from the upper end opening thereof in a metal case 1 which is supported upright with the first lead wire 2 caulked and fixed downward. The compression spring 6, the pressing plate 5, the movable contact 7, and the weak compression spring 11 are sequentially inserted, and then the insulating bushing 8 in which the second lead wire 9 is integrated is fitted into the upper end opening of the metal case 1.

The outer peripheral surface and the outer end surface of the trapezoidal portion 8a of the insulating bushing 8 in which the lead wire 9 is integrated are shown in FIG.
As shown in (a) and (b), it is previously covered with an integrally formed cap-shaped packing member 14 made of a material such as silicon rubber, polyurethane, or polypropylene.
This is designed to be closely fitted to the inner peripheral surface of the open end of the metal case.

After that, the insulating bushing 8 of the metal case 1
The insulating bushing 8 is fixed by caulking the portion 16 protruding beyond the central axis toward the central axis. At this time, since the cap-shaped packing member 14 interposed between the upper opening of the metal case 1 and the insulating bushing 8 is mechanically tightened,
It has a role as a packing material and has a sealing effect at this interface.

Subsequently, a fluid sealing resin 12 is supplied to the upper surface of the insulating bushing 8, and the insulating cylindrical body 13 is inserted into the second lead wire 9 before the sealing resin 12 is cured.
It is pressed against the sealing resin 12. Then, the sealing resin 12 rises through the gap between the second lead wire 9 and the insulating cylindrical body 13, flows out to the upper part of the insulating cylindrical body 13, and opens at the upper end of the metal case 1 with respect to the thermal fuse shown in FIG. A similar thermal fuse as shown in FIG. 1 is obtained except that a cap-shaped packing member 14 is interposed between the portion and the insulating bushing 8.

[0022]

According to the present invention, a cap-shaped packing member made of an insulating and heat-resistant material is interposed between the upper opening of the metal case and the insulating bushing, so that the metal case is firmly fixed. In addition, since the airtightness is maintained and the upper portion is sealed with epoxy resin or the like to form a double seal structure, the second lead wire is cut or bent at the joint portion of the sealing resin and the metal case. Even if mechanical stress is applied due to heat, or if thermal stress is applied during use of the thermal fuse and cracks occur, the sealing part is kept airtight by the packing material, so it is installed in the metal case. The metal parts are not oxidized and the pellets are not adversely affected, and therefore malfunction-free long-term reliable temperature heat It is possible to production of over's.

[Brief description of drawings]

FIG. 1 is an overall sectional view of a thermal fuse of an embodiment according to the present invention.

FIG. 2A is a sectional view of a main part, and FIG. 2B is a perspective view of the packing member.

FIG. 3 is an overall cross-sectional view showing an example of a thermal fuse

FIG. 4 is a cross-sectional view showing a state after the operation of the thermal fuse.

FIG. 5 is a sectional view showing a state in which the thermal fuse is being manufactured.

[Explanation of symbols]

 1 Metal Case 2 First Lead Wire 3 Temperature Pellets 4,5 Pressing Plate 6 Strong Compression Splash 7 Moving Contact 8 Insulating Bushing 9 Second Lead Wire 10 Fixed Contact 11 Weak Compression Spring 12 Sealing Resin 13 Insulation Cylindrical Body 14 Packing material

Claims (2)

[Claims] 1. A first lead wire is caulked and fixed to an opening of one end of a metal case, and a temperature sensitive pellet, a strong compression spring, a movable contact, a weak compression spring and an inner end of the movable contact are fixed in the metal case. The second case of the metal case which houses the insulating bushing in which the second lead wire having the fixed contact to be contacted is inserted
In a method of manufacturing a thermal fuse in which the other end opening from which the lead wire of the above is led out is sealed with a sealing resin, prior to sealing with the sealing resin, the upper surface and outer peripheral surface of the insulating bushing are cap-shaped made of an insulating and heat-resistant material. A method for manufacturing a thermal fuse, which is characterized in that it is covered with the packing member of. 2. A method for manufacturing a thermal fuse, wherein the packing member according to claim 1 is made of silicone rubber, polyurethane, or polypropylene.