JP2003147461A - Thermal fuse - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alloy thermal fuse which is free from lead and cadmium causing environmental problems and has excellent operation reliability at 140 to 150 deg.C. SOLUTION: This thermal fuse is a fusible-alloy-type thermal fuse using low-melting alloy as a thermosensor, and the alloy composition of the fusible alloy is: a composition consisting of 50 to 58 wt.% Bi, 4 to 7 wt.% Sb and the balance Sn; and a composition in which 0.1 to 1.1 pts.wt. of Cu is added to 100 pts.wt. of the above alloy or 0.1 to 2.6 pts.wt. of Ag is added.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature fuse using a low melting point fusible alloy in which an element of a protective element melts at a specific temperature.

[0002]

2. Description of the Related Art As a protective element for protecting electric and electronic devices from overheat damage, a thermal fuse which operates at a specific temperature and interrupts a circuit is used. Especially in this temperature fuse, the fusible alloy type thermal fuse uses a low melting point alloy that melts at a specific temperature as a temperature sensitive material to be an element, and the low melting point alloy is energized to have a low melting point due to an excessive rise in ambient temperature. The alloy melts and breaks the circuit.

Further, it comprises a low melting point alloy and a resistor,
There is also a protective element called a resistance built-in type thermal fuse that forcibly blows out the low melting point alloy by heating the resistor with electricity.

The fusible alloy type thermal fuse is used as a protective element in heat insulating kotatsu, home electric appliances such as rice cookers, OA equipment such as liquid crystal televisions and copying machines, and lighting equipment. Among these, the conventional 50Sn-32Pb-18Cd (wt.%) Ternary alloy (145 ° C) is used as the fusible alloy with an operating temperature range of 145 ± 5 ° C.
10w of lead and cadmium which are heavy metals harmful to human body
The content was t.% or more. Moreover, since it is difficult to disassemble the above-mentioned home electric appliances and OA equipment into these assembled parts, harmful metals are eluted from the electrical and electronic equipment that has been recently discarded by the action of rainwater and soak into groundwater. Contamination has become a global environmental problem and needs improvement.

By the way, the fusible alloy of the thermal fuse preferably has a eutectic alloy composition having a single melting point, because it is necessary to be spherically fused at a specific temperature. 140 of the temperature range
It is known that 43Sn-57Bi (wt.%) Binary eutectic (139 ° C) is a eutectic composition that does not contain Pb and Cd in the vicinity of 150 ° C, but the melting temperature is a little too low.
It cannot be used as a thermal fuse. Also, Sn-Bi
The eutectic alloy may contain 57% of Bi, which is a semimetal, has a relatively brittle property, and has many processing restrictions.

With a composition other than the eutectic composition, the alloy begins to melt at a temperature above the solidus temperature and completely melts into a liquid at the liquidus temperature. The difference between the solidus temperature and the liquidus temperature at this time is called the solid-liquid coexistence region.In order to melt the thermal fuse at a constant temperature without variation, select an alloy composition with the smallest possible solid-liquid coexistence region. It is important to. In practice,
The fusible alloy of the thermal fuse is required to have a solid-liquid coexistence region of less than 5 ° C.

In addition to the above, due to the characteristics of the thermal fuse mounted in series with the power supply circuit, the internal resistance value of the thermal fuse does not change even after long-term high temperature storage and is 10 mΩ or less, which is an energy saving aspect. It is also desirable from the standpoint of stability of operating temperature.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide an environment-friendly fusible alloy type thermal fuse in which Pb and Cd are not used in the fusible alloy. To do.

[0009]

A fusible alloy type thermal fuse according to claim 1 of the present invention contains Bi in an amount of 50 wt% to 58 in a temperature sensitive element.
By using a fusible alloy of wt%, Sb of 4 wt% to 7 wt%, and the balance of Sn, a thermal fuse having an operating temperature of 140 to 150 ° C. is possible.

The present invention is based on a Sn-Bi binary alloy system having a melting point of about 140 ± 2 ° C. near the 43Sn-57Bi (wt.%) Binary eutectic point, to which an appropriate amount of Sb is added to form a triple alloy. The use of the original alloy is characterized in that the melting temperature can be raised to around 145 ± 2 ° C. while suppressing the width of the solid-liquid coexistence region.

At this time, an appropriate amount of Sb is 4 wt% to 7 wt%
Is the range. In other cases, for example, the amount of Sb is 3 wt%
The solid-liquid coexistence range of the alloy composition was about 7 ° C., and it was not possible to expect stable fusing as a temperature fuse fusible alloy. Further, with an alloy composition containing Sb in excess of 7 wt%, which is the solid solubility limit of Sb with respect to Sn, the alloy became extremely hard and brittle, and fine wire processing was difficult.

Cu may be added to the above-mentioned fusible alloy within the range described in claim 2 without impairing the operating temperature for the purpose of improving the plastic workability of the wire and reducing the internal resistance.

It is also possible to add Ag to the above-mentioned fusible alloy within the range described in claim 3 without impairing the operating temperature for the purpose of improving the plastic workability of the wire and reducing the internal resistance.

Cu and Ag for the base alloy according to claim 1
Comparing the effects of addition, the effects of improving the plasticity of the base alloy and reducing the internal resistance can be obtained, but Cu has a remarkable effect of improving the plastic workability of the wire, while Ag has the effect of increasing the internal resistance of the wire. It was found that the effect of reducing was superior.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention can be applied to an axial type thermal fuse, a radial type thermal fuse, a thin type thermal fuse, a resistor built-in type fuse, etc., and is not limited to a specific type, but the following embodiments will be described. As an example, an embodiment of an axial type thermal fuse will be described.

FIG. 1 shows an embodiment of a thermal fuse,
It is sectional drawing of an axial type thermal fuse. In FIG. 1, the reference numerals and their member names are as follows. 1, 2: Terminal lead (Sn-Cu plated copper wire) 3: Soluble alloy 4: Flux (rosin, wax, activator) 5: Insulator case (alumina ceramic insulator tube) 6, 7: Sealing resin (epoxy resin)

In the embodiment, the fusible alloy 3 is joined to the terminal leads 1 and 2 made of Sn-Cu-plated copper wire by resistance welding, and then the fusible alloy 4 is made of rosin, wax and an activator flux. It can be formed by covering with 4 and inserting it into an alumina ceramic porcelain tube 5 and sealing the case end with epoxy-based sealing resins 6 and 7. In addition, Sn-Cu of terminal leads 1 and 2
The plated copper wire can be changed to an Ag-plated copper wire, a Sn-plated copper wire, a Ni-plated copper wire, etc., if necessary, and is not limited to the Sn-Cu-plated copper wire.

In the thermal fuse of the above-mentioned embodiment, the fusible alloy 3 can use a wire of φ0.3 to 0.7 mm, and if necessary, a rectangular piece of tape-shaped alloy having the same cross-sectional area can also be used.

The thermal fuse-fusible alloy of the present invention can be produced by extruding an alloy ingot, and then rolled into a tape if necessary.

Further, the wire diameter of the fusible alloy 3 can be set to φ0.3 or less according to the requirement and changed to φ0.7 mm or more according to the requirement without departing from the scope of the present invention in the future. You can also do it.

[0021]

(Example) (Example 1) 52.1 for Bi within the scope of claim 1
A φ0.6 mm wire having a composition of wt%, Sb of 4.9 wt% and Sn of 43 wt% was produced by extrusion, and this alloy wire was applied to the thermal fuse of the embodiment. 30 thermal fuses of Example 1
When operating in a thermostatic chamber (gas phase) in which the temperature rises at a rate of 1 ° C / min while applying a detection current of 10 mA, the operating temperature range was 145 ± 2 ° C. Also, at 135 ℃ for 500 hours, 1000
Each of the 10 thermal fuses of Example 1 stored for 20 hours and 2000 hours was tested, and it was possible to maintain the internal resistance value range of 5 ± 2mΩ and maintain the initial range of operating temperature of 145 ± 2 ℃ even after high temperature storage. all right.

(Example 2) The alloy 100 according to claim 1
A φ0.6 mm wire having a composition in which 1 part by weight of Cu was added to parts by weight was produced by extrusion, and this alloy wire was applied to the thermal fuse of the embodiment. When 30 thermal fuses were evaluated in the same manner as in Example 1, it was found that the internal resistance value could be lowered to 4 ± 1 mΩ without changing the operating temperature range.
Furthermore, as a result of detailed examination of the Cu addition amount, when the Cu addition amount is within the range of 0.1 to 1.1 parts by weight with respect to 100 parts by weight of the alloy of claim 1, the internal resistance value is changed without changing the operating temperature. Could be lowered.

(Example 3) The alloy 100 according to claim 1
A φ0.6 mm wire having a composition in which 0.5 parts by weight of Ag was added to parts by weight was produced by extrusion, and this alloy wire was applied to the thermal fuse of the embodiment. When 30 thermal fuses were evaluated in the same manner as in Example 1, it was found that the internal resistance value could be lowered to 3.5 ± 0.5 mΩ without changing the operating temperature range. Furthermore, as a result of detailed examination of the addition amount of Ag, the addition amount of Ag was 0.1 to 2.6 with respect to 100 parts by weight of the alloy of claim 1.
When it was within the range of parts by weight, the internal resistance value could be lowered without changing the operating temperature.

[0024]

[Comparative Example] Alloy composition with Sb content of 4 wt% or less: 53Bi-44
The thermal fuse of the embodiment using Sn-3Sb was unstable in the operating temperature range of 137 to 146 ° C. and could not reach a practical thermal fuse. Further, the composition in which the amount of Sb is 7 wt% or more: 5
An attempt was made to extrude a φ0.6 mm wire of 0Bi-42Sn-8Sb by extrusion, but it could not be made because it was too hard.

[0025]

As described above, the present invention provides 140
An alloy type thermal fuse with excellent reliability that can operate at up to 150 ° C is realized with an alloy containing no Pb or Cd.

[0026]

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an axial type thermal fuse that is an embodiment of the present invention.

[Explanation of symbols]

1 and 2 terminal leads 3 Soluble alloy 4 flux 5 Insulation case 6, 7 sealing resin

Claims (3)

[Claims] 1. [Schott1] A terminal lead is connected to both ends of a fusible alloy, the terminal lead is inserted into the case of an insulating material and the terminal lead is led out from the case of the insulating material. In the sealed thermal fuse, 50 wt.% To 58 wt.% Of Bi is added to the fusible alloy.
%, Sb is 4 wt.% To wt.% 7, and the balance is a temperature fuse characterized by using an alloy having a composition of Sn. 2. A terminal lead is connected to both ends of a fusible alloy, the terminal lead is inserted into the case of an insulating material, and the end portion for leading out the terminal lead from the case of the insulating material is sealed. In the thermal fuse consisting of 50 wt.% To 58 wt.% Bi and 4 wt.
% To 7 wt.% And 0.1 to 1.1 parts by weight of Cu added to 100 parts by weight of an alloy having a composition of Sn as the balance, a temperature fuse characterized in that it is used. 3. A terminal lead is connected to both ends of a fusible alloy, the terminal lead is inserted into a case of an insulating material, and an end portion for leading out the terminal lead from the case of the insulating material is sealed. In the thermal fuse consisting of 50 wt.% To 58 wt.% Bi and 4 wt.
% To 7 wt.% And 0.1 to 2.6 parts by weight of Ag added to 100 parts by weight of alloy having a composition of Sn, the temperature fuse being characterized by using.