JPH04259720A - Alloy-type temperature fuse - Google Patents

Abstract

PURPOSE:To speed up operation of a temperature fuse made of a low melting point fusible alloy by using a fuse element having a remaining flash formed at the molding time. CONSTITUTION:A fuse element 2 is made of a low melting point fusible alloy bridge over leads 1 and flashes 21 are formed at two points in the circumferential direction of the fuse element 2. When over current caused in an electric circuit runs in the element 2 and the temperature of the element 2 rises, liquefaction proceeds from the center part to both end parts and at the same time liquefaction is carried out along the flashes 21 since the thermal capacity of the flashes 21 is small. Since the molten metal forms a sphere owing to the surface tension of the metal, the metal in the center part is cut. In this way, liquefaction of the fuse element is accelerated by the flashes 21 and thus the fuse operation can become speedy.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloy type thermal fuse.

0002

[Prior Art] In an alloy type thermal fuse, a piece of a low melting point fusible alloy is bridged between the lead conductors, and a flux is applied onto the piece of the low melting point fusible alloy. The molten alloy flakes are hermetically surrounded by an insulating case or an insulating coating layer.

The operating mechanism of this alloy type thermal fuse is that when the electrical equipment protected by the thermal fuse generates heat due to overcurrent, the thermal fuse is heated by the generated heat. A low-melting-point fusible alloy piece melts, the molten metal is divided into spheroids based on the surface tension of the molten metal, and the distance between the shards allows the gap between the shards to block the ground between the slits as the spheroidization progresses after the sharding. When this point is reached, the current flow is virtually cut off.

0004

[Problem to be Solved by the Invention] The alloy type thermal fuse has a short time from when an electric device generates heat due to overcurrent until the current is actually cut off, that is, it has excellent operation speed. This is an essential requirement.

[0005] However, the inventor of the present invention has found that allowing burrs to substantially remain on the fuse element is extremely effective in improving the operating speed of a thermal fuse.

For example, In-Sn-Bi with a melting point of 112°C
Alloy mold temperature that uses a fuse element made by compressing a linear body of alloy with an outer diameter of 0.7 mm in a two-split mold and forming burrs with a height of 0.1 mm and a width of 0.1 mm in two places. Each of the alloy-type thermal fuses, which uses a fuse element that does not form fuses and burrs, is immersed in silicone oil maintained at 120°C, and the temperature from immediately after immersion until the fuse element blows is immersed. When the time was measured, it was found that the time T can be shortened by about 20% in the case where burrs were formed, compared to the case without burrs, and the speed of operation could be dramatically improved.

Based on this knowledge, the object of the present invention is to dramatically improve the operating speed of an alloy type thermal fuse by simple means.

[0008]

[Means for Solving the Problems] The alloy type thermal fuse of the present invention is characterized in that it uses a fuse element formed from a low melting point fusible alloy, with burrs remaining during forming. It is the composition.

[0009]

[Embodiments] Hereinafter, embodiments of the present invention will be explained with reference to the drawings. FIG. 1 is an explanatory diagram showing an embodiment of the present invention, and FIG. 2 is a sectional view taken along line II-II in FIG.

In FIGS. 1 and 2, 1 and 1 are a pair of lead conductors. Reference numeral 2 designates a fuse element which is bridged by welding between the lead conductors 1 and 1, and is formed from a piece of a low melting point fusible alloy, and has burrs 21, 21 formed at two locations 1800 mm apart in the circumferential direction. There is. 3 is a flux layer coated on the fuse element 2. 4 is a cylindrical insulating case
The fuse element 2 is inserted through the fuse element 2. Reference numerals 5 and 5 designate an adhesive, such as an epoxy resin, for sealing between the cylindrical insulating case 4 and each lead conductor. In the above, the height and width of the burr 21 are 5 to 30% of the fuse element diameter.

In the fuse element 2 of the above-mentioned alloy type thermal fuse, Joule heat is generated by the current flowing under normal conditions, and the lead wire 1 is connected at both ends of the fuse element 2. Because of the heat dissipation through the fuse element 2, the temperature at the center of the fuse element 2 is higher than the temperature at both ends of the fuse element.

However, in the above-mentioned alloy type thermal fuse, when the electrical equipment to be protected generates heat due to overcurrent, and the temperature of the fuse element 2 rises due to the heating of the thermal fuse, the above-mentioned The center surface of the fuse element, which is a high temperature area under normal conditions, becomes the highest temperature area and becomes liquid phase first. Normally (if there is no burr on the fuse element), this liquid phase progresses gradually from the center of the fuse element to the ends, but in the presence of the burr described above, this burr Because the heat capacity of the burr is small, the temperature of the burr rises rapidly and turns into a liquid phase, so the liquid phase takes priority along this burr, and after the burr turns into a liquid phase, as shown in Figure 3 (the dotted area shows the liquid phase). As shown in Figure 2), the liquid phase a from the center of the fuse element toward both ends and the liquid phase b from the burr toward the circumferential direction of the fuse element proceed simultaneously, and the entire liquid phase progresses. go.

On the other hand, as the surface of the fuse element turns into a liquid phase, the liquid phase towards the center (inside) of the fuse element also progresses, and the liquid phase reaches the center at the center of the fuse element. occurs first, and in this case, the lead conductor and the center of this liquefied fuse element are connected in a liquid phase due to the early liquefaction of the burr, so this liquefaction occurs. Interfacial energy E12 (tension) acting between the metal and the lead conductor (copper) is transmitted to the center of the fuse element through the liquid phase, and this interfacial energy E12 and the surface energy of the liquid phase itself -E2, a breaking force acts on the center of the fused fuse element, and as a result, the fuse element slowly breaks apart.

On the other hand, when there is no burr in the fuse element, even if the liquid phase reaches the center of the fuse element, the liquid phase does not occur in the vicinity of the lead conductor. The portion in the vicinity becomes liquid phase at a later time, and the interfacial energy E12 is delayed in acting on the center portion of the fuse element, thereby slowing down the disconnection of the fuse element.

[0015]The alloy type thermal fuse of the present invention, in which burrs remain on the fuse element, operates more quickly than the conventional alloy type thermal fuses that do not have burrs. Are better.

[0016] This can also be confirmed by comparing the following examples and comparative examples. Example: An In-Sn-Bi eutectic alloy wire (melting point: 112°C) with a diameter of 0.7 mm and a length of 6.0 mm is pressurized with a mold that is divided into two halves to form two parts on the outer periphery separated by 1800 mm. It was molded into a fuse element with a diameter of 0.68 mm and a burr of 0.1 mm and width of 0.1 mm. This fuse element is bridged by welding between a pair of copper lead conductors with a diameter of 0.7 mm, a flux containing rosin as a main component is applied to this fuse element, and a flux with an inner diameter of 1 mm is applied onto the fuse element. 5mm, thickness 0.
A 3 mm ceramic cylinder was inserted, and the space between the ceramic cylinder and each lead conductor was sealed with an epoxy resin adhesive.

[0017] Comparative Example I used in the example with a diameter of 0.7 mm and a length of 6.0 mm.
An n-Sn-Bi eutectic alloy wire was used as the fuse element, and no burrs were formed. Other than this, it was the same as the example.

[0018] Fifty pieces each of the above examples and comparative examples were manufactured, and each of them was immersed in silicone oil maintained at 120°C, and after being immersed in silicone oil while applying a current of 2A, the fuse element was When we measured the time until it melted, in the example product,
The average time was 2.20 seconds, whereas in the comparative example product it was 2.8 seconds.

The fuse element used in the present invention can also be produced by a die casting method using a two-piece casting mold.

Generally, eutectic alloys are used as low melting point fusible alloy pieces, but non-eutectic alloys can also be used; in this case,
It is preferable to use a composition in which the difference between the liquidus line and the solidus line is within 5°C.

In addition to the case type described above, the alloy type thermal fuse of the present invention has an insulating resin mold type (leads parallel to each other).
A fuse element is bridged to the tip of the lead conductor, and the fuse
Fuse is applied to the fuse element and this flux coated fuse element is molded with hardening resin), board type (a pair of layered electrodes is provided on one side of an insulated substrate,
A fuse element is bridged between these electrodes, a lead conductor is connected to each electrode, flux is applied to the fuse element, and one side of the insulating board is molded with a hardening resin. It can also be applied to coated items).

[0022]

Effects of the Invention The alloy-type thermal fuse of the present invention has the structure as described above, and the burr of the fuse element formed from a low-melting point fusible alloy wire material etc. makes the alloy-type thermal fuse operate quickly. The burr of the fuse element is actively used to improve the operability of the alloy type thermal fuse. Further, deburring work is not required, which is advantageous in terms of manufacturing efficiency.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II in FIG. 1;

FIG. 3 is an explanatory diagram showing the effect of burrs on the fuse element of the present invention.

[Explanation of symbols]

1 Lead conductor 2 Fuse element 21 Bali

Claims (1)

[Claims] 1. An alloy-type thermal fuse characterized by using a fuse element formed from a low melting point fusible alloy, with burrs remaining during forming.