JPH0374026A - Alloy type temperature fuse - Google Patents

Abstract

PURPOSE:To evade deformation such as waving and twisting of a fuse element even if it is unevenly heated by generation heat at the time of ordinary operation of an equipment by using a substance having a composition causing no crystal transformation of low melting point soluble alloy at a temperature between a heating temperature at the time ordinary operation and a temperature at the time of an operation stop of the equipment. CONSTITUTION:In the temperature range from a heating temperature at an ordinary operation time to a temperature at the time of an operation stop time, a low melting point soluble alloy having a stable crystal type and no crystal transformation is used for a fuse element. For instance, no crystal transformation is caused when an alloy consisting of tin: 48wt.%, lead: 18wt.%, indium: 34wt.% is used for the fuse element, and a ceramic is fused for an insulated substrate, while epoxy resin is used for a resin mold layer. Thereby, even if temperature distribution is uneven, only simple crystal constitution can be taken, no twisting and waving of the fuse element can be caused.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an alloy type temperature fuse using a low melting point fusible alloy for the fuse element.

<Prior art> In an alloy type temperature fuse, a piece of a low melting point fusible alloy is bridged between the lead conductors, a flux is applied to the piece of the low melting point fusible alloy, and this flux coated piece of alloy is covered with an insulating cover or the like. It is used by attaching it to the electrical equipment to be protected. The melting point of the low melting point fusible alloy flakes is set to the allowable temperature of the equipment, and when the equipment heats up due to overcurrent and reaches the allowable temperature, the low melting point fusible alloy flakes melt and reach the equipment. This prevents thermal damage to the equipment.

As is well known, the allowable temperature of equipment varies depending on the heat resistance class of the insulating material used, and therefore a low melting point alloy with a melting point corresponding to such allowable temperature is required. The main requirements for low melting point alloys used in fuse elements of temperature fuses are the above-mentioned melting point, and in addition, the temperature difference between the liquidus temperature and the solidus temperature must be zero (eutectic point) or small;
Additional features such as excellent mechanical workability such as extrudability, rollability, wire drawability, and punchability, low electrical resistance, high surface tension, and excellent impact resistance. requirements are required. However, it is actually extremely difficult to satisfy all of these incidental requirements, and some degree of compromise is unavoidable.

By the way, the crystalline shape of metals changes in various ways depending on the temperature due to its electronic structure, and even in the above-mentioned low-melting-point fusible alloy, the crystalline shape changes depending on the alloy composition. becomes perverted. Conventionally, the test item for alloy-type temperature fuses is to measure changes in the characteristics of the temperature fuse by increasing the temperature at a rate of 1°C/min from a temperature approximately 20°C lower than the fuse blowing temperature in an air oven. is required. According to such tests, even when a low melting point fusible alloy having a composition that exhibits crystal transformation in such a temperature range is used in a fuse element, no particular change in characteristics is shown.

However, when the present inventors conducted experiments by actually installing thermal fuses in electrical equipment, it was found that the fuse element was Abnormalities such as twisting and waving were observed. The reason for this is that in the case of the experiment in the air oven, the internal stress generated during crystal transformation is uniform because the fuse element is uniformly heated, and the strain is also uniform. When actually measuring equipment dimensions, the fuse element is heated unevenly in the lengthwise or circumferential direction, so the strain that occurs during crystal transformation is unevenly generated in the lengthwise or circumferential direction. become,
It is estimated that the fuse element becomes wavy or twisted.

An object of the present invention is to provide a temperature fuse that can avoid deformation such as waving or twisting of the fuse element even if the fuse element is unevenly heated by the heat generated during normal operation of the device.

Means for Solving the Problems> The alloy type temperature fuse according to the present invention uses a low melting point fusible alloy for the fuse element, and the fuse element is heated in the circumferential direction or longitudinal direction by the heat generated during normal operation of the equipment to be protected. In a temperature fuse that is heated unevenly to
This structure is characterized by using a low melting point fusible alloy having a composition that does not cause crystal transformation at a temperature between the heat generation temperature during normal operation of the equipment and the temperature when the equipment is stopped.

The temperature fuse of the present invention is based on the precondition that the fuse element is heated non-uniformly in the circumferential or longitudinal direction by the heat normally generated by the equipment to be protected. It is essential to use a low melting point fusible alloy for the fuse element, which has a stable crystal form and does not undergo crystal transformation in the temperature range from the temperature at which the equipment generates heat during normal operation to the temperature at which the equipment is stopped. As a result, although some of the above-mentioned incidental requirements are sacrificed, there is an advantage that disconnection due to twisting, waving, etc. of the fuse element caused by crystal transformation can be prevented.

The temperature fuse to which the present invention is applied is one that is asymmetrical in thermal resistance front and back, left and right, or up and down, and whose fuse element is heated non-uniformly in the longitudinal direction or circumferential direction. Figure 1 and Figure 2 (
As shown in Fig. 1 (cross-sectional view of Fig. 1), a pair of membrane electrodes 2, 2 are provided on one side of the insulating substrate 1, and lead conductors 3, 3 are connected to each membrane electrode 2, 2. This can be applied to a structure in which a linear low melting point fusible alloy piece 4 is bridged over the alloy piece, a flux 5 is applied on the alloy piece, and a resin mold insulating layer 6 is provided on one side of an insulating substrate. is asymmetrical in the front and back with respect to the line Eii, and is asymmetrical in the vertical direction with the line R00 as a reference. As the low melting point fusible alloy piece, in addition to a wire having a circular cross section, it is also possible to use a piece having an oval cross section, an elliptical needle, or a rectangular cross section without etching.

The temperature fuse according to the present invention is used by being attached to a device, and if the allowable temperature of the device is T1'C, the melting point is approximately T8℃, and the heat generation temperature of the device during normal operation is T.
2 (usually T1℃ - 40℃) to the operating shutdown temperature, an alloy composition with a stable crystalline form without crystal transformation is selected, taking into consideration mechanical workability, electrical resistance, surface tension, impact resistance, etc. do.

The present invention explains that if a fuse element made of a low melting point fusible alloy is heated uniformly in the circumferential direction and length direction, the temperature between the heat generation temperature during normal operation of the equipment and the temperature when the equipment is stopped is The alloy composition can be selected without being constrained by the stability of the crystal structure of the alloy in the temperature range, and only if the heating of the above fuse element is non-uniform, it is possible to select a stable crystal structure that does not exhibit crystal transformation in the above temperature range. The key is to select an alloy with the same composition. In other words, if an alloy with a composition that takes α, β, etc. crystal forms depending on the temperature is used in the fuse element, even if the temperature of the fuse element changes, if the temperature distribution of the fuse element is uniform, the crystal distribution will be maintained. However, if the temperature distribution is uneven, alpha crystals will form in some areas and beta crystals will form in other areas, resulting in an uneven crystal distribution. However, even if the temperature distribution is uneven, if only a single crystal structure is possible, crystal transformation may occur. Twisting, corrugation, etc. cannot occur.

<Description of Examples> Example In the above-mentioned substrate type temperature fuse, the fuse element contains tin: 48% by weight, lead: 18% by weight, and indinium:
An alloy consisting of 34% by weight was used, ceramic was used for the insulating substrate & M, and epoxy resin was used for the resin mold layer. The liquidus temperature of this alloy is about 130°C,
No crystal transformation occurs.

Comparative Example The same procedure as Example #1 was used except that an alloy consisting of 35% by weight of tin, 15% by weight of lead, and 50% by weight of indium was used for the fuse element. It takes the crystal form of β.

For each of the above-mentioned actual height measurement and comparative height measurement, a heat cycle test was conducted by turning on and off the current flowing with the temperature fuse having a maximum temperature of 100°C.

When the fuse element was subjected to X-ray inspection at the 100th cycle, twisting and waving were observed in the comparative height measurement, but no abnormality was observed in the actual height measurement.

<Effects of the Invention> As described above, according to the alloy type temperature fuse according to the present invention, damage to the fuse element caused by crystal transformation of the fuse element made of a low melting point fusible alloy can be avoided, and the reliability of the alloy type temperature fuse can be improved. You can exalt yourself.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention, and FIG.
It is a sectional view of ■ to ■ in the figure. 4.--Low melting point fusible alloy

Claims (1)

[Claims] In thermal fuses, in which a low melting point fusible alloy is used for the fuse element, and the fuse element is heated unevenly in the circumferential or longitudinal direction by the heat normally generated by the equipment to be protected, the low melting point fusible alloy is An alloy-type thermal fuse characterized by using a composition that does not cause crystal transformation at a temperature between the temperature at which heat is generated during normal operation and the temperature at which operation is stopped.