US3710297A - A stretched fuse device - Google Patents

Abstract

A stretched fuse device comprising a brass wire made of 45 to 48 percent of zinc and copper as the remainder with a Beta phase accounting for more than 90 percent of said alloy, said fuse being stretched in introducing electric current therethrough, wherein the cutoff of said fuse enables, if necessary, either or both of the closure of an alarm circuit and the indication of said cutoff to be effected.

Description

United States Patent 1191 Kawazoe [54] STRETCHED FUSE DEVICE [75] Inventor: Toshinohu Kawazoe, Tokorozawa,-

Japan [73] Assignee: Nippon Denzai, Ltd., Gunna ken, Japan 22 Filed: Feb.4, 1972 [21] Appl. No.: 223,626

[52] U.S. Cl ..337/290, 337/239 [51] Int. Cl. ..H0lh 85/36 [58] Field of Search ..337/190, 238, 239, 240, 290;

[56] v. 7 References Cited UNITED STATES PATENTS Horton ..337/239 11 3,710,297 14 1 Jan. 9 1973 3,510,819 5/1970 Smith ..337/190 X FOREIGN PATENTS OR APPLICATIONS 156,300 12/1920 Great Britain ..337/239 Primary Examiner-Hemard A. Gilheany Assistant Examiner-D. A. Tone Attorney-George B. Oujevolk [57] ABSTRACT A stretched fuse device comprising a brass wire made of 45 to 48 percent of zinc and copper as the remainder with a B phase accounting for more than 90 percent of said alloy, said fuse being stretched in introducing electric current therethrough, wherein the cutoff of said fuse enables, if necessary, either or both of the closure of an alarm circuit and the indication of said cutoff to be effected;

2 Claims, 13 Drawing Figures PATENTEDJAR 9 I975 SHEET 1 [1F 4 PRQPORTION (2 w m m m T\ 3 M 0% 0 IO 0 c 2 o w FIG.2

TEMPERATURE (C) CONSTANTAN (#0 cm) TEMPERATURE (C) B BRASS ncm) F I G. 3

I PATENTEDJAI 9197a TIME SHEET 2 UF 4 SECONDS MINUTES 10000 8000 6000 100 N LCDQO CURRENT PAIENTEUJ/m 9197s SHEET 3 BF 4 FIG. 5

o TENSILE STRENGTH FIG.6A

A STRETCIIED FUSE DEVICE BACKGROUND OF THE INVENTION This invention relates to a stretched fuse device and more particularly to a stretched fuse device comprising a brass wire made of 45 to 48 percent of zinc and copper as the remainder with a B phase accounting for 90 percent of the alloy(hereinafter referred to as a B brass wire"), said fuse being stretched in introducing electric current therethrough.

Already known is a stretched fuse device wherein the fuse is stretched in introducing electric current therethrough. When excess current passes through the fuse of such device, the fuse is generally cut off due to the resulting high .loules heat. Where subjected to a normal tension, the fuse or the prior art device often presents a red-hot or incandescent state, that is a temperature of over l,000C when it is cut off due to passage of excess current therethrough. Such high heat is conducted to a semiconductor element such as a transistor or diode included in an electronic apparatus where said stretched fuse device is used, most likely resulting in the deteriorated properties of said element or sometimes its eventual destruction.

If, however, the fuse is stretched with a greater force so as to allow it to be cut off before reading a red-hot or incandescent state, then said large tension gradually will elongate thefuse even during the introduction of rated current to give rise to the so-called creep cutoff with the resultant failure to provide a fuse device capable of displaying accurate current-time characteristics (that is, the relationship of the magnitude of the current and the time required for the fuse to be cut off).

SUMMARY OF THE INVENTION It is accordingly the object of this invention to provide a stretched fuse device having such mechanical strength as is free from the effect of room temperature, capable of being cut off at sufficiently low temperatures to prevent semiconductor elements and organic insulation materials from being'damaged by heat, and

moreovermaintaining a very accurate current-time relationship. 1

According to this invention, the above-mentioned object is attained by a stretched fuse device which is prepared from a B brass wire consisting of 45 to 48 percent of zinc and copper as the remainder with a B'phase accounting for more than 90 percent of said alloy and is used as a fuse in a stretched state when current is introduced.

BRIEF DESCRIPTION OF THE'DRAWINGS FIG. 4 is a curve diagram of the current-time characteristics of a stretched fuse device according to the invention prepared from a B brass wire;

FIG. 5 is a curve diagram illustrating the co-ordinate analytic method used to obtain the curves of FIG. 4;

FIGS. 6A, 6B and 6C schematically indicate the manners in which the fuse of the invention is stretched;

FIG. 7A, 7B and 7C are respectively the lateral, cross sectional and plan views of a stretched fuse device according to an embodiment of the invention; and

FIGS. 8A and 8B are respectively the plan and lateral views, partly in section, of a stretched fuse device according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION The most important feature of this invention is that the fuse used in the invention consists of a B brass wire to utilize its unique physical properties, thereby obtaining desired results. There will now be discussed the physical properties of the B brass before describing the preferred embodiments of the invention. Brass material in general use contains less than 35 percent of zinc, that is, has an a phase, as shown in FIG. 1, presenting the phase condition of a Cu-Zn system. When the proportion of zinc increases to around 40 percent, there appears a B phase, namely, a mixed phase (a B). Further when the zinc content rises to 45 percent, there only results a B phase. When the zinc exceeds 50 percent, there occurs a 7 phase. Upon appearance of the 7 phase, the brass sharply becomes brittle, failing to display physical processability, for example, wire drawing.

There is given in Table 1 below the physical con stants at normal temperature of B brass according to this invention which consists of 45 to 48 percent of zinc and copper as the remainder with a B phase accounting for more than 90 percent.

TABLE I Melting point (C) 870 Density (g/cm") 8.4 Young's modulus of elasticity (dyne/cm) ll l0 Tensility (kg/mm") to Linear expansion (cm/"C) 19x10 Heat conductivity (w/cm C) 0.6 Specific heat (cal/g/C) 0.09 Specific resistivity (pfl cm 5.610.] Resistivity-temperature coefficient (0 to C) 2.3Xl0' The present inventor conducted experiments with brass having such physical properties. Namely, a sample ofB brass consisting of 45 to 48 percent of zinc and copper as the remainder with a B phase accounting for more than 90 percent was repeatedly subjected to low temperature annealing at 350i50C during a wiredrawing process. As a result, he has discovered that this operation enabled the structure of said B brass to be formed into a fibrous state, making it possible to draw the metal into a very fine wire 0.06 mm in diameter.

It has been further found that a B brass wire thus prepared displayed an order-disorder transition at a relatively low temperature of 454 to 468C and that this type of B transition acted very effectively for the reason given below when said wire was used as a fuse for the subject stretched fuse device. The most prominent physical feature of the B brass of this invention is that it indicates an order-disorder transition at presents a disorderly lattice form where the atoms of copper and zinc are arranged at the lattice points in an irregularly mixed state. The B brass exhibits due to said order-disordertransition unique variations in its physical properties which can not be observed in other single metals or alloys.

FIG. 2 shows the relationship of the tensile strength and temperature of the B brass compared with that of constantan. The constantan used in this test was a solid solution alloy consisting of 43 to 46 percent of nickel and copper as the remainder. FIG. 3 illustrates'the relationshipvof the electric resistance and temperature of the B brass compared with that of constantan. As apparent from FIG. 2, a solid solution alloy, for example, constantan generally presents a progressively increas ing linear decline in tensile strength as temperature rises. In contrast, the B brassis reduced in tensile strength to a smaller'extent than constantan over a tema more prominent decline of tensile strength at around 250C, and at 450C as small a tensile strength as 2 kg/mm corresponding to about one-fortieth of 80 kg/mm at normal temperature.

As seen from FIG. 3, the specific resistivity of the B brass substantially linearly increases up to around 300C, but nonlinearly rises at higher temperatures and reaches at 470C 16 to 17 O. cm, a value about three times that which occurs at normal temperature.

As previously mentioned, when there passes excess current through a B brass wire, its electrical resistance grows larger due to temperature rise resulting from Joule s heat. Since the increase of temperature and that of electrical resistance synergetically act on each other,

, the B brass wire displays a sharply rising temperature.

On the other hand, its tensile strength begins to decrease prominently at around 2009C. If therefore, a

fuse made of a B brass wire is used in a stretched state,

the wire neverfails tobe cut off in an extremely short time at lower temperatures than 400C due to the heat generated by passage of excess current.

Table 2 below gives the rated current, the cut load and electric resistance at normal temperature, the

operating'tension, the ratio of said tension to the cut load and the fuse characteristics of a B brass wire according to this invention where it was used with a stretched fuse device shown in FIGS. 7A, 7B and 7C.

TABLE 2 go aa FIG. 4 shows the current-time characteristics of B brass wires of this invent-ionhaving the various diameters shown in Table 2 above, where there was actually introduced rated current of0.5 to amp. therethrough. The figure indicates that said wires were very sensitively cut off to-excess current higher than the rated cur rent.

It will be apparentfrom the foregoing description that when there was introduced current'through a B brass wire according to this invention consisting of 45 to 48 percent of zinc and copper as the remainder with a B phase accounting for more than 90 percent while it was kept stretched, then said brass wire could provide a stretched fuse device having very accurate currenttime characteristics.

' perature range of from normal to 200C, and indicates The curve diagram of FIG. 4 shows that a stretched fuse device using the B brass wire of this invention displayed prominently excellent current-time characteristics. For better understanding of the invention,

there will now be given a theoretical analysis in supplemerit to the foregoing qualitative description of the invention by reference to the curve diagram of FIG. 4

using meansderived from the co-ordinate analytical method. 7

The current-time characteristics of general stretched fuse wires may be obtained by resolving simultaneous equations consisting of the following equations (1) and u =fl (n 'r g(u) (2) The equation (1) denotes a temperature-time curve and the equation ('2) a tensile strength-temperature curve. In the above equations, u represents temperature (C), t time (sec.), and r a tensile strength (g). Since the equations (1) and (2) are associated with nonlinear values, there are presented considerable difficulties in resolving said equations (1) and (2) simply by calculation. For practical purpose, therefore, resolution by the co-ordinate analytical method is more advisable.

There will now be explained by reference to FIG. 5 the drawing procedure of the co-ordinate analytical method. First, with current value i, (n=an integer) taken as'a parameter, a curve representing the equation is drawn in thefirst quadrant to indicate atime-tem- =rr( o (4) associated with the relationship of the cutoff tension and time of a fuse determined by its material and diameter to show a temperature-tensile strength relationship From the two curves associated with the above equations (3) and (4) there can be determined the currenttime characteristics of a fuse wire in the following manner. Let it be assumed that there is applied a tension r,(0 r, 7 on the fuse wire. Here 1' is taken to represent a tension applied in said fuse wire when it is cut off at normal temperature.

Referring to FIG. 5, there is plotted in the 1 axis of the second quadrant 01', as representing the magnitude of a tension 1", applied on the fuse wire. With u taken to designate the intersection of a line drawn from 'r, in parallel with the ordinate and a curve denoting the temperature-tensile strength relationship u-r l d d then u denotes the temperature at which the fuse wire is cut off when subjected to the tension 1,. Therefore, with t, to t taken to denote the intersections of a straight line drawn parallel with the abscissa through point u and the time-temperature curves of the first quadrant obtained when there was used current having magnitudes of i, to i then said intersections indicate the lengths of time required for the fuse wire to be cut off upon introduction of current having said magnitudes. Further, there are determined intersections between straight lines drawn parallel with the ordinate through the aforesaid intersections t, to i and straight lines drawn parallel with the abscissa through points i to 0 i of the fourth quadrant which are taken to indicate the magnitudes i to 1' of current. The first mentioned intersections defined by both groups of straight lines are connected to draw a curve S. Then this curve S shows the desired current-time characteristics of the fuse wire.

As apparent from the above-mentioned co-ordinate analytic method, the current-time characteristics of a stretched fuse wire may be expressed by the following equation:

i= Mr) 5) The value of this equation is determined by resolving the following simultaneous equations:

Since the equation (6) can be determined from FIG. 3 and the equation (7) from FIG. 2, it will be apparent that unique variations in the physical properties of a B brass wire due to its order-disorder transition exert a very effective action when said wire is used as a stretched fuse.

The process of stretching the B brass wire of this invention used with a stretched fuse device may be illustrated for example, by those of FIGS. 6A, 6B and 6C. FIG. 6A indicates the process fitting a spring (not shown) to each end of a fuse wire and stretching it by applying a force thereto acting in opposite directions indicated by the arrows A and B with this process, the springs are brought back to the original condition when the fuse wire is cut off, so that if required, one of the springs can be used in its original position to close a circuit for giving an alarm on the cutoff of the fuse wire and the other spring can be used to indicate the cutoff itself.

FIG. 6B shows the process of fixing one end of the fuse wire and connecting a spring (not shown) to the other end so as to stretch the wire only in the direction direction intersecting the fuse wire, for example, at

right angles thereto, so as to be stretched as a whole.

Among the above-mentioned processes, those of FIGS. 6A and 68 cause the cutoff portions of the fuse wire to be instantaneously separated, offering the prominent effect of extinguishing an are which might otherwise occur, for example, at the time of short-circuiting. Accordingly, a stretched fuse device using a fuse wire stretched by the process of FIG. 6A or 68 can obviously have a cutoff capacity several times larger than that of a nonstretched fuse device.

There will now be described the actual application of a stretched fuse device according to this invention. FIGS. 7A, 7B and 7C jointly represent a stretched fuse device used to protect the relay circuit of an automatic telephone exchange mechanism. There is a concrete example of the process of stretching a fuse wire with two springs, namely, that of FIG. 6A. The body 1 of said fuse device is integrally formed of synthetic resin, for example, polyvinyl chloride. At the lengthwise ends are formed deep cavities 4 and 5 to receive contact terminals 2 and 3 made of elastic metal. The terminals 2 and 3 are so fitted to the device body I as to close the opening of the cavities 4 and 5 by means of holding metal parts 8 and 9 bored with plug holes 6 and 7 with electrical contact maintained therewith. One end of one holding metal part 8 extends into a recess 10 formed in the device body 1. To the end of said extended portion of the holding metal part 8 is fitted a coil spring 11, one end of which is soldered to the holding metal part 8 and the other free end of which is provided with a tubular indicator 12 made of sybnhetic resin. The device body 1 further has an aperture 13 open at one end to the recess 10 and lined with an insulation tube 14 made of, for example, phenol resin. One contact terminal 3 extends beyond the outer opening of said aperture 13. The free end of the coil spring 11 also extends beyond the inner opening of said aperture 13, though in the opposite direction. The extended portions of the contact terminal 3 and coil spring 11 are soldered to the B brass wire 14 having the aforementioned physical properties which is inserted into the aperture 13 so as to cover both openings of the aperture 13. Said contact terminal 3 and coil spring 11 thus soldered to the B brass wire impact a tension thereto. A stretched fuse device constructed as described above is used under the condition in which the plugs of a socket means are inserted into the plug holes 6 and 7 and the contact terminals 2 and 3 brought into electrical contact with said plugs.

There will now be described the operation of the stretched fuse device illustrated in FIG. 7. A B brass wire through which there is to be introduced rated current of 0.5 amp, has, as shown in Table 2, a diameter of 0.071 mm and is operated with a tension of 1 10 g which accounts for 28.2 percent of a cutoff load. While there flows through the B brass wire rated current, that is, current having 0.5 or smaller amperes, the wire does not present any creep cutoff resulting from its excess extension, because the operating tension has as small a value as 28 percent of the cutoff load, enabling a stretched fuse device using said wire to he operated under a very stable condition.

Where the B brass wire 14 receives excess current of, for example, 1 ampere, its temperature sharply rises due to the resulting .loules heat, leading to its increased electrical resistance as shown in FIG. 3. The

greater the electrical resistance, the more prominent the Joules heat tovaccelerate the temperature rise of the B brasswire 14. As a result, the wire 14 begins to be sharply reduced in tensile strenght at around 200C and is cut off at themoment the tensile strength falls to below the operating tension. As seen from FIG. 2, the wire 14 has extremely small tensile strength at around 400C, so that the temperature at which it is cut off is absolutely prevented from exceeding 400C. Accordingly, even when there is fitted to electronic appliances using semiconductor elementsa stretched fuse device consisting of a B brass wire according to this invention which is subjected to an operating tension accounting for to 30 percent of its cutoff tension, it never happens that the semiconductor elements are deteriorated in property or fully damaged by heat generated from the device when-the fuse is cut off. According to the stretched fuse device of this invention, when the B brass wire 14 is cut off by passage of excess current therethrough, the cutoff portions of the wire 14 are instantaneously separated, as previously described, from each other by the action of the coil spring 11 and the elasticity of the contact terminal 3, so that said device has a cutoff capacity several times larger than that of a nonstretched fuse device. Further upon the cutoff of the wire 14, the free end of the coil spring is brought back to its original position shown in FIG. 78, causing the indicator 12 to project from the-device body 1, showing that the fuse has been cut off. At the same time, the free end of the contact terminal 3 regains its original position to be pressed against the contact terminal of an alarm circuit (not shown) to close itfor actuation. I

FIGS. 8A and 8B jointly denote -a stretched fuse device using a B brass wire stretched by the process of FIG. 6B. To a substrate 40 is movably attached an insulation support pipe 43 by fitting metal parts 41 and 42. One end of the support pipe 43 is fitted into a fixed terminal metal part 44. A fitting metal part 45 placed on the inner bottom wall of the metal part 44 supports one end of a B brass wire 46, the other end of which is fitted to a fitting metal part 48 disposed at one end of a lead wire 47 inserted into the insulation support pipe 43. Theother end of the lead wire 47 is fixed to the fitting metal part 42 in a state engaged with the outer end of the insulation support pipe 43. Near the outer end of said pipe 43 is formeda flange 50. Across the flange 50 and fitting metal part 42 is stretched an extensible coil spring 51 wound about the pipe 43 so as normally to urge the pipe 43 to the right side of FIG. 8A. Accordingly, the B brass wire 46 is normally stretched to the right side as indicated by thecoil spring'51.

The embodiment of FIGS. 8A and "8B is adapted to against the metal part 41. If, therefore, the insulation support pipe 43 is so designed as to have its outer'end projected outside ofa cover (not shown onl when the pipe 43 IS made to move, then the cuto oft e wire 46 will be indicated.

If, in the embodiment of FIG. 8, there is connected an alarm circuit (not shown) between the metal parts 41 and 42, said circuit can be easily actuated when the outer end of the insulation support pipe 43 projects outside of the cover.

If a B brasswire according to this invention is plated in advance with corrosion resistant metal such as nickel, silver, cadmium or tin depending on the kind of an ambient atmosphere in which said'wire is used, there can be prevented the unnecessary cutoff of the wire due to corrosion.

It will be apparent that though the foregoing embodiments only indicate part of the applications of the stretched fuse device of this invention, "there may be taken, forexample, various processes of stretching the fuse wire, actuating an alarm circuit or indicating its cutoff without-departing from the principle of the invention.

What is claimed is:

1. In a stretched fuse device having a fuse wire stretched in introducing current therethrough, the improvement being that said fuse is a'brass wire consisting of 45 to 48 percent of zinc and copper asthe remainder with a B phase accounting for more that percent of the alloy.

2. The stretched fuse device according to claim 1 wherein the brass wire is plated with at least one metal of the group consisting of nickel silver, cadmium and tin.

Claims (1)

1. 2. The stretched fuse device according to claim 1 wherein the brass wire is plated with at least one metal of the group consisting of nickel silver, cadmium and tin.

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