US2171864A - Fuse link - Google Patents

Description

Sept. 5, 1939.

- L. R. POPP 2,171,864

FUSE LINK Filed March 8, 1937 2 Sheets-Sheet 1 ATTORNEYS Sept. 5, 1939. POPP 2,171,864

FUSE LINK Filed March 8, 1957 2 Sheets-Sheet 2 ATTORNEY-9 Patented Sept. 5, 1939 UNITED STATES PATENT OFFICE FUSE LINK Application March 8, 1937, Serial No. 129,555

9 Claims.

This invention relates to improvements in fuse links and more particularly to fuse links of the type which are intended for use in connection with renewable fuses in which fuse links may be inserted in a housing to replace similar links which have been broken or fused.

One of the objects of this invention is to provide a fuse link of improved construction whereby uniform and superior results may be obtained throughout the life of the link. Another object of this invention is to provide a fuse link having the ends thereof provided with terminals of a metal of better electrical and thermal conductivity than the fusible metal of the link, to produce connections between the ends of the link and the current conducting parts of the fuses. Still another object of the invention is to provide a fuse link having the terminals covered with a sheet or layer of a metal of better conductivity than that of the fusible part of the link. It is also an object of this invention to provide a fuse link in which the ends of the fusible part of the link which are subjected to clamping pressure for making contacts with current conducting parts of the fuses are covered with copper sheets or layers soldered thereto to insure a superior connection between the fuse link and the current conducting parts of the fuse. Other objects of this invention will appear from the following description and claims.

In the accompanying drawings:

Fig. l is a face View, partly in section, of-a fuse having a fuse link embodying this invention applied thereto.

Fig. 2 is a face view of a fuse link embodying this invention showing the same detached from the fuse.

Fig. 3 is a face view of the fusible part of the link.

Figs. 4 and 5 are face views of the terminal portions of the link before the same-are bent around the ends of the link.

Fig. 6 is an edge View of the link shown in Fig. 2.

Fig. 7 is a face view of a fuse link of slightly modified construction.

Fig. 8 is a face view of a terminal portion of the fuse link shown in Fig. '7, before the same is bent around an end of the link.

Figs. 9 and 10 are fragmentary edge views of fuse links of modified construction.

Figs. 11 and 12 are perspective views of the terminals of the fuse link shown in Fig. 10.

My improved fuse link may, of course, be used in connection with any suitable or desired type .of fuse, and in Fig. 1 of the drawings, I have illustrated by way of example, a renewable or refillable knife blade type of fuse with which my link may be employed. This fuse includes the usual knife blades 9 which extend into the in- 5 terior of the fuse casing or housing. ll represents my improved fuse link, the ends of which may be secured or clamped in any suitable manner to the inner ends or tangs of the knife blades 9, for example, by means of screws or bolts [2 l0 and washers l3. The fuse link is enclosed within an outer tubular shell 14 in any suitable or usual manner, the shell I4 being of insulating material. The ends of the outer shell I4 may be closed in any suitable manner, for example, by 15 means of capmembers l5, which engage with and are secured to the ends of the outer shell 14.

In fuses of this kind as heretofore commonly employed it was generally customary to form each fuse link of a single piece or strip of fusible metal, 20 such for example as zinc, as shown in Fig. 3, and the ends of the links were provided with slots or recesses I7 and I8 through which the screws or clamping bolts i2 could extend, and the ends of these links were consequently, pressed by means 25 of these bolts into contact with the inner ends or tangs of the copper knife blades 9.

I have found that the contact between the fusible metal and the copper of the blades or tangs 9 varies greatly under different conditions. Fusible metal, such as zinc, oxidizes quite readily, and consequently, a fuse link gradually acquires a coating or covering of oxide which increases in thickness as the link becomes older. This covering or coating, consequently, greatly decreases the electrical and thermal conductivity of the joint or contacting surfaces of the link and the knife blades. If a new link, practically free from oxide were clamped in to the fuse, the conductivity of the contacting faces of the link and the copper tangs or blades would initially be high but would decrease as the link becomes coated with oxide. Furthermore, a change takes place in fuse links after they have been used in a fuse for a period of time in that the metal in the clamped ends of the link becomes of reduced thickness so that the clamping connection after a period of time becomes loose, which materially decreases the conductivity of the contacting surfaces.

In order to form a fuse link overcoming these difficulties, I provide terminal pieces at the ends of the fusible link, which are made of a metal of better conductivity than the metal of the fusible link. These terminal pieces may, of course, be of any shape suitable for cooperation with the particular clamping means employed for securing the ends of the fuse link to the current carrying parts of the fuse, and the terminal pieces may be secured to one or both faces of the ends of the fuse link. In the particular construction illustrated, the terminal pieces are made of thin sheets or plates 20 and may be of such shape and form as to cover one face only of each end of a fuse link, or a terminal piece may be secured to each face of each end of the link, but preferably the terminal pieces are formed so that each covers opposite faces of an end of the link. For this purpose, terminal pieces 20 are formed withslot V or elongated holes 2| therein and are then bent or folded transversely at their middle portions, as indicated at 22, so that the two halves of a terminal piece lie flatly in contact with the two opposite faces of an end of a fuse link. 7 These two terminal pieces as shown in Figs. 1 to 6 may be of the same size and shape, the terminal piece for that end of the link having the slot ll which terminates at the extreme end of the link being "applied to the link in such a manner that the bent portion 22 is arranged along the end edge of the link, and the other terminal piece cooperating with the other end of the fuse link having a slot is which terminates at a side of the link is applied to the link in such a manner that the bent middle portion 22 thereof is at the side of the fuse link in which the slot 18 terminates, as clearly shown in Fig. 2. These terminal pieces may, of course, be made of any suitable metal having good conductivity and capable of forming, with the conductors of the fuse, contacting surfaces of a relatively high degree of conductivity. It has, for example, been found that copper is very suitable for this purpose, although other metals may also be successfully employed. Copper also has the property of resisting oxidation to a much greater degree than the Zinc commonly employed infuse links and also no noticeable change-takes place in copper when clamped for long periods of time. 7

While the terminals may be secured to the ends of the fuse links in any suitable or desired manner, it 'is preferred to secure them by means of solder. The soldered'connec'tion may be made in any suitable or desired manner, and in order to facilitate such connection, the end portions of the terminals may be provided with holes 24 through which flux and solder may be introduced for forming a soldered connection between the terminals and the ends of the link. Such soldered connection has the advantage that it securely holds the terminals in place on the link, at least until the fuse goes into use. This solder maybe melted by the heat of the fuse when in use, since obviously a solder must be used which has a lower melting point than the metal of the fuse link; The solder also has the advantage of preventing the formation of oxide or other film of high resistance on-the surfaces of those portions of the link which are covered by the terminals, Any other means for securing the terminals to the ends of the links may be employed, if desired.

In Figs. 7 and 8, I have shown a fuse link ll provided with terminal pieces 30 of slightly different construction. These terminal pieces as shown in Fig. 8 have a pair of slots or recesses 31 and 32 formed therein, which terminate at a side of the terminal piece in such a manner that when the terminal piece is bent about the middle portion 33 thereof, the recesses 3| and 32 will lie inregistration'with each other and with a corresponding recess in the fusible strip H.

These terminal pieces are applied to the ends of the fuse links in such a manner that the bent portion 33 of that terminal piece which is secured to the end of the fuse having the slot terminating in a side thereof, as shown at the left side of Fig. 7, will lie along the extreme end of the link. At the other end of the fuse link in which the slot terminates at the extreme end of the link, the bent portion 33 will lie along a side of the link. By means of this construction, the bent portion 33 of each terminal piece will form a conductor of greater cross sectional area than the bent portion of the terminal piece shown in Figs. 1 to 6, for greater conductivity between one part of the terminal piece and the other part thereof.

In Fig, 9 is shown a part of a fuse link of modifled construction whereby a pair of fusible strips: 40 and M may be secured with their ends in contact with each other and having a terminal piece d2 covering the outer faces of the ends. This terminal piece may be similarfin construction to those described in connection with Figs. 1 to'8 inclusive. 7 a

In Figs. 10 to 12, I have shown a construction in which three fusible links G, 5! and 52 may be secured together at one end thereof to a terminal piece 53 of copper or other metal different than the metal of the fusible strips. The terminal piece 53 may be: made of a single strip of metal having an intermediate portion which may bebent to form outer face portions 54 and 55 extending about the outer faces of the ends of the outer fusible strips Eil and 52, and inwardly bent parts 55a and 56 which extend along opposite faces of the middle link 5i and between this link and the two outer links. The four flat parts or faces of the terminal piece may all be provided with slots which will be in alinement with each other to form a slot or recess 5?, which will be in registration with the corresponding slots terminating in the extreme ends of the fusible strips connected with the terminal piece 53. The other ends of the fusible strips, having registering slots terminating at a side of the link may be connected by means of a terminal piece 59, as shown'in Fig. 12, in which the strip of copper or other metal from which the terminal piece is formed is bent in a manner similar to that shown in Fig. 11, but in which slots: or recesses are formed in the metal in such a, manner as to produce a recess (iii arranged to register with corresponding slots or recesses termimating in thesides of the fusible strips. The slots or openings in this construction, as well as in the constructions shown in the other figures may also be formed after unslotted end pieces; are attached or soldered to the fusible strips. 1

The terminal pieces shown in Figs. 7 to 12 may, of course, be soldered or otherwise secured to the fusible strips.

Links with terminals of greater conductivity, as herein described, have the advantage that they form terminals which when once clamped in a fuse will maintain for long periods of time a high conductivity not only within the terminals themselves, but also at thecontacting surfaces with the conductors of the fuse. The soldered connection or joint between the terminals and the ends of the fuse links prevent any oxidation of the portions of the fusible link which are in conin a fuse. This is of importance, for the reason that when these fuse links are in use and carry large loads, they frequently become heated above the melting point of the solder, so that if solder alone were depended upon to form a connection between the terminals and the fuse link, the solder would loosen and either let the link drop out, thus destroying the fuse, or the solder upon melting would run out of the space between the link and the terminal and thus form a connection between the link and the terminal of greatly increased resistance. By means of the construction herein described, this cannot happen since when installed in a fuse, the terminals are continuously pressed into contact with the ends of the link so that a contact of high conductivity would be maintained by the clamping means independently of the solder. Furthermore, in a tightly clamped contact between two faces, the solder, even if it melts, will be held in place by capillary action in minute interstices between the contacting surfaces.

It is also a desirable feature of my improved fuse link to have each terminal formed of a single piece extending around an edge of the fuse link and contacting both faces thereof. While fuse links having a terminal of copper or other metal of higher conductivity applied to one face only thereof have material advantages over fuse links without such terminals, yet when the terminals are formed as herein shown, then when either side or face of an end of a fuse link forms a better contact with the current conducting parts of a fuse, as would, of course, happen if one face of the link were clamped directly against a tang of a knife blade, as shown in Fig. 1, while the other face is contacted by a washer [3 which in turn contacts with a bolt I2, the contact face of least resistance is, of course, the one which contacts directly with the tang of the knife blade. Consequently, with my improved terminals as herein shown, a much greater proportion of the current and heat will flow to the tang from the face of the terminal contacting directly therewith and much of the current and heat passing from the fuse link to the opposite side of the terminal will flow along the terminal and around the bent portion 22 thereof to the face of the terminal contacting directly with the tang of the knife blade.

Fuse links made in accordance with my invention have been found to be greatly superior to fuse links having no such terminals in that the characteristics of the fuse links continue throughout their life. Furthermore, my improved fuse links, even if kept on hand or in reserve for long periods of time, will still have the same current carrying capacity as when new, since no film or oxide is formed at the terminal portions of the link on the fusible metal, and also fuse links which are in use in fuses, do not become loosened at their connections with the current carrying parts of the fuse.

The term soldered as herein employed is intended to include any union of the fusible strip to the copper or other terminal, whether this union is formed by a soldering compound or alloy or by the metal of the fusible strip.

I claim as my invention:

1. A fuse having current conducting parts at opposite ends thereof, a link comprising a strip of fusible metal having ends clamped to said current conducting parts of a fuse, said link including terminal parts of a different metal and which are integrally secured face to face to said ends of said fusible strip and which are substantially co-extensive in face area with the area of said ends, whereby when clamping pressure is applied to said terminal parts, said parts are also pressed into contact with the ends of said fusible strip.

2. A fuse having current conducting parts at each end thereof, each of said conducting parts being provided with parallel clamping parts, a fuse link including a part of fusible metal having ends arranged to be clamped between said clamping parts of conductors for forming electrical connections with said link, terminals of metal of better conductivity than said fusible metal, secured to the ends of said fusible part and substantially coextensive with said ends, whereby when clamping pressure is exerted upon said terminals to press said terminals into low resistance, conductive engagement with said conductors, said terminals will be pressed against the ends of said fusible part.

3. A fuse in accordance with claim 1 characterized in that the terminal parts of the link are soldered to said fusible part.

4. An integral fuse link including a strip of fusible metal having ends formed to be clamped to current conducting parts of a fuse, and a layer of a different metal of better conductivity than the metal of said fusible part and secured to a face of an end of said strip to form an air-tight joint therewith, said layer being substantially coextensive in face area with the area of the end of said link to which it is secured, whereby when said link is clamped to a conducting part in the fuse, said layer will be pressed against the end of said fusible strip.

5. A fuse link including a strip of fusible metal having ends formed to be clamped to current conducing parts of a fuse, and a layer of a metal of better conductivity than the metal of said fusible part soldered to each end of said fusible metal at the portions of the ends of said metal which are subjected to clamping pressure by said current conducting parts, said layers of metal being substantially co-extensive with said ends of said fuse.

6. A fuse link including a strip of fusible metal having ends formed to be clamped to conductors of a fuse for forming electrical connections with said link, and relatively thin terminal pieces secured in air-tight relation to the ends of said fusible strip and each comprising a flat piece of metal bent around an end of said strip to cover the opposite faces of the portion thereof to be clamped without extending materially beyond the edge portions of the end of the link.

'7. A fuse link including a strip of fusible metal having slotted ends adapted to receive clamping means for securing said fuse link to electrical conductors of a fuse, relatively thin terminal pieces of metal having better conductivity than said fusible metal and having slots formed therein, said terminal pieces being bent around both faces of the ends of said fusible strip with the slots thereof substantially in registration with the slots in said strip and without extending materially the dimensions of said fusible strip, and means for securing said terminal pieces to said strip.

8. Afuse link including a strip of fusible metal having slotted ends adapted to receive clamping means for securing said fuse link to electrical conductors of a fuse, terminal pieces of metal having better conductivity than said fusible metal and having slots formed therein, said terminal pieces being bent around both faces of the ends of said fusible strip with the slots thereof substantially in registration With the slots in said strip, said terminal pieces being confined substantially to the length and width of said strip,

and a soldered connection with both faces of said strip. 7

9. A fuse link including a fusible strip of zinc

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