US3289277A - Method of making a fuse link - Google Patents

Description

6, 1966 e. A. BERTHEL ETAL 3, 7

METHOD OF MAKING A FUSE LINK Original Filed Feb. 27, 1961 FIG. 5

INVENTORs 60 7' ALBmrBmT/fl ti mm I SCH/fFMA CHER 6 :1 2

124 By M 5.

ATTORNEY United States Patent Ollice Patented Dec. 6, 19%6 a chins. or. 29-4555) This application is a division of my application Serial No. 91,834 filed February 27, 1961, now Patent No. 3,206,579.

The present invention relates to electrical fuses and to methods of fuse manufacture.

It has for long been recognized that dual-element fuses have highly desirable characteristics for providing fastblowing operation under short-circuit conditions and delayed blowing under conditions of moderate but persistent overload. Common, widespread use of such fuses has been deterred by relative high cost, due to their construction and the methods used to make them.

Ideally, dual-element fuses include a fuse link having a region of restricted cross-section that blows almost instantly in response to a short-circuit, and a body of low-melting alloy as a series conductor which melts and clears the circuit under conditions of prolonged moderate overload. An object of the present invention resides in the provision of a fuse of novel construction having such characteristics yet which is suited to economical manufacture so as to encourage wider use of dual-clement fuses.

In an effort to simulate dual-element fuse characteristics without resorting to complicated construction and costly manufacturing methods, fuses have been made in which a strip of metal of a relatively high melting-point metal is formed with a local constriction, and a body of lowemelting alloy is mounted on the strip adjacent to the construction. The theory of operation of such fuses is that the alloy material acts as a heat sink to absorb heat developed by moderate overload current through the fuse. The current tends to raise the temperature of the strip primarily at the constriction. It is considered that, when the temperature rises to the melting point of the alloy, the melted alloy metal drops off and the temperature of the strip rises rapidly at the constriction until the fuse blows.

This type of simulated dual-element fuse recommends itself largely because of its low cost and by its seeming near approach to true dual-element fuse characteristics. However, on closer consideration it becomes clear that it has serious short-comings. The final phase of delayedblowing operation of such a fuse necessitates a temperature rise suflicient to melt the high-melting strip of metal. This contrasts with the moderate temperature prevailing at the instant of blowing of a true dual-element fuse, which occurs virtually at the instant when the alloy melts and drops off. Moreover there is a relatively wide latitude of inconsistent blowing times among simulated dualelement fuses of the same design in response to a given level of moderate overload current. Such inconsistent blowing times interferes with accuracy in ratings of such peratu-res in the fuse box than would prevail with true dual-element fuses.

Accordingly, an object of the present invention resides in novel features of construction of dual-element fuses that are economical to manufacture and yet which have attractive characteristics of low-temperature rise when blowing occurs in response to moderate overloads; of open-ci-rcuiting reliably at the region where the alloy body is mounted; and of responding to given levels of moderate, prolonged overload by blowing after delay times that are consistent for any given level of moderate overload, within .a comparatively narrow range of delay times.

A further feature of construction of the novel dualelement fuse resides in the utilization of the delay-element alloy body as a rating indicator exposed to view at a window in the fuse enclosure. This feature provides maximum assurance against possible error in manufacture, clue to the wrong size link being assembled into a fuse body whose label might not match the true rating of the fuse link.

A still further object of the invention resides in a fuse link in which a strip of fuse-link metal of moderate length is arranged to have an extended-area joint to the alloy body. This feature minimizes the possibility of contact resistance at the joint introducing an uncertain heating factor. Any uncertainty due to the joint resistance entering as a significant factor would cause blowing of the fuse at a current lower than its rating by an uncertain margin. For this reason, the provision of a large joint area (disproportionately large when compared to the width of the strip) minimizes the possibility of joint resistance entering into the fuse characteristic as a significant and erratic factor.

Still further objects of the invention reside in novel methods of manufacture of fuses, for attaining the fore going operating characteristics while at the same time achieving low unit costs.

In carrying out the foregoing objects, a fuse link is prepared by dividing a band of relatively high-melting temperature metal into endwise aligned strips having elongated projecting mutually spaced portions and integral interconnecting portions; joining a body of low-melting alloy to the elongated portions; and removing the integral interconnecting portions that join the strips. This is done, in the specifically disclosed embodiments below, by cutting away the interconnecting portions outside the areas that are joined to the body, leaving the low-melting alloy body as the only current path between the strips.

The alloy body is relatively large and massive (depending, naturally, on the current rating of the fuse) and will consistently meltand drop away whenever there is a persistent moderate overload. Consequently, by disposing the alloy body near the fuse window, a correspondingly reliable indicator is provided for evidencing the condition of the fuse. Further, by embossing or otherwise applying a rating label to the alloy body, the best possible safeguard is provided to assure correctness of the rating label. There can be no error that might otherwise result from mounting an unlabeled fuse link of one rating in an enclosure bearing a different rating label.

The nature of this invention and its further features, objects and advantages will be more fully appreciated from the following detailed description of two illustrative embodiments which are shown in the accompanying drawings.

In the drawings:

FIGS. 1 to 3 show progressive phases of manufacture of a fuse link, somewhat enlarged, according to one embodiment of the invention;

FIG. 3A is a cross-section viewed from the line 3A-3A in FIG. 3;

FIG. 4 illustrates the fuse link at the stage in FIG. 3 but viewed edgewise and being subjected to a heating operation;

FIG. 5 illustrates a further phase in the manufacture of the fuse link; and

FIG. 6 is an enlarged cross-section of a completed fuse.

FIG. 7 is a view like that of FIG. 5, illustrating another embodiment of the novel construction and manufacturing methods, having certain novel features in common with the embodiment in FIGS. 1-6.

Referring now to FIGS. 16 and, particularly to FIG. 1, a band of metal such as copper is shown, in its condition following an initial piercing operation. In this operation, slot 12 is cut and holes 14 are punched. Slot 12 has extensions 12a alongside holes 14. This slot divides the continuous band of copper into pairs of strips 18a and 1812 at the ends of each slot 12, interconnected by portions 16a and 1612. It will be understood that many slots 12 are formed in spaced sequence along a continuous supply of copper band in making a series of fuse links automatically, using automatic machinery. Attention is directed to the single illustrated fuse link of the series as it progresses through a sequence of manufacturing operations.

In the next step, areas 16a, 16b and 20 are tinned as shown in FIG. 2. A short length 22 is next cut from a strip of usual low-melting fuse alloy metal used in dualelement fuses, and body 22 is sharply bent or formed and assembled as shown across portions 16a and 16b of the band 10. Body 22, as indicated in the drawing, is relatively massive in contrast to the strips 18a and 18b and particularly in contrast to the regions of constricted crosssection flanking holes 18. The width of strip used for forming body 22 is preferably a bit smaller than the length of slot 12 disregarding extensions 120,

Tools A apply pressure to body 22 as shown in FIG. 4, squeezing it against portions 16a and 16b of band 10. At the same time, a controlled current impulse from source B is delivered by conductive jaws C and through switching device D so as to develop enough heat to form a good soldered joint between each interconnecting portion 16a and 16b and both the top and bottom layer of body 22. This heating operation may be supplemented by heating body 22 with controlled current delivered through tools A and B. It will be appreciated that this manner of forming and connecting or uniting body 22 to portions 16a and 16b as illustrated is presently preferred, but that body 22 may alternatively be applied in a casting operation. The conditions are such that a good metalto-metal union is formed between the opposed areas of body 12 and portions 16a and 16b used herein the terms connection and joint refer to such union and not to a mere mechanical fastening.

Body 22 is embossed with indicia 23, the numerals 30 in FIG. 5 representing a ISO-ampere rating. Pieces of copper 24 are cut from the band so as to leave a tongue 16a extending integrally from strip 18a and to leave another tongue 16b extending integrally from strip 1817. These strips are thus electrically interconnected only by alloy body 22. Tongues 16a and 16b are acturately spaced apart and are disposed laterally opposite each other, edgewise. The removal of pieces 24 is effected without removing and wasting any of the alloy and without interference from body 22, an operation that is made possible by the slot 12 extending outside the alloy body.

An individual fuse link is cut from the continuous series formed as described in connection with FIGS. 1-5. It is formed into the shape illustrated in FIG. 6, to be received in the plug-fuse enclosure naturally and without any stress that could bias the two strips 18a and 18b toward each other. The plug fuse enclosure shown includes a porcelain, glass or other suitable insulating body 26, and end terminal 28, a screw terminal 30 and a window 32 as of mica held across the top of body 26 by ferrule 34.

The embossed indicia 23 of body 22 are disposed reasonably close to window 32. The ends of strips 18a and 18b are soldered to terminals 28 and 30, respectively, using a higher-melting alloy than that of body 22.

The fuse shown in FIG. 6 and made as described has a number of important advantages. It is of elementally simple construction While retaining desirable properties and characteristics of true dual-element fuses. When a sudden extreme overload occurs, blowing takes place at one of the holes 14 that is opposite window 32. In the event of a moderate but persistent overload, the temperature rise needed to blow the fuse is only that required to melt the alloy body 22. As soon as it melts, it drops and leaves an open gap between tongues 16a and 16b. There is no need to melt any part of the copper in the fuse link. This construction is remarkably consistent in its overload time-current characteristic, among many fuses made in the same manufacturing operations, in contrast to fuses intended to simulate dual-element fuse characteristics but in which the alloy body is not electrically a series part of the fuse link.

When blowing occurs, the event is reliably displayed at the window because blowing of the novel fuse occurs with a high degree of uniformity (among many like fuses) at the intended region of the link. It is of course usual to expect the window to reveal any blown fuse, but unfortunately fuses may become open-circuited at other joints. This is a particular problem in fuses where higher temperatures are reached prior to blowing, in which case the break in the circuit may develop at a soldered terminal so as not to be displayed at the window. Such a troublesome occurrence is virtually eliminated by the fuse construction described.

A modification is illustrated in FIG. 7, which is most nearly comparable to FIG. 5. Reference numerals in the -series are used in FIG. 7 to designate parts corresponding to like parts in FIG. 5.

Tongues 116a and 116b' extend from strips 118a and 118b, and regions of constricted cross-section are created by pierced holes 114. When the fuse link is being made, strips 118a and 11% are interconnected and tongues 116a and 116b are fixed in relation to each other by narrow marginal bridging portions represented in broken lines. After body 122 has been united to tongues 116a and 116b, these bridging portions 124 are cut away in an operation! that occurs wholly outside the body 122.

As will be apparent, this embodiment utilizes variations of the novel features of the embodiment in FIGS. 1-6'. When assembled into an enclosure such as that in FIG. 6, it achieves many of the purposes of the first embodiment.

It will be appreciated that the foregoing embodiments of the invention in its various aspects are susceptible to detailed modification and varied application of the features of novelty, and consequently the invention should be broadly construed in accordance with its full spirit and scope.

What is claimed is:

1. The method of making a dual-element fuse link, including the steps of cutting an elongated slot lengthwise in a band of high-melting-point metal and thereby con stituting two strips integrally interconnected by a pair of elongated bridging portions, at the sides of the slot, uniting a body of relatively low-melting-point metal to both said bridging portions with the ends of the slot disposed clear of said body, parting one of said strips at one side of said body from the adjoining end of one of said bridging portions and parting the other of said strips at the other side of said body from the adjoining end of the other one of said bridging portions, leaving said body as the sole interconnection between said strips.

2. The method of making a dual-element fuse link, including the steps of cutting an elongated slot lengthwise in a band of high-melting-point metal and thereby constituting two strips integrally interconnected by a pair of elongated bridging portions, at the sides of the slot, uniting a body of relatively low-melting-point metal to both said bridging portions with the ends of the slot disposed clear of said body, cutting said strips adjacent said body to form regions of constricted cross-section, parting one of said strips at one side of said body from the adjoining end of one of said bridging portions and parting the other of said strips at the other side of said body from the adjoining end of the other one of said bridging portions, leaving said body as the sole interconnection between said strips.

3. The method of making a dual-element fuse link, including the steps of cutting an elongated slot lengthwise in a band of high-melting-point metal and thereby constituting two strips integrally interconnected by a pair of elongated bridging portions, at the sides of the slot, forming a body of low-'melting-point metal to include two opposite lateral portions integrally interconnected so as to constitute a U-shaped body, assembling the U-shaped body to said bridging portions with each of said bridging portions interposed between both said lateral portions of the U-shaped body, pressing said lateral portions of the U-shaped body against the interposed bridging portions while heating the U-shaped body and the interposed bridging portions for forming a fused joint between each of said bridging portions and said body of low-meltingpoint metal, parting one of said strips at one side of said body from the adjoining end of one of said bridging portions and parting the other of said strips at the other side of said body from the adjoining end of the other one of said bridging portions, leaving said body as the sole interconnection between said strips.

References Cited by the Examiner JOHN F. CAMPBELL, Primary Examiner.

WHITMORE A. WILTZ, Examiner.

R. W. CHURCH, Assistant Examiner.

Claims (1)

1. THE METHOD OF MAKING A DUAL-ELEMENT FUSE LINK, INCLUDING THE STEPS OF CUTTING AN ELONGATED SLOT LENGTHWISE IN A BAND OF HIGH-MELTING-POINT METAL AND THEREBY CONSTITUTING TWO STRIPS INTEGRALLY INTERCONNECTED BY A PAIR OF ELONGATED BRIDGING PORTIONS, AT THE SIDES OF THE SLOT, UNITING A BODY OF RELATIVELY LOW-MELTING-POINT METAL TO BOTH SAID BRIDGING PORTIONS WITH THE ENDS OF THE SLOT DISPOSED CLEAR OF SAID BODY, PARTING ONE OF SAID STRIPS AT ONE SIDE OF SAID BODY FROM THE ADJOINING END OF ONE OF SAID BRIDGING PORTIONS AND PARTING THE OTHER OF SAID STRIPS AT THE OTHER SIDE OF SAID BODY FROM THE ADJOINING END OF THE OTHER ONE OF SAID BRIDGING PORTIONS, LEAVING SAID BODY AS THE SOLE INTERCONNECTION BETWEEN SAID STRIPS.

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