US 3714613 A
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Description (OCR text may contain errors)
I United States Patent 11 1 1111 3,714,613
Appleton 1 1 Jan. 30, 1973 s41 CANTED FUSE ELEMENT 2,181,825 11/1939 Wood ..337/l63  Inventor: I. 38232;; 'g f fl i Primary Examiner-Harold Broome Willington, Chicago, 111. 60657 'i '1- Attorney-Jon L. L1lyequ1st  Filed: Nov. 1, 9171 211 App]. 190.; 194,377  ABSTRACT A fuse element comprises a plurality of planar heat sinks connected by integral fusible sections relatively ..337/2!l)l56l3h3;/5l/(5); Small p d to the heat Sinks. The heat Sinks a"  Fie'ld I66 232 have a common axis disposed in the planes thereof,
"" 2 6 which axis extends through the fusible sections. Ad-
jacent heat sinks have different angular positions about said'axis. In one embodiment the fusible sec-  References cued tions are defined by circular openings cut in the blank UNITED STATES PATENTS from which the element was formed.
2,313,373 3/1943 Sundt ..337/295 5 Claims, 5 Drawing Figures i5 J l J 1; v S 1 s 20 CANTED FUSE ELEMENT BACKGROUND OF THE INVENTION Depending upon the specific application, a fuse can be designed to exhibit a variety of characteristics. The protection of a particular piece of electrical equipment might require that its protective fuse interrupt the current flow if its rated value is exceeded even slightly, while appreciable short duration overloads may be completely permissible with a different piece of equipment. It is this latter situation with which this invention is concerned.
Some of the desirable features of such a fuse element are short clearing time, low clearing energy, and long melt time. In rough terms, clearing time is the duration of the sustained are between melted separation of the fuse material and complete, nonconducting severence of the are formed thereby.
Preferably the energy consumed during this disruption of current flow, or clearing energy, will be low. And, if nominal current and voltage fluctuations in the line are permissible as having no injurious effect on the equipment protected by the fuse, the melt time, or time from initiation of melting to the start of clearing time will be desirably great.
One known method of accomplishing the above objectives is to provide a plurality of heat sinks longitudinally of the fuse element to absorb and dispurse excess heat generated in the fuse by line current irregu larities. And, a practical way of achieving this is to construct the fuse element from a thin strip of fuse metal having a plurality of longitudinally spaced pairs of notches, each pair extending laterally inwardly from the outer edges of the element. This configuration produces a number of longitudinally aligned segments or links. The small bridge of material formed by each pair of notches and which joins adjacent links is thus the fusion zone, and the links or segments thus bridged are the heat sinks for these fusion zones.
In some such fuse elements, the adjacent segments have been twisted relative to one another for one reason or another, such as stiffening.
SUMMARY OF THE INVENTION The subject fuse element makes use of the foregoing known construction, but includes various dimensional differences to enhance the operating characteristics of the device. For example, the individual segments or heat sinks are arranged to maximize their ability to draw heat away from the fusion zone. Also, adjacent segments are canted relative to one another to minimize the possibility of sustaining an arc across adjacent links after the fusion zone has melted. This canting of adjacent links thus permits them to be positioned extremely close together, this improving heat removal from the fusion zone during temporary overloading and also assisting in the quick dispu'rsal of this heat by radiation.
As a result of these differences with known constructions, the subject invention exhibits improved operating characteristics over existing and commercially available products. For example, in an AC installation, a
this improved device takes 50 percent longer to burn out than commercially available types under the same 4 circumstances. Underordinary loads, the temperature of the fuse material has been found to operate typically 5F below commercially available devices. And, when used in a slow blow application, all of the other major properties associated with a desirable unit have been found to be at least as good as commercially available devices.
DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, there is shown in FIG. 1, a typical assembly incorporating the present invention and consisting of a fuse element 10 extending axially through the cylindrically shaped main body portion 11 of a fuseholder, generally 12. Rigidly attached to each end of the cylindrical main body 11 is an externally threaded end piece 13 having a semi-circular hold 15 extending through its outermost end. An internally threaded cap 16 mates with each of the end pieces 13.
Fuse element 10 is constructed of any suitable fuse material which can preferably be purchased as strip stock. This material is then sent through a blanking operation to provide pieces either of the shape shown in FIG. 3 or that shown in FIG. 5. A subsequent forming operation converts the blank of FIG. 3 to the shape of FIG. 2, or alternatively, the blank of FIG. 5 to the shape of FIG. 4.
Referring now specifically to the blankshown in FIG. 3, the fuse element 10, as stamped, includes a plurality of individual or longitudinally adjacent pairs of series connected segments or links. At each end is a relatively elongate end segment 20 which are herein shown separated by a series of intermediate heat sink segments 21. End segments 20 also act as heat sinks and, although seven intermediate segments 21 are shown, any desirable number of intermediate segments (including none) may be incorporated depending upon the specific application of the fuse element.
As is common practice, the overall length of the fuse element 10, as stamped, is greater than the distance between holes 15 of the fuseholder. Thus, when initially placed within the fuseholder, the outermost end of each segment 20 will extend through and outwardly beyond a hole 15 in threaded end piece 13 of the fuseholder. These outermost ends are then bent over to longitudinally position the fuse element within the fuseholder, and then the cap 16 is screwed tightly onto threaded end piece 13 to lock the fuse element 10 in place and provide an appropriate'electrical contact in the form of cap 16. Main body 11 is of dielectric material so that all current transferred between caps 16 is carried byfuse element 10.
Each of the heat sink elements 20 and 21 is substantially of rectangular shape and includes a leading edge 21A and a trailing edge 21B. Each adjacent pair of heat sinks thus have a leading edge 21A and a trailing edge 21B proximate one another, and these proximate edges are joined together by a centrally located and integrally formed bridge 22. Bridge 22 is formed by removing material in the form of a pair of transversely oriented and inwardly extending slots 23, this material being removed in the stamping operation. Slots 23 are preferably narrow and extend perpendicularly to the axis 24 of the fuse element 10, and thus cause the various segments of the fuse link to have their substantially rectangular shape.
As will be understood, the bridges 22 form the fusion zones for the fuse element 10, and the intermediate segments 21 provide heat and dissipation means for these fusion zones when there occurs temporary overloads which'are permissible and acceptable, and are thus more desirable than a blown fuse. In order that a maximum amount of heat can be withdrawn from the fusion zone by way of conduction, it is desirable that the fusion zones be rather short so that their entire length is proximate the heat sink elements and 21. Also, preferably, the heat sink links should be of appreciable size so as to have the capacity to absorb considerable heat and dissipate it through conduction and radiation. Quantitatively, the spacing between adjacent lengths in the embodiment shown is approximately one-sixth of the length of an intermediate link 21, although this spacing can vary somewhat depending upon the specific fuse qualities desired for a particular application.
While the configuration just described provides excellent heat sink and heat dissipation properties by making substantially complete use of the material, the as-blanked shape prior to forming into the configuration of FIG. 2 displays certain undesirable blow qualities. For example, upon rupture of a bridge 22, the are formed across the rupture might very well sustain itself by moving laterally outwardly along the slot 23, which will be recalled is of generally constant width from the bridgeto the outer lateral extremity.
Referring now to FIG. 2, it will be noted that ad- I jacent heat sink segments 20 and 21 are canted relative to one another at preferably a 90 angle. In this formed condition it will be understood that the otherwise adjacent and parallel edges which formed a slot in FIG. 3 now diverge in a generally V-shape in perspective as seen in' FIG. 2. By virtue of this divergence, it will be appreciated that the arc created by rupture of a bridge 22 cannot sustain itself by running laterally outwardly from the longitudinal axis 24 across a fixed gap. Also, during temporary overloads when the bridges 22 heat up but do not melt, conductance of this heat into adjacent heat sinks can quite effectively be radiated therefrom by virtue of their facing different portions of the internal sidewall of main body 11 of the fuse holder. Thus, radiated energy is dispursed more evenly around the inner peripheral surface of the fuseholder.
As will be understood, the narrower slot 23 is made, the greater the proximity of the heat sink segments to the concentration of heat. Also, the narrower slots 23 are made, the greater the volume of the heat sink and the greater its surface area which enhances radiation therefrom. It will be noted that as the as-blanked slot 23 diminishes in width, the more nearly the distance between the adjacent edges of two adjacent heat sink segments increases directly proportional to the radius outwardly from the bottom of the slot. As commented on before, this tends to hold any resulting arc to the central longitudinal axis of the fuse element.
The width of the bridge 22, as measured laterally of the fuse element, is preferably relatively small to avoid its being torn in the forming process. In the embodiments shown, it is perhaps less than one-seventh the overall lateral dimension of the fuse element.
Naturally, there are a number of changes which could be made to the design of FIG. 2 which would remain within the spirit and scope of the invention. For example, one minor variation is shown in FIGS. 4 and 5. In this variation, portions similar to portions on the preceding variation carry like numbers primed. In this variation, fuse element 10' includes end heat sink segments 20', intermediate heat sink segments 21', of which seven happen to be shown therein, and central bridges 22.
The principal difference between this variation and the one described previously is in the shape of the slot which separates adjacent segments.
In this variation, and with particular reference to FIG. 5, adjacent segments are separated from one another by a round hole 30 on each side of and forming the central bridge 22', and also by a zero width slit 31 extending from the laterally outward most point on the hole 30s periphery to the lateral outside edge of the fuse element. As will be appreciated, the circular hole provides stress relief and the slit permits the maximum amount of material to be used for heat dissipation.
Other and more extensive variations are also possible within the spirit of the invention, and thus the scope of this invention is not to be measured by the description and figures, but rather by the appended claims.
1. A fuse element constructed from the blanking and forming of a strip of fuse material, comprising: a plurality of heat sink segments aligned along a longitudinal axis forming a plurality of adjacent pairs of segments, each segment having a leading edge and a trailing edge, a-narrow bridge joining the leading edge of one segment with the trailing edge of the adjacent segment and forming a fusible section, said fusible section being relatively short in relation to the length of the segments, the leading edge of one segment and the trailing edge of the adjacent segment having substantial portions parallel to one another after blanking and prior to forming, after forming adjacent segments being positioned at different-angular positions about said longitudinal axis whereby the distance by which said substantial portions are separated is generally proportional to the distance outwardly from said longitudinal axis.
2. The fuse'element as defined in claim 1, wherein said substantially parallel portions are spaced longitudinally less than one-fourth the longitudinal length of said segments.
'3. The fuse element as set forth in claim 2, wherein the lateral width of said bridge is generally less than one-seventh the lateral width of said segments.
4. A fuse element blank for a fuse of the type having a plurality of series connected heat sink segments connected by an integrally formed central bridge, the improvement comprising: each of said segments including dinal station defining the shape of the bridge and being curvilinear to thereby provide stress relief for the bridge during a subsequent forming operation.
5. A blank as set forth in claim 4, wherein said holes in the blank before forming are circular.