US2243135A

US2243135A - Fuse

Info

Publication number: US2243135A
Application number: US144789A
Authority: US
Inventors: Hugh A Triplett
Original assignee: Schweitzer & Conrad Inc
Current assignee: Schweitzer & Conrad Inc
Priority date: 1937-05-26
Filing date: 1937-05-26
Publication date: 1941-05-27
Anticipated expiration: 1958-05-27

Description

May 27, 1941. H. A. TRIPLETT FUSE Filed May 26, 1937 4-Sheets-Sheet 1 May 27, 1941; -H. A TRIPLETT FUSE Filed lay 26. 193'? 4 Sheets-Sheet 2 May 27, 1941. H. A. TRIPLETT FUSE Filed May 26, 1937 4 Sheets-Sheet 3 May 27, 1941. H. A. TRIPLETT 2,243,135

FUSE

Filed may ze, 1957 4 sheets-sheet 4 @if ,gg- /00 /06 /07 [0g //3 /0/ lf2 l fr, l@ u l y--/ l* 6 l )U3 /01 J/LVHP (HELE Hue I l /05 ll .Y QQ /02 Il? Qv/l//fl /f/ v v /H- W' Jr lla "/g current therethrough.

"Planted Map2?, 194i amiss rosa nigga. Triple, wnmmani., um u poration of Delaware oagiallbaeor-` Anuman my ze, 1m, sensi No. mass (ci. :bo-113s) '44 claims.

I My invention relates, generally,` to fuse devices and it has particular relation to the construction of fuse links that are intended to be replaced once they have blown. It is further particularly related to the construction of fuse links that are l especially adapted. for use in the secondary or low voltage. high current, circuit of a distribution transformer, although their use is not limlted to this application.

'I'he thermal duty to which a fuse device in the secondary or low voltage, high current, circuit of a distribution transformer is subjected is considerably greater than the thermal duty imposed'on a fuse device inthe primary or high voltage. low current, circuit of the transforrner. This difference in thermal duty is caused by the requirement that the fuse device in the secondary circuit protect the transformer during overload and clear the circuit during overload or short circuit without blowing the primary fuse. 'Thus it must operate close to its minimum.` fusing cur-` rent without deterioration.

The object of myinventlon, generally stated, is'to p\ovide a fuse link that will operate under the foregoing conditions and which may be readily and economically manufactured and installed.

An object of my invention is to provide for constructing a fuse link in vsuch manner that it will operate close to its minimum fusing current at a relatively low temperature with little heat dissipation or watt loss and, at .the same time, will not deteriorate because of flowing of metal, oxidation and the like.

A further object of my/invention is to increase the resistance of a fuse element on ow of predetermined current therethrough by the interaction .of two or more metals forming the element in such manner that the rupturing of th element is accelerated. l

Another object of my invention is to take advantage of the alloying characteristics of two metals such as silver andl tin, to effect the interruptlon of a circuit on flow of predetermined Still `another object of my invention is to provide a composite fusible element having a sheath formed of a metal having a relatively high conductlvity enclosing a core formed of a metal having a lower conductivity.

A specific object of my invention is to provide acomposite fusible element having a tin core and a silver sheath.

' Anothfl'object of my invention is to provide for electrical connection to a composite fusible element comprising a. core formed of metal havlng a. relatively low melting point and a surrounding sheath formed of a metal having a relatively high melting point in such manner that heat generated in the core is rapidly conducted away from it.

Still another object of my invention is to p vide for interconnecting a metal sheathed fusible element and a stranded conductor in which the cross-sectional area of .the latter is not limited 'Another object of my invention is to provide a readily replaceable fuse link construction em- -ploying-a pair of terminals adapted to be biased -apart and interconnected by a strain element and composite fusible element formed by, a'

low melting point core and a highvmelting point sheath.

Other objects of my invention will, in part, be obvious and in part appear hereinafter.

Accordingly, my invention is disclosed in the embodiments hereof shown in the accompanying drawings, and it comprises .the features of construction, combinationof elements and arrangement of parts which will be exemplied in the constructions hereinafter set forth, and the scope of the application of which will be indicated in the appended claims.

For a more complete understanding of the nature and scope of my invention reference may be had to the following detailed description taken in conjunction with the accompanying drawings,

. in which:

v ing a different length of core.

Figure 3 is a sectional view, at an enlarged scale, taken along the line '3 3 of Figure 2;

Figure 4 is a view, in front elevation, of another embodiment of a fuse link constructed in accordance with my invention, a portion being shown in section;

Figure is a sectional viewtaken along the line 5 5 of Figure 4;

Figure 6 is a view, partly in front elevation and partly in section, illustrating another embodiment of my invention;

Figure 7 is a sectional view taken along the line 4'l---l of Figure 6;

Figure 8 is a view, in side elevation, of a fuse housing in which the fuse links shown in the preceding figures may be positioned;

Figure 9 is a longitudinal sectional view taken along the line 9-9 of Figure 8;

Figure 10 is a detail cross-sectional view taken along the line l-Ill of Figure 9;

Figure 11 is a. detail sectional View taken along the line II-II of Figure 9;

Figure 12 is a fragmentary sectional view of a fuse device of the liquid arc extinguishing ty-pe in which another embodiment of the present inven-tion is employed;

Figure 13 is a sectional view, at an enlarged scale; taken along the line i3-I3 of Figure 12; Figure 14 is a view, at an enlarged scale, of the composite fusible element shown in Figure 12, the sheath being shown in section and the remaining parts being shown in elevation;

Figure 15 is a longitudinal sectional view of a replaceable fuse link employing a strain element and a composite fusible element;

Figure 16 is a sectional view, at an enlarged scale, taken along the line I S-IS of Figure 15; and

Figure-17 is a sectional view, at an enlarged scale, taken along the line I1-I1 of Figure 15.

Referring now particularly to Figure 1 of the drawings, it will `be observed that the reference character l5 designates, generally, a fuse link which includes a composite fusible element shown generally at i6, to .which flexible conductors I1, in the form of a plurality of strands of wire, are connected. It will be understood that the flexible conductors I1 may be connected to suitable circuit terminals in the circuit in which the fuse link l5 is connected for projecting the same. The composite fusible element I6 comprises a core i8 and a sheath or sleeve I3. 'I'he core I8 is composed of a metal having a relatively low melting point, such as tin, while the sheath or sleeve I9 is composed principally of 'a metal having a relatively high melting poin't, such as silver.

'Ihe action on blowing of the composite fusible `element I6, formed of two distinct metals such as silver and vtin which are capable of alloying with each other, is entirely different from that which takes place when a fusible element is formed entirely of metal, such as silver, tin, lead, zinc or aluminum or alloys of A these or other metals. When suiiicient current flows through a fusible element of the latter type to heat it to its melting point, the metal passes from the solid to the liquid state and, while the heat of fusion is being applied, the temperature renains substantially constant. Since the metal is in the liquid state and unrestrained, it flows away from its solid state position or is vaporized by the heat of the resulting arc and opens the circuit. This action takes place at'a rate depending solely upon the heat generated in the fusible element for a given set of operating conditions.

When sufficient current flows through a composite fusible element under this same set of operating conditions to raise its temperature to the melting point of the lower of the two metals forming it, analloying action begins to take place. Since the melting point of the alloy thus formed is lower than that of eithery of the two metals, the change from the solid to the liquid state is accelerated. Moreover, since the resistance of the alloy formed is greater than the comblned resistance of the two metals in the solid state, the change is further accelerated for the reason that the heat generated in the fusible element is a function of its resistance. Once the alloying action sets in, the change of a portion at least of the fusible element from the solid to the liquid state takes place with extreme rapidity due to vchanges in these two factors, namely, melting point and resistance. At the same time,

until the melting point of the lower of the two metals is reached, substantially no change takes place. With a'proper proportioning of the relative amounts of the two metals forming the composite fusible element I6, it is possible to provide a fusible element the characteristics of which will remain unchanged until it is heated to the tem- -perature at which the lower melting point metal melts. At this definite point the change from the solid to the liquid state begins to take place and, because of the lowering of the melting point of the resulting alloy and the increase in its 'resistance, the action is somewhat cumulative and positive circuit interruption takes place. It is then possible to more accurately predict the conditions under which a composite fusible element, such as a silver sheathed tin element, will lblow than is the case when the element is formed of a metal such as pure tin for example.

In the design of fusible elements it is necessary not only to consider the current at which an element will blow when it is heated to fusion temperature for the first time but also it is necessary to consider the operating characteristics of the ,element after it has once been heated nearly to the melting point, such as may occur as a result of transients,`short time overloads and the llke,`

and then the temperature of the element decreases so that, at that time, it does not blow.y Under such conditions there may be a change in the crystal structure of the metal as well as a change in its physical appearance.

Considering, for example, a fusible element formed of pure tin, it has been found that it will conduct a certain overload for a given time without blowing but the application of the same overload -conditions for the same time subsequently may cause it to blow. 'Ihis somewhat inconsistent action Inay be attributed to the fact that the tin fusible element is necked down or somewhat reduced in cross section intermediate its ends because of its having been heated to a temperature approaching its melting point so that the same cross-sectional area is not available for conducting current as was previously the case. With such a fusible element it is not possible to accurately predict just when it will blow under substantially all operating conditions. When the composite fusible element I6 is employed, this necking down action cannot take place for the reasonthat the tin core I8 is restrained by the surrounding sheath or sleeve Il of silver.- However, as soon as the fusible element I6 is heated to a temperature that is sufficient to initiate the melting of the tin core IB, the alloying action takes place with the accompanying increase in resistance and the circuit is positively opened without delay.

The action of a fusible element of the prior art, such as an element composed of silver, tin,

and conductor I1. respectively, to

to the rapid change from the solid to the liquid state of the composite fusible element, while the other ball rolls along a dat surface correspond-f ing to'the relatively slow change from the solid l to the liquid state of the fusible elements of `the mm-1mmimisitinsminiman.` nwinusw.

dersfcod that a fusible element composed entirelyof silver will operate at a,relatively bieb temperaturewhenitiscalledupontocarrycurrent for appreciable lengths of time close to the minimum fusing current. By combining the characteristics of tin andsilver it'is possible to take advantage ot the low temperature at which the composite fusible element i. will operate over sustained-periods ol current now close to the minimum fusing-current snd,.at the same time, to obtain the durabilitcharacteristic ofA silver because of its non-deteriorating ability.

As'shown in ligure 1 of the drawings, the endsv 0 2l of the sleeve 'or sheath ii extend well beyond the ends 21 of the core Il.- The ends I! oi' the flexible conducwrs i1 mens inw un ends il of thesleeve orsheath il-and into abutting relation withthe ends 2i of thecore i8. The ends llofthesleeveorshesth llarethen illustratedmntotheends 2i and!! the same therein. Since the ends!! of the nexible conductors II are readily deformable. they arewellsuite'diorthepurposeofnllingtheends ,zeonnesleeveonham lstcproviseeieetrien connection thereto and to conduct heat away from the core il.- y With a view to improving the connection lie-i connectingsleevesllsevetoreinforcetheends not the sleeve or sheath il, particularly at elevatedtemperatureaandtoholdthesameintight fitting engagement with the ends I2 o! the nexible conductors I1.

i It will bel understood that the several parts formingthefuselink llmaybeotdiiferentrelative sise than illustrated in the drawings. Por the construction of a fuse link for one particular rating the following dimensions and materials were employed. The core Il may be composed oi' pure tin wire 1%" long and having a'diameter of .107". 'I'he sleeve or sheath Il may be composed of pure silver tubing having a length oi' 2%1' side diameter of .148". copper sleeves Il are 9S" long. while the ble conductors ll may be of any suitable length, for example, 3" long. Tests have indicated that the temperature of the sheath Il oi' a fuse link having these dimensions will be about250" C. iustprior to blowing. It is pointed out that these figuresare by way of illustration only and are not to be con-l strued as in any way limiting the proportions in which the various elements may be employed.

Because of the presence of the low melting pointcore il thefuselinkilwilloperateata relatively low temperature even though it is called upon to conduct current in an amount that is close to the minimum fusing current. It is then possible' to provide a suitable housing for the fuse link Il in close proximity thereto which will not be subjected to a relatively high temperature,

such as the temperature that obtains when a fuse link formed solely of silver is operated close to its minimum-fusing current. K In Figure 2 of the` drawings another embodiment of the invention isillustrated. The fuse linkii'thereshownissimilartothefuselink' Il shown in Figure 1. However, the core Il is relatively somewhat the nexible conductors Il extend well within the sleeve or sheath il and beyond the deformed ends thereof.v This construction is desirable for two reasons. Hrst, it is unnecessary to deform the solid tin forming the core, as is the case in the rconstruction ahem in Figure 1. Second, the heat that is gencratedin the tin core il ismore readily. conducted away since the nexible conductors i'l are formed of strands of copper and are. therefore. capable of conducting heat much more'readily than is tin.

f -It will be understood that the length oi the tween the composite fusible element il and the iieble' conductors I1, tubular connectors 2l in the ion of copper sleeves may be positioned are formed oi' alloy metal rather than pure metal,

aroundtheendslloithesl'eeveorsheathl.

low melting 'point core relative to the length maybedesired. Itwillalsobelmdel'stomzlthat l'br example, copper may be employed orsleeveaudthecoremaybe formed oi bismuth Aso the core may be formes of sincor'lead or other like metals. It is not intended to limit this invention to the use of pure metals for the core and sheath. Either or both of these members may be formed of suitable alloys 'as may be found to be desirable.

While the present inventionis concerned pri- It will now be apparent that I have provided and deformed therewith, as shown. The tubular `'H5 a new method of opening an electric circuit on and an inside diameter of .128" and an outl shorter vand the ends 22 of the high melting point sheath may be varied well as therelative cross-sectional areas, ss-

metals thanmilvcr .and tin may be em,

i (2) Forming an alloy having a melting point lower than that of the lower melting point metal, thereby accelerating the change of a portion of the fusible elemen-t from the solid tothe liquid state; and

(3) At the same time increasing the resistance of the fusible element, due to the formation of the alloy,.to further accelerate the change in state by the generation of additional heat.

By varying the relative cross-sectional areas of the core and sheath or sleeve, by varying the relative lengths thereof, and by varying theheat conducting capacitybetween the core and the terminals, it is possible to provide a wide variety of fusible elements the operating char-acteristics of which can be accuratelyv predetermined. Such fusible elements may be applied in circuits where highly selective action is required between two or more fuse devices connected in series circuit relation, depending upon the' particular point a-t which the f-ault occurs or at which the overload occurs that requires the circuit to be interrupted.

In Figures 4 and 5'of 'the'drawings another then flattened, as shown, to provide the desired connection.

It will'be observed that the intermediate portions 34 between the

ends

32 and 33 of the terminal connectors 3l form closures for the drilled apertures in the ends 33. These closures prevent the escape of the core metal 28. If desired. the core 28` may be substantially shorter than the sleeve or sheath 29, as shown in Figure 2 for example, and the ends of the sleeve or sheath may be filled with conducting material, such as strands of copper wire as will herein-after appear, to conduct heat away from the core 2B for the purpose of increasing the rating of the link as well as for other purposes which will also be set forth.

With a view to protecting the composite fusible element from injury while it is being handled and carried about, the construction shown in Figures 6 and '1 of the drawings may be employed. As there shown, a fuse link 31 is provided havingL terminal connectors 38 that are arranged to interconnect a composite'fusible element, shown generally at 39 and comprising a low melting point core 40 and a high melting point sleeve or sheath 4| formed of tin and silver, respectively, for the reasons set forth hereinbefore, and flexible conductors 42. Intermedil ate the ends of the terminal connectors 38 will be noted that the sleeve 44 completely enembodiment of the invention is illustrated. The p closes the composite fusible element 39 and-there-- by serves to protect it from injury during handling thereof. vIn addition, the sleeve 44, when composed of a material .such as fiber, serves to evolve larc extinguishing gases, on the occurmelting p oint, such as silver. These metals are 4Circuit connections are provided by the flexible conductors 30.

In the construction of the fuse link |15, shown in Figures l and 2 of the drawings, the size of the flexible conductors i1 is vlimited by the size of inside diameter of the end portions 20 of the sleeve or sheath I9. For the purpose of providing for the use of exible conductors the size of which is not dependent upon the inside diameter of the highmelting point sleeve or sheath, the terminal connectors 3i are provided between the ends of the composite fusible element 21 and the flexible conductors 30. The terminal connectors 3| are somewhat tubular in construction and they may be formedfrom suitable lengths of solid -copper rod. The ends 32 are provided with suitablydrilled apertures for receiving the ends of the flexible conductors 30. These ends 32 are flattened onto the ends of the flexible conductors 30 in orderto secure them in position and provide electrical contact engagement therewith. In like manner the other ends 33 of the terminal connectors 3l are provided with suitably drilled apertures for receiving the composite fusible element 21 formed by the core 28 and the sleeve or sheath 29. Initially the core 28 and sheath 29 are of substantially the same length and the inside diameters of the ends 33 are such as to readily permit the insertion of the ends of the composite fusible element 21.` The ends 33 are rence of an arc, that assist in extinguishingfthe same;

In order to house the fuse link 31, shown in Figure 6 of the drawings, or the fuse links shown in Figures 1 and 4 of the drawings, the housing shown generally at 46 in Figures 8 and 9 may be employed. The housing 46 comprises a fuse tube41 that is preferably formed of fiber and has relatively thick walls, with a longitudinal bore 48 for receiving the fuse link, such as the fuse link 31. The ends of the fuse tube 41 are externally threaded for receiving in threaded engagement therewith fuse tube ferrules 49.- The outer ends 59 of the ferrules 49 are generally cylindrical in shape and are provided with cylindrical apertures 5I therethrough that are arranged to form extensions of the bore `48. Each of the cylindrical end portions 50 is provided with a longitudinal slot 52 through which the flexible conductors 42 may be positioned for placing them around the cylindrical portions 50, as is more clearly shown in Figure 10 of the drawings. It will be observed that a shoulder portion 53 is provided intermediate the ends of the fuse tube ferrules 49 for receiving the flexible conductors 42 in contact engagement therewith. Suitable pins 54 extend through the threaded ends of the fuse tube 41 and the ferrules 49, as shown, for holding them securely in place.

With a view to holding the flexible conductors 42 is position, cable clamp nuts 55 are provided. It will be noted that the inner ends of the clamp nuts 55 are internally threaded for engaging corresponding external threads about the inner ends ananas screwed into positionwiththeexible'ccnductors Ildisposedasshownaroimdthecylindricalends' Ilvoftheferrulesll-,theywillbeclampedbetweentheshoulderportionsIIanidli.

Itisdesirahlethatsomeindicationbeprovidedthatthefuselinktlhssblcwn. Invmost .insulating material such as Bakelite."

cases, when the fuse link I1 blows, a` considerable .volume of gas is generated inside of the bore Il ofl the fuse tube Il. Advantage is taken of the 'generation of gas pressure inside oi the fusotulael'lbyprovidingreadilyexpellableplugsv Il in cylindrically shaped extensions I8 of the clamp nuts Il; The plugs llare preferably formedofcorkandtheymaybepaintedasuitable color, for example, red, as shown, to more readily provide for determining whether or not the fuse devicelhas operated.

Itwillbelmdersioodthattheiusehousing maybeplacedinasuitablempportdeviceand that suitable terminals may be provided for con,- nection to the cylindrical end portions Il of theclamp nuts IB.

As indicated; considerable pressure may vbe generated within the bore Il of the fuse tube Il when the fuse device Il blows. If thehousing Il werearrangedtobeventedfromoneendonly.it

pute ,relrmdorv tingmstenal, ammaedintotheferruleuformountingthereinan arcing tube il that also'ls formed of a suitable As shown, the mounting plate Il and the arcing tube Il are provided with cooperating ilanges by means of which the latter is supported bythe former.

Suitable washers 88, formed of readily frangible material, such as Bakeliteff are secured to the mounting plate by screws. (l in overlapping relation with the arcing tube Il to hold the same in position until suillcientpressure is generated Y within the housing or sleeve' t! to blow it out of its upper end.

'lhe fuse link t2 is provided with upper and lower terminals l0 and TI. The upperterminal Il is mounted in a supportspider 12 and is secured thereto by a nut ll. The lower terminal 1I is provided with outwardly extending pins Il that are arranged to carry a liquid director 'il that is retracted with the terminal 1l o'n blowing ofthe fuse link l2 by a coil tensionspring Il to direct liquid, which illls the housing or sleeve I3 to the level indicatedyinto the varcing chamber would be necessary to provide a support that would have sumcient strength to withstand the reaction applied to the housing; In order to lavoidthis diiilculty the housing Il is vented att be possible that suillcient pressure wlllgn'ot be generated within the bore 4l to cause the plugs I'I to be expelled. However, this condition is notv often encountered. Y

` Bincethefusetubellisformedofamaterial suchasbengaseswhichassistinextingulshing thearciormedonblowingofthefuselinkllare levolved'i'rom the bore Il. The blast action thereby created materially assists in quickly extinguishing the arc. l

The presentinvention may be embodied in a fuse device of the blast actiorrarc extinguishing type. such as shown in the co-pending application 0f Nicholas J. Cnrd, Serial N0. 470,416, lcd

July 24, 1930, and assigned to the assignee' of this application, n0w.Patent No. 2,091,430,l This embodiment of the invention is illustrated in Figure l2 of the drawings.

As shown, a fuse device, designated generally hy the reference character 0I; is provided, that is generally of the type disclosed in the copendingl application of Conrad, but which is provided with a fuse link, shown generally at Il, that is constructed in accordance with this invention. 'Ihe details of construction of the fuse device 0i willbe set forth herein only insofar as is necessary to illustrate the present invention.

The fuse device 0i includes a sleeve or housing that may be formed of glass or Bakelite" and it has as its ends suitable terminal ferruies, one of which is'shown at Il. A vent cap Il is suitably pressed onto the upper end of the ferrule Il and is adapted to be blown oi! on generation of suillcient pressure inside of the sleeve or housing I3, when the fuse link I2 blows. A mounting or tube Il for assisting in extinguishing thearc drawn therein. A ilexible conductor 1l is provided for interconnectingv the lower terminal 'Il and the lower ferrule oi' the housing or sleeve Il,

'aswillbereadilyunderstood 'I'he 99er and lower terminals 'III and Il are arranged to he electrically interconnected by a composite fusible element that is shown generally v at Il. The fusible element l0 extends into suitable drilled apertures IZ and Il in` the opposing faces of the terminals 'III and 1I.

i relieve the fusible element 80 of the tension Astress that would otherwise be imposed by the spring 1l, a tension element Il in the form ot a wire composed of a high strength metal, such as a nickel-chromium alloy, is also provided between the terminala Il and Il withits corrugated ends Il disposed in suitable apertures I6 and Il therein With a view to protecting the fusible element Il and the strain element I4 of the fuse link t! during installation, and from vibration afterinstallation, a sleeve Il formed of suitable insulating material such as Bakelite" is provided Y. around them andy around suitable cylindrically shapedporti'ofnsof the terminals lll and 1i, as

Illustrated. The sleeve 8l isA provided with apertures Il adjacent its ends to provide for the escape of liquid therefrom so that no liquid will remain in engagement with the fusible element Il when the fuse device 8| is in the upright position for the purpose of avoiding change in its time-current characteristics.

The details of construction of the fusible element Il are shown more clearly in Figure 14 of the drawings. As there shown, the fusible element Il comprises a core li, formed of a suitsleeve or sheath $2, formed of a` relatively high melting point metal such as silver. The ends I3 of the sleeve or sheath 92 extend substantial distances beyond the ends of the core 0I and these ends are filled with short lengths 94 of conductive material formed by a plurality of small strands of wire. If desired, metal plugs may be substituted for the strands of wire u. These plugs would be preferably formed of high heat conducting metal such as silver in order to readily conduct the heat generated in the core Il to the terminals .10 and 1|'.

As indicated hereinbefore, the ends of the fu- In order to.

- 82 and 83 in the terminals. 10 and 1|.

sible element 80 extend into suitable apertures These ends are secured therein by deforming the adjacent wall of the terminals, as indicated at 95 in Figure 13 of the drawings. ende'd tool is provided for deforming the adjacent terminal material to provide not only for securely holding the fusible element 80 in place,

' but also to provide fon electrical contact engagement therewith.

ln a similar manner the corrugated ends 85 of the strain element 84 are secured in the apertures 86 and 81 of the

terminals

10 and 1|. As indicated at 96 in Figure 13, the adjacent wall of the upper terminal is deformed onto the corrugated end 85 in the aperture 86.

Since the ends of the composite fusible element 80 are secured to the

terminals

10 and 1| by deorming a portion of the Walls thereof, it is desirable that these ends be so constructed that the deforming operation may be readily and eiilciently performed, and the desired contact engagement obtained. It is for this purpose that the ends 93 of the sleeveor sheath 92 are preferably filled with the readily deformable strands 94. Since the core metal 92 may become softened when the fuse link 62 is called upon to conduct current for sustained periods close to the minimum fusing current, it

is further desirable that some material such as .y

composite fusible element is present for the reason that its operating temperature is much lower than that of a silver fusible element when conducting current close to its minimum fusing current. The major portion of the heat that is generated in the liquid fuse is conducted away from it through its end terminals, such as the ferrule 64. It will be noted that Vthis ferrule is cemented onto the glass housing 63. lt

A suitable blunt is essential foi-satisfactory operation of a liquid fuse that a fluid tight'sealbe maintained to insure that the insulating properties of the liquid will remain unchanged so that, on operation, it X will be capable, not only of assisting in extinl guishing the arc, but also of providing a suitable .comprise a pair of relatively infusible terminals that are interconnected by fusible means.I A sleeve of insulation is ordinarily secured to one of me and other terminal to protect the link during handling and to provide certain arc extinguishing characteristics. Such links are ar:

gig' terminals and it extends over the fusiblel ranged and constructed so that they are interchangeably adapted to Ibe inserted in practically any of the commercial types of fuse tube housings that are now being sold.

Such a construction is illustrated in Figure l5 of the drawings.4 As there shown, the reference character |00 designates, generally, a vreplaceable fuse link of the universal type that is provided with a .pair of relatively infusible terminals |0| and |02 that are arranged to be in-r terconnected by a composite fusible element |03 and a strain-element |04. 'Ihe fusible element S03 may be constructed similarly to the fusible element as shown in detail in Figure 14 of the drawings.

for receiving the ends of the fusible and strain elements |03 and |04. The outer surface of the lower portion ||2 is deformed, as shown at ||5 and H6 to secure the ends of the fusible and strain elements |03 and |04 therein.

The upper end portion |1 of the lower terminal 502 is formed similarly to the lower portion ||2 of the 'terminal |0| for receiving the other ends of the fusible and strain elements |03 and |04.

The outer surface of,.this portion is likewise de" formed to securely hold these elements in position. Since the ends of the sheath forming a part of the composite fusible element |03 are iilled with readily deformable material, such as the fiexible conductors 94, (Figure 14), its ends may be readily deformed as described hereinbefore, so that proper contact engagement will `be provided with the terminals |0| and |02 and the tin ycore will not be permitted to flow when it is in the softened state.

g The lower end ||8 of the terminal |02 is provided with an axially drilled aperture I9 for receiving one end of a flexible conductor |20 that comprises a plurality of strands of wire. As shown in Figure 17, the opposite sides of the lower end portion ||8 are deformed inwardly both longitudinally andV transversely for the purpose of securing the ilexible conductor |20 therein and maintaining contact ngagement therewith under relatively high pressure.

Since this .particular terminal constructionl is illustrated and described in the copending application, Serial No. 138,188, led April 21, 1937, by myself and Sigurd I. Lindell, and assigned to the assignee of this application, a more detailed description will not be set forth herein.

With-a view to providing for connection to an external terminala cone terminal |2| is pressed onto the exible conductor |20. It will be understood that the fuse link |00 may be mounted in fuse housings in which one or more springs are` provided for biasing the terminals I 0| and |02 apart so that the arc may be rapidly extinguished. In such case, it will be uitderstood that the strain element m relieves the fusible'eiement m or the stress that would otherwise be imposed there' on by the biasing forces.- However, it lwill be understood that the fuse link Ill may be mounted in fuse housings in which springs or other biasing means arenotv employed. y I

Since certain further changes may be made in l the foregoing constructions, and different embodiments of the invention may be made without del. Ima fuse, in combinatioma core formed of metal having a relatively low melting point, a

metal' sheath having a relatively high melting point and forming a self-supporting container for Y said core unbonded thereto with at least one end extending beyond the corresponding end of said core, and metal plug means extending into said one end of said metal sheath for conducting heat away from mid core.

2. In a fuse,in combination, a core formed of metal having a relatively low melting'point, a metal sheath having a relatively high melting point and forming a container for said core with at .least'one end lextending beyond the corresponding end of -said core, and a flexible conductor formed by a phirality of strands of 4wire extending into said one end of said metal sheath 'and said one end being deformed thereon.

3. In a-fuse link, in combination, a core formed of metal having a relatively low melting point, a

.4 metal sheath having a relatively high melting point and forming a container for said 'core with at least one end extending beyond the corre'- sponding end of said core, a ilexible conductor formed by a plurality of strands of wire extending ametalsleevearmmdsaid oneendof saidnietal sheath, said metal sleeve and said one end of said metal sheath being deformed about said ilexible conductor.

4. A fuse comprising, in combination. a core formed of metal having a relatively low melting point, a 'metal sheath having a relatively high melting point and forming. a container for said core of such length that its ends extend beyond the ends of said core, and conductor means exrtendinginto said ends of said metal sheath for conducting heat away-from said core.

5. A fuse comprising, in combination, a core formed of metal having a relatively low melting point, a metal sheath having a relatively high melting point and forming a container for said core of such length that its ends extend beyond the ends of said core, and a pair of flexible conductors each 'formed by a plurality of strands of wire extending into said ends of said metal sheath and said ends being deformed thereon.

6. A fuse link eomprising, in combination, a core formed of metal, having a relatively low melting point, a metal sheath having a relatively high melting point. and forming a container for said core of such length that its ends extendbeyond the ends of said core, a pair of nexible obnductors eachli'ormed by a plurality of strands of wire. extending into said ends of said metal sheath and into abutment with the ends of said core, and a metal sleeve aroundeach end of said metal sheath, said ends of said metal sheath and said sleeves thereon being deformed about said ilexible conductors.

'1. Inafuselink,incombination,ametei core, a self-supporting continuous container surrounding said core formed of metal which alloys therewith on ow of current suillcient to-melt the same, a terminal conductor, and a terminal connector having one end adapted-to receive said container and said` core and to retain thelatter in the liquid state and the other end adapted to receive said terminal conductor.

8. In afuselink,\in combination, a metal core, a self-supporting continuous container surrounding said core formed of metal which alloys there with on flow of current sumcient to melt the A same, a terminal conductor, a terminal connector having one end adapted to receive said core and container and the otherend adapted to receive said terminal conductor, and closure means between said ends of said terminal connector adapted to retain said core inthe liquid state.

9. In a fuse link, in combination. a metal core, a yself-supporting container surrounding said core formed of metal which alloys therewith on ilow of current suillcient Vto melt the same, a terminal conductor, and a te connector having one end adapted to receive said container and core and to retain the latter in the liquid state and the other end adapted to receive said terminal conductor, said one end of said terminal connector being deformed about said container and said other end of said terminal connector being deformed about said terminal conductor.

10. In a fuse link, in combination, a core ccmposed principally of tin, a continuous tubular container composed principally .of silver surrounding said core. a flexible conductor, and a terminal connector having one end adapted to receivesaid continuous container andsaid core and to retain the latter in the liquid state and the other end adapted to receive said ilexihle conductor.

il. In a fuse link, in combinationI acore com posed principally of tin, a tubular container com;

posed principally of silver surrounding said core,

a flexible conductor, and a terminal connector having one end adapted to receive said container and said core and to retain the latter in the same, a pair of flexible conductors, and apair of terminal connectors. each having one end adapted to receive said container and said core and to retain the latter inthe liquid state and the other end adapted to receive one of said ilexible conductors.

13. A fuse link comprising, in combination, a

core composed principally of tin, a tubular 'container composed principally of silver surrounding said core, a pair of ilexible conductors formed by a plurality of strands of wir'e, and a pair of tubular terminal connectors each having one end adapted to receive said container and said ocre and to retain the latter in the liquid'state and the other end adapted to receive-one of said ilexible conductors.

in combination, a j

14. A fuse link comprising, in combination, a core composed principally of tin, a tubular container composed principally of silver surrounding said core, a pair of flexible conductors formed by a plurality of strands of wire, a pair of tubular terminal connectors each having one end adapted to receive said core and container and the other end adapted to receive one of said' flexible conductors, and closure means intermediate the ends of each of said terminal connectors.

l5. A fuse link comprising, in combination, a metal core, a self-supporting container surrounding said core formed of metal which alloys therewith on flow of current suilcient to melt the same, a pair of flexible conductors, a pair of terminal connectors each having one end adapted to receive said container and said core and to retain the latter in the liquid state and the other end adapted to receive one of said fiexible conductors, and means mechanically interconnecting said terminal connectors in addition. to said core and container.

i6. A fuse link comprising, in combination, a metal core, a container surrounding said core formed of metal which lalloys therewith on flow of current suflicient to melt the same, a pair of flexible conductors@ pair of terminal connectors each having one end adapted to receive said container and said core and to retain the latter in the liquid state and the other end adapted to receive one of said flexible conductors, and a sleeve surrounding said container and said terminal connectors. l

i7. A fuse link comprising, in combination, a metal core, a container surrounding said core formed of metal which alloys therewith on ow of current sufficient to melt said core, a pair of flexible conductors, a pair of terminal connectors each having one end adapted to receive said core and container and the other end adapted to receive one of said flexible conductors, a knurled portion intermediate the ends of each of said terminal connectors, and a sleeve formed of insulating material surrounding said container and interiitting with said terminal connectors at the knurled portions thereof.

i8. In a fuse, in combination, a metal core, a container closely surrounding and extending beyond the ends of said core and formed of metal which alloys therewith on flow of current .suilicient to melt the same, and means filling the ends of said container for holding said core in place in the molten state.

19. in a fuse, in combination, a metal core, a

container closely surrounding and extending beyond the ends of said core and formed of metal which alloys therewith on flow of current sufficient to melt the same, readily deformable means liing the ends of said container for holding said` core in place in the molten state, and a relatively infusible terminal interfitting with and deformed onto each of said ends of said container.

'20. A fuse linkcomprlsing, in combination, a core formed principally of tin, a cylindrical sleeve vformed principally of silver closely fitting.

lf beyond the ends of the same, a plurality of strands of wire filling the extended ends of said sleeve for holding said core in place in the molten state, and a relatively infusible terminal interfltting with and deformed onto each of said ends of said sleeve.

22. A fuse link comprising, in combination, a pair of relatively infusible terminals adapted to be biased apart by a spring; a composite fusible element electrically interconnecting said terminals includinga metal core having a relatively low melting point, a metal sleeve surrounding said core and extending beyond its ends into said terminals, and a plurality of strands of wire filling.the ends of said sleeve extending into said terminals; and a strain element extending into said terminals for relieving said fusible element of stress imposed bythe spring tending to separate said terminals, said terminals being deformed onto the ends of said fusible and strain elements. A

23.' A fuse link comprising, in combination, a pair o relatively infusible terminals; a composite fusible element electrically interconnecting said terminals including a metal core having a relatively low melting point, a metal sleeve surrounding said core and extending beyond its ends into said terminals, and a plurality of strands of wire filling the ends of. said sleeve extending into said terminals; a strain element extending into said terminals for relieving said fusible element of stress tending to separate said terminals, said terminals being deformed onto the. ends of said fusible and strain elements, and a sleeve of insulation interfltting with said terminals and surrounding said fusible and strain elements.

24. A fuse link comprising, in combination, a pair of relatively infusible terminals, a composite fusible element electrically interconnecting said terminals including a core composed principally of tin, a sleeve composed principally of silver surrounding said core and extending beyond its ends into said terminals, and a plurality of strands of wire filling the ends of said sleeve extending into Y saidterminals; and' a strain element extending into said terminals for relieving said fusible element of stress tending to separate said ter-v minals, said terminals being deformed onto the lends of said fusible and strain elements.

25. A fuse link comprising, in combination, a metal core, a self-,supporting container surrounding said core composed' of metal which remains substantially unchanged on flow of current sumcient to melt said core; a pair of relatively infusible terminals secured to the ends of said container and adapted to retain said core in the liquid state, one having a terminal fitting receiving portion and the other having a conductor receiving portion; and a fiexible conductor securedin'said conductor receiving portion.

26. A fuse link comprising, in combination, a metal core, a. containerksurrounding said core formed of metal which alloys therewith on flow of current sufficient to melt the same; a pair of relatively infusible terminals secured to the ends of. said container, one having a' terminal fitting receiving portion and the other having a conductor receiving portion; a flexible conductor secured insaid conductorl receiving portion, and' an insulating sleeve secured to said one of said terminals and extending over the other of said terminals.

27. A fuse link comprising, in combination; a pair of relatively infusible terminals, one having a terminal fitting receiving portion and the -other having a conductor receiving pmtion; a fusible element electrically interconnecting said terminals including a corev formed of metal having a relatively low melting point and a surrounding self-supporting sheath formed of .metal adapted to allow'with said core on flow of current sufiicient to melt the same, said terminals being adapted to retain said core in the liquid state, af

strain element mechanically interconnecting said terminals, and a exible conductor secured' in said conductor receiving portion.

V28. A fuse link comprising, in combination; a pair of vrelatively infusible terminals, one having a terminal ntting receiving portion and the other having a conductor receiving portion; a fusible element electrically interconnecting said terminals including a core formed of metal having a relatively low melting point and a surrounding sheath formed of metal adapted to alloy with said core on flow of currentl sumcient to melt the same, a strain element mechanically interconneeting said terminals, a exible conductor secured in said conductor receiving portion, said terminals being deformed onto thev respective ends of said fusible and strain elements and' said flexible conductor, and an insulating sleeve secured to said one of said terminals and extending over the other of said terminals and aroimd said' fusible and strain elements.

29. In a fuse link, in combination, a core formed of metal having a relatively low melting point, a metal sheath having a relatively high melting point and forming a container for said core with at least one end extending beyond the corresponding end of said core, and a flexible conductor formed by a plurality of strands of wire secured in said one end of said metal sheath.

30. In a fuse, in combination, a tin core, a silver sheath forming a self-supporting container for said tin core and extending beyond the ends of the same, and metal means carriedI by said silver 4sheath at the ends of said tin core for conducting heat away therefrom.

31. In a fuse, in combination, a tin core, a silver sheath forming a wif-supporting container for said tin core and extending beyond the ends of the same, and a metal plug withinsaid silver sheath at each end of said tin core for conducting heat away therefrom.

32. In a fuse, in combination, a core formed of metal having a relatively low melting point, a metalsheath having a relatively high melting point and forming a container for said core and extending beyond the ends of the same, and metal means having relatively high thermal capacity and heat conductivity carried by said sheath at the ends of said core for conducting heat away therefrom and limiting the transmission of heat thereto.

33. In a fuse, in combination, a core formed of tal having a relatively low melting point, a

meial sheath having a relatively high melting a terminal tting receiving portion and the other having a conductor receiving portion; a fusible element electrically interconnecting said terminals including a core formed of metal having a relatively low melting point and a surrounding sheath formed or mem adapted to alloy with said core on sow 75 or 'current sumcient to meu the same, a strain velement mechanically interconnecting said tersaid fusible and strain elements.

35. A fuse link comprising, in combination; a pair of relatively infusible terminals, one having a terminal fitting receiving portion and the other having a conductor receiving portion; a fusible element electrically interconnecting saidterminals including a tin core and a surrounding silver sheath, a strain element mechanically interconnecting said terminals, a flexible conductor secured in said conductor receiving portion, and an insulating sleeve extending between said terminals and aroimd said fusible and strain elements.

36. In a fuse, in combination, a core formed of metal having a relatively low melting point, a metal sheath having a relatively high melting point and forming a container for said core and extending beyond the ends of the same, metal plus means nlling the ends of said sheath for conducting heat away from said core, and a relatively infusible terminal intertltting with and deformed onto each end of said sheath and the metal plug means therewithin.

37. In a fuse, in combination, a core formed of metal having a relatively low melting point. a metal sheath having a relatively high melting point and forming a container for said core, and terminal means at the ends ofvsaid sheath at least one of which includes flexible conductor means and metallic sleeve means cooperating with said sheath and flexible conductor means whereby the same are mechanically and electrically interconnected.

the element and is capable of alloying with the.-

tin core when heated to its melting temperature, thereby increasing the resistance of the element so that it ruptures once the alloying action is initiated.

40. In a fuse, in combination, a core formed of metal having a relatively low melting point, a sheath formed of metal having a relatively high melting point surrounding said core and extending beyond the ends if the same, and an imperforate plug formed of metal having a relatively high melting point filling each end of said sheath and engaging the ends of said core for conducting heat away therefrom. V

41. In a fuse, in combination, a core formed of metal having a relatively low melting point. a sheath formed of metal having a relatively high melting point surrounding said core and extending beyond the ends of the saine, an imperforate plug formed of metal having a relatively high melting point lining each end of said sheath and engaging the ends of said core for conducting heat away therefrom, and a relatively infusible terminal inter'fltting with and deformed onto each end of said sheath.

silver sheath surrounding said core and extend-- ing beyond the ends of the same, and 'a silverA plug illling each end of said sheath and engaging the ends of said core for conducting heat away therefrom.

44. a fuse, in combination, a tin core, a silver sheath surrounding said core and extending beyond the ends oi' the same. an imperforate plug formed of metal having a relatively high melting point lling each end of said 1 sheath and engaging the ends of said core for conducting heat away therefrom, and a relatively infusible terminal interiltting with and deformed onto each end o! said sheath.

HUGH A. TRIPLETT.