US2074538A

US2074538A - Fuse

Info

Publication number: US2074538A
Application number: US539436A
Authority: US
Inventors: Nicholas J Conrad
Original assignee: Schweitzer & Conrad Inc
Current assignee: Schweitzer & Conrad Inc
Priority date: 1931-05-23
Filing date: 1931-05-23
Publication date: 1937-03-23
Anticipated expiration: 1954-03-23

Description

Patented Mar. 23, 1937 PATENT OFFICE FUSE Nicholas J. Conrad, Winnetka, Ill., assignor to Schweitzer & Conrad, Inc., Chicago,lll., a corporation of Delaware Application May 23, 1931, Serial No. 539,436

37 Claims.

This invention relates to fuses in general and more particularly to means for sealing the end of a liquid filled fuse tube and providing a vent cap therefor.

In my prior Patent No. 1,743,322 of January 14, 1930 I show a fuse known as the Schweitzer & Conrad fuse which comprises a glass tube substantially filled with an arc quenching liquid such as carbon tetrachloride or the like and containing, at its upper end, a fuse wire which is maintained under tension by a spring and which controls a circuit extending between contact ferrules at the upper and lower ends of the tube. At the upper ferrule there is provided a vent cap which is adapted to be blown outwardly should the pressure within the tube become excessive upon the blowing of the fuse wire, thereby tending to prevent shattering of the glass tube. It is to such fuses that the present invention is particularly applicable and it is one of the objects of the present invention to provide an improved vent cap and means for securing the same, so as to effectively prevent contamination or outward creepage of the liquid within the fuse tube and yet to permit blowing of the cap when the pressure within the tube reaches a predetermined value.

In connection with fuses of the kind here contemplated it is highly desirable that the vent cap be secured in place without the use of solder, venting compounds, or other foreign material. Solder and the soldering process tends to introduce impurities for which the fuse liquid has a great affinity, resulting in internal contamination which lowers the dielectric strength of the insulating arc quenching liquid used, and also resulting in corrosion of the internal parts, particularly the fuse wire. Also, it is quite difficult to make a soldered joint entirely leak proof to a highly pene- 0 trating, highly volatile liquid such as is here used. These are but a few of the objections to the use of solder and they are equally applicable to the use of sealing compounds for sealing the vent cap in place. In the previously known methods of sealing the vent caps in place there was always great difdculty involved in maintaining a uni= iormity. of blowout pressure and at the same time maintaining a leak proof seal.

It is an object of the present invention to pro-= vide a vent cap construction which eliminates the use of solder or other foreign material and which admits of close predetermination and control of the blowout pressure, the arrangement being such that the vent cap will blow at the same pressure even after it has been in service for prolonged periods of time. A definite blowout pressure means:

(a) Prevention of glass breakage.

(b) Building up of definite internal pressure to assist in arc. extinction by the violent passage of the arc extinguishing liquid through the are at the time the cap blows.

(c) On extremely heavy blowing there is a positive and certain ejection of the metal laden vapor resulting in the prompt dissipation and deionization thereof.

There is another distinct advantage in providing a venting arrangement which does not require the use of solder or other sealing compounds. As previously pointed out, it is difficult to make a soldered seal which will not contamihate. the insulating liquid used and which will also not be penetrated by the same. In this type of fuse it has heretofore not been practical to replace the fuse link in the field, it being customary instead to ship the parts back to the factory for reassembly after the fuse has once blown. In my present fuse thevent cap comprises a thin dia-- phragm which is clamped in place, the clamping action being preferably around the entire periphery of the diaphragm to provide a mechanical seal between the diaphragm and its adjacent part. A nut threads onto the ferrule for producing the tight clamping action on the diaphragm. This renders the diaphragm easily removable and replaceable to produce a good seal, thereby permitting field reassembly of the fuse after the fuse link has blown.

Whereas, in prior fuses of the Schweitzer & Conrad type, the closure has been made by a disc or cap of relatively heavy metal sealed to the upper ferrule by a joint of graduated strength, according to the present invention the closure is made by a rupturable diaphragm, the body of which is graduated to retain only a certain definite pressure. In other words, the prior structure graduated the strength of the joint, but according to the present invention, the joint is made as firmly as may be desired, but it is the diaphragm. itself which is graduated to yield at the desired pressure.

The present invention provides another important function, i. e., directional control of the gases upon venting of the fuse to atmosphere.

In prior. fuses employing a disc held to the ferrule by a joint of predetermined strength, the release of the disc generally begins at some point on the periphery which results in the projection of a stream of arc gases in a lateral direction through such initial opening. The lateral projection of arc gases is undesirable because it y be directed in such a directionas to cause an interphase fault or fault to ground. Even if the disc should lift evenly on the top of the ferrule. there is nevertheless the tendency to release the arc gases in a sheet at right angles to the axis of the ferrule and expanding into a cloud. This is knovm as mushrooming of the discharge of the fuse. The same action tends to occur in the case of a cap blown ofi the end of the ferrule.

According to one phase of the present inven= tion, the thin rupturable diaphragm tends generally to burst at the center and thereby discharge the arc gases endwise of the housing. This is highly advantageous for then a definite direction is secured, and the gases issue as a stream and not as a sheet or cloud. Even if the rupturable diaphragm should yield first along the margin where it is clamped, the inner tubular walls of the ring which secures the diaphragm into place tend to direct the gases endwise of the ferrule instead of transversely thereof. The result is a direction of the gases in the region intended for the discharge and. not uncontrollably toward the mounting or adjacent conductors and the like.

The attainment of the above and further on jects of the present invention will be apparent from the following specification taken in conjunction with the accompanying drawings forming a part thereof.

In the drawings:

Figure 1 is a partial sectional view of a well known type of fuse to which my present invention has been applied;

Figure 2 is an enlarged frentary view of a portionoi the fuse shown in Figure l;

Figure 3 is a fragmentary sectional view of a different, and also well known, form of fuse to which my invention has been applied:

Figure 4 is a fragmentary sectional view of a portion of the fuse shown in Figure 3;

Figure 5 is a fragmentary sectional view of the top portion of a. ferrule of a fuse such as is shovm in Figures 1 or 3 and illustrating a modified form of my invention; and

Figures 6 to 16, inclusive, are enlarged frag mentary sectional views illustrating difierent forms of my invention.

In Figures 1 and 3 I have illustrated two to of my invention applied to fuses of the type shown in my Patent No. 1,743,322 of January 142, 1930 to which reference may be hadfor a more complete description of those fuses. It is, however,

\ to be understood that mypresent invention is not limited to fuses of this particular construction,

but that the fuses of this particular construc ion have been shown only for illustrative purposes.

The body of the fuse illustrated in Figure l. is formed of a tube or sleeve i of glass or other suit-= able insulating material upon the ends of which are secured metal ferrules 2 and 3 whichform terminals for the conducting parts of the fuse wire or link contained within the same. The ferrules are secured in position by suitable means providing a seal and packing for producing a fluid tight joint.

A terminal supporting member it which may comprise merely a fiat spring of a generally 8= v shaped formation rests upon a. shoulder on the accuses and in turn supports a lower terminal member l by means of a strain wire 3 of nichroxne or othehigh resistant material having a relatively grea tensile strength. A fuse wire it serves to main tain the electrical connections between the terminals it and l. The fuse wire and the strain wire are both located in a passage i i' formed in a non conducung plug 5 2 of cork or the like and secured to the upper terminal 6 as by making a close fit therewith. A coiled spring is is mechanically connected to the lower terminal 1 and exerts a continuous pull upon the same to snap it away from the upper terminal when the fuse and the strain wire yield. A flexible conductor it connects the lower terminal i with the lower ferrule thereby completing the electrical connections between the upper and the lower ferrule.

Ween the fuse wire it blows there is a momentary flow of a large current through the high resistance wire 3 which immediately heats and breaks under the combined action of the heat and the pull of the spring it. The lower terminot i is thereupon rapidly pulled downward to lengthen the gap between it and the upper terminal. The tube 5 is filled with a suitable insulatlog are quenching liquid such as carbon tetrachloride or the like for quickly extinguishing any are that may form. A liquid director E? is secured to the lower terminal l and moves therewith. As the liquid director moves downwardly it violently projects the insulating liquid into the region of the arc to quickly extinguish the same.

The portion of the fuse thus far described is well Known in the art and does not, per se, constitute the present invention, except in combinatlcn with the parts to be hereinafter described. The fuses of this general type must be closed against the entrance of foreign material therein and the closure should be so arranged as to permit an escape of some of the vapors produced upon violent blowing of the fuse in the event that the pressure within the tube 8 becomes excessive. if this means of escape is not provided then, under such circumstances. the glass tube i will shatter with the consequent objectionable. results. Such fuses are provided with vent caps and the present invention is particularly concerned with the provision of an improved vent cap and an improved way in which the vent cap is secured in position.

The vent cap comprises an exceedingly thin diap an it which is clamped in place in a cylindrical groove tiformed in the ferrule 2, by means of an annealed brass ring 22 which is pressed into the groove and then upset by means of a suitable punch or the like, thereby expanding the same to produce a very tight clamping action to prevent the creepage of liquid from within the copper foil of a thickness in the order of .0015 inch, although it is to he understood that I am not limited, to this precise thickness. The thickness of the foil used is determined by the size of the opening at the top of the ferrule and the blow-out pressure at which it is desired to have the cap 2% yield. An inverted cup-shaped cap 26 is pressed into the top'of the ferrule 2 in order to protect the exceedingly thin diaphragm 28 against external injury. Any other means'for protecting the diaphragm 26 against external injury may used. For instance. as shown in Figure 5, I may use a cap which fits over the outside of the ferrule 2. It is to be noted that the vent cap it is socured in place without the use of solder or any ing compounds are objectionable for the reasons previously pointed out. By the present arrangement I provide a seal which is free of all foreign matter and which will blow at a more or less definite pressure which does not appreciably change after the fuse has been in use for a period of time. For renewal of the fuse, the fusible link and its connected terminals can easily be replaced, The replaceable unit, including the terminals 6 and 'I with the terminal head or supporting member 5, is attached to the upper end of the spring, as by means of the screw shown in Figure 1. The supporting member 5 slides into place name upper ferrule 2, which has a seat for the same. This supporting member 5 is held in good conductive relation by the spring as well as by its own contact with the seat in the ferrule.

In Figure 3 I have shown a fragmentary portion of a somewhat different form of liquid filled fuse to which my invention has been applied. In this form of fuse the upper ferrule 30, which is of a somewhat different construction than that of the ferrule 2 of the fuse shown in Figure 1, is secured to the glass tube l in any desired manner so as to maintain a liquid-tight seal. An annular ring 3| rests upon a shoulder within the ferrule 30 and supports a non-conducting washer 32 through which extends the shank 33 of an arcing terminal lid. The shank of the arcing terminal is supported against downward movement by a strain wire of nichrome or other high resistance wire of great strength. The strain wire 3:? passes through the shank 33 and is secured at each end under the heads of suitable screws 36 mounted at diametrically opposite points in the flared or tapered surface 3? or" the ferrule 3d. The top or upper end of the shank 33 is provided with a removable screw 38 under which a fuse link 38 is secured at approximately its mid-point. The opposite ends of the fuse link 39 are mechanically and electrically connected to the tapered surface 31 or the ferrule at points mid-way between the screws 36. The fuse link serves to carry the current from the ferrule 30 to the shank 33 of the terminal 3d whereas the strain wire 35 serves to relieve the fuse wire of any mechanical stress incident to the supporting of the terminal 3%.

A liquid director ll is secured to the shank 33 in any preferred manner, as for instance by means of three screws spaced 120 degrees apart. A block 4a is secured to the shank 33 of the terminal in any desired manner, as by means of a number of set screws, so as to hold the block against longitudinal and rotative movement on the shank. The lower end of the terminal 34, of which the shank 33 comprises a part, is counterbored to receive a flexible conductor 45 of high electrical conductivity and is thereafter flattened on the conductor to produce a good electrical joint, as indicated at 5. The conductor corresponds to the conductor is of the fuse shown in Figure 1 and it is secured at its lower end to a ferrule corresponding to the ferrule 3 of the fuse shown in Figure l. A spring i5 is secured to the block 44in any desired manner, as by means of a pair of onset projecting pins ill- 3? which cooperate with the upper convolutions of the spring. One or more of the screws which secure the block 44 to the terminal 3d may also be utilized to help secure the upper end of the spring to the block #4. Wire guiding fingers fit are'secured to the terminal 3 5 and guide the terminal 7 within the tube 3 as the terminal snaps downward under the action of the spring 46 when the strain wire gives upon blowing of the fuse.

Upon occurrence of an overload the fuse 39 blows thereby removing the shunt across the strain wire 35'between the terminal shank 33 and the ferrule 30. The high resistance strain wire therefore immediately becomes heated and under the combined action of the heat and the tension of the spring 46 it gives, thereby releasing the shank 33. The terminal 34 is immediatelysnapped downward under the action of the spring to increase the gap in the circuit between the upper and the lower terminals. The fuse tube i is filled with insulating arc quenching liquid substantially to the level of the washer 32 and as the terminal 34 recedes the arc is drawn into this insulating liquid. In addition, the liquid director 34 violently projects fresh liquid into the region of the arc as the liquid director is drawn downward with the terminal. The are is therefore quickly extinguished. It is to be noted that the arc is initially drawn in the region above the washer 32 which region comprises an explosion chamber. The upper portion of this explosion chamber is provided with a vent cap which constitutes a releasable wall. In the event of a viclent blowing of the fuse the resulting pressure may become excessive, in which case the vent cap is ruptured thereby permitting the escape of the metallic vapors and preventing such a high rise of pressure as would shatter the glass tube l.

The present invention is particularly concerned with the construction of the vent cap which has been shown as applied to an otherwise standard and well known form of fuse for illustrative purposes only, it being understood that the venting arrangement, to be presently more fully described, is equally applicable to othertypes of fuses.

The upper portion of the ferrule 35] is internally threaded as indicated at 5d, the threads terminating at a shoulder 5i which extends around the inside of the ferrule and is provided with an upstanding circular ridge 52 having well rounded edges. The vent cap comprises a circular metallic diaphragm 53 which is exceedingly thin and may comprise hard copper foil of a thickness in the order of .0015 inch, although this thickness may be departed from to a considerable extent in order to provide the proper strength for the diaphragm to sustain a predetermined maximum internal pressure. A gasket 54 of annealed brassor the like is interposed between the diaphragm 53 and a nut 55 which is threaded into the threads 50 at the upper end of the ferrule and which securely clamps the diaphragm 53 in place. The nut 55 comprises a circular ring open on top to permit the escape, of

the pressure which causes the blowing of the diaphragm 53. The nut 55 affords a protection against external injury of the diaphragm 53. The

nut 55 serves a further useful function in preventing injury by the arc to the ferrule. The ferrule is a permanent part of the fuse housing, whereas the nut 55 is replaceable. Sometimes in the blowing of a fuse of this type. the arc persists and it will burn and injure the uppermost part of the ferrule to which the extremity of the arc is driven by the outward flow of arc extinguishing material. The nut 55 forms an extension of the upper end of the ferrule, and injury to it by the arc is not serious, inasmuch as the nut 55 is replaceable. The same function is performed by other forms herein disclosed, in which the clamping nut or ring forms an extension of the ferrule. If desired, an additional cap may be fitted over the end of the ferrule 3h toi'urther protect the diaphragm against external injury. The additional cap does not make such a tight fit as would prevent its expulsion upon blowing of the diaphragm.

An arrangement including an externally fitted cap for further protecting the diaphragm is illustrated in Figure 5. In this case I have illustrated only a portion of the upper end of a ferrule which portion may be representative of the ferrule of the fuse shown in Figure 3 or of the ferrule of the fuse shown in Figure l. The diaphragm is indicated at he, the clamping nut at ti, and the protecting cap at 62. The diaphragm may comprise a somewhat softer disc than the disc 53 of Figure 4-. in which case a somewhat thicker material is used with the result that the brass washer or gasket 5% of Figure 4 may be omitted. It is however to be understood that the diaphragm as may be made of harder material, in which case it is thinner, and a soft ring gasket is used.

In Figures 6 to 16, inclusive, I have illustrated various modifications of my invention. In these figures only a portion of the upper ferrule has i been illustrated and while I have shown in connection with some of the modifications a ferrule the top of which is provided with a tapered portion corresponding to the portion 3? of Figure 3 and in other of the modifications a ferrule of the type corresponding more nearly to that shown in Figure 1, it is to be understood that these showings are merely illustrative and the venting arrangements shown in any of these iigures may be applied equally well to either type of ferrule or to ferrules specifically different from the ferrules here illustrated. In the form of my invention illustrated in Figure 6, the diaphragm 65 is wedged into a tapered groove or slot 656 formed in the shoulder El of the ferrule and extending around the entire periphery of the same. A wedge 68 comprising an endless ring is jammed into the groove 66 by means of a nut as which is threaded into the ferrule. The taper on the wedge is preferably made very small, in the order l of 5 or degrees, so that the wedge may be forced into place to a considerable extent in order to produce a tight seal around the entire periphery at idl l. The rim of the diaphragm I5 is curved around the lower curved edge of the wedge ring is and is wedged in place by means of -a nut 76 which threads into the ferrule and forces the wedge ring against the corner of a shoulder ll extending around the inside of the ferrule. As the nut 16 is turned downward the lower edge of the wedge ring 13 is extended outwardly to produce a liquid tight seal around the entire periphery of the diaphragm l5. It is to be noted that in this arrangement there is produced in effect two seals, one along the ring where the wedge 13 jams the diaphragm against the horizontal portion of the shoulder ill and the other along the ring where the wedge It bears against the vertical portion 'on the inside of the ferrule.

In Figure 8 I have shown an arrangement which is very much similar to that shown in Figure '7, difiering therefrom mainly in that I here use a diaphragm which is upwardly curved. 'I'he curaovasse vature approaches'that of a portion of a spherical surface, and the lower edge of the clamping nut 56 is curved as indicated at iii to conform with this surface. Since the portion of the diaphragm that bears against the curved surface Si or" the nut is reinforced at itsback by this clamping nut, it is apparent that the total unpacked area of the diaphragm which must oppose the internal pressure resulting from the blowing of the fuse is materially decreased, as a result of which a thinner diaphragm may be used or, stated conversely, a diaphragm of the same thickness may be used upon a fuse ferrule of an appreciably larger internal diameter.

In Figure s I have illustrated an arrangement for clamping the diaphragm in place by the use of an endless ring of a triangular cross section. The endless ring is illustrated at 85 and is held in place by a nut t6 provided with a generally curved lower corner 8'? which "nears against the triangular wedge 85. In other respects this clamping arrangement is similar to that shown in Figure 8.

In the arrangement shown in Figure 10, a clamping ring so, of a somewhat difierent cross section, is used. The lower surface of the clamping ring so is well rounded and presses the diaphragm against a shoulder on the ferrule along substantially a circular line. The clamping nut is indicated at 9i and the foil diaphragm at at.

In the form of my invention illustrated in Figure 11 the seal between the diaphragm and the ferrule is formed by clamping an endless wire ring Q5 between the nut 85 and the diaphragm. The lower outer corner of the nut 96 is tapered or chamfered oif so that upon tightening of the nut 95 the wire ring 935 is forced outwardly and downwardly, thereby jamming the diaphragm against the ferrule along the entire periphery of the dia-- phragm.

In the form of my invention illustrated in Figure 12 the diaphragm 9? is made of a somewhat larger diameter with the outer portion thereof folded around the endless circular wire ring 95 and then bent back upon itself. The wire ring 95 with the diaphragm folded around it bears against the shoulder within the ferrule, the corner of which shoulder is preferably outwardly and downwardly tapered as indicated at 98. The diaphragm with the wire ring 95 therein is clamped in place by the clamp nut 95, a gasket 99 of an-' healed brass or the like being interposed between the nut and the diaphragm. A

In Figure 13 a filler ring Hill bears against a self-expanding gasket iii! of annealed brass or the like in theform of an endless ring that bears against a shoulder m2 and the cylindrical wall of the ferrule. The upper portion of the filler ring ltd is well rounded asindicated at we and it is upon this well rounded ring that the diaphragm ili l rests. Agasket m5 of annealed brass or the like is interposed between the diaphragm ltd and the clamping nut me which threads into the ferrule and clamps the diaphragm against the filler ring and the filler ring against the gasket Mi. The gasket mi provides a liquid tight seal for preventing the outward creepage of the liquid from the fuse along the inner walls of the ferrule. The diaphragm iiil provides a liquid tight seal at its contact with the curved portion we of the filler ring Hit. By using filler rings of various sizes the size of the vent opening may be varied.

The form of my invention illustrated in Figure 14 differs from that illustrated in Figure 13 in two respects. In this form of my invention the filler ring, which is indicatedat MD, threads into the ferrule and itself exerts a pressure upon the gasket IOI independently of the clamping nut I06. A second difference between this filler ringterposed between the diaphragm- I04 andthe clamping nut I06.

clamping nut I06 acts as a lock nut to lock the In this arrangement the filler ring in place.

In the form of my invention illustrated in Figure 15 the brass filler ring I I5 is provided with an outwardly projecting circular rim H6 at the bt-' tom thereof, the outer edges of the rim being well erably copper, is interposed between the filler I I and the ferrule. The ring I" is preferably of a thickness in the order of .005 inch, although the present invention is not limited to this particular size. The top of the filler ring II! is provided with circular ridges or corrugations extending around the entire periphery thereof as indicated at I I8. The rolled copper diaphragm vent cap is indicated at I20, said ventcap being held in place by means of the nut I2I and the washer I22 as in the form shown in Figure 14. The foil III provides a seal for preventing the outward creepage of liquid along the inner wall of the ferrule and the diaphragm I20 constitutes a vent cap as previously explained.

In Figure 16 I show still another means for securing the vent cap in .place. In this arrange-, ment the upper inner shoulder on the ferrule is provided with a plurality of circular depressions I21 extending around the shoulder and forming corrugations across the top of the shoulder. The washer I28 is provided with similar mating projections. The diaphragm I30 is clamped in place between the shoulder on the ferrule and the projections on the washer I28. The nut I20 threads into the top of the ferrule and exerts its clamping action through the washer I28 to tightly clamp the diaphragm I30 in place to produce a liquid tight seal between it and the ferrule.

In each of the forms of my invention illustrated in Figures 6 to 16, inclusive, I have not illustrated an additional cap, such as the cap 62 of Figure 5, for protecting the diaphragm against external injury. It is however to be understood that such a cap may be provided for any of the forms of my invention above referred to, if desired.

A thin circular diaphragm held rigidly at: the edges and subjected to internal pressure tends to burst at the center if its radius of curvature begreater than the radius of the opening. This is of distinct utility in the present device in causing the gases to be dischargedendwise, and not later ally. Even if in the forms just referred to, the diaphragm be weakened at the margin by the clamping pressure, so that the diaphragm should begin to tear first at the edge of the clamping ring, the internal tubular walls of the clamping ring direct the gases endwise and avoid the lateral squirting effect or the mushrooming effect of the gases caused by blowing off a nonsrupturable disc sealed by a yieldable seal at the end of the ferrule.

In compliance with the requirements of the patent statutes 1 scribed a few preferred embodiments of my invention. It is however to be understood that the invention is not limited to the precise arrangement herein shown, the same being merely illushave herein shown and de-' ratlve of the general principles of the invention.

What I consider new and desire to secure by Letters Patent is:

1. A fuse comprising a tubular member having contact ferrules at the opposite ends thereof and a fuse wire maintaining an electric connection between them, spring means normally under tension and released upon blowing of the fuse to produce an extended gap in the circuit between the ferrules, a bath of insulating arc quenching liquid within the tubular member for quenching any are that may form during the drawing of said gap, and a vent cap closing the top of the upper ferrule and adapted to be blown outwardly upon the violent blowing of the fuse, said vent cap comprising a diaphragm mechanically clamped along its entire periphery tightly against the ferrule by curved. An'L-shaped ring III of thin foil, pref-- means including a nut threaded to the ferrule and a wedge held in position by the nut, said clamped diaphragm providing a seal against outward creepage of the liquid within the tube which seal is free of self setting plastic sealing compounds.

fusible conductor, said disc comprising a diaphragm mechanically clamped along its entire periphery tightly against the ferrule, said clamped diaphragm providing a seal 'against outward creepage of the liquid within the tube which seal is free of self setting plastic sealing compounds,

and an outer cap member above the disc to protect the disc against external injury, said outer cap being blown away upon violent blowing of the disc.

3. A fuse comprising a tubular member having ferrules at both ends thereof and a fuse link maintaining an electrical connection between them, spring means normally under tension and released upon blowing of the fuse to produce an extended gap in the circuit between the ferrules, anexplosion chamber and an arc quenching liquid both within the tube for quenching any arc that may form during the drawing of said gap, said explosion chamber having a releasable end wall comprising a diaphragm closing off the same, and means for clamping the end wall in place to form a liquid-tight seal between the end wall and the explosion chamber.

4. A fuse comprising a tubular member having ferrules at both ends thereof and a fuse link maintaining an electrical connection between them, spring means normally under tension and released upon blowing of the fuse to produce an extended gap in the circuit between the ferrules, an explosion chamber and an arc quenching liquid both within the tube for quenching any are that may form during the drawing of said gap, said explosion chamber having a releasable end wall comprising a diaphragm sealing off the same, and means for clamping the end wall in place, said means comprising a jam nut having threaded engagement with one of the ferrules.

5. A fuse comprising a. tubular member having ferrules at both ends thereof and a fuse link maintaining an electrical connection between .them, spring means normally under tension and wall in place, said means comprising a jam nut and a wedge exerting a clamping action along the entire periphery of the releasable endwall. I

6.1 fuse including an open top receptacle containing a liquid arc quenching dielectric, a

, closure for the open top comprising a diaphragm of metal foil, and means clampingthe foil in place to provide a liquid tight seal, said means including a wedge contacting with the foil along the entire periphery'thereof.

7. A. fusev including an open top ferrule at the upper-end thereof, afusible link adjacent said ferrule, a vent cap comprising a thin, fragile diaphragm member sealing the open top of the ferrule, and a screw threaded member thread d on the top of the ferrule and clamping the diaphragm in place and sealing the top of the ferrule said link having a terminal connecting it with said ferrule independently of said diaphragm. 4 I

8. A fuse including an open top ferruleat the upper end thereof, a fusible link adjacent said ferrule, a vent-cap comprising a thin rupturable diaphragm member sealing the open top of the ferrule, a screwthreaded member threaded on the top of the ferrule and clamping the diaphragm in place and sealing the top of the ferrule, and a second cap spaced from and overlying the diaphragm to protect the same from ex ternal injury, saidi link havinga terminal connecting it with said ferrule independently of said diaphragm, said terminal being expellable from the receptacle when'the diaphragm is ruptured by the internal pressure created upon blowing of the link. I

9. A fuse including an open top ferrule at the upper end thereof, a vent cap comprising a thin diaphragm member sealing the open top of the ferrule, said vent cap being mechanically separate and readily separable from the ferrule to permitreplacement of the parts within the fuse through the open topof theferrule, and a removable clamping member on the fuse external of the diaphragm, said clamping member clamping the diaphragm in place to form a sealfor the open end of the fuse by the clamping action on the diaphragm.

. 10. A fuse including an open top ferrule at the upper end thereof, a vent cap comprising a diaphragm' member closing the top of the ferrule, and means for sealing the diaphragm in place comprising a wedge ring around the entire periphery of the diaphragm wedging the same in place.

11.,A fuse including an open top ferrule at the upper end thereof, a vent cap comprising a diaphragm member closing the top of the ferrule, and means for sealing the diaphragm in place comprising a wedge ring around the entire periphery of thediaphragm wedging the same in place, anda nut jamming the wedging ring in place.

' 12. A fuse including an open. top ferrule at the upper end thereof, said ferrule having a cylindrical groove formed therein between its inner and its outer ends, a vent cap comprising a diaphragm member closing the top of the ferrule, the periphery of the diaphragm extending into the groove, and a wedge ring also extending into the groove and tightly wedging the diaphragm member in place to provide a liquid tight seal along its periphery.

13. A fuse including an open top ferrule at the upper end thereof, said ferrule having a cylindrical groove formed therein between its inher and its outer ends, a vent cap comprising a diaphragm member closing the top of the ferrule, the periphery of the diaphragm extending into the groove, a wedge ring also extending into the groove and tightly wedging the diaphragm member in place to provide a liquid tight seal along its periphery, and a threaded nut jamming the wedge in place.

l4. A fuse including an open top ferrule at the upper end thereof, said ferrule having a cylindrical groove formed therein between its inner and its outer ends, a vent cap comprising a diaphragm member closing the top of the ferrule, the periphery of the diaphragm extending into the groove, a wedge ring also extending into the gs: and tightly wedging the diaphragm memberin place to provide a liquid tight seal along its periphery, a threaded nut jamming the wedge in place, and an outwardly expellable cap member for protecting the vent cap against external injury. I

15. A liquid filled fuse including an open top ferrule, a thin metallic diaphragmclosing the top of said ferrule and means for clamping the diaphragm. in place to provide a liquid tight seal free of foreign compounds, said means comprising a self-expanding wedge ring, and a nut threaded onthe ferrule and clamping the wedge Y top of said ferrule and means for clamping the,

diaphragm in placeto provide a liquid tight seal free of foreigncompounds, said means comprising a self-expandingwedge ring comprising an endless wire of a circular cross section, and a nutthreaded on the ferrule and clamping the wedge ring along the entire periphery of the diaphragm.

18. A liquid filled fuse including an open top ferrule, a thin metallic diaphragm closing the top of said ferrule and means for clamping the diaphragm in place to provide a liquid tight seal free of foreign compounds, said means comprising a self-expanding wedge ring, and a nut threaded on the ferrule and clamping the wedge ring along the entire periphery of the diaphragm, said nut being substantially spherically shaped on its inner side against which the diaphragm bears adjacent its rim.

19. A liquid filled fuse including an open top ferrule, means for preventing outward creepage of liquid along the inner wall of the ferrule, said means comprising a metalliacircular member and a nut threaded on the ferrule and clamping said member in place along the entire periphery of the member, a vent cap for closing the top of the ferrule, and means including said nut for clamping said vent cap in place.

-20. A liquid filled fuse including an open top ferrule, a fusible link connected to said ferrule, a filler ring at the top of the ferrule making a liquid tight joint therewith, a thin diaphragm on top of the filler ring, and a clamping nut threaded on the ferrule and clamping the diaphragm in place to form a liquid tight seal said connection of said fusible link to said ferrule being independent of the filler ring and the diaphragm.

21. A liquid filled fuse including an open top ferrule, a filler ring at the top of the ferrule making a liquid tight joint therewith, a thin diaphragm on top of the filler ring, and a clamping nut threaded on the ferrule and clamping the diaphragm in place to form a liquid tight seal, the top surface of the filler ring having circular corrugations and the edges of the diaphragm being clamped into the corrugations.

22. A liquid filled fuse including an open top ferrule, a filler ring at the top of the ferrule making a liquid tight joint therewith, a thin diaphragm on top of the filler ring, and a clamping nut threaded on the ferrule and clamping the diaphragm in place to form a liquid tight seal, the top surface of the filler ring having circular corrugations and the edges of the diaphragm being clamped into the corrugations by means including a gasket having mating corrugations.

23. In a fuse 'of the type comprising a sealed casing having an arc quenching liquid for quenching the arc formed upon blowing of the fuse, means for protecting the casing against the building up of excessive pressures by the vaporization of the arc extinguishing liquid, said means including a rupturable diaphragm closing an opening in the casing, and clamping means sealing the diaphragm to the casing.

24. A sealed fuse comprising a tubular member having a ferrule at its upper end, a replaceable fusible unit having means at its lower end for securing it to a tension spring and contact .means at its upper end cooperating with the inside of the ferrule below the top thereof for supporting the unit from the ferrule, whereby it is held in place by the pull of the spring, a rupturable diaphragm at theouter end of the ferrule and sealing the same, and a member clamping the diaphragm in place independently of the contact means to form 'a fluid-tight seal by the clamping pressure.

25. A sealed fuseof the type comprising a tubular member containing a fuse link and substantially filled with an arc quenching liquid and having a vent, characterized by-the fact that the fuse is made to facilitate refilling after blowing of the link, said vent cap comprising a vent cap in the form of a rupturable diaphragm and a threaded clamping means clamping the diaphragm in place to form a liquid tight seal by clamping pressure.

26. A sealed fuse of the type comprising a tubular member having ferrules at both ends thereof, means including a fuse link maintaining a circuit between the ferrules, spring means normally under tension and released upon blowing of the link to draw a gap in the circuit, an arc quenching liquid for quenching any are that may form during the drawing of the gap, and a vent cap, characterized by the fact' that the fuse is made to permit refilling, said vent cap being in the form of a rupturable diaphragm and means for sealing the diaphragm in place including a clamping nut whereby the fuse may be refilled and rescaled in the field by clamping a new diaphragm in place.

27. A sealed fuse of the type herein disclosed, comprising a tubular housing enclosing a charge of arc extinguishing material, said housing having a ferrule fixed at the upper end thereof, said ferrule having a terminal seat, and a seat for a diaphragm, said seats being independent of each other, a replaceable fuse unit comprising a fusible link, a spring in the housing for separating the terminals of the link upon fusing of the same, said replaceable unit having a separable coupling with the spring and having a terminal slidable into engagement with the terminal seat, a rupturable diaphragm engaging said diaphragm seat, and a replaceable mechanical clamping member for clamping said diaphragm to said seat to form a readily renewable seal, said diaphragm being rupturable at a predetermined pressure-to permit expulsion of the products of the arc and of the arc extinguishing material.

28. A sealed fuse of the type herein disclosed,

comprising a tubular housing enclosing a charge of arc extinguishing material, said housing having a ferrule fixed at the upper end thereof, said ferrule having a terminal seat and a seat for a diaphragm, said seats being independent of each other, a replaceable fuse unit comprising a fusible link, a spring in the housing for separating the terminals of the link upon fusing of the same,

said replaceable unit having a separable coupling 3 with the spring and having a terminal slidable into engagement with the terminal seat, a rupturable diaphragm engaging said diaphragm seat, and a replaceable mechanical clamping member for clamping said diaphragm to said seat to form a readily renewable seal, said diaphragm being rupturable at a predetermined pressure to permit expulsion of the products of the arc and of the arc extinguishing material, said clamping member constituting a ring which forms an extension of the ferrule, said ring serving to sustain the are formed upon blowing of the fusible link and serving to save the ferrule from injury by the arc.

29. A sealed fuse of the type comprising a fuse housing employing a tubular sleeve of insulation having an upper ferrule sealed thereto, an upper fuse terminal in the housing connected to said ferrule, a fuse connected to said terminal, and a releasable closure for the ferrule comprising a thin disc of metal exposing a definite area to internal pressure and being of a thickness and material so calibrated as to permit rupture thereof substantially at a predetermined pressure which is less than that which wou d injure the remalnder of the housing, and a screw threaded ring readily attachable for securing the disc over the opening of the ferrule in fluid tight condition,

of substantially at a predetermined pressure which is less than that which would injure the remainder of the housing, and a screw threaded ring readily attachable for securing the disc over the opening of the ferrule in fluid. tight condition, said disc and its attaching means being spaced from the terminal to remove the disc from the ind ace of the fuse terminal'ancl fuse, and a proton 1e device carried on the upper ferrule and mechanically shielding the thin disc from external injury which would change the calibration and hence the pressure at which it would rupture.

31. A device of the class described, comprising ahousing adapted to contain a liquid fill and comprising a sleeve with an open ferrule at its upper end and a closed ferrule at its lower end, a renewable fuse linl: having terminals and being connected between the ferrules, said link being readily renewable, a spring for tensioning the link, a readily renewable seal for said upper ferrule, said seal comprising a disc of calibrated thickness and ofa material suitable to provide a definite rupturing value for internal pressure and threaded means for securing the disc to the ferrule to close and seal the housing.

32. A device of the class described, comprising a housing adapted to contain a liquid fill and comprising a sleeve with an open ferrule at its upper end and a closed ferrule at its lower end, a renewable fuse linlr having terminals and being connected between the ferrules, said link being readily renewable, a spring for tensioning' the link, a readily renewable seal for said upper ferrule, said seal comprising a disc of calibrated thickness and of a material suitable to provide a definite rupturing value for internal pressure, and threaded means for securing the disc to the ferrule to close and seal the housing, said seal being independent of the fuse terminals, and pro tective means for the seal to guard it against external injury. 1

33. A sealed fuse comprising a tubular member having a ferrule at its upper curl, a replaceable fusible unlt having means at its lower end for securing it to a tension spring and contact means at its upper end cooperating with the inside of the ferrule below the top thereof for supporting the unit from the ferrule, whereby it is held in place by the pull of the spring, said 6ontact means being readily replaceable upon re-fusing the device, a rupturable diaphragm at the outer end of the ferrule and sealing the same, and a readily replaceable member clamping the diaphragm in place independently of the contact means to form a fluid-tight seal by the clamping pressure, said clamping member comprising a tubular extension above the diaphragm for directing the gaseous products of blowing of the fusible unitendwise of the tubular member.

34. In a fuse of the class described, a tubular fuse housing having an open ferrule at one end,

a fusible linl; and cooperating arc extinguishing v material within the housing, a thin rupturable diaphragm of predetermined strength to resist pressure closing said open ferrule, and means providing a tubular wall extending endwise of the housing beyond the diaphragm and serving to direct the gaseous products of blowing of the fuse arc extinguishing medium, and having a vent for the end of the fuse characterized by the fact that the fuse is made to facilitate refilling after blowing of the fuse, said vent comprising a closure in the form of a rupturable diaphragm, and a ring clamping the edges of the diaphragm to the ferrule to form a fluid-tight seal by clamping pressure, said ring providing an inner peripheral axially extending wall which tends upon rupture of the diaphragm to direct the gaseous are extinguishing medium and the arc vapors endwlse of the housing.

36. In a fuse, a fuse housing terminating in a tubular open ended ferrule, a fusible link in the housing and are extinguishing material in the housing acted upon by the blowing of the fuse to produce a gaseous medium, and a diaphragm disposed across the bore of the ferrule below the free end thereof, said diaphragm being removable by internal pressure of said gaseous medium at a value less than that which would cause failure of the housing, and the end of the ferrule beyond the normal position of the diaphragm causing the gases when released to be projected substantially endwise away from the fuse housing.

87. The combination of claim 35, characterized by the provision of a relatively stiff backing plate disposed in reenforcing engagement with the rupturable diaphragm which is thin and flexible, said backing plate having holding means by which it is releasably held to the casing with a predetermined resistance to displacement, said thin rupturable diaphragm forming a fluid-tight closure for the casing keeping the backing plate and its holding means normally out of contact with the contents of the housing but transmitting the internal pressures to said backing plate whereby the internal pressure must rise to a definite value which will overcome the predetermined resistance of the plate to displacement before rupture of the diaphragm can occur, the diaphragm alone being rupturable by internal pressures substantially less than that required to dis= place the backing plate.

NICHOLAS J. CONRAD.

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