US2017491A - Cartridge ferrule type refillable fuse - Google Patents

Description

OGL 15, 1935 i J. B. GLOWACKI 2,017,491

CARTRIDGE FERRULE TYPE REFILLABLE FUSE Filed March 26, 1954 3 Sheets-Sheet l 'Il 'i I if 2 EMEL-/ UE CARTRIDGE FERRULE TYPE REFILLABLE FUSE Filed March 26, 1954 3 Sheets-Sheet 2 l IIA ZTEJT si., i159 w3., J. E. GLQWAQKU MWA-m l CARTRIDGE FERRULE TYPE REFILLABLE FUSE Filed March 26, 1954 4 5 Sheets-Sheet 3 UNITED STATES PATENT OFFICE CARTRDGE FERRULE TYPE REFILLABLE FUSE John B. Glowacki, Chicago, Ill.

Application March 26,

20 Claims.

This invention relates more particularly to a cartridge ferrule type rellable fuse comprising a barrel or shell having a plurality of flat outer surfaces adapted to prevent rolling of the fuse when placed on a fiat surface and furthermore serving as a means for holding the fuse casing when end caps are secured on the ends thereof. The improved fuse includes removable end caps provided with combustion or gas outlet chambers iilled with coils of screening or with superimposed layers of screen discs secured in place by means oi multiple grooved contact bushings secured in the caps in position to aiford cont-acts for the ends of a fuse element held in position within the fuse casing by means of suitable casing end plates.

It is an object of this invention to provide a cartridge ferrule type reflllable fuse including a molded casing having an integral closure plate at one end and a removable closure plate at the other, said casing having the end sections thereof externally threaded for the reception of internally threaded end cylindrical caps the inner ends of which contact the multiple surfaced main body portion of the casing.

It is also an object of this invention to provide a cartridge ferrule type fuse wherein the casing has the outer peripheral surface thereof multiple sided to obviate rolling of the fuse and facilitating gripping of the fuse for the assembly of the removable and replaceable parts of the fuse.

Another object of the invention is the provision of an improved type of cartridge ferrule type fuse including a molded casing having a permanent closure plate at one end and a removable closure plate at the other, said casing having the end portions thereof externally threaded to the ends of the multiple sided intermediate portion of the casing.

It is furthermore an object of this invention to provide an improved cartridge ferrule type fuse including a multiple sided casing having removable metal end caps provided with gas outlet chambers filled with a plurality of layers of screening or perforated material for thoroughly breaking up the products of combustion resulting from the blowing of a fuse element in the fuse casing.

A further object of the invention is the construction of a fuse including a molded casing having screw sleeves partially imbedded in the end portions thereof for the reception of removable metal end caps containing means for thoroughly breaking up the products of Combustion 1934, Serial No. 717,320

(Cl. 20G- 131) resulting from the blowing of a fuse element in the casing.

Another object of the invention is to provide a cartridge ferrule type rellable fuse having end caps containing grooved bushing units having 5 screening means therein for breaking up the products of combustion resulting from the blowing of a fuse element within the fuse.

A further object of the invention is the construction of a fuse including a casing having chambered end caps removably engaged thereon, said caps having screen carrying contact bushings engaged therein, with said bushings provided with ilanges having the outer surface thereof provided with a network of gas escape grooves communicating with the screening means Within the end caps of the fuse.

It is an important object of this invention to provide an improved type of cartridge ferrule type rellable fuse including a molded casing 2o having the major portion of the body thereof provided vvith exterior fiat surfaces and having the ends of the casing formed for the removable reception of chambered end caps containing flangedv members or plates provided with a network of intercommunicating gas outlet grooves for permitting the products of combustion resulting from the blowing of a fuse to enter the chambered caps and be disseminated by superimposed layers of screening in the end caps of the fuse.

Other and further important objects of this invention will be apparent from the disolosuresin the specification and the accompanying drawings.

The invention (in a preferred form) is illustrated in the drawings and hereinafter more fully described.

On the drawings:

Figure 1 illustrates an elevational view of a cartridge ferrule type refillable fuse embodying the principles of this invention.

Figure 2 is a longitudinal central section of the fuse with parts shown in elevation.

Figure 3 is an enlarged fragmentary longitudinal section of the fuse, with the fuse element omitted, and with the enclosed mechanisms in the fuse caps illustrated in section.

Figure 4 is an enlarged end view of the closed end of the fuse casing taken on line IV-IV of Figure 2 with the end cap omitted.

Figure 5 is an enlarged outer end view of a cap 50 bushing and grooved flange removed from a fuse cap.

Figure 6 is a perspective view of a screen disc a stack of which is usable in place of the screen @Oil illllStrated in Figure 3.

Figure 7 is a fragmentary enlarged longitudinal section through one end of a fuse illustrating a modified form of a gas outlet and filtering unit including a grooved plate with an insulation Washer disposed adjacent a bushing sleeve containing a filtering screen.

Figure 8 is a similar sectional view through one end of a fuse illustrating another modified form of filtering unit including a grooved disc for holding a filtering screen secured in the fuse cap without the use of a bushing sleeve.

Figure 9 is an enlarged tr-ansverse section taken on line IXIX of Figure 2.

Figure l is a transverse detail section taken on line X-X of Figure 3,

Figure 11 is a top plan View of the fuse element in flat form.

Figure 12 is a side view of the fuse element showing the end flaps deflected.

Figure 13 is an end elevation of the open end of the fuse casing.

Figure 14 is an elevational view of the inner side of the closure plate for the open end of the fuse casing.

Figure 15 is a diametrical section taken on line XV-XV of Figure 14.

Figure 16 is a view taken on line XVI-XVI of Figure 8 showing the grooved face of the modified form of the contact or closure disc.

Figure 17 is a fragmentary longitudinal detail section through a modified form of fuse casing, of a molded type, including flanged screw thimbles molded around the reduced end sections of the casing.

Figure 18 is a fragmentary side elevation of one end of the modified form of fuse c-asing shown in Figure 17 showing means for holding the metal thimble secured in position against rotation.

Figure 19 is an end view of the open end of the fuse casing shown in Figure 17.

Figure 20 is an enlarged fragmentary elevational view of another modiiied form of fuse casing with parts shown in section and including threaded thimbles for engagement on the reduced threaded ends of the casing, 4and also showing means for holding the thimbles in place against rotation on the casing,

Figure 21 is an end view of the open end of the fuse casing shown in Figure 20.

Figure 22 is a diametrical section of the closure thimble for closing one end of the casing shown in Figure 20.

As shown on the drawings:

The improved cartridge ferrule type refillable fuse of this invention comprises a tubular body or casing constructed of a molded insulating material. The molded casing is designated by the reference numeral I and has the major portion of the exterior thereof formed with a plurality of longitudinally directed flat surfaces 2 which serve as a means for preventing rolling of the fuse when placed on a at surface, and also serving as a means whereby the fuse casing may be readily gripped and held against rotation during the assembly of the fuse. One end of the fuse casing I is reduced in diameter to form an exteriorly threaded sleeve or end section 3 having an integral end closure plate 4 provided with a pair of oppositely positioned outlet passages or openings 5 and with a fuse element receiving slot 6 positioned off center. The opposite end of the molded casing I is also reduced in diameter to form an exteriorly threaded open sleeve or end section 1 the end of which is provided with a ring recess 8 having a guide or centering rib or bead 9 form-` ing an integral part of the end section 1 and projecting into the circular recess 8.

The open end of the casing end section 'i is adapted to be removably closed by means of an insulation closure plate or disc I0 provided at its outer end with a step flange or rim II adapted to engage the outer end of the end section I to limit the insertion of the closure disc ID into the Open end of the casing. The peripheral surface of the closure disc I0 is provided with a transverse groove or slot I2 (Figures 14 and 15) to register with the guide rib or bead 9 so that the closure disc can only be inserted in a single pre determined position with respect to the end of the casing. The closure disc IG is provided with -a pair of oppositely positioned gas outlet openings or passages I3, Also provided in the closure disc IO below the center line thereof is a fuse element receiving slot I4.

Engaged diagonally through the fuse casing I is a fuse element I5 having pairs of oppositely positioned notches I6 in the longitudinal margins thereof. Irregular or I-shaped openings I1 are provided in the strip I5 between the pairs of i;

marginal notches I6 thereby forming fusing strips I il between the ends of the I slots and the notches Iii. The fuse strip I5 is also provided with pairs of marginal notches I9 near the end portions of the fuse strip forming reduced fusing strips 20 which are wider than the fusing strips I8 and divide the main body of the fuse strip from the end portions 2|. The end portions of the fuse element are adapted to be bent or deflected along the dotted line 22 leaving end flaps 2,3 which are adapted to be defiected outwardly in opposite directions to be disposed against the outer faces of the casing end members.

Removably threaded on each end section 3 and I of the fuse casing is a metal cap 24 which is internally threaded for engagement with the threads on the casing end section. Th'J open end of the cap 24 is provided with a beveled end surface which is adapted to tightly engage against a beveled surface at the end of the main body section of the casing I, when the cap is in its innermost position. Each end cap 24 is provided with a chamber 25 between the outer surface of the end closure plate of the fuse casing and the inner wall of the closure plate 25 of the end cap. The cap end plate 25 is provided with a centrally disposed boss or hood 2l provided with. a diametrical slot `28 to receive a tool for tightly screwing the cap in position upon the threaded end section of the fuse casing. The hood 2i is provided with a central outlet aperture or opcning 29 which communicates with a chamber pro-- vided in the hood 21. The end plate 26 of the cap is provided with a central opening which registers with the chamber in the hood 2l, and said end plate 26 has the inner peripheral edge thereof cut away to provide a beveled surface leaving a circular escape groove 30 between the cap cham ber 25 and the chamber within the cap hood 2?.

Y Rigidly secured within the closed end of each the fuse caps 24 is a bushing unit comprising a sleeve 3I provided on the exterior peripheral surface with a straight knurled section 32 the straight rib portions forming the same adapte-fl to cut into the inner surface of the hood chamber 21 to securely hold the bushing unit in place. The bushing sleeve 3l is provided with a pluralityrv of spaced vent apertures or openings 33 which communicate with the groove 3U formed within the cap. The inner end of the bushing sleeve 3| is closed by means of an integral contact head or plate 34 provided with a peripheral groove for receiving an inner peripheral ange of an insulation ring or flange plate 35 through which the contact head 34 of the metal bushing projects as clearly illustrated in Figure 3. The insulation flange or ring 35 has the outer surface thereof provided with a network of communicating grooves 3B as clearly illustrated in Fiiure 5, and said grooved surface lits tightly against the inner surface of the end wall or plate 28 of the fuse cap With the grooves 36 communicating with the ring groove 3D to establish communication between the cap chamber 25 and the chamber within the bushing sleeve 3i. Seated within the chamber of the bushing sleeve 3l is a filling of porous material such as a spiral roll or coil of wire screening 31. A modified form of porous filling may be substituted for the wire coil 31 and may consist of a plurality of perforated plates or wire screen discs 38u (Figure 6) which may be superimposed upon one another to form a stack of wire screen discs sufficient to ll up the chamber within the bushing sleeve 3|.

With the fuse assembled as illustrated in Figure 2 the end flaps 23 of the fuse element are tightly clamped between the ends of the fuse casing and the contact plates 34 forming part of the contact bushing units engaged in the fuse end caps 24. By gripping the fuse casing around the hat sided body portion, the fuse may be securely held to permit the end caps 24 to be tight-ly threaded into position upon the end sections of the fuse casing.

When the improved cartridge errule type rellable fuse is connected in an electrical circuit the connection is established between the end caps and the fuse element to close the circuit. When a short circuit occurs or when an excess amount of current passes through the fuse the fuse element |5 will blow at the fusing strips I8 permitting the middle section of the fuse strip to drop out to break the circuit. The gases and other products of combustion resulting from the blowing of the fuse are permitted to escape from the fuse casing through the vent openings 5 and I3 in the end closure plates of the casing into the cap chambers 25. From the chambers 25 the products of combustion and gases are permitted to escape through the network of grooves 35 in the insulation flanges or plates 35 through the hood grooves 3U and the bushing sleeve apertures 33 into contact with the porous material or wire coil lling 31 which acts to thoroughly break up the products of combustion and reduce the velocity of the gases which are eventually permitted to iind their way through the labyrinth of passages and openings in the wire llng until the gases escape through the outlet openings 29 provided in the hoods 21 formed on the closed ends of the fuse caps 24.

In the modied form of fuse illustrated in Figure 7 the construction of the casing and end caps is substantially the same as that hereinbefore described with the exception that the end caps are each provided with a modified form of a contact bushing unit.

The modied form of bushing unit of Figure 7 comprises a bushing sleeve 38 having a plurality of spaced outlet or vent openings 39 provided therein to communicate with the groove 30 of the fuse caps. The outer peripheral surface of the bushing sleeve 38 is provided with a ring or" straight knurling, similar to that illustrated in Figure 2, to permit the bushing sleeve to be tightly driven into the hood portion 21 of the fuse cap. The bushing sleeve 38 is lled with a lling of porous material such as a coil of wire screening 40er a stack of superimposed wire discs similar to the type illustrated in Figure 6. integrally formed on the inner end of the bushing sleeve 33 is a closure plate or disc 4| having formed in the outer face thereof a network of Ventilating or escape grooves or passages 42 similar to the arrangement illustrated in Figure 5. Integrally formed on the middle portion of the inner side of the bushing closure plate 4| is a contact boss 43 adapted to be clamped against the deflected end flaps 23 of a fuse element I5 to clamp the same tightly against the end closure plates of the fuse casing. Securely engaged around the boss 43 and contacting the inner face of the closure plate 4| is an insulation ring or washer 44 which serves as a means for preventing the products of combustion escaping from the fuse casing from adhering tof the metal closure plate 4| to clog up the interior of the fuse cap and thereby prevent proper escape of the gases resulting from the blowing of a fuse element.

Figure 8 illustrates a fragmentary portion of another fuse constructed similar to the fuse illustrated in Figure 3 with the exception that another modied form of gas disseminating ller unit is enclosed in the fuse caps. In this modied form a porous filling such as a coil of wire screening 45 is securely packed within the chamber of the fuse hood 21 and is held in place by means of a metal closure plate or disc 46 the outer peripheral surface of which is provided with a straight knurling 41, as illustrated in Figure 16, to permit the closure plate to be tightly driven into the cap chamber 25 to seat against the inner surface of the end plate 26 of the cap. The outer surface of the closure plate 45 is provided with a network of escape passages or grooves 48 which communicate with the ring groove 3|! thereby allowing gases and products of combustion from the fuse cap chamber 25 to escape through the knul-ling 4"! and the grooves 48 into the wire lling 45 to be broken up or disseminated before escaping through the outlet opening 29 provided in the hood 21 of the closure cap.

It will be noted that with the various forms of iilling units provided in the end caps of the fuse that the products of combustion are thoroughly broken up so that no ilames are permitted to esf cape through the openings in the ends of the fuse through which only the resultant gases of the blowing of a fuse element are permitted to escape at a comparatively slow rate of speed.

Figures 17, 13, and 19 illustrate a modified form of fuse casing molded from an insulation material and comprising an intermediate or main body portion de having end sections. 5i) and 5| of reduced diameter integrally formed on the ends thereof. The exterior of the body portion 5S of the casing is provided with a plurality oi adjacently positioned at surfaces 52 which serve to facilitate tight gripping of the fuse casing during the assembly of the same and furthermore serve as a means for preventing the fuse from tion 50.

Molded around the exteriorly threaded end sec- A"tion 50 of the fuse casing 49 is a threaded metal sleeve or thimble 55 having an integral inwardly directed outer flange 56 which seats tightly against the outer end of the fuse casing end sec- Also integrally formed on the thimble 55 is an outwardly directed inner ange 51 which `seats tightly against one end of the main body velement receiving slot 6| which is positioned off center for receiving one end of a fuse element similar to the arrangement illustrated in Figure 2. Molded around a threaded portion of the casing end section l is a threaded metal thimble 62 having an integral inwardly directed outer flange 63 which is imbedded in the material forming the end closure plate 59 of the fuse casing. Integrally formed on the inner end of the threaded thimble A62 is an outwardly directed inner flange 64 which seats tightly against one end of the main body portion of the fuse casing 49.

For the purpose of holding the threaded thimbles 55 and 62 against Yrotation on the reduced end sections of the fuse casing each of the thim- `bles has the threaded portion thereof provided with one or more inwardly struck indents 65. The inner flange of each of the threaded thimbles is provided with an indented or deflected portion 66 which is molded into the casing material to assist the indents 65 in holding the thimbles tightly secured in place against rotational movement.

Figures 20, 21, and 22 illustrate another modied form of fuse casing which is constructed of tubular insulation material and comprises a cylindrical main casing body 61 having integrally formed on the ends thereof reduced exteriorly threaded end sections 68 and 69. The outer end of the casing end section 68 is provided with a circular recess or ring groove 1U for the reception of an end closure cap I0 of the type illustrated in Figures 14 and l5.

Threaded onto the exterior of the threaded casing end section 68 is a metal threaded thimble 1l having an integral outwardly directed inner flange 12 which seats tightly against one end of the main body portion 61 of the fuse casing. Integrally formed on the outer end of the threaded thimble 1| is an inwardly directed flange 13 having a centering flap or guide member 14 integrally formed thereon and positioned to the outside of the circular groove to insure positive positioning of the end closure plate l0 so that a fuse element can only be engaged Within the fuse casing in a predetermined position similar to the arrangement illustrated in Figure 2. For the purpose of holding the threaded thimble 1I in position against rotation on the end section 68 of the fuse casing the thimble is provided with one or more indents and the inner ange 12 of the thimble is also indented at 16 to obviate rotation of the thimble.

The end casing section 69 has threaded thereon a threaded metal thimble 11 having an inner outwardly -directed flange 18 and an outer inwardly directed flange 19 which is imbedded in a molded insulation end plate 80 which is adapted to seat ytightly against the youter end of the `:casing end lsection 69. The insulation closure ?p'late 80 isprovided with a pair of oppositely po- `:sitioned vents or outlet openings`8l and with a :slot 82 positioned oil center for the reception of 5 one end 'of a fuse element. `The threaded thimble 1.1 .provided with one or more indents 83 which project into the material forming the casing end section 69 to hold the thimblelocked lagjainst rotation with respect to the casing. The l0 inner flange 18 of the thimble 11 is provided with one or more indents 84 which cut into the end of the main body 61 of the casing to assist the in- 4dents`83fin holding the thimble in proper position against rotational movement with respect l to the casing.

Attention is calledV to the fact that in the various forms of fuse casing that the same may be iormedof molded material or may be constructed out of tubular-stock suchas illustrated in Figure 20 and the end sections of the casing may be reduced in diameter and exteriorly threaded for ythe reception of removable metal end caps such as illustrated in Figures 7 and 8 or the reduced end sections of the casing .may have' threaded metal 25 ithimbles secured thereon similar to the arrange- :ment` illustrated infigures 17 and 20 in which rconstructions the metal end caps are threaded onto the metal thimbles which are rigidly secured yon the casing endfsections.

Attention is specically directed to tthe fact that in this improved type of reilllable cartridge fuse that the 4chain body or casing is completely constructed fo insulating material including ythe casing walls and the end closure walls so that the only .metal within the casing proper is the blowable fuse element. All othermetal parts of the improved fuse are contained in Ithe fuse end caps. When a fuseelement is blown within the fuse casing the hot metal resulting from the blOwl0 .ing or melting of the fusible strips of the fuse ele- .ment move into contact with the insulating walls tof the casing and do not adhere thereto as they 'would to metallic walls. The resultant hot air and gasespass outwardly thiough'the vent open- 5 ings in the end plates of ythe casing into the cap chambers and 'any hot metal which may find its way into the cap chambers contacting the insulation plates forming part of the bushing unit within the caps vbecomes cooled and does not adhere to the Vmetal parts to clog up the caps. The gases and hot air entering the cap chambers 25 gradually nd their way into the circuitous passages or groove network 36 inthe bushing disc and enter the hood portions of the end caps 55 through the grooves 30 and the bushing apertures 33 and engage the porous filling or the wire :screening within the end chambers of the caps so that the gases and air are practically cooled oil before they issue through the outlet openings 29 00 in -the ends of the fuse caps. Tests show that there is only a slow gradual discharge of the practically cooled air and gases from the end apertures of the fuse after the blowing of a fuse element. Any flames which might result from 05 the blowing of a fuse element within the improved fuse are completely destroyed or broken up before they reach vthe outlet openings 29 in the ends of the fuse caps.

After the blowing of a fuse element the fuse is removed from its support and is held by the body portion, the flat outer surfaces of which permit tight gripping of the fuse to facili-tate removal of the end caps 24. After the end caps have been removed the removable end plate I 0 of the casing 75 is removed thereby allowing the remaining parts of the blown fuse to be taken out to be replaced by a new fuse element. The end plates of the fuse casing have the fuse element receiving slots formed with straight and inclined surfaces as clearly illustrated in Figures 7 and 17 to facilitate mounting of the fuse element. The partially deflected end 23 of the fuse element is first inserted through the slot in the permanent closed end of the casing until the completely deflected opposite end of the fuse element comes in contact with the outer surface of the closed end of the casing. The removable closure plate ii) is then engaged over the partialy deflected end of the fuse element which now projects diagonally through the fuse casing and said closure plate lil is then inserted in the open end of the casing to close the same thereby properly positioning the fuse element in the diagonal position illustrated in Figure 2 after which the partially deflected projecting end of the fuse element is bent over against the outer surface of the removable closure plate l0. The end caps are now reengaged on the ends of the casing with the contact bushings within the caps clamping the end portions 23 of the fuse element tightly against the end plates of the fuse casing.

The network of circuit-ous escape passage-s in the bushing plates disposed within the fuse end caps and 'the cirouitous passages provided by the porous or screen llings in the chambers of the end cap hoods are instrumental in assuring the destruction of any flames which might result from the blowing of a fuse element within the fuse casing and furthermore serve to reduce ythe speed of the escaping hot air and gases to such an eX- tent that the gases and air are practically cooled off and are slowly discharged out of the escape openings in the ends of the usecaps.

It will of course be understood that many details of construction may be varied through a wide range without departing from the principles of this invention and it is therefore not the purpose to limit the patent granted hereon otherwise than necessitated by the scope of the appended claims.

I claim as my invention:

i. A cartridge ferrule type reillable fuse comprising an insulation casing having reduced threaded end sections, an apertured and slotted insulation disc integraly formed on one end of the casing, an apertured and slotted insulation disc removably engaged in the opposite end of the casing, a fuse element in said casing having the ends thereof projecting throughthe slots in the end discs and bent over to lie against the outer surfaces of said end discs, apertured end caps removably engaged on the reduced threaded end portions of the casing, contact means secured in the end caps and contacting the ends of the fuse element, disc means forming a part of the contact means and having a network of escape passages formed therein, and layers of wire screening rein the caps by the contact means.

2. A cartridge ferrule type rellable fuse comprising an insulation casing having an apertured and slotted closure disc integrally formed on one end thereof, an apertured and slotted closure disc removably engaged in the opposite end of the casing, grooved and apertured contact cap members removably engaged on the ends of the casing, grooved and apertured contact means in the caps, and coils of wire screening clamped in position between the end caps and the contact means.

3. A cartridge ferrule type rellable fuse comprising an insulation casing having the end por-tions thereof reduced and exteriorly threaded, an apertured and slotted insulation closure disc integrally formed on one end of the insulation casing, an apertured and slotted closure disc re- 5 movably engaged in the opposite end of the insulation casing, a fuse element engaged in the insulation casing and having the ends thereof projecting through the slotted insulation end closure discs, with the ends of the fuse element bent over and lying ilat against the outer surfaces of the closure discs. and contact caps removably engaged on the reduced threaded end portions of the insulation casing and contacting the deflected end portions of the fuse element. el. In a fuse of the class described including in combination an insulation casing comprising an insulation body closed at one end and open at the opposite end, said open end having a groove formed therein, a projection extending into the groove, a grooved insulation closure plate extending into the groove in the open end of the insulation body with the projection registering with the groove in the closure plate to hold the` same in a predetermined position, and threaded thimbles secured against movement around the end portions of the insulation body.

5. In a fuse of the class described including in combination a casing comprising an insulation body, a slotted and apertured insulation closure plate integrally formed in one end of the body,

a slotted and apertured insulation closure plate removably engaged in the opposite open end of the body, means for insuring the insertion of the removable end closure plate in only a single predetermined position in the open end of the insulation body, threaded metal thimbles engaged around the end portions of the insulation body, and means for holding the threaded thimbles in position against rotation with respect to the body.

6. In a fuse of the class described the combination with an insulation casing, of an apertured cap removably engaged thereon, an apere tured contact member secured in the cap, said cap having a groove therein registering with the apertures in the contact member, a screen lling in the contact member, and a plate forming part of the contact member and having a network of air and gas escape grooves formed therein and communicating with thegroove in the cap.

7. A cartridge type fuse comprising an insulation casing having insulation end closure members, metal caps removably engaged on lthe ends of the insulation casing, grooved contact means secured in the caps adjacent the closed ends of the insulation casing, and coils of wire screening in the caps held in position by the contact means. v ao 8. In a fuse of the class described including in combination a cap, a contact means secured therein and having a surface provided with a network of escape grooves, and a screen lling in the cap held in position by the contact means. (5

9. In a cartridge type fuse including in combination a cap, an apertured hood extension formed thereon, an apertured contact member in the cap and projecting intoI the hood, a plate forming a part of the contact means and 10 having a surface thereof provided with a network of escape grooves, and a screen filling in the apertured contact means and in said hood.

l0. In a cartridge type fuse of the class described the combination with a cap having a groove therein, of an apertured hood formed on the cap, a screen filling in the hood, and a contact member' secured in the cap and having a surface thereof provided with a network of escape grooves communicating with the groove in the cap.

11. In a cartridge type fuse of the class described an end closure unit comprising a cap having a groove therein, an apertured hood integrally formed on said cap, an apertured contact member in said cap projecting into the hood with the apertures in the contact member registering with the cap groove, a flange on the contact member having a network of escape grooves formed therein and positioned to communicate with the groove in the casing, and a wire screen filling held in position between the apertured contact member and said apertured hood.

12. A cartridge type fuse including in combination a closure unit comprising a grooved cap, an apertured hood integrally formed thereon, an apertured contact member in said cap projccting into the hood, with the apertures in the Contact member registering with the groove in the cap, a porous lling in the contact member and in contact with the apertured hood, and an insulation flange secured on the contact member and having one surface thereof provided with a network of escape grooves communicating with the groove in the cap.

13. In a fuse of the class described including in combination a casing closure unit comprising a grooved and apertured cap, a knurled and apertured Contact member rigidly secured in the cap, a multi-passaged ller in the contact member, and an insulation ilange on the contact member having a network of intersecting grooves therein communicating with the groove in said cap and with the apertures in the contact member.

14. A cartridge type fuse comprising an insulation casing, a threaded thimble secured on one end of the casing, a second thimble for engagement on the opposite end of the casing, and an insulation closure plate in the outer end of the second thimble.

15. A cartridge iuse including in combination a casing, and a closure unit therefor comprising a threaded metal thimble, and an apertured and slotted insulation end closure plate secured in one end of the thimble.

16. In a fuse of the class described including in combination a grooved cap, and a peripherally knurled contact means secured therein and having one surface thereof provided with a network of escape grooves communicating with the cap grooves.

17. In a fuse of the class described including in combination a contact means having a peripherally knurled exterior surface and an outer end surface having a network of escape grooves therein communicating with the grooves in the knurled surface.

18. In a fuse of the class described including in combination an apertured cap, a contact means therein having a surface provided with;

a network of escape grooves, and a porous filling in the cap in contact with the grooved surface of the contact means.

19. A cartridge fuse including in combination a casing comprising a main body portion having threaded end portions integral therewith and provided with notches in the ends of said main body portion adjacent the inner ends of the threaded end portions, threaded thimbles engaged on said threaded end portions, and means integral with the inner ends of said thirnbles and seated in said notches to hold the thimbles locked against rotation.

20. In a fuse, a casing comprising an insulation body including an insulation closure disc integrally formed in one end thereof and having a fuse element slot and gas escape apertures therein, said body having the opposite end open and grooved to provide a stop shoulder, and a flanged, slotted and apertured insulation closure disc removably engaged in the open end of the body and double seated against said shoulder and against the end of the body.

JOHN B. GLOWACKI.

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