US2337938A - Electric fuse - Google Patents

Description

Dec. 28, 1943. a. R. SEI-QFLING ETAL ELECTRIC FUSE Original Filed Sept. 11. 1941 lNDlC/A MOLDED l/VEND OF TERMINAL Inventors George RSerHing, Carl LSchuck Their Attorney.

Patented Dec. 28, 1943 ,ussc

ELECTRIC FUSE George R. Serfling,

Merchants, N. it, and Carl L. schucml'hilallelphlmfa acsignors to General Electric Company,

York

Original application September a corporation of New Elli, 191 1, geriall Divided and this application dirgust 28, 1942, Serlal'No. tt'ad iitfitl (Cl. Ziid lidl) 1 Glalm.

Our invention relates to electric fuses and particularly to improvements in the construction and method of construction of enclosed highvoltage fuses of the current-limiting type.

This application is a division of our applica tion, Serial No. 410,382, filed September 11, 1941, entitled Electrical fuses and assigned to the same assignee as the present application.

Current-limiting fuses consist in the main of a fusible element in the form of one or more conductors of suitable metal, such as silver or zinc, embedded in a granular inert or refractory arc extinguishing material of high dielectric strength, such as sand or relatively quartz In most of the commercial currentlimiting fuses, the conductor or conductors are wound on a suitable supporting core of high temperature resistant ceramic material. Tothese parts are added an enclosing housing and terminals for the conductors. Y

The process of assembling current-limiting fuses of this type has heretofore required a large number of steps and it would be desirable to be able to reduce greatly the assembly operations by simplifying the construction with the consequent reduction in cost of such fuses without in any way impairing the operating characteristics thereof.

Accordingly, it is an objectlof our invention to provide a new and improved fuse construction which not only performs very. satisfactorily in every respect but which is simple and rugged in construction and considerably less complicated to manufacture.

It is a further-object of our invention to provide a new and improved process for assembling fuses of the current-limiting type.

It is another object of our invention to provide a new and improved fuse construction in which the end cap of the fuse is sealed to the fuse container by molding or die casting a ferruleof metal about one end of the fusecontainer to form the fuse terminal.

Still another object of our invention is to provide a new and improved means of centering the fuse wire of a current-limiting fuse without the supporting core usually required by the priorart constructions. I

Further objects and advantages of our invention will become apparent as the following description proceeds and the features of novelty which characterize our invention will be pointed out with particularity in the-claim anexed to and forming a part of this specification.

For a better understanding of our. invention,

finely divided.

reference may be had to ing in which Fig. l is the accompanying drawa partly sectional view of an exemplary form of current-limiting fuseshown in Fig. i, Fig. 3

constructed in accordance with our invention, Fig. 2 is an exploded view of the parts. of the fuse is a view partly in section to indicate the assembly of the fuse during the manufacturing process, Fig. e is an enlarged view of one of the parts of the fuse shown in Figs, 1 to 3, Figs. 5 and 6 illustrate two different steps in the process of manufacturing a current-limiting fuse embodying our invention, and

Fig. '7 illustrates a partial sectional View oi a fuse device embodying a modification of our invention.

' Although, as will be evident to one skilled in the art, certain parts of the present invention may be practiced to advantage with different types and forms of electric fuses, the invention lends itself most advantageously to practice with the enclosed type of fuse, such as is disclosed and claimed in United States Letters Patent No. 2,157,907, grantedMay-Q, 1939, upon an application of K. A. Lohausen, and assigned to the same assignee as the present application, "wherein the fusible conductor is shown as being enclosed in a tubular casing of suitable insulating material and surrounded by or embedded in a pulverulent or sandy arc-quenching material.

Referring now to the drawing, we have illustrated an electric fuse device which has a housing structure or casing til of open ended tubular form constructed of suitable insulating material,

- Fig. 2, with an insert it such as glass or fiber. A suitable fuse link, generally indicated at H, is mounted within tubular casing It, This fuse lint: may, if desired, embody the construction. disclosed and claimed in the above-mentioned United States Letters Patent so as to include a central section of reduced cross section. thereby providing more satisfactory operation. Although the particular size of crosssection of the fuse wire and the material from which it is made form no part of the present invention, we have found that we obtain very desirable operating characteristics by constructing the fuse link or fusible element ii,-best shown in of a high resistance wire of suitable cross-sectional area while the two end portions It of the fuse link ii may be formed of a low resistance wire, such as silver, having a somewhat larger cross-section than the insert E2. The insert it is maintained in conductive relation with the end sections it of fuse H by soldering or the like as indicated at it. The ends of the fusible element H are preferably looped or folded back upon themselves for a short distance and twisted as indicated at I, and each of these twisted portions is bent in the form of a U which has a central portion ID of a length substantially equal to one half the outside diameter of tubular housing or casing III as will be described in greater detail hereinafter.

In order to maintain the ends of the fuse link II at the central axis of tubular casing ID, We have provided a fuse link attachment plate I! for each end of tubular housing I which includes a small central opening l8 through which the fuse link |l may extend. Each plate I1 is also provided with a somewhat larger opening I! through which the tubular casing l0 may be filled with the granular arc-quenching material after the fuse link II is supported therein as shown in Fig. 3.

We have discovered that the central core usually required for centering the fuse link in the prior art constructions during the process of filling the tubular casing with the inert granular material may be dispensed with if the fuse link is formed as a helix with the generating radius thereof decreasing near the ends of the fuse link. With such a construction, we have found that, when the fuse link is under a slight tension as in Fig. 3, the tensile forces applied thereto act along the axis of the helix so that the fuse link tends to remain centered within tubular housing "I.

In order to close the open ends of tubular casing or housing l0 after the fuse link and fuse link attachment plates have been assembled, we have provided saucer-shaped end closure members or end caps 20, which are adapted to fit over the ends of tubular casing l0. As shown in the drawing, these end caps are provided with an interlocking means illustrated as an offset shoulder 2| and they are adapted to be held in sealed relationship with tubular casing ID by metallic ferrules 22 which are molded or die cast around the end of tubular casing i0 so as to envelop the ofi'set shoulder 2| of end cap 20 while permitt ing the major portion of the end cap to remain exposed. The inherent irregularities of the end caps 20 might be depended upon for obtaining the desired mechanical grip. Accordingly, any suitable end cap with means for obtaining the desired mechanical interlock when such means are enveloped by the die casting material may be employed in accordance with our invention. The die cast or molded ferrules 22 are also cast around the looped end l5 of fuse link H which extends outside of tubular casing l0 in the manner shown in Figs. 1 and 3 and, accordingly, provide the terminals for the fuse.

Since the major portion of the end caps 20 remain exposed after the molding or die casting operation, suitable indicia may be provided on this surface of the end caps 20, as indicated in Fig. 4, to set forth the fuse size or any other pertinent information.

The new and improved fuse construction described above permits the number of assembly operations required heretofor in fuses of the current-limiting type to be reduced greatly while, at the same time, eliminating the requirement of a ceramic core and other additional parts. The manufacturing process can now be reduced to a few relatively simple steps, one of which requires the forming of the fusible element or fuse link into the helical form, the generating radius of which decreases near the ends. For the particular fuse link ll described above in which a more resilient center section I2 is utilized, it is necesportions must be wound section 24 is required since the inserted section l2 of the fuse link being more resilient than the end in a smaller diameter helix so that, when removed from the mandrel, the free diameter of the helix composed of the insert will approximate that of the adjacent coils in the end portions (see Fig. 2). The ends of the wire are looped back upon themselves, as indicated at I! in Fig. 2, and, as was mentioned above, the twisted ends of the fuse link are formed in the shape of a U.

The next step in the process includes the placg of the fuse link in the tubular casing It with the fuse link attachment plates ll seated on "process. Because the fuse link II is in the form of a helix, the generating radius of which decreases near the ends, the tensile forces on the ends of the fuse link exerted at the central axis of tubular housing N by fuse link attachment plates 1 I provide a centering action to maintain the fuse link in the center of tubular casing l0.

In order that the casing may be completely filled with the desired insert granular arc-extinguishing material, the fuse link as assembled in Fig. 3 is preferably mounted on a vibrator 26 of any suitable form, as indicated schematically in Fig. 4, and suitable inert granular material to a suitable source, to tubular housing l0 through opening IS in the upper fuse link attachment plate l1. As soon as the tubular housing I0 is filled with the granular arc-quenching material, the upper end cap 20, which may include any suitable indicia, such as is shown in Fig. 4, is placedover the end of casing I 0 and, as shown in Fig. 3, a short portion of each end of fuse link I I extends along the outside wall of tubular casing I0.

The final step in the assembly of our new and improved fuse construction comprises molding or die casting the ferrules 22 around the ends of tubular casing I so as to envelop the interlocking means specifically illustrated .as offset shoulders 2| of end caps 20 and hold them in sealed relationsh p with housing It as well as to form good electrical contact with the ends of fuse link housing It and provide the terminals of the fuse device in a manner well understood by those skilled in the art. The suitable indicia on end caps 20 remain visible after the d e casting or molding operation since the major portion of each end cap 20 is exposed and the die cast metal merely grips the interlocking means illustrated as the offset shoulder 2|.

Although we have shown a fuse device including an. end closure member 20 which is held in place by a molded or die cast ferrule 22, which construction is shown with the .looped end I5 of fuse link ll extending outside of the casing, it should be understood that a molding or die casting operation may be used in which the metal would flow somewhat inside the casing as shown in Fig. 7, the corresponding parts of which are designated by the same reference numerals as in Figs. 1 and following. casing is provided with an annular recess 10' upon which fuse link attachment plate I! may be seated. With this arrangement, the end caps 20 may be entirely eliminated and the die cast ferrule 22', as shown in Fig. 7, constructed to surround completely the ends of tubular casing Iii to seal the casing as well as to provide an electrical terminal for the fuse. In this case, the mold for the die casting operation may be provided with suitable indicia so that the desired indicia will appear on the ends of ferrule 22' upon completion of the die casting operation as indicated in Fi 7. I

From the foregoing, it will be seen that the improved fuse construction while being of simple and rugged construction greatly simplifies the manufacturing processes with consequent cost reduction and provides a very satisfactory fuse in every respect.

Although we have elected to describe and illustrate herein a preferred embodiment of our invention as employed in a fuse device as well as the process of construction thereof, it is contemplated that other applications of our invention to fuses or like electrical devices other than the In Fig. 7, the tubular particular form illustrated will suggest themselves to those skilled in the art. It is intended that such other applications or modifications as do not depart from the true spirit and scope of our invention shall be covered by the appended. claim.

What we claim as new and desire to secure by Letters Patent of the United States is.

In a fuse of the current-limiting type, a tubular casing, a body of inert granular refractory arc-quenching material of high dielectric strength contained in said casing, an elongated fusible element embedded in said body of arcquenching material in said casing, and a molded or die-cast terminal ferrule associated with one end of said casing, saidelongated fusible element having an end thereof effectively extending out of said casing so as to be molded into said ferrule and electrically connected therewith, said fusible element being in the form of a helix the generating radius of which decreases near one end thereof so that tensile forces thereon will be transmitted along the axis of the helix and centering of said fusible element while filling said tubular casing with said are quenching material is obtained.

GEORGE R. SERFLING. CARL L. somJcK.

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