Abstract:
Electric fuses having a helically wound fusible element are provided with simple, cost-effective sheet metal means performing the dual function of supporting insulating plates which, in turn, support the helically wound fusible element, and of establishing conductive connections between the ends of the helically wound fusible element and a pair of ferrules by which the casing of the fuse is closed.

Description:
BACKGROUND OF THE INVENTION 
     In electric fuses for elevated circuit voltages it is often necessary to wind the fusible element, or elements, helically around a supporting structure of electric insulating material. Such insulating structures may take various forms, e.g. that of an extruded mandrel. In recent times it has often been found more desirable to fabricate supports for helically wound fusible elements out of plates of insulating material rather than to resort to extruded or similarly formed mandrels. Typical structures of this description are shown in U.S. Pat. No. 3,680,019 to F. J. Kozacka, 7/25/72, for HIGH-VOLTAGE FUSE HAVING A PLURALITY OF FUSE LINKS WOUND HELICALLY AROUND AN INSULATING MANDREL, in U.S. Pat. No. 3,846,728 to E. Salzer, 11/5/74, for HIGH-VOLTAGE FUSE INCLUDING INSULATING MANDREL FOR SUPPORTING FUSIBLE ELEMENTS, and in U.S. Pat. No. 3,851,289 to F. J. Kozacka, 11/26/74, for HIGH-VOLTAGE FUSE HAVING HELICALLY WOUND FUSIBLE ELEMENTS AND SUPPORT FOR HELICALLY WOUND FUSIBLE ELEMENT, all these patents being assigned to the same assignee as the present invention. 
     The above referred-to prior art relates to fuses wherein the helically wound fusible element extends between a pair of plug terminals. 
     The present invention relates to fuses wherein the helically wound fusible element extends between a pair of ferrules, or terminal caps, rather than between a pair of plug terminals. 
     SUMMARY OF THE INVENTION 
     Fuses embodying this invention include a pair of disks of sheet metal arranged inside the casing or fuse tube adjacent the ends thereof. Each of said pair of disks forms a support for the axially outer ends of plate means of insulating material around the edges of which the fusible element is wound helically. Each of said pair of disks has connector tabs whose ends are interposed between the outer surface of said casing or fuse tube and the inner surfaces of a pair of ferrules supported by the ends of said casing and closing said casing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an electric fuse embodying this invention, partly in longitudinal section, and partly in elevation, the center region of the fuse being broken away; 
     FIG. 2 is an end view of a detail of the structure of FIG. 1 seen in the direction R of FIG. 3; 
     FIG. 3 is a side elevation of the structure shown in FIG. 2; and 
     FIGS. 4a and 4b are front views of insulating plates for forming a mandrel structure for supporting the fusible element and FIG. 4c is an isometric view of such a mandrel structure. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     In the drawings reference numeral 1 has been applied to indicate a tubular casing of electric insulating material, e.g. of a synthetic-resin-glass-cloth laminate. Casing 1 houses a pulverulent arc-quenching filler 2 such as, for instance, quartz sand. A pair of ferrules or terminal caps 3 is supported by the ends of casing 1 and closes the latter. Reference numeral 4 has been applied to indicate a helically wound fusible element inside of casing 1, embedded in filler 2, conductively interconnecting the pair of ferrules 3. How this is achieved will be explained below in more detail. Reference numeral 5 has been applied to generally designate plate means of electric insulating material arranged inside casing 1 having edges extending in a direction longitudinally thereof supporting helically wound fusible element 4. The latter may either be in the form of a wire -- as shown in FIG. 1 -- or in form of a metal ribbon. In the embodiment of the invention shown in the drawing plate means 5 are made up of a relatively wide plate 5&#39; and two relatively narrow plates 5&#34;. The latter are arranged at right angles to the plane defined by wide plate 5&#39;, at opposite sides of wide plate 5&#39;, and cemented to the latter with their edges situated adjacent to plate 5&#39;. A pair of sheet metal disks 6 are arranged inside casing 1 adjacent the ends thereof. In FIG. 1 the disks 6 have been shown in part in elevation and in part in section. Each of the pair of disks 6 forms a support for the axially outer ends of plate means 5 and each of the pair of disks 6 has connector tabs 6&#39; whose ends are interposed between the outer surface of casing 1 and the inner surface of one of ferrules 3. The ends of fusible element 4 are conductively connected by solder joints 4&#39; to disks 6. Connector tabs 6&#39; are bent around the axially outer edges or rims of casing 1 and conductively connected to ferrules 3 by means well known in the art to achieve this end, e.g. solder joints. To minimize the weight of disks 6 the latter are provided with four circular apertures or holes 6&#34;&#34;. Each of the pair of disks 6 is arranged adjacent, parallel to, and in spaced relation from, the end surface 3&#39; of one of ferrules 3. Each of disks 6 is provided with slot means or slots 6&#34; and plate means 5 project through slots 6&#34; into spaces S bounded by the end surfaces 3&#39; of ferrules 3 and by disks 6. This greatly increases the dimensional stability of the mandrel structure formed by parts 5&#39;, 5&#34; supporting fusible element 4. The dimensional stability of that mandrel structure is further increased by tabs 6&#39;&#34; engaging the sides of plate means 5. Tabs 6&#39;&#34; are formed by portions of disks 6 partly stamped out of the planes defined by disks 6 to establish slots 6&#34;. Tabs 6&#39;&#34; enclose angles of 90 degrees with the respective plane defined by each of disks 6. 
     As mentioned above, the weight of disks 4 is minimized by the circular apertures or holes 6&#34;&#34; therein. The apertures or holes 6&#34;&#34; facilitate also filling of casing 1 with pulverulent arc-quenching filler. 
     Plates 5&#39; and 5&#34; may be joined together by adhesive means when the production volume is relatively small. Where the production volume is relatively large, the plate means 5 are preferably formed by a pair of slotted plates 5a, 5b as shown in FIGS. 4a and 4b in front elevation. Plate 5a is provided with a slot 5a&#39; extending in a direction longitudinally thereof and having an opening at the lower narrow edge of plate 5a. Plate 5b is provided with a slot 5b&#39; extending in a direction longitudinally thereof and having an opening at the upper narrow edge of plate 5b. Plates 5a, 5b are arranged at right angles in such a way that the upper portion of plate 5b is arranged inside the slot 5a&#39; of plate 5a and that the lower portion of plate 5b is arranged inside of the slot 5b&#39; of plate 5b.