Solderless Fuse Terminal

U.S. Pat. No. 3,979,709 to Daniel P. Healey, Jr.; Sept. 7, 1976 for ELECTRIC FUSE HAVING A MULTIPLY CASING OF A SYNTHETIC-RESIN-GLASS-CLOTH LAMINATE describes a novel fuse tube that has characteristics different from conventional fuse tube materials such as, for instance, ceramic fuse casing, or fuse casings of glass. The casings according to the above referred-to patent, particularly if made with a binder of synthetic polyester resin, are relatively soft and relatively easily deformable in comparison to the prior art casings listed above. This is the starting point of the present invention on which the latter is predicated.

While this invention is not limited to fuse casings as described in the above patent, but may be used, for instance, in connection with casings of convolutely wound melamine impregnated glass cloth and other laminates of synthetic resin, best results are obtained with casings manufactured in accordance with U.S. Pat. No. 3,979,709 and impregnated with polyester resins.

According to this invention a fusible element is placed inside of a tubular fuse casing easily deformable, for instance, a casing as described in U.S. Pat. No. 3,979,709 impregnated with polyester resin. The fusible element is bent over one of the rims of the casing, and has a portion engaging the outer surface of the casing. A ferrule mounted on said casing has a radially inward directed indentation in registry with said portion of said fusible element on the outer surface of said casing, said indentation engaging and deforming said portion of said fusible element on the outer surface of said casing and exerting sufficient pressure against said portion of said fusible element to establish an electrically connective solderless joint between said portion of said fusible element and said ferrule. The indentation in the ferrule and the portion of the fusible element in registry with it and with the casing at this particular point are backed-up by a portion of the ferrule inside the casing of the fuse.

FIG. 1 shows in longitudinal section a first embodiment of the invention;

FIG. 2 is a transverse section along II--II of FIG. 1;

FIG. 3 shows in longitudinal section a second embodiment of the invention; and

FIG. 4 is a transverse section along IV--IV of FIG. 3.

Referring now to the drawings, and more particularly to FIGS. 1 and 2 thereof, numeral 1 has been applied to indicate a tubular casing of a relatively easily deformable electric insulating material combining glass-fiber layers, or plies, e.g. with polyester, as described in the above referred-to U.S. Pat. No. 3,979,709. The tubing may be produced by the so-called pultrusion process described in detail in U.S. Pat. No. 3,979,709. FIGS. 1 and 2 show but one end of an electric fuse. The other end is identical with the end shown in FIGS. 1 and 2, and also in FIGS. 3-4. The fusible element 2 inside of casing 1 is of silver or copper and bent over rim 1a thereof, and has a portion 2a engaging the outer surface 1b of casing 1. Mounted on casing 1 under pressure is a ferrule 3. Ferrule 3 has a radially inward indentation 3a in registry with said portion 2a of fusible element 2 on the outer surface of casing 1. Said indentation 3a engages and deforms the portion 2a of fusible element 2 on the outer surface 1b of casing 1, and exerts such a pressure against said portion 2a of said fusible element 2 to establish an electrically conductive pressure joint between said portion 2a of said fusible element 2 and said ferrule 3. The indentation 3a in ferrule 3 may be effected by means of a prick punch, or like instrument. The pressure used to jointly deform ferrule 3 at 3a and fusible element 2 at 2a tends to produce a bulge at the inside of casing 1 juxtaposed to joints 2a and 3a where a pressure-joint is established between portion 2a of fusible element 2 and groove 3a of ferrule 3. To avoid such internal bulge inside of casing 1 to occur the portion of ferrule 3 engaging the inner wall of casing 1 provides a back-up for the solderless conductive pressure connection between parts 2a and 3a.

Referring now to the structure in FIGS. 3 and 4, casing 1 is made of a material of the kind shown in, and described in connection with, FIGS. 1 and 2, i.e. relatively deformable material such as produced by the pultrusion process disclosed in U.S. Pat. No. 3,979,709. Casing 1 is circular in cross-section, having a rim 1a and housing fusible element 2 on its inside. Fusible element 2 is bent over rim 1a and engages the outer surface of casing 1. Reference character 1b has been applied to indicate the outer surface of casing 1 engaged by the surface of ferrule 3. The surface of ferrule 3 has a radially inwardly projecting circularly shaped indentation 3a engaging and deforming said fusible element and establishing a solderless conductive pressure-joint between the portion 2a of said fusible element 2 engaging the outer surface 1b of said casing 1 and said annular indentation 3a of said ferrule 3. In order to apply two-sided clamping pressure, i.e. to avoid radially inward movement of the point where the portion 2a of fusible element 2 and annular groove 3a overlap, ferrule 3 has a portion 3b engaging the inside of casing 1 and backing-up the internal wall thereof juxtaposed to said circularly shaped indentation 3a. That back-up portion 3b may be in the same plane as indentation 3a (FIG. 3), or project beyond that plane (FIG. 1).

Regarding the material of which fuse tube 1 is made, it comprises preferably a radially outermost ply and a radially innermost ply of woven glass fibers and at least an intermediate ply of matte material having random oriented fibers, as disclosed in considerable detail in U.S. Pat. No. 3,979,709.

FIGS. 3 and 4 show the preferred embodiment of the invention. It will be understood that the circular groove formed in casing 1 for receiving the portion 2a of fuse link 2 is merely produced by the pressure of annular groove or annular indentation 3a, or the pressure of a machine producing annular groove or indentation 3a, but is not machined by a process removing material from casing 1. The axially outer surface of ferrule 3 extends beyond the axially annular indentation 3a and is crimped into soft casing 1 at 3c in the absence of any pre-machined edge-receiving groove therein.

The fuse casing may or may not be filled with a pulverulent arc-quenching filler 4. Where the engaging surfaces 2a, 3a are not of silver, e.g. of copper, silver plating is indicated for good current transfer, e.g. fusible elements should always be silver plated at points 2a.