US 3676574 A
A tapered coiled spring wire secured within an insulating shell containing interior deformable fins for engagement with the spring wire to form retaining threads in the fins and avoid any substantial tensioning or deformation of the shell.
Claims available in
Description (OCR text may contain errors)
[4 1 July 11,1972
United States Patent J ohansson et al.
m Mm a w mm m T h S m U m U m P s W. F ma 0 AT MC R w no no 4 I 1  332: an's: lif i i 2,825,750 3/1958 Stockwell................................
3,297,816 l/1967 Waddington.. 3,448,223
 Assignee: Minnesota Mining and Manufacturing Company, St Paul, Minn Primary Examiner-Darrell L. Clay Dec. 18, 1970 ] Appl.No.: 99,365
Attorney-Kinney, Alexander, Sell, Steldt & Delahunt 221 Filed:
ABSTRACT A tapered coiled spring wire secured within an insulating shell containing interior deformable fins for engagement with the spring wire to form retaining threads in the fins and avoid any substantial tensioning or deformation of the shell.
F88 8N 35 1 4 nm nd "F a 7 MB t .7 "8 "4 m7 .1
5 Claim, 5 Drawing figures DEFORMABLE FIN SPRING CONNECTOR BACKGROUND OF THE INVENTION This invention relates generally to screw-on type wire connectors providing a secure connection between electrical wire ends without use of soldering, welding or the like.
A number of two-piece connectors, that is a connector including a coiled spring and a surrounding insulating shell, have been devised. Such connectors commonly include molded interior threads within the shell into which the coiled spring is tightly screwed, thus longitudinally securing the spring within the shell. Forming of the interior threading of the insulating shell requires additional time during the molding operation and results in high manufacturing costs. A tight interference fit between the spring and shell such as caused by mismatching of the threads or excessive expansion of the coiled spring caused by joining of large electrical wires, can cause substantial deformation of the shell resulting in deterioration of its physical and electrical properties.
SUMMARY OF THE INVENTION The invention in one aspect involves the combination of a tapered coil spring wire fastening element with an insulating shell having internal deformable fins for forming threads between the spring wire and the fins. As the element is inserted within the shell the spring wire forms threads, closely corresponding to the physical dimensions of the element, by local deformation of the fins. Also, as the element is twisted over a plurality of electrical wire ends whereby the element is radially expanded and longitudinally shortened, the changing physical dimensions of the element can be compensated for within the readily deformable fins without any substantial deformation of the insulating shell so that degradation of the shell is minimized.
These and other attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing in which like numerals designate like parts throughout the figures and wherein:
FIG. 1 is a longitudinal sectional view of a preferred embodiment of the invention;
FIG. 2 is a longitudinal sectional view similar to FIG. 1 illustrating the present connector securing together two electrical wire ends;
FIG. 3 shows a section of the insulating shell illustrating the end wall of the shell with the spring wire removed for clarity, taken on line 3-3 ofFlG. 1;
FIG. 4 represents a portion of the interior of the shell illustrating in plan view a single deformable fin; and
FIG. 5 shows a section of insulating shell, with the spring wire removed, taken along lines 55 of FIG. 1.
Referring now to the embodiment illustrated in FIGS. l-5, the wire connector has been denoted in its entirety by the reference numeral and includes a tapered coil spring wire fastening element 12 secured within an insulating shell 14. The connector 10 is used to provide a firm electrical connection between two or more electrical wires having their insulation previously removed, as for example, wires 16 and 18.
The element 12 is formed of a spring wire 20 and has an enlarged foremost end to permit easy insertion of the electrical wires l6, 18 therein and progressively decreasing convolutions to guide the wires 16, 18 to the restricted throat opening. The throat opening has a diametric dimension less than the combined thickness of the minimal sized wires to be electrically connected. Although the spring wire may terminate rearwardly adjacent the restricted throat opening, in the illustrated embodiment the element 12 progresses in increasing diametrical convolutions from the restricted throat portion to the rearmost end of the element. The enlarged rearmost end provides a longer spring wire lever arm, and thereby permits a lesser force against the terminous tip of the wire while applying the required torque in twisting the element over the wire ends 16, 18.
The elongated insulating shell 14 has an open front end 26 .defined by a skirt 27 and an integrally connected body 29 terminating at the closed rearward end 28. The enlarged interior opening of the skirt 27 provides clearance for electrical wires 16, 18 having insulation thereon and the longitudinal length of the skirt 27 shields the stripped ends 16, 18 against arcing between conductors and ground. As illustrated particularly in FIGS. 1 and 5, the interior surface 30 has a plurality of deformable fins 31 extending inwardly and along the surface 30 in a generally longitudinal direction. The interior surface 32 of the rearward end 28 is circumferentially grooved to provide a ramp 33 extending uniformly from the level of the surface 32 in the direction shown to a depth of 0.075 inch at the abutment 34. Wings 35 provide leverage to enable an operator to manually twist the element 12 over the wires 16, 18 by way of surface 34 abutting the terminous tip of the rearmost end of element 12.
EXAMPLE Although this invention is subject to considerable variation without departure from the spirit thereof, it is believed that the following specific example will facilitate understanding.
The element 12 is formed of steel spring wire having a square cross section measuring 0.041 inch across a side and I disposed diagonally as illustrated. The element consists of two forward turns at an inside diameter of 0.253 inch followed by 42 slightly overlapping turns of uniformly progressively decreasing diameter reaching a minimum diameter of 0.135 inch. One turn at the minumum diameter is followed by 11/; turns increasing to two end turns at 0.188 inch interval diameter, making a total of ll close-wound turns to provide an overall length of 0.620 inch. The coiled spring wire is then zinc coated for corrosion resistance and wax coated for lubrication during application of the connector 10 to the wires l6, 18.
The shell 14 is integrally molded of polypropylene. The interior wall 30 progresses inwardly from a diameter of 0.388 inch adjacent the skirt 27 to 0.314 inch adjacent the surface 32 and is provided with 16 uniformly spaced longitudinal fins 31. Each fin has a substantially equilaterally triangular crosssection and progresses uniformly from a forward maximum height of 0.035 inch to a rearward minimum height of 0.010 inch. The abutment 34 extends 0.075 inch past the level of the surface 32.
Upon insertion of the coiled spring wire fastening element 12 within the shell 14, the sloping front surfaces 36 of the fins 31 initially guided the element 12 therein. As the element 12 is further advanced, by screwing the element therein, the spring wire 20 engages the fins and deform the same to define threads therein. The element 12 is advanced until the rearmost terminous tip of the wire 20 engages the abutment surface 34. As shown in FIG. 1, when the element is fully inserted within the shell 14 the foremost and rearmost ends 22, 24 thereof will be in contact with the deformable fins 31 whereas the intermediate section 23 will be separated from the fins 31 to permit radial expansion of section 23 into the deformable fins 31, without deformation of the body 29, as the element is twisted over the wires l6, 18. The radially inward circumferential rim 38 (with a radial thickness of 0.015 inch) causes momentary deformation of the skirt 27 and rim 38 and molecular orientation of the polypropylene as the shell 14 is removed from the core pin, forming the interior cavity of the shell 14, during the molding operation. This molecular orientation strengthens the periphery of the skirt 27.
The several structures described and illustrated, and other analogous modifications, may be combined in other ways without departing from the spirit and scope of the invention as set forth in the appended claims.
What is claimed is:
l. A wire connector comprising a coil spring wire fastening element which is convergingly tapered from a foremost end toward a rearmost longitudinally spaced end, said rearmost end having a terminous tip to which a force may be applied to threadably rotate the fastening element over a plurality of electrical wire ends, and an elongated insulating shell having a cavity in which said fastening element is positioned, said cavity extending from an open front end to a longitudinally spaced closed rear end which rear end has means in engagement with the terminous tip of the fastening element for transferring rotational forces thereto, and said shell having a multiplicity of circumferentially spaced longitudinally extending deformable fins projecting from the interior surface of said shell into said cavity, said deformable fins being deformed by and in engagement with the exterior surface of said fastening element adjacent said foremost end of said fastening element and retaining said fastening element within said shell.
2. A wire connector according to claim 1 wherein said fins extend along said interior surface approximately the length of said element.
3. A wire connector according to claim 2 wherein said fins increase in height from said interior surface as they extend toward said front end.
4. A wire connector according to claim 1 wherein said shell is formed with a skirt portion spacing said fastening element from said open end of said shell and having a radially inward projecting circumferential rim about said open end.
5. A wire connector according to claim 1 wherein said fastening element is convergingly tapered from said foremost end to a section of minimum diameter intermediate its ends and is divergingly tapered from said section of minimum diameter to said terminous tip affording spacing between said fastening element and said fins adjacent said section of minimum diameter.