US 3111554 A
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Nov. 19, 1963 cs. N HARRIS 3,111,554
METHOD AND APPARATUS FOR PRODUCING AN ELECTRICAL CONNECTION WITH INSULATED WIRES Original Filed June 5, 1956 C C g GEORGE N.HARR|S ii-h INVENTOR.
1-- -I 40' 4 I a hmq 1% 3,111,554 Patented Nov. 19, 1963 ice 3,111,554 METHOD AND APPARATUS FOR PRODUCING AN ELECTRICAL CONNECTION WITH INSULATED WIRES George N. Harris, Madison, Wis., assignor to AMP Incorporated, Harrisburg, Pa. of application Ser. N 589,544, June 5, 30, 1962., Ser. No.
Continuation 1956. This application Oct.
6 Claims. (11. 174-84) This invention relates to electrical connectors of the type adapted to join together one or more wires or conductors by pressure forming and more particularly to a pressure formed electrical connector of the type adapted to join wires coated with tough film insulations.
Many wires commonly used in the electrical industry and which must be joined together are coated with a tough film insulation such as enamel, polyvinyl acetal and the like. In addition many wires become dirty and develop corrosion or oxide layers which act as insulation. Obviously to make a good low resistance connection with such wires these insulating layers must be removed.
Heretofore various connectors and methods of forming them about conductors have been proposed including sharp piercing teeth to penetrate the insulation, scraping of the insulating coating before connection, partially shearing of the conductors to expose virgin metal and the like. These have included some connectors and crimps that have been successful for limited ranges of wire sizes and types.
According to the present invention I have provided an improved connector and method of applying same which provides improved electrical and mechanical properties over a Wider range of wire and connector sizes and combinations thereof than heretofore known. Briefly I accomplished this by rupturing the insulating film and then causing it to be moved longitudinally from a portion of the wire to expose a greatly increased area of bare metal to provide improved low resistance contact through the connection.
Accordingly it is an object of the present invention to provide an improved crimp for an electrical connector that will make contact through the toughest film type insulation coatings over a wide range of Wire sizes without destroying the mechanical strength of a connection made therewith. It is another object of the present invention to provide a crimp for an electrical connector of the solderless type for joining together wires coated with tough insulating films that will expose an increased area of low resistance electrical contact between connector and wires without mechanically weakening the wires. It is another object of the present invention to provide a crimp for a solderless connector for joining wires coated with enamel, polyvinyl acetal and similar coating that has improved tensile strength, bend and securcness performance. It is another object of the present invention to provide an electrical connector which gives a greater area of stripped wire and a more positive contact therewith. It is a still further object to provide an electrical connector that will provide an increased area of virgin metal contact at a larger cross-sectional area point of the conductors being joined than heretofore possible. These and other and further objects will be in part apparent and in part pointed out as the specification proceeds.
In the drawings:
FIGURE 1 is a perspective view of a connector and connection according to the present invention showing a solid copper wire being joined to a stranded conductor;
FIGURE. 2 is a view similar to FIGURE 1 showing the reverse side of the connector of FIGURE 1;
FIGURE 3 is a longitudinal sectional view of the con ncction of FIGURE 1;
FIGURE 4 is a diagrammatic view in exaggerated scale showing the piercing burrs on the edges of the serrations;
FIGURE 5 is a longitudinal sectional view through the crimping dies of the present invention;
FIGURE 6 is a cross-sectional view of the dies of FIGURE 5; and
FIGURE 7 is a cross-sectional view similar to FIG- URE 3 showing another embodiment of the present invention.
This application is a continuation of my prior copcnding application, Serial No. 589,544, filed June 5, 1956, now abandoned.
Referring now to FIGURES l and 2 a connector 10 according to the present invention is shown orimped about the stranded wires 12 of an insulated cable 14 and a solid wire 16 insulated with a tough film insulation such as enamel, polyvinyl acetal or similar substance. In the embodiment shown in the present invention no contact or tongue portion is shown for the connector 10 but it is obvious that the present invention is applicable to connectors having as a part thereof one of the various contact portions adapted for attachment to another conductor, binding post or terminal device. Similanly while the solid wire 16 is shown as the one being covered with the film insulation 18 the strands of Wire 12 might similarly be insulated (eg. acetate wound stranded Deltahcston Range Wire) and a good connection still obtained. The connector 10 is generally made of a metal such as brass, Phosphor bronze, nickel plated steel and the like which is relatively harder than the conductor metal which is usually copper or a soft aluminum.
Referring now to FIGURE 3 the tough insulation film 18 is shown as a heavy line on the surface of the solid wire 16. The connector is shown as carrying therein a number of grooves or serrations 20 which extend transversely across the barrel portion of the connector and are located about the mid point of the connector 10. The grooves 20 are shown extending across the bottom (FIGURE 3) of the connector and part way up the side walls thereof. In certain applications these grooves may extend throughout the entire width of the connector particularly where two solid wires insulated with Formvar or the like are to be joined.
The grooves or serrations 20 are advantageously of smaller width than the diameter of the Wire 16 although generally they are of greater width than the diameter of the strands of the cable 14. In FIGURE 4 it will be seen that when the grooves 20 are formed in the connector 10 the edges 36 are actually raised a little bit to form sharp projections or burrs that aid in the penetration of the insulation film 18. Also the sides are tapered to give an improved contact action as described and claimed in the copending application, Serial Number 361,205, filed June 12, 1953, to Kemper M. Hammell, now US. Patent No. 2,800,638, issued July 23, 1957. The serrations 20 are shown as having a depth greater than the thickness of the film 18 and less than the diameter of the wire to be crimped, however this is not always necessary for a successful connection. Also it should be noted that the grooves or serrations 20 may vary in depth from the bottom where they contact wire 16 and the top where they contact the strands of cable 14. Naturally the depth would be less at the top so as not to completely sever the smaller strands of cable 14. As may be seen in FIGURE 3 the grooves 20 are well spaced to provide substantial land areas for good mechanical contact while still providing sufficient shearing edges for good electrical contact. Details as to the desired spacing, depth, width, and so on of the grooves for varying wire sizes are discussed in the 3 above Hammell application and are not repeated here for the sake of brevity.
Turning now to FIGURES 2, 5 and 6 it will be seen that the anvil portion 24 of the die assembly 26 has a generally concave face with longitudinal fiat edges and a raised central portion 28. Die 26 tapers from portion 28 toward each edge thereof. This taper is equal on both sides and forms enlarged ends on the connector providing a gradually tightening grip on the wire as it enters the connector. A taper angle of about six degrees has been found to be advantageous and helps to give an accentuated extrusion as will be described herein.
FIGURE 5 shows the face portion 28 of the anvil extending through the central serration area of the connector and the tapered portions 30 extending outwardly to the ends of the connector 10. The other die 32 overhangs the left end of the connector FIGURE 5 (with rounded corners to avoid nicking the wire) but is overhung by the connector on the right end to provide a portion of the connector accessible for stripping.
In the actual crimping operation as the dies force the connector into contact with the wires therein the burrs 36 rupture the insulation film 18 at the points shown by the arrows in FIGURE 4 deforming the burrs in the process. Additional pressure on the connector causes the conductor 16 to bend down into the serrations 20. Next the conductor surface starts to shear at the points of the arrows in FIGURE 4 and a ring of insulating coating and wire is forced down toward the bottom of the serrations. At the center serration this process continues until the ring of insulating coating rests in the bottom of the serration and freshly sheared virgin conductor surfaces are wedged, by virtue of the tapered side walls of the grooves as described above, into the serration to make good electrical contact with the edges thereof.
Continued pressure from the dies on the connector 10 starts to cause the wire 16 to extrude longitudinally from between the dies in the center section corresponding to the face 28. This conductor motion is accentuated by the double tapered anvil 24 and, aided by the difference in hardness of the metals, is greater than the motion of the adjacent metal in the connector 10. The motion of the conductor carries with it the insulating coating 18 which starts to expose additional areas on either side of the central serration as indicated at 38. This sliding causes the insulation to slide over the inner edge of the outer serrations and down into the bottom thereof. This covers the inner edge and bottom of the outer serration but is stopped at the outer edge thereof. Also at the outer edge of the outer serrations this sliding causes the insulation to flow outwardly from the burrs at the edge of the serrations. This flow, accentuated by the double taper anvil as mentioned above, causes an increasingly larger annular ring to be exposed outwardly of the greatest amount of crimping indentation as indicated at 40. As may be seen in FIGURE 2 this pressure forming results in a flat impression in the bottom of connector 10 which coincides with the area of maximum reduction in cross-sectional area and tapered portions 22 of progressively lesser reductions which gradually relieve the pressure outwardly to the edge of the connector. This changing reduction of cross-sectional area helps produce an accentuated extrusion of wire 16 causing a large relative movement thereof past the serrations which scrapes and moves the insulating layer 18 from a large, at least semi annular area adjacent the edge of the serrations.
As can be readily seen the cross-sectional area of the wire 16 has not been reduced as much at areas 40 as it has at the areas 38 for instance, and thus there is provided a path of reduced resistance from the uncrirnped wire through the area 40 into the connector 10, which has large current carrying capacity and low resistance. Thus the current flows from the wire 16 through the connector 10 and thence to the cable 14 reducing the millivolt drop in the splice connection and in turn reducing the temperature rise encountered in the usual connection of this type.
Since the major portion of the low resistance contact area is uncovered by the relative sliding of the insulated solid wire after rupture of the insulation and the connector 10 the serrations or grooves 20 need not he as deep as where the electrical contact must be obtained by the exposure of sheared surfaces as by partially shearing the wire. This together with the double tapered effect gives a much stronger mechanical connection and electrical conductivity.
Referring now to FIGURE 7 there is shown another embodiment of the present invention wherein the com nector 10' has only one tapered area 22' and a flat central area. A plurality of grooves 20 are provided on the inner surface of connector 10 as in the embodiment of FIGURE 3 and in addition they extend down into the tapered area 22'.
The crimping dies for the embodiment of FIGURE 7 are the same as for FIGURE 3 except that the taper 30 is omitted from one end. The flat portion is impressed the deepest to cause the serrations 20' to rupture the coating 18 and extrude the conductor 16' longitudinally from within the connector 10'.
A similar separating action occurs at the edge of the serrations 20 as in the previous embodiment with the largest exposure of virgin metal occurring at the outer edge of a serration intermediate the fiat portion and the end of the tapered portion 22'.
It is thus apparent that I have provided an improved connector and method of connecting conductors, at least some of which are coated with tough enamel, polyvinyl acetal and similar film type insulations, resulting in both improved electrical and mechanical characteristics for the connection.
While there is given above a certain specific example of this invention and its application in practical use, it should be understood that this is not intended to be exhaustive or to be limiting of the invention. On the contrary, this illustration and explanation herein are given in order to acquaint others skilled in the art with this invention and the principals thereof and a suitable manner of its application in practical use, so that others skilled in the art may be enabled to modify the invention and to adapt and apply it in numerous forms each as may be best suited to the requirement of a particular use.
1. A crimp for an electrical connector of the type adapted to join one or more electrical conductors together by pressure forming which comprises in combination with at least one wire coated with a tough insulating film and an electrical connector of a harder metal than the conductors and having a plurality of transverse grooves therein formed thereabout, a transverse imp-ression located about the mid point of the connector bottom, a taper portion at each end of said impression gradually releasing the pressure from said impression outwardly to the edge of said connector, and said impression and taper portions having a convex outer surface forming the bottom of said connector.
2. A crimp for a sheet metal electrical connector of the type having a barrel portion carrying therein a plurality of transverse serrations adapted to be curled up around a plurality of conductors coated with a tough insulating film comprising a smoothly curving upper portion coined into intimate contact with the conductors therein and a bottom portion tapering from one end of the barrel to the other from a maximum coining of the conductors therein to substantially no coining thereof whereby said serrations will require the insulating film and said bottom taper will accentuate the extrusion of the conductors to expose substantial areas of bare condoctor to intimate contact with the connector, the connector being of harder metal than the conductors.
3. In an electrical connection joining a conductor coated with a film insulation to a connector, a metallic connector barrel disposed around said conductor and having a plurality of substantially transverse serrations between substantial land areas on a surface thereof, the edges of said serrations being sharp and breaching said insulation along transverse lines, a major portion of said barrel being compressed in substantially uniformly increasing tightness relative to the length of said conductor to provide an accentuated extrusion of the conductor in the direction of decreasing tightness, and a plurality of gaps in said insulation exposing bare wire for contact with surfaces of said barrel adjacent said serrations, said gaps being respectively defined between an edge of said serrations and the limit of conductor extrusion relative to said edge.
4. The method of crimping a conductor having a tough resilient film-type insulation in a harder metal connector having transverse sharp-edged grooves which includes the steps of disposing the conductor in the connector to lie across the grooves, reducing the connector cross-section to bring the groove edges into cutting relation with the conductor insulation, pressure-forging a first portion of the connector inclusive of at least some of the grooves with sufficient pressure to substantially reduce the cross-sectional area of and to extrude the conductor and the insulation longitudinally outward from the center thereof while simultaneously pressure-forging the remaining connector portions with a progressively decreasing pressure away from the first portion, the grooves and the outer edges thereof relative to the center of the first portion presenting barriers to outward movement of insulation so that substantial areas of bare conductor for contact with the connector are exposed adjacent the outer edges upon extrusion of the conductor and insulation outwardly therefrom.
5. The method of crimping a conductor having a tough resilient film-type insulation in a harder metal connector having transverse sharp-edged grooves which includes the steps of disposing the conductor in the connector to lie across the grooves, reducing the connector cross-section to bring the groove edges into cutting relation with the conductor insulation, cylindrically pressure-forging a portion of the connector inclusive of some of the grooves with sufficient pressure to substantially reduce the crossscctional area of and to extrude the conductor and the insulation longitudinally outward in either direction from the center thereof will simultaneously pressure-forging the remaining connector portions with a progressively decreasing pressure away from the cylindrical portion, the grooves and the outer edges thereof relative to the center of the cylindrical portion presenting barriers to outward movement of insulation so that substantial areas of bare conductor for contact with the connector are exposed adjacent the outer edges upon extrusion of the conductor and insulation outwardly therefrom.
6. The method of crimping a conductor having a tough resilient film-type insulation in a harder metal connector having transverse sharp-edged grooves which in eludes the steps of disposing the conductor in the connector to lie across the grooves, reducing the connector cross-section to bring the groove edges into cutting relation with the conductor insulation, pressure-forging a first portion of the connector inclusive of at least some of the grooves with sufficient pressure to substantially reduce the crosssectional area of and to extrude the conductor and the insulation longitudinally outward from. the center thereof, and pressure-forging the remaining connector portions inclusive of the remaining grooves with a continuously progressive compression away from the first portion to cause a differential pressure to progress along the length of the connector for accenturating the extrusion of the conductor and insulation in the direction of the progressive compression, the grooves and the outer edges thereof relative to the center of the first portion presenting barriers to outward movement of insulation so that substantial areas of bare conductor are exposed in contact with the lands between the grooves of the connector adjacent the outer edges upon extrusion of the conductor an insulation outwardly therefrom.
References Cited in the file of this patent UNITED STATES PATENTS 2,622,314 Bergan Dec. 23, 1952 2,692,422 Pierce Oct. 26, 1954 2,800,638 Hammell July 23, 1957 2,802,257 Hotzapple Aug. 13, 1957 FOREIGN PATENTS 573,920 Great Britain Dec. 12, 1954