US 3200190 A
Description (OCR text may contain errors)
10, 1965 E. w. FORNEY, JR 3,200,190
DUAL FERRULE CONNECTOR FOR A COAXIAL I CABLE HAVING A FLAT BRAID Filed May 9, 1962 2 Sheets-Sheet l TIN ANTIMOMY ALLOY INVENTOR. Enema w. FoRNEY JR. BY
Mg MM Aug. 10, 1965 E. w. FORNEY, JR 3,200,190 DUAL FERRULE CONNECTOR FOR A COAXIAL CABLE HAVING A FLAT BRAID Filed May 9, 1962 2 Sheets-Sheet 2 7 PRIOR ART INVENTOR.
Enema w. FORNEY JR. BY
United States Patent 3,2tiii,1% DUAL FERRULE CQNNECTQR FGR A (IOAXKAL CABLE HAVEJG A FLAT BRAKE Edgar W. Forney, J12, Harrisburg, Pa, assignor to AMP Incorporated, Harrisburg, Fa. Filed May 9, 1962, Ser. No. 193,5tl3 2 Claims. (Cl. 17475) This invention relates to a device for making permanent electrical connections to fiat braid shielding on coaxial type shielded wires.
In the following the trend toward minaturization of electronic equipment, wire and cable manufacturers have developed coaxial cables and shielded wires employing interwoven flat copper ribbons for shielding. As compared with conventional cable shielded by wire braiding, the newly developed fiat braid cable is smaller, lighter and in certain respects provides superior electrical characteristics. Unfortunately, the flat braid shielding has proven difficult to terminate with existing devices and procedures. The usual problems affecting soldered connections such as damage to components and insulation due to overheating, cold joints, braid embrittlement and the like are aggrevated by the foil-like surface of flat braid. The use of known solderless connectors has also been found to be unsatisfactory due to an undesirable cable deformation .and incidental breakage of the relatively delicate flat braid ribbons. This has been the case with crimped devices employing a backing ferrule inserted beneath the braid as well as with crimped devices utilizing only an outer sleeve. In addition to poor reliability, connections made with solder or solderless devices of the prior art have proven considerably more expensive to make on flat braid shielding than appears justified when compared with the reliability and cost of similar connections made on conventional wire braid.
Accordingly, it is a primary object of the present invention to provide a reliable and low cost electrical connection to cable shields of flat braid construction.
It is another object of invention to provide a device for making connections to flat braid cable shields having simple and inexpensive components and compatible in use with existing tools and crimping procedures.
It is still another object of invention to provide a one piece, two component device for splicing pig-tail or grounding leads to flat braid shielded coaxial cable.
It is a further object of invention to provide a connector for flat braid shielded cable minimizing cable deformation and braid breakage.
It is a still further object of invention to provide a novel crimp type ferrule assembly for interconnecting a wire conductor with a foil conductor.
Other objects and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings in which there is shown and described an illustrative embodiment of the invention; it is to be understood, however, that this embodiment is not intended to be exhaustive nor limiting of the invention but is given for purposes .of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and the manner of applying it in practical use so that they may modify it in various forms, each as may be best suited to the conditions of a particular use.
The present invention accomplishes the foregoing objects by providing a one piece construction employing a thin walled outer ferrule capable of being crimped into a relaxation resistent band and a relatively thick inner ferrule of soft conductive eating material capable of being driven by crimping forces into a substantial interface connection with the conductors to be con utilizing abnormal crimping pressures.
Bidhldd Patented Aug. iii, M965 nected. The outer ferrule serves to evenly distribute crimping forces in a manner making the assembly compatible with the existing crimping tools and additionally serves to hold or restrain the conductors and the inner ferrule against relative movement. The inner ferrule serves to mechanically and electrically engage the conductors to be terminated without imparting excessive tensile and shearing stresses to the flat braid. By reason of its flow characteristics, the inner ferrule is worked into the interstices of the shielding braid and accommodates along its outer diameter the volume of an auxiliary pig-tail lead without breaking the foil ribbons of the braid. The interface connection .achieved by the invention is thereby capable of holding the conductors against relative movement without relying solely upon the insulating material surrounding the cable central conductor. In this manner, the device of the invention facilitates the rapid and reliable connection of flat braid shielded cable without the use of solder and without the use of complicated crimping devices and procedures.
In the drawings:
FIGURE 1 is an exploded View of one embodiment of the invention;
FIGURE 2 is a perspective View of the device of FIG- URE 1 assembled and positioned to receive an auxiliary conductor and a flat ribbon braid shielded cable;
FIGURE 3 is a perspective View of the device of FIG- URE 1 showing it in its crimped state;
FIGURE 4 is a section of FIGURE 3 lines 4-4;
FIGURE 5 is a sectional elevation of FIGURE 4 taken along lines 55;
FIGURE 6 is a perspective of a further embodiment of the invention capable of accommodating an auxiliary conductor and a flat braid shielded two conductor cable;
FIGURE 7 is an enlarged sectional view taken along lines 7-7 of FIGURE 4; and
FIGURE 8 is a perspective view of a typical flat braid shielded cable included to explain the problem solved by the invention.
Prior to describing the device of the invention, reference will be made to FIGURE 8 in order to point out the technical aspects of crimping flat braid of shielded cable which give rise to the problems and shortcomings of prior art devices and which make evident the advantages of the invention.
The section of cable 1% in FIGURE 8 represents an enlarged View of a typical flat braid shielded cable having a central stranded conductor itlil surrounded by a tubular sheathing of insulating material 104 and a braided jacket of foil-like ribbons 1%. The central conductor 102 and the insulating tubing 1% are dimensionally and materially similar to their counter parts in conventional shielded cables. The shielding, comprised of ribbons 1tl6,'however, differs substantially from conventional wire shielding in that it is thinner (typically 1.5 mils), has a relatively smooth outer surface, and forms a tight fit against the insulating material 104. As a result of the thinness, the ribbons 1% are fiexure sensitive and may be easily severed. As a result of the smooth outer surface of the braid and the relatively soft backing of the insulating material, it is difficult to establish a mechanically sound interconnection without For this reason, the use of a copper or other relatively hard ferrule against the shielding is generally unsatisfactory. The practice of the prior art in inserting a backing or support ferrule between the shielding and the insulating material 104, as in the position indicated by numeral 110, is made difricult by the tight fit of the shielding against the insulation and by the susceptibility of the ribbons to being broken.
taken along 3 The section of cable ltltl in FIGURE 8 includes a portion representative of the deformation which occurs by reason of crimping; the ferrule 1% representing a typical relatively hard ferrule crimped over the cable Ill-t As with any crimp-type ferrule, there will be a reduction in diameter resulting in an elongation or extrusion of the ferrule in turn exposing the conductor to be terminated to forces represented by arrows 114. Additionally, the
inner edge of the ferrule upon being crimped will effect a transition in cable diameter in the manner shown by numeral 112. It is at this point of transition that the greatest flexure of braid takes place and that breakage is most likely to occur both during the crimping operation and thereafter. The use of a relatively hard copper fer i smooth transition of the cable diameter.
. Turning now to a detailed description of the invention, FIGURE 1 shows an embodiment of the assembly of the invention for use with the flat braid of a single conductor shielded cable. The inner ferrule 26 is comprised of a tube or cylinder having an inner diameter slightly larger than the diameter of the shield. To simplify handling and assembly, the ferrule 26 should be slightly compressed or otherwise retained within the ferrule 24 so as to provide a single piece device. The ferrule 29 comprises a sleeve or tube having a raised portion 24 along its length to accommodate the insertion of an auxiliary conductor or pig-tail grounding lead. The particular size and shape of the raisedportion 24 is determined by the configuration of the auxiliary conductor to be terminated. For example, the raised portion 24 could be considerably flatter than that shown in FIGURE 1 if the pig-tail lead utilized were a fiat strip conductor rather than the cylindrical conductor 43 as shown in FIGURE 2. Furthermore, the raised portion could accommodate more than one pig-tail lead if desired. The Wall thicknesses T and t are determined by the material characteristics of the metals employed in conjunction with the functional requirements of each ferrule. The thickness T of ferrule 26 must be sufiicient to accommodate a partial penetration by the body of the auxiliary conductor along its outer surface and also a working of the ferrule material along its inner surface into the cable braid. The thickness 1 of ferrule Ztl must be sufficient to prevent rupture of the ferrule during crimping and to preclude excessive relaxation of the ferrule thereafter. More fundamental to the operation of the invention, the inner ferrule 26 must be sufficiently ductile to flow into the interstices of the flat braid under normal crimping pressures and yet, it must be sufficiently resistant to creep to preclude a relaxation of the forces tending to hold the conductors within the assembly. Additionally, the flow characteristics of the inner ferrule 26 must permit the elongation and reduction in cable diameter resulting from crimping without damage to the braid or excessive deformation of the insulation of a printed circuit board.
4 which would result in a permanent deformation of the insulating sheath.
The outer ferrule 20 may be comprised of the usual ferrule material such as tin plated copper. While not shown in FIGURE 1, it is contemplated that the ferrule 263 may include one or more tab-like extensions from either end to serve as additional contact points capable of being soldered or otherwise affixed to the conductors It is further contemplated that the outer ferrule 23 may be surrounded by an insulating sleeve applied in a manner well-known in the art. Additionally, while not shown, it is further contemplated that the invention may be adapted to connect fiat braid cable without the insertion of an auxiliary condu'ctor. In this latter use, the outer ferrule may be of the same configuration as the inner ferrule, i.e., without the raised portion 24:.
Referring now to FIGURE 2, there is shown the ferrulesZil and 26 assembled and aligned to receive a flat braid cable 42 and an auxiliary pig-tail lead 48; both conductors being suitably stripped of their insulating coverings 5i) and 52 to a length L, which should be at least the length of the ferrule assembly. If the size of the ferrule assembly is properly chosen with respect to the cables to be connected, the severed edge of the insulating coatings 5th and 52 will serve to butt against the edge of the outer ferrule and the inner ferrule, respectively, to provide a feel assuring that the cables have been properly inserted. Alternatively, and in certain instances, it is also possible to choose a ferrule which will slide over the insulating jacket to make connections away from the ends of the cable. After this step and with the ends of the cables 42 and 48 visibly protruding from the passages 34- and 32, the assembly may then be placed in a suitable crimping tool and crimped to assume the configuration shown in FIGURES 3-5. In order to assure that the crimping operation will result in a minimum distortion of the design shape of the shielded conductor, the configuration of the crimping dies should generally conform to a configuration of the metallic braid. Reference may.
be had to US. Patent No. 3,010,184 to Edgar W. Forney, ]r., for an example of the crimping procedure applicable.
Following the crimping operation, the conductors 42.
and 48 and the ferrules 2t) and 26 are mechanically interlocked into a unitary assembly with an electrical path existing between the flat braid 40 and the conductor 48 through the ferrule 26. As indicated in FIGURE 4, the configuration of the insulating material about the center conductor 42 is substantially unchanged with a slight reduction in diameter and, more importantly, without the distortion which would occur if the auxiliary conductor 48 were crimped against the braid. As is further apparent from FIGURE 4, the braid 40 has been driven by crimping forces against the relatively soft insulating material surrounding the central conductor 42 by a relatively soft metal. In this manner, the sectional deformaidinal transition of braid diameter shown in FIGURE 5 tube surrounding the cable central conductor] At the same time,'in order to provide a terminator having present commercial utility, the inner ferrule metal must be sufficiently hard and resistant to creep or relaxation to maintain its structural integrity when exposed to high is similarly affected by the characteristics of the inner ferrule 26 and the insulating material 43. Ideally and practically, the elongation and extrusion of the ferrule assembly, as it is crimped from the configuration shown by the dotted line 49 to the configuration shown in section in FIGURE 5, exerts a minimum stress upon the braid 4-0 by reason of the flow characteristics of the ferrules 26 relative to the now characteristic of the insuapproxirnately 95% tin and 5% antimony; thetin pronection with the cable and yet soft enough, as compared with characteristics of the usual insulating materiahto permit axial flow rather than further radial compression lating sheath 4-3. a
As shown in FIGURE 7, the ductility of the ferrule I 26 enables the ferrule materials to be worked into the V interstices of the braid 40 to form'projections 44 which interlock the braid and the ferrule assembly against relative transverse movement. In a similar fashion, thematerial of ferrule 26 is worked into the auxiliary conductor 48 as indicated by numeral 45. The nominal contraction or expansion of the insulating material 43, due either to heat, aging or low temperature exposure, will have no substantial effect on the connection of the ferrule assembly and the conductors 48 and 42 due to the fact that the assembly does not rely upon the insulating material for holding the assembly together. The particular interface connection achieved by the working of the inner ferrule 26 assures that the conductors 48 and 42 will be held against transverse movement even though the insulating material flows into a state of little or no compression.
As a further result of a use of a soft inner ferrule, the transition of the conductors 42 and 48 from their normal dimensions to the reduced dimensions achieved during crimping is much smoother than might be achieved by the use of a relatively hard ferrule as in the prior art. This feature is particularly advantageous with regard to the braid which due to its thinness and stiffness may be easily broken by bending. As is well appreciated by those skilled in the art, the most typical point of failure in crimp-type terminations is at the point of entry of the conductors into the ferrule assembly. The characteristics of the inner ferrule 26 automatically assure a dimensional relief at this point with the additional advantage that movement of conductors such as 42 and 48 will tend to displace ferrule material rather than place the conductors in a severe breaking flexu re.
Referring now to FIGURE 6, there is shown a further embodiment of the assembly of the invention capable of accommodating two conductor flat braid cable. As in the case of the embodiment above described, the interior barrel 62 of the inner ferrule 66 has a cross-sectional configuration approximating that of the cable 7%. The crimping dies utilized with the embodiment of FIGURE 6 should leave the configuration of the ferrules similar to the original configuration of the cable 70 in the manner and for the reasons set forth in the description of the embodiment of FIGURES 1-5.
In an actual device construction in accordance with the invention for use with single conductor fiat braid shielded cable having an overall diameter of 89 mils, a shield diameter of 65 mils and an insulated conductor diameter of 58 mils (in inches) the following ferrule materials and approximate dimensions were utilized.
Outer ferrule Inner ferrule- Crimped 'Iin plated Tin antimony Assembly copper (95.5%)
Length 205 205 235 Max. outside diameter. 226 150 162 Min. outside diameter. 182 Wall thickness 015 031 Changes in construction will occur to those skilled in the art and various apparently different modifications and embodiments may be made without departing from the scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective against the prior art.
1. An electrical connection between a cable and a ferrule assembly comprising in combination a shielded cable having at least one central conductor surrounded by an insulating sheath of soft plastic material in turn surrounded by a tight fitting shielding of braid-ed foil-like metal conductors; a tubular crimped ferrule assembly secured to the cable including an inner ductile and conductive ferrule of a material substantially softer than the material of said foil-like metal conductors, and having portions of the interior surface thereof worked into the interstices and against the edges of the foil-like metal conductors; an outer metal ferrule of relatively harder metal material than said inner ferrule encircling and contacting the inner ferrule along its length supporting and retaining the exterior surface of the inner ferrule against dimensional changes.
2. In an electrical and mechanical connection for grounding the shielding of coaxial cable, the combination comprising a shielded cable having at least one central conductor surrounded by an insulating sheath of soft plastic material in turn surrounded by a tightly fitted braid of foil-like conductors, a grounding conductor, a ferrule assembly including an inner ductile and conductive ferrule and an outer metal ferrule having the grounding conductor fitted therebetween, the said ferrules being deformed inwardly along the length thereof into a tubular confi uration to effect a connection between the cable braid and the grounding conductor, the said inner ferrule having a thickness substantially greater than the crosss ectional area of the grounding conductor, the material of said inner ferrule being substantially softer than the material of the foil-like conductors and being worked along the interior surface thereof into the interstices between the foil-like conductors with a slight radial deformation of said sheath, the said outer ferrule being of a relatively hard malleable material forming a relaxation resistant band holding the inner ferrule in engagement with the said braid and the grounding conductor.
References Cited by the Examiner UNITED STATES PATENTS 1,575,656 3/26 Stratford et al. 339-276 2,554,813 5/51 Buchanan 339-276 2,901,528 8/59 Lazar 17475 JOHN F. BURNS, Primary Examiner.
JOHN* P. WILDMAN, Examiner.