US 3143595 A
Description (OCR text may contain errors)
H. B. MARTIN 3,143,595
POLYTETRAFLUOROETHYLENE INSULATED SPLICE CONNECTOR Filed Dec. 29, 1960 INVENTOR. fl/wazp J. MAW/1v @aww 59 United States Patent v O 3,143,595 POLYTETRAFLUUROETHYLENE INSULATED SPLICE CONNECTOR Harold B. Martin, Roselle, N.J., assignorto The Thomas & Betts Co., Elizabeth, NJ., a corporation of New Jersey Filed Dec. 29, 1960, Ser. No. 79,379 1 Claim. (Cl. 174-84) The invention relates to solderless connectors of the type which are adapted to be crimped on bare end portions of insulated electrical conductors to connect two such conductors in coaxial relation or to provide a terminal connector on each of said conductor end portions. More particularly, the invention relates to a novel method of making an improved pre-insulated splice connector and to the pre-insulated connector thus produced.
Solderless connectors of the type to which the present invention relates usually comprise a barrel or ferrule of ductile conductive metal and an insulating sleeve of suitable plastic material covering the ferrule in telescopic relation. The bare end portion of an insulated conductor that is to be connected to another conductor is intruded in one end of the ferrule and compressive force exerted on the exterior of the insulating sleeve by means of a suitable crimping tool to force the metal of the ferrule against the intruded conductor endportion to effect a physically strong and electrically efficient connection therebetween.
Similar connectors to which the present invention is applicable are shown in application Serial No. 858,266, filed December 8, 1959, now Patent No. 3,098,688, for Insulated Terminal Connector and Patent Number 2,832,816 to L. M. Curtiss for Self Insulated Two-Way Butt Connector. The aforesaid application shows a terminal connector for terminating an insulated conductor and the aforesaid patent discloses a butt connector or splice for use in connecting two conductors together in end-to-end relation. In both examples, the connector includes a ductile metal ferrule mounting a plastic insulating sleeve. The invention is applicable not only to the aforesaid types of connectors but also to other connectors comprising a ductile metal ferrule and an insulating sleeve of suitable plastic material.
It has been found, however, that the insulating material on connectors as aforesaid (usually molded nylon) has a tendency to extrude axially or circumferentially of the connector, when subjected to the pressure of a crimping tool, to such an extent that the residual Wall thickness of the insulating sleeve, in the crimped areas, may be and often is reduced to the point where it is insuflicient to provide the desired and necessary physical and dielectric strength.
More recently, a tetrafluoroethylene plastic, the Du Pont Company commercial product being known commercially under the trademark Teflon, has become availablewhich has the unusual and highly desirable property of being heat-shrinkable, if so processed, in addition to being adapted for high temperature applica tions and a good insulator suitable for cold plastic flow in response to a crimping operation thereon. An insulating sleeve of Teflon while it greatly facilitates securing the same on a ferrule of ductile conductive metal, by reason of its heat-shrinkable properties, would nevertheless be open to a considerably greater objection than nylon, in that its wall thickness is more readily reduced, in response to crimping pressure thereon, were it not for the novel ferrule construction utilizable therewith, in accordance, with the present invention.
Accordingly, it is an object of the invention to provide a pre-insulated electrical connector as described wherein an insulating sleeve is heat-shrunk thereon.
Another object of the invention is to provide a pre insulated connector as described which is particularly adapted for hightempera'ture applications.
A further object is to provide a pre-insulated electrical connector as described wherein means are provided for controlling the spread or cold plastic flow of portions of its insulating sleeve in response to crimping operations thereon.
Another object of the invention is to provide a preinsulated connector as described wherein a point of applied maximum pressure, during a crimping operation thereon, moves toward the longitudinal center of the connector whereby cold plastic flow of its insulating sleeve, at said point of applied pressure, flows laterally in front thereof.
A further object of the invention is to provide a preinsulated connector as described wherein a ferrule of ductile, conductive metal is adapted for controlling cold plastic flow of a Teflon insulating sleeve in response to crimping pressure on selected areas thereof whereby its wall thickness in said selected areas is not seriously reduced.
Another object of the invention is to provide a preinsulated connector as described wherein an improved ferrule of ductile conductive metal is adapted to receive an insulating sleeve of Teflon thereon in heat-shrunk relation without impairing its physical and dielectric strength in any part thereof.
A further object of the invention is to provide a preinsulated connector as described wherein cold plastic flow of portions of its insulating sleeve occurs in opposition toward the longitudinal center of said connector upon crimping each end portion thereof whereby excessive reduction of the wall thickness of the insulating sleeve is obviated in the crimped portions thereof.
Another object of the invention is to provide a pre-' insulated connector as described wherein an improved ferrule of ductile, conductive metal forms a V-notch in its insulating sleeve, upon heat-shrinking the same on said ferrule, to facilitate locating the connector in a suitable crimping tool.
Various other objects, advantages and features of the invention will become apparent from the following detailed description when read in connection with the accompanying drawing, in which:
FIGURE 1 is a plan view of the improved, pre-insulated connector showing the same as crimped on a bare end portion of each of a pair of insulated conductors in spaced, coaxial relation;
FIGURE 2 is a similar view of the pre-insulated connector as rotated through an angle of ninety degrees, showing a locating notch in elevation as formed centrally of the length of said connector;
FIGURE 3 is an exploded view in perspective showing theimproved conductive metal ferrule and plastic insulating sleeve adapted to be heat-shrunk thereon; FIGURE 4 is a longitudinal sectional view of the improved conductive metal ferrule and heat-shrinkable insulating sleeve, as it appears in assembled relation, prior to heat-shrinking the Teflon insulating sleeve on the ferrule; and
FIGURE 5 is a similar longitudinal sectional view of the improved conductive metal ferrule and Teflon insulating sleeve substantially as they appear after a heatshrinking operation thereon.
Referring to the drawing, the improved, pre-insulated, electrical connector, generally indicated at 10, comprises a ferrule 12, of ductile, conductive metal, and an insulat ing sleeve 14, of Teflon heat shrunk thereon in telescopic relation, the length of the insulating sleeve 14, being greater than that of the ferrule 12, whereby its opposite end portions 16, extend beyond the opposite ends 18, of the ferrule 12, for full insulation coverage beyond the ends 18, of the ferrule 12, and over the end portion of the insulation covering adjacent the intruded bare end portion of the conductor C.
, The ferrule 12, of ductile, conductive 'meta1,'has an axial bore 20, extending inwardly from each of its opposite ends 18, and terminating short of the mid-length thereof, as clearly shown in FIGURES 3 through 5, to define opposed conical inner ends or shoulders 22, the outer openend of each of said-bores 20, being suitably counterbored, as at 24, whereby a bare or stripped end portion of an insulated wire conductor C, of smaller size or diameter may be "freely intruded into each of said bores 20, to the full depth thereof with the adjacent end portion of the insulation covering on the Wire conductor C, disposed in the counterbored end portion 24, of each of the bores 20.
Furthermore in accordance with the invention, the ferrule 12, is provided, mid-way of its opposite ends, with a semi-circular cut-out portion 26, of suitable length, in intersecting relation with its axial center and with its defining end walls 28, inclined and diverging outwardly with respect thereto to expose the inner ends of the bores 20, for inspection, and to provide means for forming a locating notch 32, transversely of the insulating sleeve 14, upon heat-shrinking the same upon the ferrule 12, whereby the. connector 10, maybe located in a predetermined position with respect to the jaws or dies of a crimping tool.
As best shown in FIGURE 3, the intermediate portion of the ferrule 12, is tapered outwardly from each diverging or inclined end wall ofthe cut-out 26, in opposite directions to a point adjacent each of its opposite ends, as at 30, where its outer diameter remains constant for a short distance to the ends of, the ferrule .12. Thus, the ferrule 12, is substantially of Hour Glass configuration for a purpose now to be described.
Further in accordance with the invention, the tubular insulating sleeve-14 of Teflon (polytetrafluoroethylene), or equivalent insulating material possessing heat-shrinking characteristics, having an inner diameter at least equal to the outer diameter of the straight ends 18., ,of the ferrule 12, and of a greater, length, is telescopedon the ferrule 12, with. its opposite ends extending equally therefrom, and subsequently subjecting the connector to a suitably generated degree of heat suflicient to cause its insulating sleeve 14, to shrink securely thereon.
In thus shrinking the Teflon insulating sleeve 14, on the ferrule 12, the sleeve 14, not only partakes of the configuration of the ferrule 12, but its mid-length portion also. shrinks or recedes substantially-into the cut-out portion 26, forming a V-notch 32, in and across the insulating sleeve 14, in the longitudinal center thereof whereby a complementary means integral with the jaws of a conventional crimping tool is adapted to seat in the notch 32, and properly position the connector 10, with respect thereto prior to performing a crimping operation thereon.
In crimping each end portion of the connector 10, with a conventional crimping tool inknown manner, portions of its Teflon insulating sleeve 14, by virtueof the known characteristics thereof and the Hour-Glass configuration of the ferrule 12, exhibit cold plastic flow or spread in front of the crimping tool, in response to squeeze pressure thereon, or toward the longitudinal center of the connector 10, such plastic flow or spread terminating at or adjacent each side of the V-notch 32, by reason of the fact that the seating therein of a complementary locating element, integral with the jaws of the crimping tool, forms a dam or wall across the connector 10, in opposition to such flow or spread. Thus, the plastic flow or spread of the Teflon insulating sleeve 14, as aforesaid, slightly increases the Wall thickness thereof on each side of the V-notch 32, while the wall thickness at the end portions of the Teflon sleeve 14, decreases but not sufficiently to impair the physical and dielectric strength thereof by reason of the resistance to free plastic flow or spread of the Teflon insulating sleeve 14, offered by the thickened wall portions thereof adjacent each side of the V-notch 32.
From the foregoing it will be readily apparent that the provision of a connector as described, precludes the splitting or rupturing of the Teflon insulating sleeve in response to a crimping operation on the end portions thereof.
While theinvention has been illustrated and described with respect to a preferred embodiment thereof, it is to be expressly understood that various changes and modifications may be made therein without departing from the inventive concept underlying the same. Therefore, the invention is not to be limited except as is necessitated by the prior art and the scope of the appended claims.
What is claimed is:
An electrical connector comprising a ferrule of ductile, conductive metal, an insulating plastic sleeve of polytetrafluoroethylene disposed on said ferrule with its opposite ends extending beyond the ends of said ferrule, said ferrule having a cut-out portion formed in the periphery thereof intermediate its length having diverging end walls and forming a V-notch in and across the periphery of said insulating sleeve when positioned in said notch, adapted for locating said connector in a crimping tool, said ferrule tapering outwardly, in opposite directions, from the diverging ends of said cut-out portion to a point short of its opposite ends, adapted for controlling cold plastic flow of said insulating sleeve from its opposite ends, to said diverging end walls of said cutout portion in response to a crimping operation through said insulating sleeve at a point therein between said V-notch and each end of said ferrule, whereby the wall thickness of said insulating sleeve is not substantially reduced in the region of said crimping operations.
References Cited in the file of this patent UNITED STATES PATENTS 2,802,257 Holtzapple Aug. 13, 1957 2,809,365 'Broske Oct. 8, 1957 2,832,816. .Curtiss Apr. 29, 1958 2,861,439 Carlson June 5, 1958 2,863,132 Sowa Dec. 2, 1958 2,941,911 Kumnick et al June 21, 1960 2,958,723 Logan et al. Nov. 1, 1960