US 3475545 A
Description (OCR text may contain errors)
Oct. 28, 1969 F. B- STARK ETAL CONNECTOR FOR METAL-SHEATHED CABLE Original Filed 001:. 16, 1963 2 Sheets-Sheet 1 INVENTORS FPANK 4? 5 74 91? Pam-up a MP/4 ArratwE/S Oct. 28, 1969 F. s. STARK ETAL CONNECTOR FOR METAL-SHEATHED CABLE Original Filed Oct. 16, 1963 2 Sheets-Sheet 2 United States Patent M 3,475,545 CONNECTOR FOR METAL-SHEATHED CABLE Frank B. Stark, Wormleysburg, and Ronald C. Laudig,
Camp Hill, Pa., assignors to AM? Incorporated, Harrishurg, Pa. Continuation of application Ser. No. 316,552, Oct. 16, 1963. This application June 28, 1966, Ser. No. 561,309 Int. Cl. I-I02g 15/08, 15/24 US. Cl. 174-88 4 Claims ABSTRACT OF THE DISCLOSURE This application is a continuation of our copending application, Ser. No. 316,552, filed Oct. 16, 1963, now abandoned.
The present invention relates to electrical crimp-type connectors. More particularly it pertains to solderless connectors, and the resulting connections, for metalsheathed cable which provides a permanent, mechanically strong, corrosion resistant connection of good electrical conductivity and having high tensile strength. Additionally, it pertains to such connectors and connections as applied to thin-metal-sheathed heater cable and using standard butt splice crimp connectors to join the conductors thereof.
Splicing of heater cable, which is formed of a solid core of Nichrome wire with a thin insulation layer of Teflon (polytetrafiuoroethylene) and a thin outer sheathing of copper, serves to illustrate several kinds of problems which the present invention is intended to overcome. For example, solid Nichrome heater Wire is very hard (as compared to normal stranded copper wire) and requires such high crimping pressures tov effect a solderless connection that the insulation commercially available for use on the so-called pre-insulated type of crimp connector would be severely damaged, thus making a preinsnlated connector impractical, if not presently impossible, for crimp-splicing Nichrome wire. Pre-insulated connectors are initially disclosed and broadly claimed in Reissue Patent No. 23,688.
Nichrome wire is normally used with high amperage, since the heat produced rises with the square of the amperage. This means that the inner connector chosen to splice the Nichrome wire should be heavy duty enough to take a high pressure crimp and to conduct high amperage, should be a butt splice to reduce bulk, and still should be simple for ease of manufacture and competitive pricing. Such an inner butt splice with its insulation often will be bulkier than the heater cable; especially since the latters insulation and sheathing for the sake of thermal efficiency are kept minimal (within the bounds of the electrical requirements) to reduce their effect as a heat-sink.
Heater cable is often used in corrosive environments, such as in pipes in chemical plants to keep liquids (which may be under pressure as well), at 300 to 400 F. to prevent them from solidifying. Thus, the inner butt connection must also be insulated with a protective cover which is effectively sealed to the thin-copper outer sheathings:
3,475,545 Patented Oct. 28, 1969 ing. The outer sleeve (i.e. protective cover) of the splice connection should conductively join the cables thincopper sheathing, because the later is often used as a ground return for the heater circuit. The outer sleeve should also be readily heat conductive to avoid damaging the connection by overheating the insulation, and further should be able to handle a substantial portion of the tensile stresses to which the cable is normally subjected.
In forming the environment-proof high-tensile seal between the outer sleeve and the copper sheathing the crimping pressures must not unduly deform the insulation layer or sheathing of the cable or else a short or other impairment of the desirable electrical properties of the cable will result.
In view of the foregoing and similar additional problems in splicing metal-sheathed insulated cable, it is an object of this invention to provide a connector which will give a high-tensile, environment-proof, insulated solderless connection which is electrically and mechanically superior, which will not work loose or otherwise tend to break down if subjected to flexing, and yet which preserves the effectiveness of the insulation layer and metal sheathing of the cable without undue permanent deformation or fracture thereof. It is further an object of this invention to provide such a connector which could be employed on cables having conductors, such as Nichrome wire, that are particularly hard (and which therefore require very high crimping pressures to effect a quality electrical connection, which pressures would destroy by deforming flow or fracture or the like, any of the presently feasible insulation materials normally employed on pre-insulated connectors). It is an advantage of this connector that though the insulated inner connections may be bulkier than the cable yet the connection as a whole is readily and effectively sealed by a simple, inexpensive, but highly ingenious, sub-portion of this inventive connector. It is a further advantage that this inventive connector reduces the amount of crimping pressure which is normally necessary to complete an effective environmental and high tensile seal between the outer sleeve of the connector and the metal sheathing of the cable.
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 a preferred 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 more 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. In the draw- FIGURE 1 is an exploded perspective view of the preferred embodiment of the present invention together with two metal-sheathed cables prepared for joining;
FIGURE 2 is an enlarged cross-section in side elevation of one of the grooved bushings;
FIGURE 2A is a magnified view of a portion of the bushing shown in FIGURE 2;
FIGURE 3 is a side elevational cross-section of the outer sleeve showing a bushing in side elevation factoryclinched in one end;
FIGURES 4, 5, and 6, illustrate how the various parts of the connector preferentially embodying this invention are oriented during assembly;
FIGURE 7 is a perspective view of the completed connection.
The preferred embodiment of this invention is a connector 9 illustatively shown splicing a heater cable 10a to a supply cable 1012 (see FIGURE 1). These cables differ only in that the central conductor 12 of the former is a solid Nichrome high-resistance heater wire while that of the latter is a stranded low-resistance copper wire. As shown, these cables 10 have been prepared by baring a portion of the conductor 12 of each cable enough to fit into the splice connector 14. This connector 14 advantageously may be a commercially available tubular, tinned, copper, crimp-type butt connector having a wirecentering dimple 15 (as is commonly practiced in the art). The metal sheathing 16 of the cables is then advantageously stripped back a little further to expose the Teflon insulation 18. This is to ensure that the bared conductors 12 are far removed from any potentially shorting element, such as a burr from sheathing 16.
The various parts of this connector 9 are next assembled and oriented on the two cables 10 (see FIGURE 4), preparatory to combining them into a completed connection. The outer sleeve 20 is slipped on over one of the cables 10 with the end containing one of the grooved bushings 22 going on first. If the bushing 22 has not been pre-assembled in the outer sleeve 20, then of course the bushing should precede the outer sleeve onto the cable with the bell-end of the bushing first. The outer sleeve 20 is followed by the insulating sleeve 24.
On the other cable is placed the remaining bushing, bell-end first as before. With the other elements of the connector 9 thus arranged, the conductors 12 are then introduced respectively into either end of the butt connector 14 and seated against the dimple 15. With the conductors 12 in place within the connector 14, the inner electrical connection is completed by crimping the connector 14 near either end, as illustrated by the vertical arrows in FIGURE 4. Insulating sleeve 24 is centered protectively over the resulting inner connection. This centering may advantageously be facilitated by placing location marks spaced equally on either side of the inner connection and spaced a distance from one another, which is just greater than the length of the outer sleeve 20, see FIGURE 5. The outer sleeve 20 is slid over the insulating sleeve 24, into place between the location marks. FIGURE 6 illustrates the remaining bushing 22 being pressed home, in the direction of the arrow at the lower right, into the overlap between the outer sleeve 20 and the sheathing 16. Finally, sealing O-crimps are applied to the outer sleeve 20 at either end beyond the crimpingmarks 26 to constrict said sleeve 20 and the bushing 22 contained therein together, down onto said sheathing 16, to form a substantially solid copper matrix therebetween which results in a sealed, high-tensile connection.
These O-crimps are applied so that the crimping forces act substantially radially; normally employing crimping dies which enclose most of the full periphery of the outer sleeve 20. In order to have a mechanically strong connection the width of the crimp should be sufficient to withstand normal flexing of the cable to avoid the cable from Working loose from the connection. To avoid awkwardly high crimping pressures it has been found better at each end to apply two crimps instead of one broad one. This is especially true where hand tools are expected to be used and is advantageous with respect to preventing pivoting of the cable.
The crimping pressure must be carefully limited, particularly with a thin-metal sheathed cable, so that the outer sleeve 20 and the bushing 22 are cold forged together and onto the cable sheathing 16 but are not so severely constricted as to damage the insulation layer 18 of the cable 10 under the crimp, or the sheathing 16 at that point, e.g. by an undue amount of cold flow of either out from under the direct action of the crimping forces. It was found that the use of multiple substantially parallel circumferential grooves 28 with projections 30 on bushing 22 enabled a strong and effective seal to be made on thin-metal sheathed cables at lower crimping pressures thereby avoiding otherwise inevitable damage to the cable 10.
The use of serrating is doubly important. First, the projections of the serrations bite into the sheathing 16 and the inner bore of the outer sleeve 20 at a multiplicity of points thus distributing the tensile stresses of the connection among a large number of positive anchor points thereby reducing the stress at any one given point. Second, since these projections are substantially parallel, circumfercntially continuous, and non-communicating rather than screw threaded, the moisture and other corrosive elements cannot work along the groove in a longitudinal direction. This latter was found to be particularly important where the cable has thin-metal sheathing and thin insulation, because the limitation on the permissible crimping pressures prevented a complete marriage throughout of the groove surfaces With the sheathing or outer sleeve metal, but nevertheless the use of parallel circumferential serrating gave a truly effective seal, where a threaded serration under similar conditions had not.
The bushings 22 have their inside diameter only slightly larger than the outside diameter of the cable 10. The same is true of the bushings outside diameter and the outer sleeves inside diameter. This ensures that the bushings readily slip in place, and yet do not require too deep a crimp which might otherwise weaken the connection by distorting the outer sleeve 20 and the bushing 22 too much.
The bushings 22 are advantageously made of half hard copper. This ensures that the bushing 22 serves as a support to the cable 10 during crimping to prevent undue damage thereto, and it also makes sure that projections 30 get a good bite into the annealed copper sheathing of the cable. The grooving and the resulting projections of these bushings 22 are preferably rolled in, rather than cut, in order to eliminate burrs and thereby to improve the quality of the grooving. These grooves 28 are illustrated with their surfaces advantageously making 45 angles to the vertical, or in other words, making angles with each other and being vertically symmetrical. This form of grooving was chosen, because it is easily fabricated, and because it produces serrations having a peak angle acute enough to ensure a good bite but which are broad-based enough to support the crimp against tensile stresses. The cross-sectional form of these grooves 28 may be varied so long as the resulting serrations remain properly buttressed and retain a good bite.
A commercial form of the preferred embodiment of this connector invention was fabricated for use as a splice on Nichrome wire heater cable, which latter has an annealed copper sheathing only 15 or 16 mils (thousandths of an inch) thick, with an even thinner Teflon insulation layer. In this commercial form, right angle grooves 28 were formed, as shown in FIGURE 2A, and the cross-sectional width of the bushing shell, from inner groove peak to outer groove peak, was 0.032 of an inch. The depth of grooving was 0.010 of an inch. By simple geometry and assuming that the bushing serrations (being of a harder copper than the annealed sheathing) will substantially retain their shape, it will be seen that the bushing with a 0.012" solid center and with serrations projecting 0.010" top and bottom (total of 0.032") will bite into the sheathing with a 0.015" thickness resulting in (l) a 0.010" layer of solid relatively undisturbed sheathing, (2) a 0.010" layer comprising a substantially solid matrix formed of bushing serrations cold forged to the cable sheathing, and (3) a 0.012" layer of solid bushing. In other words, although the projections 30 of the bushings 22 are /3 the thickness of the sheathing 16, yet these projections 30 are able only to bite /3 if the way into the sheathing (because it takes only /3 of the cross-sectional area of the sheathing to fill in the air space of the grooves between the projections). This discussion of the foregoing example is only an approximation of what actually happens, since some of the layers will tend to thicken due to radial compression and conversely to thin due to cold flow out from under the crimp, and the serrations may deform somewhat, etc. However, this example serves to illustrate how this invention is able to give a strong and effective crimp seal onto the thin-metal sheathing of a cable without seriously reducing cross-sectional area thereby preserving the tensile strength of thesheathing. 1
This commercial bushing 22 has an overall inside diameter of 0.164" and an outside diameter of 0.228 with an overall length of 0.562". One end is slightly belled and free of internal grooving (see FIGURE 2) in order to facilitate placing the bushing 22 onto a cable 10. As a customer convenience one of the bushings 22 is pre-assembled in to the outer sleeve 20. The inside diameter of this sleeve is 0.234" (with a thickness of 0.031), so that the bushing 22 readily makes a snug fit within the sleeve 20 with the annular grooves 28 on the outer portion of the bushings belled end gripping the sleeve 20 thereby securing the bushing 22 therein.
This invention can be adapted for use with metalsheathed cable having any number of conductors and with a wide range of cable sizes. For example, a plurality of conductors could be spliced by using a respective number of butt connectors each with its own protective insulating sleeve 24.
Changes in construction will occur to those skilled in the art and various apparently different modifications and embodiments ma 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 joining metal-sheathed cables having respective insulated conductors with stripped ends, comprising an inner connector crimped to the stripped end of each respective conductor, an insulating sleeve protectively surrounding said inner connector and extending over at least a portion of the conductor insulation adjacent to said inner connector, an outer metal sleeve overlapping said sheathing at either end of said connection beyond said insulating sleeve, at least one bushing having substantially parallel circumferentially continuous, non-communicating projections on their internal and external surfaces and being positioned in the overlap between said outer sleeve and said respective sheathing so as to keep the insulating sleeve positioned over said inner connector to avoid shorting of said inner connector to the outer sleeve or bushing, said outer sleeve being crimped, substantially radially, along a substantial portion of the overlap between the bushing and constricting the sleeve and 'the bushing about the sheathed cable with the projections of the bushing forged into said sheath and said outer sleeve forming a plurality of seals and a mechanically strong, high tensile strength, conductive connection without significantly reducing said conductor insulation at the point of crimp.
2. An electrical connection as described in claim 1 wherein said cables are two in number at least one of which is a heater conductor having thin insulation and wherein said connection has two bushings Within either end of said outer metal sleeve.
3. A device as described in claim 1 wherein said insulating sleeve is composed of polytetrafluoroethylene and said metal-sheathing is an annealed copper of about 0.015 of an inch and wherein said outer sleeve and said bushings are formed of a half-hard copper with the projection of the latter being formed by grooves having a depth ranging from 0.008 to 0.012 of an inch.
4. A device as described in claim 3 wherein the projections form right angle peaks and make an angle of about 45 to the perpendicular.
References Cited UNITED STATES PATENTS 2,799,721 7/ 1957 Floyd 174-94 3,033,600 5/1962 Drysdale.
3,146,299 8/ 1964 Norton 174-88 FOREIGN PATENTS 1,118,630 3/1956 France.
DARRELL L. CLAY, Primary Examiner US. Cl. X.R.