Heat Shrinkable Preinsulated Electrical Connector And Method Of Fabrication Thereof

Abstract

A wire barrel and a heat pliable inner sleeve of polymeric material are maintained in fixed tandem relationship by an outer heat shrinkable polymeric sleeve which is initially only partially shrunk, radially into gripping relationship over the wire barrel and inner sleeve. An exposed conductor wire end portion is received through the inner sleeve for crimped termination to the wire barrel, the application of crimping forces being selectively transmitted through said outer sleeve to said wire barrel without damaging said inner sleeve. Heat is applied to cause the outer sleeve to shrink radially in tightly encircling relationship over the crimped connection to result in a low profile termination. The inner sleeve is heat pliable for radial relaxation upon the application of radial compression forces supplied by the shrinking of said outer sleeve. The inner sleeve is thereby radially collapsed into gripping compression on the insulation of said conductor wire to provide a seal at the end of the outer sleeve and to provide a mechanical support for the conductor wire adjacent to the crimped termination, which support limits and distributes strain on the crimped termination caused by external bending forces applied to the conductor wire. The radial shrinkage of the outer sleeve provides compression forces sufficiently high to displace the inner sleeve to a slightly protruding position from the end of the outer sleeve. The inner sleeve thus provides a seal for the end of the outer sleeve and radially compresses into encircling sealing engagement over the conductor wire insulation, thereby forming a strain relief and mechanical support for the conductor wire.

Description

It is therefore an object of the present invention to provide a low-profile preinsulated electrical connector covered sealably with a heat shrinkable sleeve, and with a heat pliable inner sleeve providing a seal and a mechanical support and strain relief for an electrical wire terminated to the electrical connector.

Another object of the present invention is to provide a method for fabricating a low-profile preinsulated electrical connector with an outer heat shrinkable sleeve and an inner heat softenable and radially collapsible sleeve providing a seal, mechanical support and strain relief for a conductor wire terminated to the connector.

Another object of the present invention is to provide a preinsulated electrical connector with a heat shrinkable outer sleeve and an inner heat softenable sleeve which, upon heating, will be displaced slightly to protrude from the end of the heat shrinkable sleeve and provide a seal therefor.

Other objects and many attendant advantages of the present invention will become apparent upon perusal of the following detailed description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is an enlarged perspective of a preferred embodiment according to the present invention with the component parts thereof exploded to illustrate the details of fabrication thereof;

FIG. 2 is an enlarged elevation in section of a fully assembled preferred embodiment according to the present invention;

FIG. 3 is an enlarged elevation in section illustrating the preferred embodiment as shown in FIG. 2 crimped to corresponding ends of two conductor wires and prior to heating a heat shrinkable outer sleeve;

FIG. 4 is an enlarged elevation in section of the preferred embodiment illustrated in FIG. 3 with the heat shrinkable outer sleeve thereof having been heated to shrink radially and to radially collapse a heat softenable inner sleeve into sealing compressive engagement over the conductor wire insulation to provide a sealing, mechanical supporting and strain relieving function for the conductor wire insulation;

FIG. 5 is a section taken along the line 5--5 of FIG. 3;

FIG. 6 is a section taken along the line 6--6 of FIG. 4;

FIG. 7 is an enlarged perspective with parts shown exploded of a modification of the preferred embodiment as shown in FIG. 2;

FIG. 8 is an enlarged perspective of the preferred embodiment as shown in FIG. 7 connected to respective ends of conductor wires; and

FIG. 9 is a section along the line 9--9 of FIG. 8.

With more particular reference to the drawings, there is shown in FIG. 1 generally at 1 a low profile preinsulated electrical connector according to the present invention. The connector comprises an outer, generally cylindrical sleeve 2 of heat shrinkable polymeric material which is assembled over a reduced diameter, generally cylindrical elongated compressibly deformable metal sleeve, more generally identified as a wire barrel. With the wire barrel 4 generally assembled entirely internally of the outer sleeve 2, a reduced diameter cylindrical inner sleeve 6 of heat softenable polymeric material is inserted with each open end of the outer sleeve 2. As shown in the figure, the inner sleeves 6 may be each received initially over a mandrel 8. Each mandrel 8 is provided with a tapered portion defining a reduced diameter tip 10 to facilitate insertion of the mandrel and corresponding inner sleeve 6 in a corresponding end of the outer sleeve 2. The tip 10 of the mandrel may be received partially in the end of the wire barrel 4 with the tapered remainder of the mandrel positively stopped against the end of the wire barrel to facilitate positioning of the inner sleeve 6 within the outer sleeve 2. With the component parts thus assembled, heat is applied in any well known manner to the outer sleeve 2 causing it initially to partially shrink radially and conform to the shape of the reduced diameter wire barrel 4 and the tapered shape of the mandrel 8. Although the inner sleeves 6 are made pliable upon the application of heat, the presence of the mandrel therein ensures that the inner sleeves 6 retain their original diameter. Thus, upon removal of the mandrels 8 from the assembly, the outer sleeve 2 will be of a shape wherein the open end portions 3 of the outer sleeve 2 are of relatively large diameter, and in encircling relationship with and conforming to the exterior shape of the inner sleeves 6. After shrinkage, the assembly is cooled to allow the sleeve 2 to take a "set". The sleeve 2 upon taking a "set" thus tightly encircles and grips the wire barrel 4 and the sleeves 6, thereby fixedly retaining them in serial tandem relationship in proper alignment for the introduction of a conductor wire for termination to the wire barrel 4, in a manner to be hereinafter explained in detail. In the typical application, the wire barrel 4 is provided with generally central opening 12 providing a window. To positively anchor the sleeve 2 to the wire barrel 4, the sleeve 2 includes a recessed portion 14 partially received in the window portion 12 of the wire barrel 4. Often, the described, radial shrinkage alone of the sleeve 2 upon heating is sufficient to provide the recessed portion 14. However it is sometimes necessary to physically deform the sleeve 2 by forcibly depressing the sleeve with a tool (not shown) to form the recessed portion 14. It is necessary that the recessed portion 14 is created during heating of the sleeve 2 since, upon cooling, the sleeve 2 will take a "set". However, even after the sleeve has been initially shrunk and then cooled to a "set", it may be repeatedly heated and the recessed portion 14 formed while the sleeve is in its heated state. Upon cooling, the recessed portion 14 will take a "set" recessed within the window 12, thereby physically anchoring the sleeve 2 in position on the wire barrel 4. As shown, the sleeves 6 can partially protrude from the open end portion 3 of the sleeve 2 as shown in FIG. 2. Alternatively, the inner sleeves 6 may be trimmed flush with the open end portions 3 of the outer sleeve 2 if desired.

To make a completed electrical connection, a wire end portion having a conductor wire 18 exposed from its outer insulation covering 20 is received through a corresponding inner sleeve 6. As shown with reference to FIGS. 2 and 3, the exposed conductor wire 18 is received internally of a corresponding open end of the wire barrel 4 in stopped relationship against a wire stop 19 in the form of a tang struck from a medial portion of the wire barrel 4 and projecting internally of the wire barrel 4. The insulation 20 of the conductor wire will then be disposed within a corresponding inner sleeve 6, such sleeve completely encircling the insulation 20. As shown in FIG. 3, the wire barrel 4 is compressibly deformed into crimped engagement with a corresponding conductor wire 18 by the application in any well-known manner of crimping forces transmitted directly through the outer sleeve 2. With the wire barrel 4 and the inner sleeves 6 in tandem relationship, the crimping forces may be applied to the wire barrel without disturbing or damaging the sleeves 6.

To ensure proper location of the conductor wire 18 in stopped position against the stop 19, the outer sleeve 2 may be manufactured from a heat shrinkable transparent polymeric material such as Kynar, a trademark of Pennwalt Chemical Corporation. By visual observation through the transparent recessed portion 14 and window 12, the position of the conductor wires 18 may be observed.

With reference to FIG. 4, the resulting electrical connection may be sealed, and a mechanical support and strain relief for the terminated conductor wires 18 may be provided upon again applying heat to the heat shrinkable outer sleeve 2 especially at its end portions 3 thereof. Such application of heat causes the end portions 3 to shrink radially in even tighter compression over the inner sleeves 6. Such inner sleeves 6 are fabricated from non-irradiated and thereby substantially non-cross-linked Kynar such that it does not have heat shrinking properties similar to that of the outer sleeve 2. Instead, the sleeves 6 became pliable upon the application of heat sufficient to cause shrinking of the outer sleeve 2. Thus application of heat which shrinks the end portions 3 of the outer sleeve 2 also causes the sleeves 6 to become limp and less resistant to the radial compression forces supplied by radial shrinkage of the outer sleeve end portions 3. Thus upon radial shrinkage of the end portions 3, the heated inner sleeves 6 readily relax or collapse radially into encircling relationship compressibly over the insulation 20. Since the inner sleeves 6 are only made pliable and do not become fluid or fusible, they do not become bonded to the insulation 20 but only tightly encircle and grip the insulation with a gripping force provided by the shrunk outer sleeve end portions 3. The sleeves 6 accordingly provide a compression, moisture resistant seal for the end portions 3 of the outer sleeve 2 and also mechanically support the conductor wire and provide strain relief to prevent concentration of bending forces at the wire barrel which would tend to break the conductor wire which is crimped within the wire barrel 4. Thus provision of the sleeves 6 eliminates the need for crimping the wire barrel 4 to the insulation, a practice heretofore regarded in the prior art as necessary to provide such strain relief. As a further feature, since the inner sleeves 6 are not fusible, and are thereby not reduced to a fluid state, no additional seals are required in the connector which would ordinarily be required to prevent escape of fluid or fusible adhesives should such be used to seal the outer sleeve end portions 3.

As the outer sleeve end portions 3 are shrunk the resultant compressive forces on the inner sleeves 6 has a tendency to cause the sleeves to partially protrude from the open ends of the outer sleeve end portions 3 as shown at 22 in FIG. 4. Such protruding condition is produced upon a slight displacement of the inner sleeve mass occasioned by the progressive application of compression forces produced by the progressive shrinking of the outer end portions 3 of the sleeve 2. The protruding condition of the inner sleeves 6 serves as a visual inspection aid indicating, that sufficient shrinkage of the end portions 3 has occurred to cause the inner sleeves 6 to be compressed into sealing engagement over the insulation 20, and that sufficient additional compression forces have occurred to produce, not only a seal, but the protruding condition as shown at 22. Thus, even if some relaxation of the end portions 3 occurs upon cooling, sufficient additional compression forces have been initially provided to prevent such relaxation from dissipating entirely the compression forces required for the sealing effects of the inner sleeves 6. Upon cooling, the inner sleeves become less pliable and provide creep-free polymeric seals.

In accordance with accepted chemical principles, the heat shrinking properties of the outer sleeve 2 are provided, by extruding Kynar into tube form, irradiating the the tube form with electron energy to cross-link the Kynar, then physically expanding the tube to an enlarged cylindrical configuration, followed by cooling the tube to retain it in a "set" condition in its expanded form. The inner sleeves 6 are fabricated from tubes of non-irradiated Kynar. By experimentation it was found that the application of a flame of about 450.degree.F. to the irradiated Kynar in its expanded form, causes it to radially shrink back to its original extruded form, without noticeable limpness or pliability being observed. However, upon the application of a flame of that temperature to the non-irradiated Kynar, two significant observations were made. First, the non-irradiated Kynar tube was found to become limp and in a pliable condition. It was observed however that the non-irradiated Kynar did not become fluid or fusible and did not bond to surfaces of materials at ambient temperatures. Again testing the non-irradiated Kynar, a length of tubing was supported only at one end, and a flame of about 450.degree.F. was applied to the other end, which was unsupported in space. The heated Kynar was observed to become limp and pliable but was not reduced to a fluid state. No fluid or semi-fluid catenaries or droplets were observed. Instead the unsupported end of the tube did not behave as a fluid but remained in a pliable, solid state. The flame was continued to be applied until the Kynar began to char. As a result of such observations, it was concluded that the non-irradiated Kynar upon the application of heat became limp but not fluid, even when heated to its charring point. The application of heat to the irradiated and expanded Kynar caused it to return to its original non-expanded form but without becoming limp. Accordingly, with the sleeve 2 being fabricated from irradiated and expanded Kynar, upon the application of heat sufficient to cause radial shrinkage to its original non-expanded form, substantial radial compression forces could be created by such shrinkage without the sleeve becoming limp. By fabricating the inner sleeves 6 of non-irradiated Kynar, which became limp at elevated temperatures but not reduced to a fluid state, a desired sealing function was obtainable without a need for separate seals to prevent escape by fluid flow of the inner sleeves from the outer sleeve 2.

As shown in FIG. 4, when heat is applied to shrink the end portions 3 of the outer sleeve 2, the entire connection will possess a low profile, by shrinkage of the end portions 3 and crimping of the wire barrel 4 to only the conductor wire 18. By eliminating the need for crimping the wire barrel to the insulation 20 for mechanical support thereof, a much lower profile connection is achieved as shown in the figure. As a practical matter, it is not necessary to apply heat only locally to the end portions 3. Instead, to complete the low profile connection heat is permitted to be applied along the entire length of the outer sleeve 2. This will often cause the recessed portion 14 to become less conforming to the shape of the window 12. More specifically, as shown in FIG. 3, upon crimping the wire barrel to the conductor wire 18, the recessed portion 14 is shown conforming to the shape of the window 12. However upon reheating, of the recessed portion 14, as shown in FIG. 4, the sleeve 2 will tend to shrink an additional amount with the result that the recessed portion stretches across, and becomes less conforming to the shape of, the window 12.

With more particular reference to FIGS. 7 and 8, a modification of the embodiment shown in FIG. 1 will be described in detail. FIG. 7 illustrates an outer sleeve 2' of irradiated, heat shrinkable Kynar with one enlarged open end portion 3' receiving an inner sleeve 6' of heat softenable non-irradiated Kynar. A wire barrel 4' is received internally of the sleeve 2', with the sleeve 2' being initially shrunk to grip and retain the wire barrel 4' and the inner sleeve 6' in tandem serial relationship. The other end of the sleeve 2' is closed off as shown at 24 by radially compressing the end portion to form tightly associated folds. Such folds can be readily formed during heating of the sleeve 2' to produce its initial shrinking. The result is a preinsulated electrical connector having only one open end adapted to receive a pair of adjacent conductor wires 18' partially exposed from their surrounding insulation sheaths 20'. In a manner as heretofore described, and with reference to FIG. 8, the exposed conductor wires 18' are terminated to the wire barrel 4' by the application of crimping forces transmitted directly through the outer sleeve 2' without damaging the inner sleeve 6'. By the application of heat, the end portion 3' of the outer sleeve is caused to radially shrink and compress the inner sleeve 6' into radial tightly gripped compression on the conductor wire insulation 20'. Although the sleeve 6' does not bond to the insulation 20', it is heat pliable to the extent that it will completely encircle each of the conductor wire insulation sheaths 20', as shown in FIG. 9. Between the adjacent insulation sheaths 20', a definite seam 26 is observed in the heat pliable sheath 6'. The seam 26 indicates that no fusion of the pliable sleeve 6' has occurred. However, the compression forces resulting from radial shrinkage of the outer sleeve end portion 3' is sufficient to force the heat pliable sleeve 6' into tight compression with itself along the seam to provide an effective compression seal without the need for fusion along the seam 26.

Although preferred embodiments of the present invention have been shown and described in detail, other modifications and embodiments of the present invention are intended to be covered by the spirit and scope of the appended claims, wherein:

Claims

What is claimed is:

1. In a low-profile preinsulated electrical connector covered sealably with a heat-shrinkable sleeve, the combination comprising: a compressibly deformable metal sleeve for crimping onto an electrical wire, a heat pliable and substantially non-fusible sleeve of polymeric material in serial tandem relationship with respect to said metal sleeve, said heat-shrinkable sleeve being initially received over and partially shrunk in radial compression over said metal sleeve and said heat softenable sleeve, thereby retaining said metal sleeve and said heat-shrinkable sleeve in serial tandem relationship and in fixed position with respect to said heat-shrinkable sleeve, said metal sleeve being entirely contained within said heat-shrinkable sleeve, said heat pliable sleeve including an open end portion thereof partially protruding from the end of said heat-shrinkable sleeve and adapted to receive therethrough an electrical conductor wire.

2. The structure of claim 1 wherein said heat-shrinkable sleeve is resistant to extrusion upon the application of radial crimping forces applied thereof during crimping of said metal sleeve to a conductor wire received therein.

3. The structure of claim 1 wherein said heat pliable sleeve is in serial tandem spaced relationship with respect to said metal sleeve allowing the application of crimping forces selectively to said metal sleeve without damaging said heat pliable sleeve.