GB2202393A

GB2202393A - Heat-shrink tube attached to connector backshell

Info

Publication number: GB2202393A
Application number: GB08806663A
Authority: GB
Inventors: Gary L Dibble; James H Reynolds; Susan L Stene
Original assignee: Sigmaform Corp
Current assignee: Sigmaform Corp
Priority date: 1987-03-20
Filing date: 1988-03-21
Publication date: 1988-09-21
Anticipated expiration: 2008-03-21
Also published as: GB2202393B; FR2612699B1; GB8806663D0; DE3809471A1; FR2612699A1

Description

2 -793 0 2 BACKSHELL ASSEMBLY AND METHOD The present invention relates in

general to backshells for connecting an electrical cable to another electrical device and the method of making and assembling the assembly and the connection.

Background of Invention

Various backshell structures are known for making a mechanical connection at the end of a cable and typically where a grounding connection is required such as with metal sheath cable and coaxial cable.

The desired features for a backshell for connection of electrical cables are abrasion protection, strain relief, and an. environmental seal. The prior art devices have suffered in one way or another in providing the desired features in a simple easy to assemble and apply structure.

Brief Summary of the Invention

The object of the present invention is the provision of a backshell assembly and method of making and assembling the same which results in desired shielding, abrasion protection, strain relief and an environmental seal.

Broadly stated, the present invention, to be described in greater detail below, is directed to a backshell assembly and method of making and assembling same for connecting an electrical cable to other electrical devices and comprising a hollow cylindrical body member having a first end for engagement with the other electrical device and a second end and a hollow cylindrical, heat shrinkable tube, previously heat shrunk and stress relieved to a diameter for sliding onto said second end of said body member and surrounding and bonded to the outside surface of the body member and extending axially beyond the second end of the body member whereby the body member can be attached to the other device and then the tube extension can be shrunk down onto the cable.

1 one feature and advantage of the present invention is the provision of a simple, easy to assemble backshell structure which provides good mechanical integrity from the cable to the other electrical device and which at the same time provides a stress relieved connection and an environmental seal.

Another feature and advantage of the present invention is a backshell assembly such that the tubing, upon heat shrinking, will not tend to move or slide longitudinally. As a result of this stress relieving when the backshell assembly is assembled with the cable, the end extension of the heat shrinkable tube will be located at its ultimate desired location. Upon subsequent heating to shrink the tube end extension onto the cable, the free end of the tube will be at the desired location on the cable.

The adhesive used for bonding the heat shrinkable tube must be such that the melting temperature of the adhesives is greater than the temperature required to shrink the tube to prevent the tube from "milking off" the backshell body during subsequent heating.

In accordance with another aspect of the present invention,the backshell assembly as set forth above includes a hollow cylindrical nut having an outside surface and a first end for attaching to the second end of the connector member.

In accordance with another aspect of the present invention, the axial extensions of the tube beyond the ends of the body member or nut may have a layer of sealant on the inside surface thereof and have an inside diameter greater than the diameter of the outside surface of the nut.

A feature and advantage of this aspect of the present invention is that the body member and the cable can be inserted into the extensions of the tube when the backshell is being mechanically assembled and sufficient heat will have to be applied to the tube extensions to soften the sealant before the tube shrinks onto the cable and the backshell body.

A A In accordance with another aspect of the present invention, the inside diameter of the tube extensions is at least 1.08 times the outside diameter of the body member.

In accordance with another aspect of the present invention, the tube extensions have been stress relieved by being heat shrunk from a larger diameter when the central portion of the tube was heat shrunk onto the nut to prevent any longitudinal movement during subsequent heat shrinking. Upon subsequent heat shrinking onto the cable and the body member, the tube extensions will then have their ends at the desired locations on the body and the cable as a result of this stress relieving.

In accordance with still another aspect of the present invention, the outside surface of the body has a diameter the same as or less than the diameter of the outside surface of the nut.

In accordance with the last aforementioned aspect of the present invention, the body member having a diameter less than the outside diameter of the nut provides a backshell wherein the tube is captured lengthwise by the nut and will not "milk off" from the nut. The extensions provide an environmental seal from the exterior surface of the cable to the exterior surface of the body.

In accordance with still another aspect of the present invention, the backshe-11 includes a spin coupling member for connecting the backshell t o the other electrical devices and one end of the tube extends over the spin coupling so that the environmental seal is created from the surface of the cable to and including the spin coupling.

These and other aspects, features and advantages of the present invention will be more appreciated upon a perusal of the following specification and the accompanying drawing wherein similar characters of reference referred to similar elements in each of the separate views.

Brief Description of the Drawings

Fig. 1 is an elevational, partially cross-sectional view of one backshell assembly in accordance with the present invention.

Fig. 2 is a view similar to Fig. 1 with an electrical cable inserted in the backshell assembly.

Fig. 3 is a view similar to Fig. 2 after the tube of the backshell assembly has been heat shrunk.

Figs. 4 - 7 are views similar to Fig. 1 showing alternative embodiments of the present invention.

Figs. 8A - 8E are elevational views, partially in section, illustrating the preferred method of making the backshell assembly in accordance with the present invention.

Fig. 9 is an elevational, partial cross-sectional view of one backshell assembly in accordance with the present invention.

Fig. 10 is an elevational, partial cross-sectional view of a backshell assembly of this invention with the backshell body attached to the metal braid of a cable and ready for attachment of the bonded tube and nut to the body.

Fig. 11 is a view similar to Fig. 10 with the nut and bonded tube threaded fully up onto the body of the backshell assembly ready for heat shrinking the tube of the backshell assembly.

Fig. 12 is a view similar to Fig. 11 after the tube of the assembly has been heat shrunk.

Figs. 13 - 19 are views similar to Fig. 9 showing alternative embodiments of the present invention.

Figs. 20A - 20D are elevational views, partially in section, illustrating the preferred method of making the backshell assembly in accordance with the present invention.

Fig. 21 is a view illustrating important dimensional aspects of the backshell assembly in accordance with the present invention.

With reference to Fig. 1, there is shown a side elevational view, partially in section, of a backshell assembly 10 in accordance with the preferred embodiment of the present invention ready for attachment to an electrical cable (not shown) at the A right side of the backshell assembly 10 and to another electrical device (not shown) at the left side of the backshell assembly 10. The backshell assembly 10 includes a hollow cylindrical backshell body member 11 having a first end 11A for engagement with the other electrical device and a econd end 11B for entrance of the electrical cable and attachment of a heat shrinkable tube or boot as described below. In the specific illustrated physical configuration of the backshell assembly 10 the second end 11B of the body member 11 has an inwardly stepped diameter.

In the embodiment illustrated in Fig. 1, internal threads 12 are provided at the first end 11A of the body member 11 for making the engagement or physical attachment of the backshell assembly 10 to the electrical device. A sealing 0-ring 13 is provided at the first end of the body member 11.

A hollow heat shrinkable tube or boot 14 is provided at the body second end 11B. The tubing 14 has a first portion 14A surrounding the second body end 11A and an extension or end portion 14B extending beyond the body second end 11B and around the cable that will be connected via this backshell assembly 10.

The tube 14 has been previously shrunk down for stress relieving and for sliding onto the second body end 11B and has been bonded with an appropriate bonding material 15 such as one of the quick setting adhesives in the manner described below with reference to Figs. 8A - 8E. The melting temperature of the bonding material 15 should be sufficiently high, such as at least 1000C, so that the bonding material 15 will not melt when the appropriate heat is applied to the tubing 14 to shrink the end extension 14B onto the cable. Examples of appropriate adhesives are the lower (such as methyl or ethyl) alkylcyanoacrylate type adhesives. An appropriate commercially available adhesive is Loctite 495. A sealant material 16 such as a hot melt adhesive is provided on the inside surface of the end extension 14A for creating a waterproof seal between the tubing 14, the backshell body 11, and the electrical cable when the backshell assemble 10 is installed.

The heat shrinkable tube 14 is made of a thermoplastic polymer such as polyolefin which has been chemically or radiation cross-linked or which inherently possesses the property of heat recoverability. The tube or boot 14 is made from medium to thick wall tubing which has a shrink ratio of at least 3 to 1. With such a shrink ratio a backshell assembly of one specific size of body 11 and tube 14 can be utilized with cables of various different diameters and still provide the desired environmental seal and required strain relief.

Fig. 2 illustrates an electrical cable 17 positioned within the backshell assembly 10 ready to have the tube extension 14B shrunk down onto the cable 17. The cable 17 has had its outer insulation layer removed part way back and its conductors passed through the body member 11 for appropriate usage at the other electrical device (not shown).

Fig. 3 illustrates the attachment of the body member 11 to the electrical cable 17 with the tube extension 14B heat shrunk onto the electrical cable 17. Heat is typically applied beginning at one end of the tube extension 14B and gradually applied lengthwise of the tube extension 14B. As shown in Fig. 3 after heat shrinking and due to the previous stress relieving of the tube 14, the free end of the tube extension 14B is located on the cable 17 at the same desired location as when the backshell was assembled with the cable as shown in Fig. 2. The diameter of the tube 14 being larger than the diameter of the cable insures that the sealant 16 will have softened by the time sufficient heat has been applied to the tube extension 14A to cause it to shrink down onto the cable C and the body member 11.

Referring now to Figs. 4 - 7, there are illustrated alternative embodiments of the present invention. In the embodiment of Fig. 4, the body 41 of the backshell assembly 40 has a spin coupling 41C for connection to the other electrical device. Also, the diameter of the body member is uniform through its length.

0 4 m In Figs. 5 and 6, the backshell assemblies 50 and 60, respectively, include body members 51 and 61 which include bends of 45' and 900, respectively. The backshell assembly can include other typical angles such as 300 and 60. Fig. 7 illustrates a backshell assembly 70 with a body member 71 having a square corner rather than the arcuate corner of the backshell assembly 60 of Fig. 6.

Referring now to Figs. 8A - 8E, there is illustrated the method of manufacturing the backshell assembly 10 of Fig. 1. A low friction mandrel 80, such as of Teflon, or a Teflon coated mandrel is provided having a diameter of the ultimate diameter desired for the interior surface of the tube 14. A piece of heat shrinkable tubing or boot 81 of the desired length but previously expanded to a greater inside diameter than the mandrel outside diameter is slipped over the mandrel 80 as shown in Fig. 8A. Heat is then applied to the tubing 81 until the tubing 81 has shrunk down onto the mandrel 80 as shown in Fig. 8B. The mandrel assembly with the shrunk tubing is then cooled such as by being placed in cold water, and the mandrel is then removed. The sealant 16 is then coated on the interior surface of the tube extension 14B as shown in Fig. 8C, and the adhesive 15 is applied to the outside surface of the body second end 11B as shown in Fig. 8D. Next, the tube first end 14A is slid onto the adhesive coated body second end 11B, and the bond between the body second end 11B and the tube first end 14A is made as shown in Fig. 8E.

When the tubing 81 is shrunk down ont the mandrel 80, longitudinal stresses in the tubing 81 are alleviated so that the tube 14 does not tend to shrink longitudinally when heat is later applied to the tube 14 to shrink the extension 14B down ont the cable 17.

With reference to Fig. 9, there is shown a side elevational view, partially in section, of a backshell assembly 110 in accordance with the present invention ready for attachment-to an electrical cable (not shown) at the right side of the backshell assembly 110 and to another electrical device (not shown) at the 1 X left side of the backshell assembly 110. The backshell assembly 110 includes a hollow cylindrical backshell body member 111 having a first end 111A for engagement with the other electrical device and a second end 111B for entrance of the electrical cable and attachment to the metal, cable braid. A hollow cylindrical nut 112 has a first end 112A for removable attachment to the body member 111, such as via the illustrated threads 111C and 112C and has a second end 112B.

In the specific illustrated physical configuration of the backshell elements the second end 111B of the body member 111 has a reduced diameter from the inside surface of the nut 112. This construction enables attachment of the metal shield of the cable at the body reduced diameter portion such as by a clamping band B (See Fig. 10).

In the embodiment illustrated in Fig. 9, a spin coupling element 113 is included on the first end 111A of the body member 111 for making the engagement or physical attachment of the backshell assembly 110 to the electrical device. A connector sealing 0-ring 114 is provided at the first end of the body member, and in the embodiment of Fig. 9 is captured within a annular recess on the inside surface of the spin coupling member 113.

A hollow heat shrinkable tube or boot 115 is provided surrounding the nut 112. The tubing has first and second extensions or end portions 115A and 115B extending beyond the first and second nut ends 112A and 112B, respectively, around the body 111 and the cable that will be connected via this backshell assembly 110. The central or medium portion 115C of the tube 115 has been shrunk down and bonded with an appropriate bonding material 118 such as one of the quick setting adhesives. Examples of these adhesives are the lower (such as methyl or ethyl) alkylcyanoacrylate type adhesives. An appropriate commercially available adhesive is Loctite 495. Upon assembly of the nut 112 and body 111, the nut precisely locates the tubing with respect to the body 111 and the cable and shields the attachment of the metal, cable braid or shield to the body ill.

The tube extensions 115A and 115B. which have also been shrunk down to their illustrated shape as will be described in greater detail below with reference to Figs. 20A - 20D, have an inside diameter greater than the diameter of the outside surface of the nut 112 and with the tubing bevelled in a smooth transition from the larger diameter end extensions to the smaller diameter median portion. A sealant material 116 such as-a hot melt adhesive is provided on the inside surface of the end extensions 115A and 115B for creating a waterproof seal between the tubing 115, the backshell body ill, the coupling member 113 and the electrical cable when the backshell assembly 110 is installed.

The heat shrinkable tube 115 is made of a thermoplastic polymer such as polyolefin which has been chemically or radiation cross-linked or which inherently possesses the property of heat recoverability. The tube or boot 115 is made from medium to thick wall tubing which has a shrink ratio of at least 3 to 1. With such a shrink ratio a backshell assembly of one specific size of body 111 and nut 112 can be utilized with cables of various different diameters and still provide the desired environmental seal and required strain relief.

Fig. 10 illustrates the attachment of the body member 111 to the metal shield S of a cable 117 which has had its outer insulation layers removedpart way back and its conductors passed through the body for appropriate usage at the other electrical device(not shown). The cable shield S has been attached to the reduced diameter portion of the body second end 111B by a clamping band B ready for sliding the nut 112 and tubing 115 in place for attachment to the body 111.

Fig. 11 illustrates the nut 112 and bonded tube 115 threaded onto the backshell b ody 111. The backshell assembly 110 in-this configuration is ready to have the tube 115 shrunk down by heat applied typically beginning at one end of the tube 115 and f gradually applied lengthwise of the tube 115. The enlarged diameter end extensions 115A and 115B are such that the sealant 116 will have softened by the time sufficient heat has been applied to the tube 115 to cause it to shrink down onto the cable C7 C and the body member ill.

Fig. 12 illustrates the completed backshell assembly after the end extension 115A has shrunk down onto the body member 111 and coupling nut 113 and the end extension 115B has shrunk down onto the cable C.

Referring now to Figs. 13 - 19, there are illustrated alternative embodiments of the present invention. The backshell assemblies in these embodiments utilize tubing shorter at its first end than that in the embodiment of Figs. 9 - 12 so that the tubing shrinks down only on the backshell body and does not capture the spin coupling nut 113 as well.

In the embodiment of Fig. 13 the body 151 has a spin coupling 153. The first end extension 155A of the tube 155 shrinks down onto the body 151 but not onto the spin coupling 153.

The backshell assembly 160 shown in Fig. 14 employs a straight threaded connection at its first end 161A instead of a spin coupling.

In Figs. 15 and 16 the backshell assemblies 170 and 180, respectively, include body members 171 and 181 which include bends of 45' and 900, respectively. The backshell can include other typical angles such as 30' and 60.

Fig. 17 illustrates a panel or bulkhead rear mounting assembly structure 190. As shown, the backshell or adapter body member 191 includes an outwardly projecting retaining flange 199 on the first end 191A thereof. In use the second end 191B of the body 191 is first passed through an aperture in a panel or bulkhead and a jam nut 199f is threaded onto threads 191E on the body 191 to attach the body 191 to the panel which is the other electrical device in this embodiment. An "0" ring 194 is C provided on the flange 199 to make the seal between the body 191 and the backside of the panel from the assembly 190.

In the alternative bulkhead front mounting assembly 200 illustrated in Fig. 18 an outwardly projecting flange 209 is provided midway along the length of the body 201 and a jam nut 2091 threads onto the first eng 201A of the body 201 for clamping the assembly 200 to a panel or bulkhead.

In the front flange mounting assembly 210 shown in Fig. 19 an outwardly projecting flange 219 is provided on the first end of the body member 211. The flange 219 is provided with mounting holes 219" for attaching the assembly 210 to a panel or bulkhead, such as by screws (not shown).

While the backshell assembly 110 includes the two members 111 and 112which are screwed together and which are metallic for achieving the necessary grounding connection with the cable, members of constructions other than those illustrated by body 111 and nut 112 of Figs. 9 - 12 and alternative structures of Figs. 13 - 19 can be utilized within the scope of the present invention. Therefore, the terms "body" and "nut" are used herein to mean hollow cylindrical members for passing conductors of a cable and generally for attachment to the cable and to another electrical device.

Referring now to Figs. 20A - 20D, there is illustrated the method of manufacturing the backshell assembly 110 and principally the nut 112 bonded to the heat shrinkable tubing 115. A pair of low friction mandrels 221 and 222, such as Teflon or Teflon coated mandrels, are provided having a diameter of the ultimate diameter desired for the interior surface of the tube end extensions 115A and 115B, each mandrel having a bevelled end, 221A and 222A respectively, to provide the smooth transition from the larger diameter extensions 115A and 115B to the diameter of the outside surface of the nut 115. The mandrels 221 and 222 have axial bores for receiving a spindle 223, and an annular centering insert 224 is provided having a central bore for_ sliding on the spindle- 223 and an outside cylindrical surface p 1 4 'i that slides closely within the nut 112. A tubing stop 221C is provided on the external surface of mandrel 221 at the desired longitudinal distance along the mandrel 221 for the end of the extension 115A on the resulting tube 115.

With the mandrel 221 and centering insert 224 positioned on the spindle 223, the nut 112 is placed over the insert 224 and the other mandrel 222 slipped in place on the spindle so that the nut 112 is clamped between the beveled mandrel ends 221A and 222A. The bonding adhesive 118 is applied to the outside surface of the nut 112. Next, a piece of heat shrinkable tubing or boot 225 of the desired length is slipped over the entire assembly up to the tubing stop 221C on mandrel 221 as shown in Fig. 20B. Heat is then applied to the tubing 225 beginning at the end next to tube stop 221C until the ends of the tubing 225 have shrunk down onto the mandrels 221 and 222 and the medium or central portion of the tubing 225 has shrunk down onto the nut 112 and is bonded thereto as shown in Fig. 20C. The mandrel assembly with the nut and shrunk tubing is then cooled such as by being placed in cold water and the mandrels removed. The sealant 116 is then coated on the interior surfaces of the extensions 115A and 115B.

When the tubing 126 is shrunk down onto the mandrels 221 and 222, longitudinal stresses in the tubing 225 are alleviated so that precise positioning of the end extensions 115A and 115B can be achieved when the tube is shrunk in the final application down onto the cable and backshell body. The precise position of the end of the tube extension 115A is important because in the preferred embodiment of Figs. 9 - 12 the tube extension 115A shrinks down onto the spin coupling 113 and keeps the spin coupling from rotating.

Fig. 21 illustrates the preferred relationship of the diameter of the tube extensions 115A and 115B relative to the outside diameter of the body 111 for achieving softening of the sealant 116 before the tubing 115 shrinks onto the cable and the body 111. It has been found that the preferred relationship is p 1 such that the inside diameter of the tube extensions is at least 1.08 times the outside diameter of the body.

The terms and expressions which have been employed here are used as terms of description and not of limitations, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described, or portions thereof, it being recognized that various modifications are possible within the scope of the invention claimed.

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Claims

1. A backshell assembly for connecting an electrical cable to other electrical devices comprising, in combination: a hollow cylindrical body member having a first end for attachment to the other electrical device and a second end and a hollow cylindrical, heat shrinkable tube surrounding and extending axially beyond said second end of said body member, said tube having been stress relieved by being heat shrunk to the diameter of said scond end of said body member and the interior surface of said tube being bonded to the outside surface of said second end of said body member whereby said body member can be attached to the cable by heat shrinking the extension of said tube down onto the cable.

2. The backshell assembly of claim 1 wherein the axial extension of said tube beyond said second end of said body member has a layer of sealant on the inside surface thereof.

3. The backshell of claim 1 wherein said tube is formed from tubing having a shrink ratio of at least 3 to 1.

4. The backshell assembly of claim 1 wherein the melting temperature of the material bonding said body member and said shrinkable tube exceeds the shrinking temperature of said tube.

5. The backshell assembly of claim 1 including a hollow cylindrical nut having an outside surface, a first end for attachment to said second end of said body member and a second end, said heat shrinkable tube surrounding said nut and extending axially beyond both said first and said second ends of said nut with the interior surface of said tube being bonded to the outside surface of the nut whereby the body member and saidnut can be attached together and to cable and the extensions of said tube shrunk down onto said b6dy member and said cable.

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6. The backshell assembly of claim 5 wherein said inside diameter of said tube first end is at least 1.08 times the outside diameter of said body member.

7. The backshell assembly of claim 5 wherein said extensions of said tube have been stress relieved by being heat shrunk to said diameter greater than the diameter of said outside surface of said nut.

8. The backshell assembly of claim 5 wherein the outside surface of said body member has a diameter the same as or less than the diameter of said outside surface of said nut.

9. The backshell assembly of claim 8 wherein said body member includes at said first end thereof a spin coupling member.

10. The backshell assembly of claim 5 wherein said body member and said nut are metallic for grounding a metal shield of the electrical cable.

11. The method of forming a backshe 11 assembly comprising the 5 steps: forming a backshell body member for passing an electrical cable therethrough and for attachment at one end to an electrical device; heat shrinking a heat shrinkable tube to a diameter at which the tube is still heat shrinkable and so that the inside tube diameter will slide onto the outside surface of the other end of the body member; sliding the tube and the body other end together; and bonding the tube to the outside surface of the body member whereby said body member can be attached to the cable by heat shrinking the extension of said tube-down onto the cable.

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12. The method of claim 11 including the step of forming a nut for passing an electrical cable therethrough, heat shrinking the tube so that the medium portion of the tube is shrunk onto the outside surface of the nut with portions of the tube extending beyond both ends of the nut and bonding the medium portion of the tube to the outside surface of the nut.

13. The method of claim 12 wherein said shrinking step includes the step of shrinking the extensions of the tube beyond the ends of said nut to a diameter greater than the diameter of the outside surface of said nut.

14. The method of claim 13 wherein said shrinking step includes maintaining the diameter of the extensions of the tube at least 1.08 times the diameter of the outside surface of the body member.

15. The method of forming a mechanical and an electrical connection between an electrical cable and another electrical device employing a backshell having a hollow cylindrical body member and a hollow cylindrical nut with a heat shrinkable tube having the medium portion thereof shrunk and bonded onto the outside surface of the nut comprising the steps of: attaching the nut and the body member together and to the cable; and shrinking the ends of the tube onto the connector and the tube.

16. The method of claim 15 wherein said shrinking step includes capturing the cable and the other device together with the extensions of the tube beyond the ends of the nut shrunk down to a diameter less than the outside diameter of the nut.

Published 1988 at The Patent Office,.State House, 66f71 High Holborn, Jondon. WC1R 4TP. Further copies may be obtained from The Patent Offtce, Sales Branch, St Mary Cray. Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Maxy Cray, Kent. Con. 1187.

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