WO1992020129A1

WO1992020129A1 - Coupling device

Info

Publication number: WO1992020129A1
Application number: PCT/GB1992/000770
Authority: WO
Inventors: Martin Bonsey
Original assignee: Martin Bonsey
Priority date: 1991-05-01
Filing date: 1992-04-27
Publication date: 1992-11-12

Abstract

A sleeve (1) for coupling two lengths (12, 13) of conduit has a pair of keyways (6) and slots (4, 5) extending in from the outer surface of the sleeve to the keyways. The conduits have grooves (16) aligned with the keyways (6). Flexible keys (20) are introduced into the keyways and grooves via the slots. The sleeve is rotated on the conduits, with the result that the keys are drawn into the keyways and grooves. The keys ae serrated to engage the conduits and assist the drawing in action.

Description

COUPLING DEVICE

Field of the Invention

The present invention relates to a coupling device, particularly though not exclusively for coupling together protective conduits used to carry cables such as are used in telecommunications, for fibre optic and coaxial electric communication cables.

Background of the Invention

Conventionally fibre optic cables have been protected from external loading and their environment by being placed inside protective plastics material conduit. Of necessity a long run of cable requires a number of sections of conduit. Prior means employed for coupling sections of conduit has been both expensive to produce, and difficult to install. Such means have been either clamped or screwed onto the conduit. Both arrangements are awkward in situ , that is to say in a trench where power tools are not available.

The Invention

It is the object of the present invention to provide an improved coupling device.

in accordance with one aspect of the invention there is provided a coupling device for connecting conduit with a flexible key, the coupling device comprising a right circular cylindrical sleeve, an internal bore of the sleeve for receiving the conduit from at least one end of the sleeve and having a respective circumferential keyway, the or each keyway having a respective access opening into it from an external surface of the sleeve, the opening being at least substantially tangential to the keyway to allow threading of a key into and around the keyway. Whilst the coupling device will normally having be adapted to receive two lengths of conduit - one from each end - and connect them together, it is envisaged that the sleeve may be single ended for capping and or anchoring a conduit. Normally, the sleeve will include two keyways and a sealable lateral aperture therebetween.

Preferably the sleeve is made from plastics material. A plastics material of the same composition as the conduit to be connected is preferred as the coefficient of expansion will be the same in each case and hence problems of differential expansion will be avoided. Normally high density polyethylene will be used. However, where heavy tensile loads in the conduit have to be accommodated, the sleeve may be of more rigid material such as PVC material or indeed metal such as aluminium.

Conveniently the internal bore of the sleeve is sized to receive the conduit with a sliding fit. Preferably, the sleeve includes a respective abutment formed in the internal bore inwardly of the or each keyway for abutment of the end(s) of the conduit. Further the sleeve preferably includes a respective 0-ring groove and 0-ring in the internal bore inwardly of the or each keyway for sealing the sleeve to the conduit.

Whilst a helical keyways in the sleeve and grooves in the conduit may be used, they are both preferably annular. Preferably, the or each keyway is of greater overall diameter at its edge nearer to the respective end of the coupling.

The coupling device will normally be supplied as a combination of the sleeve and a respective flexible key for each keyway, the flexibility of the key allowing it to be threaded into its keyway to engage the sleeve and the conduit.

The keys may be rectangular, or parallelogram shaped to suit the corresponding shape of the combined keyway and groove in the conduit. However in order to simplify fitting without need to match the direction of parallelogram skewing of the key to the keyway, the keys are conveniently trapezoidal.

In accordance with a particular feature of the invention, each key is provided serrations, whereby it can grip the conduit in being fed into its keyway. Whilst the serrations may be of saw-tooth shape, they are preferably of symmetrical triangular cross-section to allow the key to be fed into its keyway from either of its ends. Conveniently the flexible key is of nylon material; although it is envisaged that other materials may be used.

In accordance with another aspect of the invention, there is provided a method of connecting a coupling device and key combination of the first aspect to a length of conduit having an external groove, the method consisting in: fitting the sleeve to an end of the length of conduit with the external groove in the conduit aligned with the keyway, or one of the said keyways, and inserting the key into the keyway and the groove via the access opening to circumferentially interconnect the sleeve and the conduit.

Alternatively, for connecting two lengths of conduit each having an external groove the method consists in: fitting the sleeve to an end of each of the lengths of conduit with external grooves in the conduits aligned with a respective one of the said keyways, and inserting the keys into the keyways and the grooves via the access openings to circumferentially interconnect the sleeve and the conduits.

Preferably, the or each key is inserted into its keyway and groove by relative rotation of the sleeve around the conduit. Normally the method will include the preliminary step of cutting the external groove(s) in the external surface of the length(s) of conduit, the or each groove being of greater depth at its edge nearer to the respective end of the coupling.

The Drawings To help understanding of the invention, a specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which:

Figure 1 is a cross-sectional end view taken on the line I-I in Figure 2;

Figure 2 is a cross-sectional side view of the coupling of Figure 1, taken on the line II-II in Figure 1;

Figure 3 is plan view of a coupling strip of the invention; Figure 4 is a side view of the coupling strip, with an enlarged detail;

Figure 5 is a cross-sectional view of the coupling strip;

Figure 6 is a detailed, cross-sectional, scrap view of the the coupling strip in its use position;

Figure 7 is a cross-sectional end view on the line VII-VII in Figure 8 of a hand tool for cutting a groove in a conduit; and

Figure 8 is a cross-sectional side view on the line VIII-VIII in Figure 7 of the hand tool. The coupling device shown in Figures 1 and 2 comprises a cylindrical sleeve 1 which has an external surface 2 and an internal bore 3. The external surface 2 of the sleeve has two slots 4,5 of width W tangential and coplanar with a keyway 6 formed in the interior surface 3 and extending fully around the inner circumference. The keyways 6 are asymmetric. They are deeper at their edges 7 closer to the ends of the sleeve than their inner edges 8. Inwardly of the keyways 6, further grooves 9 are provided for 0-rings 10. Centrally of the sleeve it has an access port 11 for a lubricant to assist drawing of cables through conduits 12,13. The port is threaded and would normally be closed by a screw-in plug - not shown. The sleeve is stepped at 14 to provide an abutment for the ends of the two conduits 12,13 connected by the sleeve.

The sleeve is an injection moulding of high density polyethylene. The keyways 6 are machined into the bore 3.

The conduits are internally and externally chamfered at their ends 15. At a distance in from their ends, complementary to the distance between the keyways 6 and steps 14, the conduits have external grooves 16. These also are asymmetric, being deeper at their edges 17 closer to the ends of the conduits. The conduit grooves 16 can be cut by hand with a tool as described below with reference to Figures 7 and 8.

Turning now to Figures 3 and 4, a flexible key 20 of Nylon 66 is there shown. It is a trapezoidal strip, with blunt end pointing 21 at both ends to ease introduction of the key through the slots 4,5. On one side, the strip has serrations 22. They can have a 60° symmetrical triangular shape. Typically they are 0.50 to 0.75mm (0.020" to 0.030") deep. The total thickness of the strip, from the points of the serrations to the opposite side of the strip is typically 0.05 to 0.12mm (0.002" to 0.005") greater than the combined depth of the keyway and groove 6,16, the combined depth being half the difference between the diameters to which the keyway and groove are cut (allowing for their asymmetric shape). In other words 0.002" to 0.005" of interference is provided between the strips and the keyway-and-groove when the former are fully engaged in the latter.

In use, with the grooves 16 cut in the conduits 12,13, the ends of the latter are inserted from opposite directions into the sleeve 1. The ends 15 abut the steps 14, whereby the O-rings 10 engage the conduits 12,13 and the respective keyways and grooves 6,16 align. The flexible keys 20 are introduced through each of the slots 4,5 and firmly pushed into the exposed portions of the keyways with the serrations against the conduits. This causes the serrations 22 to dig into the conduits. Rotation of the sleeve around the conduits in the appropriate direction causes the strips to be drawn into the keyways. The degree of interference mentioned above has been found to provide adequate grip between hard nylon strips and high density polyethylene conduits for the strips to be reliably drawn in.

Once the key strips have been drawn in, they provide a connection between the conduits via the sleeve to resist normal tension stress in conduits in service. The trapezium cross-sectional shape of the strips 20 causes each to abut with its edge 31 the edge 32 of the corresponding groove 16 in the conduits and to engage at the root 33 of the groove. Typically the edge face 32 of the groove is radial and the bottom face of the groove is at 15° to the axis of the conduit. The trapezium angle is 75° to correspond. Whilst the keyways 6 in the sleeve could be cut with their root angle 34 also corresponding to the opposite angle of the trapezium,

i.e. 90 + 15 = 105°,

this would result in the abutment edge face 35 of the keyway being non-radial. It is preferred for accurate longitudinal positioning of this face 35 for it to be radial. The misalignment of it and the corresponding face 36 of the key strip is not found in practice to present a difficulty.

Referring now to Figures 7 and 8, there is shown a hand tool for cutting the grooves 16. The cutting tool 100 comprises a length of bar having end bores 101,102. Bore 101 is provided with a slot 103 for receiving a cutting bit 104. The cutting bit is pivotally attached within the slot by a bolt 105 and extends at its cutting edge 106 into the bore 101 of the barrel. Abutment of the cutting bit with the bottom 107 of the slot regulates the extent of projection of the cutting edge 108 of the bit into the bore. In Figure 8, the shape of the cutting edge 108 for cutting the groove in the conduit deeper at its edge adjacent the end of the conduit is shown. The bore 102 has a second, shaped tool bit 109 secured in a radial bore 110 for chamfering the end of the conduit. The outside surface of the sleeve is knurled to form a grip 111.

In use to groove the conduit, the tool is slid onto the end of a length of conduit so that the end of the conduit abuts the blind end 112 of the bore 101. This ensures that a groove is cut at a predetermined axial distance from the free end of the conduit. Rotation of the tool in the sense indicated by R on Figure 7, causes the cutting bit to cut into the surface of the conduit so that continued rotation removes material from the conduit to form a groove. The depth of the groove is limited by the bit 104 abutting the bottom 107 of the slot 103. The end of the conduit is chamfered by inserting the conduit into the bore 102 and twisting the tool with the shaped bit 109 cutting internal and external chamfers whose extent is regulated by engagement of the conduit with the end 113 of the bore 102.

Claims

CLAIMS :

1. A coupling device for connecting conduit with a flexible key, the coupling device comprising a right circular cylindrical sleeve, an internal bore of the sleeve for receiving the conduit from at least one end of the sleeve and having a respective circumferential keyway, the or each keyway having a respective access opening into it from an external surface of the sleeve, the opening being at least substantially tangential to the keyway to allow threading of a key into and around the keyway.

2. A coupling device as claimed in claim 1, wherein the sleeve is of plastics material.

3. A coupling device as claimed in claim 2, wherein the plastics material of the sleeve is substantially the same as that of the conduit to be connected.

4. A coupling device as claimed in any preceding claim, wherein the internal bore of the sleeve is sized to receive the conduit with a sliding fit.

5. A coupling device as claimed in any preceding claim, including a respective abutment formed in the internal bore inwardly of the or each keyway for abutment of the end(s) of the conduit.

6. A coupling device as claimed in any preceding claim, including a respective O-ring groove and O-ring in the internal bore inwardly of the or each keyway for sealing the sleeve to the conduit.

7. A coupling device as claimed in any preceding claim, wherein the or each keyway is annular.

8. A coupling device as claimed in any preceding claim, wherein the or each keyway is of greater overall diameter at its edge nearer to the respective end of the coupling.

9. A coupling device as claimed in any preceding claim, including two keyways and a sealable lateral aperture therebetween.

10. A coupling device as claimed in any preceding claim, in combination with a respective flexible key for each keyway, the flexibility of the key allowing it to be threaded into its keyway to engage the sleeve and the conduit.

11. The combination as claimed in claim 10, wherein the or each key is trapezoidal.

12. The combination as claimed in claim 10 or claim 11, wherein the or each key is provided serrations, whereby it can grip the conduit in being fed into its keyway.

13. The combination as claimed in claim 12, wherein the serrations are of symmetrical triangular cross-section to allow the key to be fed into its keyway from either of its ends.

14. The combination as claimed in any one of claims 10 to 13, wherein the flexible key is of nylon material.

15. A method of connecting a coupling device and key combination as claimed in claim 10 to a length of conduit having an external groove, the method consisting in: fitting the sleeve to an end of the length of conduit with the external groove in the conduit aligned with the keyway, or one of the said keyways, and inserting the key into the keyway and the groove via the access opening to circumferentially interconnect the sleeve and the conduit.

16. A method of connecting two lengths of conduit each having an external groove with a combination of a coupling device and two keys as claimed in claim 10, the method consisting in: fitting the sleeve to an end of each of the lengths of conduit with external grooves in the conduits aligned with a respective one of the said keyways, and inserting the keys into the keyways and the grooves via the access openings to circumferentially interconnect the sleeve and the conduits.

17. A method of connection as claimed in claim 15 or claim 16, wherein the or each key is inserted into its keyway and groove by relative rotation of the sleeve around the conduit.

18. A method of connection as claimed in claim 15, claim 16 or claim 17, the method including the preliminary step of cutting the external groove(s) in the external surface of the length(s) of conduit, the or each groove being of greater depth at its edge nearer to the respective end of the coupling.