GB2169982A - Joint for connecting tube or rod members - Google Patents

Abstract

A joint is provided comprising a rod or tube member (6) and a connector member (2), the rod or tube member (6) comprising a spigot or socket portion and the connector member (2) comprising a complementary socket or spigot portion (4). The external surface of the spigot portion or the internal surface of the socket portion includes wedge surfaces (8) and the other of said surfaces includes longitudinally extending ribs (10) which cooperate with the wedge surfaces (8) to tighten 4 the joint when the spigot portion is inserted into the socket portion and the portions are relatively rotated. Longitudinally extending stops (9) limit the relative rotation of the spigot and socket portions in at least one direction. The joint is suitable for forming from rod or tube members structures such as fruit cages, racking and shelving systems and constructional toys. <IMAGE>

Description

SPECIFICATION Joint for connecting tube or rod members This invention relates to joints for connecting tube or rod members and to structures comprising tube or rod members connected by such joints.

There are many occasions when it is desired to connect together tube or rod members and various means have been proposed for connecting such tube or rod members together. For light duty structures such as fruit cages for horticultural or agricultural use, light industrial or domestic racking or shelving systems, constructional toys and the like it is usual to use connector elements having sockets therein for tightly receiving end portions of the tube or rod members spigot-and-socket fashion.

The tightness of the fit of the tube or rod members in the sockets of the connector elements depends on the accuracy with which these parts are produced. Convenient manufacturing methods, such as extrusion, tend to produce variations in the cross-section of the rod or tube members that affect their fit in the sockets and so cause difficulties.

The present invention has as its object to enable the aforesaid difficulties to be overcome.

According to the present invention there is provided a joint comprising a rod or tube member and a connector member, the rod or tube member having at least an end portion comprising a spigot or socket portion and the connector member being provided with a complementary socket or spigot portion adapted to cooperate therewith to form the joint, wherein one of the external surface of the spigot portion and the internal surface of the socket portion includes at least one wedge surface, and the other of the external surface of the spigot portion and the internal surface of the socket portion is provided with at least one longitudinally extending rib thereon, the at least one wedge surface being of progressively increasing radius from the axis of the joint in a circumferential direction between initial and final radii, the said one spigot or socket surface that includes the wedge surface also including a longitudinally extending stop connecting adjacent surface portions of said one surface, the relative dimensions of the said external surface of the spigot portion and the internal surface of the socket portion, including the at least one wedge surface and the at least one rib, being such that at a first relative orientation of spigot and socket the spigot can readily be inserted into and withdrawn from the socket, and the spigot can then be rotated within the socket into a second relative orientation of spigot and socket in which the rib bears against the wedge surface between its initial and final radii and the joint is relatively tight.

The internal wall of the socket portion and the external wall of the spigot portion are preferably substantially uniform along their lengths, subject to the optional provision of a circumferential groove in the portion that includes the at least one wedge surface, as hereinafter described.

A single wedge surface may extend over the entire circumference of the said one spigot or socket portion including the wedge surface, or a plurality of wedge surfaces may extend over the entire circumference. Alternatively the ends of the wedge surface or wedge surfaces may be spaced apart, and suitably a part cylindrical surface portion provided therebetween.

Such a part cylindrical surface may be provided at least at that end of the wedge surface that corresponds to the location of the rib in the first relative orientation of the spigot and socket portions, in which the joint is relatively loose. Where the rib is on the external surface of the spigot portion, and the wedge surface is on the internal surface of the socket portion, the part cylindrical surface will then lie at that end of the wedge surface that is at the greater radial distance from the joint axis. Conversely, where the at least one rib is on the internal surface of the socket portion, as is the case in a preferred embodiment of the invention, and the wedge surface is on the external surface of the spigot portion, the part cylindrical surface will lie at that end of the wedge surface that is at the lesser radial dstance from the joint axis.

Where a plurality of wedge surfaces are provided, these may increase in radius from the axis of the joint in the same circumferential direction, in which case tightening of the joint can only be effected by relative rotation of the spigot and socket portions in a single direction, or wedge surfaces may be provided which increase in radius in each circumferential direction so that tightening of the joint can be effected by relative rotation of the spigot and socket portions in either direction. The said longitudinally extending stop may serve to limit relative rotation of the spigot and socket portions in one or both directions. In the case where the wedge surfaces increase in radius in the same circumferential direction the said stop may be in the form of a step which connects adjacent surface portions of initial and final radii.In the case where wedge surfaces are provided which increase in radius in both circumferential directions the stop may be in the form of a longitudinally extending rib between adjacent surface portions.

The joint may be relatively freely assembled when the rib is aligned with one end of the wedge surface. Where a part cylindrical surface is provided at the end of the wedge surface corresponding to the assembly alignment of the spigot and socket portionS, the joint can be assembled in a range of relative rotational orientations corresponding to the circumferential length of the part cylindrical surface, so that a user can readily insert the spigot into the socket without undue searching for one particular correct relative rotational position. The joint is tightened by turning the spigot in the socket to move the rib over the wedge surface until a sufficient resistance is felt, at which point the rib bears against part of the wedge surface.

In this way two advantages are achieved. First, since it is not necessary to turn the components of the joint against resistance into a single specific relative orientation, every user can tighten the joint to his own ability; and further, the same user can then loosen the joint from the tight condition, by turning in the reverse sense, without undue difficulty. Second, the joint overcomes a difficulty with other friction-fit joints produced by methods such as extrusion, especially extrusion of thermoplastic polymeric materials, in that the dimensional tolerances are not so critical. The tightness of the joint is not a constant value that depends on the accuracy of manufacture of the components.Reasonable variations in the diameter of the spigot and socket portions are accommodated by the ability of the rib to tighten the joint at any position on the wedge surface between the initial and final radii of the surface. Known joints which require a specific looking position are much less tolerant of dimensional variations arising in the manufacture of the spigot and socket portions, deriving for example from the difficulty of achieving accurate final diameters in thermoplastc polymeric tubing extruded from a hot melt.

The joint preferably comprises a plurality of wedge surfaces spaced circumferentially about the spigot or socket portion of the joint, as the case may be. The plurality of wedge surfaces are preferably symmetrically disposed about the axis of the joint. Ribs corresponding in number and spacing are provided on the other of the spigot and socket portions. Increasing the number of wedge surfaces and ribs increases the holding power of the joint.

In an embodiment of the invention, the at least one wedge surface is interrupted longitudinally of the joint by a transverse groove extending circumferentially through the wedge surface within the joint. The rib which bears against the wedge surface in the tightened joint accordingly crosses over the groove. Where the rib bears against the edges of the groove at the transitions between the groove surface and the wedge surface on either side of the groove, the resistance of the joint to axial disassembly is generally increased, according to the deformability of elasticity of the rib. Where the rib is of a thermoplastic material, a degree of deformability can be expected, and that part of the rib that overlies the groove is not deformed by pressure from the wedge surface to the same extent as the rib on either side of the groove.Accordingly, the rib material will tend to enter the groove and markedly increase the resistance of the spigot portion to being pulled from the socket portion by axial forces.

The rod or tube may be made by extrusion, since the joint of the invention can accommodate the slight variations in dimensions that can arise in this process, and accordingly a thermoplastic polymer is a particularly preferred and advantageous material for the rod or tube although it could, if desired, be formed from metal, e.g., aluminium alloy, or other suitable material. The cross-section of the rod or tube may be unchanged throughout its length, so that it can be cut to any length and still exhibit end portions which have the necessary conformation to form a spigot, in the case of a rod, or either a spigot or a socket, as the case may be, in the case of a tube.

The present invention also provides a structure comprising a plurality of tube or rod members connected by joints in accordance with the invention. Preferred structures include fruit cages, racking and shelving systems, and constructional toys.

The invention is illustrated by way of example in the accompanying drawings, in which: Figure 1 is a perspective view of an assembled joint; Figure 2 is cross-section through a tube member used in the joint of Figure 1; Figure 3 is a cross-section through a socket of the connector member used in the joint of Figure 1; Figure 4 is a diagram showing the form of the external surface of the tube member; and Figure 5 is a side elevation of one end of the tube member showing transverse grooves through the wedge surfaces thereof.

Figure 6 is an enlarged fragmentary cross-section of another embodiment of a joint according to the invention.

In Figures 1 to 5 of the drawings, which are not to the same scale, the connector 2 shown in Figure 1 has five socket portions 4. Four are angled at 90" intervals in a common plane and are moulded on the concave side of a slightly dished circular web 5 which provides reinforcement and, where the connector is used in, for example, the construction of fruit cages, functions to prevent netting draped over the connector from becoming caught on the outwardly projecting socket portions adjacent the web, while the fifth socket portion 4 extends perpendicularly thereto and is shown making a joint with a tube member 6.Clearly, other connectors with different numbers and arrangements of sockets may be used to form joints in accordance with the invention; it is not even necessary that the connector have more than one socket since it may be used to connect a rod or tube member to part of a structure other than further rod or tube members.

The tube member 6 is generally cylindrical in form but is provided with four equiangularly spced wedge surfaces 8 on its outer surface which extend the length of the tube member parallel with its axis.

Each socket 4 has a generally cylindrical inner surface of marginally greater diameter than the overall diameter of the tube member 6, and which is provided with four equiangularly spaced ribs 10 which are raised relative to the rest of the surface and which extend the length of the socket parallel with its axis.

The surface contour of the tube member 6 is generally cylindrical with wedge surfaces 8 superimposed thereon. As is illustrated particularly in Figure 4, four similar part cylindrical surface portions 7 separate four similar curved wedge surfaces 8. As indicated in one quadrant of Figure 4, the part cylindrical surface portions 7 extend over the arc A-A while the wedge surfaces 8 extend over the arc B-B.The transition between the part cylindrical surface and the wedge surface at AB is smooth and gradual, particularly so since due to the aforementioned dimensional variations that occur during manufacture the nominally part cylindri cal surface portions 7 may well tend to be of somewhat varying radius over the length of the arc A-A even if the corresponding parts of the extrusion die are cylindrical, and the point AB may not be discernible in a tube member nominally produced to the form illutrated; the term "part cylindrical" as used herein should be construed accordingly.

The wedge surfaces 8 increase progressively in radial distance from the axis of the tube member, from an initial radius at the junction AB to a final radius at the point B, where the tube member reverts to the radius of the part cylindrical surface portion 7 at a step or shoulder 9.

Figure 5 shows transverse grooves 11 interrupting each wedge surface 8 adjacent to the end of the tube member 16 that forms the spigot portion of the joint and that lies within the socket portion in the assembled joint. The grooves may also extend into all or part of each part cylindrical surface 7. The grooves are preferably formed by cutting circumferentially into the previously formed tube member so as to leave relatively sharp edges to each groove to assist its locking effect against a rib 10.

In order to assemble the joint, the ribs 10 of the socket are aligned with the part cylindrical surface portions 7 of the tube. The tube is held in the socket by light pressure between the ribs and the surface portions 7, and/or between the cylindrical walls of the socket and the outermost end of the wedge surfaces 8. The tube member is then turned counterclockwise relative to the connector to cause the ribs 10 to bear hard against the wedge surfaces of the tube member and to overlie the grooves therein. The other end of the tube member may be assembled similarly in a further connector by clockwise rotation.

The material of at least one of the tube member (or rod member) and socket should be capable of a degree of deformation to allow the joint to be locked into its tightened condition. Preferably the material is resiliently deformable to allow repeated use, while naturally retaining sufficient structural strength to suit its intended application. Many synthetic resins satisfy these requirements and also lend themselves to extrusion as a means of manufacturing the rod or tube members in continuous lengths to be cut as required. A preferred material is a thermoplastic polyvinyl chloride resin, desirably including an ultraviolet stabilizer.

The interior of a tube member can function as a socket and a connector member can be provided with spigot portions as well as or in place of sockets. The wedge surfaces can be provided in the socket portion of the joint, preferably being raised, i.e. extending towards the joint axis, over the underlying cylindrical surface contour of the socket, the ribs then being provided on the spigot portion of the joint.

The joint of Figures 1 to 5 can only be tightened by relative rotation of the spigot and socket portions thereof in a single direction.

Figure 6, in which like parts have been given like reference numerals, illustrates an embodiment wherein tightening of the joint can be effected by relative rotation of the spigot and socket portions in either direction.

In the embodiment of Figure 6 the outer surface of the tube member 6 is provided with eight wedge surfaces 8 (only two of which are shown), four of the wedge surfaces 8a increasing progressively in radial distance from the axis of the tube member 6 in one circumferential direction and the four alternate wedge surfaces 8b increasing progressively in radial distance from the axis of the tube member 6 in the other circumferential direction. Between each pair of wedge surfaces 8a, 8b is a longitudinally extending stop in the form of a rib 12 which connects the portions of maximum radii of adjacent wedge surfaces 8a, 8b of adjacent pairs. The ribs 12 cooperate with the ribs 10 to limit the relative rotation of the spigot and socket portions of the joint.

Claims (17)

1. A joint comprising a rod or tube member and a connector member, the rod or tube member having at least an end portion comprising a spigot or socket portion and the connector member being provided with a complementary socket or spigot portion adapted to cooperate therewith to form the joint, wherein one of the external surface of the spigot portion and the internal surface of the socket portion includes at least one wedge surface, and the other of the external surface of the spigot portion and the internal surface of the socket portion is provided with at least one longitudinally extending rib thereon, the at least one wedge surface being of progressively increasing radius from the axis of the joint in a circumferential direction between initial and final radii, the said one spigot or socket surface that includes the wedge surface also including a longitudinally extending stop connecting adjacent surface portions of said one surface, the relative dimensions of the said external surface of the spigot portion and the internal surface of the socket portion, including the at least one wedge surface and the at least one rib, being such that at a first relative orientation of spigot and socket the spigot can readily be inserted into and withdrawn from the socket, and the spigot can then be rotated within the socket into a second relative orientation of spigot and socket in which the rib bears against the wedge surface between its initial and final radii and the joint is relatively tight.

2. A joint according to claim 1, wherein the at least one wedge surface is provided on the external surface of the rod or tube member and said at least one longitudinally extending rib is provided on the internal surface of the socket portion.

3. A joint according to claim 1 or 2, wherein the internal wall of the socket portion and the external wall of the spigot portion are substantially uniform along their lengths.

4. A joint according to claim 1, 2 or 3, wherein a plurality of wedge surfaces are provided around the circumference of the said one spigot or socket portion including the wedge surface.

5. A joint according to claim 4, wherein said wedge surfaces increase in radius from the axis of the joint in the same circumferential direction.

6. A joint according to claim 5, wherein said stop comprises a longitudinally extending step which connects adjacent surface portions of initial and final radii.

7. A joint according to claim 4, 5 or 6, wherein the ends of said wedge surfaces are spaced circumferentially and a part cylindrical surface portin is provided therebetween.

8. A joint according to claim 4, comprising at least one first wedge surface which increases in radius from the axis of the joint in one circumferential direction and at least one second wedge surface which increases in radius from the axis of the joint in the other circumferential direction.

9. A joint according to claim 8, wherein each wedge surface increases in radius in the opposite circumferential direction to its adjacent wedge surface or surfaces.

10. A joint according to claim 9, wherein said first and second wedge surfaces are in pairs and wherein said pairs are connected by a said stop in the form of a longitudinally extending rib.

11. A joint according to claim 8,9 or 10, wherein four first and four second wedge surfaces are provided uniformly around said circumference and wherein said other of the external surface of the spigot portion and the internal surface of the socket portion is provided with four said longitudinally extending ribs spaced at 90 to one another.

12. A joint according to any one of the preceding claims, wherein the at least one wedge surface is interrupted longitudinally of the joint by a transverse groove extending circumferentially through the wedge surface within the joint.

13. A joint according to any one of the preceding claims, when formed from a thermopiastics material.

14. A joint according to any one of the preceding claims, wherein the rod or tube member is formed by extrusion.

15. A joint according to any one of the preceding claims, wherein the rod or tube member is of uniform cross- section throughout its length.

16. A joint substantially as herein described with reference to Figures 1 to 5 or Figure 6 of the accompanying drawings.

17. A structure comprising a plurality of rod or tube members connected by joints according to any one of the preceding claims.