GB2117072A - Tube coupling - Google Patents

Abstract

A tube coupling comprises a socket 10 for receiving a tube 18 to be coupled and an open cap 20 threadably connected to the socket 10, the cap and socket having opposed shoulders 24, 28. A sheet metal lock washer 34 of shallow, truncated conical form locates between the shoulders 24, 28 and is sandwiched therebetween and generally flattened as the cap 20 is tightened on the socket 10, so as to reduce the internal diameter of the lock washer 34 whereby it grips the tube 18. A seal washer 30 will normally be provided to be sandwiched together with the lock washer 34 between the shoulders 24, 28. <IMAGE>

Description

SPECIFICATION Tube coupling Field of Invention This invention relates to mechanical couplings for pipes. Whilst it particularly relates to coupling for plastic tubes used for plumbing purposes, it is not necessarily restricted thereto.

Background of Invention Mechanical couplings are of two general types, the first wherein an axially split clamp surrounds a tube end to be coupled, and a radial clamping pressure is generated by the use of bolts or the like. Difficulty is often experienced in providing a proper seal onto the tube, as the seal may also be axially split. Also the clamping hardware is normally exposed and may be subject to corrosion in hostile environments. The other coupling may be referred to as an axial coupling comprises a socket for receiving the end of a tube to be coupled and a cap threadably connected to the socket through which the tube passes. The cap and socket define an inner recess within which recess there is disposed a sealing ring to surround a tube inserted into the socket.As the cap is tightened on the socket to reduce the volume of the inner recess, the sealing ring is forced into contact with the outer surface of the tube, so provide a seal thereabout. In addition to providing a fluid tight seal between the tube and socket, it is usually desired that a pipe coupling provide an anchoring force upon the tube so as to resist axial forces which tend to withdraw the tube from the socket. The complexity of the coupling depends in part upon the desired degree of resistance to such axial forces. In a simple collet seal fitting wherein the seal ring and socket are provided with mating ramp surfaces of limited axial extent, the seal ring itself provides an anchoring function, due to it being compressed onto the tube surface, such that a coupling for plastic tubing of about 5 cm diameter may resist an axial force of about 10 kg.

In more complex structures where the seal ring and the cap or socket are provided with mating ramp surfaces of considerably greater axial extent, enhanced forces may be generated. Such forces may be increased still further by providing the seal with means for localizing the gripping pressure.

Such means may be in the form of localized deformations of the seal material, or as an alternative other, usually harder materials may be used. In each case the anchoring force is generated primarily as a compressive force transmitted through the body of the seal material, which may unduly limit the selection of seal material.

Summary of Invention The present invention seeks to provide in a tube coupling improved anchoring means. In accordance with one embodiment of the invention, the tube coupling comprises a socket and cap which are threadably interconnected and which provide an inner recess for surrounding a tube to be coupled by the coupling. A lock collar having thin wall portions defining surface portions of a shallow truncated cone is provided within the Inner recess, with the inner edge of the collar, that is to say with the apex of the cone, preferably being directed towards the socket. The socket and cap have opposed shoulders associated therewith which are engageable with the lock collar.As the cap is tightened on the socket, the lock collar becomes sandwiched between the shoulders, thereby becoming progressively flattened; otherwise expressed, the conical angle of the conical surface of the lock collar is decreased. This flattening of the lock collar causes the diameter of the inner edge portions of the lock collar to decrease and thereby interfere with a tube inserted into the socket, so, as to anchor the tube.

Preferably the lock collar is in the form of a thin, unitary washer which may be conveniently formed from sheet metal, stainless steel being particularly preferred where corrosion resistance is desired.

Relatively small axial forces only are required to reduce the conical angle of the lock collar, particularly where the inner edge of the lock collar is weakened as by providing a plurality of radial slots therein, in effect the inner edge of the lock collar forming a plurality of fingers. The provision of fingers may also be advantageous in increasing the incisive action of the inner edge of the lock collar.

Generally speaking the socket will be provided with some type of seal. Expediently the seal will locate within the inner recess, and will be sandwiched, together with the lock collar, between the shoulders of the cap and socket.

Typically the seal will be of a simple collet type, particularly where the tube is of relatively small diameter, say up to about 5 cm. Since the axial force necessary to urge the lock collar to its flattened form is relatively small, and since the axial force upon the lock collar is expended in compression once the lock collar is flattened, it is found that the choice of seal type and material is not unduly limited and seals other than simple collet types may be preferred.

The above aspects of the invention and advantages accruing therefrom will be further described in relation to the accompanying description of a preferred, illustrative embodiment of the invention, taken in conjunction with the accompanying drawings, from which still further aspects and advantages of the invention will appear to practitioners in the art.

Brief Description of the Drawings FIG. 1~is an exploded, perspective view of a tube coupling constructed in accordance with the invention, with a tube for coupling; FIG. 2 - is a tube coupling similar to FIG. 1 in exploded axial section; and FIG. 3 - is similar to FIG. 2, but shows a tube coupling with a tube to be coupled therein on the right hand side, and a tube coupled therein on the left hand side.

Description of the Preferred Embodiments Referring now to the drawings in detail, a double ended socket is denoted generally therein by the number 10. Since socket 10 is symmetrical about the central radial plane, only one end thereof is particularly described. Socket 10 is externally threaded at 12, and is provided with an abutment 14 for limiting the penetration of the undressed end 16 of a tube 18 into the socket.

The internal radial diameter of socket 10 is such as to preferably closely surround tube end 16. A cap 20 is provided having an opening 22 therein, surrounded by a radially aligned shoulder 24 permitting the passage of tube end 16 therethrough. Cap 20 is internally threaded at 25 so as to threadably connect to threads 12 of socket 10, thereby forming an inner recess 26, seen in FIG. 3, surrounding tube 18 when engaged in socket 10. The outward facing end of socket 10 provides a shoulder 28 opposed to radial shoulder 24 defining the inward limit of inner recess 26.

Shoulder 28 is provided with a downwardly, inwardly directed ramp surface 29. A sealing collet 30 having a ramp surface 32 complementary to surface 29 is disposed within inner recess 26. It will be appreciated that the device so far described is well known in the prior art as a coupling for tubes.

In order to provide an anchor for resisting the axial withdrawl of tube 16 from socket 10, there is provided a lock collar 34. Lock collar 34 comprises a thin, sheet metal washer which is upset whereby the major surface portions define surface portions of a shallow, truncated cone. The inner edge of lock collar 34, that is to say the edge of least diameter, is provided with a plurality of small radial slots 36 which serve to weaken that edge and also to provide a plurality of fingers 38.

Lock collar 34 is disposed within inner recesses 26 adjacent radial shoulder 24. The diameter of the inner edge of lock collar 34, that is to say the distal ends of fingers 38, when the lock collar is in its shallow conical form, is such as to closely surround tube end 16. Preferably lock collar 34 locates within recess 26 with the apex of the conical surface pointing towards the interior of socket 10, so as to facilitate the passage of tube end 16 therethrough, as it is engaged in the socket. In practice, the ends of fingers 38 may, when the lock collar 34 is in its shallow conical form, define an opening marginally less than the diameter of tube end 1 6, as the fingers tend to flex to increase the conical angle as the tube end is passed through the lock collar.The somewhat flexible nature of fingers 38 permits a reasonable tolerance in the diameter of tubes that can be firmly anchored in the tube coupling. As cap 20 is tightened on socket 10, lock collar 34, and collet 30 together therewith, is sandwiched between opposed shoulders 24, 28 thereby causing the conical angle of the lock collar to decrease.

Correspondingly the diameter of the inner edge of lock collar 34 decreases, and fingers 38 constrict about tube 18, to interfere strongly therewith.

Where tube 18 is of plastic material it is normally found that lock collar 34 assumes a planar condition, with the inner edge of the lock collar incising the surface of the tube. It will be appreciated that the provision of fingers 38 at the inner edge of lock collar 34 localizes the incising forces, thereby tending to decrease the axial force necessary to deform the lock collar to its flattened, planar condition. It will also be appreciated that lock collar 34 tends to be self clenching when oriented in the preferred manner, that is to say with the apex of the cone directed towards the interior of the socket, as a tensile force on tube 1 8 will tend to flatten collar 34 and increase the interference of fingers 38 with the surface of tube end 16.It is, of course, desirable that the outer of the shoulders sandwiching lock collar 34, that is to say shoulder 24 on cap 20, be configured to prevent significant over-centre movement of the lock collar such as would tend to occur when tube 18 # is subject to tensile forces. Normally shoulder 24 will be planar and right radial for this purpose.

It may be noted that it is not normally required to dress or otherwise prepare tube end 16, as by threading or flaring, for example, particularly where tube 18 is of a plastic material, as fingers 38 will incise and penetrate the surface thereof.

Where it is desired to anchor tubes of harder materials it may be preferred to provide a channel circumscribing the tube end within which to receive fingers 38, but this will depend upon the degree of anchoring desired, for without any channel or other similar means being provided a strong interference would be nevertheless expected.

Whilst in the illustrated embodiment a double ended coupling is illustrated for coupling together the opposed ends of tubes, it will be understood that couplings having one, two or more ends constructed in accordance with the invention.

Also, whilst a collet seal is illustrated it will be appreciated that other sealing means may be effective for a particular application. It is to be understood that the invention is not limited to the precise form illustrated, and that changes may be made thereto without departing from the spirit and substance of the invention.

Claims (12)

1. An axial tube coupling comprising: a socket and an open cap therefor threadably interconnected and adapted to provide an inner recess disposed for surrounding a tube inserted into the coupling; a lock collar having thin wall portions defining surface portions of a shallow truncated cone, said lock collar locating in said inner recess, and opposed shoulders associated with said cap and said socket to engage said lock collar therebetween, whereby as said cap is tightened on said socket the conical angle of said lock collar is decreased so as to decrease the diameter of inner edge portions of the lock collar, causing said inner edge portions to grip a tube inserted within said coupling.

2. An axial tube coupling as defined in Claim 1, wherein said lock collar is weakened at the inner edge thereof.

3. An axial tube coupling as defined in Claim 1, wherein said inner edge is formed with a plurality of fingers.

4. An axial tube coupling as defined in Claim 1, 2 or 3, wherein said lock collar is formed as a unitary construction from thin sheet metal.

5. An axial tube coupling as defined in Claim 1, 2 or 3, wherein said lock collar is oriented with the apex of the conical surface directed inwardly to said socket.

6. An axial tube coupling as defined in Claim 1, 2 or 3, further including a seal.

7. An axial tube coupling as defined in Claim 1, 2 or 3, wherein a seal is provided in said inner recess intermediate said lock collar and said shoulder associated with said socket.

8. An axial tube coupling as defined in Claim 1, 2 or 3, wherein said socket is double ended and is provided with an abutment therein for locating a tube end received therein.

9. A lock collar for a tube coupling comprising an annular washer having thin wall portions defining surface portions of a shallow truncated cone, the inner edge of said washer being provided with a plurality of fingers.

10. A lock collar as defined in Claim 9, wherein said annular washer is of unitary construction from thin sheet metal.

11. A lock collar as defined in Claim 10, wherein said thin sheet metal is stainless steel.

12. An axial tube coupling constructed and arranged substantially as herein particularly described with reference to the accompanying drawings.