GB2181201A

GB2181201A - Coupling pipes

Info

Publication number: GB2181201A
Application number: GB08524006A
Authority: GB
Inventors: John Benjamin Glover
Original assignee: Hepworth Iron Co Ltd
Current assignee: Hepworth Iron Co Ltd
Priority date: 1985-09-30
Filing date: 1985-09-30
Publication date: 1987-04-15
Also published as: GB2181201B; EP0218429A1; EG18671A; US4711473A; ATE61095T1; GB8524006D0; EP0218429B1; DE3677690D1

Abstract

A clay or similar pipe has a coupling socket at one end formed by a shrink-fitted plastics sleeve (4). A sealing ring or band (7) is interposed between the sleeve and the pipe surface. External compression is applied to the plastics sleeve (4) over the sealing member (7) during shrinkage of the sleeve (4). This compresses the sealing member (7) and ensures reliable sealing without requiring the use of an additional bonding or sealing composition. Alternatively or additionally, a shrink-fitted plastics socket (14) on a claywear or similar pipe end may have a region (17) spaced from the pipe end, provided with a seal ring (18), and not subjected to shrink-fitting. The seal ring (18) provides a secondary seal.

Description

1 GB 2 181 201 A 1

SPECIFICATION

Coupling pipes 4 This invention relates to the coupling togetherof pipes such as are used for sewers, drains, or conduits, of the kind in which a spigot end of one pipe length is inserted into a socket atthe end of another pipe length.

The invention is particularly applicableto pipes of glazed or unglazed vitrified clayware, asbestos compositions, and other mineral materials.

The pipejointing system in which each pipe length has a spigot at one end and an intergral bell atthe other end, has now been largely superseded byjointing means of plastics material. Plastics jointing means mayforexample comprise pipe coupling sleeves of plastics material provided with rubberor similarsealing rings at both ends,for receiving the ends of respective plane pipe lengths. Alternatively, pipe lengths may befitted with plastics sleeves which projecttoform socketsfor receiving spigot pipe ends. Pipejoints of the latter kind aredisclosed forexample in our British patent specifications

971,124and 1,152,740, and in specification 1,417,371.

According to one aspect of the present invention, a pipe length has a spigoted end, and a socketed end, and the socketed end comprises a sleeve of flexible resilientthermoplastics material protruding beyond the pipe end for receiving a spigoted end of a similar pipe length, a resilient sealing ring or band is provided on the external circumference of the end of the pipe length between the pipe length and the plastics sleeve, the plastics sleeve having been shrink-fitted overthe pipe end and the said ring or band under radial or hoop stress wherebythe said ring or band is maintained under compression. Preferably, the regions of the plastics sleeve which are not in contact with the ring or band, are shrink-fitted into intimate contactwith the surface of the pipe length.

The plastics sleeve is fitted for example by heating an injection-moulded or extruded sleeve of thermoplastics material, forcibly expanding the heated sleeve before or during mounting of the sleeve on the pipe end, fitting the expanded sleeve overthe pipe end and the said ring or band, and subjecting the hot sleeveto radial or hoop compression at least in the region of the said ring or band as the hot sleeve cools and shrinks.

UK patent specification 1,417,371 discloses a pipe jointing system, in which one end of a pipe length is provided with an external sealing band which may be a sealing ring, or a moulded-on collar of plastics material. The other pipe end has a plastics socketfitted on by being forcibly expanded and then allowed to shrink onto the outside circumferential surface of the pipe, with a polymeric adhesive or sealant between the pipe surface and the plastics sleeve.

The use of a polymeric sealant substantially in- creases the cost and difficulty of production.

UK patent specification 971,124 discloses a pipe jointing system, in which a pipe length has an external rib or sealing ring at one end, and a plastics socket atthe other end, attached in a similar manner, however a polymer bonding agent or sealant is not used, but a resilient sealing ring maybe fitted on the pipe end to be trapped by the shrunk-on plastics sleeve. This is not a practical arrangement, because in practice, the shrinking plastics sleeve does not exert significant pressure on the sealing ring and therefore does not compress it, so that the sealing ring does not significantly enhance sealing between the plastics sleeve and the pipe surface, on the contrary by holding the plastics sleeve away from the pipe surface it may impair sealing.

The present invention overcomes the disadvantages of previously proposed processes and provides a simple method of securing a plastics sleeve on a pipe end with an excellent seal, by shrinkage fitting.

By applying pressure to the hot plastics sleeve, and through it, to a resilient sealing ring or band trapped between it and the pipe surface, the sealing ring or band is pre-compressed to a substantial extent while the plastics sleeve is enabled to shrink into intimate contactwith the pipe surface and with the sealing ring or band while the latter is compressed. When the plastics sleeve has cooled and set, the externally applied compression is removed, and the stress in the sealing ring or band provides excellent sealing be- tween the plastics socket and the pipe surface. The need for a polymer bonding agent or sealant is eliminated.

Before assembly, the sealing ring or band isfitted eitherto the circumference of the pipe, orto the plas- tics sleeve. In the latter case, the sleeve and sealing ring must be initially slightly under-sized relativeto the external circumference of the pipe. In the former case, the sealing ring or band can befitted on the plain external surface of the pipe end, or can be loc- ated in a circumferential groove in the pipe surface. A locating groove will usually be desirable, when an O-ring is used.

According to another aspect of the present invention, a pipe length isfitted with a plastics socket at an end of the pipe length, by heating, expanding and shrink-fitting a thermoplastic sleeve onto the end of the pipe length, and the plastics sleeve is provided with a resilient annular sealing elementfor engaging the external circumferential su rface of the pipe length, in a region of the plastics sleeve that is not heated, expanded and shrunk onto the pipe length but instead is dimensional to fit on the pipe length.

In this case, a polymer bonding agent or sealant may additionally be provided between the shrink- fitted region of the plastics sleeve, and the external surface of the pipe length, of a resilient sealing ring or band may be provided between the external surface of the pipe length and the internal surface of the plastics sleeve where the latter is shrink-fitted, being subjectto externally applied compression as described above. The resilient sealing element provided in a region of the sleevethat is not shrink-fitted, provides a back up seal relative to the region that is shrink-fitted.

The portion of the sleeve that projectsfrom the end of the pipe length to form a socket, may be provided with a resilient annular sealing elementto seal on the spigot end of an inserted pipe length. Alternatively or in addition, the other end of each pipe length (not provided with a socket) may have an external per- GB 2 181 201 A 2 ipheral rib,sealing ring orband (resilient or stiff) to make sealing engagement with the internal surface of the plastics socket of an adjacent pipe length.

The plastics socket elements may for example be made of moulded or extruded polyolefine, including reinforced grades e.g. polyethylene, polypropylene, or polyvinyl chloride of suitable grade, or other thermoplastic material which has a "themal memory" so as to shrink on cooling, and which has suitable mechanical properties and chemical inertnessJor use in the required environment, forexample as underground drains.

According to anotheraspect of the present invention, a prefabricated plastics sleeve, to form a socket, is fitted to a pipe end by heating and expanding the sleeve and fitting it on the pipe end, then allowing it to cool and contract onto the pipe end, a bonding andlor sealing agent being provided between the external surface of the pipe and the internal surface of the sleeve, and the hot sleeve being subjected to radial or hoop compression at least in the region of the said agent, as the hot sleeve cools and shrinks.

The compressible sealing band or ring, if provided, can be of any suitable elastomer (thermoplastic or thermosetting), with adequate mechanical properties, resistanceto compression set, and chemical inertness. Typicallythe sealine ring or band, to be compressed between the shrink-fitted plastics socket and the pipe surface should be relatively soft, for ex- ample 35-60 Shore. It mayfor example comprise a relatively soft 0-ring seated in the groove in the circumferential surface of the pipe length, ora band of material such as that used fortyre innertubes.

The invention will be further described with refer- ence to the accompanying drawings, which respectivelyshow, in fragmentary axial cross-section, respective embodiments of pipejoints according to the present invention.

Figure 1 shows first and second pipe ends of fired clay pipes 1, 2. Each pipe has a plain spigoted end 3. Atthe other end, each pipe has a sleeve 4 of thermoplastics material of which one portion 5 is fastened on the external surface of the pipe, and the other portion 6 projects from the end of the pipe to form a socketwhich in use receives the spigot end 3 of the adjacent pipe.

The plastics sleeve is injection-moulded, with dimensions such that its internal diameter is somewhat less than the external diameter of the pipe, so that in its as-moulded state it could not be pushed onto the pipe end. It is made of a thermoplastic meterial which exhibits "shape memory" or "thermal memory", that isto say, when heated until it is soft it can be deformed, in particular by being expanded, and when itsubsequently cools is shrinks backto its initial dimensions. Tofitthe plastics sleeve on the pipe end, the region 5 of the sleeve that is to fit overthe pipe end is heated to a temperature belowthatat which its plastic material is degraded, causing the sleeveto expand to an internal diameter greaterthan the external diameterof the pipe end. The heated and softened plastics sleeve may beforcibly expanded while it is hotand soft, bythe act of pushing itover the pipe end, or by means of an expansion mandrel.

The sleeve preferably has a register rib or register lugs 11 to locate itrelativetothe end ofthe pipe 1. The presence of the register rib or lugs is believed to contribute to maintaining the shape and dimensions of the socket region 6 while the opposite region 5 of the sleeve expands and shrinks. The region 5 can be heated in any convenient way for example by hot water, steam, hotair, radiant heat, but is preferably heated by being dipped in a fluidised bed of hotsand as this has been found to provide very uniform and controllable heating. Afterthe region 5 of the plastics sleeve has been fitted overthe pipe end in this way, it is allowed to cool, whereupon itshrinks onto the external surface of the pipe, and conformsto any irregularities in the surface of the pipe end by localised deformation of the innersurface of the sleeve.

Sealing between the inner surface of the socket and the outer surface of the pipe, depends on the accuracywith which the plastics material can conform tothe pipe surface, and in practice, simple shrink- fitting does not provide a reliable seal.

To provide a seal, the pipe has an annular band 7 of relatively soft elastomerfitted onto its external surface, at a position spaced from the pipe end and fairly close to the end of the regions 5 of the plastics sleeve.

Afterthe hot plastics sleeve has been fitted overthe pipe end and overthe sealing band 7, compression dies (which may be rigid, flexible, or inflatable by internal pressure) are applied to the external surface of the region 5 of the plastics sleeve at least in the area radially in line with the sealing band 7, and pressure is thereby applied to the plastics sleeve. Even whilst soft, the material of the plastics sleeve remains capable of transmitting compression from the dies to the sealing band 7, so that the latter is compressed with a force substantially greaterthan that which can be exerted by simple thermal shrinkage of the plastics material of the sleeve. The material of the sealing ring is thereby pre-stressed so that, afterthe plastics sleeve has cooled and set in position, and the pres- sure dies have been removed, a very substantial radial pressure exists between the sealing ring, the pipe, and the internal surface of the plastics sleeve, providing a reliable seal.

To form a seal between the inserted spigot end 3 and the socket 6, the spigot end may have an external sealing ring or band to engage the internal su rface of the plastics socket, for example as described in 1,417,371 or971,124. Alternatively or additionally the socket maybe fitted with a sealing ringof re- silient material, in any convenient way. Forexample the sealing ring may be secured in the end of the socket by adhesive, by solventwelding, by direct bonding, or mechanically. in the case of a sealing ring bonded directlyto the plastics socketJorex- ample by a thermal bond, or by having the sealing ring and plastics socket injection moulded one in contactwith the other, it may be necessaryto ensure thatthe socket region of the thermoplastic sleeve is notsubjected to the heating, expansion and shrink- ing process needed to fitthe other region 5 onto the pipe end.

In the illustrated embodiment, the socket has a sealing ring 8 with a f lange 9 held in position by a locking ring 10 snap-fitted on the end of the socket, in a manner analogous to the well known Hepsieve pipe 3 l& GB 2 181 201 A 3 coupling.

The use of a pre-stressed sealing ring between the pipe end and the shrunk-on plastics sleeve, substantially eliminates any need for a bonding orsealing composition between the pipe and plastics sleeve, however such a material may be provided if desired, for example in the manner described in 1,417, 371.

Figure 2 illustrates another embodiment of the invention. A plastics sleeve 14 is shrink-fitted on one end of a clay pipe 1 to form a projecting socket 16. In this embodiment, the region 15 of the plastics sleeve that is shrink-fitted on the pipe 1, is an intermediate region. The sleeve end region 17 opposite the socket region 16 has a greater internal diameterthan the ex- ternal diameter of the pipe, and is provided with a sealing ring 18 at its end. The sealing ring 18 is attached to the sleeve region 17 in any convenient way, for example in any of the ways mentioned with reference to the sealing ring of the socket described with referenceto Figure 1.

Thesleeve region 17 is initially moulded over-sized relativetothe external surfaceofthe pipe length whereasthe intermediate region 15 is initiallyundersized relativetothe external surface of the pipe length. The sealing ring 18 is designedtoform acornpression seal between the internal surface of the sleeve region 17, and the external surface of the pipe, when the plastics sleeve 14 is fitted overthe pipe end.

To fitthe plastics sleeve 14 on the pipe end. the intermediate region 15 and optionallythe socket region 16 are heated to a temperature belowthe degradation temperature of the plastics material of the sleeve, at leastthe region 15 is expanded and fitted overthe pipe end, and the sleeve is allowed to cool so thatthe region 15 shrinks into intimate contactwith the external surface of the pipe end. A bonding or sealing agent may be provided between the region 15 of the sleeve, and the external surface of the pipe. The shrink- fitted region 15 provides a primary seal between the socket and the pipe. The sealing ring 18 provides a secondary or back up seal.

The socket region 16 can seal againstthe inserted spigot pipe end 13 in any convenient way for example any of the ways mentioned above with reference to Figure 1. In the illustrated embodiment, an elastomeric 0-ring 19 is seated in a circumferential groove in the external surface of the spigot end 13,to seal againstthe internal surface of the socket 16.

The illustrated pipejoints have plastics coupling sleeves onto the external surfaces of the pipe lengths 115 of uniform external diameter. This construction is suitable for conventional pipe laying in trenches. Pipes are however also laid by direct insertion in the ground, the pipe lengths being pulled or pushed into the ground (for example by a mole plough or a pipe jacking technique). For such techniques,the pipe joints should have external diameters not greater than the external diameter of the pipes themselves. Accordingly, the pipes may be provided with rebates attheir endsto receivethe plastics sleeves so that these are flush with, or inset relative to, the external surfaces of the pipes. in this case, the plastics sleeve will usually be a simpletube of constant internal and external diameter, for example a length cutfrom an extruded plastics pipe.

Claims

1. Asocket-ended pipe comprising a pipe length, a sleeve of flexible resilient shrinkable thermoplastics material partly embracing and partly protruding beyond an end of the pipe length, for receiving a spigotend of a further pipe length, and a resilient annular sealing member on the external circu- mference of the said socketed end, trapped between the external surface of the pipe length and the internal surface of the plastics sleeve, the plastics sleeve having been shrink-fitted overthe said pipe end and sealing member under compressive stress wherebythe said sealing member is maintained under compression.

2. Asocket-ended pipe as claimed in claim 1 in which the regions of the sleeve which are not in contact with the sealing member, have been sh rink-fitted into intimate contact with the external surface of the pipe length.

3. Asocket-ended pipe as claimed in claim 1 or2, in which the sealing member is a flat band.

4. Asocket-ended pipe as claimed in claim 1 or2, in which the sealing member is an 0-ring.

5. Asocket-ended pipe as claimed in claim 4in which the sealing ring is located in a circumferential groove in the external surface of the pipe length.

6. A method of providing a socketon an end of a pipe length, for receiving a spigot end of a further pipe length, comprising providing a sleeve of flexible resilient shrinkable thermoplastics material, heating the sleeve, expanding at least one end portion of the sleeve, fitting the expanded sleeve end portion over the end of the pipe length, disposing an annular sealing member between the external surface of the pipe length and the internal surface of the sleeve, subjecting the heated sleeve to inward compression at least in the region of the said sealing member, and allowing the sleeve to cool and shrink onto the pipe length end and the sealing memberwhile subjected to the said compression, and removing the said compression.

7. The method claimed in claim 6, comprising forcibly expanding the heated sleeve before orduring fitting of the sleeve onto the end of the pipe length.

8. Asocket-ended pipe comprising a pipe length, and a thermoplastics sleeve having a first portion projecting from an end of the pipe length to form a socket, an intermediate portion shrink-fitted on the end of the pip3 length to secure the sleeve, and a further portion encircling the pipe length but not shrink-fitted thereon, and a resilient annularsealing element provided on the last-mentioned region of the sleevefor engaging and sealing againstthe external circumferential surface of the pipe length.

9. Asocket-ended pipe as claimed in claim 8, having a polymer material between the shrink-fitted re- gion of the sleeve, and the external surface of the pipe length.

10. A socket ended pipe as claimed in claim 8 or9 further comprising a resilient annular sealing member provided between the external surface of the pipe length and the internal surface of the sleeve 4 GB 2 181 201 A 4 in the shrink-fitted region of the latter, this region having been shrink-fitted while subjected to exter nally applied compression.

11. A method of making a socket-ended pipe, comprising providing a pipe length, providing a sleeve of shrinkable thermoplastic material having a firstend region provided with a resilient annularsea ling element and dimensioned to fit on an end of the pipe length, a socket-forming second end region, and an intermediate region, fitting the first end region and the intermediate region of the sleeve onto an end of the pipe length, and shrink-fitting onlythe said intermediate region of the sleeve into firm engagementwith the external surface of the pipe length.

12. The method according to claim 1J further comprising providing a resilient annular sealing member between the said intermediate region and the external surface of the pipe length, and applying compression to the intermediate region during the shrink-fitting thereof and therebyto the said sealing member.

13. The method of claim 11 or 12 further comprising providing a polymer bonding agent or sealant be- tween the said intermediate region and the external surface of the pipe length.

14. A method of making a socket ended pipe comprising providing a pipe length, providing a prefabricated shrinkable plastics sleeve, heating and ex- panding the sleeve and fitting it on an end of the pipe length, with a portion projecting from the pipe length end to form a coupling socketfor receiving a sprigot end of a further pipe, allowing itto cool and contract onto the pipe length, providing a bonding and/orsea- ling agent between the external surface of the pipe length and the internal surface of the sleeve, and subjecting the heated sleeve to inwards compression at least in the region of the said agent as the sleeve cools and shrinks onto the pipe length.

15. Socket-ended pipes substantiallyas herein described with reference to figure 1 orfigure 2 of the drawings.

16. Methods of making socket-ended pipes, substantially as herein described with reference to figure 1 orfigure 2 of the drawings.

Printed for Her Majesty's Stationery Office by Croydon Printing Company (L1 K) Ltd,2i87, D89916135. Published by The Patent Office, 25Southampton Buildings, London, WC2A l AY, from which copies may be obtained.