GB2160144A - Shaping pipe ends - Google Patents

Abstract

The invention relates to a method of shaping an end of a thermoplastic pipe to provide it with an external profiled formation suitable for use in creating an end to end joint between two similar pipes by means of a coupling, in particular a vitaulic coupling. The method comprises the steps of locating a heated end zone of a pipe over a mandrel and inside a mould defining a mould cavity complementary to the required profiled formation and applying an axial compressive force between the heated end of the pipe and a position remote therefrom to cause the wall to be urged into the mould cavity to be moulded into the required shape. The invention also relates to moulds suitable for use in the method and to a pipe section having a shaped end fitted with a load transfer sleeve which defines a shoulder formation and a ridge formation spaced inwardly therefrom. <IMAGE>

Description

SPECIFICATION Shaping pipe ends This invention relates to a method of shaping pipe ends. The method may be used in providing extruded pipes produced from thermoplastic material with various forms of end configurations, for example, for providing an extruded pipe section with an integral external shoulder formation, end flange or the like. The invention also relates to mould arrangements suitable for use in carrying out the method, to pipes having ends produced by the method and to pipes having shaped ends reinforced by means of a load transfer sleeve as disclosed herein.

Various industries in South Africa, and particularly the mining industry, have over the years made extensive use of a coupling known as the "vitaulic coupling" for the joining together of metallic pipe sections. The vitaulic coupling has been used to such an extent that it has been made the subject of a Standard Specification of the South African Bureau of Standards under the number 815-1978. Accordingly, for each pipe size on which the vitaulic coupling is to be used it is required for the pipe sections to be joined by such couplings to be fitted, adjacent the pipe ends, with an external shoulder formation of specific dimensions.

With the advent of the PVC piping, and in view of the large supply and stocks of vitaulic couplings or clamps clamps still available to end users, the need arose for an acceptable shoulder construction on the PVC piping whereby the PVC piping could be joined together or incorporated in existing metallic pipe lines by using vitaulic couplings. Various solutions for this need have been suggested and the present applicant is presently successfully marketing the arrangement disclosed in S.A. Patent 82/ 3703.

It is one of the objects of the present invention to provide an alternative method of modifying the end zone of a pipe of thermoplastic material to provide it with a vitaulic shoulder formation, an end flange or with a similar type of profile on the external surface of the pipe wall adjacent the pipe end.

According to the invention a method of modifying the end zone of a plain ended pipe section of thermoplastic material to provide it with an integral profiled formation extending proud of the external surface thereof comprises the steps of [ a ] heating the end zone of the pipe to a temperature at which the pipe constituting material is in a mouldable state, [b] introducing the heated end zone of the pipe into a mould cavity of a mould arrangement comprising a mandrel adapted in use to be received internally of the heated end zone of the pipe end in close fitting relationship therewith, an end member adapted to engage the end surface of the pipe, and a set of jaw members which define a mould cavity complementary to the required profiled formation, [ ci applying an axial compressive force between the pipe end surface disposed in the mould and a position on the pipe remote therefrom thereby to urge the mouldable material in the heated zone to be moulded into the mould cavity and [d] removing the mould arrangement from the modified pipe end after allowing the moulding to set to a suitable degree.

In one form of the invention the axial compressive force may be applied to the heated end surface of the pipe section while the pipe section is held against axial movement relative to the mould.

In another form of the invention the axial compressive force may be applied to the end of the pipe section remote from the heated end thereof, thereby ramming the heated end zone of the pipe section against the end member of the mould arrangement and urging the material of the heated end zone to fill the mould cavity.

In a preferred form of the invention the method is practiced on a pipe section having a wall which has been thickened up in the zone where the profiled formation is to be formed.

The walls of the pipes which are to be shaped accordingly to the invention may be thickened up during extrusion of the pipe section be reducing the take off speed or in any other convenient manner known in the trade. Such thickened up walls produced during extrusion of the pipe section according to known techniques will of necessity result in a pipe section having a reduced inner diameter in the thickened up zone as extruders are conventionally calibrated for the required outer diameter of the extruded pipe.

In this form of the invention the mandrel is selected to be of a diameter equal to the inner diameter of the pipe, and the mandrel is inserted into the pipe while the material from which the pipe is formed is at a temperature at which the material is mouldable at least in the zone to be shaped. Such introduction serves to convert the pipe section from one having a reduced inner diameter to one having an increased outer diameter in that zone.

However, it should be understood that it is not essential in all cases to apply the method of the invention to a pipe of which the wall had been thickened up.

Further according to the invention there is provided a mould arrangement including a mandrel comprising an elongated cylindrical member of circular cross section defining a tip at the front end thereof and a rear end fast with a transverse flange-like base which base defines an annular recess about the cylindrical member, the recess housing an end member in the form of a tamping ring which is operatively associated with a force transmitting arrangement which extends through the base and which is in turn adapted in use to be connected to a drive means adapted to impart linear movement to the force transmitting arrangement thereby to cause the tamping ring to move along at least part of the length of the cylindrical member.

Preferably the tamping ring is received in flush relationship with the face of the base member of the mandrel. The width of the tamping ring is preferably equal to the desired overall final wall thickness of the pipe at the finish of the pipe at which the shoulder is to be formed.

The force transmitting arrangement may comprise a plurality of push rods secured to the tamping ring and extending through the base in the recessed zone thereof.

The push rods may be secured at their ends remote from the tamping ring to a pressure plate and the pressure plate may be adapted to be connected to a drive means.

In a preferred form of the invention the drive means is in the form of an hydraulic ram.

Further according to this aspect of the present invention the mould arrangement includes two or more forming jaw elements including recesses which in operative disposition relative to one another collectively define a tubular arrrangement having a stepped bore, the forming jaws being mounted for movement towards and away from each other to close and open the mould, the jaws being positioned to exend about the mandrel and to slide over the base.

According to an alternative form of the invention the mould arrangement comprises a plurality of mould segments mounted on a support structure to be movable towards and away from each other respectively to close and open the mould, a mandrel located centrally of the mould segments and constituted by a cylindrical member of circular cross sectional configuration defining a tip at the front end thereof and a rear end which rear end is secured to a base member which in turn is supported by the support structure, and an end member in the form of a ring formation constituting a sliding fit about the mandrel, the mould segments and the end member being suitably recessed collectively to define a stepped bore locate about the mandrel when the mould is in closed condition.

In the preferred form of the invention the bore which is collectively defined by the mould segments and end member when the mould is in closed condition defines a stepped bore featuring two radially extending annular steps and three annular landings adjacent the steps being an outer annular landing the diameter of which is equal to the outer diameter of the pipe to be adapted by the means of the mould, a central annular landing the diameter of which is larger than that of the outer landing and an inner annular landing the diameter of which is again larger than the diameter of the central annular landing.

The inner annular landing may in part be constituted by a landing formation formed in the jaw members and in part by a shoulder formation formed in the end member.

In a further preferred form of the invention the central annular landing defines an annular recess formation intermediate the steps flanking the central annular landing.

The annular recess in the central annular landing preferably defines a floor zone and a pair of outwardly diverging sloping side walls extending between the floor zone and the surface constituting the central landing.

In a preferred form of the invention when employing a mould having an annular recess in the central landing a load transfer sleeve arrangement is located in the mould before the heated zone of the pipe is located in the mould, the sleeve being shaped to be accommodated neatly in the stepped bore to overlie at least the central landing, to line the annular recess therein, to extend along the step between the central landing and the inner landing and to extend partway across the inner landing.

Preferably the load transfer sleeve further includes an inwardly directed flange formation at its periphery which is to be located nearest the step between the outer annular landing and the central annular landing.

The load transfer sleeve is preferably constituted by a metal sleeve, the composition of which would be dependent on the application to which the pipe is eventually to be put.The sleeve may accordingly comprise a mild steel or stainless steel sleeve.

The mandrel and mould segments preferably include passages therein through which passages a heating fluid is in use caused to flow to heat the mould to an operating temperature.

The mould is in use preferably heated to an operating temperature of about 70or.

The heated zone of the pipe should preferably be introduced into the mould while the temperature of the material is about 160- 170"C.

Further according to the invention there is provided a pipe section having a wall formation of thermoplastic material and defining end surfaces at the extremities thereof, at least one end zone of the pipe section being fitted with an exterior load transfer sleeve, the sleeve defining a shoulder surface located inwardly of the end surface and facing opposite to the end surface, and the sleeve further defining a circumferential external ridge formation and an associated valley formation in the internal surface thereof, the ridge formation being disposed intermediate the shoulder surface and the end of the sleeve remote from the shoulder to define and external groove between the ridge and the shoulder surface, the thermoplastic material covered by the sleeve being shaped to fill at least the valley formation and to define an abutment formation between the end surface of the pipe wall and the shoulder surface.

Preferably the sleeve defines a forwardly projecting peripheral lip formation which extends partway across the transverse surface of the abutment formation which interconnects the shoulder surface and the end surface.

It is further preferable for the end of the sleeve remote from the shoulder surface to include a radially extending and inwardly directed flange formation.

An example of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic cross sectional representation of a pipe section having thickened up walls; Figure 2 is a schematic cross sectional representation of the pipe of Figure 1 after introduction of the mandrel into the pipe and with the forming jaws of the mould in open condition [with both jaws and the mandrel shown in cross sections; Figure 3 is a view similar to that of Figure 2 but with the jaws of mould in closed disposition and the tamping ring in forward disposition; Figure 4 is a side view of an alternative end shaping installation according to the invention;; Figure 5 is a plan view of a mould arrangement according to the invention as used in the installation of Figure 4, the left hand half of the drawing showing the left hand mould half in open condition with the end ring in its forward disposition while the right hand half of the drawing shows the right hand mould half in closed condition and the end ring in its retracted disposition; Figure 6 is a front view of the mould arrangement of Figure 5 showing the open position of the left hand mould half in chain dotted lines; Figure 7 is a sectional view on line VII-VII in Figure 6, the drawing illustrating a pipe end in the lower part of the mould cavity only; Figure 8 is a sectional view of an alternative mould to the one shown in Figure 7, again with a pipe end in the lower part of the mould cavity only; and Figure 9 is a partly sectioned elevational view of the end zone of a pipe section fitted with a load transferring sleeve according to the present invention.

In Figure 1 is shown a section of an unplasticised polyvinylchloride [u-PVC] pipe 1 produced in the conventional manner by means of an extrusion process. The pipe shown in Figure 1 was extruded in the direction shown by arrow Z and during the extrusion process the haul off speed was reduced to cause a thickening up of the pipe wall and a consequent reduction of the inner diameter of the pipe from an original value b to a value a in the thickened up zone.

It will be understood by those skilled in the art that the extrusion process need not be interrupted after each thickened up zone had been produced. It would be preferred in a continuous extrusion process to run the extrusion process at a reduced take off speed at predetermined intervals and to subsequently cut the continuously extruded element to desired lengths at the thickened up zones.

In order to shape the end of a pipe as shown in Figure 1 to provide it with an external profiled formation defining two spaced shoulders,the pipe end is heated in an oven at about 180 so that the material is heated to a temperature at which it is plastic enough to be worked. The forming cylinder 3 of a mandrel 2 is then introduced into the reduced bore of the pipe. It will be seen that the leading end of the mandrel is chamferred to facilitate such introduction.

The introduction of the mandrel into the pipe causes the pipe wall in the thickened up zone to bulge outwardly [as can be seen at 1a in Figure 2] and accordingly that zone is converted from an arrangement having a reduced inner diameter [relative to the nominal inside diameter of the rest of the pipe length] to one having an increased outer diameter.

As can be seen in Figures 2 and 3 the mandrel comprises a forming cylinder 3 having a chamferred tip and which is fast at its trailing end to a base 4.

The base is provided with an annular recess 5 [see Figure 3] in which recess an annular ring 6 is received to be flush with the face of the base. The ring 6 is connected to a plurality of push rods 7 [of which two are shown] which push rods 7 are in turn connected to a pressure plate 8. The pressure plate 8 is operatively connected to the moving arm of an hydraulic ram arrangement 9.

Also shown in Figures 2 and 3 are two mounted halves or forming jaws [10a, 10b] which collectively define a cylindrical element having a stepped bore presenting two steps indicated at 11 and 12 and three annular landings namely an outer landing 14, a central annular landing 15 and an inner annular landing 16.

Once the forming cylinder 3 of the mandrel has been introduced into the pipe section, as shown in Figure 2, the mould halves 10a and 10b are closed by means of hydraulic rams [not shown] arranged to move the mould halves towards one another in the directions indicated by arrows X and Y.

It will be appreciated that in this manner a precharged mould arrangement is achieved with the material indicated at 1a presenting the charge of the mould defined between the forming jaw 10a, 10b and the forming cylinder 3 of the mandrel 2. In order to ensure proper moulding of the charge, the hydraulic ram 9 is activated thereby to move the tamping ring 6 into the mould cavity to compress the material 1a in the mould cavity to ensure accurate moulding in conformity to the configuration of the mould cavity.

After allowing due time for setting of the material to a required degree, the tamping ring 6 is withdrawn and the forming jaws are opened to remove the formed pipe from the mould.

In the embodiment illustrated in Figures 2 and 3 of the accompanying drawings the shoulder formation indicated at 13 is intended to be used to form a vitaulic joint with the aid of a standard vitaulic clamp and seal ring.As moulded the length C of the shoulder 13 may be excess of the length of standard vitaulic shoulders and would accordingly be trimmed to conform to the standard vitaulic shoulder length, if necessary.

In Figures 4 to 7 of the accompanying drawings an alternative method for shaping a pipe end according to the invention is illustrated.

In Figure 4 an installation for carrying out the method of the invention is schematically shown to comprise a mould housing 40 which houses a mould arrangement 40a of the type which will be described in greater detail below. A plurality of pipe supports 41 are erected in line and arranged accurately to guide a pipe to be modified into the mould arrangement. Each pipe support comprises a standard 42 on which a pair of rollers 43 are mounted in V-configuration relative to one another by means of a mounting frame 44. The installation further includes a hydraulic ram 45 arranged upon activation to move the end of a pipe 46 supported on the rollers 43 into the mould 40a.

Prior to locating the pipe 46 onto the rollers to have its end zone shaped in the mould, the end zone to be shaped is heated in the oven at about 190-195-C to ensure that when the pipe is moved into the mould 40a the temperature of the material constituting the pipe wall is at about 160-170 C.

The hydraulic ram is then activated to move the pipe 46 into the mould [which may still be partially open at this stage ] at a speed of about 5 cm per second until the leading end of the pipe contacts the inner end of the mould at which point the mould is closed [if not already closed] and the hydraulic ram 45 is caused to exert a strong thrust on the trailing end of the pipe thus causing the heated material disposed in the mould to be deformed and moulded in the mould cavity. Once the material has been allowed to set to a sufficient extent, the mould is opened and the pipe is urged off the mandrel by means of the end ring or stripper as will be described in greater detail below.

Turning now to the detailed representations of a mould arrangement used in the method of the present invention, it should be noted that the same reference numerals are used in Figures 5 to 8 to denote corresponding parts but such parts are not necessarily indicated by the same reference numerals as used in Figures 1 to 4.

In Figures 5 to 8 a mould arrangement 50 is shown to include a support structure comprising a platform 51, a back plate 52, side plates 53 and bracing brackets 54.

The mould arrangement further comprises a pair of mould halves or forming jaws 55 which are slidably received on the platform 51 and held in place by means of track elements 56.

A forming mandrel 57 is located centrally of the forming jaws and secured to the back plate 52.

An end member 58, which also serves as an ejector ring is slidably received about the mandrel and is secured to a set of push rods, one of which is shown at 89, which push rods extend through bushed apertures 52a provided through the back plate.

The mandrel 57 is shown to be made up of three segments and the central portion of the mandrel is provided with a plurality of axial passages, one of which is shown at 57a. These passages are cross linked by means of recesses provided in the end pieces of the mandrel and connectors 60 connected to the rear end of the mandrel 57 and extending through an aperture in the back plate 52 to provide an inlet and an outlet for heating fluid which fluid may be circulated through the passages in the mandrel to heat the mandrel.

Similarly the forming jaws are heated by means of a circulating heating fluid introduced into the one forming jaw at an inlet illustrated at 61 in Figure 6 to flow through a series of passages to an oulet from that jaw which is linked by a flexible pipe 62 to an inlet of the second forming jaw which is in fluid connection with an outer 63 in that jaw via a series of passages in that jaw.

The end ring 58 is provided with an external ridge formation 58a which is arranged to mate with a complementary recess 55a in the forming jaws 55 to provide a key arrangement by which proper orientation between the ring 58 and the forming jaws 55 is ensured when the mould is in closed condition.

As can best be seen in Figure 5 [right hand side] and in Figures 7 and 8, an annular mould cavity 64 is formed between the mandrel 57 and the internal surface of the stepped bore defined by the two mould halves 55 when these are in closed condition.

The stepped bore of the mould of Figures 5 and 7 comprises a first step 65 and a second step 66 to define three annular landings namely an outer landing 67, a central landing 68 and an inner landing 69. The central landing 68 includes an annular groove 70 constituted by a floor region 70a and a pair of opposed walls 70b which diverge outwardly and upwardly from the floor to the surface of the central landing 68.lit will further be seen from Figure 7 that the inner landing 69 is constituted partly by the forming jaw 55 and partly by the ring 58.

The mould cavity further has an outwardly diverging outer end 71 [which is shown to be sectioned in Figure 5] to facilitate guiding of the heated segment of the pipe into the mould.

In use of the mould of Figures 5, 6 and 7 a load transfer sleeve 72 of cross sectional configuration as shown in Figures 7 and 9 is located in the stepped bore to line the recess 70 and to extend over the landing 68, along the step 66 and partway over the landing 69. The heated end of a pipe section 46 is then introduced into the mould, while the latter is in closed condition, until the edge of the pipe comes into contact with the end surface 73 of the mould cavity. The hydraulic ram referred to above with reference to Figure 4 is then caused to exert a strong axial thrust to the remote end of the pipe thereby to cause the heat softened material disposed in the mould cavity to be deformed to fill the mould cavity in the area between the central and inner landings [68 and 69] and the mandrel and, of course, the area of the recess 70.

Once the deformed material has cooled and set to a sufficient degree the mould is opened by moving the jaws away from each other by means of the hydraulic rams 80 and 81 which are connected to the mould halves 55 and arranged to cause the mould halves to slide along the platform 51.The end member or ejector ring 58 is then caused to move forward along the mandrel 57 by means of an hydraulic ram secured to the rods 89 thereby to strip the pipe from the mandrel.

The arrangement shown in Figure 8 is in most respects indentical to the arrangements shown in Figures 5 to 7 but with the exception that the central landing does not include an annular recess.

The arrangement of Figure 8 may be used to produce a shaped pipe end without a load transfer sleeve. The pipe so produced should be suitable for use in relatively low pressure applications where the incorporation of a load transfer sleeve may be considered superfluous due to relatively low stresses being applied to the shoulder surface of the shaped pipe end which is utilized to create a vitaulic coupling.

Referring now to Figure 9, the thermoplastic pipe 46 is shown to have a wall formation 91 which defines an end face 92 at the extremity thereof. The end zone of the pipe 46 is fitted with a load transfer sleeve 72 which is preferably of stainless steel.

The sleeve 72 defines a shoulder surface 93 which faces in the direction opposite to the direction in which the end surface 92 faces. Intermediate the shoulder 93 and the remote end 94 of the sleeve there is provided a circumferential, exterior ridge formation 95 on the sleeve which ridge formation 95 has a valley formation 96 associated therewith in the interior surface of the sleeve. The sleeve further includes a forwardly projecting peripheral lip formation 97 which extends partway across a surface 98 which together with the shoulder 93 and the end surface 92 define an abutment at the end of the pipe. Finally the sleeve includes a radially inwardly directed flange formation 99 at the remote end 94 thereof. The thermoplastic material from which the pipe is constituted is shaped and moulded completely to fill the valley 96 and to be disposed about the flange 99 to anchor the sleeve to the pipe wall.

It will be seen that axial forces applied against the shoulder surface 93 are in use in part transferred via the sleeve 72 to the ridge formation located in the valley 96 and further to the pipe material disposed about the flange 99.

In use the flange of a vitaulic coupling may be received in the groove 100 to bear against the shoulder 93 while the surface 98 serves as a seat for the standard vitaulic seal.

Many variations of the invention may be thought of without thereby departing from the scope of the invention.

Claims (43)

1. A method of modifying the end zone of a plain ended pipe section of thermoplastic material to provide it with an integral profiled formation extending proud of the external surface thereof comprising the steps of [a] heating the end zone of the pipe to a temperature at which the pipe constituting material is in a mouldable state, [b] introducing the heated end zone of the pipe into a mould cavity of a mould arrangement comprising a mandrel adapted in use to be received internally of the heated end zone of the pipe and in close fitting relationship therewith, an end member adapted to engage the end surface of the pipe and a set of jaw members which define a mould cavity complementary to the required profiled formation, [c] applying an axial compressive force between the pipe end surface disposed in the mould and a position on the pipe remote therefrom thereby to urge the mouldable material in the heated zone to be compressed and moulded into the mould cavity and [d] removing the mould arrangement from the modified pipe end after allowing the moulding to set to a suitable degree.

2. The method of claim 1 wherein the axial compressive force is applied to the heated end surface of the pipe section while the pipe section is held against axial movement relative to the mould.

3. The method of claim 1 wherein the axial compressive force is applied to the end of the pipe section remote from the heated end thereof, thereby ramming the heated end zone of the pipe section against the end member of the mould arrangement and urging the material of the heated end zone to fill the mould cavity.

4. The method of any one of claims 1 to 3 wherein the pipe section has a wall which has been thickened up in the zone where the profiled formation is to be formed.

5. The method of any one of claims 1 to 4 wherein the mandrel is selected to be of a diameter equal to the inner diameter of the pipe, and the mandrel is inserted into the pipe while the material from which the pipe is formed is at a temperature at which the material is mouldable at least in the zone to be shaped.

6. The method of any one of claims 1 to 5 characterised therein that the mould arangement includes a mandrel comprising an elongated cylindrical member of circular cross section defining a tip at the front end thereof and a rear end fast with a transverse flange-like base which base defines an annular recess about the cylindrical member, the recess housing an end member in the form of a tamping ring which is operatively associated with a force transmitting arrangement which extends through the base and which is in turn connected to a drive means arranged on activation to impart linear movement to the force transmitting arrangement thereby to cause the tamping ring to move along at least part of the length of the cylindrical member.

7. The method of claim 6 characterised in that the tamping ring is received in flush relationship with the face of the base member of the mandrel.

8. The method of claim 7 characterised in that the width of the tamping ring is equal to the overall final wall thickness of the pipe at the finish of the pipe at which the formation is to be formed.

9. The method of any one of claims 6 to 8 characterised in that the force transmitting arrangement comprises a plurality of push rods secured to the tamping ring and extending through the base in the recessed zone thereof.

10. The method of claim 9 characterised in that the push rods are secured at their ends remote from the tamping ring to a pressure plate and wherein the pressure plate is adapted to be connected to a drive means.

11. The method of any one of claims 6 to 10 in which the drive means is in the form of an hydraulic ram.

12. The method of any one claims 6 to 11 characterised in that the mould arrangement includes two or more forming jaw elements including recesses which in operative disposition relative to one another collectively define a tubular arrangement having a stepped bore, the forming jaws being mounted for movement towards and away from each other to close and open the mould, the jaws being positioned to extend about the mandrel and to slide over the base.

13. The method of any one of claims 1 to 5 characterised in that the mould arrangement comprises a plurality of mould segments mounted on a support structure to be movable towards and away from each other respectively to close and open the mould. a mandrel located centrally of the mould segments and constituted by a cylindrical member of circular cross sectional configuration defining a tip at the front end thereof and a rear end which rear end is secured to a base member which in turn is supported by the support structure, and an end member in the form of a ring formation constituting a sliding fit about the mandrel, the mould segments and the end member being suitably recessed collectively to define a stepped bore located about the mandrel when the mould is in closed condition.

14. The method of claim 13 characterised in that the bore which is collectively defined by the mould segments and end member when the mould is in closed condition defines a stepped bore featuring two radially extending annular steps and three annular landings adjacent the steps being an outer annular landing the diameter of which is equal to the outer diameter of the pipe to be adapted by means of the mould, a central annular landing the diameter of which is larger than that of the outer landing and an inner annular landing the diameter of which is again larger than the diameter of the central annular landing.

15. The method of claim 14 characterised in that the inner annular landing is in part constituted by a landing formation formed in the jaw members and in part by a shoulder formation formed in the end member.

16. The method of claim 13 or 14 characterised in that the central annular landing defines an annular recess formation intermediate the steps flanking the central annular landing.

17. The method of claim 16 characterised in that the annular recess in the central annular landing defines a floor zone and a pair of outwardly diverging sloping side walls extending between the floor zone and the surface constituting the central landing.

18. The method of any one of claims 16 or 17 characterised in that a load transfer sleeve arrangement is located in the mould before the heated zone of the pipe is located in the mould, the sleeve being shaped to be accommodated neatly in the stepped bore to overlie at least the central landing, to line the annular recess therein, to extend along the step between the central landing and the inner landing and to extend partway across the inner landing.

19. The method of claim 18 characterised in that the load transfer sleeve includes an inwardly directed flange formation at its periphery which is located nearest the step between the outer annular landing and the central annular landing.

20. The method of claim 18 or 19 characterised in that the load transfer sleeve is of metal.

21. The method of any one of the preceding claims characterised in that the mould halves and the mandrel are heated to an operating temperature of about 70 C.

22. The method of any one of the preceding claims characterised in that the heated zone of the pipe is introduced into the mould while the temperature of the material is about 160-170C.

23. A mould arrangement including a mandrel comprising an elongated cylindrical former of circular cross section defining a tip at the front end thereof and a rear end fast with a transverse flange-like base which defines an annular recess about the cylindrical former, the recess housing an end member in the form of a tamping ring which is operatively asociated with a force transmitting arrangement which extends through the base and which is in turn adapted in use to be connected to a drive means adapted to impart linear movement to the force transmitting arrangement thereby to cause the tamping ring to move along at least part of the length of the cylindrical former.

24. The mould arrangement of claim 23 in which the tamping ring is received in flush relationship with the face of the base member of the mandrel.

25. The mould arrangement of claim 24 in which the force transmitting arrangement comprises a plurality of push rods secured to the tamping ring and extending through the base in the recessed zone thereof.

26. The mould arrangement of claim 25 in which the push rods are secured at their ends remote from the tamping ring to a pressure plate and the pressure plate is adapted to be connected to a drive means.

27. The mould arrangement of claim 26 in which the pressure plate is adapted to be connected to a drive means in the form of an hydraulic ram.

28. The mould arrangement of any one of claims 23 to 27 which includes two or more forming jaw elements including recesses which in operative disposition relative to one another collectively define a tubular arrangement having a stepped bore, the forming jaws being mounted for movement towards and away from each other to close and open the mould, the jaws being positioned to extend about the mandrel and to slide over the base.

29. A mould arrangement comprising a plurality of mould segments mounted on a support structure to be movable towards and away from each other respectively to close and open the mould, a mandrel located centrally of the mould segments and constituted by a cylindrical member of circular cross sectional configuration defining a tip at the front end thereof and a rear end which is secured to a base member which in turn is supported by the structure, and an end member in the form of a ring formation constituting a sliding fit about the mandrel, the mould segments and the end member being suitably recessed collectively to define a stepped bore located about the mandrel when the mould is in closed condition.

30. The mould arrangement of claim 29 in which the bore which is collectively defined by the mould segments and end member when the mould is in closed condition defines a stepped bore featuring two radially extending annular steps and three annular landings adjacent the steps being an outer annular landing the diameter of which is equal to the outer diameter of the pipe to be adapted by means of the mould, a central annular landing the diameter of which is larger than that of the outer landing and an inner annular landing the diameter of which is again larger than the diameter of the central annular landing.

31. The mould arrangement of claim 30 in which the inner annular landing is in part constituted by a landing formation formed in the jaw members and in part by a shoulder formation formed in the end member.

32. The mould arrangement of claim 30 or 31 in which the central annular landing defines an annular recess formation intermediate the steps flanking the central annular landing.

33. The mould arrangement of claim 32 in which the annular recess in the central annular landing defines a floor zone and a pair of outwardly diverging sloping side walls extending between the floor zone and the surface constituting the central landing.

34. The mould arrangement of any one of claims 23 to 33 in which the mandrel and mould segments include passages therein through which passages a heating fluid may in use be caused to flow to heat the mould to an operating temperature.

35. A pipe section having a wall formation of thermoplastic material and defining end surfaces at the extremities thereof, at least end one zone of the pipe section being fitted with an exterior load transfer sleeve, the sleeve defining a shoulder surface located inwardly of the end surface and facing opposite to the end surface, and the sleeve further defining a circumferential external ridge formation and an associated valley formation on the internal surface thereof, the ridge formation being disposed intermediate the shoulder surface and the end of the sleeve remote from the shoulder to define an external groove between the ridge and the shoulder surface, the thermoplastic material covered by the sleeve being shaped to fill at least the valley formation and to define an abutment formation between the end surface of the pipe wall and the shoulder surface.

36. The pipe section of claim 36 wherein the sleeve defines a forwardly projecting peripheral lip formation which extends partway across the transverse surface of the abutment formation which interconnects the shoulder surface and the end surface.

37. The pipe section of claim 35 or claim 36 wherein the end of the sleeve remote from the shoulder surface includes a radially extending and inwardly directed flange formation which extends into the wall constituting material.

38. The pipe section of any one of claims 35 to 37 wherein the sleeve is a metal sleeve.

39. A method of shaping a pipe end substantially as herein described with reference to the accompanying drawings.

40. A mould arrangement substantially as herein described with reference to the accompanying Figures 2 and 3.

41. A mould arrangement substantially as herein described with reference to the accompanying Figures 4 to 7.

42. A mould arrangement substantially as herein described with reference to the accompanying Figure 8.

43. A pipe section substantially as herein described with reference to the accompanying Figure 9.