WO2000007803A1

WO2000007803A1 - Socket joint of plastic pipe sections

Info

Publication number: WO2000007803A1
Application number: PCT/NL1999/000496
Authority: WO
Inventors: Jan Visscher
Original assignee: Wavin B.V.
Priority date: 1998-08-07
Filing date: 1999-08-04
Publication date: 2000-02-17
Also published as: AU5309199A; NL1009822C2

Abstract

Method for producing a socket joint between a first pipe section (1) and a second pipe (2) section, in which the first pipe section is provided with a socket (3) of biaxially oriented thermoplastic plastic material for accommodating an insert end of the second pipe section which fits into the socket, the second pipe section being inserted with its insert end into the socket. An annular region (c) of the socket is heated, in such a way that the heated annular region of the socket shrinks onto the insert end inserted therein.

Description

Socket joint of plastic pipe sections

The present invention relates to the joining together of plastic pipe sections, such as pipes and other pipe parts, for example bends, T-pieces, flanges, shut-off valves etc. In particular, the invention relates to the joining of pipe sections of biaxially oriented plastic material .

It is generally known to produce pipelines from pipes which are provided at one of their ends with an socket, so that the pipes can be joined to each other by inserting one pipe with its insert end into the socket formed on the adjacent pipe. In order to obtain the desired seal between the socket and the pipe section inserted therein, it is known to provide an internal circumferential groove in the socket, in which groove a sealing ring is accommodated. NL-A-9400894 and W097/33739 describe methods for forming such an socket on the end of a pipe of biaxially oriented thermoplastic plastic material, in particular polyvinyl chloride.

In practice, the medium which is conveyed through such a pipeline will often be under pressure, so that the joint between the pipes is axially loaded and the insert end of one pipe will tend to move out of the socket of the other pipe. Mechanical loads acting upon the pipeline, such as, for example, those caused by settling of the ground in the trench in which the pipeline has been laid, can also give rise to an axial load upon the socket joint between the pipes.

The object of the present invention is to provide a socket joint, in particular between pipe sections of biaxially oriented thermoplastic plastic material, which can resist in particular axial loads, which tend to move the pipe sections away from each other.

In particular, the object of the present invention is to provide a socket joint which in practice can be achieved in a simple manner and with great reliability even when the work needed to establish the socket joint has to be carried out in a trench in the ground.

According to a first aspect thereof, the present invention provides a method according to the preamble of claim 1, which method is characterized in that, after the insert end has been inserted into the socket, only an annular region which forms part of the socket is heated, in such a way that the heated annular region of the socket reduces in diameter and shrinks onto the insert end inserted into it.

The invention provides for use to be made of the tendency of biaxially oriented thermoplastic plastic material to shrink when appropriately heated, both in the axial and in the radial direction, with the result that the socket ultimately sits tightly on the insert end. If the insert end is also made of biaxially oriented thermoplastic plastic material, the heating of the socket must be carried out in such a way that the insert end itself heats to a lesser degree or hardly at all, so that the insert end is prevented from shrinking (too) greatly, which would lead to the socket not resting - or not resting sufficiently - against the insert end.

There is preferably a positively locking joint between the insert end and the socket, which is advantageously achieved by the fact that the insert end is provided beforehand with a circumferential groove on the outside, or by proceeding in such a way that the shrinking annular region of the socket presses a groove into the insert end. At a distance from the free end of the socket, the socket is preferably provided with an internal sealing ring, which is designed to rest against the insert end of the second pipe section, the socket being heated mainly in the region between the sealing ring and the free end of the socket, with the result that this part grips clamps down on the insert end. If the insert end is likewise made of biaxially oriented thermoplastic plastic material, it is preferable for the insert end, at least at the position of the sealing ring, to be subjected to little or no heating when the socket is being heated. Provision may even be made for cooling of the insert end. This ensures that the insert end itself does not shrink through heating, which would result in the desired contact pressure with the sealing ring not being achieved, or a gap even occurring. Provision can also be made for the insert end to be supported internally by a bush, so that the insert end retains its diameter at the position where the sealing ring rests against it . In a preferred embodiment of the method according to the invention, provision is made for a shrink ring to be placed between the socket and the insert end, which shrink ring is made of at least tangentially oriented thermoplastic plastic material, and which shrink ring at the time of placing has such an internal diameter that the insert end fits into it, the method further comprising the step of heating of the shrink ring, so that the shrink ring shrinks and clamps down on the insert end. The shrink ring is preferably made of thermoplastic plastic material, which is substantially and preferably exclusively stretched in the tangential direction, thus in the circumferential direction. The degree of tangential stretching of the shrink ring is preferably greater than that of the insert end. It is preferable when using a shrink ring to heat the shrink ring to a temperature at which the shrink ring shrinks in such a way that substantially in the circumferential region which comes into contact with the shrink ring the insert end reaches a temperature at which the insert end becomes deformable in that region under the influence of the pressure of the shrink ring. This produces an annular groove or constriction in the outer circumference of the insert end, in which groove or constriction the shrink ring then partially lies, while the remainder of the shrink ring projects beyond the insert end. If the socket then projects with an end thereof behind the projecting part of the shrink ring and preferably encloses the shrink ring, said socket joint can take considerable forces without breaking. In order to ensure that it is the shrink ring and possibly the immediately adjacent region of the insert end that are heated and that the region of the insert end situated further away from the shrink ring is barely heated, the invention provides for mainly the shrink ring to be heated. This can be carried out from the outside by heating the surrounding part of the socket, as a result of which the shrink ring situated inside it heats up and shrinks. However, it is preferable to heat specifically the shrink ring itself, for example by placing heating means in the socket near the shrink ring or between the shrink ring and the insert end or providing the shrink ring itself with heating means, which are, for example, (electric) heating elements embedded in or fitted around the shrink ring. As an alternative, provision can also be made for heating of the shrink ring by means of induction.

In particular, if the insert end is made of biaxially oriented plastic material, it is advantageous if the shrink ring, viewed in the lengthwise direction of the socket, has a width which corresponds approximately to the thickness in the radial direction of the shrink ring, so that the contact surface with the insert end is relatively small and during heating of the shrink ring not too much heat is transferred to the insert end, while the contact pressure of the shrink ring remains concentrated on a relatively small surface of the insert end. If there is a considerably larger contact surface, the risk is that the insert end itself will shrink too much.

With the method according to the invention it is preferably ensured that the shrink ring forms a constriction in the insert end, so that on its outside the insert end acquires a circumferential groove in which the shrink ring lies taut. The shrink ring then forms a positively locking joint between the joined parts, so that the joint can be subjected to a heavy load.

In the case of the method according to the invention the shrink ring can be placed loose in the socket when the socket joint is being manufactured, but provision can also be made for the shrink ring to be placed and (provisionally) fixed, for example wedged, in the socket at an earlier stage, preferably at the time of production of the first pipe section. The shrink ring could also form an (detachable) assembly with the sealing ring and could be fixed in the socket in that way.

If the insert end is made of biaxially oriented plastic material, it is also advantageous to place a supporting bush in the insert end. Said bush preferably sits in such a position that the insert end is supported internally against the forces exerted by the shrinking socket and/or the shrink ring. Said bush can be fitted already at the time of manufacture of the pipe and can be, for example, clamped down or glued therein. It is also preferable for the bush to be fitted at the precise point against which the sealing ring of the socket will come to rest, in order to guarantee a correct seal in this way.

The socket for forming the socket joint according to the present invention can be a separate part, by means of which two plastic pipe sections can be connected. If desired, it is possible for said plastic pipe sections not to be biaxially oriented, but to be, for example, stretched or oriented only in the axial direction. The present invention relates in particular to the joining of pipes made of biaxially oriented thermoplastic plastic material by means of a socket joint, each pipe having on one end an socket and on its other end an insert end which fits into the socket of an adjacent pipe. In particular, such a pipe has a uniform cross section along its length, with the integral socket at one end. The present invention will be explained in greater detail below with reference to the drawing, in which exemplary embodiments of the invention are shown. In the drawing : Fig. la shows in longitudinal section and diagrammatically a first pipe provided with an socket with internal sealing ring, and a second pipe which is inserted with its insert end into the socket and the sealing ring;

Fig. lb shows the joint of Figure la after the socket has been heated from the outside near its free end; Fig. 2a shows in a half section according to Fig. la a first pipe provided with an socket which has an internal sealing ring and a shrink ring, and a second pipe which is inserted with its insert end into the socket. Fig. 2b shows the joint of Fig. 2a after the shrink ring and the socket near its free end have been heated; Fig. 3 shows an illustration according to Fig. lb, in which the socket is locally intensely heated; and

Fig. 4 shows an illustration according to Fig. 2b, in which the shrinkage relative to Figure 2a is illustrated.

Figures la and lb show a first pipe 1 and a second pipe 2, which are both made of biaxially oriented thermoplastic plastic material, for example of polyvinyl chloride. The pipes 1, 2 are identical cylindrical pipes, for example intended for the conveyance of (drinking) water or natural gas .

An integral socket 3 is formed on the end of the first pipe 1 shown in Figures la, lb, and the second pipe 2 is designed identical . A relevant feature is that the plastic material of the socket 3 is oriented biaxially, i.e. in the circumferential (tangential) direction and in the axial direction, during the manufacture of the socket 3. The degree of axial stretching of the wall of the socket 3 can be less than that of the wall of the pipe 1, and the degree of axial stretching of the socket 3 may be slight.

The socket 3 serves to accommodate the insert end 4 of the second pipe 2 inserted therein.

In order to guarantee a reliable seal between the two pipes 1, 2, at a distance from the free end of the socket 3 , the socket 3 is provided with an internal flexible sealing ring 5, which is intended for resting in sealing engagement against the insert end of the second pipe 2 , thereby forming a seal . Said sealing ring 5 can be made of, for example, a suitable rubber or rubber-like material. For the accommodation and retention of the sealing ring 5, the wall of the socket 3 defines an internal circumferential groove. The manufacture of such an socket 3 with a sealing ring fitting in an internal groove of the socket is described in the publications mentioned earlier.

In order to produce a socket joint between the pipes 1, 2, the pipe 2 is slid with its insert end 4 into the socket 3, the sealing ring 5 preferably resting directly against the insert end 4, thereby forming a seal. The socket 3 is subsequently heated not over its entire circumference but locally in an annular region having an axial length less than the total axial length of the socket 3. The socket 3 is preferably heated in the annular region "A" which lies between the sealing ring 5 and the free end of the socket 3. This local heating of the socket 3 can be carried out, for example, by winding a narrow strip-shaped electric heating element around the annular region "A" , and thus heating region "A" . If region "A" of the socket 3 is heated sufficiently, it will be found that said region "A" will shrink in the radial direction and also in the axial direction to the state shown in Figure lb. Figure lb shows the original shape by dashed lines, so that it can be seen clearly that the diameter becomes smaller as a result of the heating. In this process, the outer edge region of the socket 3 curls inwards . Since the heating of region "A" also causes the annular region "B" of the insert end 4 below it to heat up and thus become softer and more easily deformable, the shrinking annular region "A" will form a constriction in the annular region "B" in the insert end 4. This produces an external circumferential groove in the insert end 4, in which annular region "A" of the socket 3 engages, thereby forming a positive joint. This method, which is easy to carry out, leads to a socket joint which can take considerable (axial) forces.

It will be clear that the insert end 4 can already be provided beforehand - preferably at the time of production of the pipe 1 - with a circumferential groove or similar recess (es), in which the shrinking part of the socket 3 then ultimately lies, thus forming a positive joint .

It is preferable for the region around the sealing ring 5 to be subjected to little or no heating, in order to prevent shrinkage of that part of the socket 3 and of the insert end 4 situated inside it, since this would lead to a poorer quality of seal. This part may therefore, if desired, be thermally shielded from the effect of the heating means with which annular region "A" is heated and/or a forced cooling of that part of the socket can be carried out. In a variant which is not shown, a supporting bush is placed in the insert end 4, which supporting bush prevents the part of the insert end 4 on which the sealing ring 5 engages from shrinking. If desired, said supporting bush can extend to the position where the constriction occurs or, as will be explained further on, to the position where the shrink ring constricts the insert end. The supporting bush can also extend further inwards and then have a circumferential groove on the outside, which permits the earlier mentioned constriction to be formed. In that way the supporting bush is therefore securely locked into position. Figure 3 shows what happens if the local heating of the socket 3 is concentrated on an annular region "C" between the free end and the sealing ring 5, while the region adjacent to the free end is not heated. Such concentrated annular heating means that the free end does not curl inwards, but annular region "C" forms a constriction in the insert end 4, so that annular region "D" is pressed inwards by it. This also leads to a socket joint which can bear a heavy axial load.

It will be clear that a joint which is resistant to tensile strain is also obtained if the annular region "B" does not form a constriction and it is only by shrinkage of the annular region "A" locally that the socket 3 is made to rest securely against the insert end.

Figures 2a and 2b show two pipes 10, 11 of biaxially oriented plastic material, in which pipe 10 is provided with an integral socket 12 for receiving the insert end 13 of pipe 11.

The socket 12 has a first part 14, with an internal diameter slightly greater than the external diameter of the pipes 10, 11. Closer to the free end of the pipe 10, the socket 12 has a circumferential groove 15 which is open towards the inside, and in which a flexible sealing ring 17 is accommodated. The part 16 of the socket 3 between the free end and the sealing ring 17 has an internal diameter which is clearly greater than that of the pipes 10, 11. In this widened part 16 a shrink ring 18 can be seen in Figure 2a. Said shrink ring 18 can already be fitted during or immediately after the production of the pipe 10, or it can be fitted at the start of making the socket joint shown. The shrink ring 18 is a closed ring of thermoplastic plastic material, for example the same material as that of the pipes 10, 11. A relevant feature is that the plastic material of the shrink ring 18 is stretched in the tangential or circumferential direction, so that the shrink ring 18 has the tendency to shrink in the circumferential direction to a smaller diameter when suitably heated. It is preferable for the shrink ring 18 to be stretched only tangentially, and not axially. In the case of the method according to Figures 2a,

2b the pipe 11 is inserted with insert end 13 into the socket 12, so that the insert end lies in the shrink ring 18 and the sealing ring 17. Heating is then applied in the region of the shrink ring 18, in such a way that the shrink ring 18 itself and the region 16 of the socket 12 around it shrinks to the state shown in Figure 2b. The shrink ring 18 is enclosed in the socket as a result .

In Figure 4 the original shape, prior to heating, is shown by dashed lines. Heating is preferably carried out in such a way that the region "E" of the insert end 13 lying in the shrink ring 18, which region may already be in contact with the shrink ring 18 which has not yet shrunk, also becomes warmer and thereby softer, so that the shrinking shrink ring 18 forms a constriction in the insert end 13. In Figures 2b and 4 it can be seen that part of the shrink ring 18 is projecting beyond the surface of the insert end 13 and that said part is enclosed by the shrunk part 16 of the socket 12. A socket joint between the pipes 10 and 11 which can bear a heavy load is obtained in this way .

The heating of the shrink ring 18 and possibly the region close to the shrink ring can be achieved in various ways. For instance, a preferred embodiment provides for the shrink ring 18 itself to be heated. This could be carried out by placing heating elements in or around the shrink ring 18, for example electric heating filaments. The shrink ring 18 could also be provided with a layer which can be heated by induction by means of an induction heating appliance.

However it is also conceivable for the region 16 to be heated from the outside, which heat is then transferred to the shrink ring 18 and the region "E" lying inside it. In a variant, provision can be made for the shrink ring 18 and the sealing ring 17 to be connected to each other and placed as an assembly in the socket 12.

The shrinking and constricting effects are shown in an exaggerated manner in the figures, purely in order to make the invention clear. The present invention also relates to a joining element (not shown) for plastic pipe sections, which may be made of biaxially oriented plastic material, in which case the joining element then preferably comprises two or more sockets of biaxially oriented plastic material, such as described above in various embodiments. Such a joining element can, for example, be formed from a cylindrical plastic casing which is stretched in the axial direction, and the ends of which are also stretched in the radial direction by the formation of sockets .

Claims

1. Method for producing a socket joint between a first pipe plastic section and a second plastic pipe section, in which an socket of biaxially oriented thermoplastic plastic material is used for joining the first and second plastic pipe sections, into which socket the insert end of at least one of the plastic pipe sections is inserted, characterized in that, after the insert end has been inserted into the socket, the socket is heated locally in an annular region thereof having a lesser axial lenght then the socket, such that the heated annular region of the socket reduces in diameter and shrinks onto the insert end inserted into it.

2. Method according to claim 1, in which the annular region of the socket is heated such that the annular region shrinks into a circumferential groove of the insert end.

3. Method according to claim 2, in which the circumferential groove of the insert end is formed during and as a result of the shrinking of the heated annular region of the socket .

4. Method according to one or more of the preceding claims, in which at a distance from the free end of the socket said socket is provided with an internal flexible sealing ring, which is designed to rest against the insert end, thereby forming a seal, and in which the socket is heated locally in the annular region between the sealing ring and the free end of the socket .

5. Method according to one or more of the preceding claims, in which a shrink ring is placed between the socket and the insert end, which shrink ring is made of at least tangentially oriented thermoplastic plastic material, which shrink ring at the time of placing has such an internal diameter that the insert end fits into it, preferably without deformation of the shrink ring, the method further comprising the step of heating of the shrink ring, so that the shrink ring reduces in diameter and shrinks onto the insert end.

6. Method according to claim 5, in which when heated the shrink ring enters into an external circumferential groove in the insert end, which circumferential groove may be provided beforehand or may be formed as a result of the shrinking of the shrink ring.

7. Method according to claim 5 or 6 , in which the heating is carried out in such a way that the socket encloses the shrink ring.

8. Method according to one or more of claims 5-7, in which the socket is locally heated in the region near the shrink ring, such that the socket shrinks at least in the tangential direction.

9. Method according to one or more of claims 5-8, in which use is made of heating means which are provided in and/or near the shrink ring.

10. Method according to one or more of claims 5-9, in which the shrink ring is designed such and heated such, possibly by heating the socket - in which case the adjacent region of the insert end possibly resting against the shrink ring may also be heated - that the shrink ring forms a constriction in the insert end of the second pipe section.

11. Method according to one or more of the preceding claims, in which the first and second plastic pipe sections are pipes of biaxially oriented thermoplastic plastic material, and in which each pipe has an integral socket at one end thereof and an insert end at the other end thereof .

12. Method according to one or more of claims 1-10, in which the pipe sections are joined by a separate joining part, which joining part comprises at least an socket of biaxially oriented plastic material.

13. Method according to claim 12, in which the first and second pipe sections are made of plastic without biaxial orientation of the plastic material.

14. Method for producing a socket joint between a first plastic pipe section and a second plastic pipe section, in which an socket of biaxially oriented thermoplastic plastic material is used, into which socket the insert end of at least one of the pipe sections is inserted, characterized in that a shrink ring is placed between the socket and the insert end, which shrink ring is made of at least tangentially stretched thermoplastic plastic material, which shrink ring at the time of placing has such an internal diameter that the insert end fits into it, the method further comprising the step of heating of the socket locally in an annular region around the shrink ring and/or heating the shrink ring itself, so that the shrink ring reduces in diameter and shrinks onto the insert end.

15. Pipe section of thermoplastic plastic material, comprising on one end thereof an integral socket of biaxially oriented thermoplastic plastic material and on the other end thereof an insert end, such that such a pipe section can be accommodated with its insert end in the socket, characterized in that, in an annular region of the socket the degree of tangential stretching of the plastic material is such that on heating of said annular region the diameter thereof can shrink to a diameter which is smaller than that of the insert end.

16. Pipe section of thermoplastic plastic material, comprising an socket of biaxially oriented thermoplastic plastic material for accommodating an insert end of another pipe section which fits into the socket and which with an insert end can be inserted into the socket, characterized in that a separate shrink ring is accommodated in the socket, which shrink ring is made of at least tangentially oriented thermoplastic plastic material, which shrink ring at the time of placing has such an internal diameter that the insert end fits into it, preferably without deformation of the ring.

17. Pipe section according to claim 16, in which heating means associated with the shrink ring are provided for heating the shrink ring, in such a way that the shrink ring shrinks and clamps down on the insert end inserted into it .

18. Pipe section according to claim 16 or 17, in which at a distance from the free end of the socket said socket is provided with an internal sealing ring, which is designed to rest against the insert end of the other pipe section, thereby providing a seal.

19. Socket joint between a first plastic pipe section with an socket of biaxially oriented thermoplastic plastic material and an insert end of a second plastic pipe section of biaxially oriented plastic material which fits into the socket, characterized in that, the socket is shrunk onto the insert part by heating at least a part of the socket.

20. Socket joint according to claim 19, in which a sealing ring is situated between the insert end and the socket, and in which a supporting bush is present in the insert end, which supporting bush stabilizes the insert end at least at the position of the sealing ring.

21. Socket joint according to claim 20, in which a separate shrink ring is accommodated in the socket, which shrink ring is made of at least tangentially oriented thermoplastic plastic material, which shrink ring by heating thereof is shrunk onto the insert end and preferably into a circumferential groove in the outer circumference of the insert part which has been produced by heating of the shrink ring.

22. Sealing assembly for a socket joint between a first plastic pipe section and a second plastic pipe section, said assembly comprising a sealing ring and a shrink ring connected to the sealing ring, which shrink ring is made of thermoplastic plastic material which is stretched in the circumferential direction and shrinks in diameter when suitably heated.

23. Sealing assembly according to claim 22, in which the assembly is provided with heating means for heating the shrink ring.