The present invention relates to the coupling of plastic pipes, according to the preamble of Claim 1.

Such a coupling comprises a mechanical coupling which rigidly connects pipes of large dimensions.

Plastic pipes of different dimensions can be attached to each other, for example by welding or by means of mechanical couplings. The advantage of mechanical couplings for plastic pipes of large dimensions is that such couplings can be used in all weathers and installation conditions as opposed to welding procedures, which often require dry conditions.

Examples of conventional mechanical couplings are sleeve couplings, wherein a cylindrical, often threaded length of pipe, i.e. a sleeve, which is short relative to the pipe, is attached at one end of one pipe, and the end of another pipe is inserted into the sleeve in order to attach the pipes to each other. Sleeve solutions on the market are popular and easy to install. A disadvantage of conventional sleeve couplings is that they cannot handle tensile loads across the joint.

A standard snap connection is based on the principle that a "plastic wedge" of a first part climbs over a counterpart of a second part and grips around that counterpart, and in that way locks the parts mechanically. Snap connections render it possible to achieve couplings that can axially absorb tensile loads. Snap couplings thus make installations possible for instance in hilly areas, such as above-ground installations, without the need for anchoring over each joint. In renovation projects it may also be necessary to have a pipe that withstands tension loads if the pipe has to be pulled back during adjustment of the pipeline.

For pipes having a structural wall construction, also the joint area must have the same ring stiffness properties as the part of the pipe itself. This means that the material thi ckness of the coupling parts must be relatively large. A consequence of this is that as the thickness of the components to be deformed during the installation of snap connection pipes increases, the force for coupling increases rapidly to the point where it is in practice too great.

If the force does become too great, the installation process may require special arrangements: the already installed part of the pipe must be kept in place by a special arrangement (an excavator/extra weight) in order that a ready-lined piping system, comprised for instance of pipes and wells, does not move when an additional pipe is connected.

The use of larger snap connections is difficult to implement in practice.

The purpose of the present invention is to eliminate the disadvantages associated with the state of the art and to provide a new way of coupling plastic pipes of large dimensions (large diameters). The present invention is based on the idea of forming a snap connection between pipes which have a dimension of at least 300 mm by providing the ends of the two pipes to be coupled with part of a snap connection sleeve comprising a female and a male part, in which case the female part is arranged to temporarily deform when the pipes are coupled together due to the fact that the edge is divided into flexible wedges that fold out radially when the male part is inserted into the female part.

According to a preferred embodiment, the flexible wedges of the edges of the female part whi ch on the inside of the pipe are designed so as to form an inwardly and backwardly directed edge which forms an abutment surface which, in turn, is able to grip around an edge of the male part. Multiple, at least 2, preferably at least 3 and up to approximately 15 axial slits extending through the wall of the female part and included in the edge of the female part, at a distance from each other, in such a way that the edge pieces between the slits are able to fold out to facilitate engagement of the male part. More specifically, the equipment for the pipe coupling is characterised by what is stated in the characterising part of Claim 1.

Considerable advantages are obtained by means of the present invention. By arranging the female part of the coupling in such a way that it is divided into multiple flexible claws, the edge is folded out radially during engagement of the male part of the incoming pipe, thus reducing the force demand significantly. An advantageous way of achieving this is to produce the female part in such a way that it is slitted axially. Surprisingly, it has been found that a snap connection which is carried out according to the present method provides a coupling with a fully sufficient stiffness and tensile strength for large pipes (diameter in the range of 300 to 3500 mm) having a substantial weight. In a preferred embodiment, the coupling is applied to pipes with lightweight walls, in which case the stiffness of the sleeve/snap connection is even greater than that of the pipe wall. By simultaneously arranging a seal in the joint, preferably such that the seal is outside the slitted area, a manageable compression in the sealing area and a good tightness are achieved.

Further details and advantages of the present invention are found in the following detailed description, wherein reference is made to the accompanying drawings of which

Figure 1 shows a perspective view of two pipes which are attached to each other by means of a pipe joint according to an embodiment of the present invention; and

Figure 2 shows a cross section of a pipe joint according to an embodiment of the present invention, with an installed sealing ring.

The two pipes, 10 and 12, shown in Figure 1 are made of hollow pipe profiles. These profiles 1 1 and 13, are shown as cross sections in Figure 2. By that means, the pipes according to a preferred embodiment of the present invention have a light wall structure. Such a large but relatively lightweight thermoplastic pipe can be manufactured by spirally winding a thermoplastic hollow profile 1 1 and 12, which has an essentially rectangular cross section, around a cylindrical rotating drum and by joining adjacent turns of the hollow profile by means of welding.

Plastic pipes formed by spiral winding of hollow pieces or profiles along with methods of manufacturing such tubes, and methods of joining them are described in US Patents Nos. 5,127,442, 5,411,619, 5,431,762, 5,591,292, 6,322,653 and 6,939,424. The contents of these patents are herewith included by reference.

The ends of the tubes, 10 and 12, are joined by means of a sleeve, 14, 16 and 18, which forms a snap connection. In this case, the female part 16 is welded to the end 13 of the first tube 12 and the male part 14 to the end 11 of the second tube, 10. Reference number 18 indicates the slits included in the edge of the female part and which extend through the entire thickness of the edge of the wall.

Figure 2 shows how the meeting edges of the female part 16 and the male part 14 are wedge-shaped, 20 and 22 respectively, and each edge is provided with a back-facing gripping edge, 21 and 23, both of which are adapted to engage or abut against an abutment, 24 and 25 respectively, both of which are formed in the opposing male (14) and female (16) parts.

Figure 1 shows further how the edge 16 of the female part is axially slitted, 18. The axial length of the slit 18 may vary, but is typically large enough to extend, in the embodiment of Figure 2, from the edge of the female part 24 towards the area to be sealed, having the seal 28. The dashed line shows how far the slit typically extends. It should be noted that the slit can extend partly over the area to be sealed because the material provides a sufficient stiffness and sealing effect even in this case. Typically, the length of the slits are at least equal to the width of the pipe profile; typically it is about 0.8-5 times, preferably about 0.9-3 times, the width of the pipe profile (i.e. the height of the winding of the pipe).

The male part of the sleeve is unslitted and essentially provides the ring stiffness of the sleeve. Its material thickness is equal to the profile height ("PrH") or only slightly less than this. Typically, the thickness of the male part is at least 50 % of the PrH, preferably at least approximately 60 %, most preferably approximately 70-100%.

The seal, 28, which is installed in the area to be sealed, may be a plastic bulb seal made of the sleeve material and shaped into a ring. However, it is preferable to prepare the sealing ring of a material different from that of the sleeve. Preferably, the material used is of the type thermo-elastic polymers (TPE) or various qualities of silicone rubber, EPDM, as well as SBR and nitrile rubber. Most preferable is the use of a rubber/elastomer material having good chemical resistance in order to achieve good sealing.

For a desired sealing effect, it is important that the edge part of the female part is intact, essentially or mostly at the area to be sealed, as mentioned above. If desired, the female part can be further provided with marks, i.e. shallow grooves in the surface, which provide the slitted parts with greater flexibility. The marks preferably run perpendicular to the slits and are located on the slitted parts or further in on the sleeve, near the bottom of the slits.

The joint section between the two pipes 10 and 12 is indicated by the reference numbers 24 and 26. The length of the coupling sleeve, 14, 16, 18, can vary but typically it is at least equal to the width/height of the pipe profile, preferably it is 1-5 times the profile width/height.

According to an embodiment, the outer diameter of the sleeve is essentially equivalent to the outer diameter of the pipe, which is appropriate for instance in renovation projects where a pipe is installed, such as at penetrations into existing pipes and other applications where the space is predetermined.

According to another embodiment, the outer diameter of the sleeve is substantially greater than the outer diameter of the pipe, which is suitable in applications where no limitations are placed on the outer diameter, over the joints, of the pipe or the pipeline.

In all cases, it is desirable that the inner diameter of the sleeve is the same as the inner diameter of the pipe so as to avoid edges which slow down the flow inside the

pipe/pipeline.

The pipe profile is typically made of a polyolefin material, such as polyethylene or polypropylene, and the snap coupling sleeve is preferably made of a similar material which can be welded to the pipe material. For pipe couplings of the type shown in Figure 1, the closing force of the coupling is measured as a function of the diameter. The results are given in the table below: DN Closing force of the snap connection [daN]

600 420

800 570

1000 670

1200 2400

The coupling is suitable for pipe diameters DN within the range of 300-3500 mm, although it is particularly suitable for diameters approximately 500-2000 mm.

It should also be mentioned that it is possible to shape the gripping edge of the slitted parts of the female part to provide different angles, depending on the abutment surface of the male part and taking into account the estimated tensile force required to pull the pipes apart. A smaller angle (for instance less than 90° to the central axis of the pipes, in which case the surface slopes forward somewhat towards the mouth of the pipe) gives a lower tensile strength and reduces the pulling power required for separating the pipes. A smaller angle can be advantageous when one wishes to easily separate the pipes, as when relocating a pipeline. In general, however, the angle of the gripping edge is at least 90°, i.e. it is perpendicular to the central axis, or possibly even slopes backwards from the mouth of the pipe.