PIPE JOINT

Abstract: A pipe joint where a first pipe (1) and a second pipe (2) are joined together by means of a connecting piece (3) positioned between them. The connecting piece (3) comprises a sealing ring (4) and at least one wing (5) joined together. The wing (5) is provided with at least one inward curved projection (5a).

Description: PIPE JOINT The invention relates to a pipe joint for joining together a first pipe and a second pipe, the second pipe of the pipe joint being arranged inside the first pipe and a connecting piece being arranged between the pipes, which connecting piece comprises a sealing ring and at least one wing, the sealing ring and the wing being joined together. In pressure pipe use, forces proportional to the medium pressure in a pipe are caused in pipe joints and sockets. A decisive factor for dimensioning a pipe socket is the peripheral stress arising in the pipe wall, the stress requiring the wall thickness of the socket to be at least the same as that of the rest of the wall. As disclosed in Finnish Patent 94902, for instance, it is often considered necessary to emphasize the strength properties of the socket portion especially in the peripheral direction, to achieve a tight and reliable pipe joint. The strength properties of the pipe portion are instead mostly directed both peripherally and axially according to the loads the pipe portion is subjected to. If the pipe is provided with a socket afterwards by expanding, the wall becomes thinner when expanded, and accordingly, the pipe blank has to be thicker at the place of the future socket than the rest of the pipe. This can be implemented for instance in such a way that, at the manufacture, the draw rate of the pipe is slowed down at the place of the future socket. However, a solution of this kind is uncomfortable and complicates the manufacture of a pipe. A thickening is known from U.S. Patent 4,428,900, for instance. At reducers, branch joints, bent angles or valves in a pipeline, there occur axial forces tending to open the joint. It would be most ideal if the pipe joint itself were provided with a mechanism preventing the opening, but in pipes provided with sockets this is not possible because of the big forces caused by locking means and the dimensional accuracy required. In practice, the locking problem is solved for example by casting the problematic places in concrete or by winding cast iron bands interconnected by bars around the joined pipes. Moreover, a solution to reinforce a socket is known from Finnish Publication 97036, for instance, where a sufficient axial and radial strength of a locking solution inside the socket is achieved by a reinforcement outside the socket. A third problem associated with the use of a pipe socket consists in after-shrinkage of sockets. The socket tends to revert to its original measures and to make a joint is difficult, especially if pipes have to be stored exposed to sun shine, for example, for a long time after the socket has been made. In these conditions, it is difficult to make sockets with accurate measures, and especially difficult to make sealing grooves having accurate inner measures, particularly if there are many of them. This is an especially severe problem with pipes made of polyethylene PE, and therefore, these pipes are joined together by welding, in practice. Another common problem affecting a weak socket coupling is that the end of the pipe expands and the sealing ring slides out of the joint. An attempt has been made to solve this problem by using for example sealing rings which have a metallic or plastic support bracing the ring. This solution is disclosed for example in US Patent 4,030,872. Another solution has been a metal band installed around the pipe mouth. Molecule-orientated MOPVC pipes are made of polyvinyl chloride by blow moulding in such a way that a plastic tubular blank is positioned inside a mould, it is heated and expanded against the mould by blowing from the inside, as disclosed in British Patent 1 ,432,539. This allows a socket to be formed simultaneously in the pipe, but in this case the outer dimensions of the socket become accurate, whereas the inner, i.e. significant, dimensions are inaccurate. The same problem concerns for instance the method and apparatus for the manufacture of a biaxially orientated pipe by heating a tubular blank and by pressing it with fluid pressure against the mould, as disclosed in WO 98/13190. For the above reasons, more demanding socket applications are found among fittings manufactured by casting or injection moulding. WO 96/07048, for instance, discloses an injection moulded socket provided with a locking ring. However, the major part of the sockets of a pipe line are pipe sockets, and to replace them by fittings is not economically sensible. Further, a joint is known where the socket portion is manufactured by injection moulding and connected to the end of a straight pipe by butt welding. However, such a solution is complicated and expensive to implement, and moreover, all pipe materials used at present are not weldable. SE publication 465,792 discloses a pipe joint where a sealing ring is arranged between the socket and the insert end. The sealing ring is provided with an auxiliary portion which is supported to a groove at the insert end to resist to the opening of the joint. When the joined is pulled to open, the outward force acting on the socket via the auxiliary portion is directed to the sealing groove of the socket, the sealing groove being the weakest point in the socket. The joint is therefore fairly weak structurally. At its largest diameter, the sealing groove is only provided with a resilient sealing ring which does not support the socket sufficiently, so it is a point where the pipe joint may break fairly easily. Finnish Publication 945107 discloses a pipe joint for insert pipes, the end of a first pipe being expanded and a sleeve being positioned inside it, or the sleeve being expanded and the first pipe being positioned inside the sleeve. Subsequently, the end of a second pipe is positioned inside the sleeve. Such a joint is suitable for joining insert pipes, but it is difficult to achieve a tight joint and said joint would not last at pressure pipe use, but the force caused by pressurized medium would move the first pipe and the second pipe loose from each other quite easily. DE publication 3,003,040 discloses a pipe joint comprising a connecting piece with an insert and a clamping ring arranged inside it, the pipe to be joined being innermost in the joint. Between the insert and the clamping ring there is a wedge surface, the clamping ring being wedged against the pipe when the inner pipe is withdrawn from the joint. This kind of a pipe joint is most complex and it is very difficult to form the joint in such a way that the insert and the connecting piece can be made immovable with respect to each other. GB publication 2,028,945 discloses a socket joint suitable for vacuum cleaner hoses. The joint comprises a sleeve arranged around an inner tube. To lock the sleeve and the inner tube together, the sleeve has inner projections, the inner tube being provided with holes into which the projections are engaged. The outer tube end's diameter is so large that the tube can surround the sleeve. In the inside, the joint is provided with a spring ring which has an outward projecting pin. The inner tube, the sleeve and the outer tube have an opening through which the pin is engaged. The spring ring holds the pin in place, and the pin can be pressed down to release the outer tube, for example, from the sleeve. The pipe joint in question is very complex, and for example the withdrawal of the inner tube from the inside of the sleeve is most difficult. Moreover, the joint is cumbersome and cannot be applied for example to pipes carrying liquids, and particularly not to pressure pipes. US Patent 5,299,838 discloses a pipe joint comprising a connection slot and a sleeve arranged inside it with a screw thread. Inside the sleeve is arranged a clip assembly, the pipe to be joined being pushed inside the clip assembly. The clip assembly comprises retaining members made of bent plates arranged about the axis, the outer ends of the retaining members being arranged to clamp to inner grooves of the sleeve when the inner pipe is pulled outward, their inner ends being arranged to clamp to the outer surface of the inner pipe. In other words, the retaining members are meant to prevent the inner pipe from being withdrawn from the inside of the connection slot. This is a most complicated pipe joint and difficult to implement, and, in pressure pipe use in particular, it is extremely difficult to make sure the joint is tight. It is an object of the present invention to provide a fairly simple and tight pipe joint. The pipe joint of the invention is characterized in that the wing is elongated and provided with at least one inward curved projection which is at a distance from the sealing ring. An essential idea of the invention is that inside the end of a first pipe to be joined is a connecting piece and the end of a second pipe to be joined, the connecting piece being set between the first pipe end and the second pipe end. The connecting piece comprises a sealing ring and at least one elongated wing which are joined together. The wing comprises at least one inward curved projection arranged at a distance from the sealing ring. A preferred embodiment of the invention is based on the idea that the inner pipe has a groove on its outer surface, the projection setting into the groove. Another preferred embodiment is based on the idea that the projection is formed to the wing by die cutting, the wing being bent inward in the die cutting. An advantage of the invention is that a most tight joint is obtained which is also suitable for pressure pipes and withstands the impact of the force caused by the medium in a pressure pipe, without the pipes that are to be joined together substantially moving in an axial direction with respect to each other. In addition, the pipe joint as a whole is structurally fairly strong. The wing and its projection provide a simple means for preventing an axial, opening movement between the connecting piece and the inner pipe. The pull- out strength of the pipe joint is particularly good if the outer surface of the inner pipe is provided with a groove into which the projection sets. The invention will be described in greater detail in the accompanying drawings, in which Figure 1 is a schematic, partly sectional side view of a pipe joint of the invention; and Figure 2 is a side view of a connecting piece of the joint of Figure 1. Figure 1 shows a pipe joint, in which a connecting piece 3 is positioned inside the end of a first pipe 1 , the first pipe having a pipe socket at its end. Inside the connecting piece 3 is arranged the end of a second pipe 2. The pipe joint of the invention is particularly suitable for pipes with large diameter. The inner diameter of the first pipe 1 , for example, may vary from 75 to 1000mm. The second pipe 2 may be an insert end, for example. The connecting piece 3 can be arranged inside the end of the first end 1 for example by attaching the connecting piece 3 to a mandrel, heating the end of the first pipe 1 and pulling the pre-heated pipe 1 onto the connecting piece 3. The outer diameter of the connecting piece 3 is dimensioned bigger than the inner diameter of the pipe 1 , which makes the joint between the first pipe 1 and the connecting piece 3 tight. The outer surface of the point of the connecting piece 3 and the inner surface of the end of the pipe 1 can be provided with chamferings, which facilitate the pushing of the connecting piece 3 into the pipe 1. The end of the first pipe 1 can also be heated and expanded and the connecting piece 3 can be pushed into the expanded first pipe 1. Upon cooling, the first pipe 1 presses tightly on the connecting piece 3 and the joint between the connecting piece 3 and the first pipe 1 becomes tight automatically. In the manufacture of molecule-orientated PVC pipes or other pipes orientated in peripheral and possibly axial direction, the connecting piece 3 can be positioned inside the first pipe 1 for example by blow moulding and then cooling the first pipe 1. The connecting piece 3 is then pushed into the expanded end of the first pipe 1 and the first pipe 1 is heated so that it presses tightly on the connecting piece 3. The first pipe 1 is provided with a sealing groove into which the thickest portion of the connecting piece 3 sets. Further, the outer surface of the connecting piece 3 can be provided with grooves, protrusions, chamfered surfaces, or barbs 3b, and the like, by the effect of which the connecting piece 3 and the first pipe 1 remain immovable with respect to each other. For example, the outer surface of the connecting piece 3 can be attached with a hot-melt adhesive to the inner surface of the socket formed by the first pipe 1. Furthermore, the connecting piece 3 can be placed to an injection moulding machine to press the socket of the first pipe 1 onto the connecting piece. The connecting piece 3 and the first pipe 1 are thus welded together extremely tightly. In addition, between the pipe and the connecting piece, or for example into the connecting piece 3, can be added welding wires or welding mass, for example, which allow the pieces to be welded together. Another possibility is to use friction welding for example in such a way that the connecting piece 3 is rotated or rotated back and forth by means of a rotary mandrel inside the pre-expanded first pipe 1 such that the connecting piece 3 and the first pipe 1 are welded together. The connecting piece 3 can be easily locked onto the rotary mandrel by means of the projections 5a in the wing 5 of the connecting piece 3. The connecting piece 3 can be positioned inside the first pipe 1 at the factory and prefabricated products comprising the connecting piece 3 and the pipe 1 can be stored for a desired time. The remaining part of the pipe joint can then be made at the site of use. The connecting piece 3 comprises a sealing ring 4 and at least one elongated wing 5. The sealing ring 4 can be made for example of cross-linked thermoplastic elastomere, such as rubber. The wing 5 can be made of plastic, such as polyethylene PE, cross-linked polyethylene PEX or polyvinyl chloride PVC. Further, the wing 5 can be made of metal. The sealing ring 4 and the wing 5 are joined together for example by gluing. If the wing 5 is made of plastic, the wing 5 and the sealing ring 4 can also be vulcanized together. The wing 5 is arranged to reach onto the periphery of the sealing ring 4, the wing 5 preventing the sealing ring 4 from expanding, thereby ensuring a good tightness of the joint in all circumstances. In addition, the wing 5 supports the first pipe 1 at the sealing groove. The wing 5 is provided with one or more inward curved projections 5a at a distance from the sealing ring 4. The projections 5a prevent the end of the second pipe from sliding out of the connecting piece 3. The outer surface of the second pipe 2, in turn, is provided with an annular groove 2a extending around the entire periphery of the pipe 2. Therefore, when the second pipe 2 is pushed inside the connecting piece 3, the projection 5a bends, thereby allowing the pipe 2 to be pushed in. The second pipe 2 being pushed far enough inside the connecting piece 3, the projection 5a bends into the groove 2a in such a way that the second pipe 2 and the connecting piece 3 are locked in an axial direction with respect to each other, thereby providing a joint which has an extremely good pull-out strength and which can be used in pressure pipes as well. Since the wing 5 is elongated and the projection 5a is at a distance from the sealing ring 4, the outward force acting on the first pipe 1 when through the projection 5a when the joint is pulled open is directed to the wing 5 area at a distance from the sealing groove into which the sealing 4 sets. This is an area where the socket of the first pipe 1 is not so weak as for instance at the sealing groove, the pipe joint as a whole being therefore fairly strong. For example, the connecting piece 3 used with a pipe having a diameter of 110 mm can be dimensioned such that the distance between the tip of the projection 5a and the sealing ring 4 is approximately 20 mm. Thus sealing is not subjected to excessive force, provided that the distance between the tip of the projection 5a and the sealing ring 4 is over 15%, preferably over 20% and most preferably over 50% of the diameter of the connecting piece 3. The end of the second pipe 2 can be provided with a chamfering 2b that makes it easier to push the second pipe 2a inside the connecting piece 3. The chamfering 2b and the annular groove 2a can be formed to the second pipe 2 at the same time, i.e. the chamfering 2b and the groove 2a are most preferably made using one and the same machine. The projections 5a are of the same structure as the wall of the wing 5, and they are most preferably manufactured by first injection moulding, for example, the wing 5 without the projections 5a and the projections 5a are then die cut into the wing 5. In the die cutting, the projection 5a is bent inward into the position shown in Figure 1. The end of the projection 5a is at a distance from the end of the wing 5, thus allowing a very strong wing 5 structure to be easily obtained. When the wing 5 is made of cross-linked polyethylene PEX, the memory of the PEX material can be used when the projection 5a is formed. The projections 5a can be formed to curve inward at the same time when the wing 5 is cross-linked. The projections 5a can then be bent straight in normal temperature. When the wing 5 is re-heated, the projections bend inward due to the memory of the material, i.e. the heating of the wing 5 can be used to renew the pull-out strength of the joint in connection with re-installations, for example. The end of the first pipe 1 is provided with a collar-like additional reinforcement 6 of the pipe 1 mouth, which particularly increases the peripheral strength of the mouth. The cross-section of the groove 2a formed on the outer surface of the second pipe 2 can be either triangular or rectangular. A socket joint which has a good pull-out strength and which also allows the pipe 2 to move slightly inside the connecting piece 3 can be obtained by arranging the distance between the counter surface of the projection 5a in the groove 2a and the end of the second pipe 2 to be smaller than the distance between the corresponding points on the connecting piece 3, i.e. the distance of the projection 5a from portion where the end of the second pipe can extend to as shown in Figure 1. The second pipe 2 cannot move to the left from the position shown in Figure 1 to any significant degree, i.e. the joint has an extremely good pull-out strength, but the pipe 2 can, however, move to the right slightly. In many plastic pipe lines this is very important because the coefficient of heat expansion for plastic is high. The wing 5 can be discontinuous in the peripheral direction, i.e. it need not be uniformly annular in shape. The tightness of the joint is in this case provided by the sealing ring 4 which is arranged between the first pipe 1 and the second pipe 2. The axial force that draws the joint open further increases the sealing effect of the sealing ring 4. The first pipe 1 is provided with a sealing groove into which the sealing ring 4 and the wing 5 end facing the sealing ring set. This locks the connecting piece 3 tightly in the axial direction and immovably with respect to the first pipe 1. The wing 5 can, however, be uniformly annular in shape, i.e. it can be a cylindrical sleeve joined to the sealing ring 4, thereby supporting the pipe joint at the socket formed in the first pipe 1. Figure 2 shows an embodiment in which the wing 5 is cylindrical, but made of a plurality of rigid parts 5b with resilient parts 5c arranged in-between. This allows the entire outer diameter of the connecting piece 3 to be modified, which allows the connecting piece 3 to be pushed into an existing socket, for example. The rigid parts 5b can be made of metal and the resilient parts 5c of rubber, for example. The wing 5 can be made substantially thinner than in the schematic view of Figure 1. A wing 5 made of metal, for example, can be so thin that the connecting piece can be arranged even in existing socket joints where the first pipe 1 and the second pipe 2 are meant to be substantially tightly against each other. The drawings and the related specification are only intended to illustrate the idea of the invention. The details of the invention may vary within the scope of the claims. Consequently, the pipes 1 , 2 may comprise more than one material layer. Outside the joint can be arranged an outer band to ensure that the sleeve stays inside the first pipe. The outer band can be for example a band made of stainless steel which is tightened onto the joint by means of suitable tools. The joint can be opened for example by pushing a thin-walled metal sleeve between the second pipe 2 and the connecting piece 3 which bends the projection 5a away from the groove 2a in the second pipe 2 and the second pipe 2 can be withdrawn from the inside of the connecting piece 3. The socket into which the connecting piece 3 is arranged does not need to be cylindrical: a conical connecting piece 3 can be inserted into a conical socket, which allows a small axial angle of the second pipe 2. By choosing suitable positions and/or length for the wings 5a and by making the groove 2a spiral, the second pipe 2 can be detached from the joint without a special tool simply by turning the second pipe 2 in the connecting piece 3, and thus the projections push the second pipe 2 out along the screw line formed by the groove 2a.

Claims: CLAIMS 1. A pipe joint for joining together a first pipe (1 ) and a second pipe (2), the second pipe (2) of the pipe joint being arranged inside the first pipe and a connecting piece (3) being arranged between the pipes (1 and 2), which connecting piece comprises a sealing ring (4) and at least one wing (5), the sealing ring (4) and the wing (5) being joined together, characterized in that the wing (5) is elongated and provided with at least one inward curved projection (5a) which is at a distance from the sealing ring (4). 2. A pipe joint according to claim 1, characterized in that the outer surface of the second pipe (2) is provided with a groove (2a), the projection (5a) setting into the groove (2a). 3. A pipe joint according to claim 1 or 2, characterized in that the projection (5a) is substantially of the same structure as the rest of the wing (5) wall. 4. A pipe joint according to claim 3, characterized in that the projection (5a) in the wing (5) is made by die cutting. 5. A pipe joint according to any one of the preceding claims, characterized in that the wing (5) is at least mostly made of metal. 6. A pipe joint according to any one of claims 1 to 4, characterized in that the wing (5) is at least mostly made of plastic. 7. A pipe joint according to claim 6, characterized in that the wing (5) and the sealing ring (4) are attached together by vulcanizing. 8. A pipe joint according to any one of claims 1 to 6, characterized in that the wing (5) and the sealing ring (4) are attached together by gluing. 9. A pipe joint according to any one of the preceding claims, characterized in that the sealing ring (4) is made of cross-linked thermoplastic elastomere. 10. A pipe joint according to any one of the preceding claims, characterized in that the wing (5) comprises at least one rigid part (5b) and at least one resilient part (5c) alternating in the peripheral direction. 11. A pipe joint according to any one of the preceding claims, characterized in that the wing (5) is a uniform cylindrical sleeve. 12. A pipe joint according to any one of the preceding claims, characterized in that the inner diameter of the first pipe (1 ) is at least 75mm. 13. A pipe joint according to any one of the preceding claims, characterized in that the end of the projection (5a) is at a distance from the end of the wing (5). 14. A pipe joint according to any one of the preceding claims, characterized in that there is unevenness on the outer surface of the connecting piece (3) to ensure that the connecting piece (3) and the first pipe (1) are immovable with respect to each other.

Inventors: JAERVENKYLAE JYRI, JAERVENKYLAE, JYRI
Applicants: JAERVENKYLAE JYRI, UPONOR INNOVATION AB, JAERVENKYLAE, JYRI
Application year: 2001
Main classification: F16L21
IPC codes: F16L21