COUPLING FOR RIBBED PIPE

Abstract: Lengths of ribbed tube (10) having ribs which upstand appreciably from the main body of the tube may be coupled together using novel coupling ends (12, 112 and 14, 114, 214) of the tube. Alternatively, such ribbed tube may be coupled to plain walled tube (100). The lengths of tube are provided with first and second cuffed ends, the first end being a smooth walled cuff having a cuff having only shallow ribs reduced height and the second end being belled to couple with a first end of another tube or with plain walled tube smooth first end and the belled second end may be formed to respective outer and inner diameters for good sealing between them.

Description: COUPLING FOR RIBBED PIPE TECHNICAL FIELD The invention relates to semi-rigid plastics material tube having a ribbed outer surface and having ends adapted to couple one tube to another. BACKGROUND ART Thermoplastic, semi-rigid tube has a variety of uses such as for undergound drainage or for carrying electrical wiring. For various applications it has been found that corrugated tube, either double walled or single walled has advantages and, more recently, the use of a ribbed wall tube has become widespread. The ribs of such tube are usually annular or helical ribs upstanding from the tube wall by a height appreciably in excess of the thickness of the tube. The use of such ribbed tube gives good compression strength in comparison with solid walled tubes but utilizing less weight than plastics materials. Ribbed tube has significantly larger outside diameter than plain walled tube and if they are to be joined together, coupling members of large internal diameter are generally unsuitable for joining ribbed tube with plain walled tube. For joining ribbed tubes, it is necessary to provide sealing means which must fill the entire gap between the ribbed tube base wall and the coupling sleeve. If the ribs upstand to any great degree, this gap may be extensive. For example, if ribs upstand from the base wall of the tube by an inch or more, the seal must effectively seal an annular gap of at least an inch in width. When the ribs are annular, the seal may be located between two ribs. A coupling sleeve may be provided as an independent unit or it may be provided by an expanded or belled end of one tube which fits over the end of another tube. In either case difficulties arise in accurate fit and sealing. Moreover, when the coupling sleeve is a belled end of one tube, the degree of belling has to be very large in order to fit over the ribs of the other tube. Further problems arise when it is desired to couple ribbed tube and plain walled tube together. It may be seen that, if ribbed tube of large outside diameter is to be joined to plain walled or other tube of small outside diameter, then there is a very large gap to be sealed between the two tubes. Generally, coupling between plain walled tube and ribbed tube is not carried out because of the difficulties involved. However, where it cannot be avoided, it has been found necessary to use independent coupling sleeves for the purpose. One reason for this is that bells provided in the ends of tubes to fit over ends of adjacent tubes must be sufficiently large to fit over ribbed tube. Thus, the gap presented between plain walled tube and the large coupling bell at the end of ribbed tube is too large to be sealed by conventional sealing means. Ribbed tube of the type having substantially raised ribs is usually made by means of apparatus of the travelling mold tunnel type. A tubular parison of plastics material is extruded from an extrusion nozzle into a travelling mold tunnel over a forming plug. The forming plug defines the inner tube surface and the travelling mold tunnel defines the outer tube surface. Thus, the parison is forced into the cavity between the plug and the tubular tunnel which moves axially over the plug. The tubular tunnel has a mold surface to form the ribs or other configuration on the final tube. There are various means of providing such a travelling mold tunnel but this is often comprised by two tracks of mold blocks which come together in cooperating pairs to form a tunnel on a forwardly moving run parallel and coaxial with the extrusion nozzle. It is known to introduce at least one pair of mold blocks, known as cuff blocks, adapted to mold a cuff of different outer surface of the tube into the mechanism of the travelling mold tunnel so that such different surface will be cyclically introduced on the surface of the molded tube according to the length of the runs of mold blocks. Of course such differing pairs of mold blocks may be inserted into the mold train at whatever intervals are desired. Thus, more than one such pair may be present in the runs. The introduction of such differing pairs of mold blocks is known in connection with the production of corrugated tube which requires different molding technique. In that case, the tube is blow or vacuum molded into a travelling mold tunnel and, thus, the inner surface of the tube is also modified by changing the configuration of certain mold blocks. The production of corrugated tube is a very different technique from that of producing ribbed tube which is more akin to an injection molding process. European patent application No. 0,291,136 describes a ribbed tube having ends formed as co-operating smooth walled spigots and sockets for joining lengths of tubes together. Such a system is subject to inherent difficulties in that it is not known to have been possible to make smooth walled tube in a travelling mold tunnel due to transport difficulties of the parison in the mold. It has been so well known that a travelling mold tunnel tends to slip with respect to the tube being molded in it, that it is generally regarded in the industry that molding smooth walled tube in a travelling mold tunnel is not possible. Even the manufacture of relatively short sections of smooth walled tube in an otherwise ribbed tube which is formed in a travelling mold tunnel, may give difficulty due to transport difficulty of the smooth walled section. German Offenlegenschrift No. 3,725,286 describes a system of providing saw tooth projecting annular barbs on otherwise smooth walled sections of tube, mainly with a view to proper filling of rib cavities. European Application No. 0,405,163 illustrates the use of a separate sleeve joining two ends of rib pipe having such annular saw teeth between the ribs. DISCLOSURE OF INVENTION The present inventor has tried to provide a simple, sturdy, less expensive, and secure coupling means for a ribbed tube. His intention was to make it possible for its manufacture by companies who have previously been unable to afford the expense of specialized equipment for providing coupling means for ribbed tube in which the ribs upstand appreciably from a base tube wall. According to the invention there is provided a rigid, thermoplastics material tube having ribs upstanding from an outer base wall surface, the ribs being of a height at least as great as the wall thickness of the tube, the tube having a first end and a second end, the first end comprising a short length of tube in which the ribs are of reduced height, and the second end being belled sufficiently to fit over the first end of another tube. In the region of reduced rib height, the ribs may be of zero height, i.e., flush with the outer base surface of the tube, or they may be slightly raised from the outer base surface of the tube to provide a seat for additional sealing means and for strength. This end may be belled or thickened to correspond in outside diameter of a tube with which it is to be joined. Suitably an annular channel may be molded in the inner surface of the second belled end to locate a sealing ring. The ribs may be of any configuration but it is envisaged that the invention will be of practical use with either of annularly ribbed and helically ribbed tube. The height of the ribs is not of prime importance but the invention is envisaged to be of more practical importance for tubes having ribs of appreciable height. Thus, tube having ribs which upstand from its base surface by half an inch or more is very suitably provided with coupling ends according to the invention and may be coupled by a method of the invention. Also, according to the invention, there is provided a method of coupling one ribbed tube with another ribbed tube, each tube having ribs of a height greater than the wall thickness of the tube, comprising forming an end of reduced rib height, in said one ribbed tube and forming a belled end in the other ribbed tube, the diameter of the belled section being such that the belled section fits over an end of reduced height of said one ribbed tube; and forming an annular groove in an inner wall of the belled section, locating a sealing ring in said groove, fitting the belled section over said end of reduced rib height whereby the sealing means contacts both tubes to seal between them. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a sketch showing a prior art coupling between two ribbed tubes; Figure 2 is a sketch of one embodiment of a coupling between a ribbed tube and a plain tube according to the invention; Figure 3 is a sketch of another embodiment of a coupling between ribbed tubes according to the invention; Figure 4 is a sketch of yet another embodiment of a coupling between ribbed tubes according to the invention; Figure 5 is a sketch of yet another embodiment of a coupling between ribbed tubes according to the invention; Figure 6 is a sketch of yet another embodiment of a coupling between ribbed tubes according to the invention; Figure 7 is a longitudinal section through a travelling mold tunnel suitable for forming ribbed tubes as shown in Figure 3; Figure 8 is a sketch of tube produced from apparatus as shown in Figure 7 before separation into its components parts; Figure 9 is an enlargement of a detail of the mold blocks for molding a coupling ends of the tube in apparatus as shown in Figure 7. Figure 10 is a sketch of an embodiment of a coupling modified from that of Figure 2; Figure 11 is a sketch of an embodiment of a coupling modified from that of Figure 3; Figure 12 is a sketch of an embodiment of a coupling modified for that of Figure 6; Figure 13 is a sketch of tube having essentially smooth walled spigot and socket sections with traction ridges; and Figure 14 is an enlargement of a detail of mold blocks of Figure 7 for having transport grooves for forming transport ridges. MODES OF CARRYING OUT THE INVENTION Figure 1 shows a conventional coupling between the ends of two ribbed tubes. The coupling comprises a male/female connection between adjacent ends of tubes. For this purpose, one end 12 of each tube 10 is belled so that it will fit over the other end 14 of another tube 10. It is necessary for the belled end 12 to be expanded by at least the depth of the ribs 16 which are annular around the tube and which have a height, in this example, of approximately 4 times the thickness of the base wall 18 of the tube 10. It is normally necessary to form the belled end 12 as a secondary operation after the length of the tube has been manufactured. While it may, at least theoretically, be possible to form such a bell by the provision of special mold blocks in a travelling mold tunnel, the depth of a bell may not be practicable in a travelling mold tunnel which travels over a forming plug to provide a mold cavity into which extrudate must be forced to form the tube. While pneumatic pressure may be used at intervals to make slight indentations in the internal surface of a tube formed in this manner, it is probably not practicable to use it for a bell of this size. The other end of tube 10, as exemplified by the coupled end of the adjacent tube 10 in Figure 1, is provided with an annular sealing ring 20 located between two adjacent ribs 16. While the tube shown in Figure 1 is representative of the invention in proportion and is not exaggerated in any way, it is to be noted that tubes embodying the invention may have ribs of considerably lesser height than shown. Similarly the ribs may be of greater height than shown. Figures 2 to 6 illustrate embodiments of the invention. Similar reference numbers to those used in Figure 1 are also used in Figures 2 to 6 to indicate similar or comparative parts. Figure 2 illustrates coupling between a plain walled tube 100 and a ribbed tube 10 having rib 16 and a special coupling bell 112 at one end. The coupling bell 112 is a plain walled extension of ribbed tube 10 which is only very slightly belled so that the end of tube 10 may be slid over the adjacent end of tube 100. The bell 112 includes an annular groove 115 in which may be located a standard sealing ring 116 for sealing with tube 100. Figure 3 illustrates a tube 10 similar to that of Figure 2 having a belled end 112 including a groove 115 housing the sealing ring 116. In this case, however, the end 112 of the tube 10 is coupled with the end 114 of another tube 10. End 114 comprises a short plain walled section. Thus, each tube 10 has one belled end 112 and one plain walled end 114. Each belled end 112 couples with the adjacent plain walled end 114 in a close fit so that sealing ring 116 forms a seal between the two tubes. The belled end 112 of tube 10 may be made in any convenient manner. One such manner is to cut a length of a ribbed tube 10 which does not have belled sections 112 or plain sections 114. The end of this tube may be belled in a belling machine of a conventional type. Alternatively, since the bell 112 is of slight depth, it may be formed in the original molding of the rib tube 10. It is necessary to provide special mold blocks which are configured to provide a plain wall of an outer diameter greater than that of base wall 18. Such mold blocks are hereinafter described with reference to Figures 7, 8 and 9. Moreover, it is necessary to bias the extrudate away from the wall of the inner forming plug so that the inner surface of the belled end 112 is of greater diameter than the inner surface of base wall 18. This may be done in various manners, as for example by the use of pneumatic pressure or by mechanical means. The other end 114 is easier to mold in a travelling mold tunnel than is the bell 112. All that is required is the provision of mold blocks which are configured for plain wall tube ' rather than for rib wall tube. However, improvements in traction of such sections may be achieved by the embodiments of Figures 10-14. As shown in Figure 3, the end 114 is of greater outer diameter than base wall 18. This thickening may be provided to match the ends of tube to be joined. The end portion 114 illustrated is thickened rather than belled for matching of outside diameters of tubes to be coupled. However, slight belling of this end might be an alternative manner of matching tubes. Thickening of end 114 may be achieved by momentary slowing of the travelling mold tunnel so that more plastics material is laid down in the mold. This may be achieved by adapting the shape of special mold blocks. In some instances, it may be desired to couple ribbed tube 10, having a belled end 112 as previously described, with existing rib piping, for example, in an existing installation in which old style ribbed tube which does not have a suitably plain walled section 114, is used. Alternatively, a join may be required where such section 114 is not conveniently located. In either of these instances, the tube must be cut between two ribs along its length. The ribs adjacent the cut may merely be cut off by sawing, cutting, filing, etc. to provide an end approximating to end 114. Figure 4 shows a further embodiment of tube 10 having belled end 112 coupled with a further tube 10. The end 214 of the further tube turn is provided with rib roots 216. These rib roots 216 may be of a height to correspond with the outside diameter of tube to be joined and may be provided by special mold blocks configured to produce them or may be the result of cutting away original rib 16. Whatever the manner of their manufacture, these rib roots 216 may provide additional useful sealing means. The groove between two adjacent rib roots 216 may be used to house an additional sealing ring 118. Alternatively, as shown in Figure 5, the groove between adjacent rib roots 216 may act as a container for glue which, through capillary action, will contact the inner surface of belled portion 112 when tubes 10 are coupled. Glue may also be applied between the tubes to be coupled at the ends of the rib roots 216. An intermediate smooth shave 215 may be applied over rib roots 216. Figure 6 illustrates an alternative embodiment to that shown in Figure 2. In Figure 6, belled end 112 extends from plain walled tube 100 and plain walled section 114 extends from ribbed tube 10. 0 Figure 7 illustrates a travelling mold tunnel 50 advancing in the direction of arrow A. The mold tunnel consist of two sets of mold blocks 52 circulating on the respective paths as described, for example, in U.S. Patent No. 4,226,580, issued to Gerd Lupke et al on October 7, 5 1980 or, indeed, as illustrated by any other of numerous conventional travelling mold tunnel apparatus. The travelling mold tunnel is frequently provided by means of cooperating runs of half mold blocks but it will be appreciated that the manner in which the tunnel is formed o is not relevant to the present invention. The more important features concern the configuration of the mold blocks 52 in the region of forming tube ends. The mold tunnel 50, in association with an extrusion die 54 provides an annular orifice for extruding outer tube 58 into the mold cavity 60 of the mold tunnel 50. The die may also be provided with the central core tube 66. Pressurized air may be supplied through a tube 67 running along the core tube 66 and a radial passage 68 to a chamber 70 inside the outer tube 58. This high pressure air may serve to blow mold the tube into the mold cavity 60 in the region of mold blocks 52a to form the belled end 112 of a tube length. Alternatively, a bell may be produced by the apparatus described and claimed in U.S. Patent No. 4,226,580. Thus, the mold blocks 52a are shaped to form the tube 58 into a bell. Mold blocks 52a are shown as providing an enlarged diameter, smooth wall, bell section 62 of the mold cavity 60. The tube 58 is molded into this bell section to form tube end portion 112. Somewhat similarly mold blocks 52b are provided to mold tube end portion 114. The mold block 52b may provide a shallowed bell, i.e. one having a smaller outside diameter, than that of tube end portion 112. However, unless means such as pneumatic pressure are provided to force extrudate away from the cooling plug 72, a thickened portion 114 will be formed. To promote suitable thickness of this portion, it may be possible to show the travel of mold tunnel 50 while mold blocks 52b pass the exit of extrusion die 54. Figure 8 shows tube obtained, for example from apparatus as described in connection with Figure 7. The end portions 112, 114 are connected by a web 113. It is easy to separate this continuous tube into component lengths by removal of web 113. Such removal may be by a slight cut or by two parallel cuts 6 as indicated by phantom lines B and C. Figure 9 shows in more detail one longitudinal half of the mold surface such as that of Figure 7. Figures 10-12, 13 and 14 are essentially similar to respective Figures 2, 3, 6, 8 and 9 except that every smooth walled section of tube whether belled, a thickened spigot section or a smooth walled tube is provided with traction ridges 200 (or in the case of Figure 14, traction grooves 202) which may be of rectangular corrugated or sine wave corrugated or any other suitable configuration. In particular, the smooth walled sections may be made by the apparatus and method as claimed in PCT patent application No. by Manfred Lupke filed on even date herewith and entitled Smooth Walled Tube Formed in a Travelling Mold Tunnel.

Claims: CLAIMS 1. Rigid, thermoplastics material tube (10) having ribs (16) upstanding from an outer base wall surface, the ribs being of a height at least as great as the wall thickness of the tube, the tube having a first end and a second end; the first end (14, 114, 214) comprising a short length of tube in which the ribs (100, 216) are of reduced height, and the second end (12, 112) being belled sufficiently to fit over the first end (14, 114) of another tube. 2. Tube as claimed in claim 1 in which the second end (12, 112) has an inner annular groove adapted to engage a sealing ring (116). 3. Tube as claimed in claim 1 in which a sealing ring for sealing between the first end of one tube and a second end of another tube is provided in said groove. 4. Tube as claimed in claim 1 in which the ribs (100) have zero height in the region of reduced rib height 5. Tube as claimed in claim 1 in which the ribs (216) in the region of reduced rib height are raised from the outer surface of the first end (214). 6. Tube as claimed in claim 5 in which the ribs (216) in the region of reduced rib height have a height less than the wall thickness of the tube. 7. Tube as claimed in claim 1 in which the ribs (16) are annular ribs. 8. Tube as claimed in claim 1 in which the ribs (16) are helical ribs. 9. A method of coupling one ribbed tube (10) with another ribbed tube (10), each tube having ribs (16) of a height greater than the wall thickness of the tube, comprising forming an end (14, 114, 214) of reduced rib height in said one ribbed tube and forming a belled end (12, 112) in the other ribbed tube, the diameter of the belled section being such that the belled section (12, 112) fits over an end of reduced height of said one ribbed tube, fitting the belled section (12, 112) over said end of reduced rib height. 10. A method as claimed in claim 9 including forming an annular groove in an inner wall of the belled section locating a sealing ring (116) in the groove. 11. A method as claimed in claim 9 in which the plain walled end is a plain walled end (114) of another ribbed tube. 12. A method as claimed in claim 9 in which at least one of the ribbed tubes has annular ribs. 13. A method as claimed in claim 9 in which at least one of the ribbed tube has helical ribs. 14. A method as claimed in claim 9 in which the height of the ribs on the end of reduced rib height (114) is zero. 15. A method as claimed in claim 9 in which the height of the ribs on the end (214) of reduced rib height is less than the wall thickness of the tube. 16. A method of coupling a ribbed tube (10) with a plain walled tube ribbed tube, the ribbed tube having ribs of a height greater than the wall thickness of the tube, comprising forming an end (114) of reduced rib height in said ribbed tube and forming a- belled end (112) in the plain walled tube (100), the diameter of the belled section being such that the belled section fits over an end of reduced height of said ribbed tube.

Inventors: LUPKE STEFAN A, LUPKE, STEFAN, A.
Applicants: LUPKE STEFAN A, LUPKE, STEFAN, A.
Application year: 1991
Main classification: F16L47
IPC codes: F16L47