PIPES AND COUPLINGS AND METHOD OF COUPLING PIPES

Abstract: A method of securely joining a pipe (1) to a pipe fitting (3) without the need for rotating either element. The fitting (3) or in some cases the pipe (1), is expanded by heating whereby the other element may be inserted in it and the elements are secured together upon cooling by the interengagement of matching grooves (4) and ribs (14) which are provided on the circumferential surfaces of the elements.

Description: Pipes and couplings and method of coupling pipes Field of Application The invention relates to a method of joining pipes to couplings or other fittings, and pipes and couplings or fittings for joining by the method. Disclosure of invention Various methods of joining pipes have been known in the prior art but some of these, including the screwing of one element into the other, whilst producing a secure joint, have been impractical in the assembly of complex pipework systems, and the present invention offers the advantage, among others, of ease of installation without loss of security. According to one aspect of the invention there is provided a method of joining members comprising first and second pipe elements of which one member is of thermally expansible material and has an internal cylindrical surface of diameter generally corresponding to the diameter of the cylindrical external surface of the other member, wherein one of said surfaces has at least one circumferential groove therein and the other of said surfaces at least one matching circumferential rib projecting outwardly therefrom, the method comprising expanding the said one member to an extent dependent on the outward extension of said rib or ribs by heating below its melting point to enable one of said membe to enter the other beyond the rib or ribs, assembling the members one within the other, with the or each rib in regis with a corresponding groove, and allowing the expansible member to contract by cooling on to the other member so that the or each rib engages in a corresponding groove. Preferably the said one member is expanded to such an exten that the other member can enter it only by elastic de- formation of the said rob or ribs Preferably there is a plurality of spaced grooves and matching ribs, and the grooves and ribs are of ratchet-like configuration. A sealing and/or sliding agent may be appl to at least one of said surfaces. According to a further aspect of the invention there is provided a combination of members comprising first and second elements characterized in that one member has an internal cylindrical surface of diameter generally corresponding to the diameter of the cylindrical external surface of the other member when both members are at the same temperature, one of said surfaces has at least one circumferential groove therein and the other of said surfaces has at least one matching circumferential rib projecting outwardly therefrom, and the said one member is made of material having such a co-efficient of thermal expansion that it can be expanded by heating below its melting point to such an extent that the one of said member is to enter the other beyond the rib or ribs so that on contraction of said one member the or each rib can engage in a corresponding groove. Prefereably there is a plurality of spaced grooves and matching ribs, and the grooves and ribs are of ratchet-like configuration. According to yet a further aspect of the invention there is provided a pipe element for combination with a further pipe element as aforesaid. Description of Figures Figures 1 to 4 show sections through combinations of pipes and fittings according to the invention. Description of Invention Embodiments of the invention will now be described by way of example and with reference to the drawings. The combination shown in Fig. 1 comprises a pipe 1 having a free end 2 and a flanged coupling 3. The pipe 1 is of polypropylene, but inother embodiments may be of other plastics material such as polyethylene, or of metal or other suitable material. The flanged coupling 3 is also of polypropylene, any substitute for which, in other embodiments, will be expansible by heating below its melting point to an extent indicated below. The pipe 1 has an external diameter <3, and at its free end 2 is machined or otherwise formed with circumferential grooves 4. Each groove is defined by a wall 5 substantially perpendicular to the axis of the pipe and an inwardly inclined wall 6, the perpendicular wall being nearer the open end of the pipe. The length of the grooves in the direction of the axis of the tube is 9.5mm. The coupling comprises a flange portion 7 provided with holes 8 for mounting the coupling. Extending from the flange portion is a tubular portion 9 having an internal annular flange 10 which provides an annular shoulder 11 for abutment with end face 12 of the pipe 1 when assembled as will be described below. Between the flange 10 and the open end 13 of the tubular portion 9 of the coupling 3, the internal surface is formed with what may be regarded as a series of circumferential ribs 14 extending outwardly (that is to say towards the axis of the tube) from a theo- retical cylindrical surface of diameter d_. The ribs 14 have faces which are respectively substantially perpendicula to the axis of the tube and inclined at the same angle as the walls 6 of the grooves 4 of the pipe 1. The length and the outward projection of the ribs 14 also correspond to the length and depth of the grooves 4. Between the innermost rib and the shoulder 11 the internal surface of the tube 9 is tapered at 15 at an angle corresponding to the taper 16 at the end 12 of the pipe 1. Typically, the diameter d_ is 50mm and the depth of the groov 4, equal to the projection of the ribs 14, is 2mm. As shown in the drawings that projection of the ribs 14 prevent the insertion of the end 2 of the pipe 1 into the coupling 3 without the distortion of one or other of the components. However, the material of construction of the coupling 3 is such that on heating to a temperature below its melting point, it expands by an amount at least equal to twice the projection of the ribs 14 in a length d_ of the material. Such an expansion will enable the end 2 of the pipe 1 to be inserted into the couplings; a slightly smaller expansion will permit the insertion only by a slight distortion of one or both of the components such as might be effected in a thermal plastics material under an applied load without exceeding the elastic limit. In practice of the method of the invention the coupling 3 is heated in a uniform manner by means for example of hot air, hot oil or by the fluid bed technique. The temperature rise is controlled so that the component does not reach the softening point of the material but sufficiently to ensure that the internal diameter between the peaks of the ribs 14 is only so slightly less than d_ that the end 2 of the pipe 1 can be inserted in the coupling with a snap action by imparting a sharp tap on the coupling in the direction of the axis of the pipe. The end face 12 of the pipe 1 engages the shoulder 11 and thus ensures that the ribs 14 and grooves 4 are in register with one another and, in the absence of a similar force acting in the opposite direction, the pipe 1 will not snap out again. With the source of heat removed, the coupling 3 will cool and return to its original dimensions; in the fully cooled state the components will fit tightly with one another with each rib engaged in a corresponding groove. A certain amount of tolerence can be provided by adjustment of the diameter of the pipe and coupling and of the dimensions of the ribs relative to the grooves, and improved sealing may be afforded by providing a sealing compound in the grooves or between the ribs before assembly of the components. if polytetrafluoroethylene paste is used as the sealing compound, it will also aid the slipping of one component relative to the other. Because of the ratchet-like shape of the ribs and grooves, couplings so assembled will be substantially permanent unless a means can be found of re-heating the coupling without at the same time expanding the pipe. It is envisaged that a range of fittings, such as the coupling 3, will be provided to correspond with pipes having a range of external diameters, The pipes, when cut to the required length, will be cut with external grooves in a similar manner to that in which pipes are sometimes threaded. However, the provision of grooves will be somewhat simpler than the provision of threads and the assembly of the components will be far simpler than screwing of components. Figs. 2 and 3 of the accompanying drawings show respectively an elbow and a T-joint, whilst Figure 4 shows an alternative form of flange fitting. in the fittings shown in Figures 2 to 4, the pipe elements in the form of components respectively designated 20, 21 and 22, are cut with grooves 4 on the outer cylindrical surfaces similar to the end 2 of pipe 1 in Figure 1. These components are joined to pipes, such as pipe 23, in Figure 4, by means of further pipe elements in the form of coupling sleeves 24. Each of the sleeves 24 has an internal annular shoulder 25, and between "the shoulder and each open end has a series of ribs 26 formed similarly to ribs 14 on the internal surface of the tubular portion 9of flanged coupling 3. In order to join the pipe to the component the coupling sleeve, which is of thermally expansible material, is heated and snap-fitted to the other elements. It will be understood that the coupling sleeve may be moved relative to a stationary pipe or component, may be moved relative to a stationary coupling sleeve, or there may be movement of both in the snap-fitting operation depending on the requirements of the installation. Two pipes may similarly be joined by the use of a coupling sleeve as described above. Reverting to Figure 1, it will be clear that if the coupling 3 is not used as described above, the end face 13 is available for butt jointing to a pipe of internal diameter d_, and to this extent a coupling or other fitting according to the invention may be regarded as a dual-purpose article. In an alternative embodiment, which may not be quite so advantageous, the end of a pipe may be formed with circumferential grooves at its internal cylindrical surface and a corresponding coupling or other fitting formed with matching ribs at its outer surface. In these circumstances the end of the pipe will have to be expanded by heat to enable the elements to be inserted one within the other. It will also be understood that each of the pipe elements of a combination may comprise a pipe and thus two pipes may be joined one inside the other by the method without the use of a coupling, provided that the outer pipes is thermally expandable.

Claims: Claims 1. A method of joining members comprising first and second pipe elements of which one member is of thermally expansible material and has an internal cylindrical surface of diameter generally corresponding to the diameter of the cylindrical external surface of the other member, wherein one of said surfaces has at least one circumferential groove therein and the other of said surfaces at least one matching circumferential rib projecting outwardly therefrom, the method comprising expanding the said one member to an extent dependent on the outward extension of said rib or ribs by heating below its melting point to enable one of said members to enter the other beyond the rib or ribs, assembling the members one within the other, with the or each rib in register with a corresponding groove, and allowing the expansible member to contract by cooling on to the other member so that the or each rib engages in a corresponding groove. 2. A method as claimed in Claim 1 wherein there is a plurality of spaced grooves and matching ribs. 3. A method as claimed in Claim 1 wherein the grooves and ribs are of ratchet-like configura ion. 4. A method as claimed in Claim 1 wherein a sealing and/or sliding agent is applied to at least one of said surfaces 5. A method as claimed in any one of claims 1, 2, 3 or 4 wherein the said one member is expanded to such an extent that the other member can enter it only by elastic deformation of the said rib or ribs. 6. A pipe element (9) having an internal cylindrical surface of a predetermined diameter, for combination with a further pipe element (2) having a cylindrical external surface of corresponding diameter which external surface has at least one circumferential groove (4) therein or at least one circumferential rib projecting outwardly therefrom, characterised in that said pipe element is provided εt its internal surface with a circumferential rib (14) or groove matching the or each groove or rib, respectively, of the said further pipe element (2) and that said pipe element (9) is made of material having such a coefficient of thermal expansion that it can be expanded by heating below its melting point to such an extent that said further pipe element (2) is able to enter it beyond the rib or ribs (14) so that on contraction the or each rib (14) can engage in a corresponding groove (4) . 7. A pipe element as claimed in Claim 6 having a plurality of spaced grooves or ribs. 8. A pipe element as claimed in Claim 6 or Claim 7 wherein the cr each groove or rib is of ratchet-like configuration. 9. A combination of members comprising first and second pipe elements characterised in that one member has an internal cylindrical surface of diameter generally corresponding to the diameter of the cylindrical external surface of the other member when both members are at the same temperature, one of said surfaces has at least one circumferential groove therein and the other of said surfaces has at least one matching circumferential rib projecting outwardly there¬ from, and the said one member is made of material having such a co-efficient of thermal expansion that it can be expanded by heating below its melting point to such an extent that the one of said members is able to enter the other beyond the rib or ribs so that on contraction of said one member the or each rib can engage in a corresponding groove.

Inventors: ARMITAGE ARTHUR
Applicants: ADVANCED CHEM EQUIP LTD, ADVANCED CHEMICAL EQUIPMENT LTD
Application year: 1978
Main classification: F16L13
IPC codes: B23P11, F16L13, F16L23, F16L47