GB2136074A

GB2136074A - Weldable Pipe Fittings

Info

Publication number: GB2136074A
Application number: GB8406137A
Authority: GB
Inventors: Richard George Williams
Original assignee: Victaulic Co PLC; Rutland Plastics Ltd
Current assignee: Victaulic Co PLC; Rutland Plastics Ltd
Priority date: 1983-03-09
Filing date: 1984-03-08
Publication date: 1984-09-12
Also published as: GB8406137D0; GB2136074B

Abstract

A weldable thermoplastic member, comprises a thermoplastic saddle fitting moulding 1 having a surface adapted to correspond to a wall of a pipe. Associated with the saddle fitting is a thermoplastic disc 7 provided on its surface facing the saddle a spiral groove 8. An electric resistance wire is fed from one post 6 mounted on support 12 through 8 into flap 10 which is folded across the disc so that the wire can be connected through the opposite post 6. A current passed through the wire with 7 in intimate contact over the surface 4 of the moulding welds the disc to the saddle sandwiching the wire therebetween. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Weldable Pipe Fittings This invention relates to weldable thermoplastic members such as pipe fittings of the kind formed of thermoplastic materials for connecting to thermoplastic pipes or pipe like members in which a part of a wall of the fitting is arranged to be joined by fusion or "welding" to part of the outside peripheral wall of a pipe or pipe like member, the fusion being by means of electric heating wire located at or adjacent the appropriate mating surfaces of the fitting and of the pipe or pipe like member.

The invention particularly, although not exclusively, relates to "saddle" fittings. Saddles are fittings adapted to be secured to the side of a pipe to enable a branch or side pipe to be connected thereto.

It has been proposed previously to provide such a fitting in which the fusion heating wire is provided in the form of a mat constructed from closely wound plastic coated resistance wire, the wire insulation being partially welded together.

However, such an arrangement is prone to mechanical damage, and in addition a practice is developing of utilising special alloy electric resistance wires requiring, for safety reasons a lower welding voltage for fusing the saddle fitting to the pipe. Such special alloy wires are not readily obtainable with appropriate plastic insulation coatings.

It is an object of the present invention to provide a weldable thermoplastic member which overcomes or at least substantially reduces the above mentioned difficulties.

According to one aspect of the invention there is provided a weldable thermoplastic member comprising a thermoplastic body member having a surface adapted, in use, to face a wall of a second thermoplastic member; a disc of thermoplastic material having secured thereto an electrical heating wire; the disc abutting and being fused to said surface of the body member whereby the heating wire is embedded therebetween.

According to another aspect of the invention there is provided a method of producing a weldable thermoplastic member comprising the steps of forming a disc of thermoplastic material; securing to the disc an electrical heating wire; forming a thermoplastic body member having a surface adapted to face, in use, to a wall of a second thermoplastic member; abutting the disc against said surface of the body member and fusing it thereto by passing current through the heating wire whereby the heating wire is embedded therebetween.

The thermoplastic member may be a pipe fitting and the second thermoplastic member may be a pipe or pipe like member.

By the expression "pipe or pipe like member" as used herein we mean, in addition to pipes such as, associated members for pipework usage such as couplers, tees, 450 and 900 elbows, flange adapters and reducers, for example.

The disc may be annular. Such a configuration is particularly appropriate where the pipe fitting is a saddle fitting. In this case the disc can surround the opening of the branch or side pipe.

The disc may be flexible so as to be capable of deformation to the configuration of said surface of the body member.

The electrical heating wire may be laid in a previously cut moulded or otherwise formed groove in one face of the disc. The groove across the face of the disc may have straight sided walls and may be of generally rectangular section and the portion of the disc between the groove may comprise a flat crest between the grooves. The grooves may be formed by moulding with the disc or may be cut into an already moulded disc.

After insertion of the wire in the groove, the grooved surface of the disc may be subject to mechanical working, possibly with the addition of heat, so as firmly to secure the wire into the disc.

Alternatively the wire may be secured onto one surface of the disc. Thus, for example, the wire may be set out in its desired configuration in association with a former. The wire is then applied to the face, and may be bonded thereto.

The bonding may take place by briefly passing current through the heating wire so as to melt the immediately adjacent material of the disc, which material on resolidifying holds the wire in place.

The heating and melting may be sufficient to embed, at least partially, the heating wire in the surface of the disc.

The heating wire may be set out in any desired pattern on the face of the disc of thermoplastic material. Thus, the wire may run from the outer edge of the disc towards the centre thereof in a generally helical configuration. Such a helix may be of usual curvilinear configuration, but may alternatively be provided with rectilinear portions, so that the overall plan appearance of the wire pattern is, for example, rectangular.

Where the heating wire is laid out in helical pattern, an electrically insulating bridge member, which may be grooved, may be provided across the face of the disc to enable the wire to be brought from adjacent the centre of the disc back to the edge thereof. The two ends of the wire may be connected adjacent the disc edge to electrical terminals.

In an alternative arrangement the heating wire may be laid out backward and forward across the face of the disc, or towards the centre and back from the centre of the disc in a "daisy petal" pattern.

It will be appreciated that the spacing of the wire across the face of the disc is, in practice, calculated such that when the forming fitting is to be welded to a pipe there is a sufficient length of wire of a predetermined electrical resistance to ensure that the necessary energy can be provided to carry out the welding or fusion of the saddle to the pipe.

The pipe saddle moulding may be injection moulded in a conventional manner, and may have in the said surface a recess stretching radially thereacross capable of receiving the above mentioned bridge member (where provided) upon assembly of the disc with the saddle.

After formation of the fitting as hereinabove mentioned, it will be fitted to an underlying pipe at a desired position, and may be moved into intimate contact therewith by means of pressure whilst fusing the saddle to the pipe by passing current through the wire.

In order that the present invention may be more readily understood, embodiments thereof will now be described by way of example with reference to the accompanying drawings in which:~ Figure 1 is an isometric view of a saddle moulding together with its associated resistance wire disc in accordance with the invention; and Figures 2, 3 and 4 illustrate alternative disc and wire configurations for the saddle of Figure 1.

Referring now to Figure lit will be seen that there is provided a thermoplastic saddle fitting moulding 1 incorporating an internal bore 2 and a flange portion 3 and having a surface 4 shaped to correspond to the wall of the pipe to which the fitting is to be connected (not shown).

Diametrically opposed housings 5 are provided adapted in use to receive electrical terminal posts 6. The saddle fitting moulding 1 is injection moulded.

Associated with the saddle fitting is a thermoplastic disc 7 provided on its face directed towards the saddle with a continuous spiral groove 8 of generally rectangular section extending from adjacent the outer periphery thereof to an inner opening 9 corresponding to the bore 2 of the saddle fitting. A grooved flap 10 is formed with the disc, the flap being connected to the disc adjacent the bore passing therethrough, and acting, in use, as a bridge for electrical heating wire and being capable of folding across the disc to the outer periphery 11 thereof. Also forming part of the disc are electrical terminal supports 12 which correspond in position to the terminal housings 5 on the saddle moulding 1.An electrical resistance wire (not shown) is fed from one terminal post 6 mounted to a terminal support 12, through the spiral groove 8 into the flap 10 which is then folded across the disc so that the wire can be connected through the other of the terminal posts 6 on the other support 12. The flap 10 acts as an electrically insulating bridge for the wire passing therethrough from the wire located in the groove 8.

It is to be observed that the terminal posts 6 are provided with barb-like projections 13 so that upon insertion thereof in the supports 12 and subsequently into the housings 5 the barbs 13 on the terminal posts 6 assist permanent assembly.

The internal surface 4 of the saddle moulding 1 facing towards the disc 7 is provided with a recess 14 adapted in use to receive the flap 10 extending across the disc.

For assembly the disc 7 with its associated terminal posts 6 is brought into association with the corresponding surface 4 of the saddle with the terminal posts 6 located within the housings 5 such that the barbs 13 thereon provide an interference fit therein. The disc 7 is then, by means of a suitable pressure, brought into intimate contact over the surface 4 of the saddle moulding 1. A controlled electrical current is then passed through the heating wire for a predetermined period of time whereby the disc 7 is welded to the surface 4 of the saddle moulding 1, and the resistance wire embedded and encapsulated therebetween. It is to be observed that the surface 4 of the moulding 1 is provided with a peripheral downwardly protruding rib 27 which, when the disc 7 is held against the surface 4, abuts tightly against the periphery 1 1 of the disc 7.This prevents flow of thermoplastic material from between the disc 7 and surface 4 during the step of welding the disc to the surface.

The saddle fitting is now ready for connection to a pipe by the simple expedient of placing its pipe facing surface (the surface 15 of disc 7) against the wall of the pipe concerned and then passing a current via the terminal posts 8 and through the resistance wire so as to fuse the surface 4, with the intervening disc 7, to the outer peripheral surface of the associated thermoplastic pipe. Thereafter an opening is cut in the pipe wall corresponding to the bore 2 of the saddle fitting and without cutting or disturbing the resistance wire.

It will be appreciated that the saddle fitting can be any desired shape and configuration for any particular shape or pipe or pipe like member to which it is to be connected and can indeed have a configuration adapted to receive a plurality of branch outlets, i.e. it can have a plurality of bore like portions.

The disc 20 of Figure 2 is generally similar to that of Figure 1. In this case however it is formed of thin flexible thermoplastic material in a rectangular configuration. No groove is formed or cut in the disc, but heating wire 21 previously wound around former pins into the rectangular helix shape illustrated, is placed against the surface of the disc 20 and fused thereto to briefly passing current through the wire 21. This has the effect of embedding slightly the wire 21 in the disc 20.

To enable the return of the inner end of the wire 20, a thermoplastic electrically insulating bridge piece 22 is provided, the bridge piece being notched at each end so that the wire can be secured thereto. The bridge piece is lightly fused to the disc at each end.

The disc 23 of Figure 3 is similar in general principle to that of Figure 2. In this case however the wire 24 is laid out in a generally radial "daisy petal" array such that any tendency during welding of the fitting for melted thermoplastic material to move outwardly under pressure will have a reduced likelihood of displacing any significant part of the heating wire.

Figure 4 shows a variation of the arrangement of Figure 3. In this case greater equalisation of heating across the disc 25 is ensured by arranging that alternate loops of the heating wire 26 only penetrate part way across the disc annulus.

By means of the invention as specifically described hereinabove, we have provided a saddle fitting of convenient utility readily adapted for quick and simple fusion welding to the wall of a pipe or pipe like member.

Claims

1. A weldable thermoplastic member comprising a thermoplastic body member having a surface adapted, in use, to face a wall of a second thermoplastic member; a disc of thermoplastic material having secured thereto an electrical heating wire; the disc abutting and being fused to said surface of the body member whereby the heating wire is embedded therebetween.

2. A member as claimed in Claim 1 wherein the body member is a pipe fitting adapted, in use, to be connected to a pipe or pipe like member.

3. A member as claimed in Claim 2 wherein the pipe fitting is a saddle fitting.

4. A member as claimed in any one of the preceding claims wherein the disc is annular.

5. A member as claimed in any one of the preceding claims wherein the disc is flexible.

6. A member as claimed in any one of the preceding claims wherein the disc is provided with a groove across one face within which the heating wire is disposed.

7. A member as claimed in any one of the preceding claims wherein the heating wire is secured to the disc by bonding with the thermoplastic material of one face thereof.

8. A member as claimed in any one of the preceding claims wherein the heating wire is disposed across the disc in a generally helical configuration.

9. A member as claimed in Claim 8 wherein the helix is provided with rectilinear portions whereby, in overall plan appearance, the wire pattern is rectangular.

10. A member as claimed in Claim 8 or 9 including an electrically insulating bridge member disposed across the face of the disc, the wire passing from the inner end of the helix across the bridge to beyond the outer end of the helix.

11. A member as claimed in any one of Claims 1 to 7 wherein the heating wire is disposed in a backward and forward configuration across or around the face of the disc.

12. A method of producing a weldable thermoplastic member comprising the steps of forming a disc of thermoplastic material; securing to the disc an electrical heating wire; forming a thermoplastic body member having a surface adapted to face, in use, to a wall of a second thermoplastic member; abutting the disc against said surface of the body member and fusing it thereto by passing current through the heating wire whereby the heating wire is embedded therebetween.

13. A method as claimed in Claim 12 wherein the body member is a pipe fitting adapted in use to be connected to a pipe or pipe like member.

14. A method as claimed in Claim 13 wherein the pipe fitting is a saddle fitting.

15. A method as claimed in any one of Claims 12 to 14 wherein the disc is formed in an annular configuration.

16. A method as claimed in any one of Claims 12 to 1 5 wherein the disc is formed such as to be flexible.

17. A method as claimed in any one of Claims 12 to 15 wherein a groove is formed across the face of the disc and the heating wire is secured to the disc by locating it within the groove.

18. A method as claimed in Claim 17 wherein the groove is formed by moulding with the disc.

19. A method as claimed in Claim 17 or 18 wherein the grooved surface of the disc is subjected to mechanical working after location of the heating wire therein so as to hold the wire securely therein.

20. A method as claimed in any one of Claims 12 to 15 wherein the heating wire is secured to the disc by the steps of setting out the wire in its desired configuration; applying the wire to a face of the disc; and bonding the wire to the face of the disc by briefly passing current through the wire whereby material of the disc melts and then resets to hold the wire.

21. A method as claimed in Claim 20 wherein the wire is partially embedded in the surface of the disc as it is bonded thereto.

22. A method as claimed in any one of Claims 12 to 21 wherein the heating wire is disposed across the disc in a generally helical configuration.

23. A method as claimed in Claim 22 wherein the helix is provided with rectilinear portions whereby, in overall plan appearance, the wire pattern is rectangular.

24. A method as claimed in any one of Claims 12 to 21 wherein the heating wire is disposed in a backward and forward configuration across or around the disc.

25. A weldable thermoplastic pipe fitting substantially as shown in and as hereinbefore described in relation to Figures 1,2,3 or 4 of the accompanying drawings.

26. A method of producing a weldable thermoplastic pipe fitting substantially as hereinbefore described in relation to Figure 1,2,3 or 4 of the accompanying drawings.