GB2182412A

GB2182412A - The production of pipes

Info

Publication number: GB2182412A
Application number: GB08525727A
Authority: GB
Inventors: John Maurice Adlam; Ian Fraser Patterson
Original assignee: Baj Ltd
Current assignee: Baj Ltd
Priority date: 1985-10-18
Filing date: 1985-10-18
Publication date: 1987-05-13
Also published as: GB8525727D0; GB2182412B

Abstract

Fibre-reinforced resin pipes are produced by laying-up and winding on a mandrel 15. A pin or male thread forming head 22 comprising a mounting member 23 is slidable longitudinally of the mandrel 15 and carries a plate 28 on which four blocks 34 are slidably mounted. The blocks are biassed radially outwards by springs 43 and have hydraulic rams 45 to drive them radially inwards. The blocks 34 carry permanent magnets 35 by which four pin thread former segments 36 are retained. The segments are pressed against the uncured pipe and are then temporarily retained in position by pressing retainer bars (55, Fig. 8 not shown) through grooves formed by rebates (53) in the ends of the segments, the bars being restrained at one end by the mounting member 23 and at the other end by a clamping ring (61). The blocks 34 are then radially retracted, the forming head 22 is moved longitudinally away and another clamping ring (62) secured around the segments 36. The retainer bars and ring (61) are then removed. The tube on the mandrel together with the segments still held in position by the ring (62) is removed to a curing station. <IMAGE>

Description

SPECIFICATION Pipes and methods and apparatus for the production of pipes This invention relates to pipes made of fibre reinforced resin or plastics material, such pipes having a thread on at least one end and preferably -on both ends of opposite gender so that a string of pipes may be screwed together. The invention also relates to methods of production of such pipes and to apparatus for the production of such pipes.

Various methods have been proposed for the production of threads on pipes of fibre reinforced resin material. For example, it has been proposed to cut threads in the resin material by machining in the same manner as is done with metal pipes. It has also been proposed to apply a dough moulding material in a ring around the end of the pipe and to mould the threads into this ring of material. Another method which has been proposed is to produce a separate sleeve of fibre reinforced resin material on which the threads have been formed and to incorporate such sleeve in the pipe during the course of its manufacture. All these methods suffer from disadvantages and it is one object of at least one aspect of the present invention to improve such methods.

According to one aspect of the present invention, a method of manufacturing a fibrereinforced resin pipe having a pin thread, at least at a portion thereon, comprises forming a hollow tube of uncured or partially cured fibre-reinforced resin and forming a pin thread thereon by moving radially inwards towards the axis of the tube at least three segmental pin thread formers which together substantially constitute a complete ring.

By this method, a pin or male thread is formed integrally with the remainder of the tube which may be contrasted with many of the prior proposals in which a separate component formed with the threads is secured to the tube, albeit in some cases prior to final curing of the tube. The method enables the fibre-reinforcing to enter the recesses of the thread formers so that the reinforcing will extend into the worm of the threads of the finished tube to ensure adequate strength.

According to a second aspect of the present invention, apparatus for manufacturing a fibre-reinforced resin pipe having a pin thread comprises a mounting to surround the tube, at least three segmental pin thread formers which together substantially constitute a complete ring, slide means on the mounting for supporting the thread formers and guiding the thread formers along paths which are radial to the axis of a tube being manufactured, and rams arranged to move the thread formers along the said paths.

Preferred features of the method and apparatus are set out in the claims and in the description of a preferred embodiment but it is to be noted that many of these features may be used independently or in different combinations than those at present selected for the claims.

The invention may be carried into practice in various ways, but one resin reinforced plastics pipe and its method of manufacture and apparatus by which it is manufactured will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section of the pipe as manufactured by the apparatus to be described and incorporating end portions which are parted off prior to use of the pipe; Figure 2 is a fragmentary section to an enlarged scale showing the portion of the pipe in Figure 1 within the circle II; Figure 3 is a similar view of the portion of the pipe within the circle Ill in Figure 1, Figures 2 and 3 showing the thread profiles of the pipe; Figure 4 is a fragmentary view partly in elevation and partly in longitudinal section showing one end portion of the mandrel used in the apparatus to produce the pipe shown in Figure 1;; Figure 5 is a view, partly in elevation and partly in longitudinal section showing the thread forming head used at the opposite end of the mandrel to produce the male thread of the pipe shown in Figure 1; Figure 6 is an end elevation of the thread forming head shown in Figure 5 viewed from the left-hand side in Figure 5; Figure 7 is fragmentary view on the plane VII-VII in Figure 6; Figure 8 is a fragmentary view similar to part of Figure 6 and showing clamping bars in position; Figure 9 is a view similar to part of Figure 5 showing a clamping bar in position and showing part of the thread-forming head withdrawn to the right; Figure 10 is an and elevation of a clamping ring; and Figure 11 is a side elevation of the ring shown in Figure 10.

The pipe shown in Figures 1 to 3 is of fibrereinforced plastics material and in a typical example has a length of 4800 mm, an internal diameter of 140 mm and a wall thickness of 6 mm. As will be explained in due course, at each end of the pipe immediately after manufacture there is a portion which is parted off before the pipe is in a condition for use. At the left-hand end, as viewed in Figure 1, there is a first portion 1 which is to be parted off at a point 2, a portion 3 formed with a female or box thread, a short rebate 4, a thick region 5 and a tapering region 6 leading to the main portion 7 of the pipe which has a constant cross-section. This leads to an outwardly tapering portion 8 which is followed by a portion 9 of smaller external diameter which is formed with a male or pin thread.This terminates in a-shoulder 11 which is followed by a portion 12 of constant cross-section which is parted off after manufacture of the pipe.

As can be seen from Figures 2 and 3, each of the box and pin threads is of buttress form and is tapered.

The pipe is formed on a mandrel whose construction can be seen from Figures 4 and 5. The main component of the mandrel is a hollow tube 15 to one end of which is secured a box thread former 16 having a projecting mounting spigot 17 by which the mandrel may be mounted at one and in the head stock of a fibre winding machine. The other end of the tube 15 is secured to a pin end mounting device 18 by which the mandrel may be mounted in the tail stock 19 of the winding machine. The box thread former 16 is formed at its inner end with a pin thread 21 corresponding to the box thread to be formed in the pipe to be manufactured.On the other hand the mounting device 18 at the pin and of the mandrel does not contribute directly to the forming of the pin end threads which are produced by a pin thread forming head 22 which is shown in Figures 5 to 7 and which will be described in greater detail below.

Briefly, manufacture of the pipe proceeds as follows, reference being made primarily to Figure 1.

The box thread former 16 shown in Figure 4 is assembled onto the end of the winding mandrel tube 15 and a coating of a suitable parting agent is applied over the complete mandrel assembly. The mandrel assembly is then heated to 60 C. The mandrel is then mounted in the winding machine and the two location steps A and B are blended in by winding a resin impregnated glass roving to produce tapered transitions on the outer surface. A layer of resin is then applied over the threaded portion 21 of the box end former 16 and approximately 300 mm of the adjacent surface of the mandrel. There is then laid up an approximately 0.25 mm thick sheet of unidirectional glass filaments extending along the axis of the mandrel commencing at point A and extending for approximately 300 mm along the length of the mandrel towards and beyond B.Commencing at point B, a glass roving is wound around the mandrel to draw the unidirectional glass filaments into close contact with the threads 21 of the box thread former 16 following the thread form from point B to point A. Resin is then applied over the whole length of the mandrel and one complete helical cover is wound the full length of the component, i.e. from point C to point D.

There is then applied an approximately 0.25 mm thick layer of unidirectionally and longitudinally aligned glass filaments extending from point B to point D. Resin impregnated roving is then wound onto the mandrel in a helical pattern between points B and E until the required thickness of tube has been generated.

Hoop-wound rovings are then applied between points G and H to adjust the diameter of the tube locally within the predetermined limits required by the moulds which will, as will be described, be used to produce the pin threads. The pin threads are then formed by means of the pin thread forming head as will be described. The wound assembly still on the mandrel is then removed to the curing station and the resin is cured using a procedure appropriate to the resin employed. After the composite has been cured the manufactured pipe and the mandrel are cooled to room temperature. The pin thread formers (which will be described below) are removed and the winding mandrel is partially removed and unscrewed and the box thread former is removed. The mandrel is then completely withdrawn. Finally, the tube may be machine finished and the end portions 1 and 12 parted off.

The pin thread forming head includes a cupshaped mounting member 23, the base of the cup being formed with a bore 24 in which is retained a phosphor bronze sleeve 25 which forms a plain bearing by which the pin thread forming head 22 may be mounted on the pin end mounting device 18 as shown in Figure 5 and slid longitudinally therefore onto the tail stock 19 where it may be parked. Longitudinal movement of the forming head may be achieved by means of a pair of handles 26 which are mounted on the mounting member 23 at diametrically opposite positions (the handle 26 visible in Figure 5 being in fact displaced by 90 about the axis of the forming head for convenience of illustration).The forming head may be secured in its operative position as shown in Figure 5 by means of a retractable bolt 27 which passes through the mounting member 23 and the bearing sleeve 25 into a recess 30 in the pin end mounting device 18.

Mounted on the front end (i.e. the left-hand end as used in Figure 5) of the cup-shaped mounting member 23 is an octagonal plate 28 having a central circular opening 29 for the passage of the mandrel tube 15. Extending forwardly from four evenly distributed edges of the octagonal plate are brackets 31 and secured to the octagonal plate by machine screws 32 are four dove-tail slides 33 which are symmetrically positioned with respect to the brackets 31. A slide block 34 slides on each of the dove-tails 33 radially with respect to the mandrel tube 15.

The brackets 31, the screws 32, the dovetails 33 and the slide blocks 34 form part of four pin thread former units and for convenience only one of these will be described in detail. They are substantially identical to one another. As can be seen in Figure 6, the slide block 34 carries a pair of permanent magnets 35 which releasably retain a pin thread former segment 36 which is accurately located by means of a pin 37 carried by the block 34.

Movement of the block 34 is additionally guided by a pair of headed studs 38 which project through openings 39 in the bracket 31 and whose heads carry spring guides 41 which retain the outer ends of springs 42, the inner ends of which are retained by spring guides 43 which surround the studs 38 and abut against the outer surface of the bracket 31. The springs thus bias the block 34 radially outwardly. Between the apertures 39 in which the studs 38 move there is a central aperture 50 in which is screwed a hydraulic cylinder 44 of a hydraulic ram unit having a ram 45. The cylinder 44 is retained in position by a lock nut 46 and the ram 45 engages in a recess 47 in the outer end of the block 34. A hydraulic manifold 48 extends from a coupling 49 around three quarters of the pin thread forming head and is connected to the four hydraulic cylinders 44.The coupling 49 is connected by a flexible hose to a source of hydraulic pressure.

The structure of each of the pin thread former segments 36 may be seen from Figures 5, 6 and 8, in particular. Each segment 36 extends 90 around the axis of the mandrel tube 15 and, as can be seen in Figure 5, is formed on its inner circumference with the pin forming thread 51 while its outer circumference is formed with a rectangular section groove 52 which receives a similarly shaped projection on the block 34. Each end of each segment 36 (see Figure 8) is formed with a rebate 53, the two rebates of the adjacent ends of adjacent segments 36 forming a longitudinally extending groove 54 which may receive a clamping bar 55 for a purpose to be explained.

During the course of manufacture of a pipe and when all the material has been laid up on the mandrel, the pin thread forming head 22 is advanced from its parked position on the tail stock 19 to its operative position as shown in Figure 5 and the bolt 27 is entered into the recess 30 to retain the thread former in position. At this stage the cylinders 44 are unpressurised and accordingly the slide blocks 34 are all retracted. The four thread former segments are then positioned on the slide blocks 34 where they are retained by the permanent magnets 35. All four thread formers are then in the positions shown for the righthand and left-hand formers as seen in Figure 6.Pressure is then applied simultaneously to the four cylinders 44 so that the slide blocks 34 are moved radially inwards to the positions of the upper and lower slide blocks shown in Figure 6, thus pressing the thread 51 on the inner surfaces of the thread former segments into the built-up material on the mandrel to form the pin end threads of the pipe. This brings the end faces of adjacent segments 36 into abutment as seen in Figure 8 and a clamp bar 55 is entered longitudinally into each groove 54 from the forward end towards the rear end. Each clamp bar 55 has a leading end 56 which slides into the cylindrical portion of the cup-shaped mounting member 23, a cranked portion 57 which engages the base of the groove 54 and a trailing end portion 58 which is formed with a return 59 and which projects forwardly from the segment 36 as can be seen in Figure 9.

After the four clamping bars 55 are in position a clamping ring 61 is engaged around the trailing portions 58 and is tightened sufficiently to retain the thread forming segments 36 firmly held. The pressure in the hydraulic cylinders 44 is then released and the springs 42 are then able to retract the blocks 34.

Since the thread former segments 36 are retained by the clamp bars 55 the blocks 34 separate from the thread former segments 36, the forces applied by the springs 42 overcoming the forces applied by the magnets 35. The bolt 27 is then withdrawn and by operation on the handles 26 the pin thread forming head 22 is withdrawn complete onto the tail stock 19 leaving the pin thread former segments in position and still retained by the clamping bars 55, the cylindrical portion of the cup-shaped mounting member 23 sliding over the leading ends 56 of the bars 55 but not moving a sufficient distance to become disengaged therefrom. The pin thread former segments are thus retained in position about the pipe being formed on the mandrel, but the outer circumferential surfaces of the segments are now accessible. A clamping ring 62 whose construction may be seen from Figures 10 and 11 is now placed about the outer surface of the pin thread former segments and is tightened up. The longitudinal dimension of the ring is such that it fits comfortably within the groove 52 in the outer circumferential surface of the segments 36. The ring 61 may now be released and the clamping bars 55 are withdrawn.

The mandrel, with the pipe formed thereon and with the pin thread former segments still retained thereon by the clamping ring, is now transferred to the curing station and the resin is cured. Thereafter the pin thread former segments can be recovered.

Claims

1. A method of manufacturing a fibre-reinforced resin pipe having a pin thread, at least at a portion thereon, which comprises forming a hollow tube of uncured or partially cured fibre-reinforced resin and forming a pin thread thereon by moving radially inwards towards the axis of the tube at least three segmental pin thread formers which together substantially constitute a complete ring.

2. A method as claimed in Claim 1 in which, in way of the said ring, the tube wall comprises at least one helically-wound layer and at least one longitudinal layer of fibres.

3. A method as claimed in Claim 1 or Claim 2 in which the outer layer of the tube engaged by the thread formers comprises windings extending in a generally circumferential direction.

4. A method as claimed in Claim 1 or Claim 2 or Claim 3 in which the pin thread is formed at or adjacent one end of the tube, a box thread is formed at or adjacent the other end of the tube, and the tube includes at least one layer consisting of helically wound fibres and extending from one end of the tube to the other.

5. A method as claimed in any of Claims 1 to 4 in which the thread formers are moved by rams mounted on a mounting surrounding the tube.

6. A method as claimed in Claim 5 which includes retaining the thread formers in their inwardly moved position,retracting the rams from the thread formers, and curing the tube with the thread formers retained thereon at a location relatively separated from the mounting.

7. A method as claimed in Claim 6 which includes utilizing first and second temporary retaining means respectively on opposite sides of the thread formers, retracting the rams, applying a retaining ring around the thread formers and removing the temporary retaining means.

8. A method as claimed in Claim 7 in which the first and second temporary retaining means are connected by longitudinally extending retainer elements engaging the thread formers.

9. A method as claimed in Claim 8 in which the first temporary retaining means comprises part of the mounting, the second temporary retaining means comprises a clamping ring and the retainer elements are held against radially outward movement by the said part and clamping ring.

10. A method as claimed in Claim 9 in which, after retraction of the rams, the mounting with the rams mounted thereon is moved longitudinally of the tube to move the rams away from the thread formers prior to application of the retaining ring.

11. A method as claimed in Claim 10 in which the said part of the mounting slides on the retainer elements during longitudinal movement of the mounting.

12. A method of manufacturing a fibre-reinforced resin pipe substantially as described herein with reference to Figure 1 of the accompanying drawings.

13. A method of manufacturing a fibre-reinforced resin pipe substantially as described herein with reference to the accompanying drawings.

14. A pipe when produced by a method as claimed in any of the preceding claims.

15. Apparatus for manufacturing a fibrereinforced resin pipe having a pin thread comprises a mounting to surround the tube, at least three segmental pin thread formers which together substantially constitute a complete ring, slide means on the mounting for supporting the thread formers and guiding the thread formers along paths which are radial to the axis of a tube being manufactured, and rams arranged to move the thread formers along the said paths.

16. Apparatus as claimed in Claim 15 which includes springs biassing the thread formers radially outwards, the rams being arranged to move the thread formers radially inwards against the bias of the springs.

17. Apparatus as claimed in Claim 15 or Claim 16 in which each slide means comprises a guide on the mounting, a slidable element moveable on the guide, and means for releasably retaining one of the thread formers on the slidable element.

18. Apparatus as claimed in Claim 17 in which the retaining means comprises a magnet.

19. Apparatus as claimed in any of Claims 15 to 18 in which the mounting is moveable longitudinally of the tube.

20. Apparatus as claimed in Claim 19 which includes a base, mandrel support means on the base, and a mandrel carried by the support means, the mounting being moveable longitudinally between a position in which it is supported on the mandrel and a position in which it is supported on the mandrel support means.

21. Apparatus as claimed in any of Claims 15 to 20 which includes a retaining ring engageable around the thread formers when in their radially inner positions.

21. Apparatus as claimed in Claim 19 or Claim 20 which includes a retaining ring engageable around the thread formers when in their radially inner positions and temporary retaining means for retaining the thread formers in their radially inner positions prior to engagement of the retaining ring.

23. Apparatus as claimed in Claim 22 in which the temporary retaining means comprises longitudinally extending retainer elements engaging the thread formers and first and second restraining means on opposite sides of the thread formers.

24. Apparatus as claimed in Claim 23 in which the first restraining means comprises part of the mounting slidable with respect to the retainer element during longitudinal movement of the mounting.

25. Apparatus as claimed in Claim 23 or Claim 24 in which the second restraining means comprises a clamping ring.

26. Apparatus as claimed in Claim 23 or Claim 24 or Claim 25 in which the circumferential ends of the thread formers have rebates, the rebates of the adjacent ends of adjacent thread formers forming radially out wardly facing recesses along which the retainer elements extend longitudinally.

27. Apparatus for manufacturing a fibre-reinforced resin pipe substantially as described herein with reference to the accompanying drawings.