GB2048424A

GB2048424A - Producing fibre reinforced plastics tube

Info

Publication number: GB2048424A
Application number: GB7915023A
Authority: GB
Original assignee: Railko Ltd
Current assignee: Railko Ltd
Priority date: 1979-04-30
Filing date: 1979-04-30
Publication date: 1980-12-10
Also published as: GB2048424B

Abstract

A method and apparatus for continuously producing fibre reinforced plastics tube has a section "A" in which a fibrous sheet 1 is spirally wound into a cylindrical tube 1A on a tubular needling mandrel 3 by which the walls of the tube is needled to provide radially interlocking fibres. The needled tube is longitudinally displaced into a section B where it passes over a support mandrel 3D. The mandrel 3D includes a distributor head 9 by which resin is applied to the inner surface of the tubular wall 1a to impregnate the fibrous tube until such resin is visible on the outer surface of the tube. Following impregnation, a protective coating 10 is spirally wrapped over the outer surface of the tube as the tube passes into a section "C" having heaters 13 by which the resin is cured. The cured tube 1B emerging from the heaters 13 can pass into a section D where a saw 15a which is movable longitudinally in unison with the tube can part-off pieces of the tube (as may be required for plain cylindrical bearings). <IMAGE>

Description

SPECIFICATION A method of and apparatus for producing plastic tube This invention relates to a method of and apparatus for producing plastic tube.

More particularly, the invention concerns plastic tube having fibre reinforcement and which can be economically and speedily manufactured by a continuous production technique to be of indefinite length.

According to the present invention there is provided a method of continuously producing fibre reinforced plastic tube which comprises spirally winding a sheet of fibrous material into tubular formation, needling the tubular formation to provide radially interlocking fibres within the wall of the tube; impregnating the needled tube with resinous fluid and curing the resin impregnated tube.

Further according to the present invention there is provided apparatus for continuously producing fibre reinforced plastic tube from a sheet of fibrous material comprising tube forming means for continuously spirally winding the fibrous sheet into a tube; means for displacing the fibrous tube longitudinally; means for needling the tube to provide radially interlocking fibres within the wall of the tube; means for impregnating the needled tube with resinous fluid, and heating means through which the resin impregnated tube is fed continuously for curing the resin.

Many natural and synthetic fibrous bodies can be converted into felts by the known principle of needling or felting whereby one or more sheets or layers of the fibres is pierced in reciprocating manner with an array of barbed needles so that some fibres are carried wholly or partially through the thickness of the layer or layers by the barbs of the needles and thereby form an interlock of entangled fibres. This principle has been applied to the manufacture of tubular felts either in discrete lengths or in a continuous process by needling the fibres of a fibrous sheet as such sheet is built up in layers to form a tube by winding the fibrous sheet spirally into a tube on a mandrel (or into a band tensioned between two mandrels).By this technique tubular felts of different diameter can be produced by changing the mandrel diameter (or by changing the spacing between, or the relative diameters of, the aforementioned two mandrels).

An example of a needle loom device for producing needled tubular felts in the manner described above is marketed by Oskar Dilo KG under the Trade name "RONTEX". With this known device the tubular felts produced are of a porous nature and primarily serve for filtration purposes (such filters being known generally in the art as "filter candles''). Furthermore, it has been suggested binding the filters with appropriate binding agents to vary the porosity and strength of the filter structure as required. The treatment of a filter candle with a binding agent requires a length of the needled tubular felt to be removed, coated with the binding agent and usually subjected to heat treatment to ensure that the required porosity and capillary structure of the filter is maintained.By the present invention however the needled tube which evolves continuously as the result of the spiral winding of the fibrous sheet is continuously impregnaged with the resinous fluid and thereafter fed continuously through a heat curing region. The tubular product thus formed can therefore have a non-porous structure and may serve, for example, as piping or conduiting for conveying corrosive materials.

The fibrous nature of the sheet of material should readily permit resin impregnation throughout the tube wall by the application of the resinous fluid to the wall under pressure.

Possibly the tracks formed by the needles as a result of the needling operation assist in the flow of the resin through the tubular felt. By the present invention therefore, the wall of the tube of fibrous material can be impregnated with a resin or resinous mixture which then gels and is partially or wholly cured to produce a fully impregnated, high strength, fibre reinforced plastic tube continuously, economically and with minimum labour.

The fibrous material which is wound into the tubular formation may comprise natural or synthetic fibres or mixtures of such fibres in staple or continuous fibre form which are capable of being felted by the above described needling process. The sheet of fibrous material may therefore, for example, be constructed from yarns and may be in the form of a cloth, a tow or a lap. Examples of materials in which the fibrous sheet can be formed and which are readily susceptible to needling are polyesters, polyamides, polyimides, polyaramides, fluorocarbons, polyolefins, polyacrylics and cellulosics.Less easily needled or felted fibres may be incorporated in the sheet with more readily felted fibres to give particular features or characteristics to the sheet by mixture; for example carbon fibres, glass fibres or other inorganic fibres may be blended with thermoplastic fibres to give strength and stiffness to the tubular product.

The resin fluid used will depend on the use and properties required of the finished plastic tube and a wide variety of thermosetting and thermoplastics resins and rubbers are suitable; examples of suitable resinous fluids include phenolics, cresylics, epoxies, unsaturated polyesters, polyurethanes, polyimides, castable polyamides, furanes and acrylics.

Preferably the needled tube is impregnated with the resinous fluid by the application of such fluid to the inner surface of the tube wall. This is considered particularly advantageous as it facilitates close control of the resin impregnation whereby full impregnation of the tube can readily be observed when the resinous fluid becomes visible or oozes from the outer surface of the tube wall (and the pressure and flow of the resinous fluid together with the rate of displacement of the needled tube can be monitored accordingly to provide the desired impregnation). Furthermore, it is believed that the impregnation of the needled tube from within the tube provides a relatively "clean" process whereby excess resinous fluid which may collect or drip from the outer surface of the tube can easily be cleared.Conveniently the resin is applied to the inside of the needled tube through a distribution head which is an extension of the tube forming means. The distribution head conveniently comprises a mandrel which corresponds in shape to the bore of the tube to provide a support over which the needled tube is slidable.

The needled tube will usually, but not essentially, be cylindrical. In producing needled tubes having a relatively large internal diameter by the spiral winding technique as discussed above, it is possible for the needle tube to be fed continuously from (for example two or more mandrels of) the tube forming means in a shape other than cylindrical; for example the tube as initially formed may be of generally elongated, oval or pear-shaped cross section and the process and apparatus of the present invention can include tube re-shaping means by which a non-cylindrical needled tube can be formed into a cylindrical shape, preferably subsequent to the needling operation and prior to the resin impregnation.The tube re-shaping means preferably comprises a funnel-like conduit through which the tube slides during its displacement from the tube forming mandrel(s) to be guided and ie-shaped over a cylindrical mandrel. This latter cylindrical mandrel conveniently includes the distribution head through which the resinous fluid is applied to impregnate the tube.

The present invention was primarily developed to facilitate the production of resin bonded plain bearing bushes by continuously producing the fibre reinforced plastic tube and parting off from such tube longitudinally extending pieces to provide the plain bushes as aforementioned (or for further processing to form flanged or segmental bearings). Still further therefore, the present invention includes bearing bushes when formed from fibre reinforced plastic tube produced by the method and apparatus of the present invention.As an example of the application of the invention to the formation of bearing bushes the sheet of fibrous material may be of linear polyester and the resinous fluid with which the fibrous needled tube is impregnated may be a filled unsaturated polyester containing a fine dispersion of solid lubricant such as graphite or Molybdenum disulphide with or without fine particles of metal or metal oxides.It will be appreciated that the fibre diameter and density of the fibrous material from which the tube is formed, the degree of needling, the viscosity of the resinous fluid, particle size of fillers and characteristics of lubricants which may be applied to the needled tube will be selected to give the required strength, frictional and wear properties of the fibre reinforced plastic tube consistent with even and complete penetration and distribution of the filled or unfilled resin impregnation throughout the wall of the needled tube.

One embodiment of the present invention as applied to the continuous production of fibre reinforced plastic tube and plain bearing bushes will now be described, by way of example only, with reference to the accompanying illustrative drawings, in which: Figure 1 illustrates in part section a continuous flow line for producing plain bearings from plastic tube; Figure 2 schematically illustrates the location of needling units associated with the tube forming means which forms part of the apparatus in Fig. 1, and Figure 3 shows a modified arrangement for tube forming means and resin impregnation means which can be substituted for the corresponding regions in the arrangement shown in Fig.

1 and which modification is particularly suitable for forming a large diameter needled tube.

The apparatus in Fig. 1 is shown as comprising four longitudinally consecutive regions indicated at sections A, B, C and D. Section A comprises a tubular needle felting or loom device as is known in the art and in particular a device as is marked by Oskar Dilo KG under the trade name "RONTEX 50"; Section B comprises a resin impregnation region; Section C comprises a heating and curing region for resinous fluid, and Section D comprises a saw table by which the tubular product can be cut into appropriate lengths to form bearing bushes (this latter section can optionally include an auxilliary haul-off device for the plastic tube).

A sheet of fibrous material in the form of a web 1 such as that taken from the output of a carding machine is fed continuously by means of a conveyor 2 on to a tubular needling mandrel 3 where it is wound spirally into tubular formation as indicated at 1A and to the required wall thickness. The mandrel 3 is tapered slightly to be of frusto conical form and longitudinal displacement of the spirally wound tube 1A is achieved by driven rollers 5 and 6 which apply pressure to the outer surface of the tube to urge it into contact with a spirally grooved feed roller 4 (which may be idling or driven) mounted on the mandrel 3; the reaction of the tube 1A on the feed roller 4 imparts a firm, regular and variable longitudinal displacement or traction to the tube 1A.In addition to urging the tube 1A into contact with the feed roller 4, the rollers 5 and 6 serve to wind the sheet 1 into its tubular formation.

Situated above and below the mandrel 3 are needle boards 3A each of which carries an array of barbed needles 3B (see Fig. 2). For convenience the needle boards have been omitted from Fig. 1. The barbed needles 3B are substantially parallel in their array and are reciprocated continuously and substantially vertically to repeatedly pierce the wall of the fibrous tube 1 A while the latter is rotated relative to the needle boards 3A. As seen in Fig. 2, many of the needles 3B are offset from the centre line of the tube 1A and consequently they pierce the tube wall at various angles so that the rotation of the tube produces a criss-cross pattern of needle tracks indicated at 3C to form a highly efficient interlock of fibres through the wall of the tube which serves to enhance the strength of the final plastic tube which is to be produced.

The spirally wound and needled cylindrical tube 1A is displaced longitudinally from Section A to Section B and during such displacement is supported on a tubular extension 3D of the needling mandrel 3. In the Section B the needled tube 1A is impregnated by the application thereto of resinous fluid which may be liquid resin or filled resin or resin mixture suitably catalysed. The resin is applied to the internal cylindrical surface of the tube 1A by means of a distributor head 9 which is supported in the tube 3D and is fed with resin under pressure by way of a pipe 7 from a reservoir, the pipe 7 extending through the bore of the mandrel 3 as indicated at 8.Resin is applied from the distributor head 9 to the wall of the tube 1A while the latter is displaced longitudinally and slides over the head 9 and the resin pressure, viscosity of the resin and the period of resin impregnation are controlled to give complete impregnation for a given wall thickness and density of the needled tube; complete impregnation is readily determined by observing the appearance of resin oozing from the outer cylindrical surface of the tube 1A. Immediately following resin impregnation, at a region indicated at 11, the outer cylindrical surface of the now wet resin impregnated and rotating tube may be over-wrapped spirally with a protective coating such as paper, cellulose or plastic foil or tape indicated at 10.

Such a protective coating on the impregnated tube facilitates the use of support rollers 12 which can be positioned under the tube where necessary (particularly for large thick walled tubes) and alleviates resin run-off during passage of the tube 1A through the curing section C where heat is applied to cure the resin, for example by use of heating mantels 13 or other convenient forms of heating such as radiant or hot air.

On issuing from the curing Section C the cured or partially cured fibre reinforced plastic tube 1 B may be further supported by rollers 14 or by an auxilliary haul-off unit (not shown) and sawn to required lengths on a saw table 15 to provide plain bearing bushes 1 C. The saw 1 5A on the saw table 15 is controlled to be displaceable in unison with the rate of longitudinal displacement of the tube 1 B.

The tube winding and resin impregnation regions shown in Sections A and B of Fig. 1 are primarily intended for the production of cylindrical plastic tube having a relatively small internal diameter and these Sections can be replaced by the corresponding Sections A and B in Fig. 3 for the formation and impregnation of cylindrical tubes having relatively large internal diameters.

In Fig. 3 the needling mandrel 3 is supplemented by a second mandrel 17. The mandrels 3 and 17 are located in side-by-side relationship and may be of the same shape and dimensions or of different dimensions. The needled tube 1A is developed in the case of Fig. 3 as a continuous and spirally wound band from the sheet 1 which is wound to enclose the two mandrels 3 and 17. The band length of the sheet 1 which extends around both mandrels 3 and 17 (and in fact the internal diameter of the finished cylindrical plastic tube) is adjusted by varying the diameter of one or both mandrels 3 and 17 and/or the spacing between these mandrels. As in the case of Fig. 1 needling is carried out above and below the needling mandrel 3 to provide a similar criss-cross pattern of needle tracks with appropriate fibre interlock.The spirally wound tube which is formed around the mandrels 3 and 17 and displaced longitudinally from these mandrels by the pressure rollers 5 and 6 (acting in conjunction with feed rollers 4) will have a non-circular section, usually a section of elongate, oval or pear-shaped form will be provided and the tube thus initially formed is displaced into a re-shaping device comprising a funnel-like conduit 21. The conduit 21 brings the tube 1A into a cylindrical shape and guides the tube during its longitudinal displacement on to a cylindrical mandrel extension 20 over which the tube 1A is slidable.The mandrel extension 20 supports the tube during its longitudinal displacement and includes the resin distribution head through which the needled and cylindrical tube 1A is impregnated (from its internal cylindrical face) with resinous fluid supplied (by way of conduiting 18 and 19) under pressure from a reservoir. The impregnated tube is then provided with its protective coating by over-wrapping at 10 and passed through the curing section as discussed with reference to Fig. 1.

Where required, the strength or other properties of the fibre reinforced plastic tube can be modified by feeding into the spiral winding device of Section A a layer or layers of appropriate fibres, cloth, tissue, scrim yarns or rovings which can be arranged in any desired position in the tube wall. For example, a plastic tube suitable for use in the manufacture of a very efficient and economically viable bearing material can easily be produced by feeding a thin sheet or layer of P.T.F.E. fibre (such as a carded lap, scrim, cloth or roving) to form the inside layer of a tube on the needling mandrel 3 and building up to the required tube wall thickness with a considerably cheaper backing fibre such as polyester. This can be achieved by feeding the different material sheets side-by-side on to the feed conveyor 2.Plain bearing bushes produced from such a plastic tube have excellent functional and wear properties on their inside cylindrical surface where such characteristics are required, but use a minimum of the very expensive P.T.F.E. fibre to achieve this result (while excellent adhesion of the P.T.F.E. sheet to the backing material can be achieved together with considerable strength and load-bearing properties for the bushes).

In a further example, a fibre reinforced plastic tube having exceptional regidity has been produced by incorporating a thin layer of high modulus carbon fibres amounting to only 5% by weight of the total fibre content in a polyester fibre needled tube impregnated with a catalysed epoxy resin.

Typical tube diameters which can be produced by this process and operation of the present invention are in the range 4 mm to 500 mm inside diameters with wall thicknesses up to approximately 30 mm and needled tube densities of up to 0.5 gm/cm3. Some typical production speeds are as follows: Needled tube density (prior Tube Outside Tube Inside to impregnation Output speed Diameter (mm) Diameter (mm) (g/cm3) (Metres/hour) 60 25 0.3 18 50 30 0.3 22 33 25 0.23 32 95 80 0.4 15 212 200 0.26 8.4

Claims

1. A method of continuusly producing fibre reinforced plastics tube which comprises spirally winding a sheet of fibrous material into tubular formation and longitudinally displacing said tubular formation; needling the tubular formation to provide radially interlocking fibres within the wall of the tube; impregnating the needled tube with resinous fluid and curing the resin impregnated tube.

2. A method as claimed in claim 1 which comprises impregnating the needled tube with the resinous fluid by applying such fluid to the inner surface of the tube wall.

3. A method as claimed in claim 2 which comprises controlling the application of the resinous fluid to the inner surface of the tube wall so that full impregnation of the tube wall is apparent by such fluid becoming visible on the outer surface of the tube wall.

4. A method as claimed in any one of the preceding claims which comprises controlling the application of the resinous fluid by adjusting one or more of the pressure at which the resinous fluid is applied, the flow at which the resinous fluid is applied or the rate of displacement of the needled tube relative to a position at which the resinous fluid is applied.

5. A method as claimed in any one of the preceding claims which comprises spirally winding the sheet of fibrous material into a non-cylindrical tubular formation and re-shaping such tube during longitudinal displacement thereof into a substantially cylindrical formation.

6. A method as claimed in claim 5 in which the reshaping of the tube is subsequent to the needling and prior to the impregnation with resinous fluid.

7. A method as claimed in any one of the preceding claims which comprises spirally overwrapping the outer surface of the needled tube with a protective coating.

8. A method as claimed in claim 7 which comprises applying the protective coating subsequent to impregnation.

9. A method as claimed in any one of the preceding claims which comprises spirally winding the fibrous material into tubular formation at a first station, longitudinally displacing the tube from the first station through a second station at which the tube is impregnated with the resinous fluid, and longitudinally displacing the impregnated tube from the second station through a third station at which the resinous fluid is cured.

10. A method as claimed in claim 9 in which the needling is effected at the first station.

11. A method as claimed in any one of the preceding claims which comprises longitudinally displacing the tube, at least in part, by the application of force thereto from the spiral winding operation.

12. A method as claimed in any one of the precedng claims which comprises longitudinally displacing the tube, at least in part, by haul-off means.

13. A method of producing resin bonded plain bearing bushes which comprises continuously producing fibre reinforced plastics tube of substantially cylindrical formation by the method as claimed in any one of the preceding claims and parting-off from such tube longitudinally extending pieces to provide the plain bushes.

14. A method as claimed in either claim 1 or claim 13 and substantially as herein described.

15. Apparatus for continuously producing fibre reinforced plastics tube from a sheet of fibrous material comprising tube forming means for continuously spirally winding the fibrous sheet into a tube; means for displacing the fibrous tube longitudinally; means for needling the tube to provide radially interlocking fibres within the wall of the tube; means for impregnating the needled tube with resinous fluid, and heating means through which the resin impregnated tube is fed continuously for curing the resin.

16. Apparatus as claimed in claim 15 in which the means for impregnating the tube is located within the tube whereby the resinous fluid is applied to the inner surface of the tube wall.

17. Apparatus as claimed in claim 16 in which the resinous fluid is applied to the inner surface of the tube wall through a distribution head comprising a mandrel over which the needled tube is slidable.

18. Apparatus as claimed in claim 17 in which the mandrel substantially corresponds in shape to the bore of the tube to provide support for the tube.

19. Apparatus as claimed in either claim 17 or claim 18 in which the distribution head is carried as an extension of the tube forming means.

20. Apparatus as claimed in any one of claims 16 to 19 and comprising control means whereby the application of resinous fluid to the inner surface of the tube wall can be adjusted so that full impregnation of the tube wall is apparent by such fluid becoming visible on the outer surface of the tube wall.

21. Apparatus as claimed in any one of claims 15 to 20 in which the tube forming means provides a tube in a shape other than cylindrical and tube re-shaping means is provided by which the tube is formed into a substantially cylindrical shape.

22. Apparatus as claimed in claim 21 in which the tube re-shaping means comprises a funnel-like conduit through which the tube slides during its longitudinal displacement to emerge therefrom in substantially cylindrical shape.

23. Apparatus as claimed in either claim 21 or claim 22 in which the tube re-shaping means is located longitudinally between the tube forming means and the impregnating means.

24. Apparatus as claimed in claim 23 when appendant to claim 17 in which the tube reshaping means re-shapes the tube and guides such re-shaped tube onto the mandrel which comprises the distribution head.

25. Apparatus as claimed in any one of claims 15 to 24 and comprising means for spirally over-wrapping the outer surface of the needled tube with a protective coating.

26. Apparatus as claimed in claim 25 in which said over-wrapping means is located so that the tube is provided with the protective coating subsequently to its impregnation.

27. Apparatus as claimed in any one of claims 15 to 26 in which longitudinal displacement of the tube is provided, at least in part, by the tube forming means.

28. Apparatus as claimed in any one of claims 15 to 27 in which longitudinal displacement of the tube is provided, at least in part, by haul-off means.

29. Apparatus as claimed in any one of claims 15 to 28 and comprising means for partingoff longitudinally extending pieces of the tube subsequent to said tube passing through the heating means.

30. Apparatus as claimed in claim 29 in which the parting-off means is longitudinally displaceable in unison with the tube during the parting-off of said pieces.

31. Apparatus for continuously producing fibre reinforced plastics tube substantially as herein described with reference to Figs. 1 and 2 of the accompanying illustrative drawings.

32. Apparatus as claimed in claim 31 when modified substantially as herein described with reference to Fig. 3 of the accompanying illustrative drawings.

33. Plastics tube or bearing bushes when produced by the method as claimed in any one of the preceding claims 1 to 14.