GB2245893A

GB2245893A - Fibre reinforced plastic composites

Info

Publication number: GB2245893A
Application number: GB9112318A
Authority: GB
Inventors: Alan Cooper; James Mcintosh Methven
Original assignee: SHAW JOHN Ltd
Current assignee: SHAW JOHN Ltd
Priority date: 1990-07-10
Filing date: 1991-06-07
Publication date: 1992-01-15
Anticipated expiration: 2011-06-07
Also published as: GB9112318D0; GB2245893B; GB9015149D0

Abstract

A method of manufacturing fibre reinforced, plastics composites, in which the matrix (22) and fibre reinforcement components (2) which form the precursor are combined in a die (5) wherein the matrix (22) and the fibre (2) content is controlled to the desired ratio, and to the resultant precursor emerging from the die is applied microwave energy as a heating means (11) to obtain total, partial, or completion of crosslinking of the thermosetting resin matrix (22) of such composites. The invention also includes apparatus (1 - 17, 19 - 23) for carrying out the method, and composites (18) produced by the method and apparatus. The method is particularly a pultrusion process. The die (5) may or may not be heated. The composite may be of strand, rod or web-like form. The precursor may be twisted about the longitudinal axis, or when in the form or a strand or rod, it may be overwound by one or more helically arranged fibres (10) from an overwinding means (21) before the application of microwave energy. The crosslinked composite may be cut in lengths and provided with screw threads at one or both ends. Uses:- Reinforcing and tension rods, and roof bolts in civil engineering structures and strata control. <IMAGE>

Description

FIBRE REINFORCED PLASTIC COMPOSITES This invention relates to the manufacture of fibre reinforced plastic composites.

The invention relates particularly but not exclusively to the production of elongates such as strands or webs produced by the pultrusion process, in which process, variously oriented reinforcing fibres, for example those made of glass or carbon, are drawn initially through a bath containing the matrix of an uncured thermosetting resin, and the resultant precursor - being the matrix/fibre combination is subsequently drawn, through a die which, operating at elevated pressure, forces resin into the structure of the fibre, wipes off excess resin and forms the precursor to the desired shape e.g. circular section, th- die being heated to cause crosslinking of the matrix to form an infusible material, being the finished composite, having an axially constant cross section.

Complete crosslinking of the matrix is of course dependent on the transmission of conducted thermal energy, initially from the moulding surface of the heated die to the surface of the precursor, and subsequently by conduction through the precursor to its longitudinal axis.

The greater the dimension from the surface to the axis of the precursor the longer it must remain in contact with the heated die to ensure complete crosslinking of the core matrix.

Thus, the productivity of the machine producing such composites is largely governed by the efficiency of the heating and the crosslinking processes. If the precursor is caused to move through the heated die too rapidly then a core of uncured matrix will remain downstream of the heated die exit which results in a lower quality product, as the core may or may not cure totally or partially as a result of the latent heat of the composite.

According to a first aspect of the present invention there is provided a method of manufacturing fibre reinforced, plastics composites, in which the matrix and fibre reinforcement components which form the precursor are combined in a die where the matrix and the fibre content is controlled to the desired ratio, and microwave energy is applied to the resultant precursor emerging from the die as a heating means to obtain total, partial, or completion of crosslinking of the thermosetting resin matrix of such composites.

According to a second aspect of the invention there is provided apparatus for carrying out the method of the first aspect comprising a die through which the matrix/fibre precursor is drawn, and downstream of the die exit a microwave energy unit is provided to heat the precursor to obtain total, partial or completion of crosslinking of the resin matrix.

According to a third aspect of the invention there is provided a fibre reinforced plastics composite manufactured by the method and/or apparatus in accordance with the first and/or second aspects defined above.

Thus, according to this invention, the necessary source of heating is provided by microwave energy, a method which completely eliminates any temperature gradient between the periphery and the axis of the precursor, which is the main disadvantage of prior art conductive heating.

The die may be unheated i.e. at ambient temperature, in which case total crosslinking is effected by microwave energy. Alternatively, existing heated dies may be employed, to provide at a high rate of throughput a partially crosslinked composite, so that the microwave energy is subsequently used to provide partial or completion of crosslinking.

When using an unheated die the precursor may be supported by a die extension contiguous with an exit opening of the die. With or without a die extension the precursor when in the form of a strand or rod, may be overwound by one or more helically arranged fibres which maintain the formation of the precursor before arrival at the microwave energy unit.

The helix angle and the tension at which the overwound fibres are applied, combined with the tension induced in the precursor are all variable. The surface finish and the geometrical formation of the finished composite is controlled by these variables, and after helical overwinding has taken place the matrix is crosslinked by the application of microwave thermal energy. Instead of overwinding, the precursor may be twisted about the longitudinal axis to provide stability to its shape before arrival at the microwave heating unit.

Thus, according to this invention, the necessary source of heating is provided by microwave energy, a method which completely eliminates any temperature gradient between the periphery and the axis of the precursor, which is the main disadvantage of prior art techniques relying solely on conductive heating to achieve cross linking.

The product of the inventive method and apparatus, viz. the fibre reinforced plastics composite may, when cut to suitable lengths, be used as part of a reinforcing system for civil engineering structures, i.e. when in the form of a reinforcing rod. A similar rod may be used for strata control, e.g. in the manner of a roof bolt, during tunnelling and/or mineral mining operations. In the form of a tension member, the. composite may, when provided with a screw thread for tensioning purposes, be used as a replacement wall-tie, with the non-threaded end secured in a hole by glue or resin and with a tensioning nut applied and tightened after a suitable setting or curing time. If no tensioning action were required, and.only an improvement in shear were required, e.g. in a cracked or faulted rock face, then both ends of the member could be secured by glue or resin.

The method and apparatus of the invention will now be further described, in greater detail by way of example, with reference to the accompanying diagrammatic drawing.

Reinforced fibre 2 is drawn from the storage unit 1 by the action of the pulling means 16, the speed of which is controllable. The pulling means is for example an endless belt type haul-off unit. The reinforcement fibre is tensioned by the action of the brake unit 3 the torque and clamping pressure of which is adjustable. The reinforcement fibre is next pulled through an un-heated die 5 where it is combined with the matrix 22 supplied from a storage vessel 7 by a variable volume pumping means 6. The precursor 4 is supported by a die extension 20 until downstream thereof, the helical overwinding commences. One or more fibres 10 are helically overwound by an overwinding means 21 which rotates about the axis of the precursor and is supported by guidance bearings 9. The overwinding fibre 10 is conveniently supplied from one or more storage means 8.The overwinding means 21 is driven, for example, by an electric or a pneumatic motor 13, the speed of which is controllable. Tension in the overwinding fibre is preferably adjustable by a friction means 24 whilst rotational inertia of the fibre storage means 8 is controlled by the friction means 25.

The precursor next enters a microwave energy applicator 11 which is a form of waveguide, in which microwave energy supplied by magnetron 14 is confined. The microwave energy causes excitement of the molecular structure of the matrix component of the precursor 4 which results in an increase of temperature which results in crosslinking. The absorption of microwave energy may be enhanced by the inclusion of "lossy" materials such as carbon, iron powder and spinel ferrites. Excess microwave energy is absorbed by allowing it to heat water contained in a vessel 15.

Potential leaks of microwave energy at the product entry and exit points of the applicator 11 are prevented by chokes 23.

The composite emerges from the applicator 11 as a fully crosslinked product which if required, can be conveniently cut into finished lengths 18 by a saw 17.

Claims

1. A method of manufacturing fibre reinforced, plastics composites, in which the matrix and fibre reinforcement components which form the precursor are combined in a die where the matrix and the fibre content is controlled to the desired ratio, and to the resultant precursor emerging from the die is applied microwave energy as a heating means to obtain total, partial, or completion of crosslinking of the thermosetting resin matrix of such composites.

2. A method as claimed in Claim 1, in which the die is unheated.

3. A method as claimed in Claim 1, in which the die is heated.

4. A method as claimed in Claim 2, wherein the precursor is supported by a die extension contiguous with an exit opening of the die.

5. A method as claimed in any preceding Claim, wherein the precursor when in the form of a strand or rod is overwound by one or more helically arranged fibres which maintain the formation of the precursor before the application of microwave energy.

6. A method as claimed in Claim 5, wherein the helix angle and the tension at which the overwound fibres are applied, combined with the tension induced in the precursor, are all variable.

7. A method as claimed in any one of Claims 1 to 4, wherein the precursor is twisted about the longitudinal axis to provide stability to its shape before the application of microwave energy.

8. A method as claimed in any preceding Claim wherein, after the application of microwave energy, the composite is cut into finished lengths.

9. A method as claimed in Claim 8, wherein a screw thread is provided on one or both ends of a finished length.

10. A method as calimed in Claim 9, wherein the screw thread is injection moulded onto one or both ends of the finished length using a thermo formed plastics material.

11. A method of manufacturing a fibre reinforced, plastics composite substantially as hereinbefore described with reference to the accompanying drawings.

12. Apparatus for carrying out the method of any preceding Claim, comprising a die through which the matrix/fibre precursor is drawn, and downstream of the die exit a microwave energy unit is provided to heat the precursor to obtain total, partial or completion of crosslinking of the resin matrix.

13. Apparatus as claimed in Claim 12, wherein the die is provided with heating means.

14. Apparatus as claimed in Claim 12, wherein the die has no heating means.

15. Apparatus as claimed in Claim 14, wherein the die is provided with an extension contiguous with an exit opening of the die.

16. Apparatus as claimed in Claim 15, wherein an overwinding means is provided downstream of the die extension.

17. Apparatus as claimed in Claim 16, wherein the overwinding means is rotatable about the axis of the precursor.

18. Apparatus as claimed in Claim 16 or Claim 17, wherein the overwinding means is supported on guidance bearings.

19. Apparatus as claimed in any one of Claims 16 to 18, wherein the overwinding means comprises at least one reel of overwinding fibre.

20. Apparatus as claimed in Claim 19, wherein the reel(s) is rotated in an unwinding direction by a drive motor.

21. Apparatus as claimed in any one of Claims 16 to 20, wherein friction means is provided to adjust the tension in the overwinding fibre.

22. Apparatus as claimed in any one of Claims 19 to 21, wherein further friction means is provided to control the rotational inertia of the reel(s).

23. Apparatus as claimed in any one of Claims 12 to 22, wherein the microwave energy unit comprises a waveguide, generally of inverted, square section, "U"-configuration, with the precursor adapted to be drawn through the base of the "U", and with a magnetron provided in one limb of the "U".

24. Apparatus as claimed in Claim 23, wherein the other limb of the "U" is provided with a water reservoir to absorb excess energy.

25. Apparatus as claimed in Claim 23 or Claim 24, wherein chokes are provided at entry and exit points for the precursor at opposite ends of the base of the "U".

26. Apparatus for carrying out the method of Claims 1 to 11, substantially as hereinbefore described with reference to the accompanying drawings.

27. A fibre reinforced plastics composite manufactured by the method and/or apparatus in accordance with any preceding Claim.

28. An elongate fibre reinforced plastics composite of strand or rod-like form.

29. An elongate fibre reinforced plastics composite of web-like form.

30. A composite as claimed in Claim 28 having an external surface which is roughened or deformed by the application of helically overwound reinforcing fibre.

31. An elongate fibre reinforcing and composite member for civil engineering structures manufactured by the method of Claims 1 to 11 and/or by the apparatus of Claims 12 to 26.

32. An elongate fibre reinforcing and composite member for strata control or stabilization, manufactured by the method of Claims 1 to 11 and/or by the aparatus of Claims 12 to 26.

33. An elongate, fibre reinforced composite tension member manufactured by the method of Claims 1 to 11 and/or by the apparatus of Claims 12 to 26, and provided with a screw thread for tensioning purposes.

34. A member as claimed in any one of Claims 31 to 33, having an external surface which is roughened or deformed by the application of helically overwound reinforcing fibre.

35. A fibre reinforced plastics composite substantially as hereinbefore described with reference to the accompanying drawings.