GB2106029A - Method of and apparatus for manufacturing objects from short oriented reinforcement fibres or fibre mixtures - Google Patents

Abstract

Short oriented fibers contained in a slurry are deposited in a oriented condition on a filtration base after having passed through an orientation section (6). The filtration base takes the form of a mould filter (1) has a negative mould wall conforming to a complex contour area of an object to be moulded. The mould filter can be rotated about its axis of rotation during the deposition process. The mould filter and the orientation section are three- dimensionally adjustable one relative to the other. The method and apparatus are suitable for the manufacture especially of rotationally symmetrical components of high strength and complex outer or inner wall configurations. <IMAGE>

Description

SPECIFICATION Method of and apparatus for manufacturing objects from short, oriented reinforcement fibers or fiber mixtures This invention relates to method of and apparatus for manufacturing objects from short, oriented reinforcement fibers or fiber mixtures, where the reinforcement fibers are turned into a slurry with the aid of a liquid and after passing through an orientation section are deposited in an oriented condition on a filtration base, with the slurry liquid being extracted by filtration, and where the filter cake is then processed.

The state of the art comprises plane preforms of discontinuous (short) reinforcement fibers, where the fibers are turned into a slurry using a suitable liquid (e.g. glycerine) and, having passed a hydrodynamic or other orientation section, are deposited in an oriented condition on a plane or cylindrical filtration base. In the process the liquid is drawn off under a vacuum and removed by washing once the fleece has obtained the proper thickness. The remaining flat, plane fleece is then conventionally impregnated with suitable matrix resins and is processed to form plane prepregs or is pressed to form components. (ERDE process, cf. Kelly, A.

Proc.Roy.Soc., A319 (1970)95, Cooper, G.A., Review of Physics in Technology, 2(2) (1971)49., Dingle, L.E.

Conf, Carbon Fibers, 1974, London; MBB-Vakuum Trommel-Filter-Verfahren; cf. DE-PS 2 163799 and Richter, H., Kunststoffe 67, (1977) 12, p.739).

The state of the art also includes processes by which discontinuous fibers are drawn in a nonoriented condition under a vacuum on to a porous filter mould to form a preform, which in a known fashion is pressed with matrix binder or resin added (e.g. Vacumat process (GFRP industry) or egg flat process (paper industry)).

The state of the art also includes processes by which tubular shapes are centrifugally impregnated, following insertion of dry reinforcement layers, with suitable liquid matrix resin and are compressed and cured while being spun.

Said first process (ERDE process, MBB process) provides a diadvantage in that with complex shapes (such as integral compressor or turbine blades, pronounced ribbing, flanges, etc., or abrupt changes in section), the intended orientation of the fibers is destroyed on account of the displacements and tearing the fleece layer suffers during the pressure flow. The resulting discontinuities and voids severely weaken especially these highly-stressed regions of a component.

Said second processes (Vacumat process) produce randomly oriented fiber composite shapes which lack the strength required for highly stressed components.

Said last-mentioned processes for manufacturing reinforced tubular shapes under centrifugal force will admittedly produce high-strength parts, but these will invariably have relative smooth outer surfaces, because the insertion or snug fitting of sufficiently voluminous reinforcement fibers in deep and often narrow, perhaps intersecting notches in the mould is not, or not sufficiently practicable. This is another source of flaws (e.g. matrix enrichment).

According to one aspect of the present invention, there is provided a method of manufacturing objects from short, oriented reinforcement fibers or fiber mixtures, where the reinforcement fibers are turned into a slurry using a liquid and are deposited, after passing through an orientation section, in an oriented condition on a filtration base with the liquid being extracted by filtration. and where the filtered fiber cake is processed, wherein the filtration base takes the shape of a mould filter having a negative mould wall conforming to a complex contour area of an object to be manufactured.

The mould filter may be essentially rotationally symmetrical and rotated about its axis of revolution during the deposition process.

The mould filter may be three-dimensionally variable and be maintained in defined oscillating and/or adjusting motion relative to the orientation section of the oriented reinforcement fibers introduced during the deposition process.

Moreover, the orientation system may be threedimensionally variable and at least its starting area may be maintained in defined oscillating and/or adjusting motion during the deposition process. The mould filter and the orientation section can accordingly be adjusted and maintained in adjustment if necessary, before and during a deposition phase in anythree-dimensional constellation of the mould filter with the orientation section. The position can accordingly be selected to suit the respective intended contour of the moulded article. The fiber deposition angle, e.g., an be adapted, in cooperation with a variable-speed rotating mould filter, to suit a maximally wide angular range. Since orientation of fibers is generally achieved in laminar flow induced by gravity, the orientation section is in its exit area moderately inclined from horizontal position.This inclination should preferably remain unchanged. Approximately rotationally symmetrical, three-dimensional bodies of complex moulding surface can be produced such that also deep and complex ribbing or projections can be filled with oriented fiber layers such that a selectivereproducible structure can be achieved which is an optimum in terms of fiber content, fiber angle, thickness of layer for the respective fiber angle, and continuity of layer transitions to adjacent contour surfaces. Ribbing, flange fillets, increases in cross section, etc., can be achieved by selective, repeated passes using an orientation section with one or several outlets, where increasing coverage causes layers to blend smoothly with adjacent layers to form a uniform stress structure.Angular layers are produced by suitably coupling translatory movement of an orientation section with intermittent or constant rotary movement of the mould filter, where also in the manufacture of discs, practically any desired angular position or predominantly tangential or radial fiber angles can be achieved.

The oriented reinforcement fibers of the orientation section may be introduced into a mould filter, which is nonplanar and essentially rotationally sym metrical, enabling complex external contourrs to be moulded, as for instance the external contour of a disc or cone.

For the purpose of moulding an internal contour, the oriented reinforcement fibers of the orientation section may be externally routed to a mould filter which is nonplanr and essentially rotationally symmetrical.

Nonoriented fiber material may be routed to the mould filter also during a deposition cycle. The admission of fibers is continuous, or intermittent and suitably by centrifugal insertion of nonoriented fiber material for improved three-dimensional netting or anchoring of the layers deposited.

After the deposition process the liquid is advantageously extracted by washing without delay, and/ or the fiber cake desposited is compressed - especially under centrifugal force if the mould filter is centrifuged together with the fiber cake deposited and/or under linear compression force if the filter with the filter cake on it is subjected to pressing.

Compression and centrifugal pressure also enable the moulding of simple counter contours of especially thin-walled objects, and augment the density of the fiber material without disturbing the layer angle of the material deposited.

Advantageously, known methods are modified by using a suitable resin that preferably will not cure at room temperature to make the slurry. This obviates the need for washing and filtrate drying operations, and it eliminates the risk of any attending contamination or damage to the fleece. After removal, the slurry resin can be recycled by suitable provisions.

According to a further aspect of the invention, there is provided apparatus for performing the method comprising a fiber deposition system, which includes a filtration base which takes the shape of a mould filter having a negative mould wall conforming to a complex contour area of an object to be manufactured, and an orientation section for feeding short fibers orfiber mixtures contained in a slurry to the filtration base.

Preferably, the mould filter is made of a suitable filter material, comprisig of one or several parts, and comes with or without backing.

As mould filters, use can optimally be made of practically all porous, deformable materials having the requisite mechanical and chemical resistance, such as sintered bodies made of metal powder, silicate or alumina silicate mixtures, porous carbon or graphite, or plastics or plastics-bonded ceramic materials.

The mould filter is preferably provided with a porous mask to facilitate the release of sticky fiber shapes after the slurry process. To this end the mould filter is lined, e.g., with an integral or discrete porous mask of, e.g., sintered polytetrafluroethylene as a release agent.

Another suitable improvement ot a mould filter is to premanufacture conventionally (by Vacumat process or other) on a porous positive pattern a thin, nonoriented fleece filter, or to compose a wovenfabric filter thereon which lends itself to becoming an integral part of the surface of the resulting fiber shape. Suitably selected, it may serve the function of a surface protection layer or of a finely textured surface layer (e.g. carbon glass fleece). Fortempor arilystrengthening said fiber fleece filter to facilitate handling, it can be impregnated with a binder that is compatible with resin, or with resin proper.

The mould filter may be attached inside orto a variable-speed spinning vessel. The latter is operated intermittently or continuously. When the mould filter is attached inside the spinning vessel, complex external contours can be achieved, whereas internal contours are best moulded when the mould filter is attached on or on the outside of the vessel or inside a suitably formed other revolving body.

The filtration vacuum and the slurry liquid may be evacuated by means of a deposition system having a collector vessel sealed off from the spinning vessel.

The vacuum extraction can be achieved also by drawing the slurry liquid off through a revolving tubular shaft.

The deposition system for the oriented reinforcement fibers is preferably capable of controlled pivotal and/or linear movement and is adjustable relative to the orientation section in order, for example, to permit maximally parallel and accurate adaptation of the orientation section or its nozzle heads to the respective contour of the moulded article.

The orientation section may be capable of controlled travel and adjustment relative to the deposition system additionally for adaptation of the angular deposition of fibers.

The deposition system can be fitted with a pressing device having a ram which when urged against the filtration cake deposited will improve the consistency of the fiber mixture deposited without destroying its structure. The ram more particularly includes a head or preferably split shell adapted to suit the intended free surface which is fixedly connected to the spinning vessel and which is applied under pressure, so that the deformable fiber layer compound will under the compression pressure also mould into less complex counter contours.

The present invention accordingly permits complex components or preforms thereof of short fiber-reinforced material to be produced by way of a fiber slurry and with the use of a conventional conditioning facility. The fiber slurry is oriented in an orientation section and is deposited in a defined fashion on a special mould fiber which contains the complex surface of the moulded article in negative representation. After the slurry treatment the fleece body, which may or may not have been composed by spinning or prepressing, is then released from the filter mould, trasferred to the pressing mould and there cured and concurrently postimpregnated, or it is postimpregnated with resin in the mould filter and partially cured to form a prepreg body giving improved stability of form and facilitating handling before the pressing and curing operations.

The method and apparatus of the present invention permit the manufacture of short-fiber reinforced or non-reinforced preforms also with other, perhaps glass, ceramic or metal powder matrices. Powder mixtures can also be homogeneously distributed or can be selectively distributed using several nozzles.

The powdery matrix is turned into a slurry together with short fibers, is passed through the orientation section, and is deposited on the mould filter. In the process the powder matrix and the oriented fibers remain behind in the form of filter cake, and the slurry liquid is extracted under vacuum, centrifugal forces and/or compression. Here, again, an additive can be added to the slurry liquid which as a temporary binder is compatible with the subsequent pressing cycle or which in fact is indispensible to it (e.g. reacting constituents, sintering additions).

Another advantage is provided when in the subsequent manufacturing cycle, use is made of compatible mould filter masks which in the sintering process, e.g., will decompose with no residues or reaction.

The invention will now be more particularly described, by way of example, with reference to the accompanying drawings: Figure 1 illustrates one embodiment of a conditioning and deposition system operating in accordance with the present invention, Figure 2 is a schematic variant on the deposition system of Figure 1 for the deposition of oriented reinforcement fibers to manufacture externally configured moulded articles, Figure 3 illustrates another deposition system for manufacturing externally configured moulded articles, Figure 4 illustrates a deposition system for manufacturing internally configured, conical moulded articles, Figure 5 is a schematic illustration and illustrates various routes for the outlet of an orientation section for manufacturing a rib-shaped moulded article, Figure 6 is a section taken along line AA of Figure 5, Figure 7 is a schematic arrangement and illustrates the routing of an orientation section and of a circular disc to be produced, with the mould filter being rotated in steps, Figure 8 is a schematic representation similarto that of Figure 7 iilustrating the manufacture of a circular disc, with the fibers being deposited circu larly, Figure 9 is a representation similar to those of Figures 7 and 8 illustrating the manufacture of a disc, where the orientation section oscillates and the circular mould filter continuously rotates for manufacturing a disc, and Figure 70 is a schematic representation similar two that of Figure 7 and illustrates the routing of an orientation section with reference to a continuously rotating mould filter for manufacturing a disc.

Figure 1 is a schematic representation and illustrates a process facility for manufacturing a centrifugal compressor impeller.

The system essentially comprises a conventional conditioning system 21 and connected thereto a deposition system 20.

The conditioning system 21 essentially comprises a reservoir 22 admitted into which are nonoriented reinforcement fibers 9 and slurry liquid 11 to form a slurry which is uniformly blended by means of an agitator R, a leveling vessel 24, with an agitator R, communicating with the reservoir 22 through a pump system P and with the deposition system 20 through an orientation section 6, where a further connection has been provided to the atmosphere 23, and a filtration and degassing vessel 26 for the slurry liquid extracted, which communicates with the reservoir 22 through a pump system P and has a vacuum connection 4 through which the slurry liquid from the deposition system 20 can be extracted.

The deposition system 20 essentially comprises an essentially vertically arranged spinning vessel 2 rotating about its vertical axis 5, and an internally mounted mould filter 1 at the upper end. The mount filter 1 exhibits the external contour of a centrifugal compressor impeller and is arranged relative to the orientation section 6 such that its four exit nozzles are equally spaced across the radius of the centrifugal compressore impeller such that oriented reinforcement fibers can be introduced in the one half of the moulded article in the making.

The spinning vessel 2 is rotatabiy arranged and sealed within a collector and vacuum vessel 3, and is operationally driven by means of a speed-governed motor M. Oriented reinforcement fibers 10 routed to the deposition system 20 are circularly introduced into the mould filter 1 (cf. Figure 8) until the entire mould filter 1 is filled with filter cake 7. Slurry liquid is extracted through the mould filter 1 via the evacuation connection 4 and the collector and vacuum vessel 3. The filtration effect is augmented by the rotation of the mould filter 1, which operates as an internal centrifuge. The centrifugal force acting on the mould filter 1 in operation causes oriented reinforcement fiber material to be deposited on the mould wall formed by the mould filter accurately and at considerable consistency of the fiber material without destroying the structure of the oriented fibers.After the inner region of the mould filter 1 according to Figure 1 has been filled with oriented fibers 1, the free mould surface of the mould filter 1 is compressed downwards by means of a suitable pressing device (omitted on the drawing) such that no voids remain in the mould filter 1 and that the moulding charge exhibits great overall density. The resultant preform will then be processed conventionally.

Figure 2 illustrates a variant on the deposition system of Figure 1. The system comprises a spinning vessel 2 having a mould filter 1 according to Figure 1 and an integrated vacuum extraction system 4 (tubular shaft design). The entire desposition system is arranged for rotation about a pivot 9 which essentially coincides with the center of the article to be moulded.

In a further variant on the embodimet of Figure 1 the orientation section 6 isthree-dimensionally variable and its starting area is adjustable relative to the mould filter 1 such that fibers oriented in the distribution section 6 can suitably be introduced into the mould filter 1.

Figure 3 illustrates a conical, split sheel with integral flanges, ribs and holes in its external contour (external contour moulding) in the making.

Here again the entire deposition system is pivoted into a nearly horizontal position, and the orientation section 6 is carried inwards in an essentially horizontal direction into the mould filter 1.

Figure 4 illustrates a conical, internally annularly and longitudinally ribbed shell moulded by means of lost or split filter cores. The cores 11 consist of a porous material (e.g. sand salt, gypsum, soluble open-pore core foam). The mould filter 1 is formed by. e.g., a multiple-layerfilterfabric or a porous sheet made of a metal that can be removed by melting. The deposition system according to Figure 4 essentially corresponds to that of Figure 3 and lends itself especially to moulding an internal contour. It has an orientation section 6 carried externally to the system in a nearly horizontal direction. One or more discrete deposition nozzles 6a approaching the mould filter tangentially are here used to fill the circumferentially extending ribs.

Illustrated in Figure 5 in perspective view are routes taken by a nozzle head arranged at the start of an orientation section 6; the moulded article in the making is a ribbed construction. The first route 12 of the nozzle head corresponds to a translatory movement in the long direction of the rib, and it is followed by a second, oscillating route 13 covering also the lateral regions of the moulded article. In this manner, ribs of considerable depth can be manufacture to accurately conform to true contour (cf. Figure 6) by means of stratum-oriented layers with continuous layer transitions in a rib section.

Figure 7 illustrates the route of the orietation section 6 relative to a circular mould filter designed for the manufacture of discs. Figure 7 especially illustrates the pattern of the reinforcement fibers deposited, with the orientation section 6 or its nozzle head being radially pivoted about point 10 and the disc mould being rotated stepwise. Points 0 to 9 are relative positions of the pivot point relative to the disc.

Illustrated in Figure 8 is another circular deposition pattern of fibers used in the manufacture of discs. In this arrangement the orientation section 6 is stationary, with the disc or the mould filter continously rotating clockwise.

The routing pattern illustrated in Figure 9 araing serves in the manufacture of circular discs. The reinforcement fibers exiting from the orientation section are deposited almost radially with respect to the mould filter, and with an oscillating stroke H of the deposition head of the orietation section. where the mould filter or disc rotates continuously. If the mould filter is made to rotate stepwise, deposition will be in an exactly radial direction.

The fiber deposition pattern illustrated in Figure 10 provides a rather consistent structure of a disc in the making. This pattern is produced when the orientation section 6, or its nozzle head, is pivoted radially about point DO and the mould is continuously rotated. Points Dud to D12 are relative positions for the reversal points 0 to 12 at the periphery of the disc.

Claims (29)

1. A method of manufacturing objects from short, oriented reinforcement fibers or fiber mixtures, where the reinforcement fibers are turned into a slurry using a liquid and are deposited, after passing through an orientation section, in an oriented condition on a filtration base with the liquid being extracted by filtration, and where the filtered fiber cake is processed, wherein the filtration base takes the shape of a mould filter having a negative mould wall conforming to a complex contour area of an object to be manufactured.

2. The method of Claim 1, wherein the mould filter is essentially rotationally symmetrical and is rotated about its axis of rotation as the oriented reinforcement fibers are being deposited.

3. The method of Claim 1 or 2, wherein during the deposition process the mould filter is threedimensionally variable and is maintained in defined oscillating and/or actuating motion relative to the orientation section of the oriented reinforcement fibers introduced.

4. The method of any one of Claims 1 to 3, wherein the orientation section is threedimensionally variable and at least its starting area is maintained in defined oscillation and/or actuating motion during the deposition process.

5. The method of any one of Claims 1 to 4, wherein the oriented reinforcement fibers of the orientation section are introduced into a mould filter which is nonplanar and essentially rotationally symmetrical.

6. The method of any one of Claims 1 to 4, wherein the oriented reinforcement fibers of the orientation section are routed externally to a mould filter which is nonplanar and essentially rotationally symmetrical.

7. The method of any one of Claims 1 to 6, wherein nonoriented fiber material is routed to the mould filter during the deposition process.

8. The method of any one of Claims 1 to 7, wherein after a deposition process, liquid used in the slurry is flushed out at an accelerated rate and/or the fiber cake is subjected to compression.

9. The method of Claim 8, wherein the mould filter is centrifuged together with the fiber cake deposited on it.

10. The method of Claim 8 or Claim 9, wherein the mould filter with thefilter cake deposited thereon is subjected to pressing.

11. The method of Claims 8 to 10, wherein externally fiber-coated bodies are surrounded with a porous mould shell, are pressed and are then centrifuged.

12. The method of any one of the Claims 1 to 11, wherein as a slurry liquid. use is made of a resin or resin solvent mixture wh,cn will not cure at room temperature and which is compatible with the subsequent processing routine.

13. The method of any one of Claims 1 to 12, wherein the mould filter is preformed from fleece filter material orfiberfabric.

14. The method of Claim 13, wherein the fleece filter material or the fiber fabric forms an integral part of the moulded article to be manufactured.

15. The method of any one of Claims 1 to 14, wherein fiber-reinforced preforms are produced from a glass, ceramic or metal powder slurry.

16. Apparatus for performing the method of ay one of Claims 1 to 15, comprising a fiber deposition system, which includes a filtration base which takes the shape of a mould filter having a negative mould wall conforming to a complex contour area of an object to be manufactured, and an orientation section for feeding short fibers or fiber mixtures contained in a slurry to the filtration base.

17. TheapparatusofClaim 16, wherein the mould filter is made of a deformatble porous, mechanically and chemically resistant material.

18. TheapparatusofClaim 16orclaim 17, wherein the mould filter is provided with a porous release mask.

19. The apparatus of any one of Claims 16 to 18, wherein the mould filter is a thin, nonoriented fleece filter.

20. The apparatus of anyone of Claims 16to 18, wherein the mould filter is a preformed, closely woven fiber fabric.

21. The apparatus of anyone of Claims 16to 18, wherein the mould filter is a porous metal foil.

22. The apparatus of anyone of Claims 16 to 21, wherein the mould filter is attached inside or to a variable-speed spinning vessel.

23. The apparatus of anyone of Claims 16 to 21, wherein the mould filter is accommodated within another, suitably shaped rotating body.

24. The apparatus of anyone of Claims 16 to 23, wherein the deposition system exhibits a sealed collector vessel for extracting the slurry liquid under a vacuum.

25. The apparatus of anyone of Claims 16 to 23, wherein the deposition system is capable of controlled pivotal and/or linear movement and is adjustable relative to the orientation section.

26. The apparatus of anyone of Claims 16 to 25, wherein the orientation section is capable of controlled movement and is adjustable relative to the deposition system.

27. The apparatus of anyone of Claims 16 to 26, wherein the deposition system has pressing means utilizing a ram for pressing against the filter cake deposited.

28. A method of manufacturing objects from short, oriented reinforcment fibers or fiber mixtures, as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

29. Apparatus for manufacturing objects from short, oriented reinforcement fibers or fiber mixtures, substatially as hereinbefore described with reference to anyone of the embodiments, shown in the accompanying drawings.