WO1990007423A1

WO1990007423A1 - Method of making a fibre reinforced grid

Info

Publication number: WO1990007423A1
Application number: PCT/DK1989/000303
Authority: WO
Inventors: Mogens Nielsen
Original assignee: Bms Kunstfiber A/S
Priority date: 1988-12-23
Filing date: 1989-12-21
Publication date: 1990-07-12
Also published as: DK720788D0; AU4756890A

Abstract

A mould is used for manufacturing a fibre reinforced grid which is form stable and self supporting and which is made in endless sheets in a continuous process. The grid is manufactured by intersecting resin-saturated rovings (4, 6) laid into the grooves of the mould (1) while under longitudinal tension. Displacing means (12) displace the mould and thus the grid longitudinally while the grid is provided in the grooves of the mould (1). Said grid is manufactured by longitudinal rovings (4) and transversal rovings of which one half (6A) is positioned beneath and another half (6B) is positioned on top of the longitudinal rovings. The grid is compressed (at 16) and cured whereby it becomes form stable. The groove-forming elements are displaced perpendicularly to the plane of the grid thus disengaging the grid which is then removed from the mould.

Description

METHOD OF MAKING A FIBRE REINFORCED GRID.

Background of the Invention.

The present invention relates to a method of manufacturing a fibre reinforced grid by use of a mould in which the grid is formed.

It is known to manufacture fibre reinforced elements, for instance grids, by use of a mould. However, according to the prior art methods there may only be obtained elements of limited dimensions as the di¬ mensions of the mould confine the size of the element formed.

It is desirable to make fibre reinforced grids in substantially end¬ less sheets. In many situations such grids may be used as a reinforce¬ ment instead of ordinary reinforcing frameworks of steel. However, so far it has not been possible to manufacture such fibre reinforced grids having sufficiently good properties and at sufficiently low pro¬ duction costs.

The object of the invention is to provide a method of manufacturing a fibre reinforced grid by use of a mould in which the grid is formed, which method renders it possible to manufacture a form stable self- supporting grid in a substantially continuous way and which is end¬ less.

According to the present invention this object is achieved with a method which is characterized in

- that the grid is made of intersecting resin-saturated rovings laid into the grooves of the mould while under tension in their longitudi¬ nal direction,

- that the grid, while in the grooves of the mould, is displaced sub- stantially continuously in its longitudinal direction, as the mould is displaced,

- that the formed grid is subjected to a form stabilization, preferab- in the form of a combined compression and curing, and

- that the grid is thereafter removed from the mould, by perpendicular displacement away from the plane of the grid of at least the groove- forming elements of the mould while the grid is displaced in its lon¬ gitudinal direction.

The rovings are laid down into the grooves of the mould while under tension in their longitudinal direction whereby a rigid and strong element is obtained. The rovings may intersect each other at different angles and also the angle between the rovings and the longitudinal orientation of the grid may vary. However, for technical production reasons it is preferred to use rovings orientated perpendicularly to each other, and having one orientation parallel with the longitudinal orientation of the grid. As the grid is form-stabilized while in the mould, it is possible to carry the grid through the process by dis¬ placing the mould.

Preferably, the form stabilization is effected through a compression and a curing. The compression ensures that no air is confined between the laid down rovings, and simultaneously it is ensured that the ro¬ vings are depressed into the resin used. Preferably, the compression is effected by means of a plane upper mould part having a first end portion inclined downwardly towards the bottom of the mould in such a way that the height available for the grid decreases to a predeter¬ mined level in the travell ng direction. Thus, during its passage past the first end portion of the upper mould part the grid is compressed and stays compressed as the remaining portion of the upper mould part is situated at a distance above the bottom of the mould corresponding to the desired thickness of the grid. Such plane upper mould part is preferably used as an initial step for a curing, seeing that the upper mould part is heated in such a way that the curing is effected while the grid is subjected to a compression force between the upper mould part and the bottom of the.mould. Retractable groove-forming elements are used in the mould and during said compression the elements are depressed into the bottom of the mould whereby the laid down rovings fill the grooves so formed completely.

After the grid has become form-stable the groove-forming elements of the mould are displ ced perpendicularly away from the plane of the grid as they are lowered completely into the bottom of the mould. When leaving the curing area the grid is thus free to continue through the manufacturing process for an optionally succeeding rolling up or for a cutting into suitable lengths. Preferably, the mould comprises a row of mould units and the separate mould units may be reused several ti¬ mes-, thus the grid being removed from the mould unit the mould units are conveyed back to the first method step in which the rovings are laid down into the grooves. Thus, the mould units may comprise an end¬ less chain conveyor, an endless belt or a track-like construction.

From the above it appears that the method according to the invention renders it possible to manufacture a fibre reinforced grid in a sub¬ stantially continuous way and which are endless as the sheet lengths are limited only by the length of the rovings.

Description of the Drawings. The invention will now be further explained with reference to the ac¬ companying diagrammatical drawing, wherein

Fig. 1 is a side view of an apparatus for use in the method accord¬ ing to the invention, Fig. 2 is a view as seen from the top of the apparatus shown in Fig. 1, and

Fig. 3 is a section through the apparatus.

Fig. 1 shows an apparatus for use in the method according to the in- vention in which the grid is manufactured using rovings running in two mutually perpendicular directions, one of said directions running in the longitudinal direction of the grid.

The grid is manufactured in a mould 1 consisting of separate mould units 1A,1B,1C, etc., which are placed successively in the longitudi¬ nal direction 3 of the formed grid 2. Longitudinal rovings 4 are used which pass through a resin bath 5 prior to being laid down in a prede¬ termined number of rovings in each of the longitudinal grooves of the mould 1. In the resin bath the ratio of roving and resin is controlled by wiping means (not shown) wiping off resin in order to obtain the ratio desired. The transversal rovings 6 of the grid are also carried through resin baths 7 in which wiping means (not shown) provide the desired ratio of roving and resin. One half 6A of the transversal ro¬ vings is laid down below the longitudinal rovings 4 and the other half 6B of the transversal rovings is laid down onto top of the longitu¬ dinal rovings 4. The resin baths 5,7 may be stationary or displaceable together with the associated roving laying means.

The longitudinal rovings 4 are laid down by a stationary frame (not shown) provided with a laying nozzle for each of the longitudinal grooves of the mould. A frame 8 is used for laying down the transver¬ sal rovings 6, which frame is provided with four transversal guides 8A,8B,8C,8D. The guides co-act in pairs 8A,8B and 8C,8D in order to support displaceable support beams 9,10. The support beams 9,10 sup¬ port laying nozzles 11 provided at a mutual distance corresponding to the distance between every other groove of the mould. As illustrated in Fig. 1 the frame 8 is made in such a way that each support beam 9 and 10 is placed above a mould unit 1C and 1A, respectively, whereas the distance between the support beams 9 and 10 corresponds to the width of the intermediate mould unit IB.

The longitudinal rovings 4 are laid down into the mould unit IB. Here¬ by the transversal rovings 6B which are laid down into the mould unit 1A will be positioned beneath the longitudinal rovings whereas the transversal rovings 6B which are laid down into the mould unit 1C will be positioned on top of the longitudinal rovings.

When the support beams 9 and 10 are displaced along the guides 8A-8D a desired number of rovings are laid down into every other transversal groove of the mould. When the support beams 9,10 reach their extreme positions outside the grooves of the mould the frame 1 is displaced in the longitudinal direction of the grid with a distance corresponding to the distance between two successive transversal grooves. Then the support beams 9,10 are again displaced in the transversal direction of the grid, viz. in the direction opposite the direction of the preced¬ ing laying in the transversal direction. Hereby rovings are laid into the intermediate grooves in the transversal direction and the support beams 9,10 are displaced to the extreme position where they are free of the mould. Then the mould is displaced in its longitudinal direc¬ tion with a distance corresponding to the width of a mould unit. This displacement is effected by a hydraulic piston 12 having a stroke cor¬ responding to the width of a mould unit. During said displacement of the mould units in the longitudinal direction 3 of the grid a laying of the longitudinal rovings 4 is effected automatically as these ro¬ vings are drawn through the laying nozzles. The piston 12 is retracted and a lifting elevator 13 feeds a new mould unit into the position where the mould unit 1A was situated earlier. The lifting elevator 13 is supplied with mould units by an endless conveyor 14 which conveys the mould units back to the beginning of the process from a final step as explained later herein.

When the new mould unit has been placed correctly it is again possible to effect a laying of transversal rovings 6 as explained above. When this transversal laying has been effected in both directions and the row of mould units again has been displaced in the longitudinal direc¬ tion a new mould unit is again inserted in the front of the row before a following transversal laying is effected.

Both the longitudinal rovings 4 and the transversal rovings 6 are un¬ der tension in their longitudinal direction while laid down. This ten¬ sion is provided in the longitudinal rovings 4 by the displacement of the mould 1. The tension in the transversal rovings 6 is obtained through a friction between the rovings and the mould and the tractive force effected in order to move the rovings through the laying arran¬ gement. The tension may be controlled by varying the frictions exist¬ ing in the laying arrangement.

After the laying the grid is subjected to a form stabilization in the form of a combined compression and curing. In the position illustrated for the mould unit ID the laid down grid is depressed as an upper mould part 15 comprising a first end portion 16 having a plane under¬ side inclines downwardly towards the bottom of the mould. The upper mould part 15 comprises a further portion 17 having a plane underside placed in a fixed height above the bottom of the mould. The distance between the underside of the further portion 17 of the upper mould part and the bottom of the mould corresponds to the desired thickness of the grid. In the mould 1 retractable groove-forming elements (not shown) are used which are depressed into the bottom of the mould du¬ ring said compression. Hereby, the laid down rovings fill out the for¬ med grooves completely. The upper mould part 15 is provided with heat¬ ing means and accordingly it constitutes a curing area as the grid is heat cured during its passage beneath the upper mould part 15.

After passage through the curing area activatable means 18 depress and retract the groove-forming elements in the bottom of the mould. This occurs when the mould unit is in the position illustrated at II. When the groove-forming elements are disengaged from the grid it is possible to displace the grid freely forwards. Optionally, the grid may be di¬ vided into suitable lengths with a saw 19 which is intended for making a cut while the grid moves or which saw may alternatively be a statio¬ nary saw. The grid formed may also be rolled up. In this case the use of a sufficiently large rolling up diameter is requisite in order to prevent deformation of the grid.

After the depression of the groove-forming elements the mould unit II is lowered by a lowering elevator 20 onto the endless conveyor 14 which conveys the mould unit back to the beginning of the process. During the passage from the lowering elevator 20 to the lifting eleva¬ tor 13 the groove-forming elements of the mould are again raised to their fully extended position above the bottom of the mould.

To ensure that the mould units are arranged correctly in relation to the laying arrangement a movable stop 21 is provided; when this stop is situated in the track of the mould units it is ensured that the piston 12 positions the row of mould units correctly in relation to the laying arrangement. When the mould units are to be displaced again the stop 21 is retracted and after such displacement the stop is again brought into its position for contact with a subsequent mould unit.

When laying rovings practical extreme limits will exist which determi¬ ne, on the one hand the minimum height and on the other hand the maxi- mum height for the grid formed. Accordingly, the minimum height is determined by the minimum thickness with which it is possible to lay down the rovings and practice has shown it to be about 0,5 mm. The maximum thickness of the grid is determined by the strength of the bondings between intersecting rovings.

The groove-forming elements being manufactured with rounded corners, it is possible to use up to 80% fibres and 20% resin. Tests with a mesh side having dimensions of 6 x 6 mm have shown that it is possible to obtain a tension strength of 1,200 kg.

Claims

C 1 a i m s .

1. A method of manufacturing a fibre reinforced grid (2) by use of a mould (1A-1I) in which the grid is formed, c h a r a c t e r i z e d in

- that the grid is made of intersecting resin-saturated rovings (4,6) laid into the grooves of the mould while under tension in their longi¬ tudinal direction,

- that the grid (2), while in the grooves of the mould, is displaced substantially continuously in its longitudinal direction (3), as the mould is displaced,

- that the formed grid is subjected to a form stabilization, prefer¬ ably in the form of a combined compression and curing (at 15,16,17), and - that the grid (2) is thereafter removed from the mould, by perpendi¬ cular displacement away from the plane of the grid (at 18) of at least the groove-forming elements of the mould while the grid is displaced in its longitudinal direction (3).

2. A method according to cl aim 1 , c h a r a c t e r i z e d in

- that the rovings are orientated in the longitudinal direction (4) and in the transversal direction (6),

- that the longitudinal rovings (4) are led continuously through a resin bath (5), - that the longitudinal rovings (4), while under tension in their lon¬ gitudinal direction, are laid down into a mould (1) comprising several mould units (1A-1I) arranged in a row,

- that also the transversal rovings (6) are led through a resin bath (7), - that one half (6A) of the transversal rovings (6), while under ten¬ sion in their longitudinal direction, are laid down into the grooves of the mould beneath the longitudinal rovings (4) whereas the other half (6B) of the transversal rovings, while under tension in their longitudinal direction, are laid down onto top of the longitudinal rovings,

- that the formed grid is subjected to a combined compression and heat curing (at 15,16,17) to form stabilize the grid while it is situated n the mould, and

- that the grid is moved through the process by its engagement with the mould which is displaced in the longitudinal direction (3) of the grid while being engaged with the grid until said curing is finished.

3. A method according to claim 2, c h a r a c t e r i z e d in that the one half (6A) of the transversal rovings placed beneath the lon¬ gitudinal rovings (4) is firstly laid down into the mould, and that the longitudinal rovings are laid down before the other half (6B) of the transversal rovings is laid down.

4. A method according to claim 3, c h a r a c t e r i z e d in that both the laying of the overlying and the underlying rovings are con¬ ducted in the following steps:

- the rovings are laid down into every other groove of the mould by a laying in a first transversal direction, - the roving laying means (8) are displaced in the longitudinal direc¬ tion (3) of the grid to register with the neighbouring grooves of the mould, and

- the rovings are laid down into the grooves by a laying in the oppo¬ site transversal direction.

5. A method according to claim 4, c h a r a c t e r i z e d in that the grid is displaced such a distance which corresponds to- the width over which the transversal rovings are laid down before transversal rovings are again laid down into the first transversal direction.

6. A method according to any one of the preceding claims, c h a ¬ r a c t e r i z e d in that the ratio of resin and fibres is control¬ led by the rovings being, after passage through the resin bath (5,7), wiped off in order to remove resin in excess of a desired amount.

7. A method according to any one of the preceding claims, c h a ¬ r a c t e r i z e d in that the number of rovings is controlled in each of the longitudinal and transversal grooves of the mould in order to obtain the desired section of the longitudinal and the transversal mesh sides, respectively.

8. A method according to any one of the preceding claims, c h a ¬ c t e r i z e d in that the groove forming elements may be depres¬ sed into the bottom of the mould when the grid is compressed, and that said groove-forming elements are depressed completely into the bottom of the mould, when the grid has become form stable after said curing.

9. A method according to any one of the preceding claims, c h a - r a c t e r i z e d in that the rovings may be squeezed outwards in the areas where they intersect each other as the groove forming-ele¬ ments have rounded corners.

10. A method according to any one of the preceding claims, c h a - r a c t e r i z e d in that mould units are moved forwards in steps and that the mould stand still during the laying of the transversal rovings.