In particular the invention concerns a process for fabricating reinforced drain covers out of plastic.

The purpose of the invention is to provide a process that allows the fabricating of reinforced drain covers that are maximally resistant to warping due to heavy loads, i. e., that ensures that the final product is optimally stable.

An additional goal of the invention consists in providing reinforced drain covers capable of handling very large loads, for example sewer covers with a diameter of 800 mm capable of handling 40 tons or more.

The invention provides for a process of fabricating rcinforced drain covers, characterised by the insertion into a mould of a number of layers of reinforcemcnt made up of strands of fibre with a predetermined diametcr that in turn are made up of interwoven fibres, and lying between these, also in layers, horizontal and vertical spacers, preferably more rigid than the reinforcing; filling the mould with plastic such that all fibres visible at the external perimeter come maximally into contact with the plastic, this by covering the fibre strands on all sides with a plastic layer of a predetermined thickness, and after the hardening of the plastic, removing the now complete reinforced drain covers.

By using the aforementioned structure, as will be seen in more detail below, a balance is provided that allows the reinforced drain cover, after removal from the mould, cooling and the shrinkage caused by such, to meet the stated requirements concerning flatness, shape and rigidity.

The aforementioned mould is preferably filled with plastic by means of the so-called RIM procedure (Reaction Injection Moulding). With this procedure the plastic enters the mould relatively slowly which ofEcrs the avantage, according to the invention, that the reinforcement and the spacers are not subjected to brusque forces which eliminates the risk that that they would shift.

The invention also concerns a reinforced drain cover that is fabricated according to the aforementioned process.

With the intent to better demonstrate the invention, some preferred ways of implementation are described below as examples, without them being in any way limiting, with reference to the associated drawings, in which: figure I depicts a drain covcr made according to the invention; figure 2 depicts a largcr scalc and cross-section of line 11-11 in figure 1; figure 3 depicts a mould for the fabricating of the drain cover in figure 1; figure 4 dcpicts a larger scale and cross-section of line IV-IV in figure 3; figure 5 depicts a larger scale view of the part that is indicated in figure 4 with £S, which indicates the various layers that are put into the mould before filling it; . figure 6 depicts part of a spacer that is used for the drain cover in figure 1; figure 7 depicts a larger scale and cross-section of line VII-VII in figure 6; figure 8 depicts part of a fibre strand that is used as reinforcement for the drain cover in in figure 1; figures 9,10, and 11 depict a perspective image of how, for example, one can form layers of reinforcement and can arrange layers of reinforcements with spacers.

The invention, as already mentioned, concerns a process for the fabrication of a drain cover (1) out of plastic, examples of which are depicted in figures I and 2. The drain cover (1) can be inserted in an appropriate frame (2) which preferably is also made of plastic.

In the cxample shown, a drain cover (1) is depieted that consists of a primarily flat body (3). However, it is clear that the process described below is not limited to such drain covers (1), but can also be applied to other shapes of drain covers or slabs, for example, drain covers or slabs with an underlying structures.

The process used to fabricate the drain cover (1) consists of, as depicted in figures 3 and 4, a mould (4) that can consist of multiple mould parts (5 and 6); that, as depicted in figure 5, into the mould (4) are inserted, crosswise, a number of reinforcement layers (7) made up of fibre strands (8), constructed as depieted in figure 8, that have a predetermined diameter (D2), that run parallel and at a certain distance from each other (D1), kept from each other with spacers (18) so that subsequently when the mould (4) is filled with liquid plastic (11), schematically depicted by the arrow (10) in figure 3, all fibres (9 and 9.1) that appear at the exterior perimeter (7) are maximally bonded with the liquid plastic (I I) to font one aggrcgate, compositc, and that, after the hardening of the plastic (11), the drain cover obtained (1) is removed from the mould (4).

The fibre strands (8) that make up the reinforcement layers (7) are compose of a number of fibres (9) that are woven together in such a way that all strands (9) of all fibre strands (8), however large the diameter (D2) of the fibre strands (8) might be, form a single aggregate in the composite in order thus to resist the loads (P) that will be applied to the reinforced drain cover (1) To obtain a supplementary bonding between the fibre strands (8) and the plastic (11), and also to connect the fibre strands (8) with each other via the plastic (1 I), the fibre strands (8) at the exterior perimeter are provided with a certain number of extending fibres (9.1) with a predetermined length (L) and that thus woven are located between the fibres (9) of the fibre strands (8) so that within the composite formcd, all fibre strands (8) arc attache to each other via the plastic (I I) and additionally with the fibres (9.1).

To improve the interaction bctween thc plastic (I I) and the fibre strands (8) and in this way to strengthen the composite obtained, the invention provides for the connection of the ends of the fibre strands (8) with each other, for example, by fonning a reinforcement layer (7) by one long fibre strand (8) that consists of straight and parallel fibre strands (8) as depicted in figure 11.

As already mentioned, the invention conccrns thc fabrication of a drain cover (1), provided with the necessary reinforcement layers (7) that are laid on top of each other horizontally, sideways or at a certain angle, and compose of fibre strands (8) of a certain diameter (D2) that are straight, parallel and a certain distance (D I) from each other, the structure of which is compose of interwoven fibres (9) and fibres (9.1) so that the fibres (9 and 9.1) in the fibre strands (8) interact as an aggregate within the composite fonned when the fibre strands (8) are subject to loads, more specifically, the fibre strands (8) must have the function of full-fledged reinforcement bars that with their total diamenter (D2) must be able to provide maximum support in pre-determined directions within the composite constructed in this way.

In order to keep the fibre strands (8) straight, parallel and spaced at a certain distance (D I) in the reinforcement layers (7), one preferably can use plastic nets, spacers (18) that are sufficiently rigid and have a certain structure so that the respective distances (dol) necessary between the fibre strands (8) will be maintained during the filling of the mould (4) with liquid plastic (11).

This reinforcement technique differs from all other methods of reinforcement because here there is not a total saturation of the required weave with which one wishes to renforce the plastic slabs or plastic covers, and thus the thickness of the weave is limited; this invention provides for a process that makes possible the making of fibre strands (8) with a certain diameter (D2) made up by interweaving a certain number of fibres (9) or bundles of fibres (9) and fibres (9.1) as depicted in figure 8, which are able to function as full-fledged reinforcement bars in the making of a composite consisting of plastic and reinforcement fibres. which does not require complete penetration to the centre of the fibre strands (8), but the bond between the plastic (11) and the fibre strands (8) is formed by the penetration of all the fibres (9 and 9.1) that appear at the exterior perimeter of the fibre strands (8).

The RIM proccdurc (Rcaction Injcction Moulding) is preferably used here as this offers the advantages mcntioncd in the introduction. Here, as indicated in figures 3 and 4, two components are added to the mould (4), via pipes (12 and 13), that arc combined in a mixer (14) immediately before they enter the mould (4) in order subsequently to be injecte via a common pipe into the mould (4) in which the components of the mixture react with one another and form the final plastic (11). The component mixture is preferably injecte relativcly slowly into the mould (4) to avoid the reinforcing strands (8) and the spacers (18) shifting.

In corder to obtain an optimum filling of the mould (4) and good contact with all fibres (9 and 9.1) of the fibre strands (8) of the reinforcement layers (7), the form (4) is positioned sloping upwards; the plastic supply occurs at the entrance (16) which is located at the lowest point of the mould (4) where the mould is divided; and the mould (4) is bled via an opening located above (17). The slope (A) is prcferably 60°.

For thc reinforced drain covcr (1), the aforementioned components that are added according to the RIM procedure are preferably polyol and isocyanate.

As will be made clearer below using figures 5 to 8, during the introduction of the aforementioned reinforcemcnt layers (7) and the spacers (18), flow channels are provided. These are preferably made by using the spacers (18) that each consist of onc or more layered elements (19 & 20) with a diagonal open structure, as for example depicted in figure 6, by which is intended that circulation is always possible along one or more diagonal directions (B and/or C).

The making of the flow channels (23) is moreover helped by attaching the fibre strands (8) at a certain distance (dol) from each other, parallel and straight, to the spacers (18). It is necessary that the injecte plastic (11) is forced to maximally circulate through aIl fibre strands (8) of the reinforcement layers (7) so that a predetermined outer layer forrns around the fibre strands (8), in order that maximal contact and bonding occurs between all fibres (9 and 9.1) that appear at the exterior perimeter of all fibre strands (8) and the injecte plastic (11), in order in this way to form a strong composite, to obtain a reinforced drain cover (1) able to handle predetermined loads (P). As depicted in figure 6, the spacers (18) in figure 6 consist preferably of plastic nets. In order to allow proper circulation of the plastic injecte into the mould (I 1), use can be made of nets with rectangular or square mesh (21) with, for example, a corc distance (D3) equal to 5 to 15 mm. In order to providc for the diagonal open structure, the nets are preferably made of threads (19 & 20) laid one upon thc othcr that, as depicted in figure 7, are attache to each othcr, for example by being partially melted together. The threads (19), for example, have a diameter (D4) of 2 to 6 mm, the threads (20) for example have a width (D5) which determines the distance (dol) between the fibre strands (8), and a height (H) allowing the fibre strands (8) to be attache, for example, by camping the fibre strands (8) between the threads (20) of the spacers (18).

The attachent of the fibre strands (8) to the spacers (18) can also be done by stapling, sewing, gluing or melting the fibre strands (8) to the spacers (18).

Multiple reinforcement layers (7) can also be compose of fibre strands (8) that run parallel and a certain distance (D I) from each other, attache to each other crosswise or at a certain angle (E) without using spacers (18), as depicted in figure 10 with the understanding that a sufficiently open structure is obtained in all directions betwecn all the fibre strands (8) that make up the reinforcement package so that the injecte plastic (11) will surround all fibre strands (8) with a plastic layer of a predetermined thickness.

The fibre strands (8), which form the reinforcement layers (7), are so arrange that each fibre strand (8) itself can come into contact with the injecte plastic (11), and this with a determined outer layer surrounding the fibre strand (8), in this example D4 and D5, which are predetermined so that there is, on the one hand, a maximal bond between the fibres (9 and 9.1) located at the exterior perimeter of the fibre strands (8), and the injecte plastic (1 I), and on the other hand, the aggregate, composite will provide the drain cover being made with sufficient stability to be able handle the stated loads (P).

The elements are preferably also made of plastic in order to limit or eliminate completely the possibility of warping which could arise due to differences in the expansion coefficients. Each of the aforementioned fibre strands (8) is made of interwoven fibres (9) or bundles of fibres (9), and fibres (9.1), a piecc of which is depicted in figure 8, consisting of fibreglass, carbon fibres or any possible plastic fibre, or fibres that could be suitable for this procedure.

The reinforcement layers (7) as well as the spacers (18) are prcferably provided over the complete or almost complete surface of the drain cover (1). The mould (4) is filled with reinforcement layers (7) and spacers (18) which, in turn, can be any gauge depending upon the size of the load (P) that the drain cover (I) must be able to handle.

The fibre strands (8) that fonn the reinforcement layers (7) of the drain cover (1) must be located at predetermined locations in the mould (4). This means that the mould (4) is completely filled by reinforcement layers (7) and spacers (18) with the understanding that all fibre strands (8) and spacers (18) are located at their predetermined locations in the mould (4) in order to ensure the stability and flatness of the drain cover (1) being made, and to ensure that an optimal filling of the mould (4) with plastic (11) is possible.

Note that according to thc invention, fibre strands (8) compose of thc above describcd structurc and spaccrs (18) arc uscd that allow thcmselvcs to be combine with the injecte plastic (11), so that the aggregate, composite, is very elastic, so that a load (P) on the drain cover (1), which would cause sagging, would result in practically no lasting warping and that the drain cover (1) returns to a flat condition after removal of the load (P).

It is clear that the invention also concerns drain covers or slabs characterised by a construction obtained by the aforementioncd process.

The present invention is in no way limited to the examples described and the ways of implementation depicted in the figures, but such processes for the fabrication of a drain cover and the drain cover fabricated according to this process, can be realised according to different variations without falling outside the framework of the invention.