Pre-stressed stone slabs with continuous production

Abstract

The invention relates to a virtually endless stoneware slab which is coated using prestressed endless fibres by the simultaneous application of resin. The prestressing in the stone takes place using a tensioning device which keeps the fibre tensioned on the surface of the stone strip until the liquid resin has cured. Curing is carried out using a heater, which initially pre-tempers and liquefies the resin, and a radiation source, which rapidly cures the resin. During these processes, the stone slab is continuously advanced and the fibres are unwound via braked rollers. In order for the fibre to come into frictional contact with the surface of the stoneware, the fibre is pressed onto the stone surface using a press during curing of the resin. In order to be cured, the carbon fibre laminate can be heated using electromagnetic radiation in a very wide variety of frequency ranges, in particular by heating the carbon fibre by electromagnetic induction in the low-frequency range, for example at 20 kHz.

Description

[0001] Prestressed stone slabs with continuous production

[0002] The stabilization of stone and ceramic slabs is becoming increasingly important, as the material has proven itself increasingly popular in lightweight construction. Rods, plates, or strips made of carbon fiber or stone fiber-coated stone are well known, as described in DE 20 2006 008 100.3 for the stabilization of stone slabs. Such supports made of fiber-coated stone are used, for example, under or in stone slabs below the edges as stabilizers, as described in DE 20 2006 008 100.3, or for load-bearing and self-supporting structures such as T-beams or double-T beams, as described in DE 20 2020 000 730.7. The base materials for these stabilizers or supports can stabilize the stone strips on both sides or the fiber layer stabilizing the stone strip or stone slab can also be located in the middle between two stone strips, as described in DE 20 2020 000 730.7.Individual stone slabs can be prestressed in various ways using carbon fibers, as described in DE 20 2007 015 789.4. If these strips or slabs are to be longer, a different procedure is necessary to evenly prestress very long stone strips that are longer than individual stone slabs, which are typically available on the market today with a length of 3 meters. Crucial in production is a defined prestress – of the stone material, which usually does not have very high tensile strength – by the fiber and a perfect frictional connection between the fiber and the stone surface. If this is guaranteed, then the stone can also be bent to astonishing yield points without cracking. This is of great importance for the longevity of rotor blades for wind turbines, for example.

[0003] A further development of this invention now delves into the details of automated stone coating under prestressing and corresponding fiber processing. Carbon fibers or other fibers such as glass fibers or stone fibers can be used very specifically and optimally, especially in combination with stone or ceramic materials, or even other pressure-resistant materials such as concrete, hardwood, or glass, to preferably absorb tensile forces.

[0004] This is sometimes also preferably achieved through the use of unidirectionally aligned fiber layers. The fibers are initially glued to the beginning of a stone slab to be coated using the resin required for the coating or another matrix that bonds the stone to the fiber. This start-up process can also be carried out using aids such as foils and a separate take-off unit. The fiber layers are stretched and tensioned on the stone surface and then impregnated with resin and cured while in the tensioned state. Impregnation can be carried out in various ways, such as immersion baths or injection into the tool. In this invention, stretching is carried out using braked drums or spools on which the fiber was wound before being unwound at a brake. If necessary, pre-impregnated fiber material in the form of fiber prepregs is also unwound from such spools in a targeted and controlled manner.

[0005] The targeted advance of the stone plate, to which the end of the carbon fiber is first glued and secured, creates the force with which the fiber is stretched and taut as it is unwound from the braked spool. Before the resin at the end of the stone plate has cured, another plate is placed at the end of the first plate and the continuous carbon fiber is then cured at the end of the first plate and the beginning of the second plate in a rapid process. By advancing the next plate, compressive stress can be built up in the direction of production, which counteracts the tensile stress in the fiber layers caused by the braked unwinding. The third and all subsequent plates are connected and joined in the same way as the first and second plates. The plate connections can be flat or have galvanized, dovetail-galvanized, or toothed transitions.

[0006] Once the stone strip has reached the desired length, the carbon fiber can be cut off at the end, and a second long strip can be produced. Alternatively, the process can continue virtually endlessly with the addition of additional sheets, and the coated stone strip can be completely cut off, for example, using a downstream slicing unit, while the process described above produces the next long strip. This coating, under pre-tension of the fiber, can be applied to one or both sides. The subsequent pre-tension in the composite is created by the curing of the resin, while the fiber is tensioned by the feed and the decelerated unwinding.

[0007] This invention describes a quasi-endless fiber-prestressed earthenware plate which is coated with prestressed endless fibers by simultaneous application of resin.

[0008] The pre-stressing of the stone is achieved with the help of a tensioning device, which holds the fiber taut on the surface of the stone strip until the liquid resin has hardened. Curing is achieved with the help of a heater, which first pre-tempers and liquefies the resin, and an optional radiation source, which quickly hardens the resin. During this process, the stone slab is continuously moved, and the fiber is unwound over braked rollers. To ensure the fiber has a positive contact with the surface of the stoneware, the fiber is pressed onto the stone surface using a press or a tool with a variable cross-section over the tool length while the resin hardens.A typical tool can be designed in such a way that the cross-section of the tool opening in the inlet area significantly exceeds the cross-sectional areas of the hard stone, fiber, and matrix material, and then tapers further along, resulting in compression of the layer structure. After complete compression, a region of constant cross-section can follow, in which the curing reaction can be completed. A further expansion of the cross-section for demolding can also be provided. Heating of the carbon fiber laminate for curing can be achieved using electromagnetic radiation in a wide variety of frequency ranges, in particular by heating the carbon fiber through electromagnetic induction in the low-frequency range, for example at 20 kHz. Heating via heat conduction and heat flow through a heated tool can also be used.

[0009] The invention is embodied, for example, according to Fig. 1, in such a way that a granite slab (5) with a thickness of approximately 10 mm has only stone on the underside and is coated on the top side with unidirectionally aligned carbon fibers and / or carbon fiber fabric (2). Alternatively, the stone slab can also be coated on the underside with carbon fiber scrims and / or carbon fiber fabrics and / or carbon fiber nonwovens, as shown in Fig. 2.

[0010] To achieve pre-tension in the composite, the fiber is unwound over braked rollers or spools (3). The braking torque (3a) of such a carbon fiber unwinding device (3) and the resulting tensile force applied to the fiber, as well as the compressive force acting in the opposite direction due to the stone feed, determine the degree of pre-tension.

[0011] Figure 1 shows a schematic of how the device works. The initial curing is carried out by a heatable pultrusion tool (6) with a heater (6a), through which the fiber laminate or prepreg, i.e. fabric or scrim already impregnated with resin, is guided over rollers (4) and pressed tightly and firmly onto the stone surface. The carbon fiber stone laminate is continuously moved forward by a caterpillar haul-off (8) attached to the end of the production line so that, on the one hand, the pre-tension is maintained and, on the other hand, the continuous final curing can take place in the shortest possible time with the help of, for example, IR or UV light or laser light sources (7). This means that the caterpillar haul-off can continuously pull and transport a firmly cured material.When the CFS profile has reached the desired length, it is cut with a stone saw (11) at the end of the production line. The entire production line does not have to be stopped if the saw moves at the same feed speed during the cut.

[0012] Optionally, the introduction of the radiation that completely cures the resin can be introduced through a transparent window (10), wherein the window at least partially maintains the pressure of the pultrusion tool in order to prevent removal of the fiber from the stone surface before the resin has completely cured.

[0013] The core feed (9) ensures that sufficient feed force is also applied from the other side until the resin or other fixing matrix has begun to harden and cure, so that the stone pieces are fed seamlessly with a defined force (9) by a core feed (1) as long as the resin is still in a rather liquid or viscous state and until the caterpillar pull-off can grip the hardened part of the entire gas path in order to keep the overall pre-tensioning force constant over the entire path. For this purpose, the force of the caterpillar pull-off (8) and the feed force (9) of the stone core are adjusted via a PLL control circuit (12) or phase-locked loop and kept constant in total. If necessary, the braking torque of the unwinding spool (3) for the braked unwinding of the fiber path is integrated into the PPL in order to ensure constant pre-tensioning in the hardened material composite.

[0014] Figure 3 shows a similar arrangement in which the fiber strand is arranged between two stone layers. In this case, the complete rapid curing takes place with the help of electromagnetic field generation (7a), whereby the fields heat the electrically conductive carbon fiber itself. For this purpose, a portion of the fiber is supplied in the form of fabrics, in whose short-circuited fabric loops currents are induced, which specifically heat the fibers. These inductive arrangements for generating heat in the carbon fiber itself can also be applied in the previously shown arrangements (7) instead of light radiation or directly in the pultrusion tool. Figure 4 shows the transition from one stone slab to the next with an interlocking for an optimized connection and force introduction from one stone layer to the next with as little stress peaks as possible, while also providing a useful positioning aid.

Claims

Claims 1) Stone, artificial stone or ceramic plate - hereinafter earthenware plate or earthenware strip - which is coated with fibers and resin or another fixing matrix by a continuously arranged coating device, characterized in that the fibers are tensioned by means of a pulling device and pressed onto the stone surface in the tensioned state until the resin or the other fixing matrix has hardened. 2) Arrangement according to claim 1, characterized in that the fiber layers are applied either on the top or on the bottom or on both sides of the earthenware plate and are fixed to the surface of the earthenware by curing the resin or another fixing matrix. 3) Arrangement according to claim 1 and 2, characterized in that the fiber layers are stretched and tensioned during curing by a braked unwinding device. 4) Arrangement according to claim 1 to 3, characterized in that the fiber layers are pressed onto the stone surface by a pressing tool. 5) Arrangement according to claims 1 to 4, characterized in that the resin or other fixing matrix required for the connection of stone and fiber layers is heated. 6) Arrangement according to claims 1 to 5, characterized in that the coated earthenware plate is forced through the pressing tool by a feed mechanism which presses the fibers in the wet state of the resin or other fixing matrix directly onto the surface of the earthenware. 7) Arrangement according to claims 1 to 6, characterized in that the feed mechanism is formed by a core feed at the beginning of the production strand and a caterpillar take-off at the end. 8) Arrangement according to claims 1 to 7, characterized in that the heater heats the pressing tool. 9) Arrangement according to claims 1 to 7, characterized in that the heater is an induction heater which heats the carbon fiber fabric using electromagnetic fields. 10) Arrangement according to claims 1 to 9, characterized in that the fiber layers are applied or fixed under pretension to the strip of pressure-resistant material until the resin or another fixing matrix has cured. 11) Arrangement according to claims 1 to 10, characterized in that the fiber layer consists of carbon fibers, glass fibers, basalt fibers or other stone fibers or a mixture of these fibers. 12) Arrangement according to claims 1 to 11, characterized in that the coated earthenware strip consists in its core of natural stone, basalt, granite, gabbro, marble, ceramic, glass ceramic, artificial stone, concrete, glass, other mineral materials or hardwood. 13) Arrangement according to claims 1 to 12, characterized in that the process of curing the resin or another fixing matrix is ​​carried out by means of radiation. 14) Arrangement according to claims 1 to 13, characterized in that the radiation used for curing is infrared radiation or UV radiation or radiation with a different frequency spectrum, which is applied either with non-directional radiation or with a laser beam. 15) Arrangement according to claims 1 to 14, characterized in that the pressing tool simultaneously serves both as a heater or as a tool for curing by means of radiation or both. 16) Arrangement according to claim 15, characterized in that, in the case of simultaneous pressing and curing with the aid of radiation, a window is located in the pressing tool or at the end of the pressing tool, which forms the surface of the pressing tool and is simultaneously transparent, in order to allow the radiation to act on the resin until the resin or another fixing matrix has cured. 17) Arrangement according to claim 16, characterized in that the window, as a transparent part of the surface of the pressing tool, consists of glass, quartz glass, diamond, quartz or other precious stone, plastic, artificial stone, or another pressure-stable and transparent material. 18) Arrangement according to claim 1 and 17, characterized in that the fiber layers are arranged mainly or entirely in the longitudinal direction. 19) Arrangement according to claim 1 and 18, characterized in that the forces of the caterpillar pull-off and the stone core feed are PLL-controlled for a constant pre-tension. 20) Arrangement according to claim 1 and 19, characterized in that the braking torque of the unwinding device is also adjusted via the PLL control circuit for a constant bias voltage.

Images