WO2002099218A1

WO2002099218A1 - Lightweight composite element, method for the production and use thereof

Info

Publication number: WO2002099218A1
Application number: PCT/CH2002/000276
Authority: WO
Inventors: Mehdi Farshad
Original assignee: Eidgenössische Materialprüfungs- und Forschungsanstalt Empa
Priority date: 2001-06-05
Filing date: 2002-05-23
Publication date: 2002-12-12
Also published as: CH695701A5

Abstract

The lightweight composite element consists of at least two nap films or nap sheets (2;3) made of plastic, i.e. plastic films or sheets on which a plurality of naps are formed on at least one side thereof. The nap films or sheets (2;3) are directed towards each other and are firmly welded or glued together. The method for the production thereof requires at least two nap films or sheets made of plastic which are displaced mechanically from a roll (9,10) or from stacks and which pass by an automatic machine which welds them together or glues them together as they go past, whereby a virtually endless sheet of lightweight composite elements is produced and can be subsequently separated into sections of various lengths.

Description

Lightweight composite element, its manufacturing process and its use

The present invention relates to a lightweight composite element for a wide variety of uses, as well as a method for its manufacture. Finally, some special uses of this lightweight composite element are shown.

Lightweight composite elements have been known for a long time and they are made in different constructions and from different materials. One often speaks of sandwich constructions or of constructions that include a sandwich as the core. Such a sandwich essentially consists of two spaced-apart plates or plate-like elements which are connected to one another via intermediate spacers. These spacers are usually of such a shape that they can absorb considerable compressive forces, that is to say the plates connected by them and kept apart from them can withstand large contact pressures. At the same time, the spacers ensure the absorption of displacement forces, that is to say the limiting plates can no longer be displaced relative to one another in their direction of travel. The greater the normal distance between the plates of such an element, the greater the bending stiffness of such a composite element in general. A typical application example are aluminum sheets, which are connected by means of an aluminum structure, for example in the form of honeycombs. With comparatively thin sandwich elements with a minimal weight, maximum bending rigidity and load-bearing capacity are obtained. Such sandwich panels are therefore used, for example, as aircraft interior floors. There are a multitude of other applications, with different materials and special constructions of the respective structure of the composite elements. However, two or more plates are always connected to one another at a distance from one another.

Known sandwich lightweight components are consistently relatively expensive and therefore their range of applications is accordingly limited to cases where their high price can be justified or simply has to be accepted for technical reasons.

It is the object of the present invention to provide a lightweight composite element which can be manufactured considerably more easily and from inexpensive raw material, so that completely new uses can be opened up due to its low cost. In addition, it is an object of the invention to provide a manufacturing method for the continuous manufacture of this lightweight composite element and finally to show a number of specific possible uses of this lightweight composite element.

This object is achieved on the one hand by a lightweight composite element, which is characterized in that it is composed of at least two dimpled sheets or dimpled sheets made of plastic, that is, made of plastic sheets or sheets, of which a number on at least one side Knobs are formed, and which knob films or plates are firmly welded or glued to one another with the knobs directed towards one another. The object is achieved on the other hand by a method for producing a lightweight composite element, which is characterized in that at least two dimpled sheets or sheets made of plastic, that is, at least two plastic sheets or sheets, from which on at least one side a number of knobs are formed, are guided past a machine from a roll or from a stack and are welded or glued to one another as the vehicle drives past.

Finally, the object is achieved by the use of the lightweight composite element, which consist of at least two dimpled sheets or plates made of plastic, that is to say made of at least two plastic films or sheets, from which a number of knobs are formed on at least one side, and which studded film or sheets are firmly welded or glued to one another with the studs facing each other, for the creation of wall panels, partitions and insulating walls, as well as a supporting plate in building, civil engineering and tunnel construction as well as in vehicle construction.

The invention is described below with reference to the drawings, wherein several variants of this lightweight composite element are disclosed. The process for its manufacture is also presented and some possible uses of this lightweight composite element are shown and explained.

It shows:

Figure 1: A knobbed film made of polyethylene as a basic element for the production of these lightweight composite elements;

Figure 2: A first variant of a lightweight composite element of minimal thickness from two polyethylene knobbed sheets or foils;

Figure 3: A second variant of a lightweight composite element of maximum thickness made of two polyethylene knobbed sheets or foils; Figure 4: A lightweight composite element according to the structure of Figure 3 in preparation for the application of cover plates;

Figure 5: A lightweight composite element according to the structure of Figure 3 with top and bottom welded cover plates as a finished sandwich panel;

FIG. 6: A lightweight composite element in the form of a shell element made of two knobbed foils connected to one another in accordance with FIG. 2 and welded to one another in a curved manner;

Figure 7: A schematic representation of the continuous production of a flat lightweight composite element from at least two plastic knobbed films.

Figure 1 shows a knobbed film made of plastic. It is characterized in that it has a number of knobs 1 on at least one side. The film can be made from various plastics and can also be in the form of a plate instead of a bendable film. Polyethylene will preferably be used because polyethylene is a thermoplastic that is easy to machine and weld, that is very durable and, on top of that, is relatively light with a specific weight of 950kg / m ³ . In addition, its surface is largely scratch-resistant and weatherproof. Other plastics, such as polypropylene or GRP, can also be used for special applications. Such knobbed films are already produced “endlessly” in large quantities, that is to say they are available in rolls. But knobbed sheets are also commercially available. The knobs 1 are formed, for example, by means of a deep-drawing process from the sheet or sheet material by heating it and the soft material is then sucked over an appropriately shaped tool, from which it is removed again after cooling, The pattern shown in Figure 1 can be bent elastically. The film material has a thickness of approximately 0.5 mm and the size of the knobs can be compared to that of Hand holding the knobbed film in this curved position and is also shown. However, it is also possible to use foils and plates of considerably thicker or weaker thickness and with less dense and or differently shaped knobs. In addition, the knobs can be higher or lower. With regard to their shape, the knobs can also be conical, hemispherical or pyramidal or form truncated pyramids. In any case, it is advantageous if the knobs 1 taper uniformly on all sides towards their end, because they are then able to absorb large compressive forces. Instead of the film or plate having knobs 1 on only one side, it can also have knobs on both sides, in which case the knot density is of course somewhat reduced on both sides.

Figure 2 is now presented a first variant of the lightweight composite element made of two such dimpled polyethylene films as shown in Figure 1. Here two knobbed foils 2, 3 have been placed on top of one another in such a way that their knobs 4, 5 are directed towards one another and the knobs 4 of one foil 2 each engage in the spaces between the knobs 5 of the adjacent foil 3. The ends of all the knobs 4, 5 are then welded to the foil 2, 3 lying against them. It has been shown that a weld alone, which results in a very strong connection of the two foils 2, 3 simply by piercing the foil together with the adjacent knob end wall, and that a sufficiently stable lightweight composite element is produced. Simultaneous welding at all points of a composite element to be produced can therefore be achieved by using a needle board with hot needle tips. Of course, the welding can be carried out in the form of a perfect spot weld. Hot, bolt-like stamps are moved together from both sides to a defined distance, i.e. in the picture from above onto the upper plate and from below into the interior of the knobs, while maintaining a distance of the order of between one to a maximum of two plate thicknesses or film thicknesses. Corresponding stamps also attack the film from below and into the knobs of the upper film from above. If you use foils with nubs on both sides, so Not only can two foils be connected in this way, but an entire stack of any height.

Furthermore, it is possible to place a more or less fine-meshed, perforated wire mesh over the knobs of each knob foil, so that the foil base next to the knobs is consistently covered by a wire mesh. After the two studded foils or plates have been joined together, a voltage is then applied to the wire mesh, so that all of the stud ends are welded to the respective studded foil or plate. The cross wires are also heated as a result of heat conduction within the grid wire. Instead of a wire mesh, an electrically conductive mesh made of carbon fiber-reinforced plastic can also be used, which is sufficiently electrically heatable that the adjacent surfaces are welded together. In this case, the mesh not only acts as a thermal welding element, but also as a particularly light and strong reinforcement for absorbing tensile forces.

Figure 3 shows a second variant of the lightweight composite element made of two polyethylene knobbed films or sheets. Here, the two polyethylene stud sheets or plates are connected to one another in such a way that the studs 4, 5 facing each other meet with their ends and are welded to one another at these points. The welding is also carried out either by piercing the two abutting knob ends or by means of thermal spot welding. Furthermore, it is possible to place a more or less fine-meshed wire mesh between the knobs of the knob films or plates lying against one another, which is then heated as a whole by applying a voltage, so that all the knob ends are welded together. The cross wires are also heated as a result of heat conduction within the grid wire. Instead of a wire mesh, an electrically conductive mesh made of carbon fiber reinforced plastic can be used, as already described above, which is sufficient it is electrically heatable that the adjacent surfaces are welded together. In this case, the mesh not only acts as a thermal welding element, but also as a reinforcement for absorbing tensile forces. It also applies here that this connection can also be realized with foils which have knobs on both sides and thus a stack with several foils can be welded together to form a lightweight composite element. In contrast to the lightweight composite element according to FIG. 2, the one shown here has a much greater flexural rigidity due to the double spacing of the knobbed foils or plates. Such composite elements, although they have a surface provided with recess holes on both sides as a result of the knobs, can already be used for many purposes.

Figure 4 shows a second variant of a lightweight composite element according to the structure of Figure 3 in preparation for the application of cover plates. A wire loop 6 has been placed over the surface, which in principle is flat here, which meanders from one edge to the other of the element. An electrical voltage can be applied to this wire loop 6, after which the wire acts as a heating loop as a result of resistance heating and cause the plastic to melt. But first, a plastic plate made of the same plastic material as the composite element is placed on the flat surface and the heating loop 6. Then an electrical voltage is applied for a certain period of time and the plate is pressed onto the composite element, whereby an electrical welding is achieved between the composite element and the plate placed thereon. So that a connection or permanent welding is achieved in as many places as possible or even across the board, a more or less fine-meshed wire mesh can be used instead of a heating loop, which is heated in the same way by applying a voltage as a whole. The cross wires are also heated as a result of heat conduction within the grid wire. In the same way, a plastic plate is also welded onto the opposite side of the composite element. Instead of a wire loop or a metal wire mesh, an electrically conductive mesh mesh can also be used carbon fiber-reinforced plastic are used, which is sufficiently electrically heatable that the adjacent surfaces are welded together. In this case, the mesh not only acts as a thermal welding element, but also as a particularly light and strong reinforcement for absorbing tensile forces.

Figure 5 shows a lightweight composite element according to the structure of Figure 3 with welded top and bottom cover plates 7,8 as a finished sandwich panel. Such a sandwich panel can easily be produced in any size and extremely inexpensively. The possible uses are extremely varied, because it has a number of particularly favorable properties. So its specific weight is lower than water and therefore it swims. The space between them is permeable to water. Water or another flowable medium, in particular also a gas, can therefore flow longitudinally to the cover plates within the sandwich plate. Free air spaces are formed between the cover plates. The sandwich panel therefore has a good insulation effect with regard to sound and heat. Measured by its weight, it has an extremely high level of flexural rigidity. This sandwich plate is also very easy and practical to work with. You can use sawing, drilling, milling, cutting, rasping, etc. and you can screw tapping screws firmly into them or you can even fix them with nails. In addition, a number of sandwich panels can be firmly connected to one another by means of thermal welding along their edges or elsewhere, for example by means of mirror welding or by gluing. By welding wire mesh as heating elements for the thermal welding, they also act as reinforcement and increase the tensile strength of the sandwich panels. If a particularly good reinforcement effect is to be achieved, the entire composite element structure can also be reinforced by lamination with thermosetting or thermoplastic reinforcing fabric or by means of plastic inserts, for example made of carbon fiber-reinforced plastic, or by means of or metal inserts. Instead of pure polyethylene plastics, other materials can also be used, that is, base elements or knobbed films or plates made of thermoplastic or thermosetting fiber-reinforced plastics can also be used. These can be processed in film-like roll form or as stable plate pieces by connecting knobs to knobs in the manner described. If no welding can be carried out for the connection, the knobs can also be non-positively connected to one another by gluing.

FIG. 6 shows a shell element made of two knobbed foils connected to one another in accordance with FIG. 2 and welded to one another in a curved manner. It is a particular advantage of these composite elements that they can be bent easily, at least when they are made from sheet-like, thermoplastic dimpled sheets. To connect them together, the dimpled sheets are stretched to a suitable shape and then pressed together and welded or glued in this position. The easiest way to weld is by interposing a metal grid for thermoelectric welding. After welding or gluing, the preformed shape is retained and even has a very high stability.

Finally, it should be mentioned that, of course, not only two dimpled sheets or two foil-like dimpled sheets can be connected to one another, but especially in the case when dimpled sheets or foil sheets are used which have dimples on both sides, several such foiled sheets or sheets are welded or glued to one another in each case are interconnectable in the same way. The surfaces of the outermost sheets or plates can then optionally also be provided with cover plates, as described for FIGS. 4 and 5. Such multilayer composite elements have an extraordinarily high bending stiffness.

[0018] The possible uses of such lightweight composite elements are extremely diverse. In building construction and civil engineering, such composite elements can be used, for example, as sprouting heat due to their high flexural rigidity Digging work can be used or as formwork panels for concrete. Such baffles are then many times lighter than previously used steel billets. In tunnel construction, they are particularly suitable as curved sprout elements or formwork elements as well as load-bearing surface drainages. Due to their good sound insulation properties, they can be used as partitions and insulating walls for all kinds of purposes. Basically, they can be used as load-bearing floor slabs, both exposed and laid in a foundation. Use as roof elements is also possible. Thanks to their light weight and high stability, they are suitable as an excellent building material in vehicle construction. For example, floors and walls of truck bodies, truck trailers or motorhomes and caravans can be built from lightweight composite elements of the type described. All kinds of transport containers and containers can also be produced with it. Furthermore, they can be used as rigid and load-bearing cores for all kinds of sandwiches, for example if the cover plates are to be made of alternative materials, for example metal, wood or stone, etc., they are excellently suited as composite element cores. Self-supporting seals and intermediate storage in walls, roofs and floors with cavities are also conceivable, which are subsequently foamed by means of injections for further sealing. Outdoors, they can be used as temporary floor slabs for securing paths and squares, for example if there are weak floors that are to be heavily used. Emergency slopes, emergency roads, emergency routes and places can be created with it. It can even be used to build floating bridges or floating and load-bearing floors on marshy ground.

In Figure 7, the continuous production of flat lightweight composite elements from at least two plastic knobbed films is shown schematically. From two rolls, on each of which a whole web of dimpled foil is wound, these dimpled foils are unrolled and fed to an automatic welding machine. The driven rollers 11, 12, which extend over the web width, are rubber-coated and ensure the forward movement of the two webs, while the steel roller 13 has radially projecting steel pins 14. These steel pins 14 are on an electric when the steel roller 13 rotates Heater 15 passed. Their circumference on the steel roller 13 is such that they reach into the interior of adjacent and successive knobs below. They melt through the studded bottoms and also the studded bottoms of the opposite studs of the lower studded sheet. This results in a welding of the two dimpled sheets. The roller 16 generates the necessary back pressure at the welding point. Instead of a single needle roller 13 with opposing counter-pressure roller 16, two rollers can also be provided, each having heatable bolts similar to needles or pins 14. However, these bolts are not intended to pierce the studded bottoms. Rather, the two rollers are then arranged in such a way that the bolt ends, when they engage in the nub holes from both sides, only approach a distance which is somewhat less than twice the nub base thickness. In this way, spot welding is achieved. All knobbed floors are therefore welded on their outer side to the knobbed bottom opposite each other without the knobbed bottoms being perforated. Another variant for the continuous production of the lightweight composite elements is to let a metallic grid run in between the two dimpled sheets. This grid then protrudes on both sides of the dimpled sheets lying between them. There, over a certain distance, an electrical voltage can be applied to the grid by means of sliding contacts, so that due to electrical resistance heat it is heated to such an extent that the adjacent knob ends begin to melt. Continuous electrical thermal welding is achieved with a pressure generated simultaneously by pressure rollers. Instead of metallic grids, carbon-fiber-reinforced plastic mesh grids can be used which have such an electrical conductivity that they can be heated sufficiently for a thermoelectric welding. If the "endless" composite elements produced in this way are still to be provided with cover plates, these can be welded or glued on. For the welding, metallic mesh or carbon-fiber reinforced plastic mesh can be applied in the same way, which over a certain distance in the same way be heated electrically. The cover plates to be welded on are then placed on the web by a robot and the entire assembly runs between counter-pressure rollers. The same procedure can of course also be carried out from below, so that cover plates are also placed on the underside of the welded composite element web. After the two studded foils have been welded, the web is stiff and can hardly be bent. It is then continuously cut into panels of any length, which has to be done with a rotating saw.

Claims

claims

1. Lightweight composite element, characterized in that it is constructed from at least two dimpled sheets or dimpled sheets (2; 3) made of plastic, that is, made of plastic foils or sheets, from which a number of dimples (1; 4 ; 5) are formed, and which knob films or plates (2; 3) are firmly welded or glued to one another with the knobs (1; 4; 5) directed towards one another.

2. Lightweight composite element according to claim 1, characterized in that the knobs (4) of the one knobbed film or knob plate (2) protrudes into the spaces between the knobs (5) of the adjacent knobbed film or knob plate (3) and their knob ends with the bottom the knobbed film or knobbed plate, i.e. the area where there are no knobs, are welded or glued.

3. Lightweight composite element according to claim 1, characterized in that the knobs (4) of the one knobbed film or knobbed plate (2) lie opposite the knobs (5) of the adjacent knobbed foil or knobbed plate (3) and their knobbed ends with knobbed ends of the adjacent knobbed foil or Knob plate are welded or glued.

4. Lightweight composite element according to one of the preceding claims, characterized in that the lightweight composite element is provided on one side or on both sides with a cover plate (7; 8) which is welded or glued by means of electrical welding.

5. Lightweight composite element according to one of the preceding claims, characterized in that between the two dimpled sheets, or dimpled sheets (2; 3), a grid is inserted, by means of which the two Bubble films or dimpled sheets using electrical

Resistance heating is welded.

6. Process for the production of lightweight composite elements, characterized in that at least two dimpled sheets or sheets made of plastic, that is to say made of at least two plastic sheets or sheets, from which a number of studs are formed on at least one side, from a roll (9; 10) or stacked past a machine and welded or glued to one another as it drives past.

7. The method according to claim 6, characterized in that the welding is carried out by rolling a roller (13) with hot needles (14) on the pasted knobbed sheet of two knobbed foils or knobbed plates (2; 3) and their hot needles (14) Pierce the parts of the studded foils (2; 3) to be welded.

8. The method according to claim 6, characterized in that the welding is carried out by rolling two opposing, spaced-apart rollers with hot bolts on the pasted dimpled sheet of two dimpled sheets or dimpled sheets (2; 3) and their bolts each other when the rollers rotate come to lie opposite, so that they pinch the parts of the dimpled sheet to be welded between them, weld them by heating and then move apart again.

9. The method according to claim 6, characterized in that the welding is carried out by an electrically conductive grid made of metal or carbon fiber reinforced plastic is drawn in between the two knobbed films or knobbed plates (2), to which over its edges by means of sliding contacts for a while electrical voltage is applied so that it is heated thereupon the two knobbed foils or knobbed plates (2; 3) with the heated one between them horizontal mesh is passed through two pressure rollers so that they are welded together.

10. Use of the lightweight composite element, which consists of at least two dimpled sheets or plates (2; 3) made of plastic, that is, made of plastic foils or sheets, from which a number of knobs are formed on at least one side, and which dimpled sheets or -Plates with the knobs (4; 5) facing each other are firmly welded or glued to each other, for the creation of bulkheads, partitions and insulating walls, and as a support plate in building, civil engineering and tunnel construction as well as in vehicle construction.