DE3122194A1 - Two-layer material - Google Patents

Abstract

Two-layer materials in the form of bimetal are known per se. By the joining together of two layers of materials with different coefficents of thermal expansion, bimetal strips assume different curvatures with changing temperatures and can thus be used as a temperature-dependent closed-loop or open-loop control element. However, the possible uses of bimetal are relatively restricted because of its other properties. Accordingly, the inventor has sought other two-layer materials which can be used for similar applications but with a greater scope. He has developed two-layer materials in which at least one layer consists of plastic and the other consists of a non-metallic material with a coefficient of thermal expansion which is as different as possible. In this case the two layers must have a high modulus of elasticity. The expansion coefficient of one layer must be zero or approximately zero, whereas the other layer has a high expansion coefficient. At least one of the layers must additionally have a shape-memory capacity. It has been found, surprisingly, that two-layer materials of this kind, in particular those with incorporated carbon fibres, have extremely good properties in the desired direction, so that they open up a multiplicity of fields of application which are closed to bimetallic closed-loop or open-loop control elements. <IMAGE>

Description

"Two-layer material"

The invention relates to a two-layer material that is of the with the so-called bimetal known physical phenomena when joining two layers of material with different coefficients of thermal expansion are used which, like bimetal, is preferably used as a temperature-dependent control or Control element is intended to serve, but does not have a large number of the disadvantages of bimetal, rather, through other and more extensive properties, a wider range of areas of application when this was possible with Bimetall.

Bimetal consists of two layers of different metals that are used in connected to one another in various ways, preferably by rolling or soldering are. Strips made of this material serve as temperature-dependent bending Contactor for opening and / or closing electrical regulating and control circuits. It is also known to have such strips of sufficient length for direct mechanical To use actuation or display, for example in the vehicle tool for moving flaps in dependence on changed temperatures. The scope of bimetal is on the one hand essentially limited by the fact that it is metal is a material with good electrical conductivity, the conductivity in all Directions is the same. In addition, the deflection effect occurs in the layer plane in all directions evenly, so that with bimetallic elements, one of them Expansion in the layer plane does not significantly exceed the other, the so-called The crowning effect occurs, which prevents significant bending rates in one direction. In addition, the bending rate is at least strip-shaped in the case of previously known Bimetal elements (ratio of strip length to flexural deflection) proportionate small amount. Finally, the high specific heat of metals is disadvantageous. Will for example an electrical switch that depends on a temperature difference is to be switched on and off, operated with a metallic bimetal strip, then its metallic mass and heat storage capacity determine the speed of recovery decisive. The thinnest possible bimetal strip with less thermal Indolence now results in a more nimble switch. But here are on the part of the mechanical Force that is transferred to the switch by the bending of the strip can, set narrow limits.

On the other hand, it is known that two-layer materials are also used made of non-metals due to the influence of temperature. This rejection is seen exactly, also to a different curvature in adjacent zones of this Material. However, it is not deliberately adjustable within predetermined limits and not a repeatable one, especially not repeatable within predetermined limits Occurrence. If such warping has occurred, for example in the case of multilayered ones Plastic coatings for furniture, this was considered to be the intended Purpose - felt extremely uncomfortable. These Faults should accordingly by gluing onto appropriately stable sub-or carrier layers excluded if possible.

The invention is based on the object of a two-layer material to find who is initially able to solve at least the tasks for which previously Bimetal was used, the areas of application due to its properties however, expanded and that of the bimetal due to its metallic properties does not have inherent disadvantages.

The invention solves the problem posed by a two-layer material with at least one layer of plastic, its firmly connected to one another Layers of non-metallic materials with different coefficients of thermal expansion as possible consist, one layer made of a material with a high modulus of elasticity and a coefficient of expansion of zero or approximately zero, the other layer made of a material also with a high modulus of elasticity and a high coefficient of expansion consists and at least the material of one of the layers shape memory having.

Such a two-layer material made of plastics can, as electrical non-conductive, can easily be used in electromagnetic alternating fields. The material neither disturbs the structure of the field, nor does the field influence the function of the material. In contrast to most metals, the material is corrosion-resistant and largely resistant to chemicals. By appropriate choice of the material of the two layers to be joined, a degree of flexure can be achieved that is far beyond that achievable with bimetal goes beyond.

The generally undesired crowning can thus be ruled out be that a layer consists essentially of oriented fiber material.

It has been shown that, in conjunction with a layer of Hard paper, in particular, as an additional layer one of carbon fibers embedded in plastic has proven its worth. The carbon fibers are straightened used in a plastic layer as so-called carbon fiber plastic (CFRP), there is in particular the aforementioned effect of eliminating the crowning.

As tests have shown, such a two-layer material achieves in a temperature range between room temperature to about 1200 (A t = 100) one Bend degree of 1 (one), based on a material thickness of 1.5 mm and one Length in the bending direction of 30 cm. The degree of bending 1 means that the plate or the strip occupies 1/4 of the circular cylinder jacket.

As a modification, a plastic plate, for example made of consists of a plastic known under the trade name Resopal, on one side with Be glued to carbon threads. An epoxy resin can preferably be used here as the adhesive Find. This also results in a suitable two-layer material.

Because carbon fiber plastic because of the oriented carbon fiber in a Direction a defined electrical resistance, in the other direction one has an electrical resistance of approximately infinite, this property can also be be used when using the two-layer material.

The task-dependent electrical resistance can be determined by meandering Adjust the arrangement of the fibers or fiber groups as required.

The two-layer material designed according to the invention is characterized compared to bimetal, in particular, because of its significantly lower specificity Heat from. This has the consequence that 'to achieve a certain degree of bending the Heat absorption is lower in the same ratio and thus introduced more quickly can be, which leads to a correspondingly faster bending reaction. this applies for both a temperature increase and a temperature decrease dependent bending direction. The difference in specific heat between metal and non-metal is in the range of one to two decades.

Crossing carbon threads can also be stuck onto a plastic plate will. Then this two-layer material has the same characteristics as that well-known bimetal. But the advantage of the quicker response remains. It can be snapped with this embodiment of the two-layer material switch, so-called Klixon switch, produce that at a certain temperature snap and then operate an electrical switch, for example.

For certain applications it is conceivable that the layer from which Both a high modulus of elasticity and a high coefficient of expansion are required is made of metal.

Depending on the intended use, the two-layer materials can be equipped with a Zero bend in the initial stage or equipped with any initial bend be. If the bend in the initial stage is zero, a bend after the one or other direction. Shows the material plate in the initial stage a predetermined bend, it can with progressive heating up in their flat state or, moreover, can be converted into an opposite bend.

Further features of the invention and details of the same The advantages achieved result from the following description of the attached Drawings purely by way of example and application possibilities shown schematically of the subject matter of the invention.

Fig. 1 shows an example embodiment of a plate from the material according to the invention, Fig. 2 shows the use of the new material on a Heat exchanger, Fig. 3 shows an application example in context with a room aeration and ventilation, in Fig. 4 the subject of the invention is in use reproduced on an exhaust flap, Fig. 5 shows the possible application in cooperation with a fan again, Fig. 6 shows a water pump using the new one Material.

As an example of an embodiment of the new two-layer material according to the invention is in Fig. 1 a plate 1 made of the plastic known under the trade name Resopal shown, which is pasted on one side with parallel Kohl # threads 2. Epoxy resin, for example, has proven to be a suitable adhesive. The plate is flat at normal temperature, when heated it arches into the one shown in dashed lines Shape.

As an example of application in a heat exchanger, the oil cooler is shown in FIG chosen for an aircraft. The design must be made here so that the cooling effect is particularly sufficient during the take-off and subsequent climbing process, with the slow flight movement here, the permissible upper limit of the oil temperature increases guarantee.

With the usual fast forward movement, the cooling effect would be far too high for the flowing air. Accordingly, the oil cooler needs to be regulated amount of air flowing through. To this day, this control is usually done manually by the pilot, automated controls require a complex and susceptible servo system.

On the other hand, it is sufficient, for example in the outflow opening of the oil cooler one of the outline shape of this opening adapted unilaterally fixed flap from the provide two-layer material according to the invention. Under the influence of the respective The temperature of the exhaust air from the oil cooler is this flap from one of the exhaust air openings closing position up to a maximum bending position corresponding to the opening the full cross-section of the exhaust air opening.

Another possibility is to use rectangular cut two-layer materials as ceiling elements in rooms.

(Fig. 3) to use. Depending on the crowd, for example The temperature generated in such a room will be, for example, cassette-like arranged ceiling elements more or less bend open what is of a closed position extends to a maximum open position. Since usually concurrently with the increase in temperature, the room air is consumed, results in this way an excellent silent, energy-consuming and non-contact Ventilation system, which, if necessary, can also be configured accordingly of the space above the ceiling can be supported.

The two-layer material according to the invention can also be used directly in exhaust pipes to increase or decrease the cross-section depending on the temperature the same can be used. For example, there is a gas boiler in an exhaust pipe or an oil stove (Fig. 4) a flap made of the material on a side wall area fixed with an edge running transversely to the direction of flow. When the burner is cold the thus formed exhaust flap keeps the trigger closed in order to ventilate air from the room in which the stove is placed. When the Burner opens the flap with increasing temperature and gives the cross-section of the in a chimney or the like leading exhaust pipe free. In addition, a Control of the cross-sectional opening of the exhaust pipe as a function of the burning strength of the burner. The air routing in the exhaust pipe follows the actual one Air requirement of the burner depending on the burning strength.

The example of FIG. 5 shows a conventional wall fan on a ventilation opening assigned to it in a room wall. This opening is furthermore with a flap, similar to the flaps in the ceiling, after a previous example, equipped. This flap is under normal temperature conditions closed in the room, opens when the temperature rises and thus leads to a Partial ventilation on. Is this ventilation sufficient with increasing room temperatures no longer off, the flap actuates an electrical switch in a supply circuit of the fan, so that this then becomes necessary forced ventilation performs.

This example can be supplemented by a flap, one of which Layer is designed to be electrically conductive. By switching on the circuit, in which this layer lies, the valve is heated. So, based on the Starting position, initially the bending of the plate initiated or advanced Degree of bending the bend can be reinforced.

Fig. 6 finally shows an application example in which the new two-layer material is designed as a membrane of a liquid pump, which is in communication with the piston rod of the pump. If the membrane of the Exposed to solar radiation and the associated heat absorption; she bends through and pumps liquid, for example groundwater, into the intermediate tank. When the membrane has reached a certain bending limit, the intermediate container empties on the Membrane. This can be done by any control means, which are not described here in more detail, happen. The conveyed in the intermediate container Any cold or cooling liquid, for example groundwater, flows over the Membrane made of the two-layer material, it is cooled and takes its own again shallower cold form. Under the surviving; Sun exposure starts now a new work cycle. Because the two-layer material has a very low heat content the equipment is functional, i.e. it can pump sufficient groundwater), to cool the membrane sufficiently. This also applies to higher delivery heights.

That. The water that has drained off through the membrane can then become its final Purpose supplied are for example to serve for irrigation.

Claims (9)

Two-layer material "patent claims)) Two-layer material with layers of different thermal expansion coefficients, characterized in that that these layers are made of non-metallic materials, at least one layer of which made of plastic, if possible with different coefficients of thermal expansion firmly together are connected, the one layer made of a material with a high modulus of elasticity and a coefficient of expansion of zero or approximately zero, the other layer made of a material also with a high modulus of elasticity and a high coefficient of expansion consists and at least the material of one of the layers shape memory having. 2.) Two-layer material according to claim 1, characterized in that that at least one of the layers consists essentially of aligned fiber material consists. 3.) Two-layer material according to claim 1 and 2, characterized in that that one layer of hard paper, the other layer of embedded in plastic Is made of carbon fibers. 4.) Two-layer material according to claim 3, characterized in that that the one layer made of the plastic known under the trade name Resopal and the other layer is glued on one side of this plastic layer Carbon threads. 5.) Two-layer material according to claim 3 or 4, characterized in that that the carbon fibers are stored aligned in the synthetic layer or adhesive layer are. 6.) Two-layer material according to claim 3 or 4, characterized in that that the carbon fibers are stored or glued crosswise aligned. 7.) Two-layer material according to claim 1 to 6, characterized in that that that of the two layers, of which both high modulus of elasticity and high expansion coefficient is required, consists of metal. 8.) Two-layer material according to claim 1 to 7, characterized in that that the two-layer material is equipped with a zero curvature in the initial stage is. 9.) Two-layer material according to claim 1 to 7, characterized in that that the two-layer material is equipped with an initial bend in the initial stage is.