WO1997000167A1

WO1997000167A1 - Process for joining an in particular non-textile cellular structure to textile coating layers

Info

Publication number: WO1997000167A1
Application number: PCT/EP1996/002607
Authority: WO
Inventors: Karl-Heinz HÖRSTING
Original assignee: Liba Maschinenfabrik Gmbh
Priority date: 1995-06-16
Filing date: 1996-06-17
Publication date: 1997-01-03
Also published as: EP0776268A1; AU6356296A; KR970705468A; NO970636L; DE19521946A1; NO970636D0

Abstract

A process is disclosed for joining an in particular non-textile cellular structure to at least one textile top layer and a textile bottom layer by means of a yarn system, so as to form a sandwich structure. The yarn system is generated by knitting. A honeycombed structure with substantially vertical walls is used as cellular structure. The coating layers designed as multiaxial structures are joined in a single dry operation to the honeycombed structure, forming a flexible, easy to handle mat-like structure that may be transformed in a subsequent step of the process into a hard, highly stiff sandwich material.

Description

Method for connecting an in particular non-textile cell structure with textile cover layers

The invention relates to a method for connecting an in particular non-textile cell structure with textile cover layers to form a sandwich structure according to the preamble of claim 1. In particular, any material combinations, such as Textiles, plastics, metals are connected.

It is known that with the help of stitch formation methods, such as for example the knitting or sewing technique, different textiie structures can be connected and fixed together. For example, with the help of warp knitting technology, a system of differently oriented parallel thread groups, which are called scrims, is connected by a stitch system. These products are called knitted multiaxial scrims or multiaxial warp knits. It is also known that, on the basis of the sewing technology (Malimo method), for example, fabrics are sewn with random-fiber mats or nonwovens. The advantage of these semi-finished textiles lies on the one hand in the combination of different textiles and the associated possibility for more rational further processing or for more rational transport, and in the connection of different mechanical properties. On the other hand, the good bond that can be achieved between the textiles reduces the risk of detachment due to shear stresses, with fiber composite materials in particular delamination being critical with regard to the greatly reduced strength. With this known method one obtains three-dimensional reinforced textile. The main disadvantage of the described method, however, is that the combination of the different textiles as the end product in turn results in a semi-finished textile product.

Sandwich materials, such as those used in lightweight construction with a rapidly increasing tendency, generally have cover surfaces which are glued to an inlay. The inlay glued between the cover surfaces need not be of a textile nature. So far, mainly foams and aluminum or paper honeycomb structures, the so-called honeycombs, have been used as inlays.

With the sandwich materials that have been customary and used up to now, the cover surfaces are first manufactured. This can be, for example, a semi-finished textile as reinforcement for a fiber composite. Then the cover surfaces are glued to the inlay. Such cover surface laminates are used in particular for aircraft floors. In addition to the complex manufacturing technology, there is also the disadvantage that the mechanical properties of the sandwich composite cannot be optimally adjusted. There is a risk of premature failure of the sandwich material due to delamination between the top surface and the inlay.

A flexible composite blanket is also known from EP 0 526 363 A2, which is used for thermal insulation purposes. A silicon carbide base fabric and multiple alternating layers of individual aluminized layers and / or honeycomb-like foils are held together by a suitable thread system in the form of a stitched seam, for which purpose two threads are required. Temperature-resistant ceramic thread is used as the sewing thread. The honeycomb structure used Ren serve as spacers to reduce the thermal conduction properties of the heat-insulating ceiling. Honeycombs with cell walls inclined up to 60 ° in relation to the longitudinal direction are used as the cell structure.

The disadvantages of such a composite material or of the method used for its production are, on the one hand, that the cover layers, which are so-called interlock silicon carbide fabrics, are first produced in a separate operation before the actual quilting of the multiple layers. Only then can the individual layers be arranged on top of one another and then sewn in subsequent work steps. On the other hand, the disadvantage is that when sewing through the inclined walls of the honeycomb structure, the walls are pierced by the needle and are therefore considerably weakened. This is particularly disadvantageous for materials that serve as the starting material for composite materials. This applies equally to the stacking of numerous individual thin layers of a honeycomb structure, which can never be arranged so that the needles used for topstitching do not destroy the walls of the individual honeycombs. Another limitation with regard to the strength to be achieved is the fact that only a relatively large needle spacing can be achieved when sewing through the needle heads.

Furthermore, a sandwich structure is described in WO 80/02253, which consists of cover layers which enclose a soft foam insert between them and are sewn together. In order to achieve corresponding strengths, in the structure described, sections of high-strength fibers are drawn through the outer layers covering the foam insert on opposite outer sides of the foam insert. In the subsequent sewing process, these high-strength fibers are Fibers are used, which the sewing fiber cannot be drawn into the soft foam core. In addition, in the case of the composite material described, the type of cover layers is designed as a thin skin, ie forms a relatively closed outer surface. The foam core serves to form a rigid cell-like resin structure in the interior of the composite material after impregnation with a curable resin. In the case of the sandwich material described, too, several operations are required to produce the intermediate product required for the hardened composite material. In addition, because of the application of resin to the entire cellular internal structure of the foam, such composite materials are relatively heavy and require relatively large amounts of resin, which are in the range of approximately 4-5 kg / m ² . In addition, the resin application process is relatively slow.

DE 34 18 913 C2 describes a laminar block which consists of a multiplicity of laminated plate-shaped elements made of inorganic fibers. This large number of plates or disk-shaped elements stacked on top of one another is integrated into a laminar body by sewing. Such a laminar body is primarily used for lining heat-insulating constructions and is not intended as an intermediate product for the production of a hardened sandwich material. Because there is no cell structure inside, the main disadvantage of such a laminar block is that it may not be able to penetrate the resin completely, especially when several layers are arranged one above the other, and therefore does not cure to achieve a hard composite material is accessible. The achievable thread density of the thread system is also limited by the relatively large needle spacing caused by the needle heads, which places limits on the interlaminar shear strength. It is therefore the object of the invention to provide a method for connecting an in particular non-textile cell structure with in particular textile cover layers to form a sandwich structure as a starting product for a composite material, which is easy to handle, a drastic reduction in the process steps required for its production enables and moreover the risk of delamination of the finished composite material under load is substantially eliminated by increasing the interlamina¬ ren shear strength.

This object is achieved by a method with the features according to claim 1.

The method according to the invention represents a method for connecting an in particular non-textile cell structure, which is preferably a honeycomb structure, with at least one textile upper layer and one textile lower layer to form a sandwich structure by means of a thread system. The thread system is preferably produced by the knitting technique. The cell structure located between the textile outer layers or cover layers has essentially vertical walls and is continuous over the entire width of the sandwich structure. The textile cover layers preferably consist of at least two multiaxial fabrics, preferably of inorganic materials, such as glass wool, ceramic fibers or other mineral wool. The multiaxial fabrics are preferably produced on a warp knitting machine with multiaxial weft insertion systems (System LIBA), which is fed to the honeycomb structure, which is still relatively flexible before processing, in such a way that it is arranged between the cover layers. Depending on the application, the number of scrims used for the cover layers may also be significantly higher than two. By feeding the cell structure so that it is placed between the cover layers in a dry process in a single operation by means of a thread system, which is preferably produced using the knitting technique, produces a still flexible, easy-to-handle mat-like structure, which can preferably be wound up on rolls. The smallest winding radius depends on the height of the knitted honeycomb structure and thus on its flexibility.

In a preferred embodiment, a high-performance fiber is used as the machine thread. If the flexible mat-like structure serving as an intermediate product is to be processed into hardened flat sandwich panels, which are used above all in aircraft construction as aircraft floors, it is particularly preferred in a subsequent online process step to remove the forfeited sandwich To guide structure over a device for impregnation with a curable or meltable carrier matrix, a curing device or a downstream cooling device. Panel elements of the desired length can then be cut to standard sizes or any lengths.

An important advantage of the method or of the product obtained with the method is that, especially in sandwich manufacturing, instead of a large number of individual parts to be assembled beforehand in individual steps, the semi-finished sandwich product is produced directly in a single operation can. The mechanical properties of the composite material can be optimized or oversizing avoided. Another advantage is the good drapability in cases in which, above all, curved components are to be obtained from the sandwich structure, the intermediate structure is brought to the place of processing with extremely easy handling and pressed into the respective shape can be what the actual impregnation and curing or cooling follow. The advantages consist precisely in the fact that individual layers do not have to be applied individually at such locations, and in addition that delamination of the top layers and inlay layer is avoided, above all, even in the case of curved components with increased stress due to the narrow knitting thread system.

The known so-called prepreg products are only of limited suitability because of their stickiness, especially because of the complicated handling.

The vertical arrangement of the walls of the honeycomb structure largely prevents damage to the walls of the honeycomb structure by the needles during the knitting process. In a particularly preferred embodiment, the feed movement of the cell structure into the knitting machine is synchronized with the needle position so that essentially the same number of threads is drawn through each cell of the honeycomb structure and the walls remain largely undamaged, i.e. not to be hit by the needles.

The invention will now be explained in detail on the basis of a special exemplary embodiment which is illustrated in the attached figure.

The figure shows a sandwich structure produced with the method according to the invention, which consists of cover layers 1, 3 formed as a laid scrim with a honeycomb structure 2 in between by interlocking on the basis of warp knitting technology with multiaxial weft insertion systems, e.g. according to the LIBA system.

The material combination of the sandwich structure shown in the figure shows a lower layer 1 as the lower layer 1 and a cover layer 3, which each consists of two layers and is arranged at different angles to each other. The alignment of the lay-up layers with respect to one another and with respect to the feed movement of the sandwich product to be produced is different for the underlayer 1 and the top layer 2. In the example shown, the scrim of the lower layer 1 is superimposed on one another in a 45 ° angle arrangement with respect to the conveying direction, while the two scrim layers of the cover layer 2 are placed in a 90 ° arrangement to one another. The different orientations of the fabrics serve to further increase the strength of the finished sandwich structure without increasing the material expenditure. Inorganic fibers such as glass wool, mineral wool and others are preferably used as the material for the layers of the cover layers 1, 3.

The materials stacked in this way are fed to a knitting machine and connected to one another to form a unit. The arrangement of the individual lay-up strands can preferably be matched to the spacing of the needles 4, so that when they are knocked in synchronism between the feed movement of the material package 5 and the honeycomb structure dimension and the lay-up strand thickness, the individual components of the sandwich structure are knocked as free of injuries as possible. The connecting threads, which extend through the entire material, soak during the impregnation with the hardenable carrier matrix by capillary action full of resin and thus serve as a safeguard against delamination of the top and bottom layers 1, 3 from the honeycomb. Structure 3 of an additional support and thus increasing the strength of the fully hardened sandwich structure.

Compared to known sandwich structures, the sandwich structure produced with the method according to the invention achieves an interlaminar shear strength that is at least 15% higher.

Claims

P ate nt claims

1. Method for connecting a cell structure, in particular non-textile, which runs over the entire width of a sandwich structure, with at least one textile upper layer and one textile lower layer to form a sandwich structure by means of a thread system,

characterized ,

that the textile upper layer and the textile lower layer are produced from fabrics with different preferred thread orientations;

the cell structure has substantially vertical walls; and

the textile top layer, the cell structure and the textile substructure are connected in one operation in a dry process by means of the thread system to form a flexible, easy-to-use mat-like structure.

2. The method according to claim 1, characterized in that the thread _¬ system is produced by meshing.

3. The method according to claim 1 or 2, characterized in that a high-performance fiber is used as the loop thread.

4. The method according to claim 1, 2 or 3, characterized in that in a subsequent on-line process step, the meshed sandwich structure is guided over a device for impregnation with a curable or fusible carrier matrix, a curing device or a cooling device.

5. The method according to claim 2 or 3, characterized in that the meshed flexible structure is wound up as an intermediate product on rolls.

6. The method according to any one of claims 2 to 5, characterized in that the feed movement of the cell structure for meshing with the needle position is synchronized so that essentially the same number of threads is pulled through each cell.

7. The method according to claim 6, characterized in that the feed movement and needle position are synchronized so that essentially no cell walls are hit by needles.

8. The method according to claim 6 or 7, characterized in that the synchronization is realized via an engaging in the honeycomb Stachel¬ roller, the drive is coupled to the needle drive.