DE102014117078A1 - Multilayer folding core - Google Patents

Abstract

The invention relates to a manufacturing method for a folded core and a folded core for a sandwich structure for arrangement between at least two flat cover layers, wherein Faltkernwände are connected to the cover layers in such a way that they absorb tensile, compressive and / or shear forces under load of the sandwich structure, and wherein the Faltkernwände are made of multi-layered and at least two flat Faltkerndeckschichten and at least one interposed therebetween and connected to the Faltkerndeckschichten corrugated layer form a Faltkernmaterial. The invention also provides a sandwich structure using a folding core according to the invention.

Description

The invention relates to a multilayer folding core. Folding cores are used in sandwich structures as the core material. They generally have very high specific mechanical parameters with regard to the compressive and shear strengths and the stiffnesses. Folding cores are made from a flat sheet. Using a specific folding pattern, it is possible to create a three-dimensional support structure for sandwich cores from the two-dimensional geometry. Most complex rollers and / or pin rollers are used to "set up" the core. There are different approaches to simplify setup.

So far, no solution was known according to the prior art, according to the bulging of the Faltkernwände should be prevented. Zakirov et al. but at a conference ( Zakirov, I. et. al .: Foldcore Structures: Performance, Technology and Production. Paris: SAMPE EUROPE, International Conference. 2006 ) Presented ways to increase the dent resistance of the Faltkernwände. It is proposed a partial, complete or mixed embossing of Faltkernwände. However, some of the materials to be processed can not be plastically deformed enough to sufficiently emboss them. It may happen that errors are introduced into the material, which lead to premature failure.

To simplify the installation of the cores, various approaches are known. The partial curing is in the document RU 2 267 404 C2 for a method of making a folded core layer of composites for the manufacture of the sandwich panels, copying the material in the references WO 2005/049247 A2 (Process for the production of sandwich plates with zigzag corrugated core) and RU 2 238 845 C1 (Method for producing a folded plate structure). Another approach involves scratching and is in the document WO 2005/058593 A2 described under the title sandwich plate.

The publication DE 102 52 941 A1 deals with a method for producing a core structure for a core composite. This is based on the formation of the core structure of a thin foldable starting material. For this reason alone, such a process can not be used for a multilayer foldable starting material whose foldability has just to be produced in the course of processing. In addition, the proposed geometrically complicated folding pattern are not suitable for use in a multilayer foldable starting material.

The publication DE 10 2007 050 356 A1 describes a folded core layer for a sandwich structure whose starting material is multi-layered. However, the multilayer structure results in a strong and undesirable increase in weight, which is approximately proportional to the strength gain.

From the publication WO 2005/056285 A1 A solution is known which also mentions a multilayer starting material as a prerequisite for improved strength of the core layer, while alleviating the problem of heavy weight gain. This is achieved by a perforation of the middle layer of the multi-layered structure with the result that hollow chambers can be seen in cross-section. These lead to a small weight saving compared to the solution according to document DE 10 2007 050 356 A1 , but the cost of production again increases sharply.

Due to the large free path lengths, the primary mode of failure of these cores, as used in the aforementioned prior art, is buckling of the corrugated core walls. For this purpose, the state of the art offers no solution to effectively counteract this problem, without at the same time to increase weight and manufacturing costs.

In addition, the known solutions provide reinforcement of the material in terms of its strength properties, in particular as a multilayer or composite material, or its rigidity, especially produced by embossing before. A suggestion to solve the aforementioned problems is not apparent from the prior art.

Object of the present invention is therefore to move with increased stability bumps to higher loads or even completely prevent, so that the cores can bear with the same weight higher pressure and thrust loads and are also better suited for lightweight applications. On the other hand, the production of folding cores is to be simplified.

The object is achieved by a folding core for a sandwich structure for the arrangement between at least two flat cover layers, which are made of a sheet material, e.g. made of paper, cardboard or a foil or a composite of materials. Such a composite also includes a structure as described below as Faltkernmaterial, but then unfolded.

The Faltkernwände are connected to the cover layers, preferably at the zigzag folding lines, in such a way that they are under load of the sandwich structure tensile, pressure and / or Thrusts recording. The connection is preferably by gluing. It is advantageous if the fold lines have a sufficient width and thus adhesive surface. This is especially the case when the fold lines are scratched and diverge. The effect can be improved by pressure or grinding. In this folding direction is the joint to be folded, below the level of force application. This means that at least at the beginning of the folding process with external means, such as pin rollers, the material must be pre-folded until the joints are above the level of force application and the folding process from there on solely by the introduced horizontal forces with respect to the material plane can continue. The unwanted detachment of surface layers is to be avoided.

Alternatively, the folding takes place inwardly, in the direction of the preparatory material change (for example, grooves, scratches or embossing), so that the cohesion of the layer composite is secured at the fold. In the case of continuous materials with a full cross-section, this can only be achieved by pre-grooving, with corrugated materials also by scoring. In this case, the cover layer and the middle layer fold together and the deflection in this case to each other and the folding of the folding comes about without or optionally with aids.

The Faltkernwände are made of multi-layered and form at least two flat Faltkerndeckschichten and at least one intermediate therebetween and connected to the Faltkerndeckschichten corrugated layer, a Faltkernmaterial. The different materials of which the Faltkernmaterial is constructed, may have different thicknesses and consist of different starting materials. This too absorbs tensile or shear forces when the sandwich structure is loaded. The connection is preferably by gluing. It is also advantageous if the fold lines have a sufficient width and thus adhesive surface. The use of a three-ply material (pleated core topcoat - corrugated core topcoat) to increase the dent resilience of the pleated core walls is the essential contribution of the invention to the enrichment and advancement of the prior art. The dent resistance of the Faltkernwände is increased. As a result, the compressive and shear strength of the folding core is increased. In combination with embossing, grooves or cracks a simplified production is also possible.

Preferably, two Faltkerndeckschichten and a corrugated layer are provided in the Faltkernmaterial. As a result, the tension and pressure-receiving cover layers are spaced from the neutral fiber and the folded core material obtains a greater flexural rigidity (i.e., the pure material stiffness, the modulus of elasticity remains unchanged) without having to accept a correspondingly higher material expenditure or a higher weight. In addition to the preferred variant, it is also provided to build a more than three-layer composite and to use as Faltkernmaterial. This can be done by more than one corrugated layer, but also by a layer structure of Faltkerndeckschicht, z. B. by an introduced corrugated layer. From such a structure results in a higher rigidity and also a larger possible area at the fold lines, so that less adhesive must be used. Also an approximately existing directional dependence of the strength of the material, as is the case with cardboard or paper, for example, can be compensated by a multilayer structure of individual layers.

It is provided according to the invention that in the folded core material, the corrugated layer is corrugated continuously, trapezoidal or circular arc. A continuous corrugated layer may be formed, for example sinusoidal. A trapezoidal corrugated layer offers particularly stiff walls with a short free path, but also curved walls have a high rigidity, since the material is not flat, but always curved easily. In addition, the adhesive surface for connection to the cover layer is very large. An arcuate corrugated layer consists of aligned circular arcs and thus resembles the continuous, sinusoidal corrugated layer.

According to the invention, it is provided that the corrugations of the corrugated layer are introduced in the running direction or transversely to the running direction of the material continuously fed to a production process. This has an effect on the stability especially with fiber material such as paper or cardboard because of the orientation of the fibers. It is advantageous if the folded core material is stamped or scored for erecting the folded core walls in accordance with a folding pattern. This results in clean fold lines with straight, stable walls.

The object according to the invention is also achieved by a sandwich structure comprising a folding core as described above. In such a sandwich structure, the folding core is used by the connection with cover layers, preferably along the fold lines, after the deployment of the folding core according to its intended use. Due to the connection between cover layers and pleat core, tensile and compressive forces are introduced into the cover layers and thrust and / or pressure forces into the pleated core walls during a mechanical loading of the composite, for example on bending. The present invention particularly stable executed against buckling Faltkernwände cause the sandwich structure is particularly stable and withstand higher loads compared to the prior art, in which just the under pressure compress and thus failing Faltkernwände limit the absorbable in the sandwich structure bending moment.

The object is further achieved by a method for producing a folding core for a sandwich structure, comprising the steps of providing the first Faltkerndeckschicht, the corrugated layer and the second Faltkerndeckschicht. This is preferably done by rollers on which the web-shaped material is stored. After the wave pattern has been introduced into the middle layer, the adhesive is applied to the layers via adhesive application rollers. Subsequently, the cover layers are pressed onto the middle layer via further rollers, so that the cover layers and the middle layer bond together so tightly that the splices are suitable for power transmission. This is followed by applying a folding pattern and placing the folding core, in which this folds in at the fold lines and forms an intended three-dimensional structure.

It has proved to be particularly advantageous if the waves of the corrugated layer forming the corrugated pattern are formed in the direction of travel. For this purpose, the corrugation rolls in the direction of travel (MD direction) are introduced over the corrugated rolls, wherein the paper is shirred by about 40% to 50%. Thereafter, the folding core on the side rollers can be particularly easy to set up without a rotation is required.

In an alternative variant of the method, the corrugations of the corrugated layer are formed transversely to the running direction and introduced by means of differently shaped corrugated rolls transversely to the running direction. Since in this variant the waves are introduced transversely to the running direction in the material, in this case the gathering takes place over the longitudinal direction. This hardly causes any problems in the process. A shirring in the transverse direction by about 40% to 50%, whereby the introduction of the waves is more difficult to handle, is hereby deleted accordingly. However, since the tunnel resulting from the waves should show in the thickness direction of the sandwich after setting up, in this variant, the folding pattern must be rotated by 90 °.

It is envisaged that the folding pattern is embossed with the fold lines on which the folded core material buckles and forms a planned three-dimensional structure when it is set up, or alternatively it is scored. Then the rollers with special geometries bring the folded pattern into the corrugated paper (embossed or scratched). This can be done in one or more steps. Thus, longitudinal notches for all types of Faltkerngeometrien can be introduced with a type of roller in which the notches are adjustable. Regardless, the notches are introduced into the corrugated paper structure either from above or from below so as to give a preferential direction in which the structure kinks.

The correspondingly achieved local weakening of the material and thus reduced flexural strength enable a simple and exact positioning process. This is preferably initiated by vertically oriented rolls or belts, if required assisted by auxiliary devices such as pin rollers. The final result is the erected multi-layer core for installation in a sandwich structure.

Further details, features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. Show it:

1 FIG. 2 schematically shows a sandwich structure according to the prior art; FIG.

2 FIG. 2: schematically, in perspective view, an embodiment of a folding core without cover layers under load and stability failure; FIG.

3 FIG. 2 schematically shows, in perspective view, an embodiment of a folding core without cover layers, with fold lines and a detail showing the layer structure in a sectional view; FIG.

4 FIG. 2 is a schematic perspective view of an embodiment of a folding core without cover layers at the beginning of the erection process; FIG.

5 FIG. 2 schematically shows, in perspective view, an embodiment of a folding core without cover layers after completion of the erection process; FIG.

6 FIG. 2 is a schematic sectional view of a detail of an embodiment of a folded core material with a continuous, sinusoidal formation of the corrugated layer; FIG.

7 FIG. 2 is a schematic sectional view of a detail of an embodiment of a folded core material having a trapezoidal configuration of the corrugated layer; FIG.

8th FIG. 2 is a schematic sectional view of a detail of an embodiment of a folded core material with a circular arc-shaped formation of the corrugated layer; FIG.

9 schematically a sheet material with the same basis weight as the embodiments to 6 to 8th for comparison according to the prior art;

10 FIG. 1 is a process schematic of one embodiment of a method of manufacturing a multilayer pleat core; FIG. and

11 FIG. 4 is a process schematic of another embodiment of a method of fabricating a multilayer pleat core. FIG.

1 shows schematically a sandwich structure 1 According to the state of the art. This shows beside cover layers 4 a folding core 2 on, whose Faltkernwände 3 the cover layers 4 keep at a distance and thus the sandwich structure 1 give the appropriate stability. The folding core walls 3 However, they are thin and not very stable, so that they bump and fail easily under a thrust and / or pressure load. This reduces the carrying capacity of the sandwich structure 1 , especially at a bending load, considerably.

2 schematically shows a perspective view of an embodiment of a folding core 2 without cover layers under load due to the force F _L. It is (as illustrated by the dashed lines) recognizable as the Faltkernwände 3 deform and fail completely on further loading so that they can no longer fulfill their function. The sandwich structure in which such a folding core 2 is used, is then destroyed.

3 schematically shows a perspective view of an embodiment of a folding core 2 without cover layers, with fold lines 7 and a detail showing in sectional view the layer structure of the folded core material. The fold lines 7 are partially visible (solid) on the top of the folded core material introduced, but partially invisible (dashed) on the bottom. This ensures that the folded core material in the process of setting up, preferably by lateral load, to a folding core 2 sets up. By an opposite embossing or scribing of the multi-layer sheet each on the side into which the sheet will be folded, the buckling stiffness at this point (see 3 ) Compared to the walls reduced many times. These places act like hinges and a folding core 2 is greatly simplified. In the preferred embodiment of the invention, lateral compression is sufficient around the folding core 2 to set up as in the 4 and 5 shown.

The folded core material is designed in the illustrated embodiment so that two Faltkerndeckschichten 5 a corrugated layer 6 enclose. The folded core material thus represents itself a kind of sandwich, for example by using three layers: two flat layers of folded core covering layer 5 and a corrugated or otherwise folded middle layer, the corrugated layer 6 , which provide an increased distance between the Fickelkerndeckschichten 5 generated.

4 schematically shows a perspective view of an embodiment of a folding core 2 without cover layers at the beginning of the erection process. By the side of the folding force F _{f is} applied, the Faltkernwände 3 on and the Faltkernmaterial kinks over the fold lines 7 ,

5 schematically shows a perspective view of an embodiment of a folding core 2 without cover layers after completion of the erection process. A prepared core 2 can be inserted between cover layers and thus a sandwich material can be completed.

6 Fig. 2 shows schematically a cutaway view of a detail of one embodiment of a pleat core material for use as a pleated core wall 3 with continuous, sinusoidal formation of the corrugated layer 6 between two Faltkerndeckschichten 5 , A sine wave has the length d _cfc .

7 Fig. 2 shows schematically a cutaway view of a detail of one embodiment of a pleat core material for use as a pleated core wall 3 with trapezoidal formation of the corrugated layer 6 ' , The Trapezwände are at an angle π opposite the Faltkerndeckschichten 5 sloping. A Trapezwelle has the length d _cfc .

8th Fig. 2 shows schematically a cutaway view of a detail of one embodiment of a pleat core material for use as a pleated core wall 3 with a circular arc-shaped formation of the corrugated layer 6 '' , Each arc has the radius r. The circular arcs are arranged at a distance d _cfc to each other.

After the sentence of Steiner increases an increased distance between the Fickelkerndeckschichten 5 the bending stiffness of the cross section of the folding core 2 , which leads to the improvement of dent resistance. To ensure comparability, an equivalent sheet and the multilayer sheet must have the same basis weight (cf. 9 ). The wall thickness of the equivalent sheet is defined as t _sheet , whereas the total wall thickness of the multilayer _{sheet is} defined as t _cfc and the wall thicknesses of the individual _layers as t _sw (cf. 3 ). The following applies: t _sheet = (2 + k _cfc ) * t _sw k _cfc indicates the factor by which the middle layer is longer than the cover layers. Taking this value into account can increase the flexural rigidity be estimated. If the sheet thickness of the corrugated paper is twice as large as that of an equivalent heavy sheet, then at least a five-fold bending stiffness is to be expected. Effects of the middle layer as well as its supporting effect are not considered. With this technique, the buckling of the Faltkernwände can be moved to higher loads. Thus, the lightweight character of sandwich structures with folding core can be further improved.

9 schematically shows an equivalent sheet material, as used in the prior art as Faltkernmaterial used with the same basis weights as the embodiments according to 6 to 8th for comparison. Accordingly, this sheet and the multilayer sheet of the invention have the same basis weight. If the sheet thickness of the folded core material according to the invention is twice as large as that of an equivalent heavy, simple sheet, the flexural rigidity must be expected to be at least five times as great. In this assessment, effects due to the mid-layer as well as its supportive effect were not considered.

10 shows a process diagram of an embodiment of a method according to the invention for the continuous production of a multilayer folding core 2 , the process scheme 10 ,

11 shows a process scheme of another embodiment of a method according to the invention for the continuous production of a multilayer folding core 2 , the process scheme 10 ' ,

The base material comes in both variants of the method of the invention of the roles 11 . 12 . 13 , the upper cover layer of the roll 11 , the middle layer of the roll 12 and the lower cover layer of the roll 13 , In the in 10 shown variant of the method according to the invention are on the roles 14 the waves introduced in the direction of travel.

In the variant after 11 , the process scheme 10 ' The waves, however, are transverse to the direction of rotation over the rollers 10 brought in. In the variant after 10 is the folding core on the Aufstellwalzen 18 easy to set up. However, the process of introducing the waves is more difficult to handle in that the paper passes through the corrugated rolls 14 is gathered about 40% to 50%.

As in the variant after 11 the waves are brought into the material transversely to the direction of rotation, here is the gathering over the longitudinal direction by means of corrugated rolls 19 , This hardly causes any problems in the process. But since the tunnel resulting from the waves should show in the thickness direction of the sandwich after installation, must in the variant to 11 The folding pattern can be rotated by 90 °. However, this rotation makes the deployment process more difficult.

After in the middle layer, the well layer 6 . 6 ' . 6 '' , the desired wave pattern has been introduced is via the adhesive application rollers 15 the adhesive applied to the layers. Subsequently, over the press rollers 16 the Faltkerndeckschichten 5 on the middle layer, the well layer 6 . 6 ' . 6 '' , pressed.

Then bring the folding rollers 17 Using special geometries with the fold lines, insert the fold pattern into the fold core material that is either embossed or scored. This can be done in one or more steps. Thus, longitudinal notches in the variant after 10 for all types of Faltkerngeometrien with a preferred type of folding rollers are introduced, in which the notches are adjustable. Regardless, the notches are introduced either from above or from below into the Faltkernmaterial so as to give a preferred direction in which the structure kinks during the installation process. This facilitates setting up with vertically aligned setting rollers 18 , which may alternatively be designed as bands. The end result is the corrugated multi-layered folding core 2 before, ready for use in a sandwich material.

LIST OF REFERENCE NUMBERS

1

sandwich structure

2

collapsible core

3, 3 '

Faltkernwand

4

topcoat

5

Faltkerndeckschicht

6, 6 ', 6' '

Well layer

7

fold line

10, 10 '

Process Scheme Multilayer Folding Core

11

Roll cover layer above

12

Roll middle layer

13

Roll cover layer below

14

Corrugated rolls (longitudinal)

15

Glue application rollers

16

press rolls

17

folding rollers

18

alignment rollers

19

Corrugated rolls (transverse)

F _L

Power from stress

F _f

folding force

t _sw

Wall thickness of the individual layers

t _sheet

Wall thickness of the equivalent sheet

t _cfc

Total wall thickness of the multilayer sheet

k _cfc

Factor around the corrugated layer 6 . 6 ' . 6 '' (Middle layer) is longer as the cover layers at the same thickness

d _cfc

Length of a wave of the corrugated layer 6 . 6 ' . 6 '' (Intermediate)

r

Radius arc

π

Angle trapezoidal wall

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• RU 2267404 C2 [0003]
• WO 2005/049247 A2 [0003]
• RU 2238845 C1 [0003]
• WO 2005/058593 A2 [0003]
• DE 10252941 A1 [0004]
• DE 102007050356 A1 [0005, 0006]
• WO 2005/056285 A1 [0006]

Cited non-patent literature

• Zakirov, I. et. al .: Foldcore Structures: Performance, Technology and Production. Paris: SAMPE EUROPE, International Conference. 2006 [0002]

Claims (10)

Folding core for a sandwich structure for the arrangement between at least two flat cover layers ( 4 ), where folding core walls ( 3 . 3 ' ) with the cover layers ( 4 ) are connected in such a way that, when the sandwich structure is loaded ( 1 ) Absorbing tensile, compressive and / or shear forces, characterized in that the folding core walls ( 3 . 3 ' ) are made of several layers and at least two flat Faltkerndeckschichten ( 5 ) and at least one interposed therebetween and with the Fickelkerndeckschichten ( 5 ) connected corrugated layer ( 6 . 6 ' . 6 '' ) form a folded core material. Folding core according to claim 1, wherein in the folded core material two Faltkerndeckschichten ( 5 ) and a corrugated layer ( 6 . 6 ' . 6 '' ) are provided. Folding core according to claim 1 or 2, wherein in the folded core material the corrugated layer ( 6 . 6 ' . 6 '' ) is corrugated continuously, trapezoidally or in a circular arc. Folding core according to one of the preceding claims, wherein undulations of the corrugated layer ( 6 . 6 ' . 6 '' ) are introduced in the running direction or transversely to a running direction. Fold core according to one of the preceding claims, wherein the Faltkernmaterial for erecting the Faltkernwände ( 3 . 3 ' ) according to a folding pattern, having fold lines ( 7 ), embossed, scratched or scratched. Sandwich structure comprising a folding core ( 2 ) according to one of the preceding claims. Method for producing a folding core ( 2 ) for a sandwich structure ( 1 ), comprising the steps of providing a first core plating layer ( 5 ), a corrugated layer ( 6 . 6 ' . 6 '' ) and a second Fickelkerndeckschicht ( 5 ), Introducing a corrugated pattern into the corrugated layer ( 6 . 6 ' . 6 '' ), Applying adhesive, pressing the corrugated layer ( 6 . 6 ' . 6 '' ) with the Fickelkerndeckschichten ( 5 ), Application of fold lines ( 7 ) of a folding pattern and setting up the folding core ( 2 ). Method according to claim 7, wherein corrugations of the corrugated layer ( 6 . 6 ' . 6 '' ) are formed in the running direction. Method according to one of claims 7 or 8, wherein corrugations of the corrugated layer ( 6 . 6 ' . 6 '' ) are formed transversely to the direction.  Method according to one of claims 7 to 9, wherein the folding pattern is embossed, grooved or scored.

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