EP3778163A1 - Method for producing a wooden moulded part - Google Patents

Abstract

The invention relates to a method for producing a wooden molded part (2), in particular with a three-dimensional component geometry, in which wood chips (1) are provided which are at least partially delignified in a delignification process step (I), and in which in a deformation process step ( III) the delignified wood chips (1) are placed in a tool cavity (9) of a forming tool (11) and are pressed under pressure, heat and possibly moisture, in particular via an essentially completely thermomechanical compression, to form the wood molding (2).

Description

The invention relates to a method for producing a wooden molded part in particular with a three-dimensional component geometry according to claim 1 and a wooden molded part according to claim 10. The invention provides a wood-based semi-finished product and a method for producing components therefrom, which enables the production of high-strength , at the same time enables very light and ecologically sustainable components in three-dimensional component geometries.

In the prior art, wooden components with high mechanical requirements have so far only been produced on the basis of veneers, which are pressed and glued under pressure and temperature in molding tools. The veneers are about 0.5 to 8 mm thick sheets of solid wood, which are separated from the wood trunk using various sawing and cutting processes. In the prior art, the wood veneers are compacted in a pressing step, the remaining cavities being filled with plastic. A so-called synthetic resin pressed wood (or "armored wood") is produced with a strength of, for example, approx. 160 to 210 MPa with a density of approx. 1.1 to 1.3 g / cm ³ .

The manufacture of components from such synthetic resin pressed wood is subject to severe geometrical restrictions, which result from the low strength of the veneers used across the grain. This means that only components with relatively large radii of curvature can be produced. Furthermore, the combination of several radii of curvature, for example to form so-called "case corners", is only possible to a very limited extent. Complex three-dimensional structures, such as flat components with ribs on the back, cannot be produced with this approach. Another disadvantage is the use of (usually thermoset) plastics, which at least partially destroy the ecological advantage of wood as a raw material.

From the DE 10 2013 111 393 A1 a method for producing molded parts from a vulcanized fiber material is known.

The object of the invention is to provide a method with which wood-based lightweight components suitable for large-scale production can be produced which, in comparison to the prior art Technology enable a high component strength, a low density and a high degree of geometric freedom.

The object is achieved by the features of claim 1 or claim 10. Preferred developments of the invention are disclosed in the subclaims.

According to claim 1, the molded wood part is produced in a process sequence in which wood chips are initially provided. These are at least partially delignified in a delignification process step. In a subsequent forming process step, the delignified wood chips are placed in a tool cavity of a forming tool and pressed under pressure, heat and possibly moisture to form the wood molding. It is preferred if the wood chips stick to one another during thermomechanical compression in the forming tool solely through the binding forces inherent in the wood, and in particular without the addition of plastic binders.

A new approach according to the invention therefore consists in producing a flat semi-finished product from so-called wooden strands. The wooden strands have been at least partially delignified in a preparatory process step. The flat semi-finished product is brought into the component geometry in a shaping process step and compacted in the process. Wood strands are large-scale wood chips with optimized chip geometry (length-width-thickness ratio). The production of delignified wooden strands with defined or deliberately modified chip geometry and a defined ratio of the wood components cellulose, hemicellulose and lignin enables a shaping manufacturing process for the production of complex three-dimensional wooden molded parts with a defined local beach orientation and beach length.

At the process level, the new manufacturing process can be used to produce wood-based components with complex 3D structures, such as ribs and high strength. A wide range of component requirements can also be met through a possible orientation of the wooden strands in the flat semi-finished product to be formed or through combinations with other materials, such as wood veneers, fiber-reinforced plastics and metals.

For example, the semi-finished product can be produced using a number of component-specific semi-finished panels or from a combination of veneers and wooden strands with different lengths and orientations in a semi-finished product. The semi-finished panels can be fixed to one another using process-effective adhesion promoters or precompacting.

The shaping process step according to the invention can be implemented as a temperature-controlled shaping and consolidation process (extrusion), if appropriate in connection with superheated steam (compare particle foams). If necessary, wood-compatible adhesion promoters can also be used.

An essential aspect of the invention relates to the fact that wood strands are used in the process sequence according to the invention. If, instead, the process sequence according to the invention is carried out using wood veneers made of solid wood, the following disadvantages arise: When delignifying solid wood, very long process times are to be expected, since the wood components to be removed must be loosened from the wooden framework over longer distances and flushed out. In addition, the unidirectional fiber orientation ensures a preferred direction of the mechanical properties (anisotropy) in the pressed composite and suggests that complex geometries are not possible here either.

The main advantages of the invention are listed in bullet points below, namely a high level of geometric freedom through the use of wooden strands, with ribs and case corners being possible; If possible, no or absolutely minimal use of plastic, so that the finished component consists essentially entirely of natural and renewable components; no cavities that would promote moisture absorption, resulting in good dimensional stability and resistance to environmental influences; very good mechanical properties and strength, which is roughly comparable to simple steels, but at a fifth of the weight; due to the random orientation of the wood strands over the workpiece surface, quasi-isotropic mechanical properties in the plane direction; By adapting the flat semi-finished product and the production process, however, defined anisotropy is also made possible, for example with simple load paths; In addition, a simple combination with other semi-finished products and materials (for example (delignified) veneer, fiber-reinforced plastics (FRP), metals) is possible.

The invention provides an ecologically sustainable lightweight construction based on renewable raw materials. For this purpose, the invention offers the possibility of structurally relevant components with a high strength and at the same time low density and thus a high potential for lightweight construction completely from renewable and ecologically sustainable materials manufacture. At the same time, the invention enables a high degree of geometric freedom, so that, for example, ribs can be developed to improve component rigidity.

For example, an at least partial delignification of the wooden strands can take place in a first process step. The delignification of the wooden strands is possible using different methods, for example using the sulfite method, which is used to manufacture cellulose fibers in paper production. In order to shorten the process time as well as to reduce the process temperature, different concentrations of chemicals are used compared to paper production (Na ₂ SO ₃ and NaOH). A continuous process is possible here.

To reduce the number of chemicals to be used, partial delignification can also be made possible by means of ethanol at overpressure. This process can only partially be shown continuously. A favorable ratio of area to volume of the wooden strands enables the wooden strands to be pretreated quickly.

In a further aspect of the invention, the invention uses the fact that wood has binding forces inherent in wood. By means of these binding forces, the wooden strands can be glued together. The partial delignification has a positive effect on the chemical structure of the wood in terms of wood's own binding forces, so that the amount of additional binding agents can be reduced or binding agents can be dispensed with entirely. The use of moisture, temperature and pH to implement the crosslinking is particularly considered here. Therefore, the pretreatment of the wood strands in the delignification process step enables at least partial delignification of the solid wood, which means that stable hydrogen bonds are formed again between the pressed cell walls during the subsequent thermomechanical compression.

In a second process step, the component is manufactured by pressing. For the creation and processing of the flat semi-finished product, four process variants are conceivable in the second process step, which can be combined with one another:
The first and second variants are based on conventional extrusion processes. Compound masses of defined and undefined shape and strand orientation are pressed close to their net shape. The sheet molding compound (SMC) and the bulk molding compound (BMC) are representatives of extrusion semi-finished products.

The flexible handling of the flat semi-finished products from the first two variants enables the combination with similar and different materials. Based on the manufacturing processes for multi-layer composites, combinations with other semi-finished products and with other manufacturing technologies can be implemented. Their combinations achieve synergy effects in terms of increased mechanical properties and functional integration.

In a third variant, a combination with other semi-finished products can take place, for example with veneers for optics, fiber composite plastics, metals, fabrics, nonwovens, nonwovens. In addition, functions can be integrated (for example, inserting cables, etc.).

In a fourth variant, a combination with other manufacturing technologies can take place, for example simultaneous metal forming.

In summary, the new process enables the production of high-strength, complex components that are potentially suitable for all structural applications in the automobile and other industries (e.g. for rail vehicles, aerospace, construction, wind and energy systems). There they can be used as an alternative to the plastic or plastic-metal hybrid components used today (potentially also as part of new wood-metal hybrid composites).

In the following, aspects of the invention are again highlighted individually: Thus, the wood chips can each have a large-area flat profile geometry with opposite flat sides and with opposite narrow sides. The flat profile geometry is designed with a favorable length-width-thickness ratio with regard to the delifignation process step and the forming process step.

To provide a flat semifinished product with a unidirectional fiber orientation, the wood fibers of the wood chips forming the semifinished product can be aligned unidirectionally with respect to one another.

In contrast to this, if the flat semi-finished product has a multidirectional fiber orientation, the wood fibers of the wood chips forming the flat semi-finished product are provided in a non-oriented manner in a tangled position to one another.

In a preferred embodiment, the wood molding can be constructed as a multilayer composite. To produce the multi-layer composite, the flat semi-finished product can be inserted into the tool cavity of the forming tool with at least one further insert part. For example, the additional insert part can be at least one further flat semi-finished product. Alternatively and / or additionally, the additional insert part can be a wood veneer, a fiber composite plastic insert part, a metal insert part and / or a fabric, a scrim or a fleece. Alternatively and / or in addition to this, the insert part can consist of loose wood chips.

In a further embodiment variant, the additional insert part can be a functional element, for example a cable, which is to be integrated into the wooden molded part to be produced.

With a view to simplifying the process, not only can the flat semi-finished product be pressed in a shaping manner in the shaping process step, but the insert part can also be reshaped. For example, a metal insert part can be subjected to metal forming.

In a technical implementation, the delignified wood chips can be placed loosely in the tool cavity of the forming tool, for example as bulk material. Alternatively, the delignified, still loose wood chips can be pressed into a flat semi-finished product in a preparatory process step in a press tool. The flat semi-finished product can be inserted into the tool cavity of the forming tool in preparation for the forming process step.

Exemplary embodiments of the invention are described below with reference to the accompanying figures.

Figur 1

in einer Seitenschnittansicht ein fertiggestelltes Holz-Formteil;

Figur 2

ein Blockschaltdiagramm, anhand dem Prozessschritte zur Herstellung des in der Figur 1 gezeigten Holz-Formteils veranschaulicht sind; und

Figur 3 und 4

in Ansichten entsprechend der Figur 2 weitere Ausführungsbeispiele der Erfindung; und

Figur 5

in einer Ansicht entsprechend der Figur 1 ein Holz-Formteil gemäß einer Ausführungsvariante.

Show it:

Figure 1

a finished wood molding in a side sectional view;

Figure 2

a block diagram showing the process steps for producing the in the Figure 1 shown wood molding are illustrated; and

Figures 3 and 4

in views corresponding to the Figure 2 further embodiments of the invention; and

Figure 5

in a view corresponding to the Figure 1 a wood molding according to one embodiment.

In the Figure 1 a wooden molded part 2 is shown with a three-dimensional component geometry. The wood molding 2 is formed from large wood chips 1, which are glued to one another by the binding forces inherent in the wood, specifically by means of thermomechanical compression. The wood molding 2 is in the Figure 1 exemplarily designed with a unidirectional fiber orientation.

The following is based on the Figure 2 a process sequence is described by means of which the Figure 1 Shaped wood part 2 can be produced: Accordingly, wood is first comminuted into wood chips 1 or cut to a defined chip size in a cutting station (not shown). The wood chips 1 are each dimensioned with a length-width-thickness ratio (I, b, d) which is favorable for subsequent treatment steps I, II, III, as shown in FIG Figure 2 is shown. Accordingly, the wood chips 1 each have a large-area flat profile geometry with opposite flat sides and with opposite narrow sides. The span length I is, for example, in a range from 5 to 10 mm, while the span width b can be in a range from 4 to 7 mm. The chip thickness d is in a range from 0.5 to 1.5 mm. The dimensions are to be understood only as examples and are in no way intended to restrict the invention to them.

This is followed by a delignification process step I in which the wood chips 1 are at least partially delignified. The wood chips 1 pretreated in this way are then placed in a press tool 3 in a prepared press process step II and pressed to form a flat semi-finished product 5. With regard to a unidirectional fiber orientation are in the Figure 2 the wood fibers 5 of the wood chips 1 forming the flat semi-finished product 5 are aligned unidirectionally to one another.

In the delignification process step I, the wood chips 1 are at least partially delignified. The delignification process step I is designed in such a way that stable hydrogen bonds are formed again between the wood chips 1 during the subsequent thermomechanical compression in the press process step II and in the forming process step III . Therefore, if necessary, the wood chips 1 can stick to one another in the case of thermomechanical compression solely through the binding forces inherent in the wood, specifically particularly preferably without the addition of plastic binders.

The flat semifinished product 5 produced in the pressing process step II is inserted into the tool cavity 9 of a forming tool 11. A thermomechanical compression also takes place in the forming tool 11 under pressure, heat and moisture, in which the flat semi-finished product is pressed to form the wooden molded part 2.

Based on Figure 3 an alternative process sequence for producing the wood molding 2 is described, the process steps of which are essentially identical to those based on FIG Figure 2 explained process steps. In contrast to the Figure 2 shows that in the Figure 3 produced wood molding 2 does not have a unidirectional fiber orientation, but a multi-directional fiber orientation. For this purpose, the delignified wood chips 1 in the flat semifinished product 5 with their wood fibers 7 are no longer aligned unidirectionally, but instead are positioned in a randomly random manner in the flat semifinished product 5. Otherwise, the process steps I, II, III up to the completion of the wooden molded part 2 are identical to those already based on FIG Figure 2 explained process steps I, II, III.

Based on Figure 4 Another alternative process sequence for producing the wood molding 2 is described. In contrast to the previous exemplary embodiments, in the Figure 4 the pressing process step II is omitted. For this reason, the wood chips 1 pretreated in the delignification process step II are no longer pre-pressed into a flat semi-finished product 5, but rather are placed directly into the tool cavity 9 of the forming tool 11 as bulk material. In this way, a multidirectional fiber orientation results in the wood molding 2 to be produced.

In the Figure 5 a wooden molded part 2 is shown according to a further embodiment. In the Figure 5 the molded wood part 2 has a multilayer composite 16, specifically with a wood chip layer and a metal layer. To produce the in the Figure 4 In the multi-layer composite 16 shown, the flat semi-finished product 5 in combination with a metal insert part 15 is inserted into the tool cavity 9 of the forming tool 11 in the forming process step III. The reshaping then takes place, in which not only the flat semi-finished product 5 is reshaped, but also a metal reshaping of the metal insert part 15 takes place.

List of reference symbols

1

Wood chips

2

Wood molding

3

Press tool

5

Flat semi-finished products

7th

Wood fiber

9

Mold cavity

11

Forming tool

13

Wood chip layer

15th

Metal insert

16

Multi-layer composite

I.

Wood chip length

b

Wood chip width

d

Wood chip thickness

I.

Delignification process step

II

preparatory process step

III

Forming process step

Claims (10)

A method for producing a molded wood part (2), in particular with a three-dimensional component geometry, in which wood chips (1) are provided which are at least partially delignified in a delignification process step (I), and in which the delignification in a deformation process step (III) Wood chips (1) are placed in a tool cavity (9) of a forming tool (11) and are pressed under pressure, heat and possibly moisture, in particular via an essentially completely thermomechanical compression, to form the wood molding (2). Method according to claim 1, characterized in that the delignified wood chips (1) are loosely inserted into the tool cavity (9) of the forming tool (11), in particular as bulk material, or that the delignified wood chips (1) in a preparatory process step (II) in a press tool (3) to be pressed into a flat semi-finished product (5), and that the flat semi-finished product (5) for the forming process step (III) is inserted into the tool cavity (9) of the forming tool (11). Method according to claim 1 or 2, characterized in that the wood chips (1) are glued to one another during the thermomechanical compression in the forming tool (11) and / or in the press tool (3) solely by the binding forces inherent in the wood, in particular essentially without additives of plastic binders. Method according to one of Claims 1 to 3, characterized in that the wood chips (1) each have a large-area flat profile geometry with opposite flat sides and with opposite narrow sides, and that in particular the wood chips (1) are used for the delignification process step (I) , for the preparatory process step (II) and / or for the forming process step (III) have a favorable length-width-thickness ratio. Method according to one of Claims 2 to 4, characterized in that, in order to provide a flat semi-finished product (5) with a unidirectional fiber orientation, the wood fibers (7) of the wood chips (1) forming the semi-finished product (5) are aligned unidirectionally with one another, or that to provide a flat semifinished product (5) with a multidirectional fiber orientation, the wood fibers (7) of the wood chips (1) forming the flat semifinished product (5) are unoriented in a tangled position with respect to one another. Method according to one of the preceding claims, characterized in that the molded wood part (2) has a multi-layer composite (16), and that for producing the multi-layer composite (16) the flat semi-finished product (5) with at least one further insert part (15) in the tool cavity (9) of the forming tool (11) is inserted. Method according to claim 6, characterized in that the insert part (15) is a further flat semi-finished product (5), a wood veneer, a fiber-reinforced plastic insert part, a metal insert part and / or a fabric, scrim or fleece, or the insert part ( 15) consists of loose wood chips. Method according to Claim 6 or 7, characterized in that the additional insert part (15) is a functional element, for example a cable, which is to be integrated in the wooden molded part to be produced. Method according to Claim 7 or 8, characterized in that in the forming process step (III), the insert part (15) is also formed at the same time, for example metal forming of a metal insert part (15). Wood molding produced by a method according to the preceding claims.

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