EP2119540A1 - Mould object with balsa woods and method for its production - Google Patents

Abstract

The molding body has trimmed timbers (3) made of transverse or grain section of balsa wood. The trimmed timbers are arranged in a stack, and are mutually aligned with parallel fiber direction, which deviates from an axis in a usual fiber direction at an angle from zero to three degree. An adhesive i.e. foamed polyurethane contained adhesive, is provided between the trimmed timbers, where the volume of the adhesive ranges from 3 to 5 percentages related to the volume of the molding body. An independent claim is also included for a method for manufacturing the molding body.

Description

The invention relates to moldings containing balsa wood and process for their preparation.

Balsa wood is a very light and easy to work type of wood. In addition to its use as a raft construction and as a cork replacement, balsa wood is used by model builders for aircraft and ship models. Balsa wood, however, has the greatest importance as a core material of composite materials in sandwich construction, for example in boat, ship and yacht construction, in aviation, such as in sailing and light aircraft construction, in space travel and as a core or core material of rotor blades of e.g. Wind turbines. The good insulating properties of balsa wood are also used for insulation against heat and cold, for example, from fuel tanks. In the technical field of application, the low volume weight and the unusually high compressive strength in relation to the low raw weight are exploited parallel to the fiber direction.

For the applications mentioned so-called middle layer material is produced. The basic component produced for this purpose is the so-called end grain board. For this purpose, four-sided processed balsa, also called Kantelhölzern or Balsakanteln, into large blocks, for example in cross-section about 600 x 1200 mm, glued and then sawed transversely to the fiber direction into plates of any thickness, for example about 5 to 50 mm, and then to the exact Dickenmass ground. This light end grain board can absorb very strong compressive forces over the surface, but is very unstable in itself. For example, by single or double-sided application, transverse to the fiber direction, of plastic plates, reinforced with glass, plastic or carbon fibers plastic sheets or layers, metal plates or sheets, wood panels, veneers, fabrics, films, etc. on the middle layer material or a end grain, you get heavy duty Composites.

For the construction of strongly arched components, e.g. In the manufacture of hulls for boats or sailing yachts, the end grain board is glued on one side with a thin fiber fleece, knitted fabric or fabric and carved from the opposite side cuboid or cube-shaped to a thin web. The prepared plate can be made in any concave or convex shape and can be a curved shape, such as a boat or buoyancy body or a ball tank, adapted.

Balsa wood is a natural product. Therefore, the characteristics of the balsa wood within the woods of a crop can change to sections of a tree trunk. This concerns, for example, the bulk density, the moisture, the shrinkage, the compressive strength, the tensile strength, etc., and the porosity may vary. Deficiencies in the trunks, such as internal cracks, so-called red-core or water-heart, fibrous tangles or mineral spots, unless removed prematurely with loss of wood, can influence the regularity of the properties of a end grain board.

Since a Balsaholzstamm is round, but the end grain to be produced from a variety of rectangular planks is produced, the trunk must be sawed in the fiber direction and across. The sawn-out planks are stacked tightly, pressed over the mutual contact surfaces and glued and then sawed back across the grain. By peeling off the tree bark, sawing off the curves by tendon or tangential cutting and sawing in slabs or planks, only about 25% of the available wood is used for technical purposes. The rest is produced as chips, sections and sawdust. In further processes, when planning planks or sorting, much untapped waste wood is produced.

The invention has for its object to use the wood better and in greater yield and moldings containing balsa wood with at least approximately describe the same or better characteristics than the natural balsa wood and propose a process for their rational production.

To achieve the object according to the invention, the shaped body comprises lumbers made of transverse or brain slices of balsa wood, arranged in a stack and aligned with respect to their fiber direction, and contains adhesives between the lumbers.

In the molded body, the fiber direction, resp. the fiber profile, aligned substantially concurrently and the fiber profile of the individual lumber can from 0 ° to 30 ° (degree of angle), suitably 0 ° to 10 ° and preferably from 0 ° to 3 °, from an axis in the general direction of fiber or direction of the fiber flow in Moldings deviate. Ideally, the deviation of the fiber profile of the individual lumbers is at 0 ° or as close as possible to 0 ° from a general or ideal straight line direction or from an axis parallel to the fiber flow in the molding. In other words, the grain of the lumber in the molded body should be as parallel as possible and include an angle between the axis in the direction of the fiber flow and the individual fibers in the timber of not more than 30 °.

The balsa wood lumbers are obtained from logs whose wood has, for example, a density of 0.07 to 0.25 g / cm ³ . Soft balsa wood has a density of 0.07 to 0.125 g / cm ³ , medium hard balsa wood of 0.125 to 0.175 g / cm ³ and hard balsa wood of 0.175 to 0.25 g / cm ³ .

The size of the individual lumbers can, for example, be from 1 to 50 mm, preferably from 2 to 20 mm, in their height, ie in the direction of the grain of the fiber. For starting materials of substantially polygonal cross-section, a side length of the sawn timber of 5 to 250 mm, respectively, or in the case of rounded rounded starting materials, the average diameter may be from 5 to 250 mm. In other terms, can, at a height of 1 to 50 mm, in plan view a sawn timber an area of 25 to 60,000 mm ² , suitably from 100 to 50,000 mm ² , have.

The lumber from cross or brain slices may result from the shredding of balsa wood material by cutting across the grain. As Balsaholzmaterial stems or trunk sections, even small-diameter strains, for example of young plants, planks, the cutting of planks, boards and the like. Resulting Balsaholzreste etc. are used, also residues that are obtained when sawing or cutting to length of logs or planks. The wood is made by cross-sections or end-grain wood cuts, i. by cuts across or perpendicular to the fiber or to the grain, divided, as cut, split, ev. Sawed and in particular cut. This produces lumber with a smooth surface and a very low proportion of fines. The cutting of the wood can be done by knives, by laser cutting, possibly by sawing, etc.

The lumbers are usually from fresh wood, such as logs from logs, for example, by cutting the lumber across the grain in the piece of wood produced, and after cutting the lumber, preferably dried in a drum dryer. Subsequently, the lumbers can be graded by sifting and / or screening according to size and density and stored on a case by case basis. The lumbers are glued in particular. For this purpose, the lumbers are uniformly coated with the intended amount of adhesive by pre-coating or direct coating, eg in a gluing drum, by spraying, sprinkling or dusting and mixing or by immersion. The glued lumber can be - occasionally mixed from fractions of different density and / or size - processed into moldings. In general, the glued lumbers are in a shape-giving device, filled or heaped up and, if necessary by measures such as vibration, shaking, sifting in the air stream, etc. on a parallel fiber as possible in - advantageous as dense - stacking (parking) aligned and layered. The Bulk may become discontinuous but is preferably carried out continuously. For example, the bed can be made on a belt. The edges can be trimmed and the thickness or a preliminary thickness of the shaped body can be adjusted by doctoring or between rollers or belts. Subsequently, the adhesive is activated, for example, in a continuous furnace and / or a double belt press or a heated continuous press, wherein, according to the adhesive, this foams, melts, reacts chemically, etc., and, optionally under pressure, the lumbers are mutually bonded separately. By viscous behavior of the adhesive or by the foaming process, the adhesive can get into the spaces between the lumber and fill the gaps or glued joints partially and advantageously completely. It is made of mutually bonded lumber, for example, plates. Due to the thickness set in the bulk and compaction process, the boards can be mass-produced to thickness. The thickness of a plate can be adjusted to, for example, 0.5 to 5 cm. The width of the plates depends on the circumstances of the apparatus and may for example be from 50 to 300 cm. Since the plates can be manufactured continuously, their length can be set as desired. For practical reasons of further processing, the length of the plates is usually from 100 to 500 cm. Thus, plates of preset thickness can be mass-machined with concurrent fiber direction in the direction of height or thickness of the plate. The panels already represent the end-grain panels and, according to the applications, the panels can be cut to size.

During processing, by lateral pressure by rollers or cheeks and vertical pressure by a band, double band or rollers, the applied pressure should be chosen such that the cell resp. Fiber structure of balsa wood is not changed or damaged, in particular, that the density of the balsa wood is not or only slightly changed by compression. The pressing pressure should be set low because too high pressing pressure and the wood structure is compressed in total. The applied pressure between two rollers and / or belts can be up to 50 bar, suitably 0.5 to 5 bar.

As the adhesive, for example, adhesives such as physical bonding adhesives or chemically curing adhesives can be used. Examples are one- or two-component polyurethane adhesives, one- or two-component epoxy resin adhesives, phenoplasts, such as phenol-formaldehyde adhesive, melamine-urea-phenol-formaldehyde adhesive, isocyanate adhesive, polyisocyanates, such as polymeric diphenylmethane diisocyanate, cyanoacrylate adhesive, acrylic resin adhesive, methyl methacrylate adhesive, hot-melt adhesive, rosin, etc. Foaming adhesives or foam adhesives and, in particular, foaming or foamed polyurethane-containing adhesives are preferably used. As mentioned above, by viscous behavior of the adhesive or by the foaming process, the adhesive into the pores, interstices or glued joints between the lumbers or to the mutual bearing surfaces, resp. Glued joints, get the lumber. The adhesive can partially and advantageously completely fill the pores, gaps or gaps between the lumbers and create a release-resistant connection.

The novel moldings may contain adhesives in amounts of from 1 to 15% by volume, advantageously from 2 to 10% by volume and preferably from 3 to 5% by volume, based on the volume of the molding.

Advantageously, the fully reacted, such as foamed or set etc., adhesive, the same or almost the same density as the density of the surrounding balsa wood. The reacted adhesive, based on the density of the balsa wood surrounding the adhesive, may, for example, have a 0 to 20% by weight higher or 0 to 20% by weight lower density. Adhesives with densities of the reacted adhesive that are 0 to 10 wt% over or 0 to 10 wt% below the density of the surrounding balsa wood are preferred. Foamed polyurethane adhesives are particularly suitable as adhesives with densities in the stated range. With the density is when foamed Glues meant their density. Thus, the advantageous low density of Balsaholzes can be achieved with the inventive moldings.

The present invention also relates to a method for producing the shaped bodies from wood balsa wood which mixes with adhesive, aligned with respect to the fiber direction, wherein the fiber profile of the individual lumbers from 0 ° to 30 °, suitably 0 ° to 10 ° and preferably from 0 ° to 3 °, deviates from the axis of the general fiber profile, the adhesive is activated and solidified to form adhesive force by heat and / or pressure. In an expedient embodiment for the production of the moldings according to the invention, the balsa wood lumbers are solidified in a double belt press. Preference is given to a process for the production of the shaped bodies in which adhesive is used in amounts of from 1 to 15% by volume, expediently from 2 to 10% by volume and preferably from 3 to 5% by volume, based on the volume of the shaped body.

The shaped articles are, for example, plates, but it is also possible to produce strips, beams, planks or plates which are now transversely to the fiber path in e.g. End grain boards can be shared. Beams or planks usually have a rectangular cross-section and can be further stacked into blocks with the same fiber direction or the same fiber path, mutually glued and split across the grain in end grain boards, such as sawed.

The moldings obtained according to the invention, such as end grain boards, can be used in the same way as the plates produced so far. For example, by single or double-sided application, transverse to the fiber direction of plastic plates, reinforced with glass, plastic or carbon fibers plastic sheets or layers, metal plates or sheets, wood panels, veneers, fabrics, knitted fabrics, knitted fabrics, nonwovens, films, etc. on the middle layer material or a end grain board, one obtains high-strength composite materials. The moldings according to the invention, in particular end grain boards, can be glued to one side with nonwoven fabric, knitted fabrics, knits or fabrics and can be cut into cubes or cubes from the other side to a small residual thickness in the direction of the fiber flow. The thus processed plate is thereby in bendable and can be brought into concave or convex shape.

With the present method, it is possible to use the balsa wood to a much greater extent for shaped bodies, such as end-grain wood panels, than was previously possible. Starting from the harvested balsa wood, up to a end grain wood panel, a yield of only 24% can be achieved with conventional methods. There are losses in the sawmills in the production of balsa or Kantelhölzer, the subsequent drying, when layering and gluing into blocks, and finally when sawing on. With the present method, a yield of 60 to 70% is achieved. In particular, almost all parts of the Balsaholzstammes, at least as long as the parts are still aligned after the fiber orientation, be recycled or it can be peeled without waste or waste with very low waste and peeling products are fully utilized.

Balsa wood can be glued very well and permanently. The strength of the glue joint may be, may be lower or exceed the strength of the surrounding wood fabric. Depending on the choice of adhesive, the properties of end grain or balsa wood parts can be changed. The adhesive in the adhesive joints may for example also form an actual support structure or a supporting network, which lead to even pressure and / or tear-resistant materials or the adhesive may reduce or increase the elasticity of a Balsaholzteils. The adhesive joints may also contain reinforcing materials such as fibers, for example as part of the adhesive.

The novel moldings can be used in many ways become. For example, they are starting materials or finished products in the field of laminates, sandwich materials or the so-called composites. In the field of energy production, the moldings can form parts of propellers and wind blades for windmills or wind-driven generators or turbines. The moldings can be used, for example, as core material or laminate in means of transport, such as ceilings, floors, shelves, wall coverings, covers, etc. in boats, ships, buses, trucks, railway vehicles, etc. Due to the low density of the molded body, these can serve as a replacement for conventional lightweight and core materials, such as honeycomb body, foams, etc.

Based on FIGS. 1 to 3 For example, the present invention is illustrated by way of example.

FIG. 1 represents a screed or a section of a Balsaholzstamm (2). The arrow (L) points in the longitudinal direction, which corresponds to the growth direction and thus the general fiber flow. Q represents the cross-sectional area, ie the cross-section of the fiber. Arrow (R) points in the direction of the radial section surface. Arrow (T) points towards the tangential interface.

In FIG. 2 a section of a balsa wood trunk (2) is shown. The arrow (L) points in the longitudinal direction, which corresponds to the growth direction and thus the general fiber profile. Thus, arrow (L) is also the axis of the general fiber flow. Q represents the cross-sectional area to the fiber flow. A lumber (3) is sketchy of the trunk (2) removed by transverse or brain section, respectively. may be removed from the cross-sectional area by cross-section (ie, cut transversely to the fiber direction), such as cut or sawed off. The grain of the lumber (3) also runs in the direction of the arrow (L).

FIG. 3 illustrates an example of a shaped body in the form of a plate (4) of mutually bonded timber (3). The plate has a side edge S ₁ and a second side edge S ₂ . The grain of all lumber (3) lies in Direction of the arrow (L). The arrow (L) at the same time represents the axis of the general fiber flow, from which the fiber path should deviate, for example, at most up to 30 °. By way of example and for reasons of clarity, two lumbers (3) were designated, once in plan view, once in side view. It becomes clear that the lumbers (3) abut each other as tightly stacked as possible. The stacking forms the height of the shaped body S ₃ . The grain of the lumber is as parallel as possible, resp. deviating at most at an angle, as indicated above, in an axis in the direction of the arrow (L). The interspaces that inevitably form between the irregularly shaped lumbers are filled with adhesive. The adhesive forms a release bond between the lumbers. Q ₁ denotes the cross-sectional area or brain sectional area of the screed. The balsa fibers are cut transversely across this surface. By the described mode of production can directly plates (4), which can be used as end-grain wood applications are made. Examples of such plates (4) have, for example, a side edge length S ₃ or thickness of about 0.5 to 5 cm, the width or side edge S ₁ can be from about 50 to 300 cm and the length or side edge S ₂ can at a continuous process arbitrarily long, conveniently about 100 to 500 cm long.

Claims (8)

Moldings containing balsa wood,
characterized in that
the shaped body lumber from transverse or brain slices of balsa wood, arranged in a stack and aligned with each other with the same direction of grain, and contains adhesives between the lumber. Shaped body according to claim 1, characterized in that the lumbers of transverse or brain slices, arranged in a stack and aligned with the same direction of grain, wherein the fiber direction in the individual lumbers of 0 ° to 30 °, suitably 0 ° to 10 ° and preferably from 0 ° to 3 °, deviates from an axis in the general fiber direction. Shaped body according to claims 1 and 2, characterized in that the adhesives are polyurethane-containing adhesives, preferably foamed polyurethane-containing adhesives. Shaped body according to claims 1 to 3, characterized in that the adhesives in amounts of 1 to 15 vol .-%, suitably 2 to 10 vol .-% and preferably 3 to 5 vol .-%, based on the volume of the shaped body containing are. Shaped body according to claims 1 to 4, characterized in that the reacted adhesive, the density of the surrounding balsa wood or a 0 to 20 wt .-%, preferably 0 to 10 wt .-%, higher or lower density than that of the surrounding balsa wood having. Process for the production of moldings according to claim 1, characterized in that
Edges of cross or brain slices mixed with adhesive, aligned with respect to the grain direction gleichlaufend, the fiber direction in the individual timbers from 0 ° to 30 °, suitably 0 ° to 10 ° and preferably from 0 ° to 3 °, from an axis in general Fiber direction deviates, the adhesive is activated and solidified to form adhesive force by heat and / or pressure. A method for the production of moldings according to claim 6, characterized in that the lumbers of cross or brain slices mixed with the adhesive, directed with respect to the fiber direction, the fiber direction in the individual lumbers of 0 ° to 30 °, suitably 0 ° to 10 ° and preferably from 0 ° to 3 °, deviates from an axis in the general fiber direction, the adhesive is activated and solidified to form adhesive force by heat and / or pressure in a double belt press. A process for the production of moldings according to claims 6 or 7, characterized in that cut wood from cross or brain slices with adhesive in amounts of 1 to 15 vol .-%, suitably 2 to 10 vol .-% and preferably 3 to 5 vol. %, based on the volume of the molding, blended, the glued lumber aligned with respect to the fiber direction concurrently, the fiber direction in the individual lumbers of 0 ° to 30 °, preferably 0 ° to 10 ° and preferably from 0 ° to 3 °, of an axis in the general fiber direction deviates, the adhesive is activated and solidified to form adhesive force by heat and / or pressure.

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