The present invention relates to a method for producing a flexible end grain balsa core panel according to the preamble of claim 1.

This invention relates generally to techniques for converting round logs into flexible end grain panels. Traditionally this process consists of cutting logs into pieces, drying the pieces and cleaning the surfaces of them. After that, the lumber pieces are glued together to a block from which solid panels are cut. For flexible panels, afterwards, one side of the panel is equipped with a scrim that allows vertically and horizontally cutting of the panel. This leads to defined single pieces on a scrim.

GB 178,364 describes the manufacture of a flexible parquetry slab for floors or walls which consists of a slab of suitable thickness and formed by cutting transversely a block of convenient size and composed of an assemblage of longitudinally disposed strips of wood with the grain running endwise, the strips being of the same kind, or different or stained kind, and arranged by the component pieces of the slab. The grain of the pieces running at right angles to the wearing surface of the slab, and the pieces are attached to a flexible backing.

According to GB 178,364 the strips or bars of wood constituting the block from which the slabs are cut are kept unconnected one from the other, and no glue or other adhesive being used between pairs of adjacent sides or edges, but for cutting the slab the strips or bars of wood are temporary hold together by gripping or clamping the block externally around its periphery.

US 3,376,185 describes a tessellated contour flexible balsa core blanket which is conformable to a contoured surface. The blanket consists of a layer of individual balsa blocks being secured to a mesh of non-stretchable, flexible scrim material. The balsa is fed in strip form and the balsa strips are cut into blocks in a slitting station and an adhesive-coated scrim is then applied on the blocks, i.e. the strips being converted into a continuous tessellated layer of individual balsa blocks, which are attached to a flexible carrier to form a core blanket.

According to US 3,376,185 the strips of balsa are fed on a conveyor belt, wherein they lie orthogonal to the driving direction of the conveyor belt. The balsa strips loaded onto the conveyor belt are then fed into a slitting station having a bank of circular slitting knives where the slit strips emerge from the knives as a layer of individual square blocks. The layer of individual balsa blocks onto the conveyor is then covered by an adhesive-coated scrim.

A first method for producing a flexible end-grain balsa panel developed by the inventors of present invention comprises the steps of:

A. arranging a plurality of lumber sticks of rectangular cross-section having all the same length, width and thickness parallel to each other thereby forming a block of rectangular cross-section;

B. pressing a layer of scrim, impregnated or coated with a binding agent, against end faces of the lumber sticks forming the block;

C. maintaining pressure and applying heat to the layer of binding agent containing scrim to laminate the scrim to the end faces of the lumber sticks;

D. cutting a panel consisting of end sections of the lumber sticks laminated with the scrim from the block.

The lumber sticks are held in a frame. Pressing means are preferably arranged laterally of the block. The block is subjected to compression in orthogonal directions by a pressing system. A preferred embodiment of a pressing system consists of a first pressing device holding together the lumber sticks with a pressure eliminating natural torn, bends and twists appearing in the single lumber sticks and a second pressure device applying high pressure to remove remaining voids, gaps, seams or slits between opposite contacting surfaces of the single lumber sticks. No adhesive is provided between the single lumber sticks and the block is hold together by external pressure only. As a rule, the first pressing system is arranged on the block at the end away from the cutting end. The second pressure device is arranged relative to the block near the end where the panels are cut from. The layer of scrim is provided by a roll, coil or reel and the cutting device is preferably a band saw. Pressing the scrim against end faces of the lumber sticks is performed by pressing or pressing and heating by a heatable plunger plate. The first method for producing flexible end-grain balsa panels is shown in figures 1 and 2 which show:

Fig. 1 : a perspective view of a lumber stick and cut end sections;

Fig. 2: a side view of an apparatus for the first production method;

Referring to Fig. 1 , there is shown a longitudinal strip or lumber stick 10 having a preferred uniformed length Is of between 1.5 and 3.5 m and a preferred rectangular cross section of 25,4 mm x 50,8 mm (1 inch x 2 inch) defined by a width ws and a thickness ts of the lumber stick 10.

Also shown in Fig. 1 are end sections 12 which have been cut from a lumber stick 10 and having a thickness tp corresponding to the thickness of an end grain balsa panel as described below.

The lumber sticks 10 are manufactured from raw pieces which are cut with oversize from round logs of balsa wood. The logs typically have a diameter of between 4 and 20 inches, depending on the age of the tree from which the log is cut. The raw pieces are then kiln dried in a conventional oven of the type used for lumber drying to reduce the moisture content thereof to 12 percent or less, this being standard practice in the lumber industry. The kiln-dried pieces are then milled to the preferred length and the sides planed. In a next step, defects in the lumber sticks 10 such as the piths or knots are detected and eliminated by cutting off the defect parts. The lumber sticks are selected along their density. Depending on the final use of end grain balsa panels, preferred are selections having a density of 80 kg/m ³ to 170 kg/m ³ ; densities of 96 kg/m ³ to 153 kg/m ³ are especially preferred.

In a further step, at least two of the defect-free lumber sticks 10, which are considerably shorter, are assembled to form lumber sticks 10 having a uniform length of for instance 1.5 to 3.5 m. The assembling of the shorter lumber sticks 10 can be performed with a finger jointing process. After cleaning the surface of the finger jointed sections, the uniformed lumber sticks can be used in the first process for producing a flexible end-grain balsa panel developed by the inventors of present invention as well as in the process as claimed in claim 1.

As shown in Fig. 2 the lumber sticks 10 are arranged in a vertical position within a first pressing device 16. The lumber sticks 10 having all the same length l _s , width w _s and thickness ts and are arranged parallel to each other thereby forming a block 14 of rectangular cross section. The dimensions of device 16 are selected to hold together the lumber sticks 10 with a pressure capable to eliminate natural torn, bends and twists as appearing in the lumber sticks. A vertically movable top plate 20 is positioned horizontally above the frame and is resting on the top of the block 14 formed by upper end faces 22 of the lumber sticks 10 and is vertically movable within the device 16.

Beneath device 16 a second pressing system 28 is arranged horizontally around the block 14, and the assembly of lumber sticks 10 in the block 14 is subjected to compression in orthogonal directions by pressing system 28, applying pressure to remove remaining voids, gaps, seams or slits between opposite contacting surfaces of the single lumber sticks. This condition is maintained until such time when the cutting off of end sections 12 of the lumber sticks 10 at the lower end of the block 14 is terminated, as explained further below. The length of the end sections 12 cut from the lumber sticks 10 corresponds to the thickness tp of a panel to be formed by end sections 12. Lower end faces 24 of the lumber sticks 10 in the block 14 form a rectangular plane corresponding to one of the rectangular top sections of a panel to be formed by sections 12, as described below. A layer 26 of scrim comprising a binding agent, like a hot melt scrim, is unwound from a coil 34. The unwound layer 26 of scrim is positioned within a short distance beneath and parallel to the lower end faces 24 of the lumber sticks 10 of the block 14. The layer 26 of scrim is positioned between the lower end faces 24 of the lumber sticks 10 of the block 14 and a heatable and vertically movable plunger plate 30 with a top section 32 positioned parallel to the lower end faces 24 of the lumber sticks 10. The layer 26 of hot melt scrim is provided by a roll or coil 4.

A cutting device 36, such as for instance a band saw or a circular saw, is positioned directly beneath the pressing system for cutting off the end sections 12 from the lumber sticks 10 in a horizontal plane.

The process steps of a production cycle of the first process will be explained below with reference to Fig. 2.

Step 1 : The pressing system 28, arranged around block 14 at its lower end beneath pressing device 16, and pressing device 16 at the top end of block 14 are unloaded. As a result the lumber sticks 10 forming block 14 drop with their lower end faces 24 on the layer 26 of a scrim, for example a scrim comprising a binding agent, as an example, a scrim coated with a hot melt. In another example of an embodiment, not shown, the scrim is arranged above the block. To bring block and scrim in mutual contact, block 14 moves upward. During the upward motion pressing device 16 and pressing system 28 remain loaded. After contact and bond of end face and scrim, the pressure of pressing device 16 and pressing system 28 is unloaded only. For a next cycle, pressing systems 28 and pressing device 16 are loaded again, using a lower pressure with device 16, and a higher pressure in pressing system 28. To produce a gap free panel, it is necessary to apply the pressure close to the sawing plane, as wood is a natural material and the sticks production has tolerances, and as a consequence, the sticks are not 100% straight. The pressure applied on the block 14 in orthogonal directions is preferably about 1 kg/cm ² . The plunger plate 30 is moved vertically upward to contact with the layer 26 of scrim which is pressed against the lower end faces 24 of the lumber sticks 10 forming the block 14. The top plate 20 is pressed vertically against the upper end faces 22 of the lumber sticks 10 forming the block 14, thereby applying a counter pressure from the lower end faces 24 of the lumber sticks 10 to the plunger plate 30.

Step 2: During the time the plunger plate 30 is pressed against the lower end faces 24 of the lumber sticks 10 in the block 14, the plunger plate 30 is heated and heat enters the layer 26 of scrim. Under the applied pressure condition the layer 26 of the scrim is bonded to the lumber sticks 10 in the block 14 at their lower end faces 24.

Step 3: After a defined time, when the layer 26 of the scrim is fixed to the lumber sticks 10 at their lower end faces 24, the pressure of the plunger plate 30 against the lower ends 24 of the lumber sticks 10 in the block 14 is released to allow the cutting device 36 to cut the end sections 12 of the lumber sticks 10 from the lower end of the block 14.

Step 4: The cutting device 36, preferably a special band saw for cutting balsa wood, cuts a panel 40 from the lower end of the glue-less block 14 with a slow velocity of 5-30 inch per minute for a good surface finish.

Step 5: The plunger plate 30 moves down and the panel 40 with the thickness t _p corresponding to the length of the end sections 12 forming the panel 40 is moved in a direction x, in Fig. 2 to the right. After one panel length l _p the layer 26 of the scrim is cut. The result is a flexible panel 40, held by the layer 26 of the scrim. When the panel 40 is moved to the right in the direction x, the pressure system 28 and device 16 are unloaded, the lumber sticks 14 remaining in the block 14 drop on the fresh layer 26 of the scrim and a new cycle of the first process starts again.

Above it has been disclosed, to cut the end grain balsa panel from the lower end of the block, whereby said block is standing vertical. In an advantageous embodiment, the end sections of the lumber sticks or the end grain balsa panels are cut from the top end of the vertically arranged block. Accordingly the layout of the process needs some adjustments, like moving the block in a vertical movement upwards in direction to the scrim, said scrim arranged above the block, and a plunger plate moving downwardly. In an alternative embodiment, the block is lying in a horizontal position and the end sections of the lumber sticks are cut from one end of the block. Executing the process having a horizontal lying and moving block, a vertically arranged and moving scrim and a horizontal moving vertical plunger plate applies.

Preferably, carriers or mounts, like pallets, are moving in a carrousel or loop manner. The carrousel may be turntable like or may be a loop or an endless conveyer having various stations for single process steps. To said carrousel, for example self driven or driven by belt or chain, carriers or mounts, for example in form of pallets, are fed, loaded, the load treated and the pallets unloaded. End grain balsa panels can be produced arranging a plurality of lumber sticks of rectangular cross-section having all the same length, width and thickness parallel to each other to be packed to a block. The lumber sticks are fixed by pressure only. Neither a temporary nor a permanent adhesive is used for packing the sticks to the block. Fixation is accomplished by for example two pressure devices, first device applying different pressure along the sides of the block, namely applying high pressure towards the one end of the block, the end of the panels to be cut-off, and second device applying less pressure, mainly working as a holding device, towards the other end of the block. The pressure devices are adjustable along the block according to the progress of cutting-off panels from the block. The pressure devices can be located within the carrier or fix based at a station. At least a minimum pressure on the block is maintained during the whole cycle. During scrim application and during cutting the end grain balsa panel from the block applying increased pressure is advantageous. At a first station an empty pallet is charged with the block. The lumber sticks are arranged in vertical direction. The block is compressed by the two pressure devices. Lateral high pressure is applied towards the top end of the block, less lateral pressure is applied at the lower part of the block. The charged pallet is conveyed in the loop and moves to the next station, where the scrim is applied on the top end of the block. The scrim comprising a binding agent is unwound from a coil in moving direction of the pallet and is continuously covering the top face of the block. Alternatively applying a scrim in form of single sheets can be considered. As far as necessary, preferably by applying pressure, a first intermediate bond between scrim and face of the block is provided. The pallet, loaded with the block having the scrim applied on its top end, travels in the loop to the next station, where the final permanent bond by the binding agent between top end of the block and scrim is accomplished, for example by pressing by a press or a roll and/or drying or curing, for example by way of radiation curing, like UV curing, or heat curing in an oven. After such process step, the pallet carrying the block moves forward in the loop to a next station where from the top end of the block an end grain balsa panel is cut-off by a cutting device. Depending on the wanted thickness of the end grain balsa panel, the cutting device is adjusted. The cut can be done by a saw, preferred by a band saw. Block and end grain balsa panel are cleaned and saw dust is removed. The end grain balsa panel cut from the block is removed, for example by a vacuum handling unit, by picking-up the end grain balsa panel. The end grain balsa panel can be stored for further handling on a side track or storage place. The pallet carrying the block, shortened by the end grain balsa panel is ready to travel again through the loop. Depending on the size of the carrousel, the number of pallets in the loop can vary. Once, by continuous cut-off of an end grain balsa panels in each cycle, the height of the block is reduced to a minimum, for example to 0.2 to 0.5 m, the pallet can be loaded with a new block. A remainder of the foregoing block can be reused in the as called finger joint process, putting together the lumber sticks to blocks. Also, to adjust to the output wanted, empty pallets can enter a side track to be stored outside of the loop and fed into the loop again, once needed. Also, pallets can be loaded with the panels on a side track and stored at the side track. The loaded pallets can consecutively enter the loop as needed. This first method has the drawback that the process includes a number of manual steps, as e.g. loading a block of lumber sticks in a frame. It is an object of present invention to provide a more cost-efficient method for producing flexible end grain balsa core panels that are conformable or adaptable to a contoured surface.

This object is achieved by a method as defined in claim 1. Preferred embodiments are described in the claims dependent from claim 1.

The inventive process allows the prefabrication of edge-glued-panels and the subsequent continuous and fully-automated production of flexible end grain balsa core panels being adaptable to contoured surfaces and consisting of a flexible end grain balsa core on a scrim web. The uniform lumber sticks used for the production of edge-glued-panels (EGP) may have a shape as shown in Fig. 1 and may be manufactured from raw pieces which are cut with oversize from round logs of balsa wood. The logs typically have a diameter of between 0.5 and 2.0 m, depending on the age of the tree from which the log is cut. The raw pieces are then kiln dried in a conventional oven of the type used for lumber drying to reduce the moisture content thereof to 12 percent or less. The kiln-dried pieces are then milled to the preferred length and the sides are planed.

In a next step, defects in the lumber sticks such as piths or knots are detected and eliminated automatically by cutting off the defect parts. The lumber sticks are selected along their density. Depending on the final use of end grain balsa panels, preferred are selections having a density of 80 kg/m ³ to 170 kg/m ³ ; densities of 96 kg/m ³ to 153 kg/m ³ are preferred.

In a further step, at least two of the defect-free lumber sticks, which are considerably shorter, are assembled to form lumber sticks having a uniform length of for instance 1.5 to 3.5 m. The assembling of the shorter lumber sticks can be performed with a finger jointing process. After cleaning the surface of the finger jointed sections, the uniformed lumber sticks can be used for the production of EGPs. The uniform lumber sticks used for the fabrication of EGPs have a rectangular cross-section, have all the same grain direction running lengthwise and have all the same length and thickness, but variable width.

On at least one broadside of each lumber stick an adhesive is applied. In one preferred embodiment the whole broadside is covered with a thin homogeneous adhesive layer. In a further preferred embodiment the adhesive is applied in form of dots or lines. In an even further preferred embodiment the adhesive is only applied around the edge region of the broadside.

The number of lumber sticks arranged in a single line depends on the length of the flexible panel to be produced. The broadsides of the lumber sticks are then arranged abreast and glued together resulting in a EGP having a width corresponding to the sum of the widths of the individual lumber sticks

The EGP is then cut orthogonally to the grain direction of the EGP or lumber sticks into a number of individual lumber strips having a predefined thickness and length that corresponds to the width of the EGP. Each lumber strip has two broadsides, two long sides and two front sides. The lumber strips have the form of a row of lumber blocks that are glued together. In a preferred embodiment all lumber strips cut from an EGP have the same thickness. The cutting device for getting the lumber strips preferably is a band saw or a circular saw. In a preferred embodiment the edges of the lumber strips are mechanically worked along their long sides in that the long sides become a tapered shape and the cross-section of the lumber strips have a trapezoidal form.

The lumber strips, regardless whether having a rectangular or a trapezoidal cross-section, are arranged side by side on a flat surface as e.g. a platform or a conveyor, in particular a band-conveyor, wherein one broadside of each lumber strip is in direct contact with said flat surface. The lumber strips are then compacted in that the long sides of adjacent lumber strips are in close contact and congruent, i.e. the long sides of adjacent lumber strips are aligned. The grain direction of each lumber strip runs perpendicularly to the broadsides. The lumber strips are preferably arranged longitudinally to the further process direction, i.e. when placed on a band-conveyor in the moving direction of the band.

At least one broadside of each lumber strip may then be grinded and/or sanded. Furthermore to decrease porosity and increase bond strength, the broadsides may then be coated with a lacquer or resin which may be dried or cured in a further process step. An impregnation or coating is possible, particularly on one or both broadsides of the lumber strips.

A scrim web is applied and glued onto the one common broadside of the compacted lumber strips, and the adhesive of the scrim web is then cured resulting in a transversally bendable end grain balsa core panel where the balsa strips are fixed on the common scrim web.

The scrim web may be a non-adhesive or an adhesive-covered scrim web. If a non-adhesive scrim web is used, an adhesive coating may be provided onto the broadsides of the lumber sticks in a separate process step.

The scrim web preferably is applied onto the broadsides of the lumber strips in a continuous process by using e.g. a roll, reel or coil.

The curing of the adhesive is preferably done by heat and/or radiation, in particular UV radiation. The scrim may consist of for example woven material, woven fabrics, stitch bonded or knitted fabrics, a felt or veil. Preferred are woven materials or fabrics. The materials of such fabrics include the preferred glass fibers, further plastic fibers, like polyamide fibers, aramide fibers or carbon fibers. Fibers showing non-wetting or non-absorbing properties are preferred to keep the amount of binding agent on a minimum. Glass fiber fabrics are most preferred.

The scrim preferably comprises a binding agent. Binding agents to adhere the scrim may be selected from the group of adhesives or glues, like water-based adhesives, solvent-based adhesives, glutin-, starch-, dextrin- or casein-based glues, urethane-based adhesives, epoxy-based adhesives, hot-melts, vinyl acetate-ethylene adhesives, mainly waterborne vinyl acetate-ethylene adhesives, etc. The adhesives or glues may harden by drying, by heat or by radiation, like UV-light. The bonding processes between scrim web and broadsides of the lumber strips may be supported by applying pressure by pressure plates, pressure belts or pressure rolls. The pressure devices mentioned can be heated.

In a preferred embodiment of the inventive process, the lumber strips covered on one common broadside with the scrim web additionally may be cut in a transversal direction. Therefore, the compacted lumber strips (67) covered on one common broadside with the scrim web are preferably turned by 180°, referring to a full circle of 360°, in that the scrim web lies downwards and the free lying broadsides of the lumber strips lie upwards.

The lumber strips covered on one common broadside with the scrim web and turned upside down in order to get the free lying broadsides of the lumber strips on top are then slit transversally to their long sides with a predefined spacing between the slits.

The slits have a cutting depth that is less than the thickness of the lumber strips. The cutting depth is preferably in a range between 90 and 98 %, in particular in a range between 95 and 98%, of the thickness of the lumber strips. Said cutting depths assure that the resulting end grain balsa core panel is also bendable in a longitudinal direction resulting in a flexible end grain balsa core panel that is conformable or adaptable to a three-dimensional contoured surface.

It is noted hereby that the residual balsa core between the slit and the scrim web easily breaks already with a minor force effect and therewith becomes flexible to some extent also in the longitudinal direction.

The slitting is preferably done by a knife cut, in particular with a driven roller having a bank of circular slitting knives at spaced positions. In a preferred embodiment the cross-section of the slits is V-shaped. The cutting depth of the slits preferably is just less the thickness of the strips, in particular 0.1 -0.5 mm less than the thickness of the lumber strips.

Further advantages, features and details of the invention are revealed in the following description of preferred exemplified embodiments and with the aid of the drawings wich show schematically in:

Fig. 3: a perspective view of an edge-glued panel;

Fig. 4: a perspective view of an apparatus for performing the inventive process;

Fig. 5: a side view of a panel with endless roll configuration; Fig. 6: a cross section of a panel end with tapered side;

Fig. 7a: cross section of a panel with V-shaped side of the pieces;

Fig. 7b: shows the panel of Fig. 7a placed in a curved mold. Fig. 3 shows a perspective view of an edge-glued-panel (EGP) consisting of three lumber sticks 1 0 having all the same grain orientation DG running longitudinally to the length of the lumber sticks 1 0.

An Edge-Glued-Panel (in short: EGP) is first produced from a plurality of uniformed lumber sticks 1 0 having all the same length Is and thickness ts, but variable width Ws. Each lumber stick 1 0 has a uniform grain direction DG, and the grain direction DG of each lumber stick 1 0 runs lengthwise to the lumber sticks. The broadsides 62 between lumber sticks 10 are provided with adhesive and the lumber sticks are arranged parallel to each other and are then glued together forming an edge-glued panel 60. The broadside of a lumber stick is defined by its thickness and length. Preferably, the complete broadside 62 is provided with adhesive. The EGP 60 shown in Fig. 3 consists of only three lumber sticks 1 0 glued together and having the same length l _s and thickness t _s , but different width w _S i , w _S 2, w _S 3. The length I _E GP and the thickness t _E GP of the resulting EGP 60 correspond to the length Is and thickness ts of the lumber sticks 10. The width W _E GP of the EGP corresponds to the sum of the widths wsi , w _S 2, w _S 3 of the plurality of lumber sticks glued together. The resulting edge- glued-panel 60 has a uniform grain direction D _E GP-

Typical dimensions of an EGP are as follows:

Width w _EG p: 0.6 m to 4.0 m

Length I _E GP: 1 .5 m to 2.5 m

Thickness t _E cp: 25 mm to 400 mm, in particular 25 to 50 mm

Referring now to Fig. 4, there is shown a perspective view of an apparatus for performing the inventive process. An edge-glued-panel 60, preferably in a horizontal position, is cut orthogonally to the grain direction D _EG p of the EGP into a number of lumber strips 65. The cutting device typically is a saw, preferably a band saw or a circular saw 44. The just cutted lumber strip 65 has a grain direction DG running horizontally, i.e. the grain direction D _E GP and DG are parallel to each other. Each lumber strip 65 has two broadsides 66, two long sides 68 and two front sides 69.

The thickness tsTRip of a lumber strip 65, i.e. the distance between its broadsides 66, is typically in a range between 3 mm and 100 mm.

After having cut a lumber strip 65 from the EGP 60 it is turned through a right angle in that its broadsides lie horizontally. Consequently, the grain direction DG of said turned lumber strip runs in a vertical direction. The cut and turned lumber strips 65 are typically positioned onto a flat surface e.g. of a horizontally arranged conveyor, preferably of a band-conveyor (not shown). The horizontally arranged lumber strips 65, i.e. one broadside 66 of each lumber strip 65 is in contact with the horizontally arranged flat surface of e.g. a band conveyor, are located face to face with their corresponding long sides 68. A predefined number, but in principle a random number of lumber strips 65 lying abreast with their long sides 68 are mechanically compacted, i.e. the lumber strips are laterally pressed together in order to get a row of lumber strips 65 arranged side by side and having at least one long side 68 facing a long side 68 of an adjacent lumber strip 65. All those lumber strips have a grain direction D _G running vertically. In a further process step the broadsides 66 of the compacted lumber strips 67 may be grinded and/or sanded in a grinding device 70. Preferably, the compacted lumber strips 67 are transferred to the grinding/polishing device 70, e.g. by a band-conveyor. In a further optional process step the broadsides 66 of the compacted lumber strips 67 may receive a surface coating in the form of a lacquer or resin which typically has to be dried in a subsequent process step. Therefore, the compacted lumber strips 67 are preferably transported on the band-conveyor trough a coating device 75 and a drying device 78 arranged downstream of the coating device. It should be noted hereby that usually both broadsides 66 of the compacted lumber strips 67 are processed when grinding/polishing and lacquer coating is applied.

In a next process step, a scrim web layer 26 is applied on the broadside 66 of the compacted lumber strips 67. Therefore, the compacted lumber strips 67 are transferred, preferably on the band-conveyor, to a next station where a roll 54 of scrim web 26 containing a binding agent is positioned above the band-conveyor and where the scrim layer 26 comprising a binding agent is continuously drawn from the roll 54, and with the aid of a guide roller 56 the scrim layer is brought in contact with the broadside 66 of the compacted lumber strips 67. Downstream of the guide roller 56 the compacted lumber strips 67 pass a drying or curing station 58 where the scrim layer 26 is bonded to the upper broadside of the compacted lumber strips 67. The resulting panel consists of the compacted lumber strips 67 bonded together by the scrim layer 26 applied on one broadside 66 of the lumber strips 10. Said panel has a length that corresponds to the width W _E GP of the EGP, a thickness corresponding to the thickness t _s tri _P of the lumber strips 65 and a width corresponding to the thickness ts of the lumber sticks 10 times the number of adjacent lumber strips 65 compacted. Said panel is bendable in a plane transverse to its long side and therefore in the following, said semi-finished panel is called transversally bendable panel 80.

In a further process step, the lumber strips 65 are provided with a number of parallel slits 85 transversal to the long side of the transversally bendable panel 80, wherein the slits 85 are cut from the free lying broadsides of the strips 65. As shown in Fig. 4, the transversally bendable panel 80 is turned upside down in order to get the free lying broadsides of the lumber strips 65 on top. The slits 85 are preferably done by a knife cut, in particular by using a driven roller having a bank of circular slitting knives 90 at spaced positions. The cutting depth is less than the thickness tsTRip of the lumber strips 65, in particular 0.1- 0.5 mm less than the thickness tsTRip of the lumber strips 65. The resulting flexible end grain balsa core panel 100, i.e. the flexible end grain balsa core 95 glued on the scrim web 26 is conformable or adaptable to contoured surfaces and is therefore especially suitable for use as core material in blades of wind turbines. As shown in Fig. 5 the resulting flexible end grain balsa core panel 100 as well as the transversally bendable panel 80 are rollable on a roll 62.

As shown in Fig. 6 the edges of the flexible end grain balsa core panel 100 may be processed mechanically to receive tapered sides 64.

The long sides of the lumber strips may receive a tapered profile, therewith creating a cross-sectional V-shape space 66 between adjacent lumber strips 65 (see Fig. 7a). Cross-sectional V-shape spaces 66 may also be effected when cutting the parallel slits 85 lying transversally to the long side of the transversally bendable panel 80 (V-shaped cuts). Said V-shaped gaps may be closed when the flexible panel is bended as shown in Fig. 7b where a flexible panel with V-shaped gaps between adjacent lumber strips 65 or with V-shaped cuttings is placed in a curved mold 68.

The shape of the profile of the lumber strips or the transversal cuts may limit the motion of bending. Additionally, the flexible end grain balsa core panel 100 is bendable or flexible by bending over the scrim in the one direction. In the other bending direction the shape of profile of the long sides and/or the profile of the transversal cuts may limit the flexibility of the flexible end grain balsa core panel 100. V-shaped gaps 66 or cuts 85 allow a curvature of the flexible end grain balsa core panel beyond said plane manner (Fig. 7a, b). The flexible end-grain balsa-core panels fabricated by the inventive process may be used as core material for blades of wind turbines, in transportation and handling equipment, such as for floors of railroad cars, shipping containers, cargo pallets, bulkheads, doors, reefer bodies, as well as in a wide variety of other applications as e.g. for structural insulation in aircraft applications, housing and in boating.