Structural element and method for the production thereof

Abstract

A structural element for use as a core layer in a sandwich composite element, wherein the structural element (2) is formed from a plurality of mutually welded body segments (4, 5) made from an extrusion foamed thermoplastic, and wherein the structural element (2) has a first face side (1) for bonding to a cover layer, wherein a surface of the first face side (1) that can be loaded with a resin (8) has open pores (6), wherein the surface of the first face side (1) is created by hot-element cutting, in such a manner that the surface is thermally sealed to some extent, wherein a gloss value of the surface of the first face side (1), measured at 60 in accordance with DIN 67530-1982 is between 2 and 10 gloss units.

Claims

1. A method for producing a structural element, comprising the steps of: producing plate- or rod-shaped body segments (4, 5) by the extrusion foaming of thermoplastic longitudinal, planar welding together of the body segments (4, 5) to form a foam block (12), dividing the foam block (12) into individual structural elements (2), transversely to the planar extent of flat weld seams (3) formed between the body segments (4, 5) and in the process, in each case creating a first face side (1) on the structural elements (2) with a surface having open pores, wherein the division of the foam block (12) into the structural elements (2) is carried out by hot-element cutting, wherein the temperature of the hot element, at least at the start of a cutting procedure, is set from a value range between 300 C. and 700 C., and wherein a relative speed from a range between 50 mm/min and 150 mm/min is generated between the hot element (13) and the foam block (12) during the division and as a result, the surface of the first face side (1) is thermally sealed to an extent sufficient to produce a gloss value of the surface of the first face side (1) measured at an angle of 60 in accordance with DIN 67530-1982 of between 2 and 10 gloss units.

2. The method according to claim 1, wherein the welding together is carried out by planar fusing of side faces (10, 11) of the body segments (4, 5) to be connected and subsequent joining together of the same and curing melt zones with the formation of flat weld seams (3) in the form of low-pore or pore-free plastic intermediate layers.

3. The method according to claim 1, wherein the temperature of the hot element, is set from a value range between 400 C. and 700 C., at least at the start of a cutting procedure.

4. The method according to claim 1, wherein an energy per area to be sealed in part is introduced by means of the hot element, which is calculated according to the following linear functional relationship:
E [Wh/m.sup.2]=m [Whm/kg]density of the foam block [kg/m.sup.3]+b [Wh/m.sup.2], wherein m is chosen from a value range between 0.12 and 0.20, and b is chosen from a value range between 0.5 and +0.5.

5. The method according to claim 1, wherein a hot wire with a diameter from a diameter value range between 0.25 mm and 2.0 mm is used as hot element (13).

6. The method according to claim 4, wherein m is chosen from a value between 0.12 and 0.18 and b is chosen from a value between 0.5 and 0.0.

7. The method according to claim 5, wherein the diameter value range is between 0.25 mm and 1.00 mm.

8. The method according to claim 5, wherein the diameter value range is between 0.40 mm and 0.80 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages, features and details of the invention result from the following description of preferred exemplary embodiments, as well as on the basis of the drawings. In the figures:

(2) FIG. 1: shows a plan view onto a first face side of a structural element,

(3) FIG. 2: shows a sectional view through a structural element perpendicularly to the planar extent of the first face side, after the same was loaded with adhesive resin to determine the resin absorption in accordance with the method described in the general part of the description,

(4) FIG. 3: shows a sectional view through a structural element according to the prior art by means of a face side produced by sawing, which was loaded with resin for determining the resin absorption,

(5) FIG. 4: shows two body segments, which are welded to one another along the longitudinal side face thereof,

(6) FIG. 5: shows a foam block made up of a plurality of mutually welded body segments, the foam block being divided by means of a hot wire perpendicularly to the planar extent of the weld seams in the structural elements,

(7) FIG. 6: shows an alternative foam block, produced from two or alternatively a plurality of foam blocks according to FIG. 5, which are welded to one another in such a manner that intersecting weld seams result, the foam block being divided into structural elements with the aid of hot wires,

(8) FIG. 7: shows a structural element resulting from a foam block according to FIG. 5,

(9) FIG. 8: shows a structural element resulting from the foam block according to FIG. 6,

(10) FIG. 9: shows the layer structure for measuring the resin absorption

(11) FIG. 10: shows the arrangement of the specimens for measuring the resin absorption

(12) FIG. 11: shows a sample sawn out of a sandwich composite plate for measuring the specific peeling energy,

(13) FIG. 12: shows an experimental set-up for determining the peeling energy, the sample according to FIG. 9 being fixed in a clamping device on a tensile test machine, and

(14) FIG. 13: shows a measurement curve recorded by means of a tensile test machine for determining the peeling energy, for which the tensile force is recorded as a function of the transverse path.

(15) In the figures, the same elements and elements with the same function are labelled with the same reference numbers.

DETAILED DESCRIPTION

(16) A first face side 1, more precisely the surface of a first face side 1 of a structural element 2 made from foamed PET, is shown in FIG. 1 in a plan view. A weld seam 3 can be seen, the planar extent of which runs perpendicularly to the planar extent of the first face side 1 and planarly connects the two body segments 4, 5, which were obtained by the extrusion foaming of PET, to one another. It can be seen that the body segments 4, 5 themselves have a type of honeycomb structure, which results from the fact that the PET is pressed through a hole-type nozzle at the end of the extruder and the individual strands are automatically welded to one another over the entire area, i.e. gaplessly.

(17) The surface of the first face side 1 of the structural element 2 has a gloss value of 4.3.

(18) A multiplicity of open pores 6, which were created by separating the structural element 2 from a foam block by means of a hot wire, can be seen. The surface of the first face side 1 is thermally sealed in regions 7 between the pores 6.

(19) A sectional view is shown in FIG. 2 perpendicularly to the planar extent of the first face side 1 through a structural element 2. A second face side, which is cut off in the illustration according to FIG. 2 however, runs parallel to the first face side 1. Also to be seen here is a weld seam 3, which is to be seen at a low-pore (sealed) region.

(20) The first face side 1 is loaded with adhesive resin 8 (for determining the resin absorption) in accordance with the method mentioned in the general part of the description. A certain penetration depth of the adhesive resin 8, a polyester resin, into the pore structure through the open pores 6 is to be seen. The resin absorption is 150 g/m.sup.2. Compared to FIG. 3, in which a corresponding sectional view through a structural element according to the prior art with a first face side produced by sawing is shown, the penetration depth of the resin in the exemplary embodiment according to FIG. 2 is lower, and in particular, the adhesive resin 8 in the exemplary embodiment according to FIG. 2 can penetrate through substantially fewer available open pores into the first face side 1 than in the exemplary embodiment according to the prior art in FIG. 3, which overall leads to a considerably lower resin absorption of the exemplary embodiment according to FIG. 2, with the result of a lower overall weight of a sandwich element produced using the structural element 2 according to FIG. 2.

(21) A method step in the production of a structural element is shown in FIG. 4. Two plate-shaped body segments 4, 5 extruded in an extrusion direction E can be seen, which by way of example approximately have a thickness extent of 5 cm, a width extent of approximately 1 m and a longitudinal extent of approximately 2 m. The specimen segments 4, 5 are joined in the arrow direction 9 after the mutually opposite side faces 10, 11 were fused. This procedure is carried out with a plurality of body segments, so that a foam block 12 shown by way of example in FIG. 5 results. The foam block 12 according to FIG. 5 consists of a total of four specimen segments and has three parallel weld seams 3. The foam block 12 is divided into plate-shaped structural elements 2, as are shown in FIGS. 7 and 8, using a hot element 13, which is merely illustrated by way of example as a hot wire.

(22) In this case, the separation or cutting direction 14 is preferably perpendicular to the extrusion direction E, perpendicular to the planar extent of the weld seams 3. The temperature of the hot element 13 is 640 C. in the exemplary embodiment shown and the speed with which the hot element 13 is moved through the foam block 12 is 84 mm/min, so that a face side 1 with the desired surface, having open pores and thermally sealed regions to some extent, results. On the side facing away from the first face side 1, the structural element has a second face side 15 parallel to the first face side 1, which was likewise produced by hot-element cutting. Preferably, the foam block 12 is separated into a plurality of structural elements at the same time using a multiplicity of parallel hot elements 13.

(23) In FIG. 6, two foam blocks 12 according to FIG. 5 are joined together by welding to form a joined foam block 12, specifically by welding the high sides 16 of the cuboidal structural element, which are orientated perpendicularly to the side faces and perpendicularly to the face side, so that the foam block has intersecting weld seams in a plan view onto the first face side, a plurality of parallel weld seams being provided, which are cut by at least one weld seam orientated perpendicularly thereto. In practice, it can happen that the parallel weld seams of the mutually welded foam blocks are not ideally flush with one another, but rather are arranged offset to one another in a stepped manner. This offset is even desired for increasing the stability. If a foam block 12 according to FIG. 6 is then divided into structural elements 2 analogously to the foam block 12 according to FIG. 5 with the aid of hot elements 13, structural elements 2 as shown in FIG. 8 result, it being possible to see intersecting weld seams on the first face side 1, the planar extent of which runs in the extrusion direction E, i.e. perpendicularly to the planar extent of the first face side 1 and the second face side 15 parallel thereto.

(24) A sandwich composite element can be produced, in that a cover layer, particularly made from glass-fibre-reinforced plastic, is stuck onto the first and the face side 1, 15 of a structural element 2 shown by way of example in FIG. 7 or 8, preferably by means of a resin.