DK142403B - Sandwich laminate with a core of blocks of foamed plastic. - Google Patents

Description

(11) PUBLICATION MANUAL 142403 DENMARK (51>, nt C | 3 B 32 B 3/18 UrtINIVIMnA B 29 D 9/00 § (21) Application No J040 / 77 (22) Filed on 6 Jul 1977 (24) Race day Jul 6, 1977 (44) Application submitted and petition published on Dec. 27 · Oct. 19 ^ 0

DIRECTORATE OF

PATE N T- 0 G VA R E MARCH EVENTS <3 °) Prion, a right, be it (71) £ 0PENCRAFT λ / Sj "Christianehus", Usserød Kongevej 161, 297Ο Hørsholm, DK.

(72) Inventor: Eric Tornow, Søparken 7 »Nødebo, J480 Fredensborg, DK: Per Tornow, Vedbæk Strandvej 499, 2950 Klampenborg, DK.

(74) Plenipotentiary in the proceedings:

Office of Industrial Excellence v. Svend Schønning.

(54) Sandwich laminate with a core of 1 blocks of foamed plastic material ·

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a sandwich laminate having a core of foamed plastics material enclosed between surface layers of hard, pressure, tensile and abrasion-resistant material, protective foam layer layers being provided between the surface layers and the foam plastic core.

Sandwich structures are used in a variety of structural engineering areas, e.g. for the manufacture of hulls for smaller and larger boats, for bulkheads in such, for the manufacture of containers, both closed and open, and in the automotive industry for the manufacture of barges and crates, e.g. for refrigerated vehicles, as well as for all such purposes where the lightness, strength, especially the high bending strength, and insulating properties are advantageous.

Thus, sandwich structures are known in which the core material consists of bale end wood, i.e., the fiber direction is substantially perpendicular to the surface layers. The wood is cut into small flat bricks that are placed edge to edge in the structure, being temporarily joined together by glued threads or tissues. The composition of the core of such small bricks allows the preparation of more or less curved sandwich structures.

However, balsa wood is relatively expensive, and its supply is limited, so that a cheaper and more easily accessible core material is needed. As such, different types of foam plastic have been used, where after foaming the plastic into large blocks and subsequent curing, the blocks are cut into slices and possibly further these slices are divided into small blocks.

However, this is inappropriate in several respects.

First of all, this applies to compressive strength as it can vary up to 50% over the surface of a disc cut by a larger block. Furthermore, the surface will have numerous recesses from cut cells, which will result in a reduction of the compressive strength and also cause additional consumption of binder when the material is incorporated into the sandwich structure, since all these recesses must be filled with binder in order to have a proper bond to the surface layers.

Swedish Patent Specification No. 227,310 discloses the use of foam plastic for floating bodies for installation in boats, and it is stated that a layer of impact-resistant plastic and mechanical impact can be applied to the outside of the cellular plastic; but that in some cases this can cause a chemical reaction that destroys the foam. According to the patent, this can be avoided by placing a layer of oily paper between the cellular plastic and the surface layer. Thus, the patent does not give any instruction to use foam plastic in a sandwich laminate.

The object of the invention is to overcome the disadvantages of the previous use of foam plastic as a core material in a sandwich laminate, and this is achieved by the design of the core material according to the characterizing part of claim 1.

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It is very surprising that no one has previously proposed the use of such a core material, usually called integral foam, but that bricks made of cutting have been used instead, which have the disadvantages mentioned above.

Thus, the integral foam has a foamed interior surrounded by a hard and dense surface layer, and the small bricks included in the core material are simultaneously molded and foamed in a large number, but in each shape, blocks with a dense and hard surface layer can be obtained. on all sides, ie the bricks individually constitute a type of box construction with good corner and side stiffness. In addition to contributing to the overall strength of the sandwich structure as a whole, the dense and hard surfaces result in a better distribution of local pressure over the surface and into the bricks so that the structure is not easily damaged »Furthermore, the dense surfaces result in minimal binder consumption during construction of the sandwich construction. Finally, the dense surfaces counteract or prevent moisture accumulation in the bricks, and although the surface of individual bricks should be damaged so that moisture can penetrate, it cannot spread to the undamaged neighboring bricks.

In order to simplify and facilitate the manufacture, the core material units according to a suitable embodiment of the object of the invention take the form of six-sided parallelepipeds. For example, they can have the dimensions Jo x 3o x lo mm, with the sides perpendicular to each other.

According to another embodiment, two opposing sides of the invention can take the form of parallelograms, whereby it is obtained that the individual bricks act as a kind of oblique strut in the sandwich structure.

Furthermore, it may be convenient for the core material units to be reinforced. This significantly increases the strength and stiffness, which is especially important in sandwich designs where the thickness goes up to 3o mm and above, because the robustness and strength of the sandwich construction is not only a matter of being able to withstand the effects perpendicular to the surface, but also about that it can withstand stresses parallel to the surface, i.e., that the core material is resistant to such stresses.

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For example, the reinforcement may consist of fibers, especially glass fibers, which are incorporated into the plastic prior to foaming; but also other forms of reinforcement, such as paper, woven fabric or plastic sheet in sheet or strip form, can be incorporated by placing it in the molds in which the foaming of the plastic material takes place. The reinforcement can also continue across the partitions between the molds, thereby serving to interlock a number of the units into larger flakes.

In particular, for the purpose of making larger sandwich designs, it will often be appropriate that the core material units are thus interlocked or assembled into a plate-like product by other means, e.g. by being attached to a plastic wrap, carrier tissue or carrier wires. Such attachment can be easily carried out in connection with the manufacture of the units, and the product obtained is easily manageable and can be rolled up and transported to the place of application, where it can also be built into such large sheets or flakes as is convenient to do at a time. The sandwich structures are most often built on site, in which in one mold the first surface layer of plastic material is reinforced with fibers or tissue, then the core material layer adheres thereto in suitable large pieces at a time and finally the other surface layer builds up.

It is of the utmost importance for the strength of the sandwich construction that, when adhering to the core material units, whether by using a separate adhesive or simply by depressing the units in a surface layer before it is even cured or unbound, air between units and surface layer is enclosed. . When using balsa blocks as a core material, this is not such a problem, as the balsa wood is somewhat porous, which, together with hair tube action relative to the adhesive, causes the air to dissipate and the adhesive penetrates so that such boulders almost suck.

In the case of nuclear material units referred to here, the same options are not available and, therefore, when it comes to achieving the greatest possible strength, special measures must be taken to avoid the aforementioned containment of air. In one embodiment of the object of the invention, this is achieved according to the invention in that vent holes are formed across the layer of core material units.

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Thus, according to the invention, the units can be formed with a central through-hole across the largest edge boundary surfaces of the units.

Technically, such holes can be produced in known manner by the use of retractable core pins; but it makes the casting machine quite complicated. This can be avoided by forming the holes at the corners of the core material units instead, the units according to the invention being made with chamfered corners. This will create a through-hole, where the corners of four square units collide, whether only one corner or all four corners of the units are beveled. Whether the through-hole has a cylindrical or angular surface is irrelevant to the function of escape route for trapped air behind the units.

The design of such through holes also makes it possible to attach the units by injection molding, simply injecting adhesive under pressure through some of the holes. The injected adhesive then chases air trapped in front of it to other holes or gaps between the units through which the air can escape. Also, the adhesive will be able to penetrate the same places, so that the distribution of the adhesive is controlled and the number and distribution of the injection sites can be adjusted accordingly.

In order to facilitate the spreading of the adhesive transversely, the units may further have, according to the invention, gutter-shaped recesses either on one or both surfaces with the greatest extent. Also, by adding two such units together, a thicker core with holes longitudinally and transversely through the core portion can be obtained, so that all cavities are more easily filled to obtain great strength in the construction. Optionally, the filling may be supported by establishing a vacuum.

If the sandwich structure is to be curved, such as. in parts of a boat hull, the narrow side faces of the individual core material units according to the invention may be formed as convex and concave cylinder faces, respectively, with the same radius of curvature. This results in the fact that the units can be laid along a curved surface without creating wedge-shaped gaps between neighboring units, with a convex side surface fitting and turning in a concave side surface. Thus, the core structure can become more compact and the adhesive consumption less because the gaps do not expand at the curvature.

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Each unit may be formed with two convex and two concave side surfaces, or each other unit may have exclusively convex side surfaces and each other exclusively concave.

An embodiment of a sandwich construction according to the invention is illustrated by the accompanying drawing, in which fig. 1 shows the construction in cross section; FIG. 2 shows some core material assemblies included in the structure attached to a coarse mesh tissue; FIG. 3 shows a core material unit with two oblique side faces; FIG. 4 shows a core material unit with two convex and two concave side faces; FIG. 5 shows a special embodiment of a core material unit, and FIG. 6 a curved sandwich construction.

As can be seen from the drawing, the sandwich construction consists of a core material composed of small, parallelepipedic units 5 and 6 of a foamed plastic material, e.g. polyurethane of the so-called integral-skin type, where the foamed plastic has an adhesive, hard and dense surface on all sides. The manufacture of a plastic foam of this kind is well known in the art and is therefore not to be described here.

The core material units bump edge to edge in a sheet-like structure and have on both sides a surface layer 7 and 8 that may be the same or different on the two sides.

The surface layers may be prefabricated sheets of any suitable material, e.g. metal, plastic or plywood which is adhered to the core material units by means of a suitable binder layer 9.

The surface layers may also be produced by direct spraying of self-curing plastics material which may, if desired, be reinforced with fibers 10, e.g. glass wool fibers, against a mold surface, and the core material units can be deposited in the material before cured. The core material units may also be reinforced, e.g. fiber reinforced, as indicated in the unit 6.

The structure of the sandwich structure is greatly facilitated by the small core material units 5 (or 6) being attached to a carrier material, e.g. as shown in FIG. 2, a coarse mesh, woven material 11. In this way, a large number of core material units can be put in place at one time, and the transport and storage of the units is facilitated, since the tissue with the attached units can be easily rolled or folded.

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The attachment can e.g. is made by adhering the units to the fabric, and by appropriate selection of the adhesive, the connection to the fabric can be made temporarily, i.e., the fabric is destined for tearing after the core material units are permanently attached to one of the surface layers 7 and 8 of the sandwich structure, or the fabric can be included as a reinforcing element in this.

As shown in FIG. 3, the units can also be designed as parallel lip pipes which are not at right angles on one link. Thereby, a kind of oblique stiffening effect can be obtained in the sandwich structure, and that the joints between the individual units do not open as much in curved sandwich structures, as a displacement between neighboring units takes place instead.

As shown in FIG. 4, a unit may also be formed so that one of two opposite side faces forms a concave cylinder surface 12 and the other a corresponding convex cylinder surface 13, whereby the units may be close to one another also in curved structures. This is advantageous in strength, as the sandwich structure thereby becomes more compact, and at the same time, adhesive is saved, as the gaps between the units do not open when laying on a curved surface.

Another embodiment of a unit is shown in FIG. 5. Here, the corners 14 of the unit 5 are bevelled cylindrical so that when four units are folded in a square, a through hole is formed.

FIG. 5 also illustrates that there may also be a central hole 15 transverse through the unit 5, and gutter-shaped recesses 16 from the hole 15 to the edges.

Such units allow the adhesion of the units to occur by injection of the adhesive, e.g. an adhesive in the form of or based on a polyester or epoxy compound. The adhesive is then injected through some of the transverse holes and drives the air at the adhesive points forward and out through other holes to ensure intimate connection between core material units and surface layers of the sandwich structure, thereby achieving optimum strength thereof. A vacuum may also be established to promote the removal of air pockets behind the core material units during adhesive injection.

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The transverse gutter-shaped recesses 16 can serve to facilitate the adhesive distribution and to support the adhesion, if a thicker core is desired in the sandwich structure, by placing several core material units on top of one another.

Thus, when two units are laid with the gutter-shaped recesses 16 facing each other, a thicker unit with distribution channels is obtained which is parallel to the length of the sandwich construction and can serve to inject adhesive.

FIG. 6 illustrates the structure of a curved sandwich structure by means of core material units 5 (or 6). Units are used here in the form of rectangular parallel pipes with central vent or injection hole 15, the curved layout creating larger air gap peaks and between the units, so that it is important that there is a possibility of venting, possibly supported by suction (evacuation). .