Structural Part Based on a Sandwich Fabric

The present invention relates to a structural part based on a sandwich fabric, particularly a velour fabric, having at least one first layer and intermediate links connecting said layers, in which the fabric consists of a high-tenacity yarn, such as aramid fiber, carbon fiber, ceramic fiber or, in particular, glass fiber. The fabric is impregnated with resin and cured, and the intermediate links form spacing elements between the first and second layers.

Such a structural part is known, for instance, from European Patent EP-A3-299 308 and its corresponding U.S. Pat. No. 4,840,828. In that case, the upper and lower layers are of the same weave. Such a structural part has proven satisfactory, but it is still capable of improvement for various uses, in particular in the case of strong curvature of the structural part, since in this case the inner layer tends to form wrinkles.

Proceeding from the prior art described above, the object of the present invention is to provide a structural part having a base of a velour fabric of the type described above which is suitable, in particular, for uses in which strong curvature is required.

According to the invention at least one of the layers is woven with an open weave. Open weave as used here means, for instance, that each warp thread alternates through several filling (weft) layers. With this type of weave, in which the layer having the open weave is arranged on the inside of the curvature, it is possible to produce curved parts on the basis of such a velour fabric in which, even in the event of stronger curvatures, there is no tendency towards wrinkling or the formation of wrinkles on the inner side. The weave selected for the inner layer permits the shrinking of the fabric in the warp direction by undulated displacement of the warp threads towards the inside or outside. The warp threads, in curved, cured state, as a result are in part freely stretched in arched shape. Seen by itself, the layer with the open weave is a multi-layer fabric. The particular advantage of this fabric also resides in the fact that, due to the possibility of the shrinking of the inner layer, the height of the sandwich fabric, namely the sandwich height, can be maintained constant over the entire angular periphery of a structural part. This is not possible with the sandwich fabrics of the type known up to the present time. Otherwise, the properties of the structural part mentioned at the start are substantially retained. The aforementioned United States patent is hereby incorporated by reference in its entirety. In the development thereof, it is provided that the intermediate links are formed by spacer threads in the form of a pile through-binding or on-binding. As a whole, they extend approximately in the shape of a W through the fabric. By means of such a structural part, it is possible to wrap pipes, boilers and tanks for instance, with the woven material. After the wrapping, the resin is applied and the cured structural part with spaced layers is obtained. Another possibility consists of pre-impregnating the fabric with resin and applying it in wet condition to a mold or a base body. Although it is first of all described here as preferred embodiment that one of the two layers, namely the inner layer, is developed as multi-layer fabric with open weave, the invention however also covers the development of both layers in the form of the multi-layer fabric with open weave. In this way, the drapability of a sandwich fabric is further substantially improved.

The invention is further described below on basis of the accompanying drawing, which however merely shows examples of embodiments.

FIG. 1 shows diagrammatically the arrangement of a weave for a structural part based on a velour sandwich fabric;

FIG. 2 is a diagrammatic view of the fabric of FIG. 1, curved;

FIG. 3 is a simplified showing of a cured structural part having a fabric basis in accordance with FIGS. 1 and 2;

FIG. 4 is an enlarged detail showing of the object of FIG. 3;

FIG. 5 is a stylized fragmentary sectional view of a fabric having a first layer and a second layer constructed of open weave; and

FIG. 6 is a stylized fragmentary sectional view of a fabric having a first layer and a second layer constructed of open weave, and wherein each of the layers is itself a multiple layer fabric.

FIG. 1 diagrammatically shows a sandwich fabric such as can be used for a structural part concerned here. Two layers a and b can be noted, held together by a connecting thread c. The upper layer a is formed by a 3/6-filling/pile through weave, while the lower layer consists of a multi-layer fabric having at least three warp and four filling layers. Herein, the preceding term "3/6" means that the thread c, which passes between the fabric layers to form links between the layers, alternates as a warp thread by alternating among three weft threads in one of the layers, and then alternates as a warp thread by alternating among three weft threads in a second of the layers, this giving a periodicity of six weft threads e as shown in FIG. 1. The pile threads c which form the intermediate links are bound in pile through binding into the lower layer b. The filling threads are designated as e and e1 to e3 in the drawing; the warp threads by d and d1 and d2.

The distance x between layers amounts to, for instance, about 2-20 mm in the case of an actual structural part (FIGS. 3 and 4).

As can be noted in particular from FIG. 3, in cured state the warp threads d extend in the lower layer in part freely stretched rigid and arched. In particular, the arches protrude into the inside and therefore facing the outer layer a of the sandwich fabric. The free stretching is dependent on the curing. The latter, however, is so selected that after the curing the fabric opens up correctly, i.e. without further aids, after the curing, and automatically forms the spacing x. For this, any excess resin can be removed possibly by being squeezed out.

It is clear, in particular from a comparison of FIGS. 1 and 2 that, upon a curving of the fabric, the warp threads d of the lower layer curve inward and outward and thus, in cured state, assume the arcuately stretched course shown, for instance, in FIGS. 3 and 4.

FIG. 5 is a sectional view of a fabric having a first layer and a second layer constructed of open weave, each fabric layer having a construction following the construction of the inner fabric layer of FIG. 2. In FIG. 6, each of the inner and the outer fabric layers is an open weave having multiple layer construction.

The features of the invention disclosed in the above description, the drawing and the claims may be of importance, both individually and in any desired combination, for the reduction to practice of the invention. All features disclosed are essential to the invention.