HETEROGENEOUS POINT TISSUE COMPRISING METAL FIBERS DESCRIPTION OF THE INVENTION The present invention relates to a relatively thin heterogeneous knitted fabric comprising metal fibers and other fibers in which, more specifically, the yarn composition of the surrounding area its surface differs from that which surrounds its other surface. Provided that the other fibers can also withstand extreme temperatures, knitted fabrics can be used for applications in very cold and very hot environments. Knitted heterogeneous knitted fabrics comprise metal fiber yarns which are already known from the patent O / 94/01373. The dot pattern can therefore differ in the predetermined areas on its surface, and / or through the thicknesses of the fabric. The patent O94 / 01372 also describes the application of this type of heterogeneous fabric as separation fabric in the molding of glass plate at elevated temperature. There is also an increasing demand, in such production and in other applications, for relatively thin knit heterogeneous fabrics comprising metal fibers that combine a relatively high air permeability with some insulation capacity measurements. The weight of such fabrics will preferably be kept to a minimum, despite the necessary proportion of the metal fibers contained. The heterogeneous knit fabric comprising metal fiber according to the present invention attempts to meet this requirement by providing a smooth flat knit structure in which the yarns have a high metal fiber content that are present near the surface, while the yarns have a high metal fiber content. threads that have a low metal fiber content are present close to each other. The expression "high metal fiber content" will be in the present understanding to mean at least 30% metal fibers by volume, preferably more than 40% by volume and even yarns consisting of 100% metal fiber. "Low metal fiber content" will be in the present understanding to mean less than 12% metal fiber by volume and, preferably, less than 7% by volume. The low-content yarn can still consist of 100% other fibers. These can be carbon, glass, basalt, ceramic or synthetic fibers. The knitted fabric generally weighs less than 2,000 g / m2 and preferably will weigh less than 1,500 g / m2. To obtain the best possible tissue density (air permeability), the threads surrounding a surface, and those surrounding the other surface (see on the other page) will preferably be oriented in parallel - according to the same dot pattern - and it will be contiguous with each other. They behave, so to speak, as double threads and can be plain flat fabrics, with a flattening technique, as a weft in a circular knitting machine or on a flat knitting machine. The separation of the machine can be, depending on, among other things, the thicknesses of the yarn, optionally between 5 and 30 for knitted round and between 5 and 20 for knitted flat. The yarns having a height and those having the low metal fiber content are thus simultaneously pulled for knitting towards the same needle, each placed under sufficient tension to form a flat knit fabric (stitch layer). simple) in which one of the threads always passes in front of the other. Yarns with a low metal fiber content are usually milder than those with a high metal fiber content. This facilitates the operation of flat weave. Yarns with a high metal fiber content are preferably staple fiber yarns in which metal fibers, for example, stainless steel fibers, have a diameter between 4μm and 50μm. Threads on opposite sides of the fabric can be 100% glass filament yarns, basalt or carbon or synthetic filaments with a diameter below - 40μm. Suitable synthetic filaments include polyaramide or polyimide filaments (Kevlar (R)), signature name of du Pont de Neumors, T aron (R), signature name of AKSO / ENKA). Spun yarns, twisted or non-twisted yarns, consist of one or more types of fiber, which are equally suitable. During the process of flat point, a type of thread
(with high metal fiber content) can be used like the other (with little or no metal fibers) as well as to produce a fabric with areas that have dot patterns on its surface with a weight that differs by m2, density (air permeability), elasticity or electrical conductivity. The fabric may also contain a fine interlined thread, for example, to reinforce the fabric as described in Belgian patent application 97/00614 of the applicant. Finally, a simple layer fabric area as described above can be incorporated locally into a circular knitted structure - for example double layer - on a flat knitting machine. This then produces a knitted fabric which contains the relatively thin heterogeneous knitted fabric on the part of its surface. EXAMPLE By way of example, the knitted fabric of an embodiment according to the present invention and its application as separation fabric in the compression molding of the glass plate will not be explained in greater detail. The invention is not, however, limited to this or the analogous modalities. The fabric was fabricated into a 12-spindle molding on a Stoll CMS 440 flat knitting machine for a single smooth tricot structure without hardened wire of thin spacing. After the removal of all the polishing agents from the fabric, the thickness of the cloth was approximately 1 mm. The fabric counted 158.8 cm. (62.5 inches) per cm2 and had a weight of 980 g / m2. This fabric exhibited an air permeability (l / hl0 cm2) of 4164 and was therefore suitable as a coating for the male section of the compression mold. The fiberglass surface of the fabric is in contact with the mold, the outer surface of metal fiber thereby forms contact with the glass plate during molding. - In this separation fabric, the yarn (basic fiber) the yarns contained in high metal fiber consist of 100% Bekinox fibers type AISI 316 L with a diameter of 12 μm and measurements of 133 tex. The low metal fiber content yarn consists of 100% glass filament yarn that measures 136 tex. If a heterogeneous knitted fabric "according to the present invention forms a burner membrane for the gas burners, coarse threads are used." The separation of the knitting machine can be established in, for example 5. A metal filament yarn 100% as described in the applicant's patent O97 / 04152 was fixed on the gas side (face of the burner) of the membrane The fixed layer on the side of the gas supply of the fabric can be, for example, yarn 100% glass or ceramic yarn The heterogeneous knitted fabric according to the present invention can also be used as a heat shield against a heated furnace, or as an electromagnetic shielding fabric.The glossy fabric can also be manufactured in accordance with the invention, with metal fiber yarns resistant to abrasion on the glossy side.It is also possible to fit the heterogeneous knitted fabric into a plastic matrix.The proportion of the other fibers then It will preferably comprise synthetic fibers capable of combining with the plastic of the mold.