Abstract: Preforms for producing annular parts of composite material are produced by inding a strip (1) of fibrous material around an elliptical mandrel (10) to produce an elliptical sleeve which can be cut obliquely, cutting taking place either before or after one or more densification steps. The cutting plane is inclined relative to the right cross section of the elliptical sleeve, and the inner and outer portions of the cut rings are machined to obtain circular elements. Such elements can produce annular parts of composite material having a reduced tendency to delanination under circumferential stress. The superposed layers are needling together during winding. A uniform needling density per unit area can be obtained by controlled displacement of the needle board (5) and of the elliptical mandrel (10) relative to each other as the mandrel turns, to compensate for the eccentricity of the cross section of the mandrel. These methods are particularly suitable for producing brake disk preforms.

Abstract: A process for the manufacture of a fibrous texture for producing a composite material article. The fibrous texture is formed of a yarn comprising discontinuous fibers which are made of a refractory material or a precursor thereof. The discontinuous fibers are disposed parallel to one another, without twist. A covering yarn made of a fugitive material is disposed over the discontinuous fibers to provide integrity to the yarn. The covering yarn is eliminated after formation of the fibrous texture.

Abstract: A process for the manufacture of a fibrous texture for producing a composite material article. The fibrous texture is formed of a yarn comprising discontinuous fibers which are made of a refractory material or a precursor thereof. The discontinuous fibers are disposed parallel to one another, without twist. A covering yarn made of a fugitive material is disposed over the discontinuous fibers to provide integrity to the yarn. The covering yarn is eliminated after formation of the fibrous texture.

Abstract: A fibrous preform is formed from a yarn composed of long discontinuous fibers made of a refractory material or its precursor. The discontinuous fibers are disposed parallel to one another without twist, and the integrity of the yarn is achieved by a covering yarn made of a fugitive material. The fibrous preform is intended to be densified by a matrix material for the manufacture of a composite material article. The covering yarn is eliminated before the preform is densified by the matrix material.

Abstract: The installation comprises support tooling having a shape that corresponds to that of the preform to be made and on which superposed layers of a two-dimensional fiber fabric can be draped; a needling head comprising a group of needles, a device for driving the needles lengthwise with reciprocating translation motion, and a bearing plate provided with perforations to pass the needles and suitable for being pressed against a layer draped over the support tooling; an arm carrying the needling head and possessing a plurality of degrees of freedom; and a control device for automatically controlling the displacement of the arm to move the needling head within the range of the arm along predetermined trajectories and with predetermined orientations.

Abstract: In a portion of the preform to be made in which the preform is to be of reduced thickness by having a recess formed therein, a mask is interposed between pairs of adjacent layers, the mask being made of a thin film of material through which the needles can pass during needling while opposing the passage of significant quantities of fiber taken by the needles, and after it has been needled, each layer is cut out around a line corresponding to the outline of the recess in the preform at the level where the layer is situated in the preform. A mask situated between two cutout layers occupies an area that is not less than the area between the cutout lines of the two layers, such that the portions of the layers that are delimited by the cutout lines are not securely connected to the remainder of the preform by the needling, thereby enabling the recess to be formed after all the layers have been needled by withdrawing the cutout portions of the layers and by peeling off the masks.

Abstract: In order to obtain a reinforcement texture made essentially of silicon compound based ceramic fibers in the production of a composite material, the fibers are spun from a ceramic presursor in the molten state, after which they are submitted to a partial cross-linking in view of making the fibers infusible. The cross-linking of the fibers in the precursor in the infusible state is continued and, while they are maintained in the organic state, the cross-linked fibers are submitted to one or several textile-forming operations, such as weaving, layering, needling . . . in order to arrive at the multidirectional texture. Then, the texture is submitted to a heat treatment by pyrolysis to induce the ceramic state of the fibers and so obtain the required texture, which is essentially made of ceramic fibers having a silicon compound base, in particular silicon carbide.

Abstract: In order to obtain a reinforcement texture made essentially of silicon compound based ceramic fibers in the production of a composite material, the fibers are spun from a ceramic precursor in the molten state, after which they are submitted to a partial cross-linking in view of making the fibers infusible. The cross-linking of the fibers in the precursor in the infusible state is continued and, while they are maintained in the organic state, the cross-linked fibers are submitted to one or several textile-forming operations, such as weaving, layering, needling . . . in order to arrive at the multidirectional texture. Then, the texture is submitted to a heat treatment by pyrolysis to induce the ceramic state of the fibers and so obtain the required texture, which is essentially made of ceramic fibers having a silicon compound base, in particular silicon carbide.

Abstract: Extrudable pre-ceramic polycarbosilanes are prepared by intimately contacting a crude polycarbosilane containing a fraction of high molecular weight polymers (e.g., molecular weights greater than about 25,000) with ethyl acetate, whereby selectively dissolving desired extrudable polycarbosilane essentially devoid of such fraction of high molecular weight polymers in the ethyl acetate, and then recovering such dissolved polycarbosilane from the ethyl acetate solvent.

Abstract: The present invention relates to copolymers containing --Si--N-- and --Si--Si-- bonds, which are obtained by the polycondensation ofat least one silane of the formula RR.sub.1 SiCl.sub.2and at least one disilazane of the formula ##STR1## in which formulae: R.sub.2 is a halogen atom, preferably Br and Cl, andR, R.sub.1 and R.sub.3, which are identical or different, represent a hydrogen atom or an alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, alkylaryl or alkenylaryl hydrocarbon radical which may be functional,to a process for the preparation of the said copolymers,to the polycarbosilazanes obtained by thermolysis of the said copolymers and to the silicon carbonitrides obtained by heating the said polycarbosilazanes.

Abstract: The present invention relates to functional 1,3-dihydrogeno disilazanes of formula: ##STR1## in which: R and R.sub.1, identical or different, represent an atom of hydrogen or a hydrocarbon such as an alkyl, alkenyl or alkynyl, cycloalkyl or cycloalkenyl, aryl, alkylaryl, alkenylaryl, alkynylaryl, arylalkyl, arylalkenyl or arylalkynyl radical, possibly functional, R also being able to represent a radical ##STR2## and R.sub.2 represents an atom of halogen, an OR group or an --NRR.sub.1 group, when R and R.sub.1 are both hydrocarbon radicals.

Abstract: Method and apparatus for producing homogeneously needled three-dimensional structures formed of superposed layers of fibrous material and the needled structures produced thereby. As layers of fibrous material are added to a stack of needled layers, the needling needles are moved away from the stack so as to maintain a uniform depth of needling over the entire stack, and to achieve a uniformly needled result. To permit the same density of needling in the initial layers, a substrate layer of needle penetrable material is used to support the initial layers which can then be needled as through they were layed on top of other needled layers. For the final layers, the needling rate is reduced to compensate for the lessened clogging of the needle in having fewer layers to penetrate in the final needling.

Abstract: The present invention relates to a process for preparing disilylmethanes, wherein the magnesian reaction is carried out between methylene chloride and at least one chlorosilane in a donor solvent.

Abstract: The present invention relates to a process for manufacturing an axi-symmetrical three-dimensional structure formed by superposed layers of fibrous material bonded together, said process comprising the following steps of:--bringing onto a rotary mandrel having the section of the structure to be manufactured, a tape of fibrous material whose width is several times less than the length of a generatrix of said structure:--winding the tape over the mandrel to form superposed layers, each layer being formed by successive turns of the tape of fibrous material, and--during winding, successively bonding the layers together by needling, said needling being effected at the place where the tape is superposed on the mandrel or on the previously formed layer. The invention also relates to an apparatus for carrying out said process.