Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1998-12-21
2001-05-15
Aftergut, Jeff H. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S149000, C156S173000, C156S256000, C267S148000
Reexamination Certificate
active
06231709
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to making springs out of thermostructural composite material.
BACKGROUND OF THE INVENTION
Springs are mechanical components in very widespread use. They are generally made of metal, which poses problems when the equipment in which the springs are incorporated is used at a temperature that is very high or in a medium that is very aggressive.
In order to solve those problems, it is reasonable to propose replacing the metal constituting a spring with a material that is capable of withstanding such operating conditions without damage, and in particular with a thermostructural composite material.
Thermostructural composite materials are characterized by their mechanical properties which make them suitable for constituting structural elements, and by their ability to conserve these properties up to temperatures that are very high.
Well-known thermostructural composite materials are carbon/carbon composite materials (C/Cs) constituted by fiber reinforcement made of carbon fibers and densified by a carbon matrix, and ceramic matrix composite materials (CMCs) constituted by fiber reinforcement made of refractory fibers, e.g. carbon fibers or ceramic fibers, and densified by a ceramic matrix.
In addition to their refractory nature, C/Cs and CMCs have the advantage of being capable of withstanding certain atmospheres that are particularly corrosive for metals.
Proposals have already been made for making springs out of C/C composite materials.
Thus, document U.S. Pat. No. 4,412,675 discloses a method consisting in preparing an organic material filled with carbon fibers, in shaping it to obtain a helical spring, and then applying heat treatment for carbonization purposes. Nevertheless, that method is limited to making helical springs and it is relatively complex in that it requires prior preparation of compounds that are suitable for being extruded so that they can be coiled.
Document EP-A-0 684 216 discloses two methods: one consisting in making a helical coil from a thread that is pre-impregnated or surrounded in a polymer sleeve, and then molded under pressure, the other consisting in making a workpiece out of C/C material and then in machining the spring from the workpiece. The first method is limited to making helical springs and requires equipment suitable for molding springs of particular shapes under pressure. The second method leads to springs of very high cost given that C/C composite materials are expensive and large amounts of material are lost in the machining.
Brief Description of the Invention
The object of the invention is to provide a method of making a spring out of thermostructural composite material while avoiding the above-specified drawbacks. This object is achieved by a method comprising the steps consisting in:
making a fiber preform from a fiber block by forming at least one cut in the block, so as to provide a gap between two portions of the preform corresponding to segments (i.e. leaves or turns) of a spring that is to be made; and
densifying the preform with a material for constituting the matrix of the thermostructural composite material.
The gap between portions of the preform can be obtained by removing material, preferably after the preform has been consolidated.
This gap can also be obtained by moving apart the lips of the slot and placing a temporary spacer element between them, the spacer element being held in place at least until the preform has been consolidated.
Consolidation consists in densifying the preform partially until it has acquired sufficient mechanical strength to enable it to retain its shape and to enable it to be handled without requiring supporting tooling, but without densifying the preform to a significant extent. Consolidation can be performed by pre-impregnation using a liquid composition, e.g. a resin, and then hardening the resin, or by partial pre-densification by chemical vapor infiltration, with complete densification of the preform being performed subsequently.
The method is suitable for making springs of various shapes. For example, for a leaf spring, the fiber preform can be made from a prismatic block in which a plurality of cuts are formed, substantially parallel to one another, each cut extending over part of the distance between opposite side zones of the block. For a helical spring, the fiber preform can be made from a cylindrical block with an axial bore, and a helical cut can be made through the block about its axis. For a flat spiral spring, the fiber preform can be made from a disk and a spiral-shaped cut can be formed through the disk. For a conical spiral spring, the fiber preform can be made from a hollow frustoconical block, and a spiral-shaped cut can be formed through the wall of the block.
The method of the invention thus differs from the above-mentioned prior art essentially in that the spring is shaped neither by coiling a thread nor by machining a workpiece made of thermostructural composite material, but by machining that is performed at the preform stage when the block is not densified or is incompletely densified.
Implementations of the method of the invention are described below by way of non-limiting indication.
REFERENCES:
patent: 4412675 (1983-11-01), Kawakubo
patent: 4762583 (1988-08-01), Kaempen
patent: 4826143 (1989-05-01), Latorre et al.
patent: 5503783 (1996-04-01), Nakagawa et al.
patent: 2334971 (1975-01-01), None
patent: 0 684 216 (1995-11-01), None
patent: 8-42550 (1996-02-01), None
patent: 9-79248 (1997-03-01), None
patent: 96/32527 (1996-10-01), None
Aftergut Jeff H.
Societe Nationale d'Etude et de Construction de Moteurs d&a
Weingarten, Schurgin Gagnebin & Hayes LLP
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