Machine element or mechanism – Elements – Pitmans and connecting rods
Reexamination Certificate
1995-01-25
2001-03-20
Green, Mary Ann (Department: 3682)
Machine element or mechanism
Elements
Pitmans and connecting rods
Reexamination Certificate
active
06202505
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns the production of connecting rods to be placed between two points of a structure and able to withstand longitudinal stresses, more particularly, the invention concerns monoblock connecting rods made of a composite material formed of a hollow running part, possible with a cylindrical section, connecting two connecting rod heads with the shape of a fixing strap.
BACKGROUND OF THE INVENTION
French patents FR-2,446,180 and FR-2,550,123 describe how to produce monoblock composite connecting rods whose running portion and end portions are entirely made up of preimpregnated fibers placed on a suitable mandrel which is then placed in a mould whose internal wall fits the shape of the connecting rod to be embodied for the purposes of polymerization.
In FR-2,446,180, the fibers appear in the shape of a fabric wound several turns or “folds” on a deformable mandrel which is then flattened at the two ends.
This technique, apart from the fact that it prohibits embodying heads of a strap connecting rod, does not make it possible to deliberately modulate the local characteristics of the composite material along the connecting rod since this method begins using pre-existing fabrics which are simply plated on the mandrel. In addition, this technique does not really involve genuine monoblock connecting rods as the mandrel remains inside the connecting rods.
In FR-2,550,123, the fibers are placed unidirectionally in the longitudinal axis of the connecting rod on an expansible mandrel which shall next be “inflated” to fit the shape of the mould.
This unidirectional placing required by the expanding of the coated mandrel does not make it possible to longitudinally vary on the connecting rod the fiber placing characteristics and solely concerns resistance to longitudinal stresses.
SUMMARY OF THE INVENTION
The present invention seeks to overcome the drawbacks of known techniques by providing a new technique for embodying connecting rods of the type mentioned above and making it possible to embody varying wall thicknesses and deliberately defined the positioning characteristics of the fibers.
To this effect, the invention provides a method for producing a monoblock composite connecting rod by placing preimpregnated fibers on an extractable mandrel, wherein the method includes the following successive steps:
embodying on a rigid central shaft an extractable mandrel having a shape corresponding to that of the connecting rod;
winding and/or laying down the preimpregnated fibers according to a predetermined number of layers and inclination of the fibers with respect to the longitudinal axis of the mandrel;
polymerization with a homogeneous compacting pressure being applied to the entire outer surface of the unit obtained;
then final operations for removing the mandrel and machining to the required dimensions of the connecting rod.
After winding and laying down the fibers and prior to compacting-polymerization of the composite material, each connecting head is preferably provided with suitable means for shaping the strap of fixing portion of the connecting rod.
According to one mode of operation, the entire mandrel provided with fibers and possible the means for shaping the end portions of the connecting rod are disposed inside a bladder which is then placed under a vacuum and then the unit is placed in an autoclave under pressure so as to provide the polymerization.
According to one application of the method for embodying a connecting rod comprising at each end a strap connected to a running part with a variable section and wall thickness, the fibers are wound onto the mandrel unit via circumferential and longitudinal winding and, on the straps and transition parts, the fibers are placed by winding and laying down according to the local thicknesses to be obtained.
According to one embodiment, a glue film and possibly at least one glass fabric layer is/are laid down between at least some of the layers of fibers of at least the running part.
An extractable mandrel is understood to be a mandrel which, once the composite material has been polymerized, may be removed from the inside of the connecting rod via either of its ends without damaging the connecting rod. For example and according to one embodiment, the mandrel is moulded in a meltable material, especially a mixture of sand and binder, such as the material commercially known as “arenyl”.
The method for embodying connecting rod via winding/laying down according to the invention allows for mechanization of industrial production and enables costs to be reduced with respect to rival known techniques, especially draping techniques which require a large number of operators and operations for cutting the fabrics.
Moreover, the laying down/winding technique is able to fully control the quality of the connecting rod and its performances in absorbing stresses owing to the fact of optimizing the direction and orientation of the fibers in the various portions of the connecting rod.
Finally, the conjunction of a homogeneous external pressure exerted on the entire outer surface of the connecting rod and polymerization ensure an optimal compacting of the composite material.
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Abstract of Japanese Publication No. JP63025023, Feb. 2, 1988.
Auberon Marcel
Fuchs Jean-Francois
Leard Jean-Philippe
Aerospatiale - Societe Nationale Industrielle
Green Mary Ann
Young & Thompson
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