Process for manufacturing a transmission shaft made of a composite material and shaft manufactured according to the process

A process for manufacturing a transmission shaft made of a composite material comprising:

• producing a layer comprising reinforcing fibers impregnated with a heat-curable resin;
• installing a peripheral sheath over the layer of resin-impregnated reinforcing fibers prior to curing of the resin, the peripheral sheath being a stretchable knitted article composed of intertwined loops of thread, the knitted construction of said sheath providing said sheath with elastic and stretchable characteristics, the thread being of a material that has an ability to shrink when subjected to a temperature within the polymerization temperature range of the resin;
• deforming said sheath elastically in the radial direction in order to increase its diameter prior to the installation of said sheath over said reinforcing fibers and maintaining an axial tensile force on the sheath during polymerization;
• and
• bringing the assembly of said layer of resin-impregnated reinforcing fibers and of the peripheral sheath to a temperature within the polymerization temperature range of said resin, whereby said resin impregnates said sheath and at least partially passes through said sheath due to the radial pressure effect produced by the elasticity and shrinking of said sheath, said resin defining a continuous external resin layer, said resin being cured and said sheath and said external resin layer being maintained after said resin is cured so that said sheath and said external resin layer constitute the outermost layers of said shaft.

A process for applying an external finishing layer to a transmission shaft core thereby completing its manufacture, said process comprising the steps of:

• winding reinforcing fibers around the transmission shaft core;
• impregnating said reinforcing fibers with a heat-curable resin;
• overwrapping said resin-impregnated reinforcing fibers with a peripheral sheath, said peripheral sheath being a resilient stretchable knitted article composed of intertwined loops of heat-shrinkable elastic thread, the knitted construction of said sheath providing said sheath with elastic and stretchable characteristics;
• and
• curing said resin by subjecting said core to a temperature sufficient to effect polymerization of said resin;
• wherein said peripheral sheath has sufficient resiliency and heat-shrink sensitivity so that said resin impregnates said sheath and at least partially passes through said sheath due to the radial pressure effect produced by the elasticity and shrinking of said sheath during polymerization, said resin defining a continuous external resin layer.