Process for producing double-layered structures

Claim 1

Process for the production of a closed hollow moulding substantially filled with an additional sound-absorbing material to provide for sound insulation of vehicles and engines in general by said molding, characterized by the steps of introducing a double package, each package comprising a prepolymerised or semipolymerised fibre layer and a foil of thermoplastics material, into a compression mould, the foils of the double package being disposed facing each other; providing a sound-absorbing material of sufficient porosity to allow a fluid under pressure to pass therethrough; placing a layer of said sound-absorbing material between said foils; introducing a fluid under pressure through said sound-absorbing material and between said foils in order to press each fibre layer against an internal wall of a corresponding compression mould half; applying heat of a temperature which is sufficient for melting said foil and polymerizing said fibre layers completely in order to provide a self-supporting, closed molding; and forming each of said fibre layers against said corresponding mold walls under said pressure and temperature and closing said molding by sealing edges of said packages together.