Title: Apparatus for forming thermoplastic articles

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Abstract: Apparatus is disclosed for molding foamed thermoplastic articles characterized by a cellular core and a substantially non-cellular integral peripheral shell comprising: A. extruder means adapted to flux a thermoplastic material; B. Disperser means connected to said extruder means for producing a dispersion of fluid blowing agent in the fluxed thermoplastic material comprising a cylindrical barrel having therein at least one ratatable disc dispersion unit with an alternating spaced series of perforated-solid rotating discs; said perforated disc, providing a high shear mixing zone, having outer edge surfaces in close rotating clearance with the inner walls of said barrel; the outer edge surface of said rotating disc being spaced from the inner walls of said barrel to form an intense shear mixing zone; and wherein said blowing agent is dispersed when passed through the apertures of said perforated disc and is intimately dispersed throughout the thermoplastic material when passed through said intense shear zone; C. accumulation chamber means in communication with said disperser adapted to receive the mixture from said disperser and to maintain said mixture in the molten state and at a pressure above the foaming pressure of said mixture; D. mold means adapted to be maintained at a pressure no greater than the pressure at which said mixture foams and expands; E. means for establishing and terminating communication between said mold means and said accumulation means at a point where the pressure in above the foaming pressure of said mixture; and F. means connected to said accumulator for rapidly forcing said mixture out of said accumulations means and into said mold when communication is established therebetween.


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