Abstract: A process for manufacturing expanded polystyrene panels includes the following stages:(a) Preparation of pre-expanded panels of polystyrene by extrusion and simultaneous injection of propellent agent into an extruder fitted with an extrusion die of suitable type and in particular fitted with means allowing for good mixing of the molten polymer with the propellent agent and means allowing for uniform cooling to the best value of the temperature of the expandable plastic mass before exit from the die.(b) Conditioning of said panels at room temperature or at whatever temperature higher than room temperature, provided it is such to prevent the panels from undergoing either dimensional variation or deformation due to internal stress or true expansion.

Abstract: The density of the foam is reduced and the thickness of the sheet obtained by extrusion/expansion is increased by grasping the sheet between confining walls which are permeable to gas and movable together with the sheet, and which diverge from each other in the direction of advance of the sheet, and by applying a subatmospheric pressure to the faces of the sheet and through the said walls while the sheet is in its thermoplastic state, after which the foam is gelled by cooling to stabilize the thickness achieved.

Abstract: The adaptor, which can be applied to the delivery end of the extruder barrel, comprises a plurality of ducts for feeding corresponding extrusion heads, radiating from a common manifold chamber and each provided with a butterfly valve for the mutual adjustment of the flows of thermoplastic material in the respective ducts. Preferably the ducts with their respective valves are identical to each other and the valves are adjusted to give extruded products which are identical to each other.

Abstract: A mixer-cooler device for the extrusion of thermoplastic foams comprising: a pair of radially foraminous tubular cylindrical blocks, clamped in axial alignment against opposite faces of a barrier disk by means of a headplate for connection with an extruder barrel and a headplate for connection with an extrusion head, the disk having an axial circular aperture; an advancement screw sealingly rotatable within the blocks, connectable with a screw of the extruder to constitute an extension of this latter screw, the advancement screw having an intermediate barrier section sealingly rotatable in the aperture of the disk; a tubular casing sealingly connecting the two headplates to form a tubular collector channel embracing from the outside the foraminous zones of the two blocks; and a system of passages in the headplates, blocks and disk for the circulation of a coolant liquid for the two blocks.

Abstract: A cooling/mixing device having no moving parts is interposed between the extrusion head and the screw barrel of the extruder. The device comprises a cooled metallic block having a pair of large opposed faces and a plurality of rows of through-passages interconnecting said faces. Inlet and outlet manifold channels for the melt extend along the rows of passages so that a lateral wall of a manifold channel is formed by its respective face of the block. Partial flows of melt obtained from the flow in the inlet manifold channel are individually cooled in the passages and emerge from the latter substantially perpendicularly to the outlet flow in the output manifold channel to produce turbulent mixing. Preferably a further similar cooling block is provided, acting in series with the first block. The blocks are preferably in form of cylindrical sleeves with through-passages directed radially while the manifold channel are directed axially at the inside and at the outside of the sleeves.