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: 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.