Installation for extruding plastics

Claim 1

An installation for extruding plastic material comprising a screw extruder having a cylinder provided with a hopper near the rearward end of said cylinder for introducing said plastic material into said cylinder, and with an extrusion head secured to the forward end of said cylinder, for receiving said plastic material in a fluid state, and at least one pump having a delivery pipe connected to at least one port disposed in the wall of said cylinder for delivering an additional fluid product to said extruder through said port or ports during the extrusion operation, said cylinder comprising a first zone wherein the inner surface thereof being provided with grooves and a second zone located downstream with respect to said first zone and wherein the inner surface of the cylinder is smooth, and port or ports opening out into one or more of said grooves at a location of said first zone in the vicinity of the downstream end thereof, said plastic material being at said location at a temperature higher than the temperature at said readward end and in an incompletely fluid state, the inside diameter of the cylinder in said second zone being less than the maximum diameter measured from the bottom of said grooves, and said screw extruder being of essentially uniform dimensions within said second zone and in the portion of said screw extruder immediately upsteam thereof.