Abstract: An apparatus for extruding plastic materials, particularly plastic explosives or propellants, has a casing, at least one pressing member moving therein, e.g. a rotating extruder screw and a shaping retainer plate terminating the casing at the outlet side, which is fixed to the casing and can be raised therefrom if an excessive overpressure occurs. So as to ensure rapid raising and a rapid release of the overpressure when a safety hazard occurs, the retainer plate is fixed to the casing by a mechanical or a gas pressure spring, whose spring tension is adjustable. It is also possible to provide a hydraulic pressure directed in opposition to the spring and by which the retainer plate can be raised in random manner from the casing.