Abstract: Disintegrated material is supplied to a pressure chamber by a rotatable and axially translatable screw piston. The piston is rotated while in a first axial position to transport and compact the material in a receiving chamber against a closed output valve in front of the piston. The output valve is opened and the compacted material is moved into the pressure chamber by axial non-rotative motion of the piston. The output valve then is closed, and the piston is axially returned to its first axial position while rotating in the same direction as before. The operation cycle is repeated as above. An apparatus for carrying out a process comprises an axially movable guide piston rotationally carrying and guiding the screw piston for rotation and axial movement by action of a hydraulic cylinder and a mechanism for rotationally positioning the screw piston.