fig1 and 2 show the invention in an overview . the device shown has an essentially symmetrical structure based on a machine base frame with two opposing , plane - parallel transverse walls 1 , which are connected to one another at their bottom corners by bottom longitudinal spars 2 , and at their top corners by top longitudinal spars 3 . the longitudinal walls 4 are composed over their full area of doors 5 , which can pivot on hinges 6 in order to open and close the housing , thus ensuring accessibility to the interior of the device . welded to the outside of each of the two transverse walls 1 is a bracket 7 for accommodating a shaft bearing 8 . the shaft bearings 8 carry a rotor 9 , which is composed essentially of a rotor drum 11 ; a stub shaft 10 engages each end face of the drum in a rotationally fixed manner . the free ends of the two stub shafts 10 extend through openings in the transverse walls 1 as far as the shaft bearings 8 . the rotor 9 is equipped over its circumference with a plurality of tool units 12 , which are spaced apart from one another both in the circumferential direction and in the axial direction . in this design , each tool unit 12 is replaceably fastened in a seat on the lateral surface of the rotor drum 11 , which is described in more detail under fig5 . as is indicated by the arrow 45 , the rotor 9 can be operated in both directions of rotation . the bottom circumferential section of the rotor 9 is surrounded by a screen path , which in the present example is composed of four screen elements 13 . each screen element 13 consists essentially of a screen support 14 upon which a perforated screen 15 is mounted . in cross - section , two screen elements 13 extend over nearly one quarter of the rotor circumference in mirror image ( fig1 ); in the longitudinal direction , two screen elements 13 follow one another axially ( fig2 ). for pivoting support of the screen elements 13 , journal bearings 17 in which the screen carriers 14 are rotatably supported are located on the inner side of the transverse wall 1 and on both sides of a partition 16 . with the aid of the piston / cylinder units on the outside of the transverse walls 1 , whose movable pistons act on the screen supports 14 via working levers , the screen elements 13 can each be pivoted down . with open doors 5 , access to the perforated screens 15 and the rotor 9 is thus ensured . the top longitudinal spars 3 each serve the purpose of stationary mounting of an axially parallel stator device , with a stator tool holder 19 , which extends across the entire axial distance of the two transverse walls 1 . the top of the stator tool holder 19 is inclined towards the rotor 9 and forms a support surface for platelike stator tools 21 , which are clamped against the stator tool holder 19 with the aid of clamping plates 22 and clamping screws 23 . in the region of the outer longitudinal sides of the stator tool holder 19 , adjusting screws 24 are also visible , with which radial adjustment or readjustment of the stator tools 21 can be undertaken in order to ensure the required working gap between the tool units 12 of the rotor 9 and the stator device . the rotor 9 and the stator device thus have an essentially symmetrical structure with respect to the vertical plane through the axis of rotation . the feed material is supplied through a vertical feed shaft 25 , whose longitudinal walls 26 attach directly to the stator device in the vertical direction . in the region of attachment to the stator devices , the longitudinal walls 26 each have an opening 27 that extends from one transverse wall 1 to the opposing transverse wall . the transverse walls of the feed shaft 25 are reinforced as compared to the transverse walls 1 of the machine base frame , and continue upward beyond the rotor 9 . each opening 27 is closed by a flap 28 , which is mounted in a pivoting manner in the transverse walls 1 in similar fashion to the screen elements 13 . the pivot axes 29 of the flaps 28 are located in the region of the upper longitudinal edge of a flap 28 , where axial bearing journals are provided for this purpose . to protect the joint gap between a movable flap 28 and the rigid region of the feed shaft 25 that continues upward , each of the longitudinal walls 26 has a strip - shaped skirt 30 along its lower edge on the inside , which overlaps the top longitudinal edge of the flap 28 . extending over the entire length of the flaps 28 , on their rear side facing away from the rotor 9 , is a deflector plate 33 , which is inclined towards its free edge in order to prevent material from collecting in the pivot region of the flaps 28 . the flaps 28 are driven in a similar manner to the screen elements 13 , with the aid of piston / cylinder units that are not shown , whose cylinders on the outside of the transverse walls of the feed shaft 25 are attached in a stationary manner to the transverse walls , while their movable actuating pistons are each coupled to a lever seated in a rotationally fixed manner on the bearing journal of the flaps 28 . the pivoting motion of the flaps 28 is produced by extending the piston / cylinder units . fig3 through 6 show the detailed construction of a tool unit 12 and its attachment to the rotor 9 . the tool unit 12 comprises a tool holder 34 , which is composed of a first carrier section 31 and a second carrier section 32 , which are identical in construction . each carrier section 31 , 32 has an approximately cuboid shape with a flat underside 35 and flat faces 36 , with its edges being chamfered . the front side 37 of the tool carrier section 31 , 32 essentially serves to accommodate any desired number of tools , which in the present example consist of four platelike cutter heads 38 with a square outline arranged next to one another . each cutter head 38 is oriented such that one of its diagonals is parallel to the direction of the longitudinal extent of the carrier sections 31 , 32 , and the other diagonal is perpendicular thereto . in this design , two adjacent cutter heads 38 touch in the region of their opposing points , which is explained in more detail under fig6 . this arrangement of the cutter heads 38 results in a zigzag shape of the active edge 41 of the tool unit 12 for the comminution . the top sides of the carrier sections 31 , 32 follow the course of the active edge 41 with a certain edge spacing , resulting in a slight radial projection of the cutter heads 38 above the carrier sections 31 , 32 . for secure attachment to the carrier sections 31 , 32 , the cutter heads 38 are arranged in seats 39 on the front side 37 of the carriers 31 , 32 . each of the seats 39 is composed of a bearing surface 40 offset towards the rear side 42 of the carrier sections 31 , 32 . as a result of the offset perpendicular to the bearing surface 40 , strip - shaped support surfaces 43 are produced , which accommodate two adjacent sides of a cutter head 38 in a positive - locking manner . the transition between the two support surfaces 43 here is composed of an outward rounding 44 . the bearing surfaces 40 each have a central through - hole 46 for passage of a mounting screw 47 ( fig5 ). in order to illustrate this circumstance , the cutter head 38 on the left - hand side in the plane of the drawing is not shown in fig3 . the rear side 42 of the carrier sections 31 , 32 is designed to be essentially flat . however , in the region where the through - holes 46 emerge , local indentations 48 are provided in which the ends of the mounting screws 47 are anchored with the aid of nuts 49 that are screwed on . beneath the indentations 48 , approximately halfway to the underside 35 of the carrier sections 31 , 32 , a keyway 50 that runs parallel to the underside 35 can be seen that is intended to accommodate a feather key 51 in a positive - locking manner . as is especially clear from fig3 and fig5 , for the purpose of obtaining a tool unit 12 according to the invention and preparing it for installation in a rotor 9 , two carrier sections 31 , 32 are placed one on the other so their rear sides 42 are congruent . in the common contact plane 52 , the feather key is responsible for centering the first carrier section 31 relative to the second carrier section 32 . a tool unit 12 that has been prepared in this way is inserted in a seat on the rotor 9 , where it is secured solely through clamping with the aid of a radially clamped clamping wedge 53 , which exerts on the tool unit 12 a clamping force that is directed tangentially with respect to the axis of rotation . to this end , an inclined side surface of the clamping wedge 53 works together with a wall surface of a tool seat that likewise is inclined ( fig5 ). fig6 shows the contact region between two rectangular or square processing tools — in the form of cutter heads 38 — located next to one another on a carrier section 31 , 32 . the opposing peaks have , at their end regions , truncations 54 that permit full - area contact of the processing tools in the region of the truncations 54 . this has the advantage that the active edge 41 composed of the aggregate of the processing tools is preserved as a whole even after initial manifestations of wear have appeared . a size for the truncations 54 that is advantageous for this purpose arises when the diagonal spacing of the truncations is approximately 0 . 9 times to 0 . 95 times the spacing of the two other points without truncations . the invention is not restricted to the present exemplary embodiment , but instead also encompasses embodiments in which a tool extends as a single part over an entire carrier section . in like manner , embodiments are possible in which the active edge formed by the tools has a different shape than a zigzag , for example is straight or wavy . the invention being thus described , it will be obvious that the same may be varied in many ways . such variations are not to be regarded as a departure from the spirit and scope of the invention , and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims .