the exemplary embodiment according to fig1 through 5 shows a twin - screw extruder having two conical screws 1 , 2 , which are driven by a shared motor 3 to rotate in the same direction around their axes 4 , 5 . the conicity of the screws 1 , 2 causes their axes 4 , 5 to enclose an acute angle with one another . the two screws 1 , 2 are mounted in a shared screw housing 6 and their screw channels 7 ( fig5 ) engage in one another , i . e ., the screw channels mesh with one another , but are at an axial distance to one another , so that a gap 8 ( fig5 ) remains between the screw channels 7 of the two screws 1 , 2 . the motor 3 drives the drive shaft 9 , on which multiple chain wheels 10 are seated , which are connected via drive chains 11 to further chain wheels 12 , which are seated on a further drive shaft 13 . the two shafts 9 , 13 are mounted so they are rotatable in a shared housing 14 and are driven to revolve in the same direction via the drive chains 11 . their axes are parallel to one another . the axis 15 of the shaft 9 is coincident with the axis of the screw 2 . the shaft 9 is connected rotationally fixed via an extension 17 to the core of the screw 2 . the shaft 9 having its extension 17 may be implemented in one piece with the core of the screw 2 . however , if such an implementation would be too long , a coupling 18 may be provided between the extension 17 and the core of the screw 2 . not only is the production of the screw 2 made easier in this manner , but rather also its disassembly , for example , for the purpose of replacement or maintenance . the other shaft 13 is connected via an apparatus 19 to the screw 1 , this apparatus 19 providing the screw 1 with a periodic acceleration and / or deceleration of the peripheral velocity as the drive shaft 13 rotates . for this purpose , the apparatus 19 has two cardan joints 20 , 21 which are connected to one another rotationally fixed . one cardan joint 20 is connected rotationally fixed to the shaft 13 , the other cardan joint 21 to a connection shaft 22 , which may be implemented in one piece with the core of the screw 1 or is connected rotationally fixed to the core of the screw 1 via a coupling 25 . the two cardan joints 20 , 21 form a universal shaft 26 together with a linkage 23 connecting them . the linkage 23 may be formed in the simplest case by a rod whose axis is identified by 24 . because the axes 4 , 5 of the two screws 1 , 2 are not parallel to one another , but the axes 15 , 16 of the two drive shafts 9 , 13 are , the angle α between the axis 16 of the shaft 13 and the axis 24 of the linkage 23 is greater than the angle β which the axis 24 of the linkage 23 encloses with the axis 4 of the screw 1 . the difference of the two angles α , β forms an angle of inflection , which has the result that the universal shaft 26 having the two cardan joints 23 , 24 causes the cited acceleration and deceleration of the rotational movement of the screw 1 . the screw 2 , in contrast , is driven at constant peripheral velocity . fig2 shows this drive of the connection shaft 22 in a larger scale . as shown , the drive side of the cardan joint 20 is connected rotationally fixed to the drive shaft 13 driven by the motor 3 . the other cardan joint 21 is connected rotationally fixed on its output side to the connection shaft 22 , which is in turn connected rotationally fixed to the core of the screw 1 , possibly via the coupling 25 . the output side of the cardan joint 20 is connected rotationally fixed in the way typical for universal shafts to the drive side of the cardan joint 21 . however , the angle of this connection is adjustable , so that the cited deceleration or acceleration of the rotation of the screw 1 is variable . for this purpose , the linkage 23 connecting the two cardan joints 20 , 21 rotationally fixed has a coupling 27 , using which the rotational position of the output - side cardan joint 21 is adjustably changeable in relation to the drive - side cardan joint 20 , around the axis 24 connecting the two cardan joints 20 , 21 . this coupling 27 is shown in the disassembled state in fig3 . it has a receptacle 28 connected rotationally fixed to the output side of the cardan joint 20 , which is provided with internal teeth 29 . teeth 30 , which are positioned on the circumference of a socket pin 31 connected rotationally fixed to the drive side of the cardan joint 21 , may be plugged fitting into these internal teeth 29 . the enlargement and reduction of the gap 8 caused by the cited periodically changing peripheral velocity of the screw 1 is shown in greater detail in fig5 , this gap existing between the screw channels 7 of the two screws 1 , 2 . a maximum gap width v max and a minimum gap width v min result for the screw channel 7 of the screw 1 on its forward side , seen in the conveyance direction of the screws , in operation . similarly , a maximum gap width r max and a minimum gap width r min result on the rear side of the screw channel 7 of the screw 1 . this minimum gap width may be set so small that a contact of screw channels 7 of the two screws 1 , 2 opposite to one another is still just avoided . in practice , however , one typically manages with a 40 to 60 % change of the screw gap , in relation to the maximum possible dimension of the gap 8 . it is typically not necessary to change the profile of the screw channels 7 in relation to typical profile shapes . in special cases , however , adapting the profile of the screw channels 7 appropriately because of the cited reduction and increase of the gap 8 may be indicated . the embodiment of fig6 also shows a twin - screw extruder , whose screws 1 , 2 rotating in the same direction are implemented as conical , so that the screw axes 4 , 5 do not lie parallel to one another . in this embodiment , the cited deceleration and acceleration of the rotational movement of one of the screws ( in relation to the constant rotational movement of the other screw ) is not achieved by a universal shaft , but rather separate motors 3 , 32 are provided for the two screws 1 , 2 . the motor 3 drives the screw 1 at constant peripheral velocity ( which may be adjustably selectable , however ), the motor 32 , in contrast , is provided with the cited apparatus 19 , which provides the screw 2 driven thereby with a periodic acceleration and deceleration superimposed on the constant speed . the size of this acceleration and deceleration is expediently adjustably changeable . suitable electronic controllers are available for this purpose . the embodiment of fig7 shows a twin - screw extruder whose construction is similar to that of fig1 , a difference only exists in that the two screws 1 , 2 rotating in the same direction are not implemented as conical , but rather cylindrical , so that the two screw axes 4 , 5 run parallel to one another . the two drive shafts 9 , 13 are also parallel to one another , which results in a very simple design . the two angles α , β are therefore equal to one another . to also achieve the cited desired periodic deceleration and acceleration of the rotational movement of the screw 1 in such a design , the output - side cardan joint 21 is pivoted by a suitable amount in relation to the drive - side cardan joint 20 around the axis 24 connecting the two cardan joints . this relative pivoting of the two cardan joints 20 , 21 may be achieved easily by a coupling according to fig3 , 4 . as noted therein , the cited relative pivoting of the two cardan joints 20 , 21 may be adjustably selectable , so that one may adapt to various conditions of the material to be processed . the embodiment from fig8 forms a combination of the embodiments from fig6 and 7 . the two screws 1 , 2 rotating in the same direction are cylindrical , as in fig7 , however , the apparatus 19 which provides the rotational movement of the screw 2 with a periodic deceleration and acceleration in relation to the rotational movement of the screw 1 is implemented as in the embodiment from fig6 . as shown in fig8 , a change of the type of the cited periodic rotational movement change of the screw 1 may additionally be achieved by a coupling 27 for this purpose . a further possibility for the variation of the periodic change of the axial width of the gap 8 is to make the position of the axial direction of the output shaft 22 adjustably changeable in relation to the position of the axial direction of the drive shaft 13 . the configuration of separate motors 3 , 32 for the drive of the two screws 1 , 2 makes it possible to make the drive shaft 13 adjustable in the housing 14 in regard to its direction without problems , e . g ., by a suitable pivot mount . a further possible design for achieving the periodic change of the width of the gap 8 between opposite screw channels 7 of the two screws 1 , 2 is to provide one of the two screws with a periodic back - and - forth movement in the direction of its axis , this movement being superimposed on the rotational movement of the screw . an additional drive is necessary for this screw for this purpose . this additional drive may be implemented in such a manner that a fixed curve path is provided , on which a tappet connected to the affected screw runs as the screw rotates . it is expedient to implement such a tappet as a rotor to avoid friction losses . another possible design comprises forming the cited additional drive by a piston - cylinder assembly , which causes the periodic back - and - forth movement of the screw . of course , the rotational drive of the affected screw must be implemented appropriately in both cases to permit the cited back - and - forth movement . of course , it is also possible to implement all described designs in such a manner that the two screws 1 , 2 rotate in opposite directions . a simple possible design for this purpose is to couple the two drive shafts 9 , 13 of the two screws 1 , 2 to one another via gear wheels . which of the two types of drive ( opposite or identical directions ) is selected for the screws 1 , 2 is a function of the existing conditions , conical screws running in the same direction are typically most favorable . although the pitch of the screw channels of the two screws 1 , 2 is shown as constant in fig7 and 8 , it is also possible , of course , to implement this pitch as varying over the screw length in such a manner that the desired compaction of the material results in the conveyance direction of the screws 1 , 2 . the filling of twin - screw extruders , as were described above , is shown in fig9 through 11 . the twin - screw extruder 38 ( fig9 , 10 ) provided with the device according to the invention has an intake opening 39 of the screw housing 6 situated in the area of one front end of the screws 1 , 2 . a funnel 40 is connected to this intake opening 38 , against whose top side a horizontally mounted dosing screw 41 presses , which is driven by a motor 42 via a gear 42 in such a manner that material supplied from above via a supply funnel 44 to the dosing screw 38 is always supplied in the desired quantity to the screws 1 , 2 , so that both overfilling and also idling of the screws are avoided . the material to be processed is frequently thermoplastic material which is to be reprocessed for recycling purposes . this material is frequently formed by pet milled product , which is formed by crushed bottles and must be melted under vacuum , so that oxidation and degradation of the material are avoided as much as possible . if such vacuum handling is desired , the supply of the material shown in fig9 and 10 must occur under a vacuum seal , a design suitable for this purpose is shown in fig1 . for this purpose , a vacuum hose 45 is connected to the funnel 40 , which may be terminated on the top and bottom by sliders 46 , 47 closing vacuum tight in a way known per se , so that its inner chamber 48 may be evacuated via an evacuation line 49 . the dosing screw 41 is not shown in fig1 for the sake of simplicity . another frequently existing application is the compounding of plastics of different types , e . g ., polyethylene of lower and higher densities , or polypropylene with polyethylene . the cited periodic change of the width of the gap 8 between opposing screw channels 7 favors the achievement of a desired high degree of mixing . such a high degree of mixing also results during the processing of pasty and / or powdered materials , of whatever type , e . g ., ceramic or mineral materials , such as clay , etc . at least one degassing opening 50 may be provided in the housing 6 of the screws 1 , 2 , to which a suction line ( not shown ) may be connected , via which gas may be suctioned out of the inner chamber of the screw housing 6 . the material mixed and / or plasticized and / or agglomerated by the screws 1 , 2 is discharged out of the screw housing 6 through at least one outlet opening 51 at the front end of the screw housing 6 facing away from the intake opening 39 . an extruder head or a suitable molding facility may be connected to this outlet opening 51 . in certain applications , it may be advantageous to permit a leakage flow in the two screws 1 , 2 . suitable measures for this purpose are known , e . g ., flattening at least some screw channels 7 and / or incorporating grooves on at least some flanks of the screw channels 7 .