Abstract:
A control and regulating device for a needle element ( 24 ) of a hot or cold channel ( 20 ) of a plastic molding tool, wherein a rotary movement of a drive device is converted by a converting device ( 26 ) into an axial movement of the needle element ( 24 ). In order to achieve optimum plastic production, that is to say to permit optimum movement of the needle element ( 24 ) both during the idle stroke movement and also during the process regulation phase and during deceleration, the converting device has at least one slide path ( 30 ) and a follower element ( 50 ) which is guided in the slide path ( 30 ), wherein the at least one slide path ( 30 ) which is angled, that is to say which has path pitches which are different from each other, is formed on a slide path surface which is concentric with respect to the center line ( 42 ) of the needle element.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a control and regulating device for a needle element of a hot or cold channel of a plastic molding tool, wherein rotation of a drive device is converted by means of a converting device into an axial movement of the needle element 
     Such control and regulating devices are known for example from U.S. Pat. No. 5,078,589 or U.S. Pat. No. 5,238,378. The converting devices provided in those known control and regulating devices, for converting rotation of a drive device into an axial movement of the needle element, have a screw and nut element of constant pitch. That constant pitch of the screw and nut element determines the movements of the needle element of the hot or cold channel of the corresponding plastic molding tool. 
     Demands for up-to-date processing of injection-moldable plastic materials with their individual process-specific and physical criteria to provide the respective plastic moldings are not satisfied or are only inadequately satisfied or are only satisfied by virtue of a suitable compromise, in regard to fastest possible production cycles, dealing carefully with the injection molding materials, that is to say injection-moldable plastic materials, dealing carefully with the molding tools, an optimum injection molding process control, making use of motor-driven drive devices and reducing the level of wear of the respective needle element or the drive device with such screw and nut elements of constant pitch. 
     Admittedly, small or normal pitches of the screw and nut element involve a high force and a very substantial self-locking action when pressure is applied or in terms of needle locking, as well as fine adjustability, but they suffer from the disadvantage that the respective no-load or idle stroke of the needle element is highly time-intensive and that possible process regulation can be effected only very sluggishly, that is to say involving a great deal of time. That time penalty puts a load on the operating cycle and increases costs in the above-mentioned idle stroke range for example for opening the needle element for the fastest possible quantitative through-flow of the plastic material, as for example hot channel needle elements can have a needle stroke of between 8 and 16 mm or more. Consequently, when the screw and nut element involve small pitches, reactive oscillation as rapidly as possible is not adequately afforded for process regulation purposes so that the efficiency of the regulating device which usually involves an electronic regulating device is not put to use or is not completely put to use. The respectively desired level of quality of production of the respective plastic pars can consequently not be kept stable or stabilised. 
     Admittedly, a fast movement of the needle element in the idle stroke range can be implemented with a greater or high pitch for the screw and nut clement of the converting device of known control and regulating devices for a needle clement of a hot or cold channel of a plastic molding tool, but during the process control phase the needle element becomes over-active, whereby necessary fine actuation becomes more difficult. In addition such an increased or high pitch results in an increased need for counter-holding force, which means that the expenditure in terms of energy and power is correspondingly increased. A further deficiency of such an increased or large pitch is that so-called spot-wise grinding-in of the needle element as a closure element of the runner region to the mold cavity causes considerable tool wear and is relatively force-less as the self-locking action of the needle element is at least greatly reduced as a consequence of the increased or great pitch of the screw and nut elements. 
     DE 196 11 880 A1 discloses an injection molding tool with a plurality of hot channel needle closure nozzles which are connected to an actuating device for the simultaneous actuation of a plurality of needle That known injection molding tool has a mechanical drive transmission between a stroke drive and needle carrier elements arranged at the individual needles. Elastic intermediate elements are provided between the needle carrier elements and the respective needle. Transversely with respect to the longitudinal extent of the needles, it is possible to provide a slider connected to the stroke drive, as the rigid mechanical drive transmission. The elastic intermediate elements used can be compression springs which are preferably in the form of diaphragm springs. The slider and/or the needle carrier elements can have inclined guides for converting the slider stroke movement into the working movement of the needles, which working movement is transverse with respect to the slider movement 
     The object of the invention is to provide a control and regulating device of the kind set forth in the opening part of this specification, in which the opening and closing times of the needle element are reduced, but at the same time fine control is possible. 
     SUMMARY OF THE INVENTION 
     The foregoing object is achieved by providing a converting device which has at least one slide path and a feeler or follower element which is guided on the slide path, wherein the at least one slide path is provided on a slide path surface which is concentric with respect to the center line of the needle element. 
     In consideration of those factors, the object of the invention is to provide a control and regulating device of the kind set forth in the opening part of this specification, which so-to-speak combines together the advantages of a low and a high pitch and eliminates the disadvantages thereof. 
     In a control and regulating device of the kind set forth in the opening part of this specification, in accordance with the invention that object is attained in that the converting device has at least one slide path and a feeler or follower element which is guided on the slide path, wherein the at least one slide path is provided on a slide path surface which is concentric with respect to the center line of the needle element. 
     The at least one slide path can be of optimum design in a simple manner and can be individually configured as desired in order to permit the desired axial movement of the needle element, that is to say as desired a rapid idle stroke movement and a process regulation and deceleration movement of the needle element, which is slow in comparison therewith. The needle element may involve a needle element of a full cross-section, a hollow needle combined with such a needle element, for example of a compression needle unit, or the like. Such needle elements or control and regulating devices for a hot or cold channel of a plastic molding tool are described in the present applicant&#39;s prior patent application Ser. No. 198 57 735. The control and regulating device according to the invention is suitable by way of example for all needle elements or molding tools described in said prior patent application. 
     The at least one slide path of the converting device of the control and regulating device according to the invention can in this case extend over an angle of 360 degrees of angle or more, around the center line of the needle element. It may be advantageous if two or more slide paths are provided distributed uniformly around the center line of the needle element in order, with a rotation of the drive device through a small angle, to produce the desired axial displacement of the needle element. That small rotary angle is dependent on the number of slide paths, that is to say inversely proportional to the number of slide paths. With two slide paths the rotary angle can be 180 degrees or less than 180 degrees. With three slide paths the rotary angle can be 120 degrees or slightly less. Implementation of the smallest possible rotary angle is also dependent on the diameter of the slide path surface for the slide paths. The greater that diameter is, the correspondingly greater can be the number of slide paths, that is to say the correspondingly smaller can be said rotary angle. A small rotary movement of the drive device affords the advantage that, for example when using a worm drive with an extreme transmission ratio, the speed of rotation of the drive worm can be drastically reduced, thereby resulting in a corresponding time saving. The sane applies also for example for chain, toothed belt and gear drives as well as in relation to toothed rack versions and the like, in which respect the rotary speed or the piston stroke movement can be drastically reduced. In addition—for example in clean-room production of plastic articles—it is possible to use electrical stepping or servo motors which have a high torque and which if required rotate at low speed and which afford very rapid reaction options. During the corresponding slight rotary movement, the entire axial stroke movement of the needle element is performed, that is to say the idle stroke movement and the process regulation and deceleration movement. 
     In accordance with the invention the at least one slide path can be provided in a rotatably mounted sleeve element which has the slide path surface and which is operatively connected to the drive device. In this case the at least one slide path can be provided on the internal surface of the sleeve element, which forms the slide path surface. 
     The sleeve element with the at least one slide path can be axially immovably rotatably supported and provided with a drive output gear with which a drive gear is in meshing engagement. The drive output gear may involve for example a worm gear. The drive gear is then a worm spindle. 
     The needle element can be provided non-rotatably in the case of such a control and regulating device of the above-described kind, and can have at least one radially projecting feeler or follower element. 
     Another possibility provides that the sleeve element with the needle element forms a rigid unit and is axially displaceable and rotatable about the center line of the needle element and that the at least one follower element is provided non-rotatably and axially immovably. This last-described alternative configuration involves so-to-speak a reversal of the control and regulating device or converting device, as described hereinbefore. 
     Likewise it is possible for the at least one slide path to be provided in a portion of the needle element which is disposed non-rotatably and for the at least one follower element to project from the rotatable sleeve element. This also involves only a reversal of the principle according to the invention of the converting device of the control and regulating device according to the invention. 
     In accordance with the invention the at least one follower element can be formed by a cylinder, a roller or a pin. In order to withstand very high counter pressures or counter forces in a wear-resistant manner, the at least one pin can be provided with a curved or cambered flattened sliding surface. A sliding surface of such a configuration provides for a reduced pressure in relation to surface area, which results in a corresponding reduction in wear. 
     In the case of the control and regulating device according to the invention, it is preferable if the at least one slide path has a fast-displacement portion of large pitch and an adjoining process regulation and deceleration portion of comparatively small pitch. Independent patent protection is requested in that respect. 
     It is preferred in this case if the process regulation and deceleration portion, on the side remote from the fast-displacement portion, is adjoined by a self-locking portion. The self-locking portion is preferably of a zero pitch. 
     In order in the event of over-control of the drive device to ensure that the at least one follower element is not separated from or moved away from the associated slide path, it is desirable if the fast-displacement portion, on the side from the process regulation and deceleration portion, is adjoined by a catch hook portion. 
     Desirably, provided between each of the individual slide path portions of the at least one slide path is a respective rounded slide curve portion in order to achieve a suitable movement of the follower element on the slide path and consequently a corresponding movement of the associated needle element. 
     In accordance with the invention the at least one slide path can be provided with mutually parallel slide path surfaces. In the case of such a design configuration, at least two slot-shaped slide paths can be provided on the slide path surface which is concentric with respect to the center line of the needle element, being equidistantly spaced in the peripheral direction of the slide path surface. In this arrangement, the at least two slot-shaped slide paths are provided separately from each other in the peripheral direction of the slide path surface. It is however also possible for the at least two slot-shaped slide paths to be respectively connected together by means of a needle return portion. In the first-mentioned case with mutually separated slot-shaped slide paths, it is necessary for the drive device to be driven with a reciprocating motion in order to move the needle element forward and back, while in the case of the structure in which the slot-shaped slide paths are respectively connected together by means of a needle return portion, it is possible for the drive device to be rotated only in one direction and in that situation to successively implement the closing and opening movement of the needle element. 
     An advantage of the configuration according to the invention of the control and regulating device with at least two slot-shaped slide paths which are respectively connected together by means of a needle return portion, that is to say which extend closed in themselves around the slide path surface, is that the needle return portion can be of a pitch which can be greater than the pitch of the fast-displacement portion so that, with a constant drive or angular speed of the drive device, the needle return motion takes place still faster than the fast-displacement motion, that is to say the fast feed motion of the needle element which is followed by the process regulation and deceleration movement of the needle element. 
     Another possible configuration of the control and regulating device according to the invention provides that the at least one slide path has two slide surfaces which are disposed in diametrally and also axially opposite relationship on the slide path surface and which are arranged to extend in mutually parallel relationship, wherein an associated portion of the follower element bears in guided relationship against each of the two slide surfaces. This embodiment of the control and regulating device according to the invention also provides that it is possible to have more than one slide path with two respective diametrally and axially oppositely disposed slide surfaces which are arranged to extend in mutually parallel relationship, wherein a portion of the associated follower element bears in guided relationship against each of the slide surfaces which are disposed in paired diametrally and axially opposite relationship. Those diametrally and axially oppositely disposed slide surfaces of the at least one slide track are each axially accessible from one side or the other so that in each case therefore—in contrast to the above-described slot-shaped slide paths—this arrangement affords open slide paths. That can be desirable from points of view involving manufacture. 
     A farther simplified variant, that is to say which is even easier to manufacture, of the control and regulating device according to the invention, is characterised in that the at least one slide path has a single slide surface, against which the associated follower element or the associated follower element portion is urged by means of a spring device. In this case at least two slide paths can be provided separatedly from each other in the peripheral direction on the slide path surface which is concentric with respect to the center line of the needle element, the at least two slide paths each having a single slide surface. With this design configuration it is necessary for the drive device to be driven with a reciprocating movement in order to move the needle element forward and back. 
     It is however also possible for the slide surfaces of the at least two slide paths of the last-described alternative configuration to be respectively connected together by means of a needle return portion so as to provide a slide path which is closed in itself and which extends around the slide path surface. With this design configuration it is possible for the drive device to be driven only in one direction of rotation and for the needle element to be axially reciprocated. So that with such a design configuration of the last-mentioned kind, with a constant speed of rotation of the drive device, the needle return movement can also be effected at a higher speed than the fast displacement of the needle element, the needle return portion can be of a pitch which is greater than the pitch of the fast-displacement portion. 
     The last-described embodiment of the control and regulating device according to the invention with at least one slide path having a single slide surface against which the follower element is urged by means of a spring device therefore involves an open slide path which can be precisely manufactured in a simple manner, unlike a slot-shaped slide path. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further details will be apparent tom the description hereinafter of embodiments illustrated in the drawing of the control and regulating device according to the invention for a needle element of a hot or cold channel of a plastic molding tool. In the drawing: 
     FIG. 1 is a sectional view showing part of a first embodiment of the control and regulating device, with the needle element assuming the closed position, 
     FIG. 2 shows the control and regulating device of FIG. 1, with the needle element in the open position, 
     FIG. 3 diagrammatically shows a development along section line Aw—Aw in FIG. 1 to clearly show the sleeve element, which has two diametrally appositely disposed slot-shaped slide paths, of the converting device of the control and regulating device for the needle element as shown in FIGS. 1 and 2, 
     FIG. 4 shows a view in section taken along section line IV—IV in FIG. 2 to clearly show the non-rotatable arrangement of the axially displaceable needle element, 
     FIG. 5 shows another embodiment of the converting device of the control and regulating device for a needle element of a hot or cold channel of a plastic molding tool with a rotatable and axially displaceable sleeve element, 
     FIG. 6 is a view similar to FIG. 3 showing a portion of the slot-shaped slide paths with a follower element which is in the form of a pin with a flattened slide surface, 
     FIG. 7 is a view similar to FIG. 4 showing a development along section line Aw—Aw in FIG. 1 to clearly show an embodiment of the control and regulating device, wherein the slot-shaped slide paths of the converting device for converting a rotary movement of the drive device into an axial movement of the needle element are respectively connected together by means of a needle return portion so that the slide paths are closed in themselves in the peripheral direction of the slide path surface which is concentric with respect to the center line of the needle element, 
     FIG. 8 is a sectional view similar to FIG. 5 of still another embodiment of the converting device of the control and regulating device for a needle element of a hot or cold channel of a plastic molding tool with a rotatably supported and axially immovable sleeve element and an axially displaceable needle element which is prevented from rotating, 
     FIG. 9 shows a section taken along section line Aw 1 —Aw 1  as shown in FIG. 8 as a development similarly to the developments shown in FIGS. 3 and 7, 
     FIG. 10 shows a sectional view similar to FIGS. 5 and 8 of a further embodiment of the converting device of the control and regulating device for a needle element of a hot or cold channel of a plastic molding tool wherein the needle element has two diametrally oppositely disposed slide paths which each have a single open slide surface, and the follower element is urged against said slide surfaces by means of a spring device, and 
     FIG. 11 shows a development similarly to the developments of FIGS. 3,  7  and  9  along section line Aw 2 —Aw 2  in FIG. 10 to clearly illustrate the two diametrally oppositely disposed slide paths with the respective one open slide surface. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows an injection molding  2  between two mold units  4  and  6  which are clamped and fixed between two mold plates  8  and  9 . Urged against the mold plate  8  is a spacer plate  12  which bears against a clamping plate  14 . The clamping plate  14  is covered by an insulating plate  16  which serves for heat insulation purposes. 
     Associated with the mold insert  4  is a hot channel nozzle  18  having a hot channel  20 . The hot channel nozzle  18  is provided on a hot channel distributor block  22 . 
     Arranged in the hot channel  20  is a needle element  24  which is operatively connected to a converting device  26  for converting a rotary movement of a drive device (not shown) into an axial movement of the needle element  24 . The converting device  26  has a sleeve element  28  which is formed with two diametrally oppositely disposed slot-shaped sliding guide paths  30  which are described in greater detail hereinafter in particular with reference to FIG.  3  and with reference to FIG.  6 . The sleeve element  28  of the converting device  26  is fixedly connected to a drive output gear  32  which is in the form of a worm gear ring  34 . Meshing with the worm gear ring  34  of the drive output gear  32  is a worm spindle  38  forming a drive gear  36 . The worm spindle  38  is non-rotatably connected to the above-mentioned drive device (not shown). The drive device is for example an electric motor or an electric stepping or servo motor. The drive device can also be formed by a hydraulic or pneumatic motor or the like. 
     The sleeve element  28  which is formed with the slot-shaped slide paths  30  forms a unit with the drive output gear  32  and is rotatably and axially immovably supported in the clamping plate  14 . Serving for that purpose is a holding and centering element  40  which is disposed between the clamping plate  14  and the spacer plate  12 . The holding and centering element  40  also assists with the rotatable support for the drive output gear  32  and thus the sleeve element  28  which is disposed in concentric relationship with the center line  42  of the needle element. 
     To make the needle element  24  non-rotatable and axially displaceable, the needle element  24  has at the upper end of a portion  44  of enlarged cross-section a rotation-preventing element  46 . As can be seen from FIG. 4, the rotation-preventing element  46  is of a cross-section which differs from a circular shape. The clamping plate  14  has a through hole  48  whose internal cross-section is matched to the cross-section of the rotation-preventing element  46  so that the needle element  24  is prevented from rotating about the center line  42  of the needle element. 
     Two feeler or follower elements  50  which are in the form of cylinders or rollers project diametrally in opposite directions from the portion  44  of enlarged cross-section of the needle element  24 . The follower elements  50  project into the slot-shaped slide paths  30  of the sleeve element  28  of the converting device  26 . 
     The mode of operation of the follower elements  50  and the slot-shaped slide paths  30  of the sleeve element  28  of the converting device  26 , that is to say the operating movements of the needle element  24 , will be described hereinafter in particular with reference to FIG.  3 . 
     In FIG. 1 the sleeve element  28  is in such a rotational position that the needle element  24  is in its closed position. In comparison, FIG. 2 shows the rotational angular position of the sleeve element  28  of the converting device  26 , in which the needle element  24  of the hot channel nozzle  18  assumes its open position in order to form a fluid communication between the hot channel  20  and the mold cavity  52  which is provided between the two mold inserts  4  and  6 , for the injection molding (see FIG.  1 ). 
     The same details are identified in FIG. 2 by the same references as in FIG. 1 so that there is no need for all those features to be described in detail once again with reference to FIG.  2 . It will be appreciated that other configurations and/or combinations of hot channel nozzles  18  with plastic molding tools are also possible and conceivable, from the structure illustrated in FIGS. 1 and 2 of the drawing. In this respect attention is directed by way of example to the present applicant&#39;s prior application Ser. No. 198 57 735 which has already been mentioned hereinbefore. 
     FIG. 3 is a diagrammatic view showing the sleeve element  28  (see FIGS. 1 and 2) in a development. The sleeve element  28  has two diametrally mutually opposite slot-shaped slide paths  30 . Each of the two slide paths  30  has a fast-displacement portion  54  of large pitch and an adjoining process regulation and deceleration portion  56  of comparatively small pitch The fast-displacement portion  54  of the respective slot-shaped slide path  30  is determined in the peripheral direction of the sleeve element  28  by an acceleration rotational portion  58  to which the acceleration needle stroke  60  corresponds, in the axial direction. Advantageously, a fast idle stroke movement of the needle element  24  takes place along that acceleration needle stroke  60  when the sleeve element  28  is rotated about the center line  42  of the needle element. In that case the sleeve element  28  therefore only performs a rotary movement about a rotary angle corresponding to the acceleration rotational portion  58  which is less than 180 degrees of angle. 
     The process regulation and deceleration portion  56  of the respective slot-shaped slide path  30  is determined in the peripheral direction of the sleeve element  28  by a process regulation rotational portion  62 . Associated with the process regulation rotational portion  62  is an axial process regulation and deceleration needle stroke  64  which is small in comparison with the acceleration needle stroke  60 . 
     The transition between the fast-displacement portion  54  and the process regulation and deceleration portion  56  of the respective slot-shaped slide path  30  is in the form of a rounded slide curve portion  66 , the radius of curvature of which is identified by R in FIG.  3 . 
     The process regulation and deceleration portion  56  of the respective slot-shaped slide path  30  is adjoined, on the side remote from the fast-displacement portion  54 , by a self-locking portion  68  which is of zero pitch. The self-locking portion  68  of the respective slot-shaped slide path  30  has a short locking rotational portion  70  in the peripheral direction. 
     The fast-displacement portion  54  of each slot-shaped slide path  30  is adjoined on the side remote from the process regulation and deceleration portion  56  by a catch hook portion  72  which prevents the follower element  50  moving out of the associated slot-shaped slide path  30  in the event of over-actuation of the drive device. Separation of the needle element  24  from the sleeve element  28  of the converting device  26  is therefore prevented by means of the catch hook portions  72 . 
     The pitch angle of the process regulation and deceleration portion  56  is indicated in FIG. 3 by the arcuate angle  74 , the pitch angle of the fast-displacement portion  54  is indicated by the arcuate double-headed arrow  76  and the pitch angle of the catch hook portion  72  is indicated by the arcuate double-headed arrow  78 . The pitch angles  74  and  76  are smaller than 90 degrees of angle. The pitch angle  78  of the catch hook portion  72  is greater than 90 degrees of angle in order to form a catch hook. 
     While the fast-displacement portion  54  with a large pitch angle  76 , upon rotation of the sleeve element  28 , therefore permits a fast idle stroke displacement of the needle element  24 , the pitch angle  74  of the process regulation and deceleration portion  56  of the respective slot-shaped slide path  30  is so dimensioned that when the drive is stationary a self-locking effect occurs or during process regulation the device affords balanced sensitivity and reactivity on the part of the needle element  24 . 
     FIG. 5 is a sectional view similar to FIGS. 1 and 2 showing a portion of a needle element  24 , which extends trough a hot channel distributor block  22 . A drive gear  36  with its two trunnions  80  facing in opposite directions is supported rotatably between a holding and centering element  40  above the hot channel distributor block  22  and a clamping plate  14  which is covered by an insulating plate  16 . The drive gear  36  which is operatively connected to a drive device (not shown) is for example in the form of a cylindrical pinion meshing with a cylindrical drive output gear  32  which is also in the form of a pinion. The drive output gear  32  is an integral component of a sleeve element  28  which is fixedly connected to the needle element  24 . For that purpose the sleeve element  28  is provided for example with a female screwthread and the needle element  24  on a portion  44  of enlarged cross-section is provided with a male screwthread which matches same. In this embodiment as shown in FIG. 5 the sleeve element  28  is therefore in the form of a unit with the needle element  24 . The sleeve element  28  is rotatably supported in the clamping plate  14  and is displaceable axially, that is to say in the direction of the center line  42  of the needle element. The sleeve element  28  is formed on the inside with two diametrally oppositely disposed slot-shaped slide paths  30 , as are shown in FIG. 3 as a development and as have been described in detail hereinbefore. A follower element  50  which is in the form of a pin projects into the diametrally oppositely disposed slot-shaped slide paths  30 . The follower element  50  is mounted to a holding element  82  which is axially immovably fixed between the clamping plate  14  and the insulating plate  16  and which is secured to prevent rotational movements about the center line  42  of the needle element by means of pins  84  on the stationary clamping plate  14 . In this embodiment therefore the follower element  50  is non-rotatable and axially immovable. 
     When the sleeve element  28  with its drive output gear  32  is driven in rotation by means of the drive gear  36 , the relative rolling movement between the stationary and non-rotatable follower element  50  and the slot-shaped slide paths  30  in the sleeve element  28  affords a rotational movement of the needle element  24  about its center line  42  and simultaneously a corresponding axial displacement of the needle element  24 , which takes place quickly during the idle stroke and slowly and precisely during the process regulation and deceleration stroke. 
     FIG. 6 shows a portion of a development of the sleeve element  28  with two slot-shaped slide paths  30  and the fast-displacement portion  54  thereof and the adjoining process regulation and deceleration portion  56  as well as the rounded slide curve portion  66  between the two portions  54  and  56 , of the radius of curvature R, and the self-locking portion  68  with the zero pitch. 
     In order to keep the pressure in relation to surface area as between the follower element  50  and the slot-shaped slide paths  30  at a minimum, this embodiment provides that the follower element  50  which is in the form of a pin has a flattened sliding surface  86 . The sliding surface  86  can be curved or of a flat configuration. The sliding surface  86  slides along the control curve surfaces  88  which are loaded with the highest counter pressure forces, in which respect the pressure in relation to surface area as between the follower element  50  and the slot-shaped slide paths  30 , along the process regulation and deceleration portion  56  and the self-locking portion  68 , is reduced by the enlarged sliding surface  86 . That results in a higher load-bearing capability or resistance to wear. So that adaptation of the sliding surface  86  to the control curve surfaces  88  is at the optimum, the follower element  50  can be mounted cylindrically, that is to say with a round cross-section, in the holding element  82 , thereby affording rotational adaptation to the control curve surfaces  88  of the slide paths  30 . 
     To enhance the performance of the individual components, they can be hardened or coated for hardening thereof. 
     FIG. 7 shows a development similar to that shown in FIG. 3 illustrating the sleeve element  28  with two diametrally oppositely disposed slot-shaped slide paths  30 , each of which has a fast-displacement portion  54  of large pitch and an adjoining process regulation and deceleration portion  56  of comparatively small pitch. 
     The same features are denoted in FIG. 7 by the same references as in FIG. 3 so that there is no need for all those features to be described once again in detail with reference to FIG.  7 . 
     While in FIG. 3 the two diametrally oppositely disposed slot-shaped slide paths  30  are separated from each other in the peripheral direction, FIG. 7 shows a structure in which the slot-shaped slide paths  30  are respectively connected to each other by means of a needle return portion  90  so that this involves a slide path which is closed in itself, around the slide path surface which is concentric with the center line of the needle element. The respective needle return portion  90  is of a pitch which is indicated by the arcuate arrow  92  and whose pitch angle is larger than the pitch angle of the respective fast-displacement portion  54 , as is indicated by the arcuate arrow  76 . This provides that, upon a stepwise rotary movement of the drive device, that is to say the sleeve element  28 , in a single direction of rotation, the return movement of the needle element  24  (see FIG. 1 or FIG. 2) takes place more rapidly than the fast displacement of the needle element in a direction towards the mold cavity  52 . 
     It will be appreciated that the pitch angle  92  of the respective needle return portion  90  must not be greater than the pitch angle  76  of the respective fast-displacement portion  54 . 
     FIGS. 8 and 9 show an embodiment of the converting device  26  for a needle element  24 , wherein the sleeve element  28  of the converting device  26  has a slide path  30  with two slide surfaces  94  and  96  which are disposed in diametrally and axially opposite relationship on the slide path surface concentric with respect to the center line  42  of the needle element, and which are arranged in mutually parallel relationship, wherein bearing against each of the two axially oppositely disposed slide surfaces  94  and  96  is an associated portion of the follower element  50 . This therefore does not involve a slot-shaped slide path but a slide path which is open at one respective side. The same features are also identified in FIG. 9 by the same references as in FIGS. 3 and 7 so that there is no need for all those features to be described once again with reference to FIG. 9. A corresponding consideration also applies to FIG. 8 in which identical features to those in FIGS. 1,  2  and  5  are denoted by the same references so that there is no need for all those features to be described in detail once again with reference to FIG.  8 . It is clearly apparent from FIG. 8 however that the portion of the follower element  50 , which projects radially on one side, bears snugly against the slide surface  96  and that at the same time the portion of the follower element  50 , which projects diametrally on the other side, bears snugly against the axially opposite slide surface  94  so that rotation of the sleeve element  28  in one direction of rotation or the other about the center line  42  of the needle element affords an upward and downward axial movement of the needle element  24  which is prevented from rotating. 
     FIGS. 10 and 11 illustrate a configuration of the converting device  26  of the control and regulating device according to the invention, with two diametrally oppositely disposed slide paths  30  with each have a single slide surface  94 . The diametrally oppositely disposed projections of the follower element  50  are urged in this case by means of a spring device  98  against the slide surfaces  94 , which are open at one side, of the diametrally oppositely disposed open slide pats  30 . 
     FIG. 11 in which identical features are identified as in FIGS. 3,  6 ,  7  and  9  illustrates diametrally oppositely disposed slide paths  30  which are separated from each other. That is to say, it is necessary in this case for the sleeve element  28  of the converting device  26  to be rotated with a reciprocating movement in order to move the needle element axially forward and back. It will be appreciated that it would also be possible for the diametrally oppositely disposed slide paths  30  which are open at one side to be connected together in the peripheral direction, similarly to the structure shown in FIG.  7 . That is diagrammatically indicated in FIG. 11 by the double dash-dotted lines  100 . With such a design for the sleeve element  28  with a needle return portion  90  indicated by the double dash-dotted line  100 , it would then be possible for the sleeve element  28  to be driven stepwise only in one direction of rotation in order to move the needle element  14  precisely forward and back axially in an oscillation motion. 
     FIG. 10 shows the spring element  98  which is clamped in the sleeve element  28  between the end  102  of the portion  44  of enlarged cross-section of the needle element  24  and a plug  104  which is screwed into the sleeve element  28  and which is fixedly connected thereto.