Abstract:
A machining apparatus for making a plasticizing barrel includes a clamping device for securing the plasticizing barrel, with the clamping device constructed for rotation about a rotation axis and for off-center acceptance of the plasticizing barrel to thereby cause the plasticizing barrel to wobble about its symmetry axis, when the clamping device rotates. The clamping device interacts with a machining unit to provide the plasticizing barrel with an internal conical bore for receiving a screw. The machining unit has a turning tool which is movable linearly back-and-forth in a direction of the rotation axis, wherein the conical bore being produced has a center line which coincides with the rotation axis

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of prior filed copending PCT International application no. PCT/EP20051053514, filed Jul. 20, 2005, which designated the United States and has been published but not in English as International Publication No. WO 2006/010729 and on which priority is claimed under 35 U.S.C. §120, and which claims the priority of German Patent Application, Serial No. 102004036078.2, filed Jul. 24, 2004, pursuant to 35 U.S.C. 119(a)-(d), the contents of which are incorporated herein by reference in its entirety as if fully set forth herein. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates, in general, to a machining apparatus for making a plasticizing barrel, and more particularly to a machining apparatus for providing a plasticizing barrel with at least one conical bore for accepting a plasticizing screw.  
         [0003]     Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.  
         [0004]     Conical twin screw extruders typically have converging screw axes as well as a converging screw configuration. As a result of the decrease in the outer diameter, the volume of the C-shaped transport compartments is continuously reduced as the distance to the intake zone increases. This causes a continuous compaction. The conical twin screw can be constructed with sections of different but constant helix angle. As the consequence of the conicity, the screw tip has a reduced diameter so that a smaller screw back pressure is experienced at constant melt pressure as in cylindrical screws.  
         [0005]     To date, the manufacture of plasticizing barrels with conical screw bores for such conical twin screw extruders has proven difficult because, on one hand, the screw bores converge conically toward one another in conformity with the configuration of the conical screws, while on the other hand, the bore axes extend to one another.  
         [0006]     Plasticizing barrels for conical twin screw extruders are typically manufactured heretofore by firmly clamping the plasticizing barrels and then machining a first cylindrical screw bore by means of a deep drill. Then, a coarse conical configuration is realized by using cutting tools that replicate the conical profile of the screws. Finally, conical grinding tools are used for carrying out fine-machining steps. This manufacturing process takes very long and is not only complex but also cost-intensive while still not resulting in a desired quality of the inside surface of the screw bore.  
         [0007]     It would therefore be desirable and advantageous to provide an improved machining apparatus which obviates prior art shortcomings and which allows a manufacture of high-quality plasticizing barrels with conical screw bore.  
       SUMMARY OF THE INVENTION  
       [0008]     According to one aspect of the present invention, a machining apparatus for making a plasticizing barrel includes a clamping device for securing the plasticizing barrel, with the clamping device constructed for rotation about a rotation axis and for off-center acceptance of the plasticizing barrel to thereby cause the plasticizing barrel to wobble about its symmetry axis, when the clamping device rotates, and a machining unit for providing the plasticizing barrel with an internal conical bore for receiving a screw, with the machining unit having a turning tool which is movable linearly back-and-forth in a direction of the rotation axis, wherein the conical bore being produced has a center line which coincides with the rotation axis.  
         [0009]     The present invention resolves prior art problems by the off-center disposition of the plasticizing barrel with respect to it symmetry axis so that the plasticizing barrel is caused to wobble about a rotation axis, when being rotated. The rotation axis corresponds hereby to the later screw bore axis. While the plasticizing barrel rotates, a turning tool is introduced into a previously formed crude bore, whereby the turning tool itself does not rotate but is movable back-and-forth in the direction of the rotation axis. As a the plasticizing barrel and the turning tool rotate relative to one another and the turning tool bears against the inside of the internal bore to be made, the wobbling motion causes formation of a conical inner surface. The degree of conicity may hereby be predefined by the extent of the off-center securement of the plasticizing barrel.  
         [0010]     According to another feature of the present invention, the clamping device may have a first clamping chuck for securing one end of the plasticizing barrel, and a second clamping chuck for securing another end of the plasticizing barrel. The clamping chucks may either be securely fixed to a rotating mounting or held rotatably in a bearing assembly.  
         [0011]     According to another feature of the present invention, a balance weight may be provided for compensating an unbalance as a result of the off-center securement of the plasticizing barrel. The balance weight may be secured to the clamping device, or the balance weight may be secured or securable to the plasticizing barrel.  
         [0012]     According to another feature of the present invention, the machining unit, which is intended for insertion into the interior of the crude bore of the plasticizing barrel, may have a boring bar for secure attachment of the turning tool so that the turning tool is movable together with the boring bar linearly through an opening of the plasticizing barrel. In this case, the boring bar, and possible other associated elements, have to be supported for linear movement. The linear movement may hereby be realized by a separate drive.  
         [0013]     According to another feature of the present invention, the boring bar may be constructed, at least partly or about a circumferential portion, of conical configuration similar to the screw bore being envisioned. As a result, the overall stability is enhanced and the boring bar is supported in the conical bore being made.  
         [0014]     In order to further support the boring bar to attain a secure hold, a support device in the form of a support mandrel or other type of support element may be provided on the respective ends of the boring bar outside the plasticizing barrel.  
         [0015]     According to another embodiment of the present invention, the machining unit may have a base body in the form of a boring bar, and a drive for linearly moving the turning tool back-and-forth on the boring bar. In this case, the boring bar does not move jointly with the turning tool back-and-forth. Solely the turning tool is moved by a separate drive in linear direction. Suitably, the boring bar has guide and bearing elements for proper support.  
         [0016]     According to another feature of the present invention, the drive for the turning tool may hereby be constructed in the form of a spindle-nut assembly or a rack-and-pinion assembly.  
         [0017]     In accordance with the present invention, a plasticizing barrel can be formed with a conical screw bore in a simple and rapid manner without the need for special conical tools. Conicity of the internal bore depends solely on the off-center disposition of the plasticizing barrel in the clamping device. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0018]     Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:  
         [0019]      FIG. 1   a  is a schematic, partially sectional view of a clamping device for an off-center disposition of a plasticizing barrel in accordance with the present invention;  
         [0020]      FIG. 1   b  is a schematic illustration of one embodiment of a machining unit according to the present invention;  
         [0021]      FIGS. 2   a - 2   c  are schematic illustrations of various machining steps for providing the plasticizing barrel with a conical screw bore;  
         [0022]      FIG. 3  is a schematic illustration of another embodiment of a machining unit according to the present invention;  
         [0023]      FIG. 4  is a schematic illustration, on a reduced scale, of the machining unit of  FIG. 3 ;  
         [0024]      FIG. 5   a  is a schematic, partially sectional view of a machining apparatus according to the present invention with off-center securement of the plasticizing barrel and a machining unit according to  FIG. 3 ;  
         [0025]      FIG. 5   b  is a schematic, partially sectional view of the machining apparatus of  FIG. 5   a  with depiction of a balance weight; and  
         [0026]      FIGS. 6   a - 6   c  are schematic illustrations of various machining steps executed by the machining unit of  FIG. 3  for providing the plasticizing barrel with a conical screw bore. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0027]     Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.  
         [0028]     Turning now to the drawing, and in particular to  FIG. 1   a , there is shown a schematic, partially sectional view of a clamping device, generally designated by reference numeral  10 , for an off-center disposition of a plasticizing barrel  20  in accordance with the present invention. The clamping device  10  includes two clamping chucks  12 ,  14  in spaced-apart disposition for securing opposite ends of the plasticizing barrel  20  being machined. The off-center acceptance of the plasticizing barrel  20  is shown in  FIG. 1   a , whereby the continuous line  21  depicts the outline of the plasticizing barrel  20  in a first rotation position, while the dotted line  22  depicts the outline of the plasticizing barrel  20  in a 180° rotated rotation position. Reference numeral  24  designates the intended inner conical configuration for the inner screw bore to be produced, and reference numeral  26  designates the rotation axis about which the plasticizing barrel  20  executes a wobbling motion, when the clamping chucks  12 ,  14  rotate.  
         [0029]     The clamping chuck  14  is rotatably mounted in a bearing assembly  18  which is shown only partially in  FIG. 1   a . The bearing assembly  18  may be constructed to completely enclose the clamping chuck  14  and to allow a rotation of the clamping chuck  14  in the absence of any axial movement. The clamping chuck  12  is secured to a mounting  16  which is caused to rotate by a not-shown drive. Structure and operation of such a drive for rotating the mounting  16  are known to the artisan so that a detailed description is omitted for the sake of simplicity.  
         [0030]     To compensate the unbalance caused by the off-center securement of the plasticizing barrel  20 , a balance weight  30  is provided to extend between the clamping chucks  12 ,  14 . The balance weight  30  is shown only schematically for illustrative purposes because the actual configuration depends, of course, on the dimension of the plasticizing barrel  20  as well as on the extent of the off-center disposition.  
         [0031]     Adjacent to the mounting  16 , the clamping chuck  12  is formed with a receiving bore  32  for support of a machining apparatus  40 , as shown in  FIG. 1   b , or a machining apparatus  100 , as shown in  FIG. 3 .  
         [0032]     The machining apparatus  40  includes a boring bar  42  which is vibration-damped and constructed, at least partially about its circumference with a conicity in correspondence to the conicity of the screw bore being formed. The boring bar  42  has a forward end which is extended by a ground cylindrical support mandrel  44 . A turning tool or chisel  64  is securely mounted approximately in a transition area between the boring bar  42  and the support mandrel  44 . A drive  48  is mounted to the rear end of the boring bar  42  for linear movement of the arrangement of boring bar  42 , support mandrel  44  and turning tool  46 , via a driving element  50 , not shown in greater detail.  
         [0033]     Although not shown in detail, the radial dimension of the turning tool  46  may be adjusted manually (e.g. in the range of 2 mm) using a vernier.  
         [0034]     Turning now to  FIGS. 2   a - 2   c , there are shown schematic illustrations of various machining steps for providing the plasticizing barrel  20  with a conical screw bore by means of the machining unit  40  in cooperation with the eccentrically arranged and rotatably-driven plasticizing barrel  20 . For ease of illustration, clamping chucks  12 ,  14  and balance weight  30  have not been shown in  FIGS. 2   a - 2   c.    
         [0035]     As shown in  FIG. 2   a , the support mandrel  44  is inserted through an opening of the plasticizing barrel  20  into a crude bore, having been formed previously, and juts out from the opposite end of the plasticizing barrel  20 . The support mandrel  44  extends hereby also through the receiving bore  32  of the plasticizing barrel  20 . For enhancing the overall integrity, the outwardly jutting end of the support mandrel  44  is supported by a support bushing  56 , the mounting of which is not shown in greater detail. Likewise the boring bar  42  on the opposite entry side of the plasticizing barrel  20  is held in place by a support device  58 . The machining process commences by causing the plasticizing barrel  20  to rotate which thus undergoes a wobbling motion about the rotation axis  26  ( FIG. 1 ).  
         [0036]     In the depiction of  FIG. 2   a , the turning tool  46  assumes a position at the (right) entry side of the inner bore of the plasticizing barrel  20  so that material is removed from the inside of the plasticizing barrel  20  as it turns. The entire machining unit  40  with boring bar  42 , support mandrel  44  and turning tool  46  moves continuously to the left to thereby progressively machine the inside contour for formation of the conical bore, as shown in  FIG. 2   b . After reaching the left end of the plasticizing barrel  20 , the conical screw bore has been substantially formed, as shown in  FIG. 2   c . Optionally, a further fine machining step may be executed in a same manner.  
         [0037]     Referring now to  FIGS. 3 and 4 , there are shown schematic illustrations of another embodiment of a machining unit according to the present invention, generally designated by reference numeral  100 . The machining unit  100  differs from the machining unit  40  in that the boring bar  102  is received essentially immobile within the plasticizing barrel  20 . The (left) leading end of the boring bar  102  is constructed in the form of a guide pin  104  which is ground and hardened. The guide pin  104  is received in a guide bushing  124  of the clamping chuck  12 , as shown in  FIG. 5   a . A drive  110  is attached via a screwed-on dovetail-type guidance  120  to the (right) trailing end of the boring bar  102 . The drive  110  operates a rack  106  through intervention of a gear mechanism  112 , shown only schematically, with the rack  116  being guided in a groove of the boring bar  102 , as indicated in  FIG. 4 . The rack  116  has a left-hand end for attachment of a turning tool  106 . Operation of the drive  110  causes adjustment of the rack  116  so that the turning tool  106  can be moved linearly back-and-forth. For enhancing stability, a support  118  is suitably provided to underpin the rack  116  at the side of the drive  110  distal to the turning tool  106 . Reference numeral  114  designates a coolant supply for flushing the rack  116 .  
         [0038]     Unlike the machining unit  40 , the turning tool  106  of the machining unit  100  moves in relation to the boring bar  102 . In other words, only the turning tool  102  executes a movement in the inner bore of the plasticizing barrel  20 .  
         [0039]     The interaction between the machining unit  100  and the off-center plasticizing barrel  20  is shown in  FIGS. 5   a  and  5   b . The plasticizing barrel  20  is held off-center between the clamping chucks  12 ,  14  and is caused to rotate about the rotation axis  26 . The clamping chuck  14  is held by bearing assembly  18 . As further shown in  FIGS. 5   a ,  5   b , the clamping chuck  12  of the machining unit  100  includes a sliding ring  122  in which the guide bushing  124  is arranged for acceptance of the guide pin  104  of the boring bar  102 . A sealing bush  126  is disposed in prolongation of the clamping chuck  12  and suitably connected to a supply line for introduction of water which is fed via the guide bushing  124  into the inner bore of the plasticizing barrel  20 .  FIG. 5   b  shows the disposition of the balance weight  30  for compensating the unbalance as a consequence of the off-center securement of the plasticizing barrel  20 . For ease of illustration, the balance weight  30  is not shown in  FIG. 5   a , although it is, of course, a permanent part of the machining unit  100 .  
         [0040]     Turning now to  FIGS. 6   a - 6   c , there are schematic illustrations of various machining steps by the machining unit  100  of  FIG. 3  for transforming the initially crude inner bore of the plasticizing barrel  20  into a screw bore of conical configuration. As shown in  FIG. 6   a , the boring bar  102  is inserted in the crudely pre-fabricated conical bore of the plasticizing barrel  20 , with the turning tool  106  assuming a position at the (right) entry zone of the inner bore. The guide pin  104  is hereby rotatably received in the guide bushing  124 . As the plasticizing barrel  20  is caused to rotate, the turning tool  106  moves to the left along the entire length of the plasticizing barrel  20  so as to form the inner contour  24  of the plasticizing barrel  20 , as shown in  FIGS. 6   b  and  6   c . The rotation of the plasticizing barrel  20  is realized by the motor  110  via the gear mechanism  112  and rack  116 . As an alternative, it is, of course, conceivable to apply a different type of drive such as, for example, a spindle drive with spindle and nut combination.  
         [0041]     The overall drive with motor  110 , gear mechanism  112  and rack  116 , and the boring bar  102  remain essentially immobile in axial direction during the machining operation in relation to the plasticizing barrel  20 . However, as shown in  FIGS. 5   b  and  6   c , the boring bar  102  can be shifted slightly forwards, i.e. to the left in the drawing. This can be recognized in particular by the overhang of the guide pin  104 . As a result of this shift, the diameter of the conical bore can be widened within limits so that the diameter is the greatest following the last machining step of  FIG. 6   c.    
         [0042]     While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.