Abstract:
The invention is directed to a device for extruding viscoelastic matter, in particular pastas. This device has a filling area for introducing matter or constituents of the matter into the device, a conveying area for conveying and processing the flow of matter conveyed through the device, a distributor area for deforming and distributing the flow of matter to a plurality of partial flows of matter, and a die area with a plurality of dies for forming a strand or sheet from the respective partial flows of matter. According to the invention, the inner walls of the distributor area are formed from a viscoelastic material at least in some areas or have a viscoelastic material in these areas.

Description:
[0001]    The present application claims priority from PCT Patent Application No. PCT/CH2007/000424 filed on Aug. 28, 2007, which claims priority from German Patent Application No. DE 10 2006 041 301.6 filed on Sep. 1, 2006, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention is directed to a device for the extrusion of viscoelastic matter, in particular for the extrusion of dough, with a step for forming strands or flat, foliate or sheetlike shapes from the viscoelastic matter. 
         [0004]    2. Description of Related Art 
         [0005]    Known devices for extrusion have a filling area for introducing matter or constituents of matter into the device, a conveying area for conveying and processing the flow of matter conveyed through the device, a distributor area for deforming and distributing the flow of matter to a plurality of partial flows of matter, and a die area with a plurality of dies for forming a strand or sheet from the respective partial flows of matter. 
         [0006]    During the conveying, processing, distributing and forming of strands, flat shapes, or the like, relative flow processes take place in the interior of a viscoelastic matter between different areas of the matter and tensions develop in the matter at the same time. 
         [0000]    These tensions are quickly reduced by compensating flow processes only in part, while a residual proportion of tension enters into the deformed matter, e.g., into the strands or flat shapes. Particularly when forming strands or (foliate or sheetlike) flat shapes from viscoelastic matter of this kind, the flow processes and tensions occurring inside the matter are very considerable due to the intensive deformation and distribution of the flowing matter so that the corresponding residual tensions in the strands or flat shapes are also high. This leads to internal forces and unwanted distortions in the deformed shapes (strands or flat shapes) resulting in particular in a tendency for the strands to twist or curl and in distortions in flat shapes, i.e., undesirable deviations from the straight or flat shape. 
         [0007]    These problems are especially pronounced when extruding strands from dough to form specially shaped pastas (e.g., spaghetti) which then deviates from the straight shape. In extreme cases, this can even result in complete or compound curling of the strands. 
       SUMMARY OF THE INVENTION 
       [0008]    It is the object of the invention to substantially eliminate such tensions in the extruded strands and flat shapes of viscoelastic matter or at least to reduce them to the extent that there are no sharp deviations from straightness of from the flat shape under normal conditions of strand extrusion or sheet extrusion. 
         [0009]    According to the invention, this object is met in a known device of the type described above in that the inner walls of the distributor area are also formed from a viscoelastic material at least in some areas or have a viscoelastic material in these areas. 
         [0010]    To avoid confusion, the material to be deformed will always be referred to hereinafter as “viscoelastic matter” which flows under normal operating conditions (temperature, pumping capacity), while the “viscoelastic material” in the wall areas is generally a synthetic material which, while elastically deformable under normal operating conditions, cannot flow therefrom. 
         [0011]    The viscoelastic areas can be constructed as cushiony elements having a closed flexible shell or chamber which is filled with a filling of viscoelastic material. The filling can be any viscoelastic material. At one extreme is a purely viscous filling material without elastic components. In this case, a material with elastic components and no viscous components is selected as the shell material. At the other extreme is a purely elastic filling material without viscous components. In this case, the shell is superfluous. 
         [0012]    It is important that the inner walls of the distributor area are resiliently and elastically deformable at least in some areas, but cannot flow therefrom. Therefore, at least the shell material must be purely elastic without viscous components. 
         [0013]    Solid, elastically deformable elements can also be used instead of the above-mentioned cushions with an elastic shell and a filling material having at least one viscous component. 
         [0014]    The viscoelastic areas can also have one or more gas-filled chambers, wherein the shell material forming the chambers is a flexible material whose flexibility is due to the thin-walls and/or elasticity of the shell material. 
         [0015]    In conventional distributor areas with consistently rigid inner walls, asymmetric velocity profiles result when the viscoelastic matter is pressed through the curved distributor channels. This asymmetry of the velocity profiles is incompatible with the symmetrical dies arranged at the end of the distributor channels for forming strands or sheets and leads to unwanted tensions in the formed strands or sheets of matter. 
         [0016]    In the distributor area with curved channels in which an intensive deformation (sheet extrusion) and also, as the case may be, a splitting (strand extrusion) of the viscoelastic matter to be processed takes place, the inventive flexibility and elastic deformability of the inner walls at least in some portions of this distributor area results in an improved reduction at least of the asymmetrical mechanical tensions in the deforming viscoelastic matter and a sharp suppression of the tendency to develop such tensions. This is accomplished in that the development of asymmetrical velocity profiles in the curved areas of the distributor channels which accompanies the formation of at least asymmetrical material tensions is substantially prevented and, on the whole, the remaining, substantially symmetrical velocity profiles are less pronounced. In other words, the device according to the invention generates flatter, more uniform velocity profiles whose symmetry is adapted to the symmetry of the die(s). 
         [0017]    In a particularly advantageous embodiment of the device according to the invention, the inner walls of the dies are also formed of a viscoelastic material at least in some areas. This step makes it possible to prevent or mitigate possible residual tensions, but above all asymmetric residual tensions, also in the dies, i.e., in the final phase of deformation. 
         [0018]    While the development of near-parabolic velocity profiles in the substantially laminar flow of viscoelastic matter is inevitable due to the wall friction which is always present in practice, the present invention ensures that there are substantially symmetrical and flat velocity profiles following the distributor area at the entrance into the die(s) and preferably also after the passage of the matter through the die(s). 
         [0019]    The viscoelastic material on or in the walls can have an elastomer. 
         [0020]    The viscoelastic material is advisably embedded in recesses (cavities) in the inner walls of the device. During operation, it comes into contact with the viscoelastic matter and carries out the compensating movements as a result of which the velocity profiles in the flowing matter are made more uniform or the uniformity of the velocity profiles is maintained. By “uniformity” is meant the flattest possible velocity profile whose symmetry is adapted as well as possible to the die symmetry. 
         [0021]    In an alternative construction, the viscoelastic material embedded in the inner-wall recesses (cavities) of the device is formed by a portion of the viscoelastic matter located in the inner-wall recesses (cavities). The inner-wall recesses are used in this case specifically as dead zones for the viscoelastic matter to be deformed which therefore takes over the function of the viscoelastic material described above. This constitutes an exception to the distinction between “viscoelastic matter” and “viscoelastic material.” 
         [0022]    The inner-wall recesses (cavities) are preferably arranged at the inner wall portions where the flow of viscoelastic matter is locally accelerated. This local acceleration of the viscoelastic matter is counteracted by the compensating movements of the viscoelastic material. 
         [0023]    The inner walls of the distributor area in their entirety are advisably formed of a viscoelastic material. In this case, a full lining of the dies is used. 
         [0024]    Alternatively or in addition, the inner walls of the die(s) in their entirety can also be formed of a viscoelastic material. In this case, a full lining of the distributor is used. 
         [0025]    During operation, compensating movements or compensating deformations of the viscoelastic material (“passive peristalsis”) occur in the areas of these linings. 
         [0026]    The distributor area is preferably formed in its entirety of a viscoelastic material. 
         [0027]    Alternatively or in addition, the dies can also be formed in their entirety from a viscoelastic material. 
         [0028]    It is advantageous when the partial areas in which the viscoelastic material is arranged are dead zones or retention zones of the flow of matter. 
         [0029]    In addition to the passive steps mentioned above for homogenizing the velocity profiles, active measures can also be provided in the device according to the invention. 
         [0030]    A controllable valve can be arranged between the distributor area and the respective dies of the die area. 
         [0031]    In this connection, it is advantageous when the device also has a pressure sensor upstream of the respective valve. 
         [0032]    The respective valve is preferably controllable as a function of pressure signals of the pressure sensor. 
         [0033]    The cushiony areas described above can also be provided with active elements. 
         [0034]    The viscoelastic areas can be constructed as cushiony elements which have a closed flexible shell or chamber which is filled with a filling of viscoelastic material. 
         [0035]    The filling of the cushions can be any viscoelastic material which communicates with a controllable pressure source. As was mentioned earlier with regard to the cushiony elements, the viscoelastic filling material can be a liquid or a gas that is enclosed by a flexible shell. 
         [0036]    It is also important in this regard that the inner walls of the distributor area are resiliently and elastically deformable at least in some areas, but cannot flow therefrom. Therefore, at least the shell material must be purely elastic without viscous components. 
         [0037]    Solid, elastically deformable elements which can be bent, pressed, elongated, twisted or otherwise deformed by actuators can also be used instead of the cushions with an elastic shell and a filling material having at least one viscous component. 
         [0038]    The deformation of the cushiony areas by the active elements, e.g., pressure source, actuator, etc., is preferably carried out depending on pressure signals from additional pressure sensors arranged in the distributor area and/or die area of the device according to the invention. 
         [0039]    Further advantages, features and possible applications of the invention are indicated in the following description of embodiment examples, which are not to be interpreted as limiting, with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0040]      FIG. 1  is a sectional view of a portion (distributor area and die area) of a first embodiment example of the device according to the invention along a vertical plane which contains the longitudinal axis of the device; 
           [0041]      FIG. 2  is a sectional view of a portion (distributor area and die area) of a second embodiment example of the device according to the invention along the vertical plane which contains the longitudinal axis of the device; 
           [0042]      FIG. 3  shows an enlarged sectional view of a portion (die only) of the first embodiment example of the device according to the invention along the vertical plane which contains the longitudinal axis of the device; 
           [0043]      FIG. 4  is an enlarged sectional view of a portion (die only) of the second embodiment example of the device according to the invention along the vertical plane which contains the longitudinal axis of the device; and 
           [0044]      FIG. 5  is a sectional view of a portion (conveying area, distributor area and die area) of a third embodiment example of the device according to the invention along a vertical plane which contains the longitudinal axis of the device. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0045]    It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, many other elements which are conventional in this art. Those of ordinary skill in the art will recognize that other elements are desirable for implementing the present invention. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. 
         [0046]    The present invention will now be described in detail on the basis of exemplary embodiments. 
         [0047]    Hereinafter, the viscoelastic matter to be processed and deformed will be referred to simply as “matter.” 
         [0048]      FIG. 1  is a sectional view of a distributor area  20  and a die area  30  of a first embodiment example of the device according to the invention along a vertical plane which contains the longitudinal axis of the device. 
         [0049]    The distributor area  20  has two curved channels  21  and  22  in which the matter M is divided into a first partial flow of matter M 1  and a second partial flow of matter M 2 . The distributor area  20  is formed by a housing  23  and an insert  24  which is inserted into the housing  23  and which can comprise more than one piece. The housing  23  is preferably made of metal, while the insert  24  is preferably made of a polymer such as, e.g., Teflon, PEEK, or the like. 
         [0050]    The die area  30  has two dies  31  which are inserted into a die plate  33 . Each die  31 ,  31  connects to one of the curved channels  21 ,  22 . The die plate is preferably made of metal, while the dies  31 ,  31  are made of metal or a polymer such as Teflon, PEEK, or the like. 
         [0051]    The curved channels  21 ,  22  are indicated by a solid line. The successive velocity profiles PI, P 2  and P 3  in the flow direction of the partial flows of matter Ml and M 2  flowing in the curved channels  21 ,  22  correspond to this channel geometry. These profiles are shown only for the upper curved channel  21 . However, they are also formed in the same way in the lower channel  22  symmetric to those of the upper channel  21 . Recesses (cavities) indicated by dashed lines  21 ′ and  22 ′, respectively, are incorporated into the walls of the channels  21 ,  22  at the locations where the matter Ml and M 2  is locally accelerated, i.e., on the walls in the “outside curve” of the curved channels  21 ,  22 . The velocity profiles P 1 ′, P 2 ′ and P 3 ′ of the partial flows of matter M 1  and M 2  flowing in the curved channels  21 ′,  22 ′ correspond to this channel geometry outfitted with the recesses  21 ′,  22 ′. These modified velocity profiles which occur as a result of the wall recesses in the areas of local acceleration are much flatter than profiles P 1 , P 2  and P 3 . Further, these profiles P 1 ′, P 2 ′ and P 3 ′ are practically just as highly homogenized as profile P 0  of the flow of matter M before the latter is divided into the partial flows of matter M 1  and M 2 . 
         [0052]    Another insert  28  which is preferably made of the same material as insert  24  is arranged at the respective channel-die transition from the curved channels  21  and  22  to the respective die  31 . The inserts  28  optimize the shape of the wall between channel  21  or  22  and the respective die  31  following the latter. In this respect, it is important that this wall shape or wall profile has an inflection point  29 . Naturally, the dies  31  can also be constructed to be correspondingly longer so that a die of this kind is formed of the insert  28  and the die  31  integrally. 
         [0053]    The steps mentioned above ensure that velocity profiles P 1 ′, P 2 ′ and P 3 ′ which are relatively flat and uniform across the channel cross section and whose symmetry is adapted to the die symmetry are generated in spite of the directional deflection of the partial flows of matter M 1  and M 2 . As a result, the strands M 3  and M 4  of matter or sheets M 3  and M 4  of matter proceeding from the partial flows of matter Ml and M 2  exit the dies  31  after their final deformation with very few tensions overall, these tensions being predominantly symmetric to the strand shape or sheet shape. 
         [0054]      FIG. 2  shows a sectional view of a distributor area  20  and a die area  30  of a second embodiment example of the device according to the invention along a vertical plane containing the longitudinal axis of the device. 
         [0055]    The second embodiment example is distinguished from the first embodiment example in that:
   1) instead of recesses  21 ′,  22 ′, the channels  21  and  22  are outfitted in each instance with an insert of viscoelastic material  25  and  26 , respectively, which is inserted in recesses of the channel wall;   2) instead of the inserts  28  at the transitions between the channel and die, an insert  27  of viscoelastic material is provided; and   3) instead of dies  31  (see  FIG. 3 ), dies  32  having a different shape (see  FIG. 4 ) are provided.   
 
         [0059]    The parts identical to those in the first embodiment example are provided with the same reference numbers as in the first embodiment example. 
         [0060]    The inserts  25  and  26  formed of the viscoelastic material yield to pressure but are resilient. These inserts are flexible and can retard accelerated areas of the partial flows of matter M 1  and M 2  similar to the recesses (cavities) in the first embodiment example. They carry out a kind of passive peristalsis. 
         [0061]      FIG. 3  shows an enlarged sectional view of a die  31  of the first embodiment example of the device according to the invention along the vertical plane which contains the longitudinal axis of the device. 
         [0062]    The die base body  31   a  contains a goblet-shaped passage which widens against the flow direction of matter from the center of the die to the die entrance and with the flow direction of matter toward the die outlet as can be seen from the die wall profile  31   c . The insert  28  whose passage narrows in diameter in the flow direction as can be seen from the insert wall profile  31   b  is arranged upstream of the die entrance. Together, the insert  28  and the die base body  31   a  form a die passage whose inner wall profile ( 31   b + 31   c ) is basically S-shaped, i.e., has an inflection point  29 . 
         [0063]      FIG. 4  shows an enlarged sectional view of a die  32  of the second embodiment example of the device according to the invention along the vertical plane which contains the longitudinal axis of the device. 
         [0064]    The die base body  32   a  has a goblet-shaped portion of the passage on the die entrance side which widens against the flow direction of matter from the center of the die to the die entrance as can be seen from the die wall profile  32   b.  Another portion of the passage which is substantially cylindrical but is constructed adaptively is arranged on the die outlet side. A tubular or tube-like element  32   c  of energy-elastic or entropy-elastic material is inserted into the die base body  32   a  and anchored therein by frictional and/or positive engagement. The die base body  32   a  is cut out to a greater extent in the area of the die outlet so that an annular gap  32   d  is formed between the cylindrical, adaptive element  32   c  and the base body  32   a.  This allows a great flexibility of the die outlet. The flexibility of the adaptive element is determined by the Young&#39;s modulus and the wall thickness of the elastic material of the cylindrical element  32   c,  which is preferably an elastomer, as well as by the axial length and radial width of the annular gap  32   d.    
         [0065]      FIG. 5  is a sectional view of a conveying area  10  and a distributor area  40  of a third embodiment example of the device according to the invention along a vertical plane which contains the longitudinal axis of the device. 
         [0066]    A portion of the conveying area  10  is indicated schematically and has an extruder screw  11 . A plurality of elements  41 ,  42 ,  43  and  44  serving to adjust the channel cross section in the distributor area/transitional area  40  are located in the distributor area (or transitional area between the conveying area and the die area, not shown)  40 . A spindle  41  which is rotatably mounted in the distributor housing  46  cooperates with a radial slide  42  by means of a thread connection (not shown) so that the slide  42  can be moved in radial direction by rotation of the spindle  41 . The radial slide  42  in turn cooperates with an axial slide  43  by means of a sliding connection. This sliding connection is formed by a sliding surface  42   a  of the radial slide  42  and a sliding surface  43   a  of the axial slide  43  which contact one another. An annular channel through which the matter M flows and whose cross section can be adjusted by the axial displacement of the axial slide  43  by actuation of the spindle  41  is located between an element  44 , which is arranged in the center in the area of the end of the screw and which narrows in diameter along the flow direction of matter, and the axial slide  43 . 
         [0067]    The axial slide  43  has a passage which extends in axial direction and which is goblet-shaped similar to the die  31 . Further, adaptive, i.e., elastomeric, elements  45  having an effect similar to that of the elements  25 ,  26 ,  27  and  32   c  described above are arranged in this goblet-shaped passage of the axial slide  43 . 
         [0068]    A cylindrical passage which is preferably provided with a lining  47  of non-stick material adjoins the goblet-shaped passage of the axial slide  43 . The elements  43  and  44  are preferably also made of a non-stick material of this kind or are coated with such a material. 
         [0069]    While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the inventions as defined in the following claims. 
       REFERENCE NUMBERS 
       [0000]    
       
           10  conveying area 
           11  extruder screw 
           20  distributor area 
           21  channel 
           22  channel 
           23  housing 
           24  insert 
           25  insert/viscoelastic insert 
           26  inflection point/viscoelastic insert 
           27  viscoelastic insert 
           28  insert 
           29  inflection point 
           29  die area 
           30  die 
           31   a  die base body 
           31   b  insert wall profile 
           31   c  die wall profile 
           31  die 
           32   a  die base body 
           32   b  die wall profile 
           32   c  tubular or tube-like element 
           32   d  annular gap 
           32  die plate 
           40  distributor area 
           41  spindle 
           42  radial slide 
           42   a  sliding surface 
           43  axial slide 
           43   a  sliding surface 
           44  element narrowing in diameter 
           45  elastic element 
           46  distributor housing 
           47  lining 
         M matter 
         M 1  first partial flow 
         M 2  second partial flow 
         M 3  strand or sheet 
         M 4  strand or sheet 
         P 0  velocity profile 
         P 1  velocity profile 
         P 2  velocity profile 
         P 3  velocity profile 
         P 1 ′ velocity profile 
         P 2 ′ velocity profile 
         P 3 ′ velocity profile