Abstract:
Flow restriction assemblies ( 10,10   a,   10   b ) adapted to be mounted on single or twin screw extruders ( 16,16   b,   32 ) in order to allow selective adjustment of material flow through the extruders ( 16,16   b   ,32 ), with consequent alteration in back pressure, shear and mechanical energy imparted to the material being processed. The assemblies ( 10,10   a,   10   b ) each have shearlock(s) ( 12,12   a   ,12   b ) mounted on the extruder drive shaft(s) ( 30,30   a   ,30   b ), together with restriction units ( 14,14   a   ,14   b ). The units ( 14,14   a   ,14   b ) have opposed flow restriction components ( 48,50,48   a   ,50   a,   48   b,   50   b ) supported on opposite sides of the corresponding shearlocks ( 12,12   a,   12   b ) and mounted for a substantially aligned and rectilinear back and forth sliding movement. In this fashion, the clearance between the inner surfaces ( 54,54   a   ,54   b ) of the components ( 48,50,48   a   ,50   a   ,48   b   ,50   b ) and the shearlocks ( 12,12   a   ,12   h ) can be selectively adjusted. The assemblies ( 10,10   a,   10   b ) are small in size and can be located at various points along the length of extruders ( 16,32 ). Preferably, the restriction components ( 48,50,48   a   ,50   a   ,48   b   ,50   b ) are moveable such that the inner surfaces ( 54,54   a   ,54   b ) thereof may be located inboard of the outer surfaces ( 29,29   a   ,29   b ) of the screw flighting.

Description:
RELATED APPLICATION 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 11/279,379,filed Apr. 11, 2006, entitled EXTRUDER MID-BARREL ADJUSTABLE VALVE ASSEMBLY, which is hereby incorporated by reference in its entirety. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is broadly concerned with single or twin screw extrusion devices equipped with mid-barrel flow restriction assemblies permitting selective alteration of back pressure, shear and imported energy conditions, in order to optimize extrusion cooking of comestible food products. More particularly, the invention is concerned with such extruders, and the flow restriction assemblies, wherein the later have a pair of opposed, slidable restriction components and drive apparatus for selective movement of the components toward and away from the extruder screw(s) so as to achieve selective flow restriction. Preferably, the restriction components are moveable inwardly such that the inner surfaces thereof are closely adjacent the root diameter(s) of the screw(s), and more broadly to locations where such inner surfaces are located at points at least 30% of the depth of the screw. 
         [0004]    2. Description of the Prior Art 
         [0005]    Extrusion cooking devices are used in a multitude of contexts, e.g., for the fabrication of animal feeds and human food products. Generally speaking, single screw extruders include an elongated barrel having an inlet at one end and an outlet at the other equipped with a restricted orifice die. An elongated, helically flighted, axially rotatable screw is positioned within the barrel and seives to move material from the inlet toward and through the outlet. Twin screw extruders are also widely used, and include within the extruder barrel a pair of side-by-side, flighted, intermeshed screws. All such extruder devices serve to cook and form initial starting materials into final extruded products. During the course of extrusion, the starting materials are subjected to increasing levels of pressure and shear, in order to produce the desired, fully cooked, final extruded products. 
         [0006]    It is often important during the operation of extruders to ensure that appropriate levels of pressure and shear are maintained within the extruder barrels. If too little pressure or shear is exerted upon the materials being processed, the final products may be undercooked, unsanitary, and badly formed. Various approaches have been used in the past to achieve and maintain appropriate levels of pressure and shear within extruder barrels. For example, it has been known to install one or more shearlock devices along the length of extruder screws. These shearlock devices are generally in the form of annular bodies which serve to create flow restrictions or choke points within the extruder, thereby increasing back pressure and shear. However, these devices are not adjustable during the course of extrusion runs, and considerable skill is required in the selection and placement of these shearlocks to achieve the desired end. 
         [0007]    Variable restriction devices have also been proposed in the past, in order to permit on-the-go variation in flow restriction. For example, U.S. Pat. No. 4,136,968 describes a flow restriction device specifically adapted for use with twin screw extruders. In this device, use is made of opposed rotating paddle elements designed to interact with the meshed extruder screws in order to provide restricted material flow paths. 
         [0008]    However, the apparatus as described in the &#39;968 patent has a number of deficiencies. First and foremost, the design of the restriction device means that it cannot be use with single screw extruders, which is a significant drawback because it prevents application of the device on the broad spectrum of extruders presently in use. Moreover, the degree of flow restriction can be obtained with this prior design is limited, i.e., it is incapable of creating the very severe restrictions sometimes needed. By the same token, the paddles used in this device cannot be positioned so as to permit entirely unimpeded flow therepast. Hence, the design is deficient at both extremes of potential use, where no added restriction is needed and where very high restriction levels are desired. Use of rotating paddles also means that the overall width of the device is significant, and this in turn can create “dead spots” in the device and make clean out more difficult. 
         [0009]    U.S. Pat. No. 4,332,481 describes a continuous mixing machine used for mixing high molecular weight synthetic resin materials. The machine includes a pair of juxtaposed rotors including specialized, mid-rotor mixing elements. A throttling assembly is provided adjacent the mixing elements and includes a pair of relatively shiftable components which can be moved toward and away from the mixing elements. The purpose of the throttling assembly is to increase the density of the resin product, and the throttling is controlled based upon the characteristics of the raw materials. The rotors of the &#39;481 machine are not intercalated, i.e., the flighting thereon is separate and each rotates in an individual, separate dimensional envelope. In addition, the throttling components are not moveable to points inboard of the outer surfaces of the rotors. Finally, the mixing machine is designed so that the mixing elements have opposite pitches on opposite sides of the throttling assembly so as to move material in opposite directions adjacent the throttling assembly. 
         [0010]    Japanese Patent Publication JP 2-263609 discloses a kneading controller for processing of resins, and includes a pair of rotors having mid-rotor, non-intercalated kneading vanes, with a pair of opposed, shiftable throttling dams adjacent the vanes. The vanes are arranged to have forward and reverse flighting, with the rotor sections downstream of the darns being forwardly flighted. As in the case of the &#39;481 patent, the forward/reverse flighting of the vanes serves to move material both toward and away from the dams, in order to vary the residence time of material passing through the device. The dams are moveable relative to the vanes, but cannot be positioned inboard of the outer surfaces of the rotors. 
         [0011]    There is a accordingly a need in the art for an improved extruder flow restriction device which can be used with both single and twin extruders, while allowing wide variation in flow restriction levels, and being of short length so as to eliminate dead spots while facilitating cleanout. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention overcomes the problems outlined above, and provides a flow restriction assembly adapted for use with an extruder having an elongated barrel and at least one axially rotatable screw therein presenting helical flighting having an outer surface. The flow restriction assembly comprises a pair of restriction components each presenting an inner surface, with structure supporting the restriction components in generally aligned relationship on opposed sides of a rotatable extruder screw. Apparatus is also provided for selectively moving the restriction components along substantially rectilinear and aligned paths toward and away from the screw, in order to vary the clearance between the screw and the inner surfaces of the components. The restriction components are preferably moveable to positions wherein the inner surfaces thereof are inboard of the flighting outer surface. 
         [0013]    Preferably, the overall assembly includes a shearlock element mounted on the screw and rotatable therewith, with the shearlock element presenting an outer surface generally complemental with the inner surfaces of the restriction components. Specifically, the outer operating surface of the shearlock element is normally substantially circular, whereas the inner surfaces of the restriction components are of arcuate design and generally mate with the shearlock element operating surface. However, it is preferred that the shearlock element outer surface and the inner surfaces of the restriction components be cooperatively configured such that, when the restriction components are located in closest adjacency with the shearlock element, at least one flow through passageway remains open. 
         [0014]    The restriction components are advantageously mounted within a slotted body permitting inward and outward movement of the components along the aligned paths. The drive apparatus is preferably in the form of a screw drive coupled with each component, and the drive apparatus may be operated manually via cranks, or digitally controlled motors may be used. 
     
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0015]      FIG. 1  is a perspective view of a flow restriction assembly in accordance with the invention; 
           [0016]      FIG. 2  is a vertical sectional view of the flow restriction assembly in a representative open position, illustrating the internal structure thereof and also depicting alternate drive apparatus; 
           [0017]      FIG. 3  is a fragmentary, horizontal sectional view depicting the flow restriction assembly of the invention between a pair of extruder barrel sections and associated screw sections; 
           [0018]      FIG. 4  is a vertical sectional view similar to that of  FIG. 2 , but showing the assembly in its fully closed position; 
           [0019]      FIG. 5  is a side view of the assembly, with the adjacent cover plate removed; 
           [0020]      FIG. 6  is a fragmentary, perspective, exploded view depicting the connection between the drive assembly and restriction components; 
           [0021]      FIG. 7  is a vertical sectional view of another embodiment of the invention, designed for use with a twin screw extruder; 
           [0022]      FIG. 8  is a sectional view of an extruder in accordance with the invention, including a mid-barrel valve and illustrating the extruder screw helical flighting throughout the length of the extruder barrel; 
           [0023]      FIG. 9  is a fragmentary, horizontal sectional view similar to that of  FIG. 3 , but illustrating a modified restriction assembly having opposed restriction components inwardly moveable such that the inner surfaces thereof are inboard of the outer surfaces of the helical screw flighting; and 
           [0024]      FIG. 10  is a vertical sectional view similar to that of  FIG. 2 , and showing the modified assembly of  FIG. 9  in its fully closed position. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    Turning now to the drawings, a restriction assembly  10  is illustrated in  FIG. 1  and broadly includes a central shearlock element  12  and a mating, outboard restriction unit  14 . The assembly  10  is designed for use with a single or twin screw extruder such as depicted in  FIGS. 3 and 7  respectively, and is used to provide varying levels of flow restriction through the extruder barrel, in order to generate increased levels of back pressure and shear within the extruder, increasing the mechanical energy imported to the material being processed. 
         [0026]    By way of general background, the assembly  10  is designed for use in a conventional single or twin screw extruder, such as single screw extruder  16  illustrated in  FIGS. 3 and 4 . In a single screw extruder  16 , an elongated barrel  18  is provided, made up of a series of elongated, tubular, axially aligned and interconnected head section  20 . Each of these sections  20  have a pair of endmost, radially, enlarged flanges  22  that are designed to be interconnected to form a barrel  18 . In the form shown, each of the head sections  20  is equipped with an inner, helically flighted liner or sleeve  24  (in some embodiments, straight ribbed sleeves could be used in lieu of the helical sleeves). In addition, the extruder  16  includes an elongated, helically flighted screw  26  made up of screw sections  28  each located within an associated head section  20 . The screw  26  has helical flighting presenting an outer surface  29  defining the outer diameter of the screw, and a root diameter  29 ′. The screw sections  28  are mounted on a central, axially extending, hexagonal drive shaft  30  operatively coupled with the extruder drive (not shown). Alternately, a splined or keyed shaft may be employed. A twin screw extruder  32  ( FIG. 7 ) is similar, with the barrel sections thereof designed to accommodate a pair of side-by-side, flighted, intermeshed helically flighted screws  26   a  presenting outer surfaces  29   a  mounted on respective hexagonal or keyed drive shafts  30   a.    
         [0027]    In preferred forms, the extruders of the invention include screws  26 , 26   a  having forward pitch flighting on opposite sides of the assembly  10 , and most preferably throughout essentially the entirety of screws. This is illustrated in  FIG. 8 , and is important in many cases so as to maintain the flow of material through barrel  18  in a forward direction toward the barrel outlet (normally equipped with a restricted orifice die, not shown). 
         [0028]    Again referring to  FIG. 3 , it will be observed that the restriction assembly  10  of the invention is designed to be installed between a pair of head sections  20 , and also between the associated screw sections  28  therein. Alternately, an assembly  10  could be built into an extruder barrel as a permanent feature, if desired. 
         [0029]    In detail, the shearlock element  12  of assembly  10  is a solid annular metallic body having a central hexagonal bore  36  designed to receive the shaft  30 , with a circular cross section presenting an outermost smooth operating surface  38 . As such, the element  12  rotates in unison with shaft  30  and screw  26 . 
         [0030]    The restriction unit  14  includes a generally circular primary body  40  having a laterally extending through-slot  42  ( FIG. 5 ) presenting a pair of side marginal openings  44 . The body  40  is of metallic construction and has a series of axial bores  46  designed to mate with similar bores provided in the flanges  22  of head sections  20 . Threaded fasteners (not shown) are used to interconnect the body  40  between a pair of adjacent flanges  22 , so that the body  40  is in effect sandwiched between the aligned head sections  20 . 
         [0031]    The unit  14  also includes a pair of restriction components  48 , 50  which are each slidably received within the slot  42 . The components  48 , 50  are mirror images of each other and the construction thereof is best illustrated in  FIG. 6 . Thus, it will be seen that each component has a metallic jaw-like body  52  presenting an innermost arcuate surface  54 . The central region of each surface  54  is of essentially circular radius close to the radius of element  12 , whereas the outboard region of each surface  54  has a pair of endmost, out of round projections  55  which are important for purposes to be explained. Each body  52  is equipped with a circumscribing groove  56  which receives a flexible seal  58 . Each body  52  also has an integral, outwardly extending ear  60  having an end notch  62  formed therein. A plate  64  is disposed over the notch  62  and is secured in place by fasteners  66 . 
         [0032]    Unit  14  further includes a drive apparatus  68  operatively coupled with the components  48 , 50  in order to move these components toward or away from the shearlock element  12  as will be explained. The drive apparatus  68  includes a pair of drive screws  70 , 72  having forward butt ends  74 , central threaded sections  76 , and square drive ends  78 . Again referring to  FIG. 6 , it will be seen that the forward butt end  74  of each drive screw  70 , 72  is located within the notch  62  of the associated body  52 , with the remainder of the screw extending outwardly. 
         [0033]    The drive apparatus  68  further includes a pair of arcuate cover plates  80 , 82  respectively disposed over a side opening  44 , and secured in place by fasteners  84 . Each of the plates  80 , 82  has a central, threaded bore  86  receiving threaded section  76  of an associated drive screw  70 , 72 . It will thus be appreciated that rotation of the drive screws  70 , 72  serves to slide the component  48 , 50  inwardly or outwardly so as to define a selected clearance between the surfaces  54  of the components  48 , 50  and the operating surface  38  of shearlock element  12 . Such rotational movement of the drive screw  70 , 72  can be effected manually through the use of cranks  88  affixed to the drive ends  78 . Alternately, and as schematically depicted in  FIG. 2 , respective motors  90 , 92  can be coupled to the drive screws  70 , 72  for motorized movement of the restriction components  48 , 50 . Typically, the motors  90 , 92  would be coupled to a controller  94  which may form a part of the overall digital control for the extruder. 
         [0034]    In use, the assembly  10  is installed by first sliding the shearlock element  12  onto shaft  30  at a selected location, usually at the end of a head section  20 . Thereupon, the restriction unit  14  is located in alignment with the flange  22  of the adjacent head section  20 , and the next head section  20  with the associated screw section  28 , is installed. Bolts or other fasteners (not shown) are then used to secure the unlit  14  in place between the flanged ends of the head sections  20 . 
         [0035]    During use of the extruder, the restriction unit  14  can be adjusted to give varying clearances between the inner surfaces  54  of the restriction components  48 , 50 , and the operating surface  38  of shearlock element  12 . This is accomplished by appropriate rotation of cranks  88  (or in the automated version by energization of motors  90 , 92 ) so as to slide the components  48 , 50  along essentially aligned and rectilinear paths defined by slot  42  toward and away from element  12 . Thus, a representative open position of the unit  14  is depicted in  FIG. 2 , where it will be observed that the surfaces  54  are closely adjacent to the innermost surface  96  of the barrel  18  defined by the respective sleeves  24 . The “full-closed” position of the unit  14  is shown in  FIG. 4  where a majority of each surface  54  is in close engaging relationship with the surface  38 . However, it will be seen that the projecting surface regions  55  do not fully mate with or engage the shearlock element surface  38  so as to define, even in the “full-closed” position, small upper and lower passageways  98 , 100 . This is to ensure that the assembly  10  will not completely block lower material through the extruder, even in the “full-closed” position thereof. As the unit  14  is shifted toward shearlock element  12  to increase back pressure and shear, the resultant extrudate becomes less dense, contrary to the prior art devices such as that illustrated in U.S. Pat. No. 4,332,481, wherein increasing restriction serves to increase the density of the resin output. 
         [0036]      FIG. 7  illustrates a flow restriction assembly  10   a  for use in a twin screw extruder  32  having side-by-side intermeshed and intercalated screws  26   a  within an appropriately configured barrel. As illustrated, the outer surfaces  29   a  of the screw flighting of each extruder screw extends into the confines of the adjacent screw flighting between the surface  29   a  and the inner root diameter (not shown) of the screw. The components of assembly  10   a  are, for the most part, identical with those of assembly  10 , and therefore like reference numerals have been used in  FIG. 7 , except for the distinguishing letter “a.” Thus, the assembly  10   a  has a pair of shearlock elements  12   a , each respectively mounted on one of the extruder shafts  30   a . Also, a pair of opposed restriction components  48   a , 50   a  are provided, preferably mounted in a vertical orientation, as shown. The inner operating surfaces  54   a  of the components  48   a , 50   a  have a pair of juxtaposed arcuate regions so as to simultaneously accommodate and engage both of the shearlock elements  12   a . Additionally, the surface regions  55   a  define flow passageways  98   a , 100   a  when the assembly  10   a  is in the full-closed position illustrated in  FIG. 7 . From the foregoing discussion, it will be readily appreciated that the components  48   a , 50   a  move along essentially aligned and rectilinear paths toward and away from the shearlock elements  12   a , upon rotation of the drive screws  70   a , 72   a.    
         [0037]      FIGS. 9 and 10  illustrates a modified restriction assembly  10   b  having many components identical with the previously described assembly  10 . Accordingly, like components have been identified with like reference numerals, except for the distinguishing letter “b,” and these like components need not be described in complete detail. 
         [0038]    The chief difference between assembly  10   b  and assembly  10  is that the shearlock element  12   b  has a significantly smaller diameter, such that the outer surface  38   b  thereof is essentially coincident with the root diameter  29   b ′ of the screw  26   b.  Thus, the restriction elements  48   b , 50   b  may be shifted inwardly to a point closely adjacent the outer surface  38   b,  effectively “within” 0  the depth of the helical flighting of screw  28   b.  More generally, the inner surfaces  54   b  of the restriction elements  48   b , 50   b  should be moveable to a point inboard of the outer surface  29   b  of the screw flighting, with the depth of the screw being defined by the radial distance between the outer surface  29   b  and the root diameter  29   b ′. Preferably, the elements  48   b , 50   b  should be moveable to points such that the inner surfaces  54   b  thereof are inboard of flighting outer surface  29   b  and at least 30%, more preferably at least 50%, of the screw depth, measured from the surface  29   b.  Providing an assembly  10   b  of this type allows far greater material flow restrictions to be achieved, as compared with prior art designs. This in turn greatly increases the velocity of the material passing through the extruder at the region of the assembly  10   b,  and increases the specific mechanical energy imparted to the product. The use of forward pitch helical flighting on opposite sides of the assembly  10   b  also serves to reduce retention time of the material passing through the extruder. 
         [0039]    It will also be appreciated that the design concept embodied in restriction assembly  10   b  can also be employed with twin screw restriction assemblies. That is, the range of movement of the restriction elements in such twin screw designs can be increased so that the restriction elements are moveable inboard of the outer screw surfaces  29   b  of the twin extruder screws. 
         [0040]    A principal advantage of the flow restrictions assemblies of the invention stems from use of sliding flow restriction components  48 , 50 , 48   a , 50   a ,and  48   b , 50   b  as opposed to the rotatable restrictors of the prior art, as exemplified in U.S. Pat. No. 4,136,968. Indeed, the units  14 , 14   a , 14   b  of the invention can be constructed with only a minimum width, preferably less than about three inches. Accordingly, there is little tendency to create “dead spots” within the assemblies  10 , 10   a , 10   b  which contributes to the cleanliness and operational efficiency of the assemblies and the overall extruders. Moreover, the present assemblies  10 , 10   a,   10   b  are advantageously designed so that, in the “full-open” positions thereof, the components  48 , 50 , 48   a , 50   a , and  48   b , 50   b  provide essentially unimpeded flow of material through the extruder barrel. The preferred assemblies  10   b , when the restriction components  48   b , 50   b  are shifted so that the inner surfaces  54   b  thereof are inboard of the outer screw surfaces  29   a , also provide high degrees of flow restrictions and thus impart significant mechanical energy to the material being processed (usually comestible materials, such as human food or animal feeds). 
         [0041]    It will also be appreciated that the assemblies  10 , 10   a,   10   b  of the invention may be mounted at a variety of different locations along the length of a single or twin screw extruder. This gives an operational flexibility not readily available with other designs. In addition, the size and shape of the shearlock elements and the associated flow restriction components can be varied to change minimum and maximum flow areas, as well as other material flow characteristics. Additionally, while only a single assembly is illustrated in the drawings, it will be appreciated that one or more of these assemblies may be used along the length of a given extruder. This may provide additional degrees of operational flexibility in certain extrusion contexts.