Abstract:
Flow restriction assemblies ( 10,10   a ) adapted to be mounted on single or twin screw extruders ( 17,102 ) in order to allow selective adjustment of material flow through the extruders ( 17,102 ), with consequent alteration in back pressure and shear conditions. The assemblies ( 10,10   a ) each have shearlock(s) ( 12,12   a ) mounted on the extruder drive shaft(s) ( 34,34   a ), together with restriction units ( 14,14   a ). The units ( 14,14   a ) have opposed flow restriction components ( 48,50,48   a   ,50   a ) supported on opposite sides of the shearlock(s) ( 12,12   a ) and mounted for a substantially aligned and rectilinear back and forth sliding movement. In this fashion, the clearance between the inner surfaces ( 54,55,54   a   ,55   a ) of the components ( 48,50,48   a   ,50   a ) can be selectively adjusted. The assemblies ( 10,10   a ) are small in size and can be located at various points along the length of extruders ( 17,102 )

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention is broadly concerned with extrusion devices equipped with mid-barrel flow restriction assembly permitting selective alteration back pressure and shear conditions, in order to optimize extrusion cooking. 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.  
         [0003]     2. Description of the Prior Art  
         [0004]     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, flighted, axially rotatable screw is positioned within the barrel and serves 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.  
         [0005]     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.  
         [0006]     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.  
         [0007]     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 there past. 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.  
         [0008]     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  
       [0009]     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 an axially rotatable screw therein. 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.  
         [0010]     Preferably, the overall assemble 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.  
         [0011]     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  
       [0012]      FIG. 1  is a perspective view of a flow restriction assembly in accordance with the invention;  
         [0013]      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;  
         [0014]      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;  
         [0015]      FIG. 4  is a vertical sectional view similar to that of  FIG. 2 , but showing the assembly in its fully closed position;  
         [0016]      FIG. 5  is a side view of the assembly, with the adjacent cover plate removed;  
         [0017]      FIG. 6  is a fragmentary, perspective, exploded view depicting the connection between the drive assembly and restriction components; and  
         [0018]      FIG. 7  is a vertical sectional view of another embodiment of the invention, designed for use with a twin screw extruder.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]     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 , 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.  
         [0020]     By way of general background, the assembly  10  is designed for use in a conventional single or twin screw extruder  16  illustrated in  FIG. 3 . In a single screw extruder  17 , 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 end most, 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 section  28  each located within an associated head section  20 . 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 screws now is on respective hexagonal or keyed drive shafts  34   a.    
         [0021]     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.  
         [0022]     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 .  
         [0023]     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 .  
         [0024]     The unit  14  also includes a pair of closed 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 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 .  
         [0025]     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 sherlock element  12  that 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.  
         [0026]     The drive apparatus  68  further includes a pair of arcuate cover plates  80 , 82  respectively exposed 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 , 55  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.  
         [0027]     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 unit  14  in place between the flanged ends of the head sections  20 .  
         [0028]     During use of the extruder, the restriction unit  14  can be adjusted to give varying clearances between the surfaces  54 , 55  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 ) continuing 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.  
         [0029]      FIG. 7  illustrates a flow restriction assembly  10   a  for use in a twin screw extruder  102  having side-by-side intermeshed screws within an appropriately configured barrel. 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  34   a . Also, a pair of opposed, flightable restriction components  48   a , 50   a  are provided, preferably mounted in a vertical orientation, as shown. The inner operating surfaces  54   a , 55   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 surfaces  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.    
         [0030]     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  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  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 , which contributes to the cleanliness and operational efficiency of the assemblies and the overall extruders. Moreover, the present assemblies  10 ,  10   a  are advantageously designed so that, in the “full-open” positions thereof, the components  48 ,  50 ,  48   a ,  50   a  provide essentially unimpeded flow of material through the extruder barrel.  
         [0031]     It will also be appreciated that the assemblies  10 ,  10   a  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.