Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is broadly concerned with improved extrusion systems which include an extruder barrel and screw assembly, together with a product treatment assembly designed for post-extrusion, superatmospheric pressure treatment of extrudates. More particularly, the invention is concerned with such systems and corresponding methods where, in preferred forms, a selectively adjustable back pressure valve assembly is provided upstream of an extrusion die, with a post-extrusion sealed housing for extrudate treatment. The housing may be directly coupled to the extruder assembly so that extrudate passes from the die into the housing; alternately, an atmospheric pressure, product-directing cowling may be employed with a downstream sealed housing. 
     2. Description of the Prior Art 
     Extrusion cooking systems have long been used for the preparation of human foods and animal feed products. Broadly speaking, such extrusion systems include an elongated extruder barrel with one or more elongated, axially rotatable, helically flighted extruder screws within the barrel, together with a downstream restricted orifice extrusion die. In typical processing, the feed ingredients are fed into and through the extruder barrel where they are subjected to increasing levels of heat, pressure and shear in order to at least partially cook the ingredients and form an extrudate. This extrudate may be cut or otherwise subdivided at on downstream of the die. Thereafter, the subdivided extrudate is often subjected to post-extrusion treatments such as surface application of fats and drying. 
     Another post-extrusion treatment which has long been practiced involves passing the extrudate into and through a superatmospheric pressure treatment chamber, which often involves injection of high pressure steam into the chamber so as to establish and maintain the desired superatmospheric pressure conditions therein. Such post-extrusion pressure treatment has been found to effectively condition the extruded products and improve the quality thereof. Thus, U.S. Pat. No. 4,039,691 describes a process wherein food-grade materials are extruded and then directly passed into an elongated superatmospheric pressure chamber while steam is injected into the chamber. In order to maintain superatmospheric pressures within the post-extrusion chamber (e.g., 60-80 psi), the &#39;691 patent describes the use of spring-loaded or rotary valves, or a rotary letdown pump; more generally, the patent describes the use of any device which allows product to exit the confined post-extrusion chamber while maintaining a predetermined back pressure therein. 
     Similarly, U.S. Pat. No. 4,139,648 employs an upstream extruder with a sealed chamber post-extrusion treatment device, much in the manner of the &#39;691 patent. Here again, the treatment chamber is designed so as to maintain superatmospheric pressure conditions therein, normally established via steam injection. 
     U.S. Pat. No. 3,778,522 is yet another variation of this concept, and employs an extruder equipped with a conventional apertured die and a rotary knife; extrusion pressures at the die are about 500 psig or more, and the knife serves to subdivide the extrudate into small pellets or the like. The post-extrusion treatment involves use of an upright tube having a restricted outlet and a steam inlet; in this fashion, the cut extrudate is treated within the tube at high pressures up to 140 psig. 
     PCT Publications Nos. WO 99/62361 and WO 01/72153 are still further examples of the equipment and techniques disclosed in the aforementioned U.S. patents. Hence, these publications disclose an extruder device which feeds product directly into a superatmospheric pressure treatment chamber. In order to maintain pressure conditions, one or more rotary valves are employed, together with steam injection. The WO 01/72153 publication describes a very complex arrangement wherein the post-extrusion treatment chamber is shiftably supported so that it can be moved to a non-operative position during startup of the extruder or in the event of a process upset. This is deemed to be a very unwieldy device, which is difficult to operate and entails significant operator time and effort. 
     SUMMARY OF THE INVENTION 
     The present invention provides improved extrusion systems and corresponding methods for the production of a wide variety of extrudates, especially human foods and animal feeds. Broadly speaking, the extruder systems of the invention include an elongated tubular extruder barrel equipped with at least one elongated, axially rotatable, flighted screw within the barrel. A selectively adjustable back pressure valve assembly is operatively coupled to the extruder outlet and comprises structure defining an elongated passageway with an inlet and an outlet, the inlet communicating with the extruder barrel outlet, and the outlet having a restricted orifice die. In addition, the valve assembly has an apertured valve member selectively shiftable relative to the passageway for altering the effective cross-sectional open area presented by the passageway. In this manner, operating conditions within the extruder can be effectively altered or maintained to insure optimum product output. The overall extruder systems further include a post-extrusion product treatment assembly for receiving product after passage through the extruder and back pressure valve assembly. Such a treatment assembly permits superatmospheric pressure treatment of the extruded product, so as to facilitate density control of the product. 
     In one form of the invention, the treatment assembly comprises a sealed housing equipped with a rotary outlet valve and which is directly coupled to the valve assembly so that product emerging from the latter passes immediately into the chamber without passage through the atmosphere. In another embodiment, the treatment assembly includes an open, atmospheric pressure product-guiding cowling coupled to the valve assembly outlet, together with a downstream sealed, pressurizable treatment housing. In this embodiment, the extruded product passes through the atmosphere and then into the sealed treatment housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary view in partial vertical section illustrating an extrusion system in accordance with the invention including a back pressure valve assembly and a superatmospheric pressure treatment assembly; 
     FIG. 2 is a fragmentary vertical sectional view similar to that of FIG. 1, but depicting the back pressure valve assembly in the product diversion position thereof; 
     FIG. 3 is a front view of the vertically shiftable die member forming a part of the preferred back pressure valve assembly, with the production diversion passageway being illustrated in phantom; 
     FIG. 4 is a rear view with parts broken away of the extrusion system of FIG. 1, depicting the inlet face of superatmospheric pressure treatment assembly; and 
     FIG. 5 is a fragmentary view in partial vertical section of another extrusion system in accordance with the invention, including a back pressure valve assembly and a superatmospheric pressure treatment assembly, the latter having a product-guiding cowling open to the atmosphere and a downstream superatmospheric pressure treatment housing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings, FIGS. 1-4 illustrate an embodiment of the invention in the form of an extruder system  10  broadly comprising an extruder  12 , back pressure valve assembly  14  and post-extrusion treatment assembly  16 . The system  10  is designed for processing of a wide variety of products, particularly animal or aquatic feeds. The system  10  permits the processor to formulate feeds of varying density while affording a convenient means of extrusion control and diversion of unacceptable product. 
     In more detail, the extruder  12  includes an elongated extruder barrel  18  having one or more elongated, axially rotatable, flighted extrusion screws  20  within the barrel  18  (e.g., the extruder  12  may be of the single or twin screw variety). In typical practice, the barrel  18  is formed of a plurality of end-to-end interconnected tubular barrel sections and has an inlet (not shown) for introduction of ingredients to be processed, and the screw(s)  20  are also segmented. Additionally, use may be made of a preconditioner upstream of the extruder inlet for the purpose of initially heating, moisturizing and partially cooking of these ingredients. Wenger DDC preconditioners are particularly suited for this application. As illustrated in FIGS. 1 and 2, the barrel  18  may be provided with external jacketing  22  permitting introduction of heating or cooling media about the extruder heads for temperature control. In addition, the barrel presents an outlet  24  for passage of processed material into the remainder of system  10 . The end of barrel  18  includes a pair of plates  26  and  28  which include central openings  26   a ,  28   a  communicating with outlet  24 ; it will be observed that opening  28   a  is frustoconical as shown. As will be appreciated by those skilled in the art, feed ingredients passing through extruder  12  are subjected to increasing levels of temperature, pressure and shear, and may be substantially cooked by virtue of such treatment. 
     The back pressure valve assembly  14  includes three interconnected components, namely transition  30 , valve unit  32  and tubular barrel segment  34 . These components are aligned end-to-end and cooperatively define a passageway  36  throughout the entirety of the assembly  14 . 
     In more detail, the transition  30  is secured to plate  28  and has a converging opening  38 . The valve unit includes an upright tubular segment  40  generally transverse to the longitudinal axis of passageway  36  and having a laterally extending opening  42 ; the upper and lower ends of the segment  40  include internal sealing rings  44 ,  46 . An elongated valve member  48  is situated and vertically reciprocal within segment  40 . The valve member  48  includes a somewhat triangularly-shaped, laterally extending through opening  50  as well as a product diversion passageway or channel  52  including an inlet opening  54  and outlet  56 . The valve member  48  is selectively movable within segment  40  by means of piston and cylinder assembly  58 . In particular, the assembly  58  is supported via a mounting block  60  in turn attached to laterally spaced apart, upright plates  62 ,  64 ; the latter are secured by fasteners  66  to opposite sides of the segment  40 . In order to insure smooth operation of the valve member  48 , a pair of roller blocks  68  are secured to the upper end of the valve member, and the piston rod  70  forming a part of assembly  58  is secured to the blocks  68 . The barrel segment  34  has internal passageway  72  and is bolted to segment  40  as shown. The outer end of the segment  34  supports a restricted orifice die plate  74 . Finally, a circumscribing mounting plate  76  is also secured to the outer end of segment  34 , and extends about the exit of passageway  72 . 
     The assembly  16  in the illustrated embodiment includes a housing  78  having a rear wall  80 , front wall  82 , sidewall  84  and lower product exit opening  85 . As best seen in FIGS. 1 and 4, the rear wall  80  includes an entrance opening  86 , whereas front wall  82  has a knife opening  88 . The sidewall  84  is equipped with a steam inlet  90 . The rear wall  80  of housing  78  is secured to plate  76  by means of an adaptor/sealing ring  92  and fasteners  94 . 
     A knife unit  96  also forms a part of the assembly  16  and includes a cutter  98  located within housing  78  and supporting a cutting blade  100  situated adjacent the exit face of die plate  74 . The cutter  98  is powered by means of external motor  102 , belt drive  104  and bearing assembly  106 , the latter being coaxial with cutter  98  and secured to the outer face of rear wall  82 . 
     An outlet chamber  108  is secured to the underside of housing  78  and includes a rotatable or “star wheel” valve  110 . The lower end of chamber  108  supports a delivery chute  112  and conveyor housing  114 . Referring to FIG. 4, it will be seen that the valve  110  is rotated by means of motor  116 , gear box  118 , belt drive  120  and drive shaft  122 . 
     The extrusion system  10  is designed to process feed ingredients by passage thereof in serial order through extruder  12 , back pressure valve assembly  14  and post-extrusion treatment assembly  16 . In this regard, the operation of extruder  12  is entirely conventional and thus will not be described in detail. In any case, material emerging from barrel  18  passes through openings  26   a ,  28   a  and into transition  30 . At this point, the material passes through openings  42  and  50  and passageway  72  for ultimate extrusion through die  74 . It will be appreciated, however, that valve member  48  may be adjusted so as to alter the effective cross-sectional area presented by the passageway  36 . Such adjustment is effected through appropriate operation of piston and cylinder assembly  58 , so that the valve member opening  50  may be shifted relative to the lateral opening  42 . It has been found that such adjustment is an effective way of altering the pressure conditions within the system  10 , which may be required or desirable in order to accommodate different products and/or processing conditions. 
     After passage through the assembly  14  and die plate  74 , the extrudate passes directly into housing  78 , without passage through the atmosphere. Of course the extrudate issuing from plate  74  is immediately cut through the rotation of knife blade  100  to yield pellets or pieces of desired length. The conditions within housing  78  are preferably superatmospheric, generally between 0.1-50 psi and more preferably from about 0.5-20 psi. Such conditions are established owing to the sealed nature of housing  78  and introduction of steam or other pressurizing gas into the housing through inlet  90 . Normally, the cut product will have a residence time within housing  78  of from about 0.1-3 seconds, more preferably from about 0.5-1.5 seconds. Temperature conditions within the housing  78  are typically within the range of from about 80-140° C., more preferably from about 100-120° C. After passage through the rotary valve  110 , the product descends through chute  112  and into housing  14  for conveyance of the product for downstream processing or packaging. 
     In other situations, it is possible to shift the valve member  48  upwardly to the product diversion position depicted in FIG.  2 . In this orientation, the inlet opening  54  is moved into registry with opening  40  of segment  40  that product passing through extruder  12  and transition  30  is diverted downwardly as waste or rework product. Such a functionality is very useful during system startup or during upset conditions, so as to prevent undesirable product from passing through the post-extrusion assembly  16  for mixture with acceptable product. 
     FIG. 5 illustrates another embodiment in accordance with the invention in the form of an extrusion system  124  comprising extruder  12 , back pressure valve system  14 , and post-extrusion treatment assembly  126 . The extruder  12  and valve assembly  14  are identical to the like numbered components described previously, and thus require no further discussion. 
     The treatment assembly  126  in this instance includes a two-part, arcuate, product-guiding cowling  128  having an entrance  130  and an exit  132 . The two halves of the cowling are individually and pivotally secured to opposed portions of the barrel segment  34  adjacent die  74 , using conventional hinge structure permitting the respective halves to be pivoted about individual upright axes. As illustrated in FIG. 5, the cowling includes a vent pipe  133 , with the adjacent margins of the cowling halves being relieved as at  133   a  in order to accommodate the drive for cutter  98 . 
     The assembly  126  also includes a sealed housing  134  disposed below cowling exit  132 . The housing  134  includes a rotary valve inlet section  136 , a central section  138  and a rotary valve output section  140 ; these sections are interconnected to define a continuous treatment chamber. Each of the sections  136 ,  140  are identical and include a rotary “star wheel” valve  142 ,  144  identical with previously described rotary valve  110 . The inlet valve section  136  is equipped with a top plate  146  having an entrance opening  148 . The transition section  138  has an inlet  148  as shown, permitting introduction of steam or other pressurizing gas. Finally, a chute  112  and housing  114  are secured to the bottom or outlet end of section  140 , these components being identical with similarly numbered components described previously. 
     The operation of system  124  proceeds much in the manner of system  10 , i.e., such operation is identical through extruder  12  and back pressure valve assembly  14 . However, in the FIG. 5 embodiment, as the extrudate emerges from die plate  74  and is cut by rotating blade  100 , the product passes through cowling  128  and into the housing  134 . It will be appreciated in this respect that the interior of cowling  128  is at atmospheric pressure, owing to the fact that the cowling exit  132  is open and not directly connected to the housing  134 . Generally speaking, it is preferred that the residence time within the cowling  128  before entry into housing  134  be relatively short and usually no more than about 1.5 seconds, preferably up to about 1 second. In any case, as the product passes from the cowling exit, it immediately enters housing  134  through valve  142 . Thereupon, the product is processed within the housing, preferably using the conditions of pressure, temperature and residence time described above with reference to housing  78 . Similarly, as the product exits the chamber  134  through valve  144 , it descends through chute  112  and housing  114  for downstream processing.

Technology Category: 1