Abstract:
An improved, high-capacity die assembly ( 10 ) for a food or feed extruder ( 12 ) is provided and is particularly useful for the production of high quality aquatic feeds. The die assembly ( 10 ) includes a mount ( 20 ), which is secured to the discharge end of an extruder barrel ( 14 ), with a plurality of tubular die components ( 22, 24 ) coupled with the mount ( 20 ). Each component ( 22, 24 ) includes wall structure ( 38 ) defining an outwardly diverging tubular chamber ( 40 ) with a die plate assembly ( 50 ) coupled to the outer end of the wall structure ( 38 ). A flow diverter element ( 54 ) is located within each chamber ( 40 ) and has a large diameter end adjacent the assembly ( 50 ) and a smaller diameter end closer to the chamber inlet. The assembly ( 50 ) has a plurality of openings ( 52 ) outboard of the element ( 54 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a division of application Ser. No. 14/822,019, filed Aug. 10, 2015, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention is broadly concerned with improved, high capacity die assemblies, the combination of such assemblies with food or feed extruders, and corresponding methods. More particularly, the invention is concerned with such die assemblies including a plurality of structurally distinct, tubular die components, each having wall structure defining an outwardly diverging tubular chamber with an outboard die plate; a diverging flow diverter element is located within each chamber and has a large diameter end adjacent the die plate and a remote small diameter end. The die assemblies are operable to produce high quality extrudates, such as aquatic feeds, at high production rates 
       Description of the Prior Art 
       [0003]    Many types of foods or feeds are produced using extrusion equipment. Generally speaking, such extruders include an elongated, tubular barrel having one or more elongated, axially rotatable, helically flighted extrusion screws within the barrel. The discharge end of the barrel is equipped with a die having a plurality of restricted orifice die openings therethrough. In use, starting materials are fed into the barrel and are subjected to increasing levels of pressure, temperature, and shear within the barrel, and are ultimately extruded through the die. 
         [0004]    In the production of certain types of aquatic feeds known as “micro feeds,” the outlet die has relatively small through openings to generate thin, needle-like extrudates. It has been found that production of these micro feeds is often limited by the amount of surface area on the die. Thus, while a given extruder may normally be able to produce high quantities of product, when used to produce micro feeds, the production capacity of the extruder is severely limited. Indeed, in some instances, micro feed production is limited to approximately one-half the rated capacity of the extruder. 
         [0005]    A variety of different extruders and die assemblies have been proposed in the past. Representative references include U.S. Pat. Nos. 3,230,902, 3,813,082, 5,171,090, 5,223,296, 5,242,292, 5,540,900, 6,531,077, 7,654,813, and 8,114,454; US Patent Publication No. 2005/0092365; foreign patents JP10191948 and JP11009197; and non-patent literature: “Ring Die Aquatic Feed Pellet Mill” http://www.feed-pellet-mill.com/product/Feed-Pellet-Mill/ring-die-aquatic-feed-pellets-mill.html (Accessed Jun. 30, 2015), and Sprout “Controlled starch cook and bulk density of dry pet food—Is this for real?” http://en.engormix.com/MA-feed-machinery/formulation/articles/controlled-starch-cook-bulk-t236/p0.htm (Accessed Jul. 7, 2015). 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention overcomes the problems outlined above, and provides high-capacity die assemblies for use with food or feed extruders in order to create extrudates at high production levels, even in the case of micro feeds or related products. Generally speaking, the die assemblies of the invention are mounted on a food or feed extruder including a tubular barrel presenting a discharge opening. The die assemblies comprise a die assembly mount configured to be secured to the extruder barrel, together with a plurality of tubular die components coupled with the mount and in communication with the extruder barrel. Each die component includes wall structure defining an outwardly diverging tubular chamber presenting an inlet end adjacent the mount and an opposed outlet end remote from the inlet end. A die plate is secured to the outlet end and has an inner surface and an outer surface. A diverging flow diverter element is located within the chamber and has a large diameter end adjacent the inner surface of the die plate and an opposed small diameter end closer to the chamber inlet end. The die plate has a plurality of die openings therethrough located outboard of the large diameter end of the diverter element. 
         [0007]    Preferably, the large diameter end of the flow diverter is secured to the inner surface of the die plate and is generally conical in shape, having a cone angle of from about 8-30°, more preferably from about 12-25°. Correspondingly, the wall structure of each die component is substantially frustoconical in shape and has an average diverging angle of from about 8-40°, more preferably from about 10-30 °. 
         [0008]    Additionally, in some instances it is desirable to make use of a flow-restricting venturi proximal to the inlet end of the chamber, typically in the form of a venturi ring. This serves to reduce the cross-sectional area at the inlet of the chamber, relative to the upstream mount. Normally, the venturi should present a reduction in cross-sectional area of from about 15-60%, more preferably from about 30-45%, as compared with the cross-sectional area of the inlet end of the chamber. 
         [0009]    As indicated previously, the die assemblies of the invention are normally used in combination with a food or feed extruder, and are mounted on the discharge end of the latter. 
         [0010]    Methods in accordance with the invention for the extrusion of food or feed materials from an extruder barrel having a discharge opening, comprise the steps of first directing the food or feed material from the discharge opening under pressure into and through a plurality of tubular die components. The food or feed material is caused to pass through the tubular die components to assume respective, outwardly diverging, annular flow paths. Such material is then passed through a plurality of restricted orifice die openings adjacent the end of the tubular die components remote from the discharge opening. Advantageously, the method includes the step of causing the pressures of the material passing through the restricted orifice die openings of each tubular die component to be substantially equal, and preferably at least about 90% equal. 
         [0011]    The product formulations useful in the invention can have wide variances in particular ingredients and amounts thereof. Generally speaking though, more or less conventional food or feed formulations are useful. In some instances, it may be appropriate to add small quantities of oil in order to facilitate production and to make equipment cleanup easier. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a fragmentary perspective view illustrating the output end of a twin screw extruder, with a die assembly in accordance with the invention operably coupled with the extruder output end; 
           [0013]      FIG. 2  is an elevational view of the structure illustrated in  FIG. 1 ; 
           [0014]      FIG. 3  is an end view of the structure illustrated in  FIG. 1 , depicting the output end of the die assembly; and 
           [0015]      FIG. 4  is a sectional view taken along line  4 - 4  of  FIG. 3 , illustrating the internal construction of the die assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    Turning now to the drawings, a die assembly  10  is depicted, which is designed to be mounted to the discharge end of an extruder  12 , the latter having a multiple-head barrel  14  and one or more elongated, axially rotatable, helically flighted extrusion screws  16  within the barrel  14 ; the barrel  14  has a discharge opening  18  (see  FIG. 4 ). In the depicted embodiment, the extruder  12  is a twin-screw extruder commercialized by Wenger Manufacturing, Inc. of Sabetha, Kans., although other types of twin- and single-screw extruders could also be employed. 
         [0017]    The die assembly  10  generally includes a mount  20  and a plurality (here two) of tubular die components  22  and  24  supported by the mount  20 . As best illustrated in  FIG. 4 , mount  20  includes a plate  26 , which is affixed to the terminal flange  28  of extruder barrel  14 . The plate  26  has a pair of passageways  30 ,  32  in communication with discharge opening  18 . A pair of tubular, arcuate, relatively out-turned transitions  34  and  36  are secured to the plate  26  as shown. 
         [0018]    The die components  22 ,  24  are identical, and thus only the component  24  will be described in detail. As illustrated, the component  24  has wall structure  38 , which defines an outwardly diverging tubular chamber  40  presenting an inlet end  42  adjacent the outer end of transition  36 , and an opposed outlet end  44 . In the depicted embodiment, the wall structure  38  includes a pair of interconnected, frustoconical segments  46  and  48 , although a unitary wall structure could also be employed. The component  24  also has a outermost die plate assembly  50 , which is secured to and covers the outlet end  44  of wall structure  38 . The assembly  50  includes an apertured spider plate  51  and an outermost die plate  51   a;  the latter has a plurality of restricted orifice die openings  52  therethrough, which are arranged in an annular pattern as best seen in  FIGS. 2 and 3 . An outwardly extending knife spindle  53  is also secured to die plate  50 , and supports a rotary cutting knife (not shown) which cuts the extrudate passing through the openings  52 . 
         [0019]    The component  24  is also equipped with a diverging flow diverter element  54  centrally located within and extending along the length of chamber  40 . The element  54  is substantially conical in shape and is secured to the inner face of assembly  50  inboard of the die openings  52 . As illustrated, the element  54  has a large diameter end  56  adjacent the assembly  50 , and a small diameter end  58  proximal to inlet end  42 . 
         [0020]    It will also be observed that a restricted diameter venturi ring  60  is provided at the juncture between transition  36  and the inlet end  42  of wall structure  38 . The function of ring  60  is to substantially equalize the flow and pressure of material passing through the components  22  and  24  to thereby assure that consistent products are delivered from these components. 
         [0021]    It has been found that the wall structure  38  should preferably have an average angle of divergence between the inlet and outlet ends  42 ,  44 , namely that of the segments  46 ,  48 , of from about 8-40°, and more preferably from about 10-30°. As is evident from  FIG. 4 , the angle of divergence of segment  46  is identical with that of segment  48 . In other embodiments, however, the segments may have moderately different divergence angles; nonetheless, the average angle of diversion in such situations is within the above ranges. Additionally, the element  54  should have a cone angle (between the center line of the element and the outer surface thereof) of from about 8-30° and more preferably from about 12-25°. Additionally, the venturi ring  60  should provide a reduction in cross-sectional are of from about 15-60%, more preferably from about 30-45%, as compared with the cross-sectional of the inlet end just upstream of the ring  60 . 
         [0022]    It will be appreciated that the design of the die component  24  serves to direct flow of material emerging from the discharge opening  18  into a diverging, annular, generally conical flow path between the wall structure  38  and the diverter element  54 , whereby this material passes through the die openings  52 . Of course, given the relative orientation of the components  22  and  24 , the material passes along two essentially constant flow paths, having divergence angles consistent with those set forth above, namely from about 8-40°, and more preferably from about 10-30°. 
       EXAMPLES 
       [0023]    The following examples set forth representative products and operational conditions using the die assembly  10  of the invention. It should be understood, however, that these examples are provided by way of illustration only, and nothing therein should be taken as a limitation on the overall scope of the invention. 
         [0024]    A series of production runs were undertaken to prepare standard shrimp grower micro feed pellets, using a standard shrimp feed recipe. In each run, a dual die of the type described above was secured to the outlet end of a Wenger TX-3000 twin screw extruder. For most of the runs, the two die plates each had a total of 1,138 die holes having a diameter of 1.9 mm, and each die component was equipped with a 3.75 inch venturi ring, as illustrated in the drawings; in the last two runs, each die plate had a total of 1,256 die holes having a diameter of 1.6 mm. A Wenger HIP preconditioner was used upstream of the extruder inlet in order to moisturize the feed materials prior to extrusion. A rotary knife assembly was used to cut the extrudate as it emerged from the die openings. All of the extruded products had acceptable water stability and had 100% sinking properties. 
         [0025]    In the runs, various parameters were altered, as set forth in the Tables below. 
         [0000]    
       
         
               
               
               
               
               
               
             
           
               
                   
               
             
             
               
                 Run # 
                 Run 1  
                 Run 2  
                 Run 3 
                 Run 4  
                 Run 5 
               
               
                   
               
               
                 Die Open Area/Ton  
                 921  
                 921  
                 806  
                 806  
                 1075  
               
               
                 Dry Feed Rate (kg/hr)  
                 7000  
                 7000  
                 8000  
                 8000  
                 6000  
               
               
                 Cylinder Water (kg/hr) 
                 1820  
                 1820  
                 1820  
                 1820  
                 1400  
               
               
                 Cylinder Water (%)  
                 26.0% 
                 26.0% 
                 26.0%  
                 26.0% 
                 20.0%  
               
               
                 Cylinder Steam (kg/hr)  
                 630  
                 630  
                 630  
                 630  
                 630  
               
               
                 Cylinder Steam (%)  
                   9%  
                   9%  
                   9%  
                   9%  
                   9%  
               
               
                 HIP Mix Intensity (%)  
                 High  
                 High  
                 High  
                 High  
                 High  
               
               
                 HIP Discharge Temp  
                 90  
                 90  
                 86  
                 86 
                 89  
               
               
                 (0 C.) 
                   
                   
                   
                   
                   
               
               
                 Extruder Water (kg/hr)  
                 280 
                 280  
                 280  
                 350  
                 140  
               
               
                 Extruder Water (%)  
                   4%  
                   4%  
                   4%  
                   5%  
                   2%  
               
               
                 Extruder Zone 1 (0 C.)  
                 91  
                 95  
                 93  
                 93  
                 83  
               
               
                 Extruder Zone 2 (0 C.)  
                 87  
                 97  
                 92  
                 92  
                 93  
               
               
                 Extruder Zone 3 (0 C.)  
                 86  
                 94  
                 92  
                 92  
                 97  
               
               
                 Total Wet Rate (kg/hr)  
                 9730  
                 9730  
                 10730  
                 10800  
                 8170  
               
               
                 Total Wet Rate  
                 9.7  
                 9.7  
                 10.7  
                 10.8  
                 8.2  
               
               
                 (mton/hr) 
                   
                   
                   
                   
                   
               
               
                 Wet Density (g/l) L:R  
                 605/620  
                 625/630 
                 624/638 
                 620/632 
                 646/654  
               
               
                 Dryer Exit Density (g/l)  
                 615  
                 619  
                 619  
                 620  
                   
               
               
                 Extruder Speed (rpm)  
                 300  
                 300 
                 300 
                 300  
                 300  
               
               
                 Extruder Motor Load  
                   72%  
                   63% 
                   83%  
                   87% 
                   87%  
               
               
                 (%) 
                   
                   
                   
                   
                   
               
               
                 Extruder Discharge  
                 83  
                 83  
                 83  
                 83  
                 83  
               
               
                 Temp (0 C.) 
                   
                   
                   
                   
                   
               
               
                 Knife Speed (rpm)  
                 532  
                 532  
                 517 
                 517  
                 517  
               
               
                 Color  
                 Light  
                 Dark  
                 Dark  
                 Light 
                 Dark  
               
               
                   
                 Brown  
                 Brown 
                 Brown  
                 Brown  
                 Brown 
               
               
                   
               
               
                 Run # 
                 Run 6  
                 Run 7  
                 Run 8 
                 Run 9  
                 Run 10 
               
               
                   
               
               
                 Die Open Area/Ton  
                 921  
                 921 
                 806  
                 645  
                 841  
               
               
                 Dry Feed Rate (kg/hr)  
                 7000  
                 7000  
                 8000  
                 10000  
                 6000  
               
               
                 Cylinder Water (kg/hr) 
                 1400  
                 1400  
                 1400  
                 1680  
                 1820  
               
               
                 Cylinder Water (%)  
                 20.0%  
                 20.0%  
                 20.0%  
                 24.0%  
                 26.0%  
               
               
                 Cylinder Steam (kg/hr)  
                 595  
                 595  
                 630  
                 560  
                 700  
               
               
                 Cylinder Steam (%)  
                  8.5%  
                  8.5%  
                  9.0%  
                  8.0%  
                 10.0%  
               
               
                 HIP Mix Intensity (%)  
                 High  
                 High  
                 High  
                 High  
                 High  
               
               
                 HIP Discharge Temp  
                 91  
                 91  
                 89  
                 89  
                 93  
               
               
                 (0 C.) 
                   
                   
                   
                   
                   
               
               
                 Extruder Water (kg/hr)  
                 140  
                 210  
                 210  
                 350  
                 490  
               
               
                 Extruder Water (%)  
                   2%  
                   3%  
                   3% 
                   5% 
                   7%  
               
               
                 Extruder Zone 1 (0 C.)  
                 77  
                 73  
                 74  
                 73  
                 77  
               
               
                 Extruder Zone 2 (0 C.)  
                 79  
                 77  
                 76  
                 76  
                 81  
               
               
                 Extruder Zone 3 (0 C.)  
                 88  
                 88  
                 88  
                 88  
                 93  
               
               
                 Total Wet Rate (kg/hr)  
                 9135  
                 9205  
                 10240  
                 12590  
                 9010  
               
               
                 Total Wet Rate  
                 9.1  
                 9.2  
                 10.2  
                 12.6  
                 9.0  
               
               
                 (mton/hr) 
                   
                   
                   
                   
                   
               
               
                 Wet Density (g/l) L:R  
                 646/640  
                 700/690  
                 676/680  
                 634/650 
                 670/670  
               
               
                 Dryer Exit Density (g/l)  
                   
                   
                   
                   
                   
               
               
                 Extruder Speed (rpm)  
                 300  
                 300  
                 320  
                 375  
                 255  
               
               
                 Extruder Motor Load  
                   77%  
                   73%  
                   89%  
                   86%  
                   92%  
               
               
                 (%) 
                   
                   
                   
                   
                   
               
               
                 Extruder Discharge  
                 83  
                 83  
                 83  
                 83  
                 83  
               
               
                 Temp (0 C.) 
                   
                   
                   
                   
                   
               
               
                 Knife Speed (rpm)  
                 517  
                 374/458 
                 374/458  
                 558/558 
                 658/604  
               
               
                 Color  
                 Light  
                 Really 
                 Really  
                 Really  
                 Really  
               
               
                   
                 Brown  
                 Dark  
                 Dark  
                 Dark  
                 Dark  
               
               
                   
                   
                 Brown  
                 Brown  
                 Brown  
                 Brown 
               
               
                   
               
             
          
         
       
     
         [0026]    In Run 1, the uniformity of the extrudate between the two die plates was excellent, with no white streak discolorations. In Run 2, the same conditions of Run 1 were maintained, except that 1% oil was added to the feed formulation. This caused an increase in extrudate density and a smoother surface texture. The motor load on the extruder dropped 10%. In Run 3, the feed rate was increased and 1% oil was used. This increased the extrudate density and the surface uniformity was good. Motor load increased by 83%. Run 4 was a repeat of Run 3, but without added oil. Motor load increased as did extruder screw speed. The extrudate exhibited a slightly rougher surface, but product uniformity was still good. In Run 5, the number of cutting blades was reduced to create a product having an average length of 4 mm. The density was heavy, but product uniformity was good without white streaks. Run 6 was a repeat of Run 5, except that the feed rate was increased. Product uniformity was good and density was heavy, without white streaks. A small number of the pellets expanded upon extrusion. Run 7 was a repeat of Run 6, with 1% added oil. Uniformity remained good and the density was heavy, without white streaks. Run 8 was another repeat of Run 6, with 1% oil. Uniformity was good, density was heavy, with no white streaks. Run 9 was a repeat of Run 6 with 60 Hz oil. Uniformity good, density heavy, no white streaks. In Run 10, the feed rate was decreased to 6000 kg/hr, product acceptable. In Run 11, white streak pellets were produced initially, but this was eliminated with the addition of the balance of water. 
         [0027]    These tests confirm that the use of a dual die in accordance with the invention is capable of producing high-quality, substantially uniform aquatic micro feeds at high production levels.