Title of Invention

A SHORT LENGTH COOKING EXTRUDER AND A METHOD FOR EXTRUSION COOKING OF AN EDIBLE MATERIAL

Abstract

1. A short length cooking extruder for extrusion cooking of an edible material, said extruder comprising an elongated tubular barrel having a material inlet and a spaced material outlet and presenting an inner surface defining an elongated bore which is of general frustoconical configuration over at least a portion of the length thereof; an elongated, helically flighted screw assembly positioned within said bore; means for axially rotating said screw assembly at a rotational speed of at least 500 rpm; and an apertured extrusion die disposed across said material outlet; said extruder having a L/D ratio of up to 6.

Full Text

Background of theinvention 1 Field of theinvention The presentinventionis broadly concerned with animproved extrusion cooking device and method wherein the extruderis of minimal length to reduce equipment and maintenance costs. More particularly, theinvention pertains to such a device wherein theinternal bore of the extruder barrelis of tapered, generally frustoconical configuration and the extruder preferablyincludes means presenting a material flow restrictionintermediate theinlet and extrusion die. Extrusion devicesin accordance with theinvention are operated at high speed and can essentially match the throughputs and product qualities of much larger machines. 2. Description of the Prior Art Extrusion cooking devices have long been usedin the manufac¬ture of a wide variety of edible and other products such as human and animal feeds. Generally speaking, these types of extrudersinclude an elongated barrel together with one or moreinternal, helically flighted, axiaily rotatable extrusion screws therein. The outlet of the extruder barrelis equipped with an apertured extrusion die.in use, a material to be processedis passedinto and through the extruder barrel andis subjected toincreasing feveis of temperature, pressure and shear. As the material emerges from the extruder die,itis fully cooked and shaped and may typically be subdivided using a rotating knife assembly. Conventional extruders of this type are shownin U.S. Patents Nos. 4,763,569, 4,118,164 and 3,117.006. Most conventional modern-day extrusion cookers are made up of a series ofinterconnected tubular barrel heads or sections with theinternal flighted screw(s) also being sectionalized and mounted on powered, rotatable shaft(s).in order to,achieve the desired level of cook,it has been thought necessary to provide relatively long barrels and associated screv/s. Thus, many high-output pet food machines may have five to eight barrel sections and have a length of from about 10 to 20 times the screw diameter. As can be appreciated, such long extruders are expensive and moreover present problems associated with properly supporting the extrusion screw(s) within the barrel. However, prior attempts at using relatively short extruders have not met with success, and have been plagued with problems ofinsufficient cook and/or relatively low yields. Thereis accordingly a needin the art forimproved, low-cost, short length extruder devices which are essentially equal with conventional long-barrel extrudersin terms of product throughput and quality. Summary of theinvention The present overcomes the problems outlined above, and provides a short length cooking extruder and method which yields superior products at commercially viable throughputs using an extruder substantially shorterin length than those of conventional design. Broadly speaking, the extruder of theinventionincludes the usual tubular barrel having aninlet and an outlet and presenting aninner surface defining an elongated bore. The extruder alsoincludes an elongated, helically flighted screw assembly within the bore, motive means for axially rotating the screw assembly, and an apertured extrusion die disposed across the barrel outlet. However, a number ofimportant structural features areincorpo¬ratedinto the extruders hereofin order to achieve the ends of theinvention. Thus, theinternal bore of the barrelis preferably of generally frustoconical configuration for at least about 50% of the length of the barrel between theinlet to the extrusion die and presents a generally decreasing cross-sectional area along the bore length; preferably, the barrel boreis of tapered, frustoconical configuration for substantially the entirety of the barrel length between theinlet and outlet. Moreover, the preferred extruderincludes structure defining a material flow restriction, whichis preferablyin the form of an apertured flow-restricting device; this generates a mid-barrel die resultingin a choke region of material during operation of the extruder. The screw assembly and flow-restriction are cooperatively designed so that the material displacement per revolution of the screw assembly adjacent the upstream margin of the flow-restrictionis less than the matenal displacement per revolution adjacent the downstream margin of the flow-restriction. Normally, theinner bore-defining surface of the extruder barrelis configured to present spaced, helicai rib sections along the length thereof; these ribs assistin mixing and cooking of trie material during travel along the short length of the extruder barrel. This effect tis augmented by the relatively high rotational speeds cf the screw assembly;in practice, the screw assemblyis rotated at a speed of at least about 500 rpm more preferably at least about 550 rpm, and even more preferably at least about 600 rpm. The most preferred range of rpmis from about 600-1000. The short length extruders of the invention have a length to maximum diameter ratio (UD ratio) of up to about 6, and more preferably from about 3-6. Thus, devicesin accordance with theinvention can be produced at a significantly lower cost as compared with convent jnal cooking extruders. Furthermore, maintenance and parts replacement costr are lessened. Brief Description of the Drawings Figure 1is a vertical seciional view depicting ai preferred short length extruderin accordance with theinvention; Fig. 2is a sectional view taken along line 2-2 of Fig. 1 and depicting the mid-barrel die assembly of the extruder; and Fig. 3is a sectional view similar to Fig, 2 butilustrating an alternative mid-barrel die design. Detailed Description of the Preferred Embodiment Turning now to the drawings, a short length extruder assembly 10 isillustratedin Fig. 1. Broadly speaking, the assembly 10includes a precondi-tioner 12 and an extruder 14. The latterincludes an elongated tubular barrel 16 having aninlet 18 and an endmost, apertured extrusion die 20, An elongated, flighted, axially rotatable screw assembly 22is disposed within barrel 16 along the length thereof. in more detail, the preconditioned 12is designed toinitially moisturize and partially precook dryingredients prior to passage thereof as a dough or the likeinto theinlet 18 of extruder 14. To this end, the precondi¬tioned 12is typicallyin the form of an elongated chamber equipped with rotatableinternal paddles as well asinjection ports for water and/or steam. A variety of preconditioners may be usedin the context of theinvention. However,itis particularly preferred to use Wenger DDC precondiiioners of the type describedin U.S. Patent No., 4,752,139,incorporated by reference herein. in the embodimentillustrated, the barrel 16is made up of three axially aligned andinterconnected tubular head sections, namelyinlet head 24 and second and third sections 26, 28. Theinlet head 24is configured to present the upwardly opening extruderinlet 18 andis positioned beneath the outlet of preconditioned 12 as shown.in addition, theinlet head 24 has an apertured end wall 30 equipped with seals 32 for engaging seal block 34. The screw assembly 22is mounted on hexagonal drive shaft 36 andis rotated via schematically depicted conventional bearing housing 39 and electric motor 39a. The second head 26includes an outer metallic section 38 equipped with an externa! jacket 40. The latter has aninlet 42 and an outlet 44 so as to permitintroduction of heating or cooling media (e.g., cold water or steam)into the jacket, thus allowingindirect temperature control for the head 26.in addition, the section 38is provided with a pair of through apertures 46, 48. As shown, aninjection nipple 50is located within aperture 46, whereas the aperture 48 has a removable plug 52 therein. The overall head 26 furtherincludes a removable, stationary metallic sleeve 54 secured to theinner face of section 38. The sleeve 54 has aninternal surface 56 presenting helical rib sections 57 which derlnes an axially extending bore 58. As shown, the thickness of sleeve 54increases along the length thereof such that the diameter of bore 58 decreases betweeninlet head 24 and third head 28. The sleeve 54 also has transverse apertures 59 and 59a therethrough which arein alignment with barrel section apertures 46, 48 described previously. The end of head 26 remote frominlet head 24is equipped with an apertured stator 60 (see Fig. 2), The stator 60includes an outboard flange 62 whichis sandwiched between the heads 26, 28 as shown, as well as aninwardly extending annular segment. The segment 64in turn has aninnermost bearing ring 66 secured thereto by means of screws 68.in addition, the segment 64is provided with a series of six circumferentially spaced, circular holes 70 therethrough. Fig. 3illustrates another rotor/stator assembly whichisidentical with that depictedin Fig. 2, save for the fact that,in lieu of the holes 70, a series of six circumferentially spaced slots 70a are provided. Third head 28is similarin many respects to nead 25 andincludes an outer tubular section 72 and an outboard jacket 74, the latter equipped with aninlet 76 and outlet 78 forintroduction otindirect cooling or heating media Furthermore, the section 72 has transverse openings 80, 82 therethrough which respectively receive nipple 84 and removable plug 86, A stationary, removable metallic sleeve 88is positioned within section 72 and has transverse apertures 89, 89a therethroughin registry with the apertures 80, 82. Theinner surface 90 of sleeve 88 presents helical ribs 89 and defines an axially extending central bore 92. The bore 92 decreasesin effective diameter between the end of barrel section 28 adjacent section 26 and the end of the section 28 proximal to die 20, The barrel 16is completed by provision of a shorn annular spacer 94 positioned adjacent the end of third barrel section 28 remote from barrel section 26, together with endmost die 20. The latterin the embodiment shownis a simple metallic plate having a series of die holes 96 therethrough. The screw assembly 22includes four rotatable elements mounted on the shaft 36 andinterconnectedin an end-to-end relationship.in particular, assembly 22 has aninlet screw section 98, a first screw section 100, bearing rotor 102, and third screw section 104. The first screw section 100includes an elongated central shaft 106 presenting an outer, generally frustoconical surface and outwardly extending helical rlighting 108.itis noteworthy that the pitch of flighting 108is oriented at a pitch angle whichis less than the pitch'angle o\ the helical flighting 57 defined by surface 56 of sleeve 54. Moreover,it will be seen that the overall configuration of the screw section 100 conforms with the decreasing diameter of bore 58,i.e., the outer periphery of the flighting 103 progressively decreases from theinlet end of the screw section 100 to the outlet end thereof adjacent rotor 102. The rotor 102is mounted on shaft 35 and uicludes an outermost. somewhat L-shapedin cross-section annular bearing 110 whichis closely adjacent annular bearing segment 66 of stator 60. The rotor 102 and stator 60 thus assistsin stabilizing the screw assembly 22 during high speed rotation thereof. The third screw section 104is very similar to screw section 100. Thatis, the section 104includes an elongated central shaft 112 presenting an outerriiost, frustoconical surface and helical flighiing 114; theiaiieris orieniea at a pitch angle whichis less than the pitch angle of the ribs 89. Again referring to Fig. 1,it will be observed that the overall extruder bore defined by the sleeves 54 and 88is of generally frustoconical configuration leading frominlet 18 to die 20,i.e., the barrel bore presents a generally decreasing cross-sectional area along the length thereof. Moreover,it will be seen that the effective length of the extruder from the remote end ofinlet 18 to the end of barrel 16 (shown as dimension "L"in Fig. 1) versus the maximum diameter of the barrel bore (dimension "D"in Fig. 1)is relatively low, and preferably up to about 6; the more preferred UD ratiois frorii about 3-6. As used herein, "UD ratio" refers to the ratio measuredin accordance with the exemplary length and diameterillustratedin Fig. 1. it will also be understood that the stator 60 and rotor 102 cooperativeiy present a flow-restricting deviceintermediate the length of the barrel at the region ofinterconnection between barrel sections 26 and 28. The overall flow-restricting device thus presents an upstream face 116 and an opposed downstream face 118. The screw assembly 22 and the flow-restricting device 60, 110 are cooperatively designed so that the material displacement per revolution of the assembly 22 adjacent face 116is smaller than the material displacement per revolution of the assembly 22 adjacent the downstream face 118. Moreover, the assembly 22 and device 60, 110 are designed so as to substantially continuously maintain the slots 70 forming a part of the flow-restricting device full of material during operation of the extruder.in more detail, the material displacement per revolution of the screw assembly 22 adjacent downstream face 118is up to 40% greater than the material displacement of the screw adjacent the upstream face 118; more particularly, the displacement adjacent face 118 exceeds that adjacent face 116 by a factor of from about 15-40%. Also, the depressions betv/een adjacent ribs 89in sleeve 88 are greater than the corresponding depressionsin sleeve 54. As a consequence, the free volume within the barrel bore downstream of and adjacent flow-restricting device 60, 110is greater than the free volume adjacent and upstream of the flow-restricting device. Quantitatively speaking, the free volume within head 28 at the region efface 118is up to about 30% greater than the free volume within head 26 at the region of face 116, more preferably from 15-30% greater. it has been discovered that the short length exituders of theinvention should be operated at the relatively high rotation speeds described above. Such high speed operation,in conjunction with the other preferred configuration details, gives high throughputs together with good quality of products. in typical operations employing extrudersin accordance with theinvention, an edible nnaterial to be processedis first formulated and then precondition, followed by passageinto and through the short length extruder.in the preferred preconditioned, the materialis moisturized and at least partially cooked. Preconditioningis normally carried out so that the product leaving the preconditionejf has a total moisture content of from about 15-40% by weight, and more preferably from about 22-28% by weight. The residence timein the preconditionejris usually from about 15-150 seconds, and more preferably from about 90-150 seconds; and the maximum temperaturein the preconditioner ranges from about 55-212°F, and more preferably from about 180-200°F. During passage through the extruder, the materialis subjected toincreasing levels of temperature and shear andis normally fully cooked asit emerges from the extrusion die. Typical residence times of the materialin the extruder barrel range from about 10-40 seconds, and more preferably from, about 20-30 seconds. Maximum pressure levels achievedin the extruder barrel are normally from about 150-1000 psi, and more preferably from about 300-500 psi. The maximum temperature level achievedin the extruder barrelis from about 220-300°F., and miore preferably from about 230-250°F,' During extrusion processing, the apertures of the flow-restricting device 60, 110 are completely filled so as to create a chokein the barrel at the zone of the flow-restricting device and a pressure differential across the device 60, 110 (i.e., the pressureis higher at face 116 as compared with the pressure of face 118). Moreover, owing to the fact that the displacement per revolution of the screw assembly 22 adjacent downstream face 118is greater than that proximal to the upstream face 116, the free volume downstream of the flow-restriction deviceis not fully choked with material. At a zoneimmediately adjacent the die 20, another choke of materialis formedin order to assure smooth extrusion of the product through the die apertures. The extruders and methodsin accordance with theinvention are particulahy suited for the preparation of feed products, especially animal feed products. Such products may be of the expanded variety, such as typical pet foods, or more dense peliet-type products typically fed to pigs.in such uses, the starting materials usuallyinclude a high proportion of grain at a level of at least about 40% by weight (e.g., corn, wheat, soy, milo, oats), and mayinclude fats and otherincidentalingredients. Expanded productsin accordance with theinvention would typically have a final (i.e., after drying) density of from about 15-25 kg/m3 whereas denser pellet-type products would normally have a final density of from about 30-50 kg/m^ Broadly, therefore, products of theinvention would have final densitiesin the range of from about 15-50 kg/m^ The following examples set forth preferred extrusion apparatus and methodsin accordance with theinvention.itis to be understood that theinventionis not so limited and nothingin the examples should be taken as a limitation upon the overall scope of theinvention. Example 1 in this example, a short length extruderin combination with a preconditioned was employedin the manufacture of high quality pet food at commercial production rates. The extruder was of the type depictedin Fig. 1, and consisted of three heads.in particular, the extruder configuration usedin Runs #1, #2 and #4 was made up of the following components (where all parts areidentified with Wenger Mfg. Co. part numbers): extruder barrel - 65695-001 (inlet head); 65676-001 (head No. 2); and 65689-001 (head No. 3). Head No. 2 was equipped withinternal liner 65691-001 and a stator 76598-001 between the second and third heads. Screw assembly - 76597-002 (shaft); 65670-001 (inlet screw); 65671-001 (second screw section); 65906-003 (stationary shearlock between second and third screw sections comprising 65907-001 (rotor) and 65909-001 (stator)); and 65675-001 (third screw section). Final die - 65534-009 (1" spacer); 65421-001 (die plate); and 31350-779 (dieinsert giving 3/8" die openings). A rotating knife assembly was positioned adjacent the outlet of the die for cutting the extrudateinto a convenient size. The knife assemblyincluded the following: 19462-023 (knife holder) and ten knife blades (19512-003). The extruder employed on Runs #3 and #5 wasidentical with that described above, except that the shaft employed was Wenger Part No. 76597- 001 and the final screw section (Wenger Part No. 65675-005) was of cut flight configuration. The preconditioned usedin both of these setups was a Wenger DDC preconditioner having the standard 60-60 configuration. in all of the five test runs, the starting pet food recipe was made up of 24% by weight poultry meal, 54% by weight corn meal, 8% by weight wheat, 8% by weight corn gluten meal, and 6% by weight soybean meal.in each case, the starting material was fedinto and through the preconditioner for moisturizing and partial cooking thereof, followed by passage through the three head extruder. Water and sometimes steam wasinjectedinto the extruder barrel at the second and third headinjection ports. Subsequent to extrusion, the product was conventionally dried to a moisture content of about 9-11% by weight. The following table sets forth the operating conditions for the precondi¬tioner and extruder devicesin the five runs. All of the runs gave commercially acceptable, fully cooked and formed products. The bulk density of the product from Run #1 was found to be about 19 lbs/ft3 Example 2 in this example, a short length extruder/preconditionerwas used to manufacture a high quality, dense, hard pig finishing feed. The resultant product was equivalentif not superior to those conventionally produced using an expander and pellet mill. The extruder was of the type depictedin Fig. 1 except thatit did notinclude the rotor/stator assembly defining a mid-barrel material flow restriction. Specifically, the three-head extruder configuration usedin Runs 6 and 7 was made up of the following components (where all parts areidentified with Wenger Mfg. Co. part numbers): extruder barrel - 65695-001 (inlet head); 65676-001 (head No. 2); and 65689-001 (head No. 3). Head No. 2 was equipped withinternal sleeve 65691-001, whereas head 3 also had aninternal sleeve, 76598-001. Screw assembly - 76597-002 (shaft); 65670-001 (inlet screw); 65671-001 (first screw section); 65906-001 (second screw section) and 65676-001 (third screw section). Final die - 66532-103 BH, 65534-009 AD, 74010-953 NA, 74010-954 NA, with 13inserts. A rotating knife assembly was positioned adjacent the outlet of the die for cutting the extrudateinto a convenient size. The knife assemblyincluded the following: 19452-001 (knife blade holder) and six knife blades (19430-007). in the case of Runs 8 and 9, the extruder configuration was made up of the following components: extruder barrel - 65695-001 (inlet head): 65676-001 (head No, 2); and 65689-001 (head No. 3). Head No. 2 was equipped withinternal sleeve 65691-001, whereas head 3 also had aninternal sieeve, 76598-001. Screw assembly - 76597-002 (shaft): 65670-001 (inlet screw): 65671-001 (first screw section); 65658-015 (second screw section): and 65675-001 (third screw section). Final die - 6534-009 AD and 65421-001 BH. A rotating knife assembly was positioned adjacent the outlet of the die for - cutting the extrudateinto a convenient size. The knife assemblyincluded the following: 19607-017 (knife blade holder) and five knife blades. The precondition usedin both of these setups was a Wenger Mode! 16 DDC preconditione. having Configuration No. 377. The left and right shafts were each equipped with a total of sixty beaters. in Runs 6-9inclusive, the starting recipe was made up of 76.96% by weight milo, 15.95% by weight soybean meal, 4.69% by weight tallow, 0.94% by weight salt, 0.94% by weight calcium carbonate, 0.41% by weight vitamin premix, and 0.11% by weight lysine.in each case, the starting materialis fedinto and through the preconditioner for moisturizing and partial cooking thereof followed by passage through the three head extruder. Water wasinjectedinto the extruder barrelin Runs 7-9. Runs 6 and 7 were somewhat unstable but Runs 8 and 9 were stable and gave good, high density pig feeds. Subsequent to extrusion, the product was conventionally dried using a multiple pass dryer to achieve dryer discharge densities of 35 kg/m3 (Run 6), 36 kg/m3 (Run 7), 45.4 kg/m3 (Run 8), and 45.0 kg/m3 (Run 9), The following table sets forth the operating conditions for the preconditionand extruder devicesin the four runs. The higher densities achievedin Runs 8 and 9 are believed chiefly attributable to the different die assembly employed as compared with Runs 6 and 7, Although the extruder device specifically described hereinis of the single screw type,it will be understood that short length twin screw extruders may also be fabricated and usedin accordance with theinvention. WE CLAIM : 1. A short length cooking extruder for extrusion cooking of an edible material, said extruder comprising an elongated tubular barrel having a material inlet and a spaced material outlet and presenting an inner surface defining an elongated bore which is of general frustoconical configuration over at least a portion of the length thereof; an elongated, helically flighted screw assembly positioned within said bore; means for axially rotating said screw assembly at a rotational speed of at least 500 rpm; and an apertured extrusion die disposed across said material outlet; said extruder having a L/D ratio of up to 6. 2. The extruder as claimed in claim 1, wherein flow restriction defining means is provided within said barrel and intermediate said inlet and outlet, said flow restriction defining means presenting an upstream margin and an opposed downstream margin, said upstream margin being closer to said inlet than said downstream margin. 3. The extruder as claimed in claim 2, wherein the material displacement per revolution of said screw assembly adjacent said upstream margin is smaller than the material displacement per revolution of said screw assembly adjacent said downstream margin. 4. The extruder as claimed in claim 2, wherein said flow-restriction defining means comprises an apertured flow restricting device presenting an upstream face and an opposed downstream face, said screw assembly and flow restricting device being cooperatively configured for substantially continuously maintaining the apertures of said flow restricting device full of material during operation of said extruder. 5. The extruder as claimed in claim 4, wherein said flow restricting device comprises an apertured stator secured to said barrel, and a complemental rotor forming a part of said screw assembly. 6. The extruder as claimed in any of claims 1 - 5, wherein said bore is of generally frustoconical configuration for at least 50% of the length of the bore from said inlet to said die and presenting a generally decreasing cross-sectional area as said die is approached. 7. The extruder as claimed in any of claims 1 - 6, wherein said inner bore defining surface of said barrel presents a series of spaced, helical rib sections along the length thereof 8. The extruder as claimed in any of claims 1- 7, wherein the free volume within said barrel adjacent said upstream margin is greater than the free volume adjacent said downstream margin. 9. The extruder as claimed in any of claims 1 -8 wherein injecting means is provided for injecting a fluid through said barrel into the confines of said bore. 10. The extruder as claimed in any of claims 1 to 9, wherein said extruder has one screw assembly within said bore. 11. A method for extrusion cooking of an edible material by the short length cooking extruder claimed in any one of the preceding claims, said method comprising the steps of passing said edible material into the inlet of an elongated extruder having a barrel equipped with an endmost extrusion die and an internal, axially rotatable, flighted screw assembly within the barrel, said extruder having an L/D ratio of up to 6; and rotating said screw assembly at a speed of at least 500 rpm for advancing said material from said inlet along the length of said barrel and out of said extrusion die for heating and at least partial cooking of the edible material. 12. The method as claimed in claim 11, wherein during said material advancement, said material is caused to completely fill and choke said barrel at a zone intermediate said inlet and said extrusion die. 13. The method as claimed in claim 11, wherein said material is passed through an apertured flow restricting device at said zone, said screw assembly and flow restricting device substantially continuously maintaining the apertures of the flow restricting device full of said material during operation of said extruder. 14. The method as claimed in claim 11, wherein said material is passed through a preconditioner in order to moisturize and partially cook the material prior to passage of said material into said inlet. 15. The method as claimed in claim 11,wherein moisture is injected into said barrel during rotation of said screw assembly. 16. The method as claimed in claim 11, wherein the edible material is passed to the inlet of a single screw extruder. 17. A short length cooking extruder, substantially as herein described, with reference to the accompanying drawings. 18. A method for extrusion cooking, substantially as herein described, with reference to the accompanying drawings.

Documents:

1496-mas-1996 abstract.pdf

1496-mas-1996 claims duplicate.pdf

1496-mas-1996 claims.pdf

1496-mas-1996 correspondece -others.pdf

1496-mas-1996 correspondece -po.pdf

1496-mas-1996 description (complete) duplicate.pdf

1496-mas-1996 description (complete).pdf

1496-mas-1996 drawings.pdf

1496-mas-1996 form-1.pdf

1496-mas-1996 form-26.pdf

1496-mas-1996 form-29.pdf

1496-mas-1996 form-4.pdf

1496-mas-1996 petition.pdf