Patent Application
20070237022
1. Field of the Invention
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.
2. Description of the Prior Art
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.
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.
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.
However, the apparatus as described in the '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.
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.
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.
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.
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.
Turning now to the drawings, a restriction assembly 10 is illustrated in
By way of general background, the assembly 10 is designed for use in a conventional single or twin screw extruder 16 illustrated in
Again referring to
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.
The restriction unit 14 includes a generally circular primary body 40 having a laterally extending through-slot 42 (
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
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
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
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.
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
A principal advantage of the flow restrictions assemblies of the invention stems from use of sliding flow restriction components 48, 50, 48a, 50a as opposed to the rotatable restrictors of the prior art, as exemplified in U.S. Pat. No. 4,136,968. Indeed, the units 14, 14a 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, 10a, which contributes to the cleanliness and operational efficiency of the assemblies and the overall extruders. Moreover, the present assemblies 10, 10a are advantageously designed so that, in the “full-open” positions thereof, the components 48, 50, 48a, 50a provide essentially unimpeded flow of material through the extruder barrel.
It will also be appreciated that the assemblies 10, 10a 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.
