BRIEF DESCRIPTION OF THE DRAWING FIGURES
FIG. 1 is a perspective view of a flow restriction assembly in accordance with the invention;
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;
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;
FIG. 4 is a vertical sectional view similar to that of FIG. 2, but showing the assembly in its fully closed position;
FIG. 5 is a side view of the assembly, with the adjacent cover plate removed;
FIG. 6 is a fragmentary, perspective, exploded view depicting the connection between the drive assembly and restriction components;
FIG. 7 is a vertical sectional view of another embodiment of the invention, designed for use with a twin screw extruder;
FIG. 8 is a sectional view of an extruder in accordance with the invention, including a mid-barrel valve and illustrating the extruder screw helical flighting throughout the length of the extruder barrel;
FIG. 9 is a fragmentary, horizontal sectional view similar to that of FIG. 3, but illustrating a modified restriction assembly having opposed restriction components inwardly moveable such that the inner surfaces thereof are inboard of the outer surfaces of the helical screw flighting; and
FIG. 10 is a vertical sectional view similar to that of FIG. 2, and showing the modified assembly of FIG. 9 in its fully closed position.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
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 respectively, 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, increasing the mechanical energy imported to the material being processed.
By way of general background, the assembly 10 is designed for use in a conventional single or twin screw extruder, such as single screw extruder 16 illustrated in FIGS. 3 and 4. In a single screw extruder 16, 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 endmost, 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 sections 28 each located within an associated head section 20. The screw 26 has helical flighting presenting an outer surface 29 defining the outer diameter of the screw, and a root diameter 29′. 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 helically flighted screws 26a presenting outer surfaces 29a mounted on respective hexagonal or keyed drive shafts 30a.
In preferred forms, the extruders of the invention include screws 26,26a having forward pitch flighting on opposite sides of the assembly 10, and most preferably throughout essentially the entirety of screws. This is illustrated in FIG. 8, and is important in many cases so as to maintain the flow of material through barrel 18 in a forward direction toward the barrel outlet (normally equipped with a restricted orifice die, not shown).
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.
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 (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.
The unit 14 also includes a pair of 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 be 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.
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 shearlock element 12 as 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.
The drive apparatus 68 further includes a pair of arcuate cover plates 80,82 respectively disposed 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 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.
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 unlit 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 inner surfaces 54 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) 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. As the unit 14 is shifted toward shearlock element 12 to increase back pressure and shear, the resultant extrudate becomes less dense, contrary to the prior art devices such as that illustrated in U.S. Pat. No. 4,332,481, wherein increasing restriction serves to increase the density of the resin output.
FIG. 7 illustrates a flow restriction assembly 10a for use in a twin screw extruder 32 having side-by-side intermeshed and intercalated screws 26a within an appropriately configured barrel. As illustrated, the outer surfaces 29a of the screw flighting of each extruder screw extends into the confines of the adjacent screw flighting between the surface 29a and the inner root diameter (not shown) of the screw. The components of assembly 10a 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 10a has a pair of shearlock elements 12a, each respectively mounted on one of the extruder shafts 30a. Also, a pair of opposed restriction components 48a,50a are provided, preferably mounted in a vertical orientation, as shown. The inner operating surfaces 54a of the components 48a,50a have a pair of juxtaposed arcuate regions so as to simultaneously accommodate and engage both of the shearlock elements 12a. Additionally, the surface regions 55a define flow passageways 98a,100a when the assembly 10a is in the full-closed position illustrated in FIG. 7. From the foregoing discussion, it will be readily appreciated that the components 48a,50a move along essentially aligned and rectilinear paths toward and away from the shearlock elements 12a, upon rotation of the drive screws 70a,72a.
FIGS. 9 and 10 illustrates a modified restriction assembly 10b having many components identical with the previously described assembly 10. Accordingly, like components have been identified with like reference numerals, except for the distinguishing letter “b,” and these like components need not be described in complete detail.
The chief difference between assembly 10b and assembly 10 is that the shearlock element 12b has a significantly smaller diameter, such that the outer surface 38b thereof is essentially coincident with the root diameter 29b′ of the screw 26b. Thus, the restriction elements 48b,50b may be shifted inwardly to a point closely adjacent the outer surface 38b, effectively “within”0 the depth of the helical flighting of screw 28b. More generally, the inner surfaces 54b of the restriction elements 48b,50b should be moveable to a point inboard of the outer surface 29b of the screw flighting, with the depth of the screw being defined by the radial distance between the outer surface 29b and the root diameter 29b′. Preferably, the elements 48b,50b should be moveable to points such that the inner surfaces 54b thereof are inboard of flighting outer surface 29b and at least 30%, more preferably at least 50%, of the screw depth, measured from the surface 29b. Providing an assembly 10b of this type allows far greater material flow restrictions to be achieved, as compared with prior art designs. This in turn greatly increases the velocity of the material passing through the extruder at the region of the assembly 10b, and increases the specific mechanical energy imparted to the product. The use of forward pitch helical flighting on opposite sides of the assembly 10b also serves to reduce retention time of the material passing through the extruder.
It will also be appreciated that the design concept embodied in restriction assembly 10b can also be employed with twin screw restriction assemblies. That is, the range of movement of the restriction elements in such twin screw designs can be increased so that the restriction elements are moveable inboard of the outer screw surfaces 29b of the twin extruder screws.
A principal advantage of the flow restrictions assemblies of the invention stems from use of sliding flow restriction components 48,50,48a,50a,and 48b,50b 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,14b 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,10b which contributes to the cleanliness and operational efficiency of the assemblies and the overall extruders. Moreover, the present assemblies 10,10a,10b are advantageously designed so that, in the “full-open” positions thereof, the components 48,50,48a,50a, and 48b,50b provide essentially unimpeded flow of material through the extruder barrel. The preferred assemblies 10b, when the restriction components 48b,50b are shifted so that the inner surfaces 54b thereof are inboard of the outer screw surfaces 29a, also provide high degrees of flow restrictions and thus impart significant mechanical energy to the material being processed (usually comestible materials, such as human food or animal feeds).
It will also be appreciated that the assemblies 10,10a,10b 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.
Patent Application
20070237850
