Reissue Patent
2000-05-09
2001-06-26
Alexander, Reginald L. (Department: 1761)
C099S353000, C425S38200R, C425S464000, C426S516000
Reissue Patent
active
RE037235
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present is broadly concerned with improved short length, high speed extrusion cooking devices of the type generally described in U.S. Pat. No. 5,694,833 equipped with peripheral dies allowing greater product throughputs while increasing product densities, cook values and moisture levels. More particularly, the invention pertains to such improved extrusion cookers, and corresponding methods, wherein a peripheral extrusion die is disposed across the extruder barrel outlet and has a series of extrusion outlet openings oriented transverse to the longitudinal axis of the barrel. The peripheral dies of the invention may be provided with individual, axially spaced apart series of die outlet openings (usually with different numbers of outlet openings in each series), or more preferably with a radially enlarged peripheral die having only a single series of die openings.
2. Description of the Prior Art
U.S. Pat. No. 5,694,833 (incorporated by reference herein) describes a significant breakthrough in the extruder art. Specifically, that patent discloses relatively short length extruders (having an L/D ratio of up to about 6) which are operated at high screw rotational speeds typically in excess of 500 rpm. It has been found that extruders of this type are capable of producing, at relatively high output rates, feed products of very high integrity. Moreover, such extruders can be produced at lower costs as compared with conventional cooking extruders.
Extruders of this type are heretofore have been equipped with conventional plate-type face dies bolted across the outlet end of the extruder barrel. Dies of this variety have a series of die outlet openings which are essentially parallel with the longitudinal axis of the extruder barrel. Face dies, while in widespread use, tend to restrict extruder throughputs. Furthermore, because such dies must withstand considerable pressure, they are normally relatively expensive.
It has also been known in the past to equip certain long-barrel extruders with so-called “peripheral” dies. Dies of this character have die outlet openings oriented transverse to the longitudinal axis of the extruder barrel. Generally speaking, peripheral dies have a tendency to adversely affect product quality, particularly where relatively dense extrudates are desired. Accordingly, peripheral dies have not achieved wide spread use in the extrusion art.
SUMMARY OF THE INVENTION
The present invention provides improved extrusion devices of the short-barrel, high-speed variety through the use of peripheral die structures. Broadly speaking, extrusion devices of the invention include an elongated, tubular barrel having a material inlet and a spaced material outlet with an inner surface defining an elongated bore; an elongated, helically flighted screw assembly is positioned within the bore and is coupled to a drive for rotating the screw assembly at a rotational speed of at least about 500 rpm. A peripheral extrusion die is disposed across a material outlet of the barrel and has a series of extrusion outlet openings oriented transverse to longitudinal axis of the barrel. Normally, the extruder would have an L/D ratio as hereinafter defined of up to about 7.
In preferred forms of the invention, the extruder barrel has an internal bore of generally frustoconical configuration for at least about 50% of the length of the bore from the inlet to the outlet. Usually, the bore has a general frustoconical shape substantially its full length from the barrel inlet to the outlet so as to present a generally decreasing cross-section of area along the length of the bore. Although twin screw extruders can be used in the invention, generally the screw assemblies are of the single screw variety. In terms of screw rotational speed, the preferred levels are from about 600-1500 rpm.
One peripheral die assembly in accordance of the invention makes use of a plurality of series of extrusion outlet openings, with the respective series being axially spaced apart. In such a design, the number of outlet openings in each series is different, with the smallest number of openings in the series nearest the extruder barrel outlet. In another preferred design, the peripheral die is substantially radially enlarged as compared with the outlet end of the extruder barrel. This allows provision of a substantially greater number of die outlet openings, so that only a single series of such openings is needed to provide the requisite extruder throughput.
In order to achieve a smooth material flow transition from the extruder barrel outlet to the peripheral die openings, internal flow-directing structure is normally used with the peripheral dies of the invention. Such flow-directing structure cooperates with the other die components for evenly and smoothly directing material from the extruder barrel to the peripheral die outlet openings without undue buildup of pressure within the die.
REFERENCES:
patent: 3295469 (1967-01-01), Vassalli
patent: 5641522 (1997-06-01), Satanovsky
patent: 5694833 (1997-12-01), Wenger
patent: 5700510 (1997-12-01), Hauck
patent: 5814350 (1998-09-01), Rockstedt
patent: 645835 (1979-02-01), None
patent: 1242386 (1986-07-01), None
Hauck Bobbie W.
Wenger Marc
Alexander Reginald L.
Hovey Williams Timmons & Collins
Wenger Manufacturing Inc.
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