Patent Application
20070177451
The present invention relates to serrated kneading disks, kneading blocks formed from a plurality of the serrated kneading disks, and single piece kneading blocks having serrated lobes.
Twin screw extruders are well known. Such extruders have two parallel, intersecting bores passing through an elongated extruder barrel. Each bore contains a rotatable screw element extending therethrough. The screw elements can be co-rotating, i.e., rotate in the same direction, or counter-rotating, i.e, rotate in opposite directions. However, the present invention is limited to co-rotating screw elements.
Each screw element is comprised of a shaft having compounding segments mounted along the shaft in a manner such that they intermesh with corresponding compounding segments mounted on the adjacent parallel screw element. The compounding segments typically include kneading elements, conveying elements, mixing elements, and other specialized elements.
The kneading elements are typically two or more kneading disks placed adjacent one another on an extruder screw shaft to form a kneading block. The kneading disks have truncated elliptical-shaped bodies having two crests spaced 180 degrees apart. An opening passes through the kneading disk body and has a configuration adapted to allow the kneading disks to be lockingly engaged on the shaft of a screw. The individual kneading disks in a kneading block have crests that are misaligned by pre-selected stagger angles.
The opposing kneading blocks in a typical twin screw extruder are fully intermeshing and self-wiping. They generate high and low shear regions, the high shear region being next to the crests, and the low shear region being in the screw channels.
While such prior art kneading disks and kneading blocks are satisfactory for processing polymeric materials, they are not as satisfactory for processing materials that require an extra degree of shearing and tearing such as, for example, high fiber materials such as wood and cereal grains or agglomerated materials.
It is an object of the present invention to provide a kneading disk or kneading block that provides more satisfactory processing of fibrous materials in a co-rotating twin screw extruder.
The serrated kneading disk of the present invention includes a body having a perimeter that is an ellipse having truncated ends, the curved elliptical portions forming flanks and the truncated ends forming crests. The crests are curved to form the arc of a circle having a radius slightly less than the radius of the bore of the extruder barrel within which the disk is to be used. The disk body has a passageway extending through the middle thereof, the passageway having a configuration adapted to allow the kneading disks to be lockingly engaged on the shaft of an extruder screw.
A plurality of grooves are formed in the flanks and crests. The bottoms of the grooves are preferably sloped with at least one portion of the groove being deeper than another portion thereof However, the grooves can have a uniform depth.
A plurality of the serrated kneading disks can be placed adjacent one another on an extruder screw shaft to form a kneading block Alternatively, a kneading block can be formed as a single piece having lobes that are substantially identical to the individual serrated kneading disks.
The serrated kneading disk body 10 of the present invention has a perimeter that is an ellipse having truncated ends, the curved elliptical portions forming flanks 12, 12′ and the truncated ends forming crests 14, 14′. Crests 14, 14′ are the arc of a circle having a radius substantially corresponding to the radius of the bore of the twin screw extruder barrel within which it is to be used, with allowance for a small gap between the crests 14, 14′ and the wall of the bore. Serrated kneading disk has substantially flat faces 15, 15′ having major planes that are substantially parallel.
A cylindrical passageway 16 extends through the middle of kneading disk 10 between faces 15, 15′, the axis of cylindrical passageway 16 being located at the center of truncated ellipse perimeter of serrated kneading disk 10. A plurality of spline grooves 18 are formed in the face of cylindrical passageway 16, perpendicular to faces 15, 15′, and adapted to receive splines located on an extruder screw shaft. Alternatively, a plurality of splines (not shown) can be formed in the face of cylindrical passageway 16 adapted to be received in spline grooves formed in an extruder screw shaft.
Although the foregoing are the two preferred configurations for attaching kneading disk body 10 to a screw shaft, any configuration adapted to allow the kneading disk body 10 to be lockingly engaged on the shaft of an extruder screw can be used. For example, passageway 16 can have a hexagonal or a double hexagonal shape adapted to seat in a mating shape on the extruder screw shaft. Other alternative locking means includes any suitable arrangement of hubs and keyways, pins, etc.
A plurality of grooves 20 are formed (such as by machining) in that portion of the periphery of serrated disk 10 forming flanks 12, 12′, grooves 20 extending between faces 15, 15′. Similarly, a plurality of grooves 20 are formed in that portion of the periphery of serrated disk 10 forming crests 14, 14′, grooves 20 extending between faces 17, 17, which are slightly recessed from faces 15, 15′.
Grooves 20 are preferably evenly spaced apart and preferably cover the entire surface of flanks 12, 12′ and crests 14, 14′. However, blank spaces 17, i.e., spaces having no grooves 20, may be left between adjacent sets of grooves 20 such as, for example, shown in
Grooves 20 may have a uniform depth between faces 15 and 15′ and between faces 17 and 17′, or may have a non-uniform (sloping) depth there between. Alternatively, some of grooves 20 may have a uniform depth between faces 15 and 15′ and between faces 17 and 17′, and other of grooves 20 may have a non-uniform (sloping) depth there between.
It is to be understood that the second through fourth configurations of grooves 120-320 would appear on serrated kneading disk 10 in substitution of groove 20. It is to be further understood that identical groove configurations to those described as extending between faces 15 and 15′ would also extend between faces 17 and 17′.
In the embodiment shown in
A plurality of serrated disks 10 can be assembled onto an extruder screw shaft in a manner well known in the art to form a kneading block. For example, three serrated kneading disks 10 could be inserted onto the splines of an extruder screw shaft in contact with one another, with their crests misaligned at desired stagger angles.
Alternatively, a kneading block can be formed as a single member instead of being formed from a plurality of serrated kneading disks 10.
A cylindrical passageway 116 extends through the middle of kneading block 110. A plurality of spline grooves 118 are formed in the face of cylindrical passageway 116, and are adapted to receive splines located on an extruder screw shaft. Alternatively, a plurality of splines (not shown) can be formed in the face of cylindrical passageway 116 adapted to be received in spline grooves formed in an extruder screw shaft.
Although the foregoing are the two preferred configurations for attaching kneading block 110 to a screw shaft, any configuration adapted to allow the kneading block 110 to be lockingly engaged on the shaft of an extruder screw can be used. For example, passageway 116 can have a hexagonal or a double hexagonal shape adapted to seat in a mating shape on the extruder screw shaft. Other alternative locking means includes any suitable arrangement of hubs and keyways, pins, etc.
It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments of this invention without departing from the underlying principles thereof. The scope of the present invention should, therefore, be determined only by the following claims.
