Patent Application
20190224900
The present invention is broadly concerned with self-adjusting rotary cutter assemblies used in conjunction with extruders in order to evenly cut extrudate emerging from the extruder die plate and decrease the set-up time from one die plate to another die plate with the self-adjusting feature of the cutter head. More particularly, the invention is concerned with such assemblies and methods characterized by unrestrained movement of a rotary cutting head toward the outlet face of the extruder die plate, which lengthens the service life of the cutter assembly by resiliently maintaining a desired force exerted by the cutter head against the outlet face of the die plate, even if there is a degree of oblique misalignment between the cutter head and die plate.
It is almost a universal practice to provide cutter assemblies for use in conjunction with extruders of all types. These extruders are normally equipped with a restricted orifice die plate having a central, outwardly extending mounting shaft. The cutter assemblies typically include a rotatable cutter head having a central hub with a plurality of outwardly extending cutter blades positioned adjacent the output face of the die, with the fixed position cutter head operably coupled with a driven assembly serving to rotate the head at high speed. Prior cutter assemblies have been designed with the assumptions that the cutter mounting shaft is truly perpendicular and the cutting edges of the fixed position blades are truly parallel to the die face. In practice, however, it often occurs that there is a degree of misalignment between these parts, resulting in inefficient cutting of extrudate and significant shortening of the service life of both the dies and the cutter assemblies.
Furthermore, some cutter assemblies are designed to maintain a very slight distance between the cutting edges of the blades and the die face, rather than attempting to maintain the cutting edges against the die face under a constant biasing force.
U.S. Pat. Nos. 3,196,487 and 5,284,433, and US Patent Publication No. 2015/0056322 describe various cutter assemblies typical of the prior art. The '487 patent provides a spring-loaded biasing force exerted against the cutter hub and blade, but provides adjustable stop nut means to limit the movement of the rotatable cutting head toward the output face of the die. Hence, this patent advocates a cutter assembly which maintains a slight distance between the cutting edges of the blades and the die face, by restraining the movement of the cutter head and blades toward the die face as the blade design, if not restrained by the adjustable stop nut, would damage the surface of the die and cutter edge.
The present invention provides an improved cutter assembly, the combination of a cutter assembly and a die, and corresponding methods which, contrary to the prior art, are characterized by unrestrained movement of the cutter head of the assembly, and the blades thereof, toward the outlet face of the die. It has been found that maintaining a substantially constant engagement force between the cutting edges of the blades and the die face, together with knife geometry and material, serves to materially increase the service life of the cutter assembly while permitting cutting of extrudate into very small pieces.
In general, the cutting assemblies of the invention include a rotatable cutting head carrying at least two cutting blades adapted to engage the outlet face of a die, a rotatable drive hub, and biasing structure. Coupling structure is provided to operably couple the drive hub with the cutting head for simultaneous rotation thereof. The biasing structure is designed to exert an unrestrained force upon the cutting head with consequent unrestrained movement of the cutting head toward the die outlet face during use of the rotary cutter assembly. In an embodiment, the coupling structure comprises cooperating splines on the cutting head and the drive hub, and the cutting head carries a plurality of cutting blades. The biasing structure may include a coil spring, but other biasing arrangements would also be possible.
In certain embodiments, the cutter assemblies include a drive hub having a bearing housing supporting at least one bearing for rotation of the drive hub relative to the die mounting shaft.
Also, a spring housing is coupled with the drive hub, with the coil spring biasing structure operable to unrestrainedly urge the drive hub, spring housing, and cutting head toward the outlet face, with a predetermined, substantially constant force which maintains the cutting edges of the blades in constant engagement with the die plate surface, even in situations where the cutting edges and die plate are on respective, relatively oblique planes.
While the drawings do not necessarily provide exact dimensions or tolerances for the illustrated components or structures,
Turning now to the drawings, and particularly
The illustrated die plate 12 is exemplary of a number of possible different die plate configurations having a greater or lesser number of openings 16, and the latter may also be of different shapes. The plate 12 is secured to barrel 14 by means of an intermediate mounting head 18 and screws 20. The die plate 12 also has a central, outwardly extending mounting shaft 22 having an enlarged inboard section 24 and a smaller diameter outboard section 26, the latter having a threaded bore 28 in the butt end thereof.
In the illustrated embodiments, the cutter assembly 10 is depicted in conjunction with a single screw extruder having the barrel 14. It should be understood, however, that the invention is not so limited, in that the cutter assemblies of the invention can be used with a wide variety of different extruders, including twin screw extruders. As is well-known in the art, these extruders include, in addition to a barrel 14, at least one internal, elongated, helically flighted extrusion screw (not shown) serving to move material from the inlet end of the extruder toward and through the die plate 12. During such movement, the material is typically subjected to increasing levels of pressure, temperature, and shear in order to at least partially cook the extrudate emerging from the plate 12.
The cutter assembly 10 generally includes a rotatable cutting head 30, a rotatable drive hub 32 coupled with a rotatable spring housing 34, biasing structure 35, and coupling structure 36 serving to operably connect the hub 32 and housing 34 with the cutting head 30, and a drive shaft assembly 38 operably coupled with drive hub 32.
The cutting head 30 includes an annular, central hub 40 with a series of radially outwardly extending, replaceable cutting blades 42 mounted on the hub 40. As illustrated in
The drive hub 32 includes an annular bearing housing 46 with an elongated, central, inwardly extending, tubular spindle 48 having an enlarged segment 49; it also has an outer skirt 50 disposed about spindle 48, with an inwardly extending section 50a. The housing 46 is equipped with an outboard, single race bearing unit 51 and an inboard, double race bearing unit 52, with the units 51, 52 operably coupled with spindle 48 on opposite sides of the segment 49. A bearing retainer ring 54 serves to maintain the bearing unit 51 in place against segment 49, whereas the unit 52 bears against the segment 49 and section 50a. A sealing ring 56 is also provided adjacent the inboard end of bearing unit 52.
The spring housing 34 includes an annular outer end 58 and a tapered, frustoconical section 60, the latter having a series of innermost, circumferentially spaced apart drive lugs or splines 62, which form a part of coupling structure 36 and are oriented to mate with and engage the splines 44. The housing 34 further has an upper, inwardly extending annular shoulder 64, as well as a smaller, intermediate inwardly extending, annular stop shoulder 66, and an innermost spring-retaining shoulder 69. As best seen in
The biasing structure 35 is situated within the confines of spring housing 34 and is in the form of a helical spring 72. The spring 72 is retained in place between an outer spring washer 74 abutting section 50a and shoulder 69, as best seen in
The cutter assembly 10 is designed to be rotatably mounted on the mounting shaft 22 of die plate 12. Again referring to
At this point, it is only necessary to connect the drive shaft assembly 38 to bearing housing 46. The drive shaft assembly 38 is itself entirely conventional and includes a drive shaft 78, intermediate coupler 80, and an apertured connection plate 82. A series of connection screws 84 are used to secure plate 82 by threading the screws into corresponding threaded bores 86 provided in bearing housing 46. Other means could be employed to drive the cutter, such as direct coupling to a motor or use of a chain or belt drive, owing to the supported bearing structure forming a part of the cutter assembly.
The cutter assembly 10 possesses a number of advantages not found in prior art units. First, the use of the biasing structure to urge the cutting head 30 and blades 42 in an unrestrained fashion and at a substantially constant force assures that the cutting edges of the blades are maintained in contact with the die plate throughout operation of the assembly 10. This is true even if there is a degree of misalignment between the mounting shaft 22, cutter head 30, and the blades 42. Such misalignment is taken up by the self-aligning nature of the components of the cutter assembly. Moreover, the dynamic self-alignment of the parts of the cutter assembly 10 ensures long life of the cutter assembly. This in turn permits production of very small extrudate pieces, in the 500μ range.
As previously described, the cutting blades 42 have wide surfaces 42a which engage the outer face 12a of die plate 12, and are oriented at a small angle relative to face 12a. This is to be contrasted with typical prior art blades, such as those illustrated in
All of the components of the cutter assembly are metallic, and the assembly 10 is devoid of any synthetic resin or rubber parts. This is preferable inasmuch as extruder operators wish to avoid such resilient components, which can overtime wear and break, potentially ending up in the product stream.
