Extruders generally force molten material through an extruder barrel utilizing a turning screw. During operation, the flights of the screw engage the molten material, moving it along the length of the barrel. Usually, a restriction to flow such as a die defining the desired shape for the extruder material is mounted onto the end of the barrel. The force created by the screw on the material causes it to flow through the restriction. The movement of the material via the action of the screw, as well as the channeling of the material through the restriction, tends to generate very high reaction forces that are transmitted to the device employed to drive and support the screw.
In general, the extruder screw is mounted to an output thrust shaft that in turn forms part of a gear box. The thrust shaft is usually supported by roller-type bearings with the above-described reaction force being absorbed by a thrust bearing also in communication with the thrust shaft. A thrust bearing typically consists of a series of rolling elements sandwiched between two thrust plates. The thrust plates and rollers transfer the reaction forces generated by the processing of the material through the extruder to the gear reducer housing. Due to the magnitude of the reaction force, known thrust plates are generally not stiff enough to withstand the load imposed thereon and must be replaced frequently. Extruder screw, output thrust shaft and gear box assemblies are shown in U.S. Pat. Nos. 4,304,539 (an extruder shaft supported by bearings 4 and 5 with a thrust shaft flange therebetween), 4,859,166 (an extruder shaft supported by the inner raceways of bearings and flanges), 5,545,024 (extruder shafts supported by bearings reinforced with thrust shaft flanges), and 4,033,556 (an extruder shaft supported by the inner raceways of bearings).
Additionally, thrust bearings are well known in the art. U.S. Pat. No. 3,414,341 ('341) is an example of conventional thrust bearings having retainer seals. Flat rotating and stationary plates are shown with roller or ball bearings interspersed therebetween. A bearing cage which holds the roller or ball bearings in place is also shown in '341. Conventional flat rotating plates lack the stiffness desired in extruder applications, and are reinforced by thrust flanges for such applications.
U.S. Pat. No. 4,042,284 ('284) shows a thrust bearing assembly designed to counter considerable axial thrust such as that generated by extruders. The assembly of '284 has a support, two rows of coaxially arranged bearing elements (plates) in cooperating pairs forming a line of bearings in tandem, the elements in one row rotating with the shaft and those of the other row being stationary with the support and includes tilt means that are biased by at least two adjustable bearing elements. The thrust bearing assembly of '284 is quite complicated, and is not compatible with all conventional gear box assemblies.
FIG. 1 shows a conventional gear box design which incorporates a thrust shaft flange (36) to further stiffen and uniformly distribute the thrust load over a rotating thrust plate (34) in contact with the thrust shaft (20). During operation, the direction of thrust is against the flange (36) as indicated by the arrow labeled “T” shown in FIG. 1, and the force generated from the thrust is transmitted via the peripheral lip (42) on the thrust shaft (20) to the thrust shaft flange (36) which in turn transmits the force to the thrust bearing (41). A drawback associated with the above-described flange and thrust bearing arrangement is that a separate thrust shaft flange (36) and thrust plate (34) must be provided, resulting in an increased likelihood for machining and/or assembly error as well as the possibility of localized areas of high stress due to inexact mating of the thrust shaft flange and thrust plate surfaces (35) and (37). Moreover, the requirement for a separate thrust flange (36) adds to the expense of the extruder gearbox (38). Based on the foregoing, there is a need for a one-piece, combination thrust shaft flange and thrust plate design which would eliminate the difficulties and drawbacks associated with the above-described prior art configuration, and be compatible with prior art gear boxes (38) as shown in FIG. 1.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed.