Transmission for a double screw extruder with two tapering...

Agitating – Rubber or heavy plastic working – Stirrer with specified drive means

Reexamination Certificate

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C074S66500G

Reexamination Certificate

active

06234661

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention concerns a transmission for an extruder with two tapering helical shafts.
A transmission of this genus is known from European Published Application 275 485. The shafts rotate in opposite senses and are connected to take-off shafts. A cogwheel is mounted on each take-off shaft. The cogwheels engage each other and distribute the force. Since the shafts slope toward each other, the cogwheels must be conical. Conical cogwheels, however, are more complicated and costly to manufacture than straight cogwheels. To ensure precise meshing of the extruder's threads, the cogwheel teeth must be precisely dimensioned to eliminate the need for expensive regrinding. They cannot be allowed to slip back and forth radially on the take-off shaft. The situation becomes even more complicated when both helical shafts are intended to rotate in the same sense and a third conical cogwheel is accordingly mounted between the other two.
Rotationally rigid compensating couplings (Taschenbuch für den Maschinenbau, Dubbel, 14th ed., 1981, 409) are generally employed when precisely angled transmission is necessary or when shafts are subject to errors in radial or angular alignment or to axial displacement. Cardan shafts and shafts with engaging cogs are examples.
An extruder with two parallel helical shafts is known from German OS 4 129 913. The transmission that distributes the force from the take-off shaft is separated from the processing section, which accommodates the helical shafts. The force that drives the latter is derived from the transmission by way of cardan shafts. This approach is intended to allow the transmission design to be independent of the narrow gap between the parallel helical shafts.
SUMMARY OF THE INVENTION
The object of the present invention is a simpler and less expensive transmission of the aforesaid genus for an extruder with two, tapering, helical shafts that rotate in opposite senses.
The take-off shafts in this transmission are not accommodated in the force-distribution section. There is accordingly no need for conical cogwheels, even though the helical shafts taper, and the force can be transmitted by straight cogwheels. Straight cogwheels are simpler to manufacture and can easily be mutually adjusted inside the transmission by means of a hydraulic pump. Since the rotating but rotationally rigid couplings inside the housing employ two sets of teeth, the overall transmission is very compact. Since the couplings are immersed in oil, however, there are no lubrication problems.


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