A new hydraulic device has been facilitating the screw tensioning in KraussMaffei Berstorff twin-screw extruders and ensuring reproducible installation and pretensioning.
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The new hydraulic screw pretensioning device reliably tightens the system consisting of screw mandril, screw part and screw cup in the elastic range.
Michael Behling, KraussMaffei Berstorff Development Engineer, said: "The processing tasks are becoming increasingly complex, and require higher and higher filling levels, higher throughputs and greater efficiency. That's why more and more powerful drives are being used in twin-screw extruders to enable ever higher torques to be transferred to the screws.
"In order to be able to ensure the reliable transmission of the torque, not only special, heavy-duty screw shaft materials and an optimum gear geometry are required, but also reliable tightening of the screws in the shaft."
Until now the common practice has been to tighten the segmented screws with a torque wrench. However, this method is subject to certain tolerances and, in the case of reconfiguring, involves a large amount of time.
The new pretensioner from KraussMaffei Berstorf applies an always reproducible, defined tensile load to the screw shafts, but no longer any torsional stress. It is easy to operate: The operator selects the correct pressure from the machine documentation and clamps the screw outside the extruder in the pretensioning device.
The system consisting of screw mandril, screw part and screw cup is reliably tightened at the press of a button in the elastic range using a high-performance hydraulic pump. In this condition, it can be easily installed in the procedure part. A good bit of preliminary work went into this: The materials, resulting expansion coefficients and geometric lengths and structural sizes were factored in the calculation on a cold screw when defining the required hydraulic pre-load pressures.
In addition to the time savings, the hydraulic pretension provides another positive “side effect” with clear cost benefits: The defined pretension forces prevent the melt from infiltrating between the screw part and screw mandril. This avoids time-consuming and cost-intensive work such as disassembling or cleaning the extruder.
Thanks to a well-conceived series design, we can cover all extruder sizes of the ZE BluePower, ZE-UTX and UltraTorque (UT) series with three pretensioning devices.