Torque motors offer advantages for plastics and rubber machinery

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A new range of torque motors from Parker Hannifin has been designed to help end users of heavy-duty plastics and rubber processing machinery replace traditional motor and gearbox combinations with a highly efficient direct-drive system. Used in conjunction with Parker's variable-speed drives, the new torque motors are intended primarily for use with extrusion machines and with injection moulding, mixing, crushing and winding equipment; in each case, the new motors can help to reduce energy and maintenance costs, thereby improving productivity and profitability, and provide greater reliability and overall levels of performance.

Many plastics and rubber extrusion systems use AC or DC motors and gearboxes to provide the required torque and speed to drive screws, shafts and associated components. This configuration can, however, be noisy, unreliable, draw relatively high levels of power, and be complex to install, operate and maintain.

In contrast, the latest Parker TMW Series torque motors are based on a proven design of permanent-magnet, brushless servo motor that produces high levels of torque at low operating speeds. Used in combination with Parker AC890 variable-speed drives, these torque motors enable screws to be connected directly, with speed and torque being controlled by the drive; unlike traditional gearbox systems, this enables operating parameters to be varied infinitely within the performance envelope of the motor. In practice, this is a far more efficient process, as there are virtually no power losses in the transmission mechanism, which helps to reduce energy usage and stresses on moving parts within the system; additionally, the TMW motors are quiet, have a far smaller footprint, can easily be retrofitted in a matter of hours, and require only minimal maintenance.

Parker says that, unlike competing torque motors, the TMW range of products feature an integrated thrust bearing that can be sized according to the application, plus an innovative screw extraction mechanism to simplify installation and maintenance. In addition, Parker is able to offer both standard and customised mechanical interfaces for shafts and barrels, with the shaft being hollow to improve cooling. The TMW range can be used with machinery requiring from 1200 to 22,000Nm of torque and running at speeds of between 50 and 500rpm.

Typical efficiency improvements from a TMW motor and AC890 drive combination, compared with a traditional gearbox based system, are said to be up to 10 per cent; used on a standard 110kW extruder running 7200 hours per year, this would deliver energy savings of around EUR7900 per year, based on an energy cost of EUR0.10/kWh.

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