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Direct-drive torque motors more efficient than gearboxes

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Direct-drive torque motors more efficient than gearboxesParker Hannifin's latest range of torque motors is designed to help end users of heavy-duty industrial machinery replace traditional motors and gearboxes with a highly efficient direct-drive system. Used in conjunction with Parker's variable-speed drives, the torque motors are intended primarily for use with plastics and rubber 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 providing greater reliability and overall levels of performance.

Many extrusion systems and similar high-power machines use AC or DC motors linked to gearboxes to provide the required torque and speed to drive screws, shafts and associated components. However, this configuration can be noisy and unreliable, draw relatively high levels of power, and, perhaps as importantly, be complex to install, operate and maintain.

In contrast the new Parker TMW series torque motors are based on a proven design of permanent-magnet, brushless servo motor, which produces high levels of torque at low operating speeds. Used in combination with Parker AC890 variable-speed drives, this enables a screw to be connected directly to a motor, with speed and torque being controlled by the drive; unlike traditional gearbox systems, this allows 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 consumption and stress on moving parts within the system; additionally, the TMW motors are virtually noiseless, have a far smaller footprint, can be retrofitted easily and require only minimal maintenance.

Unlike competing torque motors, Parker says the TMW range features 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 up to 22,000Nm of torque and running at speeds of 50-500rpm.

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

 
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