Motor Power and Torque

Extrusion processes are often rate limited by motor power or torque, discharge temperature, or the melting capacity of the screw. Other root causes associated with the design of the screw can limit rates as shown in previous sections. The problems, however, are typically associated with other defects such as flow surging or resin degradation. Chapters 11 and 12 discuss process defects associated with resin degradation and flow surging, respectively. Rate limitations due to inadequate motor power and torque are common problems for commercial plants. Two case studies are presented in the next sections that show rate limitations due to the lack of torque and motor power. 

The evaluation of the Personnel/Material Hoist duty, after optimization of the mechanical hoist parameters, i.e., rope selection, drum size etc., indicated that its motor power and torque requirements are very similar to the Clients new Rock Hoist already supplied for the Synclinorium Shaft at Nkana Mine which is situated in the same area. 

As discussed in Section 12-2, the ultimate drop size is determined by max, not avg. However, most correlations for drop size use avg, since data for max are not readily available. Many investigators, starting with Corrsin (1964), determined that gmax/Savg — 40. Once T, D/T, and avg have been selected, it is a straightforward task to calculate the operating speed, motor power, and torque. The power number, Np, is needed for the calculation. Power numbers for different impellers are a function of impeller Reynolds number and are found in Chapters 6 and 9. Once Np is known, the hydraulic power is calculated from... 

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