Imparting shear into the process by modifying feed rate
Twin screw extruders are starve fed devices with the feeders setting the rate. Feeders and screw speed are adjusted together to optimize mixing efficiencies. The shear history a formulation sees may be effectively increased or decreased by slowing down or speeding up the feeder(s) to increase or decrease the mastication time.
At a given screw design and rpm, as the feed rate is decreased the materials see more work, since there is a higher residence time in the mixing elements. Conversely, as feed rate is increased at a given screw rpm less mixing occurs. Therefore, by changing feeder rates the same screw design can be fairly wide spectrum and process many different polymer compounds.
