in an extruder most of the rotating energy is converted into heat.Normally the end gap on the screws (backpressure)can be regulated, by moving barrels closer to drive end the end gap decreases.So if you increase rpm,you increase the flow but more important, you increase the temperature of your product.You could open end gap more to increase the flow, but this also has an influence on your product (dencity).Unless you're a extruder manufacterer,you shouldn't calculate the rated capacity, the operating envelope should well be defined in operating manual.
