I. Basic Working Principle of an Extruder
An extruder uses the squeezing, shearing, and friction generated by the rotating screw to puff and shape materials under high temperature and pressure. Screw speed is a key parameter affecting the material's movement within the barrel:
Screw speed determines material propulsion efficiency: As the screw rotates, the threads push the material towards the discharge port. The faster the speed, the more times the screw propels the material per unit time, resulting in faster material movement within the barrel and a naturally increased output. Conversely, a slower speed reduces material propulsion and output speed.
II. Specific Logic of Speed's Impact on Output Speed
Material residence time within the barrel:
Slower speed → Longer residence time in the barrel → Longer time under compression and heating, but due to reduced propulsion, the amount of material discharged per unit time decreases, resulting in a slower output speed.
Higher speed → Shorter residence time, but stronger propulsion, resulting in a faster output speed (Note: Excessive speed may lead to insufficient material puffing, affecting product quality). Friction and shear forces between the screw and the material:
Slow speed → The shearing and frictional forces between the screw and the material are relatively weak, resulting in insufficient power for plastic deformation and expansion of the material. This may lead to increased resistance during discharge, further slowing down the discharge speed.
High speed → Increased shear and friction forces make the material easier to plasticize and expand, resulting in better flowability and faster discharge speed.
