vis d'injection

CONT: A typical injection screw is ... in effect, a series of endless buckets; that is, a mechanical conveyor.
CONT: The injection screw is divided into three parts. The first half of the screw compresses the material and removes the air. The flight depth is constant. The second part (third quarter) of the screw has decreasing flight depths, thus reducing the volume. Reduction of the volume increases the friction of the polymer molecules as they rub over each other, increasing the temperature. At the end of this section all the material should be melted (plasticized). The third part (last quarter) of the screw is a pump. The flight depth is constant but smaller than the first section because melted material takes up less volume than powder.