The better the spiral groove is closed in the vertical and horizontal direction, or the better the conjugation, the stronger the positive displacement conveying characteristics. Only with full meshing and completely closed spiral and longitudinal directions can complete positive displacement conveyance. If the spiral groove is opened to a certain extent in the longitudinal or transverse direction, it will lose a certain positive displacement conveying capacity, because under the effect of pressure gradient, the material will flow through these open channels, and leakage will occur. The loss of positive displacement conveying capacity is in return for the improvement of mixing ability or other properties (such as exhaust). For a rectangular spiral groove closed both longitudinally and laterally, the material is enclosed in a space formed by a lead screw groove and the inner wall of the barrel, which is called a C-shaped chamber. Along the axis of the screw and barrel, there are two series of C-shaped chambers which are not connected to each other. When the screw rotates once, the material in the C-shaped chamber moves forward
A lead, so its speed along the screw axis is:
V Ⅰ = t · n (3-15)
In the formula, vL --- the axial moving speed of the material;
T t — the lead of the thread;
n ——— the speed of the screw.