Conventional full-thread three-stage screws can be divi […]
Conventional full-thread three-stage screws can be divided into three forms according to their thread lift and groove depth changes:
(1) Isometric deepening screw
The speed of the isotropic deepening screw from the depth of the groove can be divided into two forms:
1 isometric gradient screw: the depth of the last groove from the beginning of the feed section to the homogenization section is a gradually shallower screw. On the longer melt section, the groove depth is gradually shallower.
2 Isometric abrupt screw: the screw with the depth of the groove of the feeding section and the homogenizing section unchanged, and the depth of the groove at the melting section suddenly becomes shallow.
(2) Isometric variable pitch screw
The iso-depth variable pitch screw means that the depth of the groove is constant, and the pitch is narrow from the width of the first groove of the feeding section to the end of the homogenization section.
The characteristics of the constant-depth pitch screw are that the screw cross-sectional area at the feeding port position is large due to the depth of the screw groove, and the strength is sufficient to increase the rotation speed, thereby improving the productivity. However, the screw processing is difficult, the flow rate of the melt is large, the homogenization is poor, and it is less used.
(3) deepening variable pitch screw
The variable depth variable pitch screw means that the depth of the groove and the angle of the thread are gradually changed from the beginning of the feeding section to the end of the homogenization, that is, the screw whose taper is gradually narrowed from the width and the depth of the groove is gradually shallower. The screw has the characteristics of the first two kinds of screws, but the machining is difficult and less used.