A typical representative of a split screw is a BM screw, also called a primary and secondary threaded screw. The structure of the BM screw is to add a thread to the melting section of the screw. The two threads divide the groove formed by the original thread into two groove grooves, one groove communicates with the groove of the feeding section, and the other groove and the groove The segments are connected. The former is used to hold the solid phase, the depth of the groove is changed from the depth of the groove of the feeding section to the depth of the groove of the homogenizing section; the latter is used to hold the liquid phase, and the depth of the groove is equal to the depth of the groove of the homogenizing section. The clearance between the additional thread and the barrel wall is greater than the gap between the original thread (main thread) and the barrel wall. The intersection of the main thread and the secondary thread begins at the end of the feeding section and finally equalizes the beginning of the section.