The structural feature of the separation type screw is to add a secondary spiral rib in the melting section, divide the main thread groove into two parts, form solid-liquid phase separation during the screw plasticization process, and the solid phase material is all left in the solid phase tank, and solid The gas in the phase tank is discharged backwards from the material under the action of pressure, reducing the bubbles in the product. At the same time, the heat exchange area between the solid phase material and the inner wall of the barrel is increased.
There are many types of separate screw structures. For the convenience of machining and the effect of use, the lift of the main and auxiliary threads is equal, the width of the liquid phase groove and the solid phase groove of the groove remain unchanged, and the solid phase starts from the compression stage. The depth of the groove is gradually shallow, and the depth of the liquid phase groove is gradually deepened to the end of the homogenization section. This structure is advantageous for a product having high transparency and a material having poor thermal stability. And the ability to adapt to raw materials is strong.
Separate screw design should reasonably select the screw parameters according to the actual situation, including the compression ratio, the distribution of the three segments and the position of the secondary screw.
1--solid material 2--molten material 3--main screw thread 4--secondary screw thread
The essential difference between a split screw and a conventional screw lies in the melting section. The split screw has a secondary thread acting as a barrier in the melt section to separate the solid plastic from the molten plastic. The outer diameter of the secondary thread is smaller than the primary thread, and the molten material passes over the secondary thread into the molten region. Since the helix angles of the main and auxiliary threads are different, the solid region is wide to narrow in terms of the axial direction, and the molten region is narrow to wide. The melting process separates the solid state from the molten phase, effectively avoiding fluctuations caused by solid bed breakage. When some of the small particles that are not completely melted pass over the gap between the secondary thread and the cylinder, they are melted by high shear, and the melting rate is improved.