What are the basic parameters of single screw extruder?

① Screw diameter (Ds).
The screw diameter is used to indicate the size of the extruder, which in a certain sense indicates the size of the extruder. The size of screw diameter can generally be reasonably selected according to the section size of the product, the processing performance of the material, the required productivity and processing capacity, that is, the extruder model. The screw diameter of extruder in China has been serialized, with specifications of 30mm, 45mm, 65mm, 90mm, 120mm, 150mm, 200mm, etc. The screw diameter widely used is 65-150mm. Generally, large-diameter screw shall be selected for large cross-sectional area of products, while small-diameter screw shall be selected for small cross-sectional area of products.
② Length to diameter ratio (L/D).
The length-diameter ratio of the extruder refers to the ratio of the effective length of the screw to the diameter of the screw. The length-diameter ratio is another important parameter of the extruder. If the length-diameter ratio of the screw and the screw speed are considered together, it indicates the plasticizing ability and quality of the screw in a certain sense. The national standard series stipulates that L/D has 15, 20, 25, 30, etc., with a maximum of 43. The extruder with moderate length-diameter ratio shall be selected according to the raw material performance and production efficiency. If the length-diameter ratio is increased, the retention time of plastic in the barrel will be extended due to the increase of screw length, and the material will be plasticized more fully and evenly, so the output and quality can be improved. However, this makes the processing and assembly of screw and barrel more difficult, and the cost increases accordingly. The screw is easy to deform, and the gap between screw and barrel is easy to be uneven. Therefore, we should try to obtain high quality and high yield under the condition of small aspect ratio. For example, when processing polyolefin and PVC materials, the length-diameter ratio of screw is 20 and 25.
③ Compression ratio（ ε)。
The ratio of the volume of the first screw groove in the screw feeding section to the volume of the last screw groove in the homogenization section is called the compression ratio. The size of the compression ratio has a great impact on the compactness of the product and the ability to remove the air contained in the material. It also affects the output of the extruder and the mechanical strength of the screw
④ Groove depth (h).
The groove depth is related to the thermal stability of the processed material. The groove depth of the conventional screw compression section is the most important and is a variable, expressed by h2. The screw groove depth of the feeding section is expressed by h1, which is generally a fixed value. The depth of the screw groove in the homogenization section is expressed by h3, which is also a fixed value generally. The depth of screw groove directly affects the plasticizing efficiency of screw and the maximum pressure in production. For example, shallow spiral groove is beneficial to plasticization, but the production efficiency is low; The deep screw groove has a large amount of extrusion, but the extrusion is not smooth and the plasticizing quality is poor.
⑤ Thread pitch (S).
The distance between two adjacent threads, usually S=D.
⑥ Thread rising angle (Q).
The included angle between the helix and the vertical line of the screw center is generally Q=17 ° 42 ′.
⑦ Number of thread heads (P).
Generally, the number of thread heads is 1.
⑧ Rib width (e).
It refers to the width of the top of the screw along the axis, in mm.
⑨ Clearance between screw outer diameter and barrel inner wall（ δ 0), in mm.