The screw thread design of an extruder is primarily determined by the screw’s structural configuration. Conventional full‑threaded screws can be divided into three sections, and based on the thread profile and its variations, extruder screws can be classified into three types. The first type is the constant‑pitch, variable‑depth screw, which itself comprises two subcategories: the constant‑pitch, gradually varying‑depth screw and the constant‑pitch, abruptly varying‑depth screw. In this configuration, the thread depth changes progressively from the feed zone to the last thread, then suddenly becomes shallower in the melt zone; such a screw is referred to as a constant‑pitch, gradually varying‑depth screw. Conversely, if the thread depth remains constant from the feed zone through the homogenization zone and then abruptly decreases in the melt zone, it is called a constant‑pitch, abruptly varying‑depth screw. The second type of extruder screw is the constant‑depth, variable‑pitch screw. In this design, the groove depth remains uniform along the entire length, while the pitch progressively narrows—from wide at the feed zone to narrow at the end of the homogenization zone. The advantage of this screw lies in its uniform groove depth and relatively large cross‑sectional area at the feed port, providing sufficient shear strength and facilitating higher rotational speeds, thereby enhancing production throughput. However, such screws are more challenging to manufacture, exhibit significant backflow after material plasticization, and offer inferior homogenization performance; consequently, they are seldom employed. The third type is the variable‑depth, variable‑pitch screw. In this configuration, both the groove depth and the helix angle change continuously from the feed zone to the end of the homogenization zone—meaning the thread pitch gradually narrows while the groove depth progressively deepens. This screw combines features of the preceding two types but is more difficult to machine and incurs higher manufacturing costs, so it is also rarely used. When selecting an extruder screw, it is essential to consider the raw material composition and the product’s structural requirements, enabling the choice of a screw that offers optimal cost‑effectiveness.

A plastic sealing strip extruder is what we commonly refer to as a plastic extruder. Since many sealing strips in our daily lives are made of PVC, it is also called a plastic sealing strip extruder or an elastomer‑plastic extruder.

The applications of plastic extruders are not limited to the extrusion production of plastic sealing strips; they can also be used for extruding products such as plastic pipes and electrical wires. When manufacturing plastic products, it is essential to adjust the raw material formulation based on the desired product quality and cost.

We use a mixer to blend the raw materials according to the formulation’s ingredient ratios. Once the materials are uniformly mixed, they can be fed into a plastic pelletizing machine to produce the desired plastic pellets. A plastic pelletizing machine is a type of plastic extruder, so its production process is similar to that of a plastic strand‑extruding machine. After the pellets are produced, they are loaded into the feed hopper of the plastic extruder. From there, the pellets pass through the feeding system into the barrel, where the screw performs shearing, compression, and compounding, among other processing steps. The material is then extruded through the die of the extruder to form the sealing strip in the required shape. Following water‑cooling, the final product is complete. Since product dimensions vary, the choice of extruder model must be tailored to the specific application; selection should be based on actual operating conditions.

Hebei Shuangda Rubber and Plastics Machinery Co., Ltd. is a modern enterprise that integrates research and development, manufacturing, and sales of complete sets of extrusion equipment for rubber, silicone, and plastics. The company’s main products include rubber extruders, rubber hose extrusion lines, three‑layer composite sealing strip extrusion lines, silicone sealing strip production lines, plastic sealing strip production lines, plastic profile extrusion lines, plastic pipe extrusion lines, elastomer extruders, and other extrusion equipment, as well as production machinery for engineering seals, automotive seals, wire and cable applications, air‑conditioning hoses, braided hoses, automotive hoses, waterstop strips, and related products.