The main body of the pin-driven screw is a standard screw. Pins can be placed in the grooves of the melting or metering sections of the screw, or on the smooth cylindrical surface without grooves at the end of the metering section. Pins are arranged in a specific pattern, with varying density and number. Cylindrical pins are formed by assembling them into holes in the screw; square or diamond-shaped pins are formed by milling directly onto the screw. If these pins are placed in the melting zone, they can break up the solid bed, disrupt two-phase flow, mix the solid and liquid phases together, increase the contact area between undissolved solid fragments and dissolved material, and promote melting. If the pins are placed in the melt conveying zone, their main function is to divide the material flow, increase the interface, change the direction of the material flow, and rearrange the flow stream. Multiple diversions and mergings change the flow direction, homogenizing the melt composition and temperature.
The mixing section is an inwardly slotted structure located at the end of the homogenization section of a standard screw, with an outer diameter equal to the outer diameter of the screw. The grooves are divided into several groups, with each group forming a material confluence zone. The material is divided by the grooves, converges in the confluence zone, and then divided and converges again, similar to a pin-type screw. The characteristic of the separable screw is that, in addition to the original screw thread (called the main screw), an additional thread (called the auxiliary thread) is added to the melting section. Its outer diameter is slightly smaller than the main thread's outer diameter, and the leads of the main and auxiliary threads are different. The auxiliary thread starts at the end of the feeding section (and connects to the feeding section there), and after passing through several threads, gradually intersects with the main thread of the homogenization section. In this type of screw, the groove depth and thread lead gradually change from the feeding section to the homogenization end; that is, the thread lead gradually narrows from wide to narrow, and the groove depth gradually shallows from deep to shallow, allowing for maximum material compression.