Applications: Depending on the screw design and mechanical configuration, this equipment can be used for pelletizing sheet or granular materials such as PP, PE, PS, PET, ABS, PC, and acrylic. It is suitable for processing both virgin and recycled resins. The pelletizer features excellent processability, low manufacturing costs, corrosion resistance, high pellet‑cutting precision, efficient hot‑cutting, and easy installation and mobility. The master–slave unit incorporates secondary filtration and delivers superior venting, producing dense, brightly colored pellets with outstanding plasticization.

For a single-screw vented extruder, the screw can be regarded as two conventional three‑section screws connected in series, with a vent port positioned at the junction between them. The section of the screw upstream of the vent is referred to as the first-stage screw, comprising the feeding zone, the first compression zone, and the first homogenization zone; the section downstream of the vent is called the second-stage screw, consisting of the venting zone, the second compression zone, and the second homogenization zone.

From the feed port to the first homogenization section, the plastic achieves a nearly fully plasticized state, and some of the gases originally contained in the material are expelled from the hopper as the material is compacted. Once the partially plasticized material enters the venting section, the screw channel suddenly deepens—by a factor of several times the depth of the first homogenization section—and, with the vent connected to a vacuum pump, the pressure drops sharply to atmospheric or negative pressure. Consequently, a portion of the compressed gases and vaporized volatiles within the material escape directly; meanwhile, another fraction of gases and vaporized volatiles dissolved in the melt causes foaming, and under the stirring action of the screw, these bubbles rupture, with their contents likewise drawn away by the vacuum pump through the vent.

The melt, from which gases and volatiles have been removed, is re‑compressed in the second compression zone, further homogenized in the second homogenization zone, and then extruded through the die at a controlled flow rate, pressure, and temperature to produce the final product.

Depending on the design of the venting system, vented extruders are classified into the following three types:

1. Direct‑suction type: This configuration features a simple structure and easy heater placement, making it widely applicable; however, its main drawback is the difficulty of achieving flow balance between the first‑stage and second‑stage screws, which can lead to material overflow or underfeed, resulting in fluctuations in extrusion output. Moreover, installing a pressure‑regulating valve upstream of the venting section poses significant structural challenges.

2. Bypass Type: At the end of the first homogenization section, there is a reverse‑threaded segment that prevents the melt from passing through; instead, it diverts into the venting zone and then enters the second‑stage screw. This configuration is relatively complex, requiring a bypass that is difficult to manufacture, and the heater at the bypass point is also challenging to install. The bypass type is not suitable for processing heat‑sensitive plastics such as PVC.

3. Hollow‑ventilation type: In the first homogenization section, the high‑pressure melt is forced by the reverse threads to pass through the screw channels into the venting section. This screw design is relatively difficult to manufacture, and the cooling length of the screw is constrained by the position of the central channel. It is well suited for large‑scale vented extruders. Compared with non‑vented single‑screw extruders, vented extruders have a more complex operating process, requiring consideration not only of venting but also of flow‑rate balance between the two screw sections during material conveyance, as well as the influence of pressure on this flow‑rate balance.