What is the difference between a venting screw extruder and a non-venting screw extruder?

1. Venting function
The core feature of a venting screw extruder is that its barrel is equipped with a venting port, which can continuously remove volatile substances (such as moisture, air, low-boiling substances, etc.) in the polymer, thereby improving the quality and performance of the product. Non-venting screw extruders do not have this function and cannot effectively remove volatile substances in the raw materials, which may cause problems such as pores, bubbles, and color differences in the products.

2. Screw structure design
The screw of a venting screw extruder is usually composed of two conventional screws in series, and the venting port is located at the connection between the two screws. The first screw section is responsible for feeding, compression and plasticization, and the second screw section contains a venting section for releasing volatile substances. The screw structure of a non-venting screw extruder is relatively simple, usually with only one screw section and no special venting design.

3. Scope of application
Venting screw extruders are suitable for processing materials that require the removal of volatile substances, such as hygroscopic polymers (such as polypropylene, polycarbonate, etc.) and materials containing additives, fillers or dry-mixed powders. Non-venting screw extruders are more suitable for processing thermoplastics (such as HDPE, LDPE, PVC, etc.), which usually do not require the removal of volatile substances.

4. Versatility
Venting screw extruders can add additives, fillers or other reactive components to polymers through the vent port, thereby improving the versatility of the extruder. Non-venting screw extruders have relatively simple functions and are mainly used for basic plastic molding processing.

5. Process optimization
Venting screw extruders can reduce the impact of impurities and volatile substances in raw materials on product quality through the design of the venting section, while improving production efficiency and yield rate. Non-venting screw extruders may require additional pre-drying or pretreatment steps when processing hygroscopic materials or raw materials containing volatile substances, which increases cost and complexity.

6. Equipment complexity
The structure of the venting screw extruder is relatively complex, especially the twin-screw venting extruder, whose design needs to consider the balance between the pressure release of the venting section and the material conveying. The non-venting screw extruder has a simple structure and lower manufacturing and maintenance costs.