Characteristics and Applications of Venting Extruder for Plastic Granulator

Venting extruder is a plasticizing extruder with the ability to remove gas. At present, the main application in industry is single-screw venting extruder.

The gas that the venting extruder needs to remove comes from three aspects: (1) air brought in between solid pellets; (2) moisture adsorbed on solid pellets, gas or liquid impurities contained in solid pellets, such as residual monomers, low-boiling plasticizers, low-molecular volatiles and moisture. When using an ordinary plasticizing extruder, a small amount of gas can be removed from the feed port. When the residual gas has a great impact on the processing quality, the solid polymer pellets must be dried in advance. The use of a venting extruder can partially or completely replace the labor-intensive and time-consuming drying process.

Venting extruder is mainly used to process highly hygroscopic polymer raw materials. Such as rigid polyvinyl chloride, ABS, nylon, polyoxymethylene and polymethyl methacrylate. Due to the good venting effect, the bubbles in the extrudate are greatly reduced, which improves the quality of the finished product. In both granulation and molding, degassing extruders suitable for production have been developed. In spinning, there are reports of successful application of degassing extruders for nylon.

This is the extrusion process of the degassing extruder. The main feature of the machine structure is that there is a degassing port in the middle of the barrel. The screw is divided into two parts with the degassing port as the boundary. The part before the degassing port is called the first stage of the screw, and the part after it is called the second stage. The first stage and the second stage are each equivalent to a three-stage ordinary screw. Generally, the material entering from the hopper is solid conveyed, melted, compressed and homogenized in the first stage, and then decompressed and enters the degassing section. The gas entrained in the melt is removed under vacuum. After degassing treatment, the polymer melt enters the second stage of the screw. In the second stage, the melt is recompressed and mixed and homogenized and then extruded from the die head.

According to the structural characteristics of the degassing section, degassing extruders are divided into two types: (1) direct degassing type; (2) bypass type. The direct degassing type has a simple structure and is widely used. The bypass type has a complex structure, but it is easy to install an intermediate pressure regulating valve, which is convenient for adjusting the normal operation of the machine.