The amount and quality of the material can be controlled by adjusting the rotating speed of the screws, and the amount of material allowed to leave the chamber. The advantage of the continuous mixer over the batch mixer is its ability to provide a continuous mix of material with optimum dispersion. The continuous mixer is capable of production in quantities from 1,000 to 10,000 pounds per hour. The continuous mixer's significantly larger outputs provides the manufacturer of PVC film with higher product rates not possible with batch mixers. Single Stage Screw Extruders Screw extruders are the process tool used in compounding, injection molding, injection blow molding, extrusion, and extrusion blow molding.
Screw extruder consist of a long auger screw that fills the opening of a steel tube.
Plastic and additives that are placed at one end of the screw are mixed and melted when the screw turns. Understanding the mixing and melting capabilities of screw extruders is important in understanding compounding technology. Screw extrusion technology is used as the plastic mixing and melting device in four more plastic processes. These four process will be covered under process technology in the second half of this text. A single screw extruders, illustrated in Figure 4-7, is classified by the ratio of the length of the screw to the inside diameter of the barrel.