Screw barrels play an integral role in the plastic extr […]
Screw barrels play an integral role in the plastic extrusion process. Proper assembly and maintenance are crucial for their longevity. Several factors must be taken into account when selecting the correct screw barrel for the job. These factors include the diameter of the screw barrel, the screw spline, and the material to be extruded.
Screw extruders use a screw to mix the feed material, which is a solid or liquid. This mixing process can increase the randomness of the composition and the dispersion of cohesive particles. These features are important for the process and are important to ensure the uniform color of the end product.
The material passing over the mixing flights undergoes high shear stress. This is because of the relative motion between the barrel and the screw. A high-shear screw barrel will have an increasing average flow velocity, and material will pass through high-stress regions while the screw rotates.
The screw and barrel are two of the most important components of a screw extruder. They determine the consistency and melt viscosity of the plastic. Moreover, they determine the flow rate. There are two types of screw extruders, one of which has a grooved barrel, and the other has a smooth bore.
A screw barrel is generally made of a through-core steel with holes and is segmented with a flange. Its design allows the material to advance forward while the heater heats the outside of the barrel. The screw barrel also mixes the plastic that flows through the threaded groove evenly. The plastic melts when subjected to various forces, and the screw barrel ensures that the raw materials are consistently extruded.
In general, plastics exhibiting low viscosity should be used for extrusion, as they do not degrade under high-shear conditions. To achieve optimum melt properties, an extruder should have a high-watt density heater in the first half of its barrel. Similarly, it should have a cooled throat that prevents melting during extrusion shutdown. In addition, the extruder screw design should have a deeper feed section that can receive granules. A shallower metering section is also required for better pumping and shear. It should also have a high compression ratio (at least 3.5) and preferably have barrier flights.
