The twin-screw plastic extruder consists of several parts, including the drive unit, feeding unit, barrel, and screws, with each component serving a function similar to that of a single-screw extruder but with much higher efficiency. In addition to its high efficiency, the key distinction of the twin-screw plastic extruder from the single-screw type lies in the presence of two parallel screws placed within the cross-sectional barrel.
Twin-screw plastic extruders for profile extrusion are typically tightly meshed and rotating in opposite directions, although some use co-rotating twin-screw extrusion, usually at lower screw speeds (around 10 r/min). High-speed, intermeshing co-rotating twin-screw extruders are used for blending, degassing, or as continuous chemical reactors, with screw speeds ranging from 300 to 600 r/min. Non-intermeshing extruders are used for mixing, degassing, and chemical reactions, and their conveying mechanism is quite different from that of intermeshing extruders, more similar to that of a single-screw extruder, although they have fundamental differences.
The twin-screw plastic extruder is easy to open, allowing for the timely detection of the wear on the screw elements and liner sleeves, enabling effective maintenance or replacement. This prevents discovering issues only when the extruded product is affected, thus avoiding unnecessary waste. When manufacturing masterbatches, frequent color changes are often required. If product changes are needed, the processing area can be opened in just minutes, and the mixing process can also be analyzed by observing the melt profile along the entire screw. Standard twin-screw plastic extruders require a significant amount of cleaning material for color changes, which is time-consuming, energy-wasting, and material-wasting. However, the twin-screw plastic extruder addresses this issue by allowing for a quick and easy opening of the barrel in minutes for manual cleaning, thus reducing or eliminating the need for cleaning material, saving costs.
Operating Principle:
From the perspective of the working principle, the co-rotating and counter-rotating, as well as non-intermeshing, types of twin-screw plastic extruders are different.
Co-rotating Twin Screw Plastic Extruder
This type of extruder comes in both low-speed and high-speed models. The former is mainly used for profile extrusion, while the latter is for specialized polymer processing operations.
(1) Tight mesh extruder. Low-speed extruder with tight mesh screw geometry, where the profile of one screw's flanks closely fits the profile of the other screw's flanks, i.e., conjugate screw profiles.
(2) Self-cleaning extruder. High-speed co-rotating extruders feature closely matched screw flanks. This screw design can achieve a very small screw gap, allowing the screw to have an enclosed self-cleaning function. Such a twin-screw plastic extruder is called a tightly self-cleaning co-rotating twin-screw plastic extruder.
2. Asymmetric Twin-Screw Plastic Extruder
The tightly meshed, opposite-rotating twin-screw plastic extruder has a very small gap between the screw grooves of the two screws (much smaller than that of the co-rotating meshing type twin-screw plastic extruder), thus achieving positive conveying characteristics.
3. Non-intermeshing twin-screw plastic extruder
The center distance between the two screws of a non-intermeshing twin-screw plastic extruder is greater than the sum of the radii of the two screws.
