A twin-screw extruder consists of several parts, including a transmission device, a feeding device, a barrel, and screws. The functions of each component are similar to those of a single-screw extruder. The difference between a twin-screw extruder and a single-screw extruder lies in the fact that a twin-screw extruder has two parallel screws placed in the same barrel. 
There are many different types of twin-screw extruders, with the main difference lying in the structure of the screws. The screw structure of a twin-screw extruder is much more complex than that of a single-screw extruder, as the screws of a twin-screw extruder also have factors such as rotational direction and degree of meshing. 
The twin-screw extruders commonly used for extruding PVC profiles typically feature tightly meshing and counter-rotating screws. A few also use co-rotating twin-screw extruders, but these can generally only operate at low speeds, approximately within the range of 10 r/min. High-speed meshing co-rotating twin-screw extruders are used for mixing, exhaust granulation, or as continuous chemical reactors. The maximum screw speed range for such extruders is between 300 and 600 r/min. The conveying mechanism of non-meshing extruders is quite different from that of meshing extruders, and is more similar to that of single-screw extruders. There are fundamental differences between the two