Structural Principle Of Twin-screw Extruder

For the basic mechanism of the extrusion process, in simple terms, a screw rotates in the barrel and pushes the plastic forward. The screw structure is a slope or slope wound on the center layer, the purpose of which is to increase the pressure in order to overcome the greater resistance. As far as the extruder is concerned, there are three kinds of resistance that need to be overcome during operation: one is friction, which includes the friction of solid particles (feed) against the barrel wall and the friction between them during the first few turns of the screw (feed zone). There are two kinds of mutual friction; the second is the adhesion of the melt on the wall of the cylinder; the third is the internal flow resistance of the melt when it is pushed forward.
According to Newton's theorem, if an object is at rest in a certain direction, then the object is in a state of force balance in this direction. For a screw that moves in the circumferential direction, it has no axial movement, that is to say, the axial force on the screw is in balance. So if the screw exerts a large forward thrust on the plastic melt, it also exerts a backward thrust of the same size and direction on another object at the same time. Obviously, the thrust it exerts is acting on the thrust bearing behind the feed inlet. Most single screws are right-handed threads, and if viewed from the rear, they are counter-rotating, and they unscrew back out of the barrel through a rotary motion. In some twin-screw extruders, the two screws rotate in opposite directions and cross each other in the two barrels, so one must be right-handed and one left-handed. For interlocking twin-screws, the two screws are in the same , and must therefore have the same orientation. However, in either case there is a thrust bearing to withstand the rearward force, still obeying Newton's laws.