EVA sheet extruder | EVA sheet extruder machinery factory | EVA sheet extruder

_3 . - r-
. r,
- rr- Structural principles
.r,
-r For the basic mechanism of the extrusion process, simply speaking, it is a screw in the barrel It rotates in the body and pushes the plastic forward. The screw structure is an inclined plane or slope wrapped around the central layer. Its purpose is to increase the pressure to overcome greater resistance. As far as the extruder is concerned, there are three types of resistance that need to be overcome during operation: First, friction, which includes the friction between the solid particles (feed) and the friction between them during the first few turns of the screw (feed area) The two mutual friction forces are the adhesion of the melt on the cylinder wall and the internal flow resistance of the melt when it is pushed forward.
.r,- -
-r According to Newton's theorem, if an object is at rest in a certain direction, then the object is in equilibrium with the forces in that direction. For a screw that moves in a circumferential direction, it has no axial movement, which means that the axial force on the screw is in a balanced state. So if the screw exerts a large forward push force on the plastic melt, then it also exerts a backward push force of the same magnitude but direction on another object. Obviously, the thrust it exerts is on the thrust bearing behind the feed port. Most single screws have right-hand threads. If you look at them from the back, they rotate in the opposite direction. They spin out of the barrel backwards through rotational 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-facing and the other left-facing. For interlocking twin-screws, the two screws rotate in the same direction. direction of rotation and therefore must have the same orientation. However, in either case, there is a thrust bearing that bears the backward force, and Newton's theorem is still followed.
.r,- -
-r
.r,- -
- r- Temperature principle
.r,
-r Extrudable Plastics are thermoplastics, they melt when heated and solidify again when cooled. Therefore, heat is required during the extrusion process to ensure that the plastic reaches the melting temperature. So where does the heat to melt the plastic come from? First, the floor scale feeds preheating and cylinder
.r,- -
- r- The mold heater may work and is very important at startup. In addition, the motor inputs energy, that is, the motor overcomes the viscous melt. The frictional heat generated in the barrel when the screw is rotated by the body's resistance is also the most important heat source for all plastics, except for small systems, low-speed screws, high melt temperature plastics and extrusion coating applications.
r,- -
- r- In operation, it is important to realize that the barrel heater is not actually the main heat source, and its effect on the extrusion is smaller than we might expect. The temperature of the rear cylinder is more important because it affects the gearing or the conveying speed of solids in the feed. Generally speaking, unless used for a specific purpose (such as glazing, fluid distribution or pressure control), the die and mold temperatures should be at or close to the required melt temperature.
.r,- -