Date：2018-07-18
The screw barrel has the advantages of high wear resistance and corrosion resistance; and after special treatment, it can effectively improve the wear resistance of the barrel screw and improve the applicable life; as well as cold and hot spraying hard metal technology; advanced nitriding technology; bimetal processing manufacturing process and other characteristics.
The screw is an important part of the injection molding machine. Its role is to transport, compact, melt, agitate and apply pressure to plastics. All of this is done by the rotation of the screw in the barrel. When the screw rotates, the plastic counters the inner wall, the bottom surface of the screw groove, the rib advance surface to make friction to be put forward. The heat generated by the friction is also absorbed to improve the plastic temperature and melt the plastic. The layout of the screw will directly affect these effects. Ordinary injection screw layout is divided into component release screw, barrier screw or split screw. The layout of the barrel is actually a round tube with a feed opening in the middle.
In the plasticizing process, the power is derived from the relative rotation of the screw and the barrel. According to the divergence shape of the plastic in the screw groove, the screw is generally divided into three sections: a solid conveying section (also called a feeding section), a melting section (also called a compression section), and a homogenization section (also called a metering section).
In the textbook on plasticization, the solid conveying section of the plastic in the screw is regarded as a solid bed without moving, and then people use it to predict speed which the plastic is transported forward. This has many differences between the actual environment, and it cannot be used as a basis to elucidate the feeding environment of plastic particles with different shapes. If the particles of the plastic are not large, they will stratify and tumbling as they are pulled forward by the inner wall of the barrel, and are gradually compacted to form a solid plug. When the diameter of the particles is similar to the depth of the groove depth, their active trajectory is essentially a linear motion along the radial direction of the groove plus a linear motion at an angle. Since the dispersion of the plastic in the groove is loose when the particles are large, the conveying speed is also slow. When the particles are large enough to enter the compression section and the diameter is greater than the depth of the groove, the plastic is caught between the screw and the barrel. If the force of pulling forward is insufficient to lower the force required to crush the plastic particles, Then the plastic will get stuck in the groove and not advance.
When the plastic is near the melting point temperature, the plastic has begun to melt to form a molten film. When the thickness of the melt film spans the gap between the screw and the barrel, the melt film goes radially from the inner wall of the cylinder toward spiral ridge, and gradually form a molten pool. Due to the gradual shallowing of the depth of the molten section and the extrusion of the molten pool, the solid bed is squeezed toward the inner wall of the cylinder, thus it will accelerate the heat transfer process of the hot cylinder to the solid bed. At the same time, the rotation of the screw shears the melt film between the solid bed and the inner wall of the barrel, thereby melting the solid between the melt film and the solid bed interface. As the spiral of the solid bed moves forward, the volume of the solid bed gradually shrinks, and the volume of the molten pool gradually increases. If the thickness of the solid bed is reduced at a speed lower than the shallower depth of the groove, the solid bed may partially or completely inflate the groove, causing the plasticization to be bumped, which may cause frictional heat due to excessive part pressure. Part overheating has occurred.
In the screw homogenization section, the solid bed has broken in the molten pool due to too small volume. These solid particles are melted by friction heat with each of the melt around the coating. At this time, the effect of the screw is mainly to stir the plastic melt to make it evenly mixed. The speed of the melt spreads from the highest speed close to the wall to the lowest speed close to the bottom of the groove. If the depth of the groove is not large but the melt viscosity is high, the friction between the melt molecules can be severe.
The above content is for reference only; the screw barrel has the advantages of high wear resistance and corrosion resistance.
