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Views: 13 Author: Site Editor Publish Time: 2022-11-04 Origin: Site
The screw is the heart and critical component of the plastic extrusion. The performance of the screw determines the productivity, plasticization quality, additive dispersion, melt temperature, power consumption, etc. It is the most critical component of the plastic extrusion and can directly affect its range of applications and productivity. The rotation of the screw exerts tremendous pressure on the plastic so that it can move, pressurize, and gain some heat from the friction inside the barrel. The plastic is mixed and plasticized as it moves through the barrel. As the viscous melt is extruded and flows through the mold, it gets the desired shape and is molded. The screw, like the barrel, is made of a high-strength, heat- and corrosion-resistant alloy.
Because there are many types of plastics, their properties are different. Therefore, different types of screws with different structures are needed to meet different plastic processing needs. This maximizes the transport, extrusion, mixing, and plasticization of plastics.
The basic parameters representing screw characteristics include the following: diameter, aspect ratio, compression ratio, pitch, groove depth, helix angle, screw and barrel clearance, etc.
The most common screw diameters d are around 45 ~ 150 mm. When the diameter of the screw increases, the processing capacity of the plastic extrusion increases accordingly, and the productivity of the plastic extrusion is proportional to the square of the screw diameter D. The ratio of the effective length of the screw to the diameter of the working part (referred to as the L/D ratio, expressed as L/D) is usually 18 ~ 25. A large L/D improves the material's temperature distribution, facilitates the plastic's mixing and plasticization, and reduces leakage and backflow. Increase the capacity of the plastic extrusion. The screw with a large L/D is highly adaptable and can be used for the extrusion of various plastics; however, when the L/D is too large, the plastic segment will degrade due to the increase of heat time, the free end will bend and sag due to the increase of the screw's self-weight, which will quickly cause scratches between the material sheet and the screw and make the manufacturing process complicated. The power consumption of the plastic extrusion increases. Too short a screw tends to lead to poor mixing and plasticizing.
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