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Breif Introduction of the Temperature and Screw in the Extrusion Process

Date:2016-05-04

Extrusion process parameters is one of the important conditions for the smooth conduct of the extrusion. Starting from powdered or granular solid material, hot products extruded from the die, through a complex process of change of temperature. Strictly speaking, extrusion temperature should refer to the plastic melt temperature, but the temperature was largely determined by the temperature of the barrel and the screw, a small portion of the heat from the friction generated when the cartridge is mixed in, so often approximated by a cylinder temperature of the molding temperature. Since the temperature of the plastic barrel and screw each segment is different, in order to transport the plastic in the barrel, melting, homogenization and extrusion process to work, in order to efficiently produce high quality parts quality, the key issue is to control temperature of each cylinder, the cylinder temperature is adjusted by the heating and cooling system and temperature control system of the extruder to achieve. Head temperature must be controlled in a plastic decomposition temperature, and the temperature of the die temperature slightly lower than the nose, but it should ensure that the plastic melt has good flowability. In addition, the molding process and temperature fluctuations in temperature, residual stress will produce plastic parts, uneven points strength and surface defects such as matte gray. This temperature difference generates fluctuations and there are many factors, such as heating, cooling system instability, screw speed changes, but screw design and selection is good or bad the greatest impact.

Changes screw groove depth, as well as filters, filter plates and die and so hinder, thus along the cylinder axis direction, in plastic inside a certain pressure. This pressure is homogeneous plastic melt and get into one of the important conditions of dense plastic parts. Increased head pressure can increase the melt extrusion mixing uniformity and stability, improve product density, but the nose excessive pressure affect production. Like temperature and pressure will produce cyclical changes over time, such fluctuations also have an adverse effect on the quality of plastic, screw speed of change, heating, cooling systems are unstable causes pressure fluctuations. In order to reduce pressure fluctuations, should be the reasonable control of screw speed to ensure the temperature of the heating and cooling device control accuracy. 3. The extrusion rate factors affect extrusion rate of many, such as the nose, the structure of the screw and barrel, screw speed, heating and cooling system structure and plastic properties. Theory and practice have proved that the extrusion rate with the screw diameter, the spiral groove depth, length and homogenizing screw speed increases, with the end of the screw melt pressure and screw and barrel gap increases. In the case of the structure and the plastic varieties and types of plastic extruder has been determined, the extrusion rate and screw speed only, and therefore, adjust the screw speed is the main measures to control the rate of extrusion. Extrusion rate in the production process there is fluctuation, which will affect the geometry and dimensions of precision plastic parts. Thus, in addition to the right to determine the structure and size of the screw parameters, should also strictly control the screw speed, strict control of the extrusion temperature, to prevent temperature changes caused by the extrusion pressure and melt viscosity, resulting in fluctuations in the extrusion rate of 4. traction speed continuous extrusion mainly produces plastic parts, it is necessary to set the traction device. Extruded from the die head and plastic parts, will occur under the effect of traction stretching orientation, the higher the degree of orientation of the drawing, plastic parts along the orientation direction of greater tensile strength, but the length of the cooling contraction It is also large. Typically, traction speed and extrusion speed considerably. The ratio of the traction speed and extrusion speed of said traction than ...

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