Extruder Screw Is the Main Factor Affecting the Quality of Plasticization

The main factors affecting the quality of plasticization are length-to-diameter ratio, compression ratio, back pressure, extruder screw speed and barrel heating temperature and so on.


Ⅰ. The length to diameter ratio of the extruder screw


The length to diameter ratio of the extruder screw is the ratio of the effective working length to the diameter of the extruder screw.


1. If the ratio of length to diameter is large, the food is easy to be averaged;


2. For plastics with better thermal stability, a longer extruder screw for sale can be used to improve the mixing performance without scorching. For plastics with poor thermal stability, a shorter extruder screw or no screw at the end of the screw can be used.


Considering the characteristics of plastics, the ordinary flow length ratio: thermosetting is 14\'16, rigid PVC, high-viscosity PU and other heat sensitivity are 17\'18, ordinary plastics are 18\'22, PC, POM and other high-temperature stable plastics are 22 \'twenty four.


Ⅱ. Compression ratio of extruder screw


1. Considering the compressibility of the material, filling level, backflow and so on. The product should be dense, heat transfer and exhaust.


2. Proper compression ratio can increase the density of plastics, make the separation between molecules and molecules more tight, help reduce the extraction of air, reduce the temperature rise due to pressure, and affect the difference in output. Improper compression ratio will destroy the physical properties of the plastic.


3. The higher the compression ratio, the higher the temperature rise of the plastic during the plasticization process in the material tube, and the better the average mixing degree of the plastic during the plasticization, and the relative output is greatly reduced.


4. High compression ratio is suitable for non-meltable plastics, especially plastics with low condensation viscosity and thermal stability. The low compression ratio is suitable for fusible plastics, especially plastics with high condensing viscosity and heat sensitivity.


Ⅲ. Back pressure of extruder screw


1. Increasing the back pressure can increase the work done by the different types of extruder screws on the molten resin, eliminate unmelted plastic particles, and increase the density of the raw materials in the barrel and its average level.


2. Back pressure is used to increase the temperature of the barrel, and the effect is more obvious.


3. If the back pressure is too large, it is easy to synthesize plastics with higher heat sensitivity, and it may cause salivation for plastics with low viscosity. If the back pressure is too small, there may be bubbles in the waste injection molded products.


Ⅳ. Rotation speed of extruder screw


1. The rotation speed of the extruder screw directly affects the shear of the plastic in the spiral groove.


2. The small screw groove is shallow, and the heat source is absorbed quickly, which is enough to promote the softening of the plastic in the compression section. The frictional heat energy between the extruder screw and the barrel wall is low, which is suitable for high-speed rotation and increases the plasticizing capacity.


3. Large screws should not be rotated quickly to avoid uneven plasticization and excessive frictional heat.


4. For plastics with high heat sensitivity, if the rotation speed of the extruder screw is too high, the plastics will be easily synthesized.


5. Generally, each size screw has a certain speed range, and the normal speed is 100-150rpm. Too low will not condense the plastic, and too high will scorch the plastic.


Ⅴ. Electric heating temperature of extruder screw


1. The chilled plastics in the barrel and the screw of the extruder will be melted, which facilitates the rotation of the screw and provides the local heat required for the melting of the plastic.


2. It sets a temperature 5-10°C lower than the melt temperature and part of temperature is provided by frictional heat.


3. The adjustment of the nozzle temperature can also be used to control problems such as drooling, condensate, and wire drawing.


4. It adopts ordinary temperature control of crystalline plastics.

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