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| The relationship between screw and the quality of PVC products |
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Since PVC decomposes molecules at high temperatures, when PVC molecules are decomposed, the firmness of the product will decrease. Here''s how to choose a screw:
What kind of screw is the best screw?
First, for example, the screw for producing PVC foam board, the most suitable use temperature is between 150-175 °C. If a screw that requires high temperature to plasticize will cause the decomposition of PVC in addition, the decomposition temperature of the blowing agent under dynamic conditions is also suitable for the best effect between 130-180 °C. Therefore, we must consider the plasticizing ability and temperature range when designing the screw.
A good screw should be a reasonable connection between each section, not a certain section of pressure is too large, a certain section of pressure is too small, the torque should be balanced, so that the material can be fully sheared. Will not block the material in the discharge section, resulting in uncontrollable temperature, resulting in the decomposition of PVC molecules. If you can do this, the firmness of the product will definitely increase a lot.
Observing the phenomenon:
Some of the barrels are equipped with water circulation at the back. Actually, the over-temperature cannot be lowered, and water is used to force the cooling. It is conceivable that this can only reduce the external temperature, and the actual temperature of the two screws is not reasonably cooled. After the surface temperature is lowered, the temperature probe responds with a low signal temperature, which can be said to be a lie to yourself.
Some screw vacuum port to see the material, it seems that the plasticization is very good, pulled into a bright strip, and the actual plasticization after the mold is not enough.
Some screws, from the vacuum port, see very little material, the part is full, and the discharge section is overheated.
It is really difficult to make a good screw. Because the pressure and flow rate are difficult to calculate accurately, the screw produced by many factories can not meet the production requirements.
A real good screw can produce large output, uniform plasticization, long boot time and long service life!
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| date：2018/8/29 Read：1238second |
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