The main factors affecting the quality of plastics: aspect ratio, compression ratio, back pressure, screw speed, barrel heating temperature.
An aspect ratio: Effective length of the screw and the screw diameter ratio.
a, large aspect ratio is expected to eat and easy uniform;
b, better thermal stability of the plastic used to improve the kneading screw longer without burning resistance, poor thermal stability of the plastic can be shorter end unthreaded screw or screw. The plastic properties of a general flow length such as the following: Thermoset 14 \ 16, rigid PVC, PU and other heat-sensitive high viscosity of 17 \ 18, usually plastic as 18 \ 22, PC, POM plastic as high temperature stability, etc. 22 \ 24.
2, the compression ratio: the last segment of the feed screw channel depth and measurement paragraph a spiral groove depth ratio.
a, considering the compressibility of the material, degree of filling, back and other effects, the product to be dense, heat of the exhaust;
b, the appropriate compression ratio to increase the density of plastic, between the molecules and the molecules more closely, to help reduce the suction of air, reducing the temperature rise due to the pressure and influences the output difference in the amount, improper compression than would destroy the physical properties of plastics;
c, the higher the compression ratio, the tube of plastics material produced during plasticizing the higher the temperature, the plastic is plasticized mixing results in better uniformity of the relative quantity greatly reduced.
d, a high compression ratio for non-fusible plastics, especially with low melt viscosity, thermal stability, plastic; low compression ratio suitable fusible plastics, especially with high melt viscosity, heat-sensitive plastics.
3, back pressure
a, increasing backpressure increases the screw on the work done by the molten resin, eliminating unmelted plastic particles, increasing raw material tube density and uniformity;
b, back pressure is being applied to improve the barrel temperature, the effect is the most significant;
c, back pressure is too large, the higher the heat-sensitive plastic decomposition, the low viscosity of the plastic may produce salivation phenomenon of back pressure is too small, the finished product may be injection bubbles.
4, the screw speed
a, the screw rotation speed of the spiral groove directly affect the plastic shear;
b, small screw groove shallow absorb heat quickly enough to induce plastic softening in the compressed period of time, the screw and barrel intramural friction heat is low, suitable for high-speed rotation, increased plasticizing capacity;
c, large screw is not rapid rotation, so as not to cause excessive friction plastics and uneven heat;
d, the higher the heat-sensitive plastic, screw speed is too large, it will be very easy to break the plastic;
e, usually the size of the screw has a certain speed range, the general speed of 100 \ 150rpm; too low, you can not melt plastic, too will be burning plastic.
5, heating temperature setting
a, so stay in the barrel and screw the screw rotation chilled plastic melt to facilitate providing access to plastic part of the heat required to melt;
b, set the temperature lower than the melting 5 \ 10 ℃ (partly by friction heat provided);
c, the nozzle temperature adjustment can also be used to control salivation, condensing material (plug Tsui), pull wire and other issues;
d, crystalline plastics are generally Temperature control: