, screw diameter (D)
A, the required amount of injection and injection volume: =1/4* PI *D2*S (*0.85 injection stroke);
B, in general, the screw diameter of D and the maximum injection pressure is inversely proportional to the capacity of the plastic.
2, conveying section
Responsible for the delivery of a, plastic, pushing and preheating, should ensure preheating to the melting point;
B, crystalline plastics should be long (such as: POM, PA) of the amorphous material (such as: PS, PU, ABS), the most sensitive short (such as: PVC).
3, compression section
A, responsible for mixing, compression and exhaust pressure of mixed plastics, through this section of the raw materials have been almost all melted, but not necessarily evenly mixed;
B, in this region, plastic gradually melting, the spiral groove volume must be correspondingly decreased, in order to correspond to the plastic geometric volume , otherwise the material pressure is not solid, heat transfer is slow, and the exhaust gas is not good;
C, generally accounted for more than 25% screw length, but nylon (crystalline material) compression section about 15% screw screw working length, high viscosity, fire resistance, low conductivity and high plastic additives such as screw, 40%'50% screw length, PVC screw can be accounted for 100% of the working length of screw, so as to avoid the intense shear heat the.
4, metering section
A, generally accounted for 20'25% of the working length of the screw, to ensure all the melting of the plastic and the temperature is uniform, uniform mixing;
B, metering section of the mixing effect is good, too long it is easy to make the melt stay too long and produce thermal decomposition, is too short, easy to make the temperature is not uniform;
C, PVC and other sensitive plastic should not stay too long, to avoid thermal decomposition, available short metering section or not metering section.
5, feed screw groove depth, metering screw groove depth
A, the feeding groove depth is deeper, the greater the amount of delivery, but the need to consider the strength of screw, screw channel depth measurement is more shallow, plasticizing fever, mixing performance index is high, but the measurement of groove depth is too shallow, the shear heat increases, authigenic heat increase, temperature rise too high, causing discoloration or plastic burning, especially not conducive to heat sensitive plastics;
B, metering spiral groove depth *D (0.03'0.07) D, =KD= increases, the K ion of small value.
The main factors affecting the quality of plastic
The main factors that affect the quality of plastic are: the ratio of length to diameter, compression ratio, back pressure, screw speed, barrel heating temperature and so on.
1, the ratio of length to diameter
Ratio of effective working length of screw and screw diameter.
A, the long diameter ratio is big then eats the material to be easy to be even;
The available long screw plastic B, better thermal stability to improve mixing performance without burning, poor thermal stability of plastic can short screw or screw thread without end. Considering the characteristics of plastic, general flow length ratio is as follows: thermosetting 14'16, hard PVC, PU heat sensitive 17'18 high viscosity, general plastic 18'22, PC, POM and other high temperature stability of plastic 22'24.
2, compression ratio
Ratio of the first spiral groove depth of the first spiral groove depth of the feed section.
A, taking into account the compressibility of the material, the degree of filling, reflux and other effects, products to be dense, heat transfer and exhaust;
B, the appropriate compression ratio increases the density of plastic, the more closely between molecules and which helps reduce air suction, reduce the pressure caused by the temperature rise, and the impact of differences in output, inappropriate material plastic compression failure than will;
C, the higher compression ratio, the temperature rise produced in plastic barrel plasticizing process is high, has a better mixing uniformity of plastic in plastic, relative to the discharge amount is greatly reduced.
D, high compression ratio for fusible plastic, especially with low melt viscosity, thermal stability of plastics; low compression ratio for fusible plastic, especially with high melt viscosity, heat sensitive plastics.
3, back pressure
A, increasing the back pressure can increase the screw to melt the work done by the resin, eliminate the melt plastic particles, increase the density of raw materials and the uniformity of the material tube;
B, back pressure is used to improve the barrel temperature, the most significant effect;
C, back pressure is too large, the higher the heat sensitive plastic easy decomposition of low viscosity plastic may produce salivation phenomenon, back pressure is too small, the injection of the finished there may be a bubble.
4, screw speed
A, the rotation speed of the screw directly influences the shear of the plastic in the spiral groove;
B, the small screw slot is shallow absorption heat source fast, enough to make plastic in the compression period of time to soften, the friction between the screw and the cylinder wall is low, suitable for high-speed rotation, increase the capacity of plastic;
C, large screw is not suitable for rapid rotation, so as not to cause excessive friction and heat caused by excessive friction;
D, on the high sensitive plastic screw speed is too large, plastic will be very easy to decompose;
E, usually the size of the screw has a certain range of speed, general speed 100'150rpm; too low can not melt the plastic, too high will be burned plastic.
5, electric temperature setting
Chilled plastic melting a, so that remaining in the barrel and screw in order to obtain the rotation of the screw, plastic part of the heat required to melt;
B, set the low melt temperature than 5'10 DEG C (partly provided by the friction heat);
C, nozzle temperature adjustment can also be used to control salivation, condensation material (Sai Ju), pull wire etc.;
D, crystalline plastic general temperature control.