Zhoushan Oushengda Plastic Machinery Co.Ltd





Screw is the main factors affecting the quality of plastics


The main factors affecting the quality of plastics are: aspect ratio, compression ratio, back pressure, screw speed, barrel heating temperature.

1, aspect ratio: for the effective working length of the screw and screw diameter ratio.

a, large aspect ratio is even easy to eat the material;
b, better thermal stability of the plastic can be used to improve the longer screw without mixing of the burning, poor thermal stability of the plastic can be shorter end of the screw or screw without thread. Plastic properties to consider, such as under the general stream length: thermosetting 14 \ '16, rigid PVC, PU and other heat-sensitive high viscosity of 17 \ '18, usually plastic to 18 \ '22, PC, POM and other high-temperature stability of plastic 22 \ '24.

2, compression ratio: the feed section of a spiral groove depth of the last paragraph with the measurement of the ratio of the depth of a spiral groove.
a, consider the compression of material, filling level, back and other affected products to be dense, heat and exhaust;
b, the appropriate compression ratio can increase the density of plastic, so that the molecules and between molecules more closely to help reduce the air absorb and reduce the stress generated due to temperature rise and affect the output of the difference, inappropriate compression than would destroy the physical properties of plastics;
c, the higher the compression ratio, the plastic tube in the plastics material produced during the higher temperature, the plastic in the plastics results in better mixing uniformity, greatly reduced relative to the fluxes.
d, high compression ratio for easy melting plastic, especially a low melt viscosity, thermal stability of plastics; low compression ratio suitable for fusible plastic, especially with high melt viscosity, heat-sensitive plastic.

3, the back pressure
a, increase the back pressure can increase the screw on the work done by the molten resin to remove the plastic particles without melting, increasing raw material tube density and uniformity;
b, back pressure is being applied to improve the barrel temperature, the effect is most significant;
c, back pressure is too large, the higher the heat-sensitive plastic decomposition, the low viscosity of the plastic may cause salivation phenomenon, back pressure is too small, injection molding of the finished product may be air bubbles.

4, screw speed
a, screw rotation speed directly affects the plastic shear in the screw slot;
b, small screw groove shallow absorption heat quickly enough to promote plastic softening in compression time, the screw and barrel wall of the lower heat of friction, suitable for high-speed rotation, increased plasticizing capability;
c, large screw rotation is not fast, so as not to cause excessive friction plastics and uneven heat;
d, the higher the heat-sensitive plastic, screw speed too much, then, the plastic can easily break down;
e, usually of a certain size screw speed range, the general speed of 100 \ '150rpm; too low you can not melt the plastic, too much plastic will be burned.

5, the heating temperature setting
a, so stay in the barrel and screw the screw rotation chilled molten plastic in order to facilitate and provide molten plastic to obtain the necessary part of the heat;
b, set the temperature lower than the melt 5 \ '10 ℃ ​​(provided in part by the friction heat);
c, the adjustment of the nozzle temperature can also be used to control salivation, condensed material (plug Tsui), pull wire and other issues;
d, crystalline plastics are generally temperature control:

Plastic types
Barrel temperature ℃
Injection Pressure kgf/cm2

HDPE (High Density Polyethylene)
180 \ '210
500 \ '1500

PP (polypropylene)
200 \ '270
400 \ '1000

PA6 (Nylon 6)
225 \ '280
700 \ '1000

PA66 (nylon 66)
260 \ '280
600 \ '1500

e, non-crystalline plastic

Plastic types
Barrel temperature ℃
Injection pressure kgf/cm2

PS (polystyrene)
180 \ '240
400 \ '1300

ABS (acrylonitrile butadiene styrene)
200 \ '230
800 \ '1500

PMMA (polymethyl methacrylate)
180 \ '220
700 \ '1500

PC (polycarbonate)
260 \ '310
800 \ '1500

Modified PPO (Noryl)
240 \ '280
850 \ '1400

Rigid PVC (rigid PVC)
165 \ '185
1000 \ '1500

Note: a, do not add more to the non-glass fiber reinforced plastic.

b, the barrel melt temperature is usually higher than the tube outside the control of the temperature.

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