First, pc material (polycarbonate) features:

1. Non-crystalline plastic, no obvious melting point, glass transition temperature 140-160 degrees Celsius, melting temperature 215-225 degrees Celsius, molding temperature 230-320 degrees Celsius;

2, high viscosity, high processing temperature, narrow range, easy to decompose, avoid the phenomenon of overheating when using the screw;

3, sensitive to moisture, the resin is easy to hydrolyze at high temperature, drying temperature 120-130 degrees Celsius, time 4 hours or so.

Parameter selection:

L/D is characterized by its high thermal stability and high viscosity, and it is necessary to take a large aspect ratio to improve the plasticizing effect;

Due to its wide melting temperature range, the feeding section is long, the homogenization section is short, and the compression ratio is moderate. In order to increase the plasticizing effect, a barrier type rubber head can be selected;

If you add flame retardant or glass fiber reinforced pc material, you can choose to use corrosion-resistant and wear-resistant high-quality stainless steel tool steel screw and three small pieces.

Second, PMMA (Plexiglas) features:

The glass transition temperature is 105 degrees Celsius, the melting temperature is greater than 160 degrees Celsius, the decomposition temperature is 270 degrees Celsius, and the molding temperature range is 180-250 degrees Celsius wide;

High viscosity, poor fluidity, sensitive to shear rate, strict temperature control during processing;

The barrel temperature is 240-250 degrees Celsius, and when it exceeds 260 degrees Celsius, the residence time is no more than 8 minutes;

Strong water absorption, drying temperature 80-90 degrees Celsius, time more than 3 hours.

Parameter selection:

L/D selects the aspect ratio 20-22, and the gradient type screw generally takes L1=35-45%, L2=35-40%;

The compression ratio ε generally takes 2.3-2.6;

For its hydrophilicity, a mixed fire structure is used at the front end of the screw.

Third, PA (polyamide), common PA6 (nylon 6), PA66 (nylon 66) characteristics:

There are many kinds of crystalline plastics, the types are different, the melting point is different, and the upper melting point range is narrow. Generally, the melting point of PA66 is 260-270 degrees Celsius;

Low viscosity, good fluidity, relatively obvious melting point, poor thermal stability;

The water absorption rate is high, the dryer temperature is 80 degrees Celsius, no more than 120 degrees Celsius, and the time is 16 hours. If the material is exposed to air for 8 hours, use a vacuum oven at approximately 105 degrees Celsius for 12 hours.

The parameters are predetermined:

L/D selects a mutant screw with a length ratio of 18-20;

The compression ratio is generally selected from 2.5 to 3.5, which prevents overheating decomposition h3: 0.067-0.089D

Because of its viscosity, the gap between the apron and the barrel should be as small as 0.05-0.08, and the gap between the screw and the barrel is 0.08-0.12.

The nozzle can be equipped with a spring self-locking nozzle.

Fourth, PET (polyester) chemical name: polyethylene terephthalate characteristics:

The melting point of 250 ° C -260 ° C, blow molding PET molding temperature is wide, about 255 ° C -290 ° C, enhanced grade GF-PET up to 290 ° C -315 ° C;

High melting point, low viscosity, high adhesion to metals, easy to hydrolyze;

Hydrophilic, the binder is sensitive to water at high temperatures, drying temperature 150 ° C -160 ° C, time 4 hours or more.

Preferences:

L/D generally takes 20-22, three-segment distribution L1=50-60%, L2=20-30%;

Use low shear, low compression ratio screw compression ratio ε = 1.8-2.2, because shear overheating leads to discoloration or opacity h3=0.09-0.10D;

When using recycled material (sheet), the conveying capacity of the feeding section is increased, and a forced feeding plasticizing system is adopted.

Five, PVC (polyvinyl chloride)

Thermally sensitive materials are generally classified into hard and soft, the difference being the amount of plasticizer added to the raw material, less than 10% being hard, and more than 30% being soft.

characteristic:

No obvious melting point, softening at 60 °C, viscoelastic state at 100 °C-150 °C, narrow melting temperature range at 140 °C, poor thermal stability, easy decomposition, rapid decomposition at 170 °C, softening point close to decomposition point, decomposition released in HCI gas.

Due to the high viscosity of UPVC melt, poor thermal stability, temperature and time will lead to decomposition, so it has a corrosive effect on general steel;

The temperature control is strict, the screw design should be as low as possible to prevent overheating, the flow channel must be smooth, there must be no dead angle, and the accumulation of material can be prevented from decomposing;

The screw barrel should be protected from corrosion;

The injection molding process needs to be strictly controlled.

Preferences:

L/D=18-21, h3+0.067-0.08D, ε-1.6-2, L1=40-45%, L2=35-45%, in order to prevent the hiding of the material without apron, head 20 ° C-30 °C, using a chrome-plated screw;

Temperature selection:

1) Multi-stage air cooling device for molten rubber cylinder;

2) Low-cut high-mixing UPVC special screw barrel device.