PET plastic injection molding process is one of very important technology in plastics processing, for the PET plastic bottles, in most cases the plastic packaging plant will adopt the way of blow molding processing, but the injection molding process is a unique advantage, for PET injection molding, the technicians need to consider many factors.
PET plastic profile: PET chemical called ethanol terephthalate, also known as polyester.
Now is the most used GF - in the customers
PET, mainly playing bottle embryo.
The rheological properties of PET in the molten state, stress on the influence of the viscosity is bigger than the temperature, therefore, mainly from the pressure to change the melt flow rate.
PET features: PET vitrification transformation temperature about 165 ℃, the crystallization temperature range is 120 ~ 220 ℃.
PET at high temperature has a strong hygroscopicity.
For glass fiber enhanced PET material, also very easy to bending deformation at high temperature.
Can be enhanced by adding crystallization agent to improve the degree of crystalline materials.
With transparent PET processing products have glossiness and heat distortion temperature.
Can be added to the PET mica and other special additives minimizes bending deformation.
If you use a lower mold temperature, then using the PET not fill material also can obtain transparent products.
Injection molding process, molding injection molding in is mainly used to enhance the PET.
Usually adopts screw injection machine.
Screw is typically require hardening treatment, lest abrasion occurs after use for a long time.
The length of the injection machine nozzle holes should be as short as possible, its diameter should be controlled at about 3 mm.
Enhance PET melting point 260 ℃, in order to prevent the nozzle blocking, power larger heater should be installed.
In addition, the tip of the nozzle hole processed into figure -
The inverse cone type 1, make the flow channel and the nozzle in the molten material can be easily cut.
Injection molding machine, injection molding is mainly used to enhance the PET molding.
PET in general can only choose screw injection molding.
Selects the mutant with non-return ring tops screw, its surface hardness and wear resistance, length to diameter ratio L/D = (
15 ~ 20)
: 1 compression ratio is about 3:1.
L/D is too big material within the cylinder for a long time, excessive heat, easy to cause the degradation property of products.
Compression ratio is too small shear heat generating less, easy plasticizing, product performance is poor.
Vice can make glass fiber fracture, more mechanical performance degradation.
When processing glass fiber reinforced PET, the inner wall of the cylinder wear more severe, cylinder use wear-resisting material or have wear-resisting lining material.
Nozzle is good with short, wall require polishing, aperture requirements as much as possible.
With hydraulic brake valve type nozzle as well.
Nozzle to have heat preservation and temperature control measures to ensure that the nozzle will not freeze.
But the nozzle temperature not too high, otherwise cause salivate.
Low pressure PP material must be used before began to take shape, the cylinder is clean.
PET's main injection molding conditions: 1, the cylinder temperature.
The discretion of the narrow range of molding temperature and temperature of the PET will directly affect the performance of the products.
If temperature is too low, the plasticizing is bad, make the plastic parts such as depression, lack of material defects;
On the other hand, the temperature is too high, can cause excessive, nozzle salivate, darker color, mechanical strength drop, even cause degradation.
Usually, the cylinder temperature control in 240 ~ 280 ℃, the glass fiber reinforced PET cylinder temperature is 250 ~ 290 ℃, shall not exceed 300 ℃, the nozzle temperature generally 10 to 20 ℃ lower than the cylinder temperature.
2, mold temperature.
Die temperature directly affect the cooling speed of melting and the degree of crystallinity, degree of crystallinity is different, the plastic pieces of different performance.
Usually, the mould temperature control in 100 ~ 140 ℃, when molding thin-wall plastic parts, desirable small value;
Thick wall molding plastic parts, desirable value.
3, the injection pressure.
Good PET melt flow, easy molding, usually USES the medium pressure, the pressure is 80 ~ 140 mpa, glass fiber reinforced PET injection pressure is 90 ~ 150 mpa.
Should consider the determination of injection pressure, viscosity of PET, the amount and type of packing, the location and size of gate, the shape of the plastic parts, mold temperature, injection molding machine type and size, etc.