|24.11.2017||Posted by petmould under Elektronika|
PET, also called poly ethylene terephthalate, is also known as polyester. At present, the most used kind is PET-GF; it is mainly for bottle PET Mould manufacturing. The rheological property of PET is better in molten state, and the pressure effect on the viscosity is greater than that of temperature. Therefore, it is mainly to change the fluidity of the melt by changing the pressure.
plastic processing .due to pet macromolecules containing grease, it is hydrophilic. Pellets in high temperature water are more sensitive, the much moisture will decrease the molecular weight of pet, which would lead to poor color and brittle parts. Before processing, the material must be dry; the drying temperature is 150 degrees, time more than 4 hours. And generally it is 170 degrees, about 3-4 hours. Whether the material is completely dry can be tested by shot to air. Recycled material ratio is generally not more than 25%, and also the reground material should be completely dry.
injection moulding machine .due to the shorter stable time after melting and high melting point, it is necessary to use the injection machine with more multi-step temperature control and less plasticizing friction heat system .and all weight(products and runner) is not less than 2 / 3 of machine injection volume .
PET preform mould and its gate design. Generally, PET bottle preform mould is installed with hot runner system. There should have insulation plates (about 12 mm thickness) between the PET preform mould and injection moulding machine, and the heat insulation plate can withstand high pressure. Air venting must be sufficient to avoid local overheating or fragmentation, but the depth of the slot is generally not more than 0.03 mm, otherwise it is easy to invite flash.
melt temperature .it is 270-295 degrees Celsius by shot to air, PET-GF can be set to 290-315.
injection speed. The fast shot can prevent premature injection solidification. But too fast will lead to high shear rate and the brittle products. Shot is usually completed within 4 seconds.
back pressure. The possible low back pressure is a better way to avoid wear. Generally the back pressure is not more than 100 bar.
stay time and temperature. Stay time shouldn’t be long to prevent the decline of molecular weight, and the temperature should avoid more than 300 degrees Celsius possibly.
If the down time is less than 15 minutes, shot to air is OK; but if over 15 minutes, it should use PE to clean barrel, and the barrel temperature decrease to PE temperature.
Note: recycled materials cannot be added much, otherwise it easy to produce poor quality products. If the mould temperature or material temperature is not proper, it is easy to produce “opaque” pet preform. The low mould temperature and the fast cooling rate would achieve transparent pet-mould.com PET Preform Mould.