Principles of blow molding
PET is divided into three forms: glass state, high elastic state, and molten stateThe glass transiti···
PET is divided into three forms: glass state, high elastic state, and molten state
The glass transition temperature of PET is about 80 degrees, and the crystallization temperature is about 150 degrees. The state between the two is generally called the high elastic state, and the preform can be blown within this temperature range. The blowing temperature of water bottles is generally between 90 and 120 degrees. Hot-filled bottles require a higher temperature, generally between 130 and 145 degrees.
The bottle is molded generally requires two blows to complete. The pre-blowing pressure is generally between 7 and 12 bars, and the pre-blowing and stretching are carried out simultaneously to stretch the preform in both directions to complete the bottle pre-forming effect. The effect of preforming determines the quality of the bottle.
High-pressure blowing is generally 25-40 bar, the higher the pressure, the faster the bottle forming speed. Low pressure will generally cause the bottle to be under-formed and insufficient in volume.
Bottle shaping: water bottles and gas-containing bottles need to be quickly cooled and shaped, so the chiller of the mold should be adjusted as low as possible without condensation. (6~12 degrees). The hot-filled bottle is completely different from the water bottle. It needs to hold pressure and heat setting, and the mold temperature is generally about 140 degrees. The purpose is to partially crystallize the surface of the bottle, and the crystallinity generally reaches about 30%, so that the heat resistance of the bottle will be better.
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