Knowledge about semi-automatic blow molding machine 4-cavity preform

The preforms after injection molding or reheated preforms must be cooled for more than 48 hours, and the preforms used should not be stored for more than 6 months.

The preforms after injection molding or reheated preforms must be cooled for more than 48 hours, and the preforms used should not be stored for more than 6 months. Different production dates, especially preforms with too long intervals, cannot be mixed. The main reason is that The type of raw material used in the preform, the proportion of the secondary material mixed in and the residual stress in the preform are different, and these factors have a major impact on the molding process of the bottle blowing bottle, and should be treated according to the actual situation. Due to the strong water absorption of PET, special attention must be paid to moisture-proof during storage, and it must be dehumidified and dried before processing. The drying condition is usually 4 hours at 150-180°C, and in order to prevent the plastic pellets from absorbing moisture again, must Keep warm at a temperature above 140°C. In order to prevent the plastic from turning yellow when shutting down, the dehumidification dryer needs to be cooled to 100°C.

In addition, if the material temperature is too high, the shear force of the screw is too high or the rotation speed is too fast during PET injection molding, acetaldehyde is likely to be produced and cause acidification. Usually, the acetaldehyde content of the formed PET bottle must be less than 3ppm. A certain water content is required, generally around 1000 ppm, at least above 900 ppm, so the preform needs to be placed for a period of time after injection and the water content meets the requirement before it can crystallize.

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