What knowledge is there about preforms (for blow molding machines)?

　　Blow molding machines? Hollow blow molding machines? Preform molds? You must be familiar with these products. Today, as a supplier, we'll introduce you to the knowledge related to blow molding machines and preforms. If you are also troubled by this issue, the following introduction will definitely help you. Let's read on.

　　Preforms for blow molding machines, also known as parisons, are injection-molded from PET pellets. They require a recycled material ratio of no more than 10%, and the number of recycling times should not exceed two. Preforms after injection molding, or preforms used after heating, must be cooled for more than 48 hours. The storage time of the used preforms cannot exceed 6 months. Preforms from different production dates, especially those with a long interval, cannot be mixed. This is mainly due to differences in the material Model, the proportion of secondary materials mixed, and the residual stress in the preforms. These factors have a significant impact on the blow molding process and should be treated specifically according to the actual situation. Due to the strong water absorption of PET, special attention must be paid to moisture prevention during storage. Before processing, it is essential to effectively dehumidify and dry it. The drying conditions are usually 150～180℃ for 4 hours. To prevent the plastic pellets from reabsorbing moisture, they must be kept warm at a temperature above 140℃. When the machine is stopped, to prevent the plastic from turning yellow, the dehumidifying dryer needs to be cooled to 100℃. No dehumidification is needed if only maintaining the temperature. In addition, if the material temperature is too high, the screw shearing force is too large, or the speed is too fast during PET injection molding, it is easy to produce acetaldehyde, leading to acidification. Generally, the acetaldehyde content of the molded PET bottle must be less than 3ppm. The preform needs a certain water content before crystallization, generally requiring around 1000 ppm, and at least 900 ppm. Therefore, the preform needs to be placed for a period of time after injection molding to allow the water content to reach the required level before crystallization.