Blow molding process The important factors that affect […]
Blow molding process
The important factors that affect the PET bottle blow molding process are the preform, heating, pre-blowing, mold and environment.
When preparing blow-molded bottles, firstly, PET chips are injected and formed into preforms. It requires that the proportion of secondary reclaimed materials cannot be too high (below 5%), the number of retractions cannot exceed twice, and the molecular weight and viscosity cannot be too low (molecular weight 31000- 50000, intrinsic viscosity 0.78-0.85cm3/g). The injection-molded preform must be stored for more than 48 hours to be used. Preforms that have not been used up after heating must be stored for more than 48 hours to be reheated for use. The storage time of preforms cannot exceed six months.
The heating of the preform is completed by a heating oven, and its temperature is manually set and automatically adjusted. In the oven, the far-infrared lamp tube emits far-infrared rays to radiate and heat the preform, and the fan at the bottom of the oven performs heat circulation to make the temperature in the oven uniform. The preform moves forward and rotates together in the oven, so that the preform wall is heated evenly.
Pre-blowing is a very important process in the two-step blowing method. It refers to the pre-blowing at the beginning of the stretch rod when the stretch rod descends during the blow molding process to make the preform take shape. In this process, the pre-blowing orientation, pre-blowing pressure and blowing air flow are three important process elements.
4 Auxiliary machine and mould
The auxiliary machine mainly refers to the equipment that keeps the mold constant. The constant temperature of the mold plays an important role in maintaining the stability of the product. Generally, the temperature of the bottle body is high and the temperature of the bottle bottom is low. For the cold bottle, because the cooling effect at the bottom determines the degree of molecular orientation, it is better to control the temperature at 5-8℃; while the temperature at the bottom of the hot bottle is much higher.
The quality of the production environment also has a greater impact on the process adjustment, and stable conditions can maintain the stability of the process and the stability of the product. PET bottle blow molding is generally best at room temperature and low humidity.