PET blow molding
machine process flow. Important factors affecting the PET bottle blowing process are preform, heating, pre-blowing, mold and production environment. 1 When the preform is prepared for blowing, the PET chips are firstly injection-molded into the preform. It requires that the proportion of secondary recycled materials should not be too high (below 5%), the number of recycling should not exceed twice, and the molecular weight and viscosity should not be too low (molecular weight). 31000-50000, intrinsic viscosity 0.78-0.85cm3/g). According to the National Food Safety Law, secondary recycled materials shall not be used for food and pharmaceutical packaging. Injection-molded preforms need to be stored for more than 24 hours before they can be used. The preforms that are not used up after heating must be stored for more than 48 hours before they can be reheated for use. Preforms should not be stored for more than six months. The quality of the preform depends largely on the quality of the PET material. Materials that are easy to inflate and shape should be selected, and a reasonable preform forming process should be formulated. Experiments show that preforms formed from PET materials with the same viscosity and the same batch of preforms have different production dates, and the blowing process may also be quite different. The quality of the preform determines the difficulty of the blowing process. The requirements for the preform are purity, transparency, no impurities, no discoloration, and the length of the injection point and the surrounding halo are suitable. 2 Heating The heating of the preform is completed by the heating oven, and its temperature is manually set and automatically adjusted. In the oven, the far-infrared lamp tube emits far-infrared rays to radiately heat the preform, and the fan at the bottom of the oven conducts thermal circulation to make the temperature in the oven uniform. The preform rotates while moving forward in the oven, so that the preform wall is heated evenly. The arrangement of the lamps in the oven is generally in the shape of a 'zone' from top to bottom, with more at both ends and less in the middle. The heat of the oven is controlled by the number of lamps turned on, the overall temperature setting, the power of the oven and the heating ratio of each section. The opening of the lamp should be adjusted in conjunction with the pre-blowing bottle. To make the oven function better, the adjustment of its height, cooling plate, etc. is very important. If the adjustment is improper, the bottle mouth will be swollen (the bottle mouth will become larger), and the hard neck (the neck material cannot be opened), etc. defect. 3 Pre-blowing Pre-blowing is a very important step in the two-step bottle blowing method, and it is also a common technology for bottle blowing manufacturers. Take shape. In this process, the pre-blowing position, the pre-blowing pressure and the air flow rate are three important process factors. The quality of the pre-blown bottle shape determines the difficulty of the blowing process and the quality of the bottle performance. The normal shape of the pre-blown bottle is spindle-shaped, and the abnormal ones are sub-bell-shaped and handle-shaped. The reasons for the abnormal shape include improper local heating, insufficient pre-blowing pressure or air flow, etc. The size of the pre-blowing bottle depends on the pre-blowing pressure and pre-blowing position. In the production process, the size and shape of all the pre-blowing bottles of the whole equipment should be kept the same. If there are differences, the specific reasons should be found. The heating or pre-blowing process can be adjusted according to the pre-blowing situation. The size of the pre-blowing pressure varies with the bottle specifications and equipment capacity. Generally, the capacity is large and the pre-blowing pressure is small; the equipment has a high production capacity and the pre-blowing pressure is also high. 4 Auxiliary machines and molds The auxiliary machines of the blow molding machine mainly refer to the equipment that maintains the constant temperature of the molds. Mold constant temperature plays an important role in maintaining product stability. Generally, the temperature of the bottle body is high, and the temperature of the bottom and neck of the bottle is low. For cold bottles, since the cooling effect at the bottom determines the degree of molecular orientation, it is better to control the temperature at 5-8 °C; while the temperature at the bottom of hot bottles is much higher. 5 Environment The quality of the production environment also has a great influence on the process adjustment. Constant temperature conditions can maintain the stability of the process and the product. PET bottle blow molding is generally better at room temperature and low humidity. 6 Other requirements The pressurized bottle should meet the requirements of stress test and pressure test at the same time. The stress test is an internal quality control to prevent cracking and leakage caused by the degradation of the molecular chain during the contact between the bottom of the bottle and the lubricant (alkaline) when the PET bottle is filled with beverages; the pressure test is to prevent the bottle from being filled. Quality control for bursting after entering a certain pressure gas. In order to meet these two needs, the thickness of the center point should be controlled within a certain range. Generally, the center point is thin, the stress test is better, and the withstand voltage is poor; the center point is thick, the withstand voltage test is better, and the stress test is poor. Of course, the results of the stress test also have a great relationship with the accumulation of materials in the transition area around the center point, which should be adjusted according to actual experience. The adjustment of the PET bottle blowing process is mainly carried out for the corresponding material. If the material is not good, the requirements for the process are very strict, and it is even difficult to blow a qualified bottle.
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