Introduction to the process of PET plastic bottle blowing
- Nov 24, 2018 -

Tea beverage bottle is mixing polyethylene naphthalate formic acid ethyl ester (PEN) two modified PET bottles or the PET composite bottle with thermoplastic aromatic esters, belong to hot bottles on classification, can be more than 85 ℃ heat; Aquarius is a cold bottle, no heat resistance requirements. The hot bottle is similar to the cold bottle in forming technology.



1 equipment



At present, the PET automatic bottle blowing machine manufacturers imported mainly from France SIDEL company, Germany KRONES company, domestic fujian quanguan company and so on. Although the manufacturers are different, but the principle of their equipment is similar, generally including the billet system, heating system, blowing bottle system, control system and five parts of the auxiliary machine.



Blow molding process



PET bottle blowing process.



The important factors that influence the blow molding process of PET bottles are preform, heating, pre-blowing, mould and production environment.



2.1 bottle preform



In the preparation of blow-molding bottles, PET slices are first injected into a bottle blank, which requires that the proportion of secondary recovery materials should not be too high (less than 5%), the recovery times should not exceed two times, and the molecular weight and viscosity should not be too low (molecular weight 31000-50000, characteristic viscosity 0.78-0.85cm3 / g). According to the state food safety law, secondary recycled materials shall not be used in food and pharmaceutical packaging. Injection molding of the bottle blank to store more than 24 hours before use. After heating, the unused bottle blank must be stored for more than 48h before it can be reheated and used. The storage time of the preform shall not exceed six months.



The merits and demerits of bottle blank largely depend on the merits and demerits of PET material. Materials that are easy to blow and shape should be selected, and reasonable bottle blank forming technology should be developed. Experiments show that the same viscosity of PET material molding bottle blank, imported raw materials than domestic materials are easier to blow molding; And the same batch of bottle blank, the production date is different, blow molding process may also have a big difference. The quality of the bottle blank determines the difficulty of the blow molding process. The requirements of the bottle blank are purity, transparency, no impurities, no color difference, the length of injection point and the appropriate surrounding halo.



2.2 heating



The heating of the flask is accomplished by heating the oven, and the temperature is set manually and adjusted automatically. The flask blank is irradiated and heated by far infrared ray from the far infrared lamp tube in the oven. The fan at the bottom of the oven circulates the heat to make the temperature in the oven uniform. The preform rotates as it moves forward in the oven so that the wall of the preform is heated evenly.



Of lamp tube decorate in oven from top to bottom general show "area" glyph, two ends are much, less in the middle. Oven heat is controlled by the number of lamp tube opening, the overall temperature setting, oven power and heating ratio of each section. The opening of the lamp tube shall be adjusted in combination with the pre-blowing bottle.



To make the oven play a better role, its height, cooling plate adjustment is very important, if the adjustment is not appropriate, blow molding is easy to appear bulging bottle mouth (bottle mouth become larger), hard neck (neck material can not open) and other defects.



2.3 preliminary blowing



Pre-blowing is a very important step in the two-step bottle blowing method. It refers to the process of pre-blowing when the stretching rod drops to make the bottle blank take shape. In this process, pre-blowing position, pre-blowing pressure and blowing air flow rate are three important technological factors.



The shape of the pre-blowing bottle determines the difficulty of the blowing process and the performance of the bottle. The normal shape of the pre-blowing bottle is spindle-shaped, while the abnormal shape is sub-bell-shaped and handle shaped. The reasons for the abnormal shape include improper local heating, preblowing pressure or insufficient air flow, etc., while the size of the preblowing bottle depends on the preblowing pressure and position. In production, the size and shape of all pre-blowing bottles of the whole equipment should be maintained consistent. If there is any difference, specific reasons should be found. Heating or pre-blowing process can be adjusted according to the situation of pre-blowing bottles.



The size of the pre-blowing pressure varies with the bottle specifications, equipment capacity, generally large capacity, pre-blowing pressure to be small; High production capacity of equipment, high pre - blowing pressure.



2.4 auxiliary machines and molds



Auxiliary machine mainly refers to the maintenance of constant temperature mold equipment. Mould constant temperature plays an important role in maintaining product stability. Generally, the temperature of the bottle body is high and that of the bottom is low. For cold bottle, due to its at the bottom of the cooling effect determines the degree of molecular orientation, to control the temperature 5-8 ℃ is preferred; The temperature at the bottom of the bottle is much higher.



2.5 environment



The quality of the production environment also has a greater impact on the process adjustment, constant temperature conditions can maintain the stability of the process and product stability. PET bottle blow molding at room temperature and low humidity is generally better.



3. Other requirements



Pressure bottle should meet the requirements of stress test and pressure test at the same time. Stress test is an internal quality control to prevent cracking and leakage of molecular chain in the process of contact between the bottom of PET bottle and lubricant (alkaline) during the filling of PET bottle. Pressure test is to prevent the bottle filled with a certain pressure gas burst after the quality control. 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 good, and the pressure resistance is poor. Thick center point, good pressure test, poor stress test. Of course, the stress test results also have a great deal to do with the material accumulation in the transition area around the central point, which should be adjusted according to practical experience.



4 conclusion



PET bottle blowing process adjustment, is for the corresponding material, if the material is not good, the process requirements are very strict, even difficult to blow out a qualified bottle.


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