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Process knowledge PET plastic bottle of bottle blowing process
Poly (terephthalic acid ethyl ester ( PET) Blow molding bottle production according to the parison preform can be divided into different injection stretch blow molding ( Short note blow) And the extrusion stretch blow molding ( Crowded blowing) 。 In the two forming methods, the injection blowing process is easy to control, high production efficiency, less waste defective goods and more general. PET blow molding bottles can be divided into two kinds, one kind is with pressure bottle, such as filling carbonated drinks bottles; Another kind of pressureless bottles, such as filling oil, tea, water bottles. Tea beverage bottle is mixing polyethylene naphthalate formic acid ethyl ester ( PEN) Modified PET bottles or the PET composite bottle with thermoplastic aromatic esters, belong to hot bottles on classification, can be more than 80 ℃ heat; Bottle water bottles are cold, with no heat resistance requirements. In the hot and cold cylinders similar molding process. The author mainly discussed the cold bottle beverage bottle pressure molding process. 1 equipment along with the advance of science and technology and the production scale, PET bottle blowing machine is more and more high degree of automation, production efficiency is becoming more and more high. Continuously improve equipment production ability, by the former thousands of bottles per hour production development to the present production of tens of thousands of bottles per hour. Operate by manual push button in the past to now also full computer control, greatly reduced the difficulty of the process operation, increase the stability of the process. Currently, the main note pull blowing equipment manufacturers have French SIDEL company, Germany KRONES our company etc. Although the manufacturer is different, but the similar equipment principles, generally include for slab system, heating system, bottle blowing system, control system and auxiliary five most. 2 blow molding process affect the PET bottle blow molding process are the important factors that bottle preform, heating, blowing, mould and environment, etc. 2. 1 bottle preform preparation blow molding bottle, the first will be PET chip for bottle preform injection molding, it requires that the secondary recycling material ratio cannot be too high ( Less than 5%) Number cannot exceed twice, and recycling and low molecular weight and viscosity can't ( The molecular weight of 31000 - 50000, characteristic viscosity of 0. 78 - 0. 85立方厘米/ g) 。 Injection molding of bottle preform need to store more than 48 h before use. After heating unused bottle preform, must be reheated to store more than 48 h can use again. A bottle of billet storage time can't more than six months. Bottle preform quality depends largely on the merits of the PET material, should choose the material easy to blow, easy to finalize the design, and formulate reasonable bottle preform molding process. Experimental results show that the same viscosity of PET bottle preform materials forming, imported raw materials than domestic material for blow molding; And the same batch of bottles billet, production date, blow molding technology may also have bigger difference. Bottle preform quality decides the difficulty of blow molding process, the requirement to the bottle preform is pure and transparent, without impurities, no color, length and halo around the spot right on point. 2. 2 bottles of billet heating by a heating oven heating, the temperature by artificial setting, automatic adjustment. In the oven by the far infrared lamp emit far infrared ray to preform radiation heating, thermal cycle by fan at the bottom of the oven, make the evenness of temperature in the oven. Bottle preform forward movement and rotation in the oven, make the bottle preform wall heated evenly. Tubes in the oven to the layout of the top-down show 'area' glyph, commonly more than two head, less in the middle. Oven heat from the tubes open quantity, the overall temperature setting, oven heating power and paragraphs than common control. Lamp of open to combine beforehand to adjust the bottle blowing. To make the oven to work better, its height, the adjustment of the cooling plate and so on is very important, if improper adjustment, easy to appear when blowing bulge bottle ( Bottle) Hard, head and neck ( The neck is expected to pull doesn't open) Wait for blemish. 2. Step 3 advance forecast wind is blowing bottle of an important step in the method, it refers to the blow molding process at the beginning of the tensile rod falling while blowing, make the bottle preform begun to take shape. Position of the process of blowing, blowing blowing pressure and flow rate are three important technological factors. Advantages and disadvantages in the process of the bottle shape determines the quality of difficulty and the performance of the bottle blow molding process. Normal bottle shape for spindle, of anomaly is fluid, handle, etc. , as shown in figure 2. The causes of abnormal shape are local heating is undeserved, blowing blowing pressure or flow is insufficient, etc, in particular the size of the bottle blowing depends on wind pressure and blow position. To maintain the equipment in the production of all bottle size and shape is consistent, if there are differences to find the specific reason, can be adjusted according to the pre bottle blowing conditions heating or blowing process. Preliminary blowing pressure varies with the size of the bottle and varies specifications, equipment capability, general and large capacity, smaller pre blowing pressure; Equipment production capacity, high pressure is high. Even with the same equipment production the same specifications of the bottle, because of the difference of PET material performance, it needs blowing pressure are also different. Glass fiber enhanced PET materials, smaller pressure can make the bottle at the bottom of the macromolecular orientation; Other materials, improper or not appropriate bottle preform molding process, note there are a lot of stress concentration near not easy fade, if blow molding, often in broken note points or in stress tests from the injection point blowout, leakage. Conditions according to the orientation, at this time to remove 2 - such as shown in the tubes 3 to note above open, heating to make note points, provide enough quantity of heat, to promote its rapid orientation. For heating have secondary use bottle preform or storage time exceeds the bottle preform, arithmetic effect due to the temperature, the molding process which is similar, compared with the normal bottle preform, the requirement of less heat, pressure can also be reduced.