PET bottle blow molding can be divided into two categories, one is pressurized bottles, such as filling carbonated beverage bottles; the other for non-pressure bottle, such as filling water, tea, oil bottle. Tea beverage bottles is blended with polyethylene terephthalate and polyethylene naphthalate (PEN) modified PET or PET bottle with a thermoplastic polyarylate composite bottle, a bottle in the classification is hot, it can heat above 80 ℃; Aquarius is the case cold bottle, heat resistance no. In the molding process similar to hot and cold bottles of bottles. The author focuses on cold pressurized bottle beverage bottle molding process.
1, the device
As technology advances and scale of production, PET bottle blowing machine increasingly high degree of automation, production efficiency is higher and higher. Equipment production capacity continues to increase, by a former hourly thousands of bottles developed to produce tens of thousands of bottles per hour. Operation is also now computer-controlled manual button from the previous development, which greatly reduces the difficulty of the process operation, increasing the stability of the process.
Currently, injection stretch blow equipment manufacturers are mainly French company SIDEL, KRONES German companies. Although the manufacturer is different, but the principle is similar device, generally including for billet system, heating system, blowing system, control system and auxiliary equipment of five parts.
2, the blow molding process
PET bottle blow molding process. Important factors affecting PET bottle blow molding preforms are heated, pre-blowing, mold and environment.
Preparing blow molded bottles, PET chips first injection molded preform, which requires regrind ratio is not too high (5%), no more than twice the number of recovered, but not too low molecular weight and viscosity (molecular weight 31000- 50,000, intrinsic viscosity 0.78-0.85cm3 / g). Injection molded preform should be stored for more than 48h before using. After heating the unused preforms must then be stored for more than 48h before being reheated to use. Preform storage time should not exceed six months.
Preform depends largely on the merits of the merits of PET materials should be selected easy to blow up, easy stereotypes of material, and develop a reasonable preform molding process. Experimental results show that the viscosity of the same material molding PET preforms, imported raw materials easily than domestic blow molding; and the same batch of preforms, different production date, the blow molding process may also be quite different. Preform the merits of the decision to ease the blow molding process, the requirements of the preform is pure, transparent, free of impurities, the same color, the length of the injection point and the surrounding halos appropriate.
Preform is heated by the heating oven to complete, the temperature is set manually, automatically adjusted. Oven emit far infrared radiation preform is heated by the far infrared lamps, fans from the bottom of the oven for heat circulation, so the oven temperature uniformity. Preforms in the oven at the same time moves forward rotation, so that the wall preform is heated evenly.
Lamps arranged in an oven from top to bottom in general was "zone" shape, more than two and less in the middle. Heat the oven by the number of lamps turned on, the overall temperature setting, and each section was heated oven power than joint control. Turn the lamp in conjunction with the pre-blowing adjustment. To play a better role oven, adjust its height, the cooling plate or the like is very important, if adjusted properly, prone to swelling during blow bottle (bottle becomes large), a hard head and neck (neck material will not pull out), etc. defect.
Pre-blowing is blowing two-step method is a very important step, it refers to the blow molding process in the stretch rod while the decline began pre-blowing, so that the preform in its shape. This process pre-blowing position, pre-blowing pressure and gas flow rate are three important technological factors.
Pre-blowing shape determines the merits of the ease and performance of the bottle blow molding technology advantages and disadvantages. Pre-blowing normal spindle shape, unusual, there are sub-bell-like, handle-shaped and so on, as shown in FIG. Causes abnormal local heating shapes are inappropriate, inadequate pre-blowing pressure or gas flow rate, etc., and the size of the pre-blowing depends on the pre-blow pressure and pre-blowing position. In order to maintain the production of the entire equipment of all the pre-blowing uniform size and shape, if the difference will have to look for specific reasons, can adjust the heating or pre-blow process according to the pre-blowing situation.
Pressure pre-blow with the size of bottle size, equipment capacity varies, generally large-capacity, pre-blowing pressure to be small; equipment production capacity, pre-blow pressure is high.
Even using the same equipment in the same size bottles, PET due to differences in material properties, the required pre-blow pressure are not the same. Glass fiber reinforced PET material, the smaller pre-blowing pressure can make the bottom of the bottle macromolecules correct orientation; improper or inappropriate preform molding process other materials, there is a lot of stress near the injection point of focus is not easy to subside, if blow, blow often broken or burst from the injection point in the stress test, the leakage in the injection point. According to the alignment condition, then it can out of the tube as shown in the 2-3 branch to open over the injection point, at the point of injection to give sufficient heat to provide enough heat to facilitate their rapid orientation.
For secondary use of the heated preform or preform excessive storage time, since the temperature arithmetic effect, similar to the two molding process, compared with the normal preforms, which requires fewer calories, pre-blow pressure may be appropriate reduce.
2.4 Auxiliary and mold
Auxiliary mainly refers to the maintenance of mold temperature equipment. Mold temperature to maintain the stability of the product plays an important role. Usually bottle high temperature, low temperature bottom. Cold bottle, because of the cooling effect of the bottom determines the degree of molecular orientation, temperature controlled at 5-8 ℃ is better; and temperature of the hot bottom of the bottle will have to be much higher.
The difficulty of the important factors affecting the PET bottle mold blow molding process, the mold shape of the pros and cons will reduce or increase the adjustment process, such as ribs, thermal conditions and the curvature of the bottom of the transition zone of the process of adjustment so influential.
The quality of the production environment has a greater impact on the process of adjustment, constant conditions can maintain the stability of the process and product stability. PET bottle blow molding generally carried out at room temperature, preferably low humidity state.
3 Other requirements
Pressure bottles should also meet the stress test and the pressure test requirements. Stress testing is to prevent the degradation of the molecular chains during PET bottle filling beverage bottle with a lubricant (basic) during contact and cracking, leakage and other internal quality control; the pressure test is to prevent the bottle charge quality have burst after a certain pressure gas be controlled. In order to meet these two needs, the center of the thickness to be controlled within a certain range, in general, is the central point of thin, good stress test, pressure is poor; thick center, pressure test better, less stress test. Of course, the results of stress tests and also the center of the area surrounding the transition bulk material has a great relationship, which should be adjusted based on actual experience.
heat resistance no. In the molding process similar to hot and cold bottles of bottles. The author focuses on cold pressurized bottle beverage bottle molding process.