Posted 16 Jan 2011 00:00
Polyethylene terephthalate (PET) blow molding bottles Production molded parison can be divided into pre-injection stretch blow (referred to as injection stretch blow), and extrusion stretch blow molding (referred to as extrusion stretch blow) . In both molding methods, injection stretch blowing process as easy to control, high efficiency, waste less and is more common defects.
PET bottle blow molding can be divided into two categories, one is a pressure bottle, such as filling carbonated beverage bottles; the other for non-pressure bottles, such as filling water, tea, oil bottles. Tea beverage bottles are mixed poly ethylene naphthalate (PEN) modified PET bottles or PET thermoplastic polyarylate with composite bottles, the classification is a hot bottle, can heat above 80 ; water bottle is an cold bottles, no requirements on the heat resistance. In the molding process on the hot and cold bottle like bottles. The author discusses a pressure bottle of cold drink bottle forming process.
As technology advances and production scale, PET blow molding machine increasing degree of automation, increasing production efficiency. Increasing production capacity of equipment, from the former production of thousands of bottles per hour developed to produce tens of thousands of bottles per hour. Manual operation is also push-button from the past into the present development of computer-controlled, greatly reducing the difficulty of process operation, an increase of the stability of process.
Currently, injection stretch blow equipment manufacturers are SIDEL France, Germany's KRONES companies. Although different manufacturers, but the principle is similar devices, which typically includes for the blank system, heating system, blowing systems, control systems and auxiliary equipment of five parts.
2 blow molding
PET bottle blow molding process.
PET bottle blow molding process of the important factors preform, heating, pre-blowing, mold, and the environment.
When preparing bottle blow molding, first slice PET preform injection molding is that it requires the second ratio can not be too much recycling material (5%), recovery times can not be more than twice, but not low molecular weight and viscosity (molecular weight 31000 -50 000, intrinsic viscosity 0.78-0.85cm3 / g). Injection molding of the preform should be stored in order to use more than 48h. Did not run out of the preform after heating must be kept more than 48h before being re-heating use. Preform of the storage time should not exceed six months.
PET preform material depends largely on the merits of the advantages and disadvantages, should choose easy to huff the material easy to shape and develop a reasonable preform molding process. Experiments show that the same viscosity of the PET preform molding materials, imports of raw materials than the easily-made blow molding; the same batch of preforms, production of different dates, blow molding process there may be quite different. Preform blow molding process determines the merits of the difficulty, the requirements of the preform is pure, transparent, without impurities, the same color halo around the injection point and the length of the right spot.
Preform heating by the heating oven to complete, the temperature set by the manual, automatic adjustment. Oven issued by the far-infrared lamp infrared radiation heating of the preform from the bottom of the fan oven to heat cycle, so the oven temperature uniformity. Preform in the oven at the same time moves forward rotation, the preform wall heat evenly.
Oven lamp arranged in the top-down general was "District" shape, more than two, the middle less. Open the oven heat by the number of lamps, the overall temperature setting, heat the oven section of the power and the ratio of common control. Lamp in conjunction with the opening of pre-blowing to be adjusted.
To play a better role oven, its height, the adjustment of the cooling panels is very important, if adjusted properly, prone to expansion when the bottle blow molding (larger bottle), a hard head and neck (cervical material will not pull out), etc. defects.
Pre-blowing is a two-step method of blowing a very important step, it refers to the stretch blow molding process of drop rod and began pre-blowing, so that preforms begun to take shape. The position of pre-blowing processes, pre-blowing pressure and blowing process flows are three important factors.
Pre-determine the merits of blowing shape the ease and blow molding bottle perform. Normal spindle shape of the pre-blowing, there are sub unusual bell-shaped, handle-like and so on, as shown in Figure 2. Abnormal shape caused due to a local heating improper flow of pre-blow pressure or insufficient blowing, but depends on the size of pre-blowing pre-blow pressure and pre-blow position. In the production of the entire piece of equipment to maintain all pre-blowing the same size and shape, will have to find the specific reasons for any difference can be adjusted in accordance with pre-heating or pre-blowing blowing process.
The size of pre-blow pressure with the bottle size, equipment capacity varies, the general capacity, pre-blow pressure to be small; equipment, high capacity, high-pressure pre-blow.
Even with the same equipment the same specifications of the bottle, the PET material performance difference, the required pre-blow pressure are not the same. Glass fiber reinforced PET material, the smaller the pre-blow pressure can make the correct orientation of macromolecules at the bottom of the bottle; other materials are inappropriate or improper preform molding process, injection near a large number of stress concentration easily dissipated, if blow, often blowing at the injection point break or stress test burst from the injection point, leakage. According orientation conditions, then you can put the lamp out as shown to the injection point 2-3 to open over support given fully heated injection point to provide enough heat to promote its rapid approach.
Secondary use for the heated preform or preforms of excessive storage time, when the temperature of the arithmetic effect of the two molding process similar to the normal preform compared to the heat required is less, may be appropriate to pre-blow pressure reduced.
2.4 Auxiliary and die
Mainly referring to maintain the mold temperature auxiliary equipment. Mold temperature to maintain the stability of the product plays an important role. General bottle temperatures are high, bottom low temperature. On the cold bottle, because the bottom of the cooling effect determines the degree of molecular orientation, temperature control will be better in 5-8 ; and heat the bottom of the bottle will have a much higher temperature.
PET bottle blow mold technology is the impact of important factors, pros and cons of the shape of the mold will reduce or increase the difficulty of the adjustment process, such as ribs, curvature of the transition zone and the bottom of the cooling conditions affect the adjustment process and so on.
The quality of the production environment to adjust to the process also affected, the condition can be maintained constant process stability and product stability. PET bottle blow molding is generally room temperature, low humidity conditions better.
3 Other requirements
Pressure bottle should also meet the stress test and pressure test requirements. Stress test is to prevent the beverage bottle PET bottle filling and lubricant (base) contact process in the degradation of the molecular chain of cracking and leakage etc. internal quality control; pressure test is sufficient to prevent the bottle After a certain generation into a burst of gas pressure for quality control. To meet these two needs, to control the thickness of the center within a certain range, in general, is the center of a thin, stress testing is better, less pressure; center thickness, pressure test is better, less stress test. Of course, the stress test results but also with the transition zone surrounding the center has a lot to the accumulation of material, which should be adjusted based on actual experience.
PET bottle blow molding process adjustment is carried out for the appropriate materials if the material is poor, the requirements on the process is very demanding, even difficult to blow out the qualified bottle.