The important factors that affect the blow molding process of PET bottle are flask, heating, preblowing, mould and environment.
Blow molding bottles, bottle preform preparation will first PET chip for bottle preform injection molding, it requires that the secondary recovery ratio cannot be too high (below 5%), recovery times no more than two times, and low molecular weight and viscosity can't (molecular weight 31000-50000, characteristic viscosity of 0.78-0.85 cm3 / g).
The injection moulded bottle billet should be stored for more than 48h before it can be used. After heating, the finished bottle must be stored for more than 48h before it can be reheated. The storage time of the billet should not exceed six months.
The advantages and disadvantages of the billet are largely determined by the advantages and disadvantages of the PET material. The materials should be easy to blow, easy to be formed, and a reasonable molding process of the bottle billet should be established. The experiment shows that the same viscosity of the PET material moulds, the imported raw materials are easier to blow molding than domestic materials; The same batch of billet, the production date is different, the blow molding process may also have the big difference.
The advantages and disadvantages of the flask are difficult to blow molding process, and the requirements of the blank are pure, transparent, no impurities, the same color, the length of the injection point and the surrounding halo.
The heating of the heating cylinder is completed by heating oven. The temperature is set manually and automatically adjusted. In the oven, the far-infrared light tube emits far infrared ray to heat the flask, and it is heated by the fan at the bottom of the oven, so that the temperature in the oven is even.
In the oven, the body of the flask is rotating and the wall is heated evenly. Tubes of cloth 臵 top-down generally is in the oven "zone" glyph, more than two head, less in the middle. The heat of the oven is controlled by the number of the lamp tube, the overall temperature setting, the power of the oven and the heating ratio of each section.
The opening of the lamp tube should be adjusted with the preblowing bottle. 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 (neck material pull not open), and other defects.
Preblowing is an important step in the two-step bottle blowing method. It refers to the beginning of the pre-blowing in the process of blowing and blowing, so as to make the shape of the billet. The process of blowing , blowing blowing pressure and flow rate are three important technological factors. The advantages and disadvantages of the shape of the pre-blowing bottle determine the advantages and disadvantages of the blow molding process and the performance of the bottle.
The normal pre-blow bottle shape is the spindle shape, and the abnormal ones have subbell shape and handle shape, 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 a beforehand.
In the production, the size and shape of all pre-blowing bottles should be maintained in the whole equipment. If there is any difference, we should look for specific reasons, and adjust the heating or pre-blowing process according to the pre-blowing bottles. The pre-blowing pressure varies with the bottle size and equipment capacity, and the general capacity is large and the pre-blowing pressure is small. High production capacity and high pre - blowing pressure. Even if the same equipment is used to produce a bottle of the same specification, due to the difference in the performance of the PET material, the required pre-blowing pressure is not the same.
Glass fiber reinforced PET materials, small preblowing pressure can make the large molecules at the bottom of the bottle correct 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. According to the orientation condition, the lamp tube can be removed from 2-3 to the top of the injection point at this time, and the injection point can be fully heated to provide sufficient heat to facilitate 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. 2.4 auxiliary machines and die auxiliaries mainly refer to equipment that maintains constant temperature of the mould. Mold temperature is important to maintain the stability of the product. General bottle body temperature is high, bottle bottom temperature 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 thermos is much higher. Mold is the important factors influencing the PET bottle blow molding process, mold shape quality will reduce or increase the difficulty of the process adjustment, such as reinforcement, arc transitional area and at the bottom of the cooling conditions and so on all have an impact on process adjustment.
The environmental production environment has a great influence on the process adjustment, and the constant condition can maintain the stability of the process and the stability of the product. PET bottle blowing molding is generally good at room temperature and low humidity. Other requirements for the cylinder shall meet the requirements of stress test and pressure test.
Stress test is the internal quality control of cracking, leakage and so on during the contact process of the bottle bottom and lubricant (alkaline) during the contact process of the PET bottle. The pressure test is the quality control which prevents the bottle from bursting after it is filled with certain pressure gas.
In order to meet these two needs, the center point thickness should be controlled within a certain range. Generally, the center point is thin, the stress test is good, and the pressure tolerance is poor. The center point is thick, the pressure test is good, the stress test is poor. Of course, the results of stress tests also have a lot to do with the build-up of materials around the central point of transition, which should be adjusted based on actual experience.