At present, most of the blow molding machine
s are still two-step blow molding machines, that is, the plastic raw materials must be made into preforms, and then blown. Nowadays, environmentally friendly plastics made of PET are commonly used. 1. Blowing principle The blowing process of the blowing machine is divided into two parts 1. Preheating irradiates the preform (embryo) through an infrared high-temperature lamp, and heats and softens the bad (embryo) body part of the preform (preform). In order to maintain the shape of the bottle mouth, the preform (preform) mouth does not need to be heated, so a certain cooling device is required to cool it. 2. Blow molding In this stage, the preheated preforms (preforms) are placed in the blow molds that have already been prepared, and high-pressure inflation is carried out inside them. Blow and draw the preform (preform) into the desired bottle. The automatic bottle blowing machine
completes the two operations of blowing the bottle together through the operation of the manipulator, eliminating the process of manually placing the preheated preform into the blow mold in the middle. Greatly accelerated the rate of production. 2. The process flow of the bottle blowing machine The blow molding process of the bottle blowing machine is a bidirectional stretching process. During this process, the PET chains are bidirectionally extended, oriented and arranged, thereby increasing the mechanical properties of the bottle wall and improving the stretching. , tensile, impact strength, and has good air tightness. Although stretching helps to improve the strength, it should not be stretched too much. It is necessary to control the stretch-inflation ratio: the radial direction should not exceed 3.5 to 4.2, and the axial direction should not exceed 2.8 to 3.1. The wall thickness of the preform should not exceed 4.5mm. Blowing is carried out between the glass transition temperature and the crystallization temperature, generally controlled between 90 and 120 degrees. In this range, PET exhibits a high elastic state, and it becomes a transparent bottle after rapid blow molding, cooling and setting. In the one-step method, this temperature is determined by the cooling time in the injection molding process (such as the Aoki blow molding machine), so the relationship between the injection and blowing stations should be well connected. In the blow molding process, there are: stretching—one blow—second blow. The three actions take a very short time, but they must be well coordinated, especially the first two steps determine the overall distribution of the material and the quality of the blowing. Therefore, it is necessary to adjust: the starting timing of stretching, the stretching speed, the starting and ending timing of pre-blowing, the pre-blowing pressure, the pre-blowing flow rate, etc. If possible, it is very good to control the overall temperature distribution of the preform, the bottle The temperature gradient of the inner and outer walls of the billet. In the process of rapid blow molding and cooling, induced stress is generated in the bottle wall. For carbonated beverage bottles, it can resist internal pressure, which is good, but for hot-fill bottles, it is necessary to ensure that it is fully released above the glass transition temperature.
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