How does the injection molding process shape the preform of Square PETG Drooper Bottle with Flat Shoulder?

In the production chain of square PETG drooper bottle with flat shoulder, preform making is an extremely critical starting link, and the injection molding process, as the core technology for shaping the preform, lays the foundation for subsequent molding with its unique processing method. To explore how the square PETG flat shoulder dropper bottle preform is made through the injection molding process, it is necessary to have a deep understanding of the details and key points of the injection molding process.
The PETG material used to make the preform is specially treated. Before being put into the injection molding machine, the PETG plastic particles need to be dried. PETG plastic itself has a certain degree of water absorption. If there is too much water in the plastic particles, during the injection molding process, the high temperature will vaporize the water, resulting in defects such as bubbles and cavities inside the preform, which seriously affects the quality of the preform. Through the drying process, the moisture in the PETG plastic particles is removed to ensure that it can be evenly heated and smoothly molded during the injection molding process.
The injection molding process starts with adding dried PETG plastic particles into the injection molding machine. The injection molding machine is equipped with a heating device inside. As the plastic particles are continuously pushed in the barrel of the injection molding machine, the temperature gradually rises. Under the action of high temperature, the originally solid PETG plastic particles gradually soften and melt, turning into a viscous liquid state with good fluidity. In this state, the PETG plastic can smoothly fill the mold cavity under the pressure.
When the PETG plastic reaches a suitable molten state, the screw of the injection molding machine moves forward driven by the hydraulic system, generating strong pressure. Under the action of this pressure, the molten PETG plastic is quickly injected into a specific mold cavity. The shape of the mold cavity determines the shape of the bottle blank. For the square PETG flat-shoulder dropper bottle, the mold cavity is designed to be a square that matches the shape of the bottle blank, and the shape structure of the bottle mouth, bottle shoulder and other parts is also reserved.
The mold plays an important role in the entire injection molding process. It not only gives the bottle blank a specific shape, but also affects the dimensional accuracy and surface quality of the bottle blank. The mold usually consists of a fixed mold and a movable mold. Before injection molding, the movable mold and the fixed mold will be accurately closed to form a complete cavity. The mold surface is finely processed and has a very high finish to ensure that the surface of the preform is smooth and flat after molding. At the same time, the temperature of the mold also needs to be strictly controlled. The appropriate mold temperature helps the PETG plastic to cool and shape quickly to avoid deformation, shrinkage and other problems.
The parameter control of the injection molding machine has a decisive influence on the quality of the preform. In terms of temperature, the barrel temperature needs to be set according to the characteristics of the PETG plastic. If the temperature is too low, the plastic cannot be fully melted and has poor fluidity, which may lead to insufficient mold filling, and defects such as lack of material and short shot in the preform; if the temperature is too high, the plastic will degrade, the color will turn yellow, and the mechanical properties will decrease, affecting the strength and toughness of the preform. Pressure is also one of the key parameters. If the injection pressure is insufficient, the plastic cannot completely fill the mold cavity, and the preform size does not meet the requirements; if the injection pressure is too high, the preform will have flash, increase the difficulty of subsequent processing, and may also cause damage to the mold.
The injection speed should not be ignored either. A faster injection speed can quickly fill the mold cavity with molten plastic, reduce the cooling of the plastic during the flow process, and help obtain a bottle blank with a clear outline and smooth surface. However, if the speed is too fast, the plastic will easily generate turbulence when flowing in the mold, entraining air, resulting in bubbles inside the bottle blank. Although a slower injection speed can reduce the generation of bubbles, it may cause the plastic to cool prematurely in the mold, resulting in insufficient filling.
After the molten PETG plastic is injected into the mold cavity, it needs to go through a cooling stage. The cooling system of the injection molding machine cools the mold by circulating cooling water, so that the PETG plastic in the mold quickly cools and solidifies. The cooling time and cooling speed must be controlled during the cooling process. If the cooling time is too short, the bottle blank will be demolded before it is fully formed, and it is easy to deform; if the cooling time is too long, it will reduce production efficiency. Uneven cooling speed will cause internal stress inside the bottle blank, and the bottle blank may crack during subsequent processing or use.
After cooling, the dynamic mold and fixed mold of the injection molding machine are opened, and the formed preform is pushed out of the mold through the ejection device. At this point, a complete square PETG flat shoulder dropper bottle preform is completed. But this does not mean that the preform production process is over. The produced preforms still need to undergo strict quality inspection. The inspectors will check whether the size of the preform meets the design requirements, including the length, width, thickness of the bottle body, the inner diameter and outer diameter of the bottle mouth, etc.; they will also check whether there are defects on the surface of the preform, such as bubbles, scratches, dents, etc.; at the same time, the physical properties of the preform, such as strength and toughness, will also be tested. Only the preforms that pass various quality inspections can enter the next production process for the production of square PETG flat shoulder dropper bottles.
From the drying of PETG plastic particles, to the melting, injection, cooling in the injection molding machine, and to the final quality inspection, each link is closely connected, and together constitutes the injection molding process of the square PETG flat shoulder dropper bottle preform. It is the strict control and precise operation of these links that enable high-quality preforms to be formed, providing a solid guarantee for the subsequent production of square PETG flat-shoulder dropper bottles with excellent performance.