Injection molding cold glue residue and solution
Cold glue residue is a common defect in injection molding. It occurs when the melt solidifies in the runner, gate, or cavity due to excessive cooling during the injection molding process, forming residual cold glue. This not only affects the appearance quality of the plastic part but can also cause problems such as blockage and material shortages. In severe cases, it can even damage the mold or injection molding machine. The causes of cold glue residue are complex and are primarily related to factors such as barrel temperature, injection speed, mold temperature, and runner design. For example, when the barrel temperature is set too low, the melt is incompletely plasticized in the barrel, resulting in poor fluidity. After entering the runner, it is easily solidified due to cooling. On the other hand, when the injection speed is too slow, the melt stays in the runner for too long, which can also lead to cold glue residue.
To address the issue of cold glue residue during injection molding, the first step is to adjust the process parameters. Proper barrel temperature setting is crucial. Operators should appropriately increase the barrel and nozzle temperatures based on the characteristics of the raw material to ensure good melt flowability. For example, for PP raw materials, the barrel temperature can be increased by 5-10°C to maintain the melt index within the appropriate range. Simultaneously, the injection speed should be adjusted, appropriately increasing the initial injection speed to shorten the melt’s residence time in the runner and reduce the chance of cooling. Furthermore, the holding pressure parameters should be optimized, reducing the holding pressure and shortening the holding time to prevent the melt from solidifying in the runner due to excessive cooling during the holding phase. When adjusting process parameters, perform multiple test shots to observe changes in the cold glue residue and gradually optimize the parameter settings.
Mold improvement and optimization also play a significant role in resolving the problem of cold glue residue. The design of the runners and gates directly affects the flow and cooling rate of the melt. For molds prone to cold glue residue, the runner diameter and gate size can be appropriately enlarged to reduce the flow resistance of the melt and accelerate the filling rate of the melt. At the same time, the layout of the runners should be optimized to avoid runners that are too long or have excessive bends, thereby reducing the residence time of the melt in the runners. Furthermore, the design of the mold’s cooling system should be strengthened, with cooling water channels installed near the runners and gates to control the cooling rate of the melt within the runners and prevent cold glue residue. For molds for small plastic parts, a hot runner system can be used to maintain the melt in a molten state by heating the runners, fundamentally avoiding the generation of cold glue residue.
Raw material processing and selection can also affect the occurrence of cold glue residue. Highly hygroscopic raw materials require thorough drying to reduce their moisture content. This prevents the rapid drop in melt temperature caused by evaporation, which can lead to cold glue residue. Raw material purity must be ensured to avoid impurities, as these can affect melt fluidity and cause cold glue residue. Raw materials with a high melt index and good fluidity should be prioritized. For materials with poor fluidity, plasticizers or lubricants can be added to improve processing properties. Furthermore, the raw material storage environment must be controlled to prevent moisture and agglomeration, which can affect plasticization and lead to cold glue residue.
Equipment maintenance and servicing are also crucial measures to address the issue of cold glue residue. Wear on the injection molding machine’s screw and barrel can lead to uneven melt plasticization, increasing the risk of cold glue residue. Therefore, regular inspections of screw and barrel wear are essential, and severely worn components should be promptly replaced. Furthermore, the nozzle and runner should be cleaned to remove any residual cold glue and impurities to ensure smooth melt flow. For hot runner systems, regular checks should be made to ensure that the heating elements and temperature sensors are functioning properly, ensuring that the runner temperature remains within the set range to avoid cold glue residue caused by temperature fluctuations. Furthermore, the hydraulic and electrical systems of the injection molding machine should be inspected to ensure stable operation and to avoid cold glue residue caused by pressure or speed fluctuations that can hinder melt flow. By strengthening equipment maintenance and servicing, the occurrence of cold glue residue can be effectively reduced, improving the stability of injection molding production and enhancing product quality.
