In the injection molding production of disposable knives, forks, and spoons, setting appropriate process parameters is crucial for ensuring product molding quality. The injection molding process involves the coordinated control of multiple parameters, including temperature, pressure, speed, and time, requiring systematic optimization based on material properties, mold structure, and equipment performance. Taking common disposable knives, forks, and spoons as examples, their materials are mostly polypropylene (PP) or polystyrene (PS). These materials have good flowability and moderate molding shrinkage, but strict control of process parameters is necessary to avoid defects such as short runs, flash, and shrinkage marks.
Temperature control is the primary step in the injection molding process, directly affecting the plasticizing effect and flowability of the material. The barrel temperature needs to be set in stages according to the material characteristics, typically increasing gradually from the feed section to the nozzle section to ensure the plastic melts fully and does not degrade. For PP materials, the barrel temperature needs to be higher than its melting point but lower than its decomposition temperature to avoid oxidation or bubble formation due to excessive temperature. Mold temperature needs to be adjusted according to the product's appearance requirements. Higher mold temperatures can improve surface finish but may prolong cooling time; lower mold temperatures can speed up the molding cycle but are prone to internal stress or warping. In actual production, the optimal mold temperature range needs to be determined through trial molding to balance quality and efficiency.
Matching injection pressure and speed is crucial to avoiding molding defects. Injection pressure must overcome material flow resistance to ensure the melt fills the mold cavity, but excessive pressure may cause flash or mold damage. Injection speed needs to be adjusted according to the product structure; thin-walled sections require high-speed injection to prevent melt solidification, while thick-walled sections require appropriate speed reduction to reduce internal stress. The application of multi-stage injection technology can further improve molding quality, for example, by reducing the speed when the melt approaches the end of the mold cavity to avoid air entrapment or scorching. Furthermore, the holding pressure and time settings must be coordinated with injection parameters to ensure product dimensional stability and a surface free of shrinkage marks.
Optimizing the cooling system is essential for improving production efficiency and product quality. Insufficient cooling time can lead to product deformation after demolding, while excessive cooling prolongs the molding cycle and increases energy consumption. Mold design requires a well-planned cooling water system to ensure uniform temperature in the cavity and core, preventing stress concentration caused by localized overheating. For thin-walled products like disposable knives, forks, and spoons, conformal cooling water systems or molds made of high thermal conductivity materials can be used to shorten cooling time and improve dimensional accuracy. Furthermore, the draft angle and ejection system design must be matched with cooling parameters to prevent product breakage due to sticking or uneven ejection force.
The control of back pressure and screw speed directly affects the plasticizing quality of the material. Excessive back pressure increases melt temperature and shear stress, leading to material degradation or increased energy consumption; insufficient back pressure may cause uneven plasticizing or bubble defects. Screw speed needs to be adjusted according to material flowability to ensure that plasticizing time matches the injection cycle, preventing overheating due to excessive screw dwell time. For materials containing additives or recycled materials, back pressure should be appropriately increased to enhance mixing, but only to the extent that black spots or silver streaks are not produced.
The design of the venting system is an effective means to solve the problems of scorching and porosity. If air within the mold cavity is not expelled in time, it will be compressed by the melt, generating high temperatures and causing material decomposition or surface defects. The location and size of the venting groove need to be optimized according to the product structure, and are usually placed in the last melt filling area or at the parting line. For products with simple structures such as disposable knives, forks, and spoons, the venting effect can be improved by adjusting the injection speed or increasing the depth of the venting groove, but it is necessary to avoid excessively large venting grooves that may cause flash.
Optimization of process parameters requires continuous improvement through trial molding and data analysis. During the initial trial molding, the recommended parameters provided by the material supplier can be used as a reference, combined with equipment performance and mold structure for preliminary settings. By observing the product appearance, measuring dimensions, and performing weighing analysis, key parameters such as temperature, pressure, and speed can be gradually adjusted until the product meets quality standards. During production, the equipment status and material properties need to be checked regularly to avoid parameter deviations due to equipment wear or material fluctuations. In addition, establishing a process parameter database and standardized operating procedures can improve production stability and product consistency.
