In the production of vinyl jewelry, particularly the naughty milk dragon ornament, controlling the shrinkage rate of vinyl is crucial for ensuring dimensional accuracy, appearance quality, and structural stability. As a thermoplastic, vinyl shrinks during cooling after being molten and injected into a mold. This shrinkage directly affects the final product's dimensions and its alignment with design requirements. Therefore, a comprehensive approach involving material selection, process optimization, mold design, and production control is necessary to accurately control the shrinkage rate.
Material selection is fundamental to controlling the shrinkage rate. Different types of vinyl resins exhibit significant differences in shrinkage rates due to variations in their molecular structure. For example, crystalline vinyl resins typically have a higher shrinkage rate than amorphous resins and are more susceptible to molding process variations. During production, priority should be given to specialized vinyl resins with stable shrinkage rates and moderate fluidity. Inorganic fillers such as talc and calcium carbonate can be added to disperse the resin molecules, disrupting their regular arrangement and reducing crystallinity, thus minimizing shrinkage. The particle size of the filler is just as important as surface treatment. Fine-grained fillers disperse more evenly in the resin, while surface-treated fillers have stronger interfacial bonding with the resin, further improving the accuracy of shrinkage control.
Optimizing process parameters is key to adjusting the shrinkage ratio. During injection molding, parameters such as injection pressure, injection time, and injection temperature directly affect the flow and filling state of molten vinyl resin in the mold cavity. Higher injection pressure promotes full filling of the mold by the melt, reducing local shrinkage differences caused by insufficient filling; appropriate injection time ensures that the melt is filled before cooling, avoiding uneven shrinkage caused by a drop in melt temperature and reduced fluidity due to excessive time; injection temperature needs to be set according to the melting characteristics of the vinyl resin. Too high a temperature may cause melt decomposition, while too low a temperature will affect the filling effect, thus affecting the shrinkage ratio. Furthermore, controlling the cooling stage is also crucial. By adjusting the mold temperature and cooling time, the vinyl resin can be guided to crystallize orderly, reducing internal stress and thus stabilizing the shrinkage ratio.
The rationality of mold design plays a decisive role in controlling the shrinkage ratio. The design of the mold cavity dimensions must fully consider the shrinkage rate of vinyl ester resin, typically allowing for a certain shrinkage margin beyond the design dimensions. Simultaneously, the mold's runner system, venting channels, and other structures must be optimized to ensure smooth melt flow during filling and avoid shrinkage differences caused by uneven flow resistance. For example, the runner size should match the melt flow rate to prevent a drop in melt temperature and reduced fluidity due to excessively narrow runners; venting channels should be located at the end of melt filling to expel air from the cavity, preventing air bubbles from forming and affecting shrinkage uniformity.
Real-time monitoring and adjustment during production are crucial for ensuring a stable shrinkage ratio. Real-time monitoring of key parameters during injection molding, such as injection pressure, melt temperature, and mold temperature, combined with product dimension data, allows for the timely detection of abnormal fluctuations in the shrinkage ratio. Once a deviation is detected, process parameters or mold conditions must be adjusted immediately, such as adjusting injection pressure, optimizing cooling time, and cleaning the mold cavity, to quickly restore the stability of the shrinkage ratio. Furthermore, regular maintenance of production equipment to ensure equipment accuracy and operational stability is also an important measure to guarantee effective shrinkage ratio control. Post-processing also significantly impacts the final stability of the shrinkage ratio. After demolding, vinyl ornaments, such as the naughty milk dragon ornament, may experience dimensional changes due to internal stress or post-shrinkage. Therefore, appropriate post-processing, such as annealing, is necessary. Annealing, by heating the product to a specific temperature and holding it for a period of time, eliminates internal stress, reduces post-shrinkage, and thus stabilizes the product's dimensions. The annealing temperature and time must be determined based on the characteristics of the vinyl resin and the product thickness to ensure effective processing while preventing product deformation.
