Through gas-assisted injection molding,products with uneven wall-thickness can be produced.The products produced by gas-assisted injection molding not only can avoid the surface shrink mark, warp and distortion and consume very small amount of materials,but also are easy to be controlled.thus the outer surface of the products are very smooth and no air bubble.It is a technology which use the high-pressure gas injected into core part of the plastic thermoplastic melt to form a hollow section and further help pushing thermoplastic melt flow,thus achieving injection,dwell and cooling.
Gas-Assisted Injection Molding Process
*Gas-Assisted Injection Molding–Thermoplastic Injection Molding.
The thermoplastic melt is quantiatively injected into the mould cavity which is very similar with traditional injection molding.But usually the gas-assisted injection volume takes up only 55%~80% of the mold cavity volume.Sure the specific injection volume varies with different molding productsto ensure that the surface of thermoplastic melt will not be blown through upon the injection of high-pressure gas and acquiring and ideal aeration volume.
*Gas Injection Molding–Gas Injection
Inject high-pressure gas such as nitrgen into the core of thermoplastic melt and the gas surround by plastic thermoplastic melt shall move forward along a direction with minimum resistance and meanwhile push the flowing front of thermoplastic melt to move further forward until the mold cavity is fully filled.At this stage, pressure of the gas must be larger than that of the plastic melt so that a hollow section can be formed in the product.This stage plays a very significant role in the whole production process in which it directly influences the final quality of a product.Many defects during the gas-assisted injection molding such as air cavitation, blowing through, underfeeding injection as well as the infiltration of gas into parts with thin walls are produced during this stage.
*Gas Injecton Molding–Gas Dwell
Afer the completion of filling in the mold cavity and gas pressure is preserved, the product should be put aside until it gradually cools to compensate shrinkage of the product due to the cooling of materials.At this stage, the gas applies uniform pressure on the plastics from inside to outside so that outer surface of the product always clings to the inner wall of mold cavity, thus left no depression on the outer surface of parts with thick walls and improving quality of the product.
*Gas Injection Molding–Discharge of gas
When the product is cooled until it takes on certain level of rigidity and intensity, pressure of the gas shall be discharged and recyceled, finally open the cavity and eject the product.