Equipment used for gas-assisted injection molding generally comprises a common injection machine and a gas injection device. A gas injection device contains such three components as a gas injection system, an air nozzle and a special gas pressure control system. The gas usually used is nitrogen and the pressure and purity of gas pressure are determined by the molding materials and the shape of products. Wherein the pressure is generally at 5—32 MPa, with a maximum level of 40 MPa.

as for strictly controlling the temperature of the mold during gas-assisted injection molding cycle, that is because the cooling of fusant in cavity can be kept at an appropriate speed, which shall be of avail for the forming of gas cavity.

as for controlling the pressure for gas injection , it shall be first high then low, wherein at the beginning of injection, higher pressure should be preserved so that the fusant can be forced to fill in the mold cavity and form hollow gas cavity. And upon the completion of this action, the pressure of filling gas, as dwell pressure, should be lowered to avoid overflow and internal stress.

as for controlling the time for gas injection, I have more details, premature injection, when the outer layer of fusant has not fully cooled, shall result in the breaking of gas through the front of fusant, whereas late injection, when fusant has cooled and solidified, shall prevent the forming of gas cavity.

the technical control of gas-assisted injection molding has it’s own strict requirement, 1) the time and pressure for gas injection should be strictly controlled. 2) temperature of the mold should be strictly controlled.

hey! Guy, I do know you are right, but please don’t forget gas-assisted injection molding can result in different gloss on product surfaces with and without gas injected, the defect shall need to be decked or covered with patterns.

the merit of the Gas-assisted injection molding—saving plastic materials, since gas in the cavity occupies part of the volume, the product shall become thinner and lighter, generally by 20%--40%.

the merit of the Gas-assisted injection molding--short production cycle. Owing to the small injection volume of gas-assisted injection molding, the injection duration is shortened, and meanwhile the hollow part in products with thick section contributes to fast heat dissipation and cooling, thereby shortening molding cycle.

the merit of the Gas-assisted injection molding--can be used to mold products with diverse wall-thickness. using gas-assisted injection molding can achieve uniform filling for products with diverse wall-thickness and, on the premises

the merit of the Gas-assisted injection molding—high surface quality. The pressure of gas in the hollow section of the products is referred to as the dwell pressure which is distributed uniformly so that no defects like shrinkage hole or dent shall not be formed on the surface of products, thereby improving the surface quality of products and reducing defective index.

the merit of the Gas-assisted injection molding—slight warp and distortion of products. Owing to the low injection pressure and the uniform distribution of fusant after the injection of gas, internal stress of products during the cooling is small, resulting in very slight warp and distortion after molding.

the merit of the Gas-assisted injection molding—low injection pressure and locking force, thereby reducing cost for equipment, since gas-assisted injection adopts “ underfeeding injection”, wherein the fusant’s filling of the mold cavity is accomplished under the pushing force of gas in the fusant, the injection pressure required thereof is relatively lower and the locking force is also low ( which can be reduced by 25%--90%), thereby saving energy, prolonging the service life of molds and reducing manufacturing cost.

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 recycled, finally open the cavity and eject the product.

Gas dwell, upon the completion of filling in the mold cavity and on the premises that the 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, thereby leaving no depression on the outer surface of parts with thick walls and improving quality of the product.

I want to say something about Gas injection stage, 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 injection, inject high-pressure inert gas such as nitrogen into the core of fusant and the gas enveloped by plastic fusant shall move forward along a direction with minimum resistance and meanwhile push the flowing front of fusant to move further forward unitl the mold cavity is fully filled. At this stage, pressure of the gas must be larger than that of the plastic fusant so that a hollow section can be formed in the product.

fusant injection, the plastic fusant is quantitatively injected into the mold cavity. In this stage, it is very similar with traditional injection molding. We often call a gas-assisted injection as “ underfeeding injection”, because in this stage, the injection volume takes up only 55%--80% of the volume of mold cavity. Whereas the specific injection volume varies with different molding products to ensure that the surface of sufant will not be blown through upon the injection of high-pressure gas and thereby acquiring an ideal aeration volume.

you ask too much! Ok! Now I have to tell you more details about a technical process of gas-assisted injection molding. Actually a complete gas-assisted injection molding cycle contains four stages: 1) fusant injection, 2) Gas injection, 3) Gas dwell, 4) Discharge of gas.

a rough technical process of gas-assisted injection molding is where in high-pressure insert gas is injected into core part of the plastic fusant to form a hollow section and further help pushing fusant flow, thereby achieving injection, dwell as well as cooling.

today you ask me some questions about Gas-assisted injection molding, now I have some information about it at hand. I want to share with you. Actually, gas-assisted injection molding is a kind of molding technology, which can produce products with uneven wall-thickness, the products thereby acquired not only show no sign of surface shrink mark, warp and distortion. The most important part is that it not only consume very small amount of materials. But also are easy to be controlled.