1.The pressurized gas (usually nitrogen) is injected into the mold by machine nozzle, runner system,sprue or gas pin, producing a bubble which pushes the plastic into the extremities of the mold cavity creating hollow sections as the bubble propagates.
2.Advantages:
2.1 Molding large cross-sections while reducing the weight and shrinkage;
2.2 Lower production costs for typical part;
2.3 Improved dimensional stability.

3. General guidelines

3.1 resin with a higher Melt Mass-Flow Rate(MFI) used;

3.2 gating part at one of the end;

3.3 Gas Injection Location is near to gate location;

3.4 Gas Injection Location is opposite to mold top side;

3.5 separate gas channel needed for every cavity in multi-cavity mold;

3.6 the hot runner system ,heating oil and even the heater is often used to maintain a higher mold temperature;

3.7 the modified trapezoid cross section of runner and overflow pocket used;

4. Process methods

1.Resin is injected into the mold cavity as a short shot;

2.the position of cylinder,slide and e.j. pin as illustrated in Sec A—A before the end of resin injection;

3. slide and e.j. pin were pushed forward by oil cylinder as illustrated in view B,shutting off the gating at the end of resin injection;

4.Gas is injected into the hot melt thru the gas channel and pin;

5.Gas pressure is maintained during the cooling cycle;

6. Gas pressure is released and mold opened.

5 the overflow well

1.used for the molten Resin pushed out by Secondary Gas Penetration;

2.the state of overflow well during the resin injection stage is as illustrated in sec A—A ,which is not connected to the cavity.

3.overflow well is connected to cavity by the retract movement of e.j. pin driven by the cylinder at the end of resin injection(View C)

4. Primary Gas Penetration begins at the end of filling and the resulted gas bubble displaces some of the molten core, pushing it into the unfilled cavity and completing the mold filling

5. Secondary Gas Penetration begins at the end of the filling stage when the polymer has reached the end of the mold and additional resin is pushed into the overflow well.