Patent ID: 8252214

Claim:
A gas extraction method for a sheet molded product, comprising: providing an injection mold apparatus including an upper mold and a lower mold, a parting plane and a sheet mold cavity defined between the upper mold and the lower mold, a material inlet defined in the upper mold, a gas vent and a connecting aperture defined in the lower mold, and a gas vent pin, the mold cavity including an entrance portion and only an end portion of a material injection path, the gas vent and the end portion positioned at opposite sides of the parting plane, the material inlet communicating with the entrance portion and the connecting aperture connecting the gas vent with the end portion, the gas vent pin being received in the gas vent and toward an inside surface of the molded product; injecting molten material into the mold cavity through the material inlet; whereby as the mold cavity begins to be filled, molten material flows toward the only end portion; venting a part of gas from a first gap between the gas vent pin and the gas vent as molten material is injected into the mold cavity; after the mold cavity is filled with molten material to about 95 percent of the mold cavity's capacity, the vent pin is driven in the connecting aperture as additional molten material and additional gas are injected into the mold cavity; making the gas vent pin coplanar with the parting plane to substantially close the connecting aperture and the gas vent of the material injection path, wherein during this time, the remaining amount of the gas and the additional gas are completely vented from the mold cavity into a second gap between the gas vent pin and the connecting aperture and out through the first gap, and whereby the gas vent pin forms a mark on the inside surface of the molded product.