Process for gas assisted injection molding

A process for fluid-assisted injection molding comprising:

• providing a mold body including a mold cavity;
• positioning a nozzle body adjacent said mold body, said nozzle body comprising an inlet end, a discharge end which communicates with said mold cavity, and a flow passage for a viscous fluid extending from said inlet end to said discharge end;
• mounting a valve element for reciprocation in said nozzle body flow passage to control a flow of the viscous fluid through said nozzle body discharge end;
• defining a flow passage in said valve element for flow of a non-viscous fluid;
• introducing the viscous fluid through said viscous fluid flow passage into the mold cavity;
• introducing the non-viscous fluid through said non-viscous fluid flow passage into the mold cavity;
• forming a non-viscous fluid cavity in the viscous fluid held in the mold cavity;
• and,
• venting the non-viscous fluid from the non-viscous fluid cavity formed in the viscous fluid held in the mold cavity, wherein said step of venting comprises the subsidiary steps of first flowing an initial portion of the non-viscous fluid into a first small volume container which cannot accommodate all of the volume of the non-viscous fluid and then flowing a remaining portion of the non-viscous fluid into a second, larger, container.

A process for gas-assisted injection molding to produce an injection molded product, comprising:

• providing a valve element mounted for reciprocation in a nozzle body flow passage to control a flow of a thermoplastic through a nozzle body discharge end and into a mold cavity, said valve element comprising:
• a barrel assembly including a barrel having a first end, said first end selectively engaging the nozzle body discharge end to prevent a flow of thermoplastic therepast and a second end,
• a bore extending longitudinally through said barrel;
• a pin located in said barrel bore, said pin having a first end located adjacent said barrel first end and a second end secured to said barrel assembly such that said pin moves with said barrel as said barrel reciprocates, and
• a gas flow passage defined between said pin and said barrel;
• retracting the barrel, and the pin therein, to introduce a molten stream of thermoplastic through the nozzle body flow passage and into the mold cavity;
• introducing a gas through the gas flow passage into the mold cavity;
• forming a gas cavity in the thermoplastic material held in the mold cavity;
• urging the thermoplastic material toward a surface of the mold cavity;
• cooling a hollow shaped body so formed to a temperature below a softening point of the thermoplastic material thereby allowing the product to take its final shape;
• and,
• venting the gas.

A method for employing an injection molding nozzle for forming an injection molded part by injecting a viscous fluid and a non-viscous fluid into a mold cavity of a mold body, the method comprising the steps of:

• controlling a flow of the viscous fluid through a nozzle body discharge end into the mold cavity by a valve element mounted for reciprocation in a nozzle body flow passage, the valve element comprising:
• a barrel having a first end, said first end selectively engaging a portion of the nozzle body discharge end to prevent a flow of the viscous fluid therepast and a second end,
• a bore extending longitudinally through the barrel, and,
• a pin located in said barrel bore and fixedly secured to the valve element, the pin and barrel bore defining between them a flow passage for flow of the non-viscous fluid;
• flowing the viscous fluid through the nozzle body flow passage and into the mold cavity;
• flowing the non-viscous fluid through the flow passage defined between the pin and the barrel bore and into the mold cavity;
• forming a non-viscous fluid cavity in the viscous fluid in the mold cavity;
• cooling the viscous fluid to form the injection molded part;
• reducing the pressure of the non-viscous fluid held in the non-viscous fluid cavity by venting a portion of the non-viscous fluid held in the non-viscous fluid cavity;
• simultaneously preventing additional non-viscous fluid from flowing into the non-viscous fluid cavity;
• further cooling the viscous fluid;
• and,
• further reducing the pressure of the non-viscous fluid held in the non-viscous fluid cavity by venting a remaining portion of the non-viscous fluid held in the non-viscous fluid cavity.