Method for gas assisted injection molding with pin and sleeve mechanism

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

• providing a valve element mounted for reciprocation in a flow passage of a nozzle body 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, the 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 such that said pin and said barrel define between them an annular opening at said barrel first end, said annular opening communicating with said barrel bore to define an annular gas flow passage between said pin and said barrel;
• securing the pin to a portion of the nozzle body other than the barrel;
• and,
• reciprocating the barrel in relation to the pin such that a front end of the pin extends toward the nozzle body discharge and at least as far as the front end of the barrel thereby allowing the thermoplastic to flow past the barrel while said annular gas flow passage remains open;
• injecting a molten stream of the thermoplastic into the mold cavity;
• leaving continuously open said annular gas flow passage throughout said step of injecting a molten stream of thermoplastic;
• flowing an annular stream of gas through the gas flow passage and into the mold cavity;
• forming a gas cavity in the thermoplastic material held in the mold cavity;
• and,
• urging the thermoplastic material toward a surface of the mold cavity.

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:

• providing a nozzle body having a flow passage extending therein and a discharge end;
• controlling a flow of the viscous fluid through the nozzle body discharge end into the mold cavity by a valve element mounted for reciprocation in the nozzle body flow passage, the valve element comprising a barrel having a first end which selectively engages a portion of the nozzle body discharge end to prevent a flow of viscous fluid therepast and a second end;
• allowing a flow of non-viscous fluid though the barrel at all times by providing a structure comprising:
• a bore extending longitudinally through the barrel, and,
• a pin located in said barrel bore and fixedly secured to the nozzle body such that the barrel can reciprocate in relation to the pin, the pin and barrel bore defining between them a flow passage for flow of a non-viscous fluid;
• reciprocating the barrel in relation to the pin to allow flow of the viscous fluid past the barrel;
• injecting 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;
• and,
• venting the non-viscous fluid held in the non-viscous fluid cavity.

A method of gas-assisted injection molding, the method comprising:

• regulating a flow of a thermoplastic through a nozzle body discharge end and into a mold cavity with a valve element, said valve element being mounted for reciprocation in a nozzle body flow passage and 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 thermoplastic therepast, and a second end, and a bore extending longitudinally through said barrel;
• positioning a pin in said barrel bore;
• defining an annular gas flow passage between said pin and said barrel, wherein the annular gas flow passage has a substantially constant thickness at and adjacent said barrel first end;
• leaving the annular gas flow passage defined between said pin and said barrel open at all times;
• injecting the thermoplastic through the nozzle body flow passage around the barrel and into the mold cavity;
• flowing an annular stream of the gas through the gas flow passage and into the mold cavity;
• minimizing a flow of the thermoplastic into the gas flow passage during said steps of flowing the thermoplastic and flowing the gas due to the relationship between the pin and barrel forming the annular gas flow passage;
• venting the gas from the mold cavity through the annular gas flow passage;
• and,
• minimizing a flow of the thermoplastic back through the gas flow passage during said step of venting the gas due to the gas flow effects caused by the cooperation of the barrel and pin in forming the annular flow passage.