Method and apparatus for generating foamed thermoplastic materials

The method of entraining water and gas as combined blowing agents in a thermoplastic melt to provide foamed thermoplastic extrudate comprising:

• introducing water into said thermoplastic melt upstream of the gate area of said extruder to provide, as an output of said extruder, an extruded flowing mass of thermoplastic melt with entrained water;
• constraining the flow of said melt into a tubular configuration over a finite distance;
• impinging an annular sheet-like flow of gas under pressure on said tubular configuration of melt substantially transversely of the direction of flow thereof to entrain said gas in said melt in addition to water;
• subsequently returning said melt with entrained gas and water to a flowing mass configuration;
• controlling the flow rate and temperature of said flowing mass with entrained gas and water to optimum values for subsequent extrusion;
• and
• extruding said flowing mass with entrained gas and water to produce said foamed thermoplastic extrudate.

The method of entraining water and gas as combined blowing agents in a thermoplastic melt to provide foamed thermoplastic extrudate, comprising:

• generating a flowing thermoplastic melt in an extruder;
• introducing a gas generating substance into said extruder for mixing therein with said flowing thermoplastic melt to entrain generated gas therein;
• introducing water into said flowing thermoplastic melt upstream of the gate area of said extruder to provide, as an output of said extruder, an extruded flowing mass of thermoplastic melt with entrained water and gas;
• subjecting said flowing thermoplastic melt with entrained water and gas to a mixing action downstream of said extruder;
• subsequent to said mixing action, controlling the flow rate and temperature of said flowing mass with entrained gas and water to optimum values for subsequent extrusion;
• and
• extruding said flowing mass with entrained gas and water at said optimum values of flow rate and temperature to produce said foamed thermoplastic extrudate.

The method of continuously entraining water as a blowing agent in a thermoplastic melt to provide foamed thermoplastic extrudate comprising:

• providing an extruded flowing mass of thermoplastic melt in an extruder;
• introducing water into said thermoplastic melt upstream of the gate area of said extruder to provide, as an output of said extruder, an extruded flowing mass of thermoplastic melt with entrained water;
• subjecting said thermoplastic melt with entrained water to a mixing action downstream of said extruder;
• controlling the flow rate and temperature of said flowing mass with entrained water to optimum values for subsequent extrusion;
• and
• extruding said flowing mass with entrained water at said optimum values of flow rate and temperature to produce said foamed thermoplastic extrudate.

The method of entraining gas as a blowing agent in a thermoplastic melt to provide foamed thermoplastic extrudate, comprising:

• providing an extruded flowing mass of thermoplastic melt;
• constraining the flow of said melt into a thin tubular configuration over a finite distance;
• impinging an annular sheet-like flow of gas under pressure on said tubular configuration of melt to entrain gas in said melt;
• subsequently returning said melt with entrained gas to a flowing mass configuration;
• and
• extruding said flowing mass with entrained gas to produce said foamed thermoplastic extrudate.

Means for entraining gases and water as blowing agents in a thermoplastic melt to provide a foamed thermoplastic end product, comprising:

• extruder means for providing a flowing mass of thermoplastic melt;
• water injection means on said extruder means for injecting water at a substantially constant rate onto said flowing mass of thermoplastic melt to entrain a preselected amount of water therein;
• gas injection means downstream of said water injection means for injecting gas into said flowing thermoplastic melt with water entrained therein at a preselected injection pressure;
• first control means for using and maintaining a substantially constant pressure in said thermoplastic melt at the point of injection of said gas therein to maintain a substantially constant pressure differential at said point of injection of said gas;
• and
• second control means for controlling the flow rate and temperature of said flowing thermoplastic melt subsequent to the entrainment of water and gas therein and delivering said thermoplastic melt so controlled to an extrusion die to ultimately produce said foamed thermoplastic end product.

Means for entraining gases and water as blowing agents in a thermoplastic melt to provide a foamed thermoplastic end product, comprising:

• extruder means for providing a flowing mass of thermoplastic melt with a preselected amount of gas generating reagent entrained therein;
• water injection means on said extruder means for injecting water at a substantially constant rate into said flowing mass of thermoplastic melt to entrain a preselected amount of water therein;
• first control means for sensing and maintaining a substantially constant pressure in said flowing thermoplastic melt downstream of said extruder means;
• and
• second control means including mixing means for imparting a mixing action to said flowing thermoplastic melt with water and gas entrained therein, controlling the flow rate and temperature thereof and delivering said thermoplastic melt to an extrusion die to ultimately produce said foamed thermoplastic end product.

Means for entraining gas as a blowing agent in a flowing mass of thermoplastic melt, comprising:

• body means having substantially aligned inlet and outlet ports and an enlarged central cavity connecting same defined therein for conveying a flow of thermoplastic melt therethrough;
• flow diverting means in said enlarged central cavity for converting a flow of thermoplastic melt from a flowing mass in said inlet port into a flowing tubular configuration over a finite distance in said cavity and back to a flowing mass in said outlet port;
• and
• injection means for impinging an annular stream of gas on said flowing tubular configuration transverse to the direction of flow thereof to entrain said gas in said thermoplastic melt.

A device for entraining gas as a blowing agent in a flowing mass of thermoplastic melt, comprising:

• body means having an inlet and an outlet port and an enlarged central cavity connecting said inlet and outlet ports for conveying a flow of thermoplastic melt therethrough;
• flow diverting means in said enlarged central cavity for converting a flow of thermoplastic melt from a flowing mass in said inlet port into a flowing thin tubular configuration over a finite distance in said cavity and back to a flowing mass in said outlet port;
• and
• injection means for impinging a thin annular stream of gas on said flowing tubular configuration to entrain said gas in said thermoplastic melt.