Injection molding method and apparatus for continuous plastication

A method of operating a reciprocating feed screw of an injection unit having a non-return valve associated therewith, the non-return valve permitting the injection unit to operate at injection pressures, the method comprising:

• rotating the reciprocating screw at a speed above zero revolutions per minute over the entire injection molding cycle;
• and
• in a chamber downstream of a non-return valve of the feed screw, accumulating melt until a desired volume is accumulated;
• increasing back-pressure in the injection system both to establish a substantially zero recovery rate for the feed screw and to prohibit any further increase in the volume for melt accumulation;
• and
• further increasing back-pressure within the system to produce injection of the melt from the chamber into a mold.

A method of operating a reciprocating feed screw of an injection unit having a non-return valve associated therewith, the non-return valve permitting the injection unit to operate at injection pressures, the method comprising:

• rotating the reciprocating screw at a speed above zero revolutions per minute over the entire injection molding cycle;
• and
• in a chamber downstream of a non-return valve of the feed screw, accumulating melt until a desired volume is accumulated;
• increasing back-pressure in the injection system both to establish a substantially zero recovery rate for the feed screw and to prohibit any further increase in the volume for melt accumulation;
• further increasing back-pressure within the system to produce injection of the melt from the chamber into a mold;
• and
• sensing at least one of a pressure environment, screw location and rotational speed of the screw;
• and
• controlling axial translation of the screw and selectively and dynamically varying the recovery rate of the injection unit during the injection cycle in response to corresponding ones of the pressure environment, screw location and rotational speed by adjusting at least one of:
• a) the back-pressure;
• and
• b) the rotational speed of the screw.

A method of operating a reciprocating feed screw of an injection unit having a non-return valve associated therewith, the non-return valve permitting the injection unit to operate at injection pressures, the method comprising:

• rotating the reciprocating screw at a speed above zero revolutions per minute over the entire injection molding cycle;
• in a chamber downstream of a non-return valve of the feed screw, accumulating melt until a desired volume is accumulated;
• increasing back-pressure in the injection system both to establish a substantially zero recovery rate for the feed screw and to prohibit any further increase in the volume for melt accumulation;
• and
• accumulating melt in the chamber until the volume of accumulated melt is equal to a sum of a shot size required for molding a part and an injection cushion volume sufficient to compensate, during injection, for potential back-flow across a non-return valve upstream of the chamber.

A reciprocating screw injection unit having a cyclic operating period, comprising:

• an axially translating screw mounted within a barrel, the screw having associated therewith a non-return valve downstream of which a volume of melt can, in use, be accumulated;
• a first actuator arranged to effect axial movement of the screw relative to the barrel and to generate, in use, back-pressure;
• a second actuator coupled to the screw to control, in use, rotational speed of the screw;
• and
• a controller for controlling operation of the screw and the first actuator, the controller arranged to set an axial position for the screw that defines the volume of melt to be accumulated downstream of the non-return valve by effecting, in use, an increase in the back-pressure to prohibit any further increase in the volume for melt accumulation and to render a recovery rate for the screw as being substantially zero and wherein the controller is arranged to ensure that the rotational speed of the screw, in use, is always above zero revolutions per minute.

A controller of an injection molding machine, the controller arranged, in use, to control axial positioning of a reciprocating and continuously rotating feedscrew through selective control of back-pressure, the controller further arranged to support and control the development, in use within the injection molding machine, of back-pressure for material injection directly into one of a mold and a runner system;

• wherein the controller is arranged to maintain, in use, a substantially zero recovery rate for the screw during an injection phase, the recovery rate relating to rotational speed of the screw and back-pressure developed, in use, within an injection unit of the injection molding machine;
• and
• wherein the controller, in use, causes selective variation of at least one of:
• a) the back-pressure;
• and
• b) the rotational speed of the screw;
• thereby to control axial translation of the screw and selectively and dynamically to vary, in use, the recovery rate during an operational cycle of the injection unit.

A controller of an injection molding machine, the controller arranged, in use, to control axial positioning of a reciprocating and continuously rotating feedscrew through selective control of back-pressure, the controller further arranged to support and control the development, in use within the injection molding machine, of back-pressure for material injection directly into one of a mold and a runner system;

• wherein the controller is arranged to maintain, in use, a substantially zero recovery rate for the screw during an injection phase, the recovery rate relating to rotational speed of the screw and back-pressure developed, in use, within an injection unit of the injection molding machine;
• wherein the controller is configured, in use, to decrease temporarily the rotational speed of the screw during an injection phase of the operation cycle relative to a rotational speed of the screw during a recovery phase of the operational cycle;
• and
• wherein the controller, in use, causes selective variation of at least one of:
• a) the back-pressure;
• and
• b) the rotational speed of the screw;
• thereby to control axial translation of the screw and selectively and dynamically to vary, in use, the recovery rate during an operational cycle of the injection unit.

A controller of an injection molding machine, the controller arranged, in use, to control axial positioning of a reciprocating and continuously rotating feedscrew through selective control of back-pressure, the controller further arranged to support and control the development, in use within the injection molding machine, of back-pressure for material injection directly into one of a mold and a runner system;

• wherein the controller is arranged to maintain, in use, a substantially zero recovery rate for the screw during an injection phase, the recovery rate relating to rotational speed of the screw and back-pressure developed, in use, within an injection unit of the injection molding machine;
• wherein the controller is configured, in use, to decrease temporarily the rotational speed of the screw during an injection phase of the operation cycle relative to a rotational speed of the screw during a recovery phase of the operational cycle;
• wherein the controller is responsive, in use, to sensed pressure, location and speed signals associated with an injection unit and the controller, in use, acts substantially to maintain a zero recovery rate during an injection phase of the operation cycle;
• and
• wherein the controller, in use, causes selective variation of at least one of:
• a) the back-pressure;
• and
• b) the rotational speed of the screw;
• thereby to control axial translation of the screw and selectively and dynamically to vary, in use, the recovery rate during an operational cycle of the injection unit.

An injection molding machine including having an injection unit base comprising:

• a barrel with an axially translating and reciprocating screw therein, the barrel having a nozzle to support, in use, injection of melt into one of a runner system and a mold, the screw having associated therewith a non-return valve downstream of which a volume of melt can, in use, be accumulated;
• a first actuator arranged to effect axial movement of the screw relative to the barrel and to generate, in use, back-pressure;
• a second actuator coupled to the screw to control, in use, rotational speed of the screw;
• and
• a controller for controlling operation of the screw and the first actuator, the controller arranged to set an axial position for the screw that defines the volume of melt to be accumulated downstream of the non-return valve by effecting, in use, an increase in the back-pressure to prohibit any further increase in the volume for melt accumulation and to render a recovery rate for the screw as being substantially zero and wherein the controller is arranged to ensure that, during use, the screw rotates continuously.