A stepped flight is formed on a screw of an injection molding machine. The stepped flight is a flight in which a step-shaped step portion is formed on a top portion thereof. The top portion of the flight includes a large diameter portion on an upstream side and a land portion on a downstream side. When a gap ratio m of a gap H.sub.1 between the land portion and a bore of the heating cylinder to a gap H.sub.2 between the large diameter portion and the bore is defined as H.sub.1/H.sub.2, the gap ratio m is selected to be 2.3≤m≤6.4.

A flange is formed on a heating cylinder in a vicinity of a center in a longitudinal direction and a predetermined joining plate adheres to the flange. A flange plate is provided on a support frame. The joining plate is fixed to the flange plate to attach and detach freely, and the heating cylinder is caused to be supported by the support frame. Accordingly, movement in an axial direction and rotation of the heating cylinder are restricted. A guide portion for positioning during attachment and detachment is provided on one or both of the joining plate and the flange plate.

A melt dispenser for plastic molding comprises a barrel unit removably mountable to a drive unit. A feed screw is received within a barrel of the barrel unit and is rotated by the drive unit to dispense molten molding material through an outlet of the barrel. A coupling mechanism can be engaged to hold the barrel unit against the drive unit and on to connect the screw to the drive. The coupling mechanism is operable by an actuator.

A melt dispenser for plastic molding comprises a barrel unit removably mountable to a drive unit. A feed screw is received within a barrel of the barrel unit and is rotated by the drive unit to dispense molten molding material through an outlet of the barrel. A coupling mechanism can be engaged to hold the barrel unit against the drive unit and on to connect the screw to the drive. The coupling mechanism is operable by an actuator.

A plasticizing device includes a drive motor, a screw that is rotated by the drive motor and that has a grooved face provided with a groove, a barrel that has an opposed face opposed to the grooved face and that is provided with a communication hole communicating with the groove at the opposed face, a first heating section that heats the material supplied to the groove, a temperature sensor that measures a temperature of the groove, and a control unit that controls the drive motor and the first heating section, wherein the control unit performs a first process for rotating the screw at a first rotation speed by controlling the drive motor, and a second process for rotating the screw at a second rotation speed higher than the first rotation speed by controlling the drive motor, and the control unit controls the first heating section so that a temperature measured by the temperature sensor falls within a predetermined range when performing the first process and the second process.

A plasticizing device includes a drive motor, a screw that is rotated by the drive motor and that has a grooved face provided with a groove, a barrel that has an opposed face opposed to the grooved face and that is provided with a communication hole communicating with the groove at the opposed face, a first heating section that heats the material supplied to the groove, a temperature sensor that measures a temperature of the groove, and a control unit that controls the drive motor and the first heating section, wherein the control unit performs a first process for rotating the screw at a first rotation speed by controlling the drive motor, and a second process for rotating the screw at a second rotation speed higher than the first rotation speed by controlling the drive motor, and the control unit controls the first heating section so that a temperature measured by the temperature sensor falls within a predetermined range when performing the first process and the second process.

A plasticizing device includes a screw that has a grooved face provided with a first groove, a barrel that has an opposed face and a communication hole communicating with the first groove at the opposed face, and a heating section that heats a material supplied to the first groove, wherein the first groove includes a central portion opposed to the communication hole, a material supply portion that is provided at an outer circumference of the grooved face , and a coupling portion that couples the central portion to the material supply portion, a second groove that is coupled to the communication hole is provided and when viewed from the rotational axis direction, an end at the outer circumferential side of the second groove is located inside a track drawn by a boundary line between the material supply portion and the coupling portion when the screw is rotated once.

A plasticizing device includes a screw that has a grooved face provided with a first groove, a barrel that has an opposed face and a communication hole communicating with the first groove at the opposed face, and a heating section that heats a material supplied to the first groove, wherein the first groove includes a central portion opposed to the communication hole, a material supply portion that is provided at an outer circumference of the grooved face , and a coupling portion that couples the central portion to the material supply portion, a second groove that is coupled to the communication hole is provided and when viewed from the rotational axis direction, an end at the outer circumferential side of the second groove is located inside a track drawn by a boundary line between the material supply portion and the coupling portion when the screw is rotated once.

A plasticizing screw for a molding machine, includes a base element which is stretched along a longitudinal axis and a screw tip which is connected to the base element, and the screw tip is located after the base element. A return flow shut-off device includes a first anterior limit stop, a second posterior limit stop, and a shut-off ring movable in a limited manner between the two limit stops along the longitudinal axis. The first, anterior limit stop comprises a first limit stop surface facing towards the base element and the shut-off ring. The shut-off ring comprises a ring-shaped screw tip abutting surface facing towards the first, anterior limit stop. The screw tip abutting surface is formed rotationally symmetric around the longitudinal axis, and the first limit stop surface comprises a convex curvature facing towards the shut-off ring.

A plasticizing screw for a molding machine, includes a base element which is stretched along a longitudinal axis and a screw tip which is connected to the base element, and the screw tip is located after the base element. A return flow shut-off device includes a first anterior limit stop, a second posterior limit stop, and a shut-off ring movable in a limited manner between the two limit stops along the longitudinal axis. The first, anterior limit stop comprises a first limit stop surface facing towards the base element and the shut-off ring. The shut-off ring comprises a ring-shaped screw tip abutting surface facing towards the first, anterior limit stop. The screw tip abutting surface is formed rotationally symmetric around the longitudinal axis, and the first limit stop surface comprises a convex curvature facing towards the shut-off ring.