A nonreturn valve includes two half-shells, arranged in a portion of the screw with a reduced screw diameter. One or more channels for the melt to flow through from the screw into the space in front of the screw is/are provided in each of the half-shells, the channels lie substantially parallel to the longitudinal axis of the nonreturn valve or of the screw. In each of the channels are a ball and, following the ball in the direction of flow of the melt, a pin arranged substantially transversely to the direction of flow of the melt. In the direction of flow of the melt, the channels have a first channel portion, with a channel diameter less than the diameter of the ball, and a second channel portion, with a channel diameter greater than the diameter of the ball, the ball and the pin are arranged in the second channel portion.

An injection moulding machine for producing fibre-reinforced plastic mouldings, having a closing unit and an injection unit, wherein the injection unit has a cylinder and a screw that can be rotated and displaced in the longitudinal direction in the cylinder, the screw having a backflow stop. In the cylinder, filling openings are provided for feeding in a plastic material to be melted and fibre material. To reduce fibre breakage and ensure good mixing, according to the invention a mixing part is provided downstream and/or upstream of the backflow stop, the mixing part being connected to the screw in a rotationally fixed manner for conjoint rotation therewith and having a cylindrical main body with drop-shaped mixing elements arranged thereon.

A nonreturn valve includes two half-shells, arranged in a portion of the screw with a reduced screw diameter. One or more channels for the melt to flow through from the screw into the space in front of the screw is/are provided in each of the half-shells, the channels lie substantially parallel to the longitudinal axis of the nonreturn valve or of the screw. In each of the channels are a ball and, following the ball in the direction of flow of the melt, a pin arranged substantially transversely to the direction of flow of the melt. In the direction of flow of the melt, the channels have a first channel portion, with a channel diameter less than the diameter of the ball, and a second channel portion, with a channel diameter greater than the diameter of the ball, the ball and the pin are arranged in the second channel portion.

An injection moulding machine for producing fibre-reinforced plastic mouldings, having a closing unit and an injection unit, wherein the injection unit has a cylinder and a screw that can be rotated and displaced in the longitudinal direction in the cylinder, the screw having a backflow stop. In the cylinder, filling openings are provided for feeding in a plastic material to be melted and fibre material. To reduce fibre breakage and ensure good mixing, according to the invention a mixing part is provided downstream and/or upstream of the backflow stop, the mixing part being connected to the screw in a rotationally fixed manner for conjoint rotation therewith and having a cylindrical main body with drop-shaped mixing elements arranged thereon.

An injection molding machine and screw therefor with which, when mixing reinforcing fibers in a molten resin and injection molding same, the reinforcing fibers can be uniformly dispersed in the molten resin. For a screw provided in an injection molding machine, a mixing section is provided on the downstream side of a compression section. Three helical flights (x, y, z) are provided in the mixing section and three grooves, which are helically disposed in the opposite or the same direction as the orientation of the flights, are formed. As a result of the grooves, it is possible to keep the fiber lengths of the reinforcing fibers long and even if the reinforcing fibers become tangled in the compression section, the fibers are defibrated in the mixing section, the shearing of long fibers in the molten resin is mitigated, the reinforcing fibers are dispersed uniformly and a good product is obtained.

A supercritical fluid microcellular injection molding method includes the following steps. Preheating: the feed pipe is preheated to a hot melt temperature of polymer. Feeding: the polymer is poured into the hopper and enters the feed pipe. A metering screw is rotatably received in the feed pipe for forwardly pushing the hot molten polymer when being rotated. Injecting SCF: the SCF is injected into the feed pipe and mixed with the hot molten polymer into a homogeneous monophasic fluid. Quantitative discharge and depressurization: the monophasic fluid flows across a first gear pump and a second gear pump mounted on the front end of the feed pipe. Discharging and molding: the monophasic fluid actuated by the first gear pump and the second gear pump is injected and molded by the die head fixed to the discharge end of the second gear pump.

An injection molding system, to produce fiber-reinforced plastics material parts, has an injection molding device with a housing and a housing bore formed therein. A screw shaft, which is rotatably drivable about a rotational axis and can be displaced along the rotational axis, is arranged in the housing bore to melt and introduce plastics material into a mold. For feeding fibers, the injection molding system furthermore has a feed device, which is configured in such a way that cut fibers can be fed through a feed opening directly into the housing bore. The injection molding system according to the invention allows simple and flexible production of fiber-reinforced plastics material parts.