EP-4737027-A1 - BACKFLOW PREVENTION DEVICE AND INJECTION APPARATUS PROVIDED WITH SAME

EP4737027A1EP 4737027 A1EP4737027 A1EP 4737027A1EP-4737027-A1

Abstract

Provided is a backflow prevention device in which a piston ring does not readily enter a gap between a backflow prevention ring and a cylinder. A backflow prevention device 4 of an injection apparatus 3 has a backflow prevention ring 41 having an annular groove 42 facing an inner surface of a cylinder 32 of the injection device 3, and a piston ring 51 fitted in the annular groove 42. The piston ring 51 has a storage part 56 stored in the annular groove 42, and an outer peripheral surface 53 located radially outside of the annular groove 42, and a rear end part 53A in the injection direction of the outer peripheral surface 53 is located in front in the injection direction with respect to the rearmost end part 55 in the injection direction of the storage part 56.

Inventors

KAWABE, CHIKARA
YAMAGUCHI, TAKESHI

Assignees

The Japan Steel Works, Ltd.

Dates

Publication Date: 20260506
Application Date: 20240415

Claims (12)

A backflow prevention device of an injection unit, comprising: a backflow prevention ring that includes at least one annular groove that faces the inner surface of a cylinder of said injection unit; and at least one piston ring, each said at least one piston ring being fitted in a respective one of said at least one annular groove, wherein each said at least one piston ring includes a housed portion that is accommodated in a respective one of said at least one annular groove and an outer circumferential surface that is located radially outward from said respective one of said at least one annular groove, and the rearward end point of said outer circumferential surface in an injection direction is forward of the rearmost end of said housed portion in said injection direction.
The backflow prevention device of said injection unit according to claim 1, wherein a surface that connects said rearward end point of said outer circumferential surface and said rearward end of said housed portion includes: a cylindrical surface whose central axis is the central axis of said cylinder; and an inclined surface that connects a forward end of said cylindrical surface in said injection direction and said rearward end point of said outer circumferential surface and that is inclined with respect to said central axis of said cylinder.
The backflow prevention device of said injection unit according to claim 1, wherein all of the surface that connects said rearward end point of said outer circumferential surface and said rearward end of said housed portion is inclined with respect to said central axis of said cylinder.
The backflow prevention device of said injection unit according to claim 2 or 3, wherein the outermost portion in a radial direction of said rearward end of said housed portion is located at approximately the same position in said radial direction as an opening of said annular groove.
The backflow prevention device of said injection unit according to claim 2 or 3, wherein the outermost portion in the radial direction of said rearward end of said housed portion is inside said annular groove.
The backflow prevention device of said injection unit according to any one of claims 1 to 5, wherein said at least one annular groove and said at least one piston ring each have a rear side surface in said injection direction, and said rear side surface of said at least one annular groove and said rear side surface of said at least one piston ring can contact each other only at their respective radially inner side portions.
The backflow prevention device according to claim 6, wherein when said radially inner side portion of said rear side surface of said at least one piston ring contacts said radially inner side portion of said rear side surface of said at least one annular groove, a gap is formed between said radially outer side portion of said rear side surface of said at least one piston ring and said radially outer side portion of said rear side surface of said at least one annular groove.
The backflow prevention device according to claim 7, wherein said radially inner side portion of said rear side surface of said at least one annular groove and said radially inner side portion of said rear side surface of said at least one piston ring are in a plane orthogonal to the central axis of said cylinder.
The backflow prevention device according to claim 6, wherein the radially outer side portion of said rear side surface of said at least one piston ring is forward in said injection direction relative to said radially inner side portion of said rear side surface of said at least one piston ring.
The backflow prevention device according to claim 9, wherein said rear side surface of said at least one annular groove is a plane orthogonal to the central axis of said cylinder.
The backflow prevention device according to any one of claims 1 to 10, wherein the outer diameter of said piston ring is smaller at a rear portion in said injection direction than at a front portion in said injection direction.
An injection unit, comprising: the backflow prevention device according to any one of claims 1 to 11; said cylinder; a screw that is housed in said cylinder; and an injection nozzle that is attached to the end of said cylinder.

Description

Technical Field This application claims the benefit of Japanese Priority Patent Application No. JP 2023-108729 filed on June 30, 2023, the entire contents of which are incorporated herein by reference. The present invention relates to a backflow prevention device and to an injection unit provided with same. Background Art An injection unit of an injection molding machine is provided with a backflow prevention device that prevents backflow of injected materials during injection. Japanese Patent Application Laid-Open No. H07(1995)-314510 describes an injection unit comprising a screw that is housed in a cylinder, a push plate that is attached to the screw, and a backflow prevention device that is provided between the screw head of the screw and the push plate. When the screw moves forward during injection, the backflow prevention device is pressed against the push plate, preventing the material to be injected from flowing behind the push plate. The backflow prevention device includes a backflow prevention ring and a piston ring that is fitted into the backflow prevention ring. Summary of Invention The piston ring is provided for the purpose of improving sealing between the backflow prevention device and the cylinder. However, because the screw moves at high speed during injection, the piston ring may deform and may enter the gap between the backflow prevention ring and the cylinder. In this case, not only will the piston ring wear out, but the piston ring that has entered the gap between the backflow prevention ring and the cylinder may damage the cylinder. The purpose of the present invention is to provide a backflow prevention device in which the piston ring is less likely to enter the gap between the backflow prevention ring and the cylinder. The backflow prevention device of the present invention comprises a backflow prevention ring that includes an annular groove, and a piston ring that is fitted in the annular groove. The piston ring includes a housed portion that is accommodated in the annular groove and an outer circumferential surface that is located radially outward from the annular groove. The rearward end point of the outer circumferential surface in the injection direction is forward of the rearmost end of the housed portion in the injection direction. According to the present invention, a backflow prevention device can be provided in which the piston ring is less likely to enter the gap between the backflow prevention ring and the cylinder. The objects, features, and advantages of the present application, above and otherwise, will become apparent from the detailed description set forth below with reference to the accompanying drawings that illustrate the present application. Brief Description of the Drawings [Fig. 1] Fig. 1 is a schematic front view of an injection molding machine according to a first embodiment.[Fig. 2] Fig. 2 is an enlarged view of area A in Fig. 1.[Fig. 3] Fig. 3 is an enlarged view of area B in Fig. 2.[Fig. 4] Fig. 4 is a cross-sectional view along line 4-4 in Fig. 3.[Fig. 5] Fig. 5 is an enlarged view of an area in a second embodiment that corresponds to area B in Fig. 2.[Fig. 6] Fig. 6 is an enlarged view of an area in a third embodiment that corresponds to area B in Fig. 2.[Fig. 7] Fig. 7 is an enlarged view of an area in a fourth embodiment that corresponds to area B in Fig. 2.[Fig. 8] Fig. 8 is an enlarged view of an area in a fifth embodiment that corresponds to area B in Fig. 2.[Fig. 9] Fig. 9 is an enlarged view of an area in a sixth embodiment that corresponds to area B in Fig. 2.[Fig. 10] Fig. 10 is an enlarged view of an area in a seventh embodiment that corresponds to area B in Fig. 2.[Fig. 11] Fig. 11 is an enlarged view of an area in an eighth embodiment that corresponds to area B in Fig. 2.[Fig. 12] Fig. 12 is an enlarged view of an area in a ninth embodiment that corresponds to area B in Fig. 2.[Fig. 13A] Fig. 13A is an enlarged view of the area that corresponds to area B in Fig. 2 in a comparative example.[Fig. 13B] Fig. 13B is a diagram illustrating an issue in a comparative example. Detailed Description of Embodiments Embodiments of the present invention will next be described with reference to the drawings. The present invention can be suitably applied to metal injection molding machines, especially those that inject metal having low viscosity when molten. However, the present invention can also be applied to injection molding machines that inject resin. In the following description, the X-direction refers to the axial direction of cylinder 32, the injection direction being referred to as the +X-direction, and the direction opposite to the injection direction being referred to as the -X-direction. Terms such as "forward," "rearward," "front," "rear" are defined with respect to the injection direction. In addition, "radial direction" is defined based on central axis CL of cylinder 32. First Embodiment Overall Configuration of Injection Molding Machine Fig.