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EP-4737028-A1 - BACKFLOW PREVENTION DEVICE AND INJECTION DEVICE PROVIDED WITH SAME

EP4737028A1EP 4737028 A1EP4737028 A1EP 4737028A1EP-4737028-A1

Abstract

The present invention provides a backflow prevention device that resists the intrusion of a piston ring into the gap between a backflow prevention ring and a cylinder. A backflow prevention device 4 of an injection device 3 has a backflow prevention ring 41 with an annular groove 42 facing the inner surface of a cylinder 32 of the injection device 3, and a piston ring 51 fitted in the annular groove 42. The annular groove 42 and the piston ring 51 each have a rear-section face 44, 55 in the injection direction of the injection device 3. The rear-section face 44 of the annular groove 42 and the rear-section face 55 of the piston ring 51 can contact each other only at respective radially inward sections 44B, 55B.

Inventors

  • YAMAGUCHI TAKESHI

Assignees

  • The Japan Steel Works, Ltd.

Dates

Publication Date
20260506
Application Date
20240415

Claims (14)

  1. A backflow prevention device for an injection apparatus comprising: a backflow prevention ring with at least one annular groove that faces an inner surface of a cylinder of an injection apparatus; and at least one piston ring fitted in the at least one annular groove, wherein the at least one annular groove and the at least one piston ring each include a rear side surface in an injection direction of the injection apparatus, and wherein the rear side surface of the at least one annular groove and the rear side surface of the at least one piston ring can contact each other only at their respective radially inner side parts.
  2. The backflow prevention device for the injection apparatus according to claim 1, wherein when the radially inner side part of the rear side surface of the at least one piston ring contacts the radially inner side part of the rear side surface of the at least one annular groove, a gap is formed between a radially outer side part of the rear side surface of the at least one piston ring and a radially outer side part of the rear side surface of the at least one annular groove.
  3. The backflow prevention device according to claim 2, wherein the radially outer side part of the rear side surface of the at least one annular groove is rearward of the radially inner side part of the rear side surface of the at least one annular groove in the injection direction, and wherein the radially outer side part of the rear side surface of the at least one piston ring protrudes rearward in the injection direction relative to the radially inner side part of the rear side surface of the at least one piston ring.
  4. The backflow prevention device according to claim 3, wherein the radially outer side part of the rear side surface of the at least one annular groove and the radially inner side part of the rear side surface of the at least one piston ring are planes orthogonal to a central axis of the cylinder.
  5. The backflow prevention device according to claim 4, wherein a distance between the radially outer side part and the radially inner side part of the rear side surface of the at least one annular groove is greater than a distance between the radially outer side part and the radially inner side part of the rear side surface of the at least one piston ring.
  6. The backflow prevention device according to claim 3, wherein the radially inner side part of the rear side surface of the at least one annular groove and the radially inner side part of the rear side surface of the at least one piston ring are inclined relative to a central axis of said cylinder.
  7. The backflow prevention device according to any one of claims 1 to 6, wherein the at least one piston ring includes an accommodated portion that is accommodated in the at least one annular groove and an outer peripheral surface that is located radially outside the at least one annular groove, and a rearward end of the outer peripheral surface in the injection direction is forward in the injection direction relative to a rearward end of the accommodated portion in the injection direction.
  8. The backflow prevention device for the injection apparatus according to claim 7, wherein a surface that connects the rearward end of the outer peripheral surface and the rearward end of the accommodated portion comprises: a cylindrical surface whose central axis is the central axis of the cylinder; and an inclined surface that connects a forward end of the cylindrical surface in the injection direction and the rearward end of the outer peripheral surface and that is inclined relative to the central axis of the cylinder.
  9. The backflow prevention device for the injection apparatus according to claim 7, wherein all of a surface that connects the rearward end of the outer peripheral surface and the rearward end of the accommodated portion is inclined with respect to the central axis of the cylinder.
  10. The backflow prevention device for the injection apparatus according to claim 8 or 9, wherein an outermost portion of the rearward end of the accommodated portion in a radial direction is located at approximately the same position as an opening of the annular groove in the radial direction.
  11. The backflow prevention device for the injection apparatus according to claim 8 or 9, wherein an outermost part of the rearward end of the accommodated portion in a radial direction is inside the annular groove.
  12. The backflow prevention device for the injection apparatus according to any one of claims 1 to 11, wherein the at least one annular groove and the at least one piston ring each include a front side surface in the injection direction, and wherein the front side surface of the at least one annular groove and the front side surface of the at least one piston ring can contact each other only at their respective radially inner portions.
  13. The backflow prevention device for the injection apparatus according to any one of claims 1 to 11, wherein an inner diameter of the piston ring is larger at a rear part in the injection direction than at a front part in the injection direction.
  14. An injection apparatus comprising: a backflow prevention device according to any one of claims 1 to 13; the cylinder; a screw accommodated in the cylinder; and an injection nozzle attached to a tip of the cylinder.

Description

Technical Field This application is based on and claims priority to Japanese Patent Application No. 2023-108728, filed June 30, 2023, which is incorporated herein by reference in its entirety. The present invention relates to a backflow prevention device and to an injection apparatus provided with same. Background of Art An injection apparatus for an injection molding machine is provided with a backflow prevention device that prevents backflow of the material to be injected during injection. Japanese Patent Application Laid-Open No. 7-314510 describes an injection apparatus having a screw accommodated in a cylinder, a pusher attached to the screw, and a backflow prevention device provided between the screw head of the screw and the pusher. When the screw moves forward during injection, the backflow prevention device is pressed against the pusher, preventing the material to be injected from flowing behind the pusher. The backflow prevention device includes a backflow prevention ring and a piston ring fitted into the backflow prevention ring. Summary of Invention The piston ring is provided for the purpose of improving sealability between the backflow prevention device and the cylinder. However, because the screw moves at high speed during injection, the piston ring may deform and enter the gap between the backflow prevention ring and the cylinder. In this case, not only will the piston ring wear out, but the cylinder may be damaged by the piston ring that has entered the gap between the backflow prevention ring and the cylinder. An object of the present invention is to provide a backflow prevention device that impedes the entry of a piston ring into the gap between the backflow prevention ring and the cylinder. . The backflow prevention device of the present invention includes a backflow prevention ring with an annular groove and a piston ring fitted in the annular groove. A rear side surface of the annular groove in an injection direction and a rear side surface of the piston ring in the injection direction can come into contact with each other only at their respective radially inner portions. According to the present invention, a backflow prevention device can be provided that impedes the entry of the piston ring into the gap between the backflow prevention ring and the cylinder. The above and other objects, features, and advantages of the present invention will become apparent from the following detailed description with reference to the accompanying drawings that illustrate examples of the present invention. 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 part A of Fig. 1.[Fig. 3A] Fig. 3A is an enlarged view of part B in Fig. 2.[Fig. 3B] Fig. 3B is an enlarged view of part C in Fig. 2.[Fig. 4] Fig. 4 is a cross-sectional view taken along line 4-4 of Fig. 3A.[Fig. 5] Fig. 5 is an enlarged view of a part corresponding to part B of Fig. 2 in a second embodiment.[Fig. 6] Fig. 6 is an enlarged view of a part corresponding to part B of Fig. 2 in a third embodiment.[Fig. 7] Fig. 7 is an enlarged view of a part corresponding to part B of Fig. 2 in a fourth embodiment.[Fig. 8] Fig. 8 is an enlarged view of a part corresponding to part B in Fig. 2 in a fifth embodiment.[Fig. 9] Fig. 9 is an enlarged view of a part corresponding to part B of Fig. 2 in a sixth embodiment.[Fig. 10] Fig. 10 is an enlarged view of a part corresponding to part B of Fig. 2 in a seventh embodiment.[Fig. 11A] Fig. 11A is an enlarged view of a part corresponding to part B in Fig. 2 in a comparative example.[Fig. 11B] Fig. 11B is a diagram illustrating a problem in the comparative example. Description of the Embodiments Embodiments of the present invention will be described below with reference to the drawings. The present invention can be suitably applied to a metal injection molding machine, and in particular to a metal injection molding machine that injects metals that have low viscosity when molten. However, the present invention can also be applied to an injection molding machine that injects resin. In the following description, the X-direction refers to the axial direction of cylinder 32, the injection direction being called the +X-direction, and the direction opposite to the injection direction being called the -X-direction. Terms such as "forward," "backward," "front," "rear," etc. are defined with respect to the injection direction. The term "radial direction" is defined with respect to central axis CL of cylinder 32. First Embodiment Overall Configuration of Injection Molding Machine Fig. 1 shows a schematic front view of injection molding machine 1 according to the first embodiment. Injection molding machine 1 is a horizontal metal injection molding machine that injects molten metal such as magnesium alloys and aluminum alloys. Injection molding machine 1 is schematically composed of mold clamping dev