JP2547242Y2 - Backflow prevention ring of injection molding machine - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backflow prevention ring mounted on a screw provided in a heating cylinder of an injection molding machine so as to be able to rotate and move straight.

[0002]

2. Description of the Related Art As is well known, an injection molding machine comprises a heating cylinder and a screw provided in the cylinder so as to rotate and move straight. In the measuring stroke, when the screw is driven to rotate, the synthetic resin material falls from the hopper to the valley of the screw and is fed to the nozzle along the valley. It is compressed in the middle of being sent, is heated and melted by the heating cylinder, and accumulates in the nozzle. When the molten resin accumulates, the screw
The amount of resin required for one cycle is measured by the amount of retreat. In the case of an injection stroke, the screw moves forward with a piston cylinder unit or the like as the role of a piston. Then, the molten resin is injected from the nozzle into the mold.

As described above, in an injection molding machine, a high-pressure molten resin is processed not only by an injection stroke but also by a measuring stroke, so that the resin passes between a heating cylinder and a screw. It may flow backward. When a backflow occurs, the amount measured by the measuring stroke is not injected, and a predetermined injection amount important for molding cannot be obtained. Therefore, a backflow prevention ring is provided.

The backflow prevention ring is generally attached to a screw head provided at the tip of the screw, and prevents the backflow of the molten resin as described above. However, with the conventional backflow prevention ring,
For example, in order to completely prevent backflow, it is known that the outer peripheral surface of the ring and the inner peripheral surface of the heating cylinder are dense, but the ring contacts the inner peripheral surface of the cylinder under high pressure, high temperature and high speed. Rotation and sliding caused metal contact, abrasion and seizure caused so-called resin burn. Also, avoiding metal contact as a measure to prevent this seizure, that is, increasing the distance between the outer peripheral surface of the ring and the inner peripheral surface of the cylinder can solve the problem of wear and seizure, but the original function of preventing backflow As a result, a stable injection amount could not be obtained.

The applicant of the present invention has disclosed in Japanese Utility Model Laid-Open Publication No. 63-7513 that a plurality of through holes extending from the inner peripheral surface to the outer peripheral surface are formed in the backflow prevention ring to prevent the backflow of the molten resin and to prevent burning and abrasion. Proposed a technology to prevent Although the above technique is effective, the formation of a lubricating film between the outer peripheral surface of the backflow prevention ring and the inner peripheral surface of the cylinder is insufficient, and seizure occurs.

In particular, since the screw of the injection molding machine performs a rotational movement and a linear movement in the axial direction during operation, it is conventionally difficult to prevent the molten resin from flowing backward and to prevent seizure in any of the movements. there were.

[0007]

[Problem to be solved by the present invention]
Irrespective of whether the screw of the injection molding machine performs rotational motion or linear motion, a lubricating film of molten resin can be suitably formed between the outer peripheral surface and the inner peripheral surface of the cylinder, and the backflow can be completely prevented. It is an object of the present invention to provide a backflow prevention ring for a molding machine.

[0008]

According to the present invention, there is provided a backflow prevention ring mounted on a screw head at the tip of a screw provided so as to be capable of rotating and moving straight in a heating cylinder of an injection molding machine. The backflow prevention ring is provided with a gap between its outer peripheral surface and the inner peripheral surface of the heating cylinder where a coating of a molten resin necessary for lubrication can be formed, and a plurality of recesses are formed in a staggered manner on the outer peripheral surface, The recess has a bottom surface formed by a partial spherical surface and a curved surface smoothly continuing from the bottom surface to the outer peripheral surface.

Preferably, the backflow prevention ring is provided on the screw head so as to be movable in the axial direction.

[0010]

[0011]

[0012]

[Explanation of the operation and effect] Since the bottom surface of the concave portion is formed by a partial spherical surface, its planar shape is circular, and even if the screw rotates or moves straight, the concave portions arranged in a staggered manner are screwed. The outer peripheral surface and the concave portion always pass on the inner peripheral surface of the cylinder alternately with respect to the moving direction. Therefore,
Backflow of the resin is prevented by the outer peripheral surface and the inner peripheral surface of the cylinder, and the lubricating film can be reliably formed on the outer peripheral surface by the molten resin accumulated in the concave portion.

Since the bottom of the concave portion is continuous with the outer peripheral surface with a smooth curved surface, the molten resin accumulated in the concave portion smoothly lubricates the outer peripheral surface when the screw moves. As described above, according to the present invention, it is possible to follow any movement of the screw, and simultaneously achieve the two previously difficult objects of forming a lubricating film to prevent backflow at the same time.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, a cylinder 1 heated by a band heater or the like has a cylindrical shape like a conventional one, and a nozzle 2 is formed at the left end thereof. As is well known, the screw 3 is rotatably driven by an electric motor or a hydraulic motor (not shown) and is provided so as to be able to move forward by a piston cylinder unit or the like. A screw head 4 is screwed to the tip of the screw 3 with a screw 5. The diameter of the screw head 4 is smaller than the diameter of the screw 3. Therefore, the screw 3 has a step, that is, an end face 6. The screw head 4 has an end face 7 which presses against the backflow prevention ring 8 in the measuring stroke.

The backflow prevention ring 8 includes a screw head 4
The screw head 4 is provided so as to be able to move in the axial direction and to rotate together with the screw head 4 by a projection 8a engaging with the plate-shaped portion 4a. The end face 8b is regulated by the end face 7 of the head during the measuring stroke moving to the nozzle 2 side, and the end face 8c is regulated by the end face 6 of the screw 3 during the injection stroke moving to the screw 3 side. It is supposed to be. That is, there is no restriction on the rotation direction, and the screw rotates together with the screw. A gap S sufficient to form a molten resin film is formed between the outer peripheral surface of the backflow prevention ring 8 and the inner peripheral surface of the heating cylinder 1 both during co-rotation and during axial movement. ing.

As shown in FIG. 1, a plurality of recesses 9 are formed in the outer peripheral surface of the backflow prevention ring 8 in a staggered manner. The shape of the recess 9 is as shown in FIG.
A bottom surface 9a formed by a partial spherical surface is connected to the outer peripheral surface of the ring 8 by a smooth curved surface 9b in all directions.

Next, the operation will be described. At the time of the measuring stroke, the end face 8b of the ring 8 is pressed against the end face 7 of the screw head 4 by the flow of the molten resin toward the nozzle portion 2, the molten resin flows into the gap S from between the end faces 6, 8c, and the lubricating film is formed. It is formed. Since the pressure of the molten resin is not high in this measuring stroke, the amount of resin flowing in the gap S is small, but a lubricating film is also formed from the molten resin filled in the concave portions 9, 9,... During the injection stroke. A sufficient amount to be supplied.

During the injection stroke, the end face 8c of the ring 8 is pressed against the end face 6 of the screw 3 to prevent the resin from flowing backward. At this time, since the pressure is high, the molten resin flows to the gap S to such an extent that there is no problem in practical use, a new lubricating film is always formed, and the concave portions 9 are filled with the molten resin.

[0020]

[Effects of the Invention] As described above, according to the present invention, the following excellent effects can be obtained. (A) Since the concave portions are arranged in a staggered manner, a lubricating film can be suitably formed on the outer peripheral surface for both rotation of the screw and linear movement in the axial direction. (B) Since the portion of the outer peripheral surface where there is no recess is continuous, backflow is reliably prevented. (C) The molten resin accumulated in the concave portion can easily lubricate the outer peripheral surface with a smooth curved surface.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an embodiment of the present invention.

FIG. 2 is a side sectional view showing a shape of a concave portion.

[Explanation of symbols]

 S ··· gap 1 ··· cylinder 2 ··· nozzle section 3 ··· screw 4 ··· screw head 4a ··· plate-shaped part 5 ··· screw 6 ··· screw end face 7 ··· End surface of screw head 8 Backflow prevention ring 8a Projection 8b, 8c End surface of backflow prevention ring 9 Depression 9a Bottom surface of depression 9b Curved surface

Claims (1)

(57) [Scope of request for utility model registration] 1. A backflow prevention ring attached to a screw head at a tip of a screw provided so as to be capable of rotating and moving straight in a heating cylinder of an injection molding machine. A gap is formed between the inner peripheral surface of the cylinder and a film of a molten resin necessary for lubrication, and a plurality of concave portions are formed on the outer peripheral surface in a staggered manner, and the concave portions are formed as partial spherical surfaces. A backflow prevention ring for an injection molding machine, comprising a bottom surface and a curved surface smoothly continuing from the bottom surface to the outer peripheral surface.