JP3291156B2 - Backflow prevention device for 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 presser provided at the tip of a screw, and a backflow prevention ring provided at an outer peripheral portion of the presser so as to be radially separated and movable in the axial direction. In the backflow prevention ring, the pressure receiving surface at the tip of the ring comes into contact with the screw head attached to the tip of the screw during metering, and at the time of injection, the sheet surface at the rear end comes into contact with the seat of the pusher to prevent the backflow of the injection material. The present invention relates to a backflow prevention device for an injection molding machine that is to be prevented.

[0002]

2. Description of the Related Art An injection molding machine, for example, an in-line screw type injection molding machine is well known without mentioning a document name, and is constituted by a cylinder and a screw which is rotated and axially driven in the cylinder. I have. Such a backflow prevention device for an injection molding machine is also well known in the art, and as shown in FIG. 2, a presser B having the same thickness attached to the tip of a screw A, and similarly formed to the same thickness. Back ring C, a screw head D with a presser B attached to the screw A, and the like. A seat E is formed at the rear end of the presser B. Further, the backflow prevention ring C is movable in the axial direction with respect to the pusher B, and a seat surface F is formed on the pusher B side, that is, at the rear end portion, to be seated on the seat E of the pusher B at the time of injection and pressure holding. . Therefore, when the screw A is rotationally driven to knead, melt, and accumulate the material, the sheet surface F of the backflow prevention ring C is moved from the seat E of the pusher B as shown in FIG. The separated molten material passes through the separated gap, the gap G between the outer peripheral surface of the presser B and the inner peripheral surface of the backflow prevention ring C, and the notch H formed in the screw head D, and the leading end of the screw A Can be accumulated. Also, when driving the screw A in the axial direction to inject it into the mold cavity and maintain the pressure,
As shown in FIG. 2B, the backflow prevention ring C
Is seated on the seat E of the presser B, and the molten material is prevented from flowing back toward the screw portion. In this backflow prevention device, the backflow prevention ring C engages with the rear end surface of the screw head D at the time of weighing, and the backflow prevention ring C rotates together with the screw A. Is known as a non-co-rotating type in which the roller does not rotate by sliding on the rear end face of the screw head D.

[0003]

Even when the screw A is driven in the axial direction to perform injection and pressure holding by the above-described conventional injection machine, the seat surface F of the backflow prevention ring C is seated on the seat E of the pusher B. In addition, it is possible to prevent the molten material from flowing back toward the screw portion. However, there are problems. For example, as is clear from the above description, in the measuring step, in order to increase the measuring efficiency of the injection material,
It is desirable that the gap between the seat surface F of the backflow prevention ring C and the seat E of the pusher B, that is, the movement stroke of the backflow prevention ring C be large. On the other hand, in order to reduce the backflow of the material during the injection process, the time required for the seat surface F of the backflow prevention ring C to be seated on the seat E of the presser B is short, that is, the movement stroke of the backflow prevention ring C is smaller. Is desirable. As described above, it is necessary to satisfy two contradictory issues in the backflow prevention device. However, materials having low melt viscosity such as low melting point metal materials such as magnesium alloy, aluminum alloy, lead alloy and zinc alloy, nylon, polyester, etc. However, the above-mentioned resin material cannot satisfy the above-mentioned problem, and has a large reverse flow rate of the injection material toward the screw portion. This is because the area of the pressure receiving surface C ′ of the backflow prevention ring C is small, the force of pressing the sheet surface F against the seat E of the presser B by the injection pressure is weak, and the outer peripheral surface of the presser B and the inner peripheral surface of the backflow prevention ring C are also small. Is large, and a large amount of injection material reaches between the sheet surface F and the seat E and flows backward. If the reverse flow rate is large, the set molding conditions such as the measured value, the injection speed, the injection / holding pressure, and the like are not accurately transmitted to the molded product, and molding defects such as sink marks, voids, short shots, and weld lines are generated. Therefore, an object of the present invention is to provide a backflow prevention device for an injection molding machine having a high backflow rate toward a screw portion, even when a material having a high melt measuring efficiency and a low melt viscosity is injected. .

[0004]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a backflow preventing element at the tip of a screw, and a predetermined gap in the radial direction with the outer peripheral surface of the backflow preventing element. It comprises a backflow prevention ring movably provided, and a screw head attached to the tip of the screw, wherein the backflow prevention ring has a pressure-receiving surface at the tip abutting on the screw head at the time of measurement, and at the time of injection. In a backflow prevention device in which a seat surface portion at a rear end is seated on a seat portion of the backflow prevention element to prevent backflow of the injection material, an inner peripheral surface of the backflow prevention ring that is more distal than a seat surface portion of the backflow prevention ring. wherein the outer peripheral surface of the distal end side of the seat of the backflow prevention element, said toward the screw head side and have smaller angle than the taper angle of the seat surface portion and the seat portion reduced in diameter in a tapered shape Configured so that. According to a second aspect of the present invention, the backflow preventing element according to the first aspect is formed separately from the screw, and is constituted by a pusher attached to a tip end portion of the screw by a screw head. In the invention, the backflow prevention device according to claim 1 or 2 is applied to an injection material having a melt viscosity of 0.01 to 1000 poise.

[0005]

As is well known in the art, the screw is rotated to melt the material and accumulate it in front of the cylinder. During this measuring step, the backflow prevention ring moves forward by being pushed by the molten material, and the pressure receiving surface at the tip comes into contact with the screw head.
Since the backflow prevention ring moves forward, the seat surface of the backflow prevention ring is separated from the backflow prevention element, for example, the seat of the presser, and a gap is generated between the seat surface of the backflow prevention ring and the seat of the presser. Is accumulated in the front of the cylinder from this gap through the space between the outer peripheral surface of the presser and the inner peripheral surface of the backflow prevention ring. Next, the screw is driven in the axial direction to inject it into, for example, a cavity of a mold and hold the pressure. During the injection step, the reaction force of the injection pressure acts on the pressure receiving surface of the backflow prevention ring, and the backflow prevention ring moves rearward. Then, the seat surface is seated on the seat of the presser. Thereby, the backflow of the injection material to the screw portion is prevented.

[0006]

Embodiments of the present invention will be described below. FIG. 1A is a cross-sectional view showing a backflow prevention device according to the present embodiment at the time of measurement. As shown in FIG. It is composed of an attached presser 10, a backflow prevention ring 20 provided concentrically with the presser 10, a screw head 30 for fixing the backflow prevention ring 20 to the tip of the screw 2, and the like. As is well known, the screw 2 is provided inside the cylinder 1 so as to be freely rotatable and axially drivable. The left end portion in the figure has a predetermined length reduced in diameter from the screw shaft 3 by the step portion 4. The mounting shaft 5 is provided. At the center of the mounting shaft 5, a female screw 6 is formed in the axial direction from the tip.

The presser 10 is mounted on the mounting shaft 5 of the screw 2 and cooperates with a backflow prevention ring 20 described later to prevent the backflow of the injection material, and has an outer taper much smaller than the inner diameter of the cylinder 1. It is roughly composed of a portion 11 and a ring-shaped convex portion 12 having a larger diameter than the maximum diameter portion of the tapered portion 11. That is, a ring-shaped convex portion 12 is provided at a position of the presser 10 that is close to the step portion 4 of the screw 2. The convex portion 12 has a slope so that the flow of the molten material is improved.
The seat 13 is provided. The tapered portion 11 having a predetermined length is tapered from the seat portion 13 toward the front.

The backflow prevention ring 20 is formed in a substantially cylindrical shape from a tapered portion 21 on the inner peripheral side, a pressure receiving surface 22 perpendicular to the front axis, and a seat surface 23 oblique to the rear axis. ing. The taper portion 21 of the backflow prevention ring 20 is
And have the same taper angle as a pair.
Since the backflow prevention ring 20 has the tapered portion 21 as described above, the area of the pressure receiving surface 22 at the front end of the backflow prevention ring 20 is increased, and the area of the seat surface 23 at the rear end is reduced. The inner diameter of the tapered portion 21 of the backflow prevention ring 20 is larger than the outer diameter of the tapered portion 11 of the presser 10 by a predetermined amount. Further, there is a gap between the outer peripheral surface of the backflow prevention ring 20 and the inner peripheral surface of the cylinder 1, and the backflow prevention ring 20 is shorter than the tapered portion 11 of the presser 10 by a predetermined amount. Therefore, the backflow prevention ring 20 can be moved in the front-back direction of the shaft by being pushed by the molten material by a short amount.

The screw head 30 includes a backflow prevention ring 2
0 has a rear end face 31 with which it abuts. In addition, a plurality of notched passages 32, 3 and 3 through which the molten material passes during measurement are provided.
2, ..., and a through hole for bolt insertion is formed at the center. Therefore, when the pusher 10 is mounted on the mounting shaft 5 of the screw 2, the backflow prevention ring 20 is inserted, the mounting bolt 33 is screwed into the female screw 6 of the screw 2, and the screw head 30 is fixed. Assembled as shown in

Next, a material having a low melt viscosity, for example, a low melting point metal material such as a magnesium alloy, an aluminum alloy, a lead alloy, or a zinc alloy, or a resin material such as nylon or polyester is injected by the injection molding machine of the above embodiment. An example will be described. The cylinder 1 is heated to a temperature suitable for the injection material, and the screw 2 is rotationally driven to plasticize. Since the screw 2 is driven to rotate, the molten material is pushed forward,
The backflow prevention ring 20 is also pushed forward by the molten material.
As a result, as shown in FIG. 1A, the pressure receiving surface 22 of the backflow prevention ring 20 comes into contact with the rear end surface 31 of the screw head 30, and the seat surface 23 comes into contact with the seat portion 13 of the presser 10.
Separate from. Therefore, the molten material is applied to the sheet surface 23.
Of the cylinder 1 through the gap between the tapered portion 11 of the pusher 10 and the tapered portion 21 of the backflow prevention ring 20 and the notched passages 32, 32,... Of the screw head 30. A predetermined amount of the molten material is accumulated and measured in the front measuring chamber. The screw 2 retreats as it is accumulated.

At the time of this weighing, the tapered portion 11
Since the diameter of the tapered portion 21 of the backflow prevention ring 20 is reduced toward the distal end, when the seat surface 23 of the backflow prevention ring 20 separates from the seat 13 of the presser 11, the presser 10
The passage 15 between the tapered portion 11 of the backflow preventing ring 20 and the tapered portion 11 of the backflow prevention ring 20 is widened. Therefore, the flow of the molten material is improved.

After the predetermined amount is measured, the screw 2 is driven in the axial direction as is well known, and is injected into a mold to hold the pressure. At this time, the pressure of the injection material to be injected and held acts on the pressure receiving surface 22 of the backflow prevention ring 20 as shown by the arrow in FIG. Therefore, the backflow prevention ring 20 is pushed rearward. As a result, the backflow prevention ring 20
Is seated on the seat 13 of the presser 10. Therefore, the sheet surface 23 of the backflow prevention ring 20 and the pusher 10
The injection material does not flow back toward the screw 2 from between the seat 13 of FIG.

At the time of injection, the area of the pressure receiving surface 22 of the backflow prevention ring 20 is large because the inner peripheral portion of the backflow prevention ring 20 is a tapered portion 21. Therefore, the reaction of the injection pressure of the molten material immediately acts, and the seat surface 23 of the backflow prevention ring 20 is seated on the seat 13 of the presser 10 at high speed. Also, since the area of the pressure receiving surface 22 is large, the seat surface 2
The force for pressing 3 against the seat 13 of the presser 10 is also large. Moreover, since the area of the seat surface 23 of the backflow prevention ring 20 is small, the pressure per unit area to be pressed is large. The passage 15 between the tapered portion 11 of the presser 10 and the tapered portion 21 of the backflow prevention ring 20 is narrowed this time. Therefore, backflow of the molten material is effectively prevented.

In the above embodiment, the presser 10 is provided separately from the screw 2. However, it is apparent that the presser 10 can be formed integrally with the screw 10. Although the figure shows a non-corotating backflow prevention device in which the pressure receiving surface 22 of the backflow prevention ring 20 simply slides on the rear end surface 31 of the screw head 30, a tongue piece is attached to the tip of the backflow prevention ring 20. On the other hand, a groove is formed in the screw head 30 in the axial direction, and the tongue and the groove are engaged with each other to
Can rotate with the screw head 30.

Example 1: An outer diameter of 66 mm, a maximum inner diameter of 48.5 mm, a length of 40 mm, and a taper angle of 1
5 ° backflow prevention ring and the maximum outer diameter of the tapered portion are 42.
A stamper having a length of 5 mm, an axial length of the tapered portion of 45 mm, and a taper angle of 15 ° was manufactured. Then, a test piece was molded under the following molding conditions. Model used: Injection molding machine with 450-ton mold clamping force Molding material: Magnesium alloy AZ91D Molding temperature: 590 ° C Injection pressure: 155 MPa Holding pressure: 60 MPa Injection speed: 2.5 m / sec Under the above conditions, length 150 mm, width 100mm, thickness 2m
m-shaped test pieces were molded. As a result, molding defects such as sink marks, voids, and weld lines were not observed.

[0016]

As described in detail above, the backflow prevention device according to the present invention comprises a backflow prevention element, for example, a pusher, a backflow prevention ring, and a screw head at the tip of the screw. the outer peripheral surface of the distal end side of the seat portion of the inner peripheral surface and the backflow prevention element on the distal end side, said toward the screw head side, at an angle not smaller than the seat surface portion and the taper angle of the seat <br/> Since the diameter is reduced in a tapered shape, the distance between the inner peripheral surface of the backflow prevention ring and the outer peripheral surface of the backflow prevention element at the time of measurement increases, and the measurement efficiency of the molten material increases. Also, during the injection process, the area of the pressure receiving surface of the backflow prevention ring is wide because the inner peripheral surface of the backflow prevention ring is tapered , and the reaction force of the injection pressure acts immediately, and the speed of the backflow prevention ring is high. The seat surface sits on the seat of the backflow prevention element. Also, because the area of the pressure receiving surface is large,
The force for pressing the seat surface against the seat of the backflow prevention element is also large. In addition, since the backflow prevention ring moves rearward, the passage between the outer peripheral surface of the backflow prevention element and the inner peripheral surface of the backflow prevention ring is narrowed. By the above-described overall action, an effect peculiar to the present invention that the backflow of the molten material is effectively prevented is obtained.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of the present invention, in which (a) is a cross-sectional view showing a state during a measuring step, and (b) is a cross-sectional view showing a state during an injection step.

FIGS. 2A and 2B are diagrams showing a conventional example, in which FIG. 2A is a cross-sectional view showing a state during a measuring step, and FIG. 2B is a cross-sectional view showing a state during an injection step.

[Explanation of symbols]

1 cylinder 2
Screw 10 Pusher 11
Tapered part 13 Seat part 20
Backflow prevention ring 21 Taper portion 22
Pressure receiving surface 23 Seat surface 30
Screw head

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B29C 45/00-45/84

Claims (3)

(57) [Claims] 1. A backflow preventing element (10) for a screw tip.
A backflow prevention ring (20) which has a predetermined gap in the radial direction with respect to the outer peripheral surface of the backflow prevention element (10) and is provided so as to be movable in the axial direction, and which is attached to the tip of the screw (2). The backflow prevention ring (20) has a pressure receiving surface portion (22) at the tip thereof abutting against the screw head (30) during measurement, and a sheet surface portion (23) at a rear end thereof during injection. ) Is seated on the seat portion (13) of the backflow prevention element (10) to prevent backflow of the injection material, wherein the seat surface portion (23) of the backflow prevention ring (20) is provided. more seat portion of the inner peripheral surface of the tip end (21) and the backflow prevention element (10) (13) from the distal end side outer peripheral surface (11), said towards the screw head (30) side, the seat face portion (2
3) and the seat (13) backflow prevention device for an injection molding machine, characterized in that it is reduced in diameter in a tapered shape at not smaller angle than the taper angle of. 2. The backflow prevention element (10) according to claim 1, wherein:
Is a backflow prevention device for an injection molding machine, which is a pusher (10) formed separately from the screw (2) and attached to a tip end of the screw (2) by a screw head (30). 3. A backflow prevention device for an injection molding machine, wherein the backflow prevention device according to claim 1 or 2 is applied to an injection material having a melt viscosity of 0.01 to 1000 poise.