JPH11245274A - Control of resin pressure of leading end of plasticizing cylinder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel method for controlling the resin pressure at the leading end of a plasticizing cylinder to reduce the irregularity of the injection wt. of an injection molding machine. SOLUTION: The leading end resin pressure immediately after the completion of the plastification by the plastifying cylinder 2 of an injection molding machine is detected by a resin pressure sensor 10 and reduced to a pressure set by a resin pressure setting device in cooperation with a plasticizing back pressure of an injection cylinder 4. At this time, the leading end resin pressure after the plastification of the plasticizing cylinder 2 is set to a value minimizing the irregularity of an injection wt. per one shot.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the resin pressure at the tip of a plasticizing cylinder of an injection molding machine.

[0002]

2. Description of the Related Art As one of the performance evaluations of an injection molding machine, there is a method of measuring the variation of the injection weight per shot.

Conventionally, immediately after plasticization is completed, hydraulic pressure is applied to the front chamber of the injection cylinder to forcibly retract the screw.
With the sock back amount of so-called suck back,
By controlling the resin pressure at the tip of the plasticizing cylinder, variations in the injection weight were reduced.

[0004]

However, in the tip resin pressure control described in the prior art, if the suckback amount is too large, the tip resin pressure of the plasticizing cylinder drops too much and the check valve during injection closes. The time it takes to close (close time) becomes longer. The closing time of the check ring is defined as the time when the screw is advanced at the time of injection so that the resin pressure on the front side of the check ring is greater than the resin pressure on the rear side of the check ring, and the check ring is retracted and closed. The lower the pressure, the more the screw is stroked (the longer the time required), and the more the check valve closes, and the greater the amount of resin movement before and after the check valve from the start of the closure to the end of the closure. In addition, the variation in the amount of resin movement increases.

If the suck-back amount is too small, for example, zero, the resin before and after the check valve does not move at the end of plasticization, and the resin pressure on the rear side of the check valve> the resin pressure on the front side of the check valve. This makes it difficult to close the check ring. In the early stage of the injection process, the resin filling pressure in the mold can be low, so that the screw moves forward without closing the check valve (while the resin pressure on the rear side of the check valve prevents the resin from flowing backward). As a result, variation in the amount of resin movement increases.

FIG. 4 shows experimental data showing a tendency of the correlation between the suck-back amount and the injection weight variation. As shown in the figure, if the suckback amount is too large or too small, the injection weight variation becomes large.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a novel resin pressure control method for the tip of a plasticizing cylinder which reduces the variation in the injection weight of an injection molding machine. And

[0008]

The present invention has solved the above problems as follows. That is, immediately after the plasticization of the plasticizing cylinder of the injection molding machine, the tip resin pressure is reduced to a predetermined pressure in correlation with the plasticizing back pressure of the injection cylinder. At this time, the tip resin pressure after plasticization of the plasticizing cylinder is set to a value that minimizes the variation in the injection weight per shot.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments with reference to the drawings.

The present inventors have determined from various experimental results that the resin pressure at the tip of the plasticizing cylinder immediately after the plasticization ends depends on the structure and size of the plasticizing device of the injection molding machine and the resin temperature conditions. It has been clarified that by reducing the pressure in correlation with the plasticizing back pressure of the injection cylinder, the closing performance of the check ring provided at the screw tip can be improved. The plasticizing back pressure is obtained by applying a certain pressure to the rear chamber of the injection cylinder and retreating the screw while giving resistance while the screw is retreating (during plasticization), thereby kneading the plasticized resin. Refers to the hydraulic pressure to promote.

An apparatus used in the method for controlling the resin pressure at the tip of a plasticizing cylinder according to the present invention will be described.

FIG. 1 is a schematic structural view of a plasticizing device of a general injection molding machine. As shown in the figure, a screw 3 is provided in a plasticizing cylinder 2 having a nozzle 1 at the tip.
It is provided so as to be able to move back and forth by hydraulic pressure acting on the front chamber 5 and the rear chamber 6 of the injection cylinder 4 connected to the screw rear end 3a.

As shown in FIG. 2, an annular check valve 7 is mounted at the tip of the screw 3 so as to be movable back and forth by a screw head 8 screwed to the tip of the screw 3. A resin passage 9 is formed between the inner wall of the check ring 7 and the outer wall of the screw head 8, and is configured to open when the check ring 7 moves forward and close when retracting.

In this embodiment, a resin pressure sensor 10 for measuring the resin pressure at the tip of the plasticizing cylinder 2 immediately after the plasticization is completed is provided at the tip of the plasticizing cylinder 2, and the resin pressure at the tip of the plasticizing cylinder 2 is set. A resin pressure setting device (not shown) is provided on a machine operation panel, and the plasticization cylinder 2 immediately after the plasticization is completed using the resin pressure sensor 10, the resin pressure setting device and a known plasticization back pressure control circuit. Controls tip resin pressure.

The resin pressure setting device and the resin pressure sensor 10 are
The resin pressure at the tip of the plasticizing cylinder 2 corresponding to a value obtained by multiplying the plasticizing back pressure by a coefficient smaller than 1 (varies depending on the structure and size of the plasticizing device, specifications, resin temperature conditions, type of resin, etc.) Set and detect.

Next, control of the resin pressure at the tip of the plasticizing cylinder will be described.

The screw 3 controls the back pressure during the plasticization, which is controlled by the known plasticizing back pressure control circuit, by the screw 3 (the plasticization is completed).
When the pressure drops to the position indicated by the arrow, the pressure starts to be reduced, and when the pressure drops to the resin pressure at the tip of the plasticizing cylinder 2 set on the resin pressure setting device, the pressure is reduced by a method such as closing an electromagnetic valve in the plasticizing back pressure control circuit. Stop descending. The tip resin pressure of the plasticizing cylinder 2 after plasticization is set to a value that minimizes the variation in the injection weight per shot.

Next, another embodiment will be described.

In the present embodiment, as shown in FIG. 3, the plasticizing back pressure control circuit does not include a resin pressure sensor and a resin pressure setting device as in the previous embodiment. In addition to the middle back pressure setting device 11, the back pressure setting device 1 after plasticization after plasticization
2 are provided.

An electric sequence configured to reduce the plasticizing back pressure during plasticization even after the plasticization is completed, and a pressure control valve 13 normally used in a plasticizing back pressure control circuit are used in combination. By lowering the plasticizing back pressure during plasticization of the injection cylinder 4 via the electromagnetic valve 14 with the flow control valve to the pressure set in the post-plasticizing back pressure setting unit 12 after plasticization is completed, Improve closing performance.

[0021]

According to the present invention, the resin pressure at the tip of the plasticizing cylinder immediately after the plasticization is completed is reduced to a value that minimizes the variation in injection weight by correlating with the plasticizing back pressure of the injection cylinder. The closing performance of the check ring provided at the tip can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a plasticizing device of a general injection molding machine used in an embodiment of the present invention.

FIG. 2 is a configuration diagram of a general check valve;

FIG. 3 is a plasticizing back pressure control circuit according to another embodiment of the present invention.

FIG. 4 shows experimental data showing a correlation tendency between the suckback amount and the injection weight variation.

[Explanation of symbols]

 Reference Signs List 1 nozzle 2 plasticizing cylinder 3 screw 3a screw rear end 4 injection cylinder 5 front chamber 6 rear chamber 7 check valve 8 screw head 9 resin passage 10 resin pressure sensor 11 back pressure setting device during plasticization 12 back pressure setting device after plasticization 13 Pressure control valve 14 Solenoid valve with flow control

Claims (3)

[Claims] 1. A plastic pressure at the tip of a plasticizing cylinder (2) of an injection molding machine is reduced to a predetermined pressure immediately after the plasticization is completed, in correlation with a plasticizing back pressure of an injection cylinder (4). A method for controlling the resin pressure at the tip of a plasticizing cylinder of an injection molding machine. 2. Immediately after the plasticization is completed, the resin pressure at the tip of the plasticizing cylinder (2) is detected by a resin pressure sensor (10) and reduced to a pressure set by a resin pressure setting device. Item 3. A method for controlling the resin pressure at the tip of a plasticizing cylinder of an injection molding machine according to Item 1. 3. The injection molding according to claim 1, wherein immediately after the plasticization is completed, the back pressure after the plasticization of the injection cylinder is reduced to the pressure set in the back pressure setting device after the plasticization. For controlling the resin pressure at the tip of the plasticizing cylinder of the machine.