JPH11207794A - Method for preventing backflow in preplasticating type injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a looseness of a valve disc tending to occur in the case of shutting OFF a resin channel due to a contact of the disc with a valve seat by forcibly retreating a screw by a way of retreating operation of the screw. SOLUTION: An injection cylinder 12 in which a plunger 10 is internally mounted communicates with a plasticizing cylinder 22 in which a plasticizing screw 20 is internally rotatably and telescopically mounted via a resin passage 3 provided over an end and the cylinders 12 and 22 are juxtaposed. A screw moving hydraulic cylinder 24 and a rotating motor 25 are provided at a rear part of the cylinder 22. When the plunger 10 is retracted by charging a material by a rotation of the screw 20 and its retracted position arrives at a position immediately before a metering ending position, a rotating speed of the screw 20 is switched to a low speed. Thereafter, the screw 20 is retracted to be moved by a lower pressure than that at the time of opening a valve, and then the valve is closed. After the valve is closed, the screw is stopped, and a backflow of the resin to the plasticizing cylinder side is prevented after the metering is finished.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing backflow in a pre-plastic injection molding machine in which plasticization and injection of resin are performed by different cylinders.

[0002]

2. Description of the Related Art In a pre-plastic injection molding machine, an injection cylinder containing an injection plunger and a plasticizing cylinder containing a screw rotatably are connected side by side by a resin path provided over the tip. After the resin melted and kneaded by the plasticizing cylinder (hereinafter, referred to as plasticizing) is measured (accumulated) at the front of the injection cylinder, the injection is performed by advancing the plunger.

In such a configuration, a part of the metering resin flows back to the plasticizing cylinder due to the injection pressure, and the metering resin is reduced by that amount. It is provided on a road or a resin road.

[0004] As this shutoff means, there is a screw movable type in which the screw is advanced when the measurement is completed, and the screw head is pressed against the inner surface of the tip end portion of the plasticizing cylinder to shut off.
Since the screw is pushed out to shut off, the resin at the front of the screw is fed into the injection cylinder even after the completion of weighing, and the amount of feed is not always constant, so the weighing stop position of the plunger is unstable. Become
It has the disadvantage of causing errors in weighing.

The inventor of the present invention has proposed a method of preventing the resin from flowing back to the plasticizing cylinder side due to the advance of the plunger after the metering. A hydraulic device for screw movement and a motor for rotation are provided at the rear of the cylinder,
The screw was forcibly retracted by hydraulic pressure together with the check valve at the tip to cut off the resin flow path around the valve body (see JP-A-8-183078).

[0006]

In this check valve, the area of the front surface of the valve body of the check valve is larger than the rear surface thereof,
Since there is an area difference, even if the resin pressure during plasticization is higher on the plasticizing cylinder side than on the valve body front side, when the plasticization is stopped, the resin pressure acting on the valve body front is larger, Immediately after the screw stops rotating, if the hydraulic device is operated to the retreat side, the screw retreats with the check valve without being affected by the resin pressure on the plasticizing cylinder side, and shuts off the flow passage around the valve body. The resin on the front side of the valve body does not extrude into the resin path and the resin is not fed into the injection cylinder after metering, preventing excessive metering. The plunger is always stopped at the metering stop position and metered. This has the effect of improving the accuracy.

However, in such a backflow prevention method,
The screw rotation is stopped at the same time as the measurement is completed, and then the screw is forcibly retracted and the valve is closed by high pressure. Acts as a large tensile force on the valve body, which tends to cause loosening of the valve body.If this looseness is left unchecked, the valve closing distance and the flow path dimension at the valve body tip will fluctuate.
Variations occur in the amount of resin sent to the injection device,
Alternatively, the valve closing may become uncertain and a measurement error may occur due to the backflow of the resin.

The present invention has been conceived in order to solve the above-mentioned problem, and has as its object the purpose of closing the valve body by closing the valve even when the resin flow path is cut off by forcibly retracting the screw. Of the present invention is to provide a new method for preventing backflow in a pre-plastic injection molding machine, which can prevent the loosening of the valve element, which tends to occur due to the contact between the valve body and the valve seat.

[0009]

According to the present invention, there is provided an injection cylinder having a plunger therein, and a plasticizing cylinder having a plasticizing screw having a check valve at a tip thereof rotatably and advancing and retracting. Are connected side by side by a resin path provided over the leading end, and a screw moving means and a motor for rotation are provided at the rear of the plasticizing cylinder. When the plunger retreats due to material charging due to the rotation of the screw, and when the retreat position reaches just before the weighing end position, the rotation speed of the screw is switched to a low speed. After that, the valve moves backward at a lower pressure than when the valve is opened, closes the valve, stops screw rotation, and plasticizes the plastic after the end of metering. Made to prevent backflow into da side, is that.

According to another aspect of the present invention, an accumulator is provided in a hydraulic circuit of the plasticizing cylinder, and pressure oil is supplied from the accumulator to the screw moving means to open and close the valve by moving the screw forward and backward. To do that.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings, reference numeral 1 denotes an injection device, 2 denotes a plasticizing device juxtaposed on the injection device, and both devices communicate with each other via a resin path 3 provided at the tip end.

The injection device 1 includes an injection plunger 1.
0, an injection cylinder 12 having a nozzle 11 at its tip, a hydraulic cylinder 13 provided behind the injection cylinder 12, and a member for holding a rear portion of the injection cylinder 12 integrally with the hydraulic cylinder 13. The plunger 10 and the piston 15 of the hydraulic cylinder 13 are connected in the rear part of the holding member 14.

The plasticizing apparatus 2 includes a plasticizing cylinder 22 having a plasticizing screw 20 rotatably mounted therein and having an outflow passage 21 at the center of the inside of a tip member 22a, and holding the plasticizing cylinder 22. Rear end holding cylinder 23
And a hydraulic cylinder 24 for screw advance / retreat integrated with the rear end of the holding cylinder 23 and a hydraulic motor 25 for screw rotation attached to the rear end of the hydraulic cylinder 24.
Consists of

The piston 26 of the hydraulic cylinder 24 is
The rear chamber side is formed to have a smaller diameter than the front chamber side so that the valve can be maintained open by high pressure. A drive shaft 25a of the hydraulic motor 25 is axially movably fitted to the rear chamber side of the piston 26. The piston 26 rotates and moves forward and backward together with the screw 20 connected to the front chamber side. A band heater 27 is attached to the outer periphery of the plasticizing cylinder 22, and a supply hole 28 is provided upward at a rear end of the plasticizing cylinder 22 fitted to the holding cylinder 23.

As shown in detail in FIG. 2, the screw 20 has a mushroom-shaped valve body 29 having a conical front end and a rear end surface formed on an inclined surface with a reduced diameter.
And a screw shaft 30 protruding from the center of the rear end of the valve body 29.
And a valve seat 31 fitted and brazed to the step formed on the inclined surface thereof, the check valve 32 is inserted into the screw shaft 30 through the washer 33, and the screw hole 3 at the tip of the screw is formed.
4 and attached as a screw head.

The inner wall of the tip member 22a where the check ring valve 32 is located is formed on an inclined wall corresponding to the tip of the valve body, and the outflow passage 21 is formed at the center thereof.
Around the valve element 29, a flow path 21a having a required gap communicating with the outflow path 21 is formed between the valve member 29 and the distal end member 22a, and the flow path 21a faces the plasticizing cylinder facing the rear surface of the valve element. An annular valve seat 35 having a sealing surface inclined at the same angle as the rear surface of the valve body is provided.

Although the flow path 21a differs depending on the resin,
When the diameter of the check ring 32 is 36 mm, at least 1.0 mm to 1.5 mm between the check ring 32 and the valve seat 35.
Are preferably formed with a gap of.

The passage 21a is cut off by the screw 2
This is carried out by forcibly retracting the check ring 32 together with 0 and bringing the valve seat 31 on the rear surface of the valve body into contact with the washer 35 against the valve seat 35 (see FIG. 3). Open the screw 2
This is performed by moving the check valve 32 forward along with the valve seat 31 to separate the valve seat 31 from the valve seat 35 (FIG. 2).
reference).

Plunger 1 by hydraulic cylinder 13
0 and the screw 20 by the hydraulic cylinder 24
The forward and backward movement of the screw 20 and the rotation of the screw 20 by the hydraulic motor 25 can all be performed by pressure oil, but the rotation of the screw can also be performed by replacing the hydraulic motor 25 with an electric servomotor. Although omitted in the drawing, the screw 20 is moved forward by a stopper or the like so that a resin flow path is secured by a required gap between the distal end surface of the valve body 29 and the distal end surface of the cylinder even when the valve is opened. By mechanical means.

In the illustrated embodiment, the drive hydraulic circuit comprises a hydraulic circuit 41 of the hydraulic cylinder 13 of the injection device 1 connected to the variable discharge pump 40, and a hydraulic circuit 42 of the hydraulic cylinder 24 of the plasticizing device 2. The hydraulic circuit 41 is connected to a hydraulic path 43 of the hydraulic motor 25 by providing a switching valve 44.

The hydraulic circuit 41 of the injection device 1 includes the switching valve 44, the switching valve 45 of the hydraulic cylinder 13, and the back pressure control device 46 in the cylinder rear chamber (injection side). 43 and the hydraulic path 47a on the cylinder rear chamber side are connected, so that the pressure oil can be switched between the cylinder rear chamber side and the hydraulic motor 25 side. Further, both the branch path of the hydraulic path 47a in the cylinder rear chamber and the hydraulic path 47b of the cylinder front chamber are connected to the switching valve 45,
Supply and discharge of pressure oil from the cylinder rear chamber and discharge of pressure oil from the cylinder rear chamber can be performed.

The back pressure control device 46 includes a sensor 48 for detecting a circuit pressure of a hydraulic passage 47, a relief valve 50 for back pressure provided in a drain circuit 49, and a pressure comparison device having a transmitter for the valve. The relief valve 50 is operated by comparing the detected circuit pressure with a set value to control the back pressure.

The hydraulic circuit 42 of the plasticizing apparatus 2 includes an accumulator (ACC) 52, a pressure reducing valve 53, and a switching valve 54 in the circuit, and the front and rear sides of the hydraulic cylinder 24 connected to the switching valve 54. The hydraulic path 55a on the chamber side,
In 55b, check valves 56a and 56b are provided in such a way that a pilot circuit is provided alternately in their hydraulic paths. Further, a pilot circuit 57 of the pressure reducing valve 53 is connected to the hydraulic path 55b, and the pressure reducing valve 53 is controlled by the circuit pressure. Reference numeral 58 denotes a pressure switch, and 59 denotes a switching valve of the drain circuit 60.

The illustrated hydraulic circuit indicates the end of the injection of the metering resin due to the advance of the plunger 10, and upon completion of the injection, the switching of the plasticizing device 2 side is performed by an electric signal from a separately provided position detector. The valve 54 is switched to the right side, and the pressure oil accumulated in the accumulator 52 is supplied to the cylinder rear chamber from the hydraulic passage 55a through the pressure reducing valve 53 together with the pressure oil from the pump. 20, the passage 21a around the valve body at the screw tip is opened (see FIG. 2).

Subsequently, the two switching valves 44 and 45 on the injection device 1 side are operated to switch to the right side, respectively, and the pressure oil is supplied to the hydraulic motor 25 via the hydraulic passage 43, whereby the pressure oil on the rear chamber side is thereby provided. Piston 2 maintained at a high pressure by
6 rotates together with the screw 20 to start plasticization of the resin and charging of the material to the injection device 1 side.

On the other hand, in the hydraulic cylinder 14 of the injection device 1, the hydraulic path 47a in the cylinder rear chamber communicates with the tank from the switching valve 44 via the relief valve 50, and the hydraulic path 47b in the cylinder front chamber passes through the switching valve 45 to the tank. Through this, the plunger 10 can be moved backward. In the drain circuit 49, the relief valve 50
Thereby, the pressure of the hydraulic pressure discharged from the rear chamber of the cylinder is adjusted to the set pressure, and the plunger 10 is retracted under the load of the predetermined pressure to measure the resin.

When the plunger 10 retreats due to the material charge due to the rotation of the screw 20, and when the retreat position reaches a preset switching position An immediately before the metering end position A, the discharge of the pump is performed by an electric signal from the position detector. By controlling the amount to be small, the rotation of the hydraulic motor 25, that is, the rotation speed of the screw 20, is changed to a lower speed than the rotation at the time of measurement.

Following the switching of the rotational speed, the switching valve 54 is switched to the left, and the hydraulic path 55b on the front chamber side of the hydraulic cylinder 24 is connected to the hydraulic path on the pump side, and the hydraulic path 55a on the rear chamber side of the cylinder is connected to the hydraulic path 55a. The pressure oil connected to the drain and accumulated in the accumulator 52 is reduced in pressure and supplied to the cylinder front chamber from the hydraulic path 55b through the pressure reducing valve 53 controlled by the circuit pressure in the hydraulic path 55b.
As a result, the piston 26 moves backward at a lower pressure than during forward movement.

Accordingly, the screw 20 connected to the piston 26 moves backward while rotating at a lower speed than at the time of measurement, and the valve body 29 of the check valve 32 comes into contact with the valve seat 35 at a low pressure. The valve will close. As a result, FIG.
As shown in (2), the flow path 21a is completely closed to cut off the flow of the plasticized resin, and at the same time, prevent the resin from flowing backward from the injection device 1 side.

The low-speed rotation time of the screw 20 by the hydraulic motor 25 is set by a timer, but it is preferable to set the rotation to be continued even after the valve is closed. The screw 20 stops when the timer is up. When the timer is up, only the switching valve 44 is switched to the opposite side. At the same time, the discharge amount of the pump is returned to the original value and supplied to the cylinder rear chamber of the hydraulic cylinder 14 for injection. Immediately after the valve is closed, the injection of the measuring resin is performed by the advance of the plunger 10.

As described above, when the valve is closed by changing the rotation speed to a low speed without stopping the rotation of the screw 20, the rotation direction of the screw 20 is opposite to the screw direction of the screw shaft 30. Therefore, even if the rotational torque acts on the valve element 29 due to the contact between the valve element 29 and the valve seat 35, the rotational torque acts as a tightening force of the screw shaft 30, so that even if the valve is repeatedly closed, The loosening of the valve body 29, which tends to occur when closing the valve by stopping the screw rotation, is eliminated.

In the valve closing by low pressure, the impact force at the time of closing the valve is reduced, and the pulling force on the screw shaft 30 is also reduced. Therefore, the rotation of the screw shaft due to the repetitively acting pulling force is also reduced. Together with the tightening force,
The valve body 29 is more difficult to loosen, and the resin backflow caused by the fluctuation of the valve closing distance due to the looseness of the valve body 29 and the fluctuation of the dimension of the flow path 21a at the valve body tip is ensured even in long-term use. Valve 29 due to looseness
It is possible to prevent the resin from remaining due to the gap between the washer 33 and the washer 33, and to eliminate the occurrence of product failure due to the carbonized or discolored resin.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a pre-plastic injection molding machine that enables the implementation of a backflow prevention method according to the present invention.

FIG. 2 is a longitudinal sectional view of a distal end portion of a plasticizing device when a flow path is opened.

FIG. 3 is a vertical cross-sectional view of a distal end portion of a plasticizing device when a flow path is blocked.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Injection apparatus 2 Plasticization apparatus 3 Resin path 10 Plunger for injection 12 Injection cylinder 20 Screw for plasticization 21 Outflow path 21a Flow path 22 Plasticization cylinder 24 Hydraulic cylinder 25 Hydraulic motor 26 Piston 29 Valve element 30 Screw shaft 32 Backflow Prevention valve 33 Washer 35 Valve seat 40 Variable discharge pump 41 Hydraulic circuit on injection device side 42 Hydraulic circuit on plasticizer side 43 Hydraulic path of hydraulic motor 44, 45 Switching valve 52 Accumulator (ACC) 53, 54 Switching valve

Claims (2)

[Claims] An injection cylinder containing a plunger therein,
A plasticizing cylinder with a plasticizing screw equipped with a check valve at the tip is rotatably and reciprocally mounted inside and connected in parallel by a resin path provided over the tip, and a screw is provided at the rear of the plasticizing cylinder. In a pre-plastic injection molding machine that includes a moving means and a rotation motor, and opens and closes the check valve by advancing and retreating the screw by the screw moving means, the plunger retreats due to material charging due to the rotation of the screw, When the retreat position reaches just before the weighing end position, the rotation speed of the screw is switched to a low speed, and then the valve is moved backward at a lower pressure than when the valve is opened to close the valve, and then the screw rotation is stopped. A method for preventing backflow of a pre-plastic injection molding machine, comprising preventing backflow of resin to the plasticizing cylinder side after completion of measurement. 2. An accumulator is provided in a hydraulic circuit of the plasticizing cylinder, and pressure oil is supplied from the accumulator to the screw moving means to open the valve by moving the screw forward and backward and close the valve by moving backward. The method for preventing backflow in a pre-plastic injection molding machine according to claim 1, characterized in that: