JP2577068B2 - Screw rotation control method for injection molding machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a screw rotation control method for a screw-type injection molding machine, and more particularly to a screw rotation control method for preventing a screw head from being cut off.

(Prior Art) Conventionally, a fluidized molding material heated in a heating cylinder is injected into a mold under high pressure, cooled and solidified or hardened therein, and then the mold is opened to take out a molded product. There are two types of molding machines: a plunger type that moves the plunger back and forth for injection molding, and a screw type that moves the screw back and forth for injection molding.The plunger type is compared to the screw type. In general, the screw type is used because the plasticizing ability of the material is inferior and the injection pressure loss is large.

The conventional injection molding machine will be described with reference to FIGS. FIG. 5 is a sectional view of a conventional injection molding machine, FIG. 6 is a sectional view of a screw head of the conventional injection molding machine, and FIG. 7 is a sectional view of another conventional screw head.

In the figure, a screw 2 is supported inside a heating cylinder 1 of an injection molding machine so as to be rotatable and forward and backward.
That is, the drive shaft 3 is connected to a drive system including an electric motor or a hydraulic motor (not shown) via a thrust bearing, and is moved forward and backward by the drive system.

The state of the screw position in FIG. 5 is a state in which the injection molding shot has been completed. Here, prior to the next shot,
An operation of melting and plasticizing the molding material 5 and storing it at the tip of the head, that is, weighing is performed. In this measurement, the screw 2 is driven by the drive system and retreats. At this time, the molding material 5 dropped and supplied from the material supply port 4 moves forward in the groove 6 by the rotation of the screw 2. While being melted and plasticized in the heating cylinder 1, it is stored at the front end of the screw 2. The pressure of the molding material 5 in the heating cylinder 1 generated due to the melt plasticization becomes a reaction force against the screw 2,
The screw 2 is retracted by the reaction force.

Thus, the molding material 5 stored at the front end of the screw 2 is subsequently injected into the mold from the nozzle 7 by pushing the screw 2 forward by the drive system.

Here, a part of the molding material 5 flows backward through the groove 6 of the screw 2 due to the reaction force of the injection force applied when the molding material 5 is injected into the mold. In order to prevent this, a backflow prevention ring 8 as shown in FIGS. 6 and 7 is provided at the front end of the screw 2. Then, the main body portion of the screw 2 and the screw head 9 are formed separately so that the backflow prevention ring 8 does not come off from the screw 2, and the female screw 10 is formed in the main body portion of the screw 2 while the screw head 9 is formed. A male screw 11 is formed at the rear end of the screw 9 so as to screw them together. The outer diameter of the screw head 9 is made larger than the inner diameter of the backflow prevention ring 8 so that the backflow prevention ring 8 does not come off.

(Problems to be Solved by the Invention) However, in the above-described conventional injection molding machine, the female screw 10 is formed in the main body of the screw 2 and fixed by screwing the male screw 11 of the screw head 9 into the female screw 10. As a result, the strength of the screw portion is weakened, and the screw 9 may be cut by various impacts.

That is, generally, the injection molding is completed when all the molding materials have been injected, and when the molding is restarted, the operation is started from the weighing stage. In addition, even when injection molding must be interrupted for some reason, it is common to interrupt the injection after the injection of the molding material, and in this case, the work is started from the weighing stage. You.

As described above, in any case, the injection molding is restarted from the measurement stage, and at the time of restart, the screw 2 is first rotated. At this time, the molding material, glass, etc., which have entered a gap of several tens of μm between the inner wall of the heating cylinder 1 and the outer periphery of the backflow prevention ring 8, are fixed in a glue state as shown in FIG. If this occurs, the backflow prevention ring 8 becomes a resistance to the rotation of the screw 2 and causes an impact to the screw head 9.

For example, as shown in FIG. 6, there is an engagement portion between the screw head 9 and the backflow prevention ring 8, and the backflow prevention ring 8 of the “rotating around type” in which both rotate together, When the screw 2 starts rotating, the backflow prevention ring 8
Is directly a resistance, and only the tip of the male screw 11 is fixed, so that a torsional force is generated in the male screw 11.

As shown in FIG. 7, there is no engagement portion between the screw head 9 and the backflow prevention ring 8, and in the case of the "non-rotating type" in which rotation can be freely performed mutually, the screw is not used. When the screw 2 moves backward while rotating, and the screw head 9 and the backflow prevention ring 8 come into contact with each other, a torsional load is applied to the screw head 9 by the rotational impact force generated by the frictional force.

In any of the above cases, the backflow prevention ring 8 attempts to fix only the screw head 9 against the torque for rotating the screw 2. I will.

In order to protect the screw head 9 from such an impact, conventionally, the following measures have been taken.

One is to make the diameter of the male screw 11 of the screw head 9 as large as possible. The larger the diameter, the higher the strength. However, since the diameter of the screw 2 is limited in design, there is a limit in increasing the diameter of the male screw 11.

The other is the main part of the screw head 9 and the male screw 11
The purpose is to form a constricted portion 13 between them to reduce the diameter and reduce the stress concentration coefficient. According to this method, it is possible to suppress the stress concentration caused by the impact,
If the constriction 13 is too large, the screw head 9 becomes too thin, and the absolute strength may be reduced.

Another is to reduce the starting torque or the starting speed when the rotation of the screw 2 starts. In this case, although the impact given to the screw head 9 is small, it is necessary to rotate the screw 2 against a large load torque such as a frictional force due to the molding material 5 in the unreacted portion at the middle and rear of the screw 2. Also had limitations.

As described above, various methods have been tried, but none of these methods completely protects the screw head 9 from impact. Particularly in a small injection molding machine, since the diameter of the screw head 9 is originally small, zinc-containing material is used. In the case of the molding material described above, the screw head 9 sometimes breaks once every several days.

The present invention solves the above-described problems, and when the molding is restarted after the end of the injection molding or after the interruption, the screw head is prevented from being cut and the rotation of the screw is started. In view of the above, an object of the present invention is to provide a screw rotation control method capable of shortening a standby time required for raising the temperature of a heating cylinder.

(Means for Solving the Problems) To this end, the present invention provides a heating cylinder, a screw rotatably and forwardly and backwardly disposed in the heating cylinder, a means for driving the screw, and a driving means. In the method for controlling the rotation of a screw of an injection molding machine comprising a control device for controlling, when the power of the injection molding machine is turned on, a forward and backward movement is performed in a state where the rotation of the screw is blocked in advance, and then the rotation operation of the screw is performed. I do it.

After the injection operation, the time counting by the time counting means is started, and after the time set by the time counting means elapses, the forward and backward movement is performed in a state where the rotation of the screw is stopped in advance, and then the screw is rotated. Is performed.

When the purging of the injection molding machine is started manually, the injection operation is performed in advance regardless of the screw position, and then suckback is performed.

(Operation) According to the present invention, when the power of the injection molding machine is turned on to restart the molding after the end of the injection molding or after the interruption, the forward / backward movement is performed in a state where the rotation of the screw is blocked in advance. Since the screw is rotated, the screw can be prevented from rotating suddenly when the power is turned on, and the molding material that has entered the gap between the backflow prevention ring and the inner circumference of the heating cylinder and adhered is The screw is peeled off by the forward and backward movement, and the resistance against the backflow prevention ring applied to the screw head is eliminated.

Also, after the injection operation, timing by the timing means is started,
After the elapse of the time set by the time counting means, the screw is rotated forward and backward, and then the screw is rotated forward and then the screw is rotated. If an impact is likely to be applied to the screw head due to the rotation of the screw, the rotation of the screw is prevented.

When purging is performed manually to replace the molding material of the injection molding machine, the injection operation is performed in advance regardless of the position of the screw at the time of starting the purging, and then the suckback is performed. Therefore, the screw can be prevented from rotating at the same time when the purging switch is turned on.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to FIG. 1 to FIG.

FIG. 1 is a view showing an injection molding machine to which a screw rotation control method for an injection molding machine according to the present invention is applied. FIG. 2 is a control circuit for implementing the screw rotation control method for an injection molding machine according to the present invention. FIG. 4 is a control operation flow chart in the automatic mode showing the embodiment of the present invention, and FIG. 4 is a control operation flow chart in the manual mode showing the embodiment of the present invention.

In FIG. 1, the screw 2 is driven by a screw drive system 21 via a drive shaft 3 so that the screw 2 can rotate or move forward and backward. The screw drive system 21 includes:
The screw 2 is driven by the control device 22 so that the screw 2 is retracted at the time of metering and is advanced at the time of injection operation.

At the time of measurement, the screw 2 rotates with the retreat, and the molding material 5 dropped and supplied from the material supply port 4 moves in the groove 6 and is sent to the front of the heating cylinder 1. Then, it is melt-plasticized in the heating cylinder 1 and stored at the front end of the screw 2. The pressure of the molding material 5 in the heating cylinder 1 caused by the melt plasticization applies a reaction force to the screw 2.

Next, in FIG. 2, reference numeral 23 denotes a power supply, and reference numeral 24 denotes a switch for turning on the power. The switch can be manually turned on / off by an operator. The switch 24 includes a manual purging switch 25 and an automatic mode screw rotation relay 26 in parallel with each other, and an injection relay switch 27 in parallel with each other.
And a relay switch 28, and a relay solenoid 29 is further connected to them.

The relay solenoid 29 operates when the injection relay switch 27 is turned on by turning on the automatic mode screw rotation relay 26 or turning on the purging switch 25, and closes the relay switch 28.

An injection relay 30 and a timer 31 are connected to the relay solenoid 29, and a metering completion switch 32, a time limit switch 33, an injection timer 34, and a screw rotation solenoid 35 are connected in parallel with the injection relay 30 and the timer 31. The injection relay 30
When the injection operation is completed, it is turned on, and the timer 31 starts counting time. When the set time has elapsed, the timer 31 turns off the time switch 33 to prevent the solenoid 35 from being energized. Note that the metering completion switch 32 is turned off when the metering is completed and the injection operation is started, so that the solenoid 35 is not energized during the normal injection operation. Even if the weighing completion switch 32 is on when the weighing is not completed, the time limit switch 33 is turned off after the set time elapses, so that the solenoid 35 is not energized. In order to prevent the injection operation and screw rotation operation from being performed simultaneously, an interlock circuit
36 are provided.

Here, the operation of the injection molding machine in the automatic mode will be described with reference to the flowchart of FIG.

Step After the injection molding is completed or interrupted, the operator turns on the power supply switch 24 of the injection molding machine to restart the molding.

Judge whether the step screw 2 is at the most forward position,
If it is the most forward position, the process proceeds to the step, and if it is halfway, the process proceeds to the step.

Step suckback is performed, and the screw 2 is retracted without rotating.

Step Injection operation is performed.

Step After the injection operation, the injection relay 30 is turned on, and the timer 31 starts counting time. The time counting by the timer 31 is set when the injection molding is completed, and returns to zero.

It is determined whether the step set time has elapsed. If the time has not elapsed, the process proceeds to the step. If the time has elapsed, the process returns to the step.

The rotation of the step screw 2 is enabled.

By the way, when purging for replacing the molding material of the injection molding machine is performed manually, a manual mode switch is provided in parallel with the time switch 33, the injection timer 34, and the solenoid 35 for screw rotation of the control circuit shown in FIG. 37, the injection timer 38 and the manual suck-back relay solenoid 39 are connected.

The operation of the injection molding machine in the manual mode will be described with reference to the flowchart of FIG.

Step Turn on the manual purging switch 25.

The injection operation is performed in advance regardless of the position of the step screw 2.

Suck back is performed to the position where step weighing is completed.

Step 2 Screw 2 is rotated until cooling is completed.

Step It is determined whether or not the purging switch 25 is turned off. If it is off, the process proceeds to the step. If not, the process returns to the step.

Step Suck back is performed, and the screw 2 is rotated while being retracted.

Step Stop the injection molding machine.

As described above, the rotation of the screw 2 is performed after the forward and backward movement of the screw 2 is performed. However, after the rotation of the screw 2 is started, the rotation speed is reduced for a certain period of time or the torque is reduced. When the screw head 9 is rotated, the impact given to the screw head 9 is further reduced.

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible based on the gist of the present invention.
They are not excluded from the scope of the present invention.

For example, although a ball check valve is used instead of the backflow prevention ring, the present invention can be applied to an injection molding machine using the ball check valve.

(Effects of the Invention) As described above, according to the present invention, when the power of the injection molding machine is turned on to restart the molding after the end of the injection molding or after the interruption, the rotation of the screw is prevented in advance. The screw moves forward and backward, and then the screw rotates.This prevents the screw from suddenly turning on when the power is turned on, and enters the gap between the backflow prevention ring and the inner circumference of the heating cylinder to be fixed. The formed molding material is peeled off by the forward and backward movement of the screw, the resistance against the backflow prevention ring exerted on the screw head is eliminated, and the screw head is not broken.

In addition, after the injection operation is completed, time counting by the time counting means is started, and after a lapse of time set by the time counting means, forward and backward movement is performed in a state where rotation of the screw is stopped in advance, and then rotation of the screw is performed. Therefore, if an impact is likely to be applied to the screw head due to the rotation of the screw, not only is the rotation of the screw prevented, but also the forward / backward movement is performed after the set time, and the rotation of the screw is subsequently performed. Therefore, it is possible to prevent the backflow prevention ring from sticking due to resin burning or the like.

And when purging for replacing the molding material of the injection molding machine is performed manually, when the purging is started, regardless of the position of the screw, it is injected in advance, then sucked back, and then the screw is removed. Since the rotation is performed, the screw can be prevented from rotating at the same time when the purging switch is turned on.

Further, in the conventional injection molding machine, in order to prevent the above-mentioned cut-off, after the temperature of the heating cylinder is raised, the screw cannot be rotated without sufficient time elapse, so that the resin is burnt. Or the operating rate of the injection molding machine is reduced, but the present invention eliminates such a waiting time.

[Brief description of the drawings]

FIG. 1 is a diagram showing an injection molding machine to which a screw rotation control method for an injection molding machine according to the present invention is applied. FIG. 2 is a control circuit diagram for implementing the screw rotation control method for an injection molding machine according to the present invention. 3 is a control operation flow chart in an automatic mode showing an embodiment of the present invention, FIG. 4 is a control operation flow chart in a manual mode showing an embodiment of the present invention, and FIG. 5 is a cross section of a conventional injection molding machine. FIG. 6 is a sectional view of a screw head of a conventional injection molding machine, and FIG. 7 is a sectional view of another conventional screw head. 1 ... heating cylinder, 2 ... screw, 3 ... drive shaft,
4 ... material supply port, 5 ... molding material, 6 ... groove, 7 ...
Nozzle, 8 Backflow prevention ring, 9 Screw head, 10 Female screw, 11 Male screw, 13 Neck,
21 ... screw drive system, 22 ... control device, 23 ... power supply,
24 ... Switch, 25 ... Purging switch, 27 ...
Injection relay switch, 28 ... relay switch, 29 ... relay solenoid, 31 ... timer.

Claims (3)

(57) [Claims] 1. An injection molding machine comprising a heating cylinder, a screw rotatably and reciprocally movable within the heating cylinder, a means for driving the screw, and a control device for controlling the driving means. In the screw rotation control method of
A screw rotation control method for an injection molding machine, comprising: when turning on a power supply of an injection molding machine, performing a forward / backward movement in a state where rotation of the screw is prevented in advance, and then performing a rotation operation of the screw. 2. A screw rotation control method for an injection molding machine comprising a heating cylinder and a screw rotatably and reciprocally movable within the heating cylinder, wherein a timing by a timing means is started after the injection operation. A screw rotation control method for an injection molding machine, characterized in that after a time set by the timing means elapses, a forward / backward movement is performed in a state where rotation of the screw is prevented in advance, and then a rotation operation of the screw is performed. 3. A method of controlling a screw rotation of an injection molding machine comprising a heating cylinder and a screw rotatably and forwardly and backwardly moved in the heating cylinder, wherein purging of the injection molding machine is started manually. In this case, a screw rotation control method for an injection molding machine, wherein an injection operation is performed in advance regardless of the screw position, and then suckback is performed.