JPS61219618A - Plasticization controlling device for injection molder - Google Patents

Abstract

PURPOSE:To enable to highly-accurately control the retreating speed of a screw so as to control the pressure of molten resin over the wide range from 0kg/cm<2> by a method wherein a resin pressure sensor to detect the pressure of molten material at the tip of a heating cylinder in the form of electric signals and a means to directly convert the rotational speed of a motor into the movement of a hydraulic piston to reciprocatingly drive a plasticizing screw are provided. CONSTITUTION:In an in-line screw type injection molder, a resin pressure sensor 54 to detect the pressure of molten material at the tip of a heating cylinder during the plasticizing process in the form of electric signals, a motor 50, the amount of revolution of which is determined by given control signals, and a means to directly convert the rotational speed of the motor 50 into the movement of a hydraulic piston to reciprocatingly drive a plasticizing screw 3 are provided. A control circuit 52 supplies the control signal to the motor, based upon the detection signal inputted from the resin pressure sensor, in order to control the retreating speed of said plasticizing screw 3 so as to control the pressure of molten material at the tip of the heating cylinder 2 nearly at 0kg/cm<2> and at the same time as low as possible over the range, within which no negative pressure produced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a plasticizing control device that controls plasticizing conditions in order to stabilize the temperature, melting, cross-wire state, etc. of a material that is plasticized in an injection molding machine. It is related to.

[Conventional technology Fine-line screw type injection molding machines do not have screws inside the barrel (heating cylinder) that rotate continuously like extrusion molding machines do, but the screws are plasticizers! It rotates and stops periodically according to the operation and injection operation. Further, in the plasticizing process, the screw retreats while being supplied with material such as molten resin from the hopper, so the effective length of the screw changes every moment. Due to the above two basic operations, non-uniformity occurs in the concentration of the plasticized resin and in the melting and cross-wire states, which causes a reduction in the quality of the molded product.

To prevent this, in the plasticizing process of the injection molding machine, plasticization is controlled by controlling the retraction speed of the screw.

Conventionally, in order to control the retraction speed of the screw, the magnitude of the action of transferring the molten resin to the front of the screw was controlled by adjusting the rotational speed of the screw, and the retraction resistance force of the screw was controlled by adjusting the back pressure of the hydraulic cylinder. Various control devices have been proposed that perform control methods individually or simultaneously.

[Problems to be Solved by the Invention] However, the retraction resistance is not due to the back pressure inside the hydraulic cylinder, but rather due to the friction resistance between the screw and the heating cylinder, and the friction between the resin in the screw groove and the heating cylinder. Resistance, gasket resistance of the hydraulic cylinder, rR dynamic resistance of the hydraulic motor unit, and other relaxation factors prevent the screw from retracting. The molten resin pressure must be equal to or greater than the above-mentioned retreating resistance force, so even if the back pressure becomes pyro, the molten resin pressure does not become zero but has a certain value. Therefore, by adjusting the back pressure, plasticization cannot be performed at a molten resin pressure lower than that value.

However, if the molten resin pressure is not properly controlled in the vicinity of zero (1), for example, not only will the screw retraction pulsate or the retraction speed locally decrease, but also the screw Sometimes the machine would stop without moving backwards.

In addition, since the screw retraction speed is indirectly controlled by adjusting the screw back pressure, adjustment is difficult;
Furthermore, even if the screw back pressure is controlled, a lag time occurs in the hydraulic piping system due to volume changes due to the compressibility of the hydraulic oil and the pressure of the hydraulic piping system, resulting in a drawback that the molten resin pressure does not follow immediately. Furthermore, it has been difficult to control the retraction resistance with a general-purpose screw in accordance with various molding conditions and resin ladder sequences.

[Means for Solving the Problem] Therefore, the main object of the present invention is to provide a plasticization control device for an injection molding machine that can control the screw retraction speed with high precision from zero to a wide range of molten resin pressure. It is to be.

Another object of the present invention is to provide a highly responsive plasticizing control device that does not have delay time caused by a hydraulic piping system.

Furthermore, another object of the present invention is to provide a plasticization control device that is easily applicable to conventional general-purpose injection molding machines and has a simple configuration.

In order to achieve the above object, the plasticization control device for an index molding machine according to the present invention detects the pressure of the molten material at the tip of the heating cylinder as an electric signal during the plasticization process in an in-line screw type injection molding machine. The rotation amount is determined by the resin pressure sensor and the supplied control signal.
jl, and means for directly converting the rotational speed of the electric motor into a hydraulic piston moving machine that reciprocates the plasticizing screw;
The detection signal of the resin pressure sensor is input, and based on this, the retraction speed of the plasticizing screw is set within a range where the pressure of the molten material at the tip of the heating cylinder does not become negative pressure and is approximately OK.
g/cf.

[Function] The plasticizing screw is rotated to plasticize the resin, and when the plasticized and melted resin gradually accumulates at the tip of the heating cylinder, the plasticizing screw retreats accordingly.

At this time, the pressure of the molten resin at the tip of the heating cylinder is extracted as an electric signal, and in accordance with the electric signal, the electric motor for retracting the plasticizing screw is continuously rotated at an appropriate rotation speed.
The plasticizing screw is retracted at an appropriate speed through a mechanical transmission mechanism such as a screw mechanism, and the pressure of the molten resin flowing into the tip of the heating cylinder does not become negative pressure, and the pressure is OK.
A/cf.

[Example] Next, the present invention will be explained in more detail by way of an example.

FIG. 1 shows the overall configuration of an in-line screw type injection molding machine according to the present invention, with solid lines showing the hydraulic system and dotted lines showing the electrical system. In the figure, a heating cylinder 2 with a nozzle 1 at its tip
A screw 3 is provided within the interior so as to be rotatable and reciprocating. are directly connected to the In addition, the heating tube 2
The outer cylinder of the two injection cylinders 5.6 is integrally fixed, and the screw 3 is attached to a thrust bearing on the mouth-shaped piston rod 7 that is shared by both injection cylinders 5.6. 8 and is rotatably supported. In the thrust bearing 8 part, a part of the screw 3 and a part of the piston rod 7 are connected to the halved coupling 8.
a, and the screw 3 rotates freely, but moves forward and backward together with the piston rod 7. A hydraulic pipe 12 equipped with a switching valve 11 is connected to the head end boat 9.10 of both cylinders 5.6, and a switching valve is connected to the rod end boat 13.14 of both cylinders 5.6. Hydraulic piping 1 with 15
7 is connected. Furthermore, a hydraulic piping 19 equipped with a switching valve 18 is connected to the hydraulic motor 4, and this hydraulic piping 19 and the hydraulic piping 12.17 are merged to form a flow valve 20 and a relief valve 21. It is connected to a hydraulic pump 23 and a hydraulic tank 24 by a hydraulic pipe 22 provided therein. A hopper 25 is provided near the base of the screw 3 to supply resin between this and the heater 82, and a heater 26 is provided on the outer periphery of the heating cylinder 2 to heat the resin inside. There is.

Furthermore, a screw shaft 51 that is directly connected to an electric servo motor 50 is screwed into the screw member 49 fixed to the piston rod 7, and when the electric servo motor 50 is rotated, the screw is screwed through the piston rod 7 by a screw action. 3 is configured to move forward and backward.

The internal threaded member 49 shown in No. 11i2I is always connected to the threaded shaft 51.
However, as shown in FIG. 6.7, the female threaded member 49 may not be threaded onto the threaded shaft 51.

In FIG. 6.7, a box 28 is fixed to the side surface of the piston rod 7 via a bracket 27.

Inside the box 28, a split nut 49a149b with a rectangular outer surface constituting the female threaded member 49 is arranged with one surface 49c on the box 28 side and the axially cylindrical outer surfaces 49d and 49e in contact with each other. . The reason why the negative surface 49c is provided in close contact with the bottom surface of the box 28 is so that when the screw shaft 51 rotates, the female threaded member 49 can move in the axial direction without rotating, and the cylinder outer surface 49d
, 496 are provided in close contact with both inner walls of the box 28 in the axial direction so that the female threaded member 49 and the box 28 can always move together in the axial direction. Cylinders 29a and 29b are fixed to the outer surfaces of both sides of the box 28, and the piston rods 3 of the cylinders 29a and 129b are fixed.
The tips of 0a and 30b are split nuts 49a and 49
Each was fixed in b. And cylinders 29a, 29
Simultaneously advance and retreat the piston rods 30a and 30b of b'c
5, the split nuts 49a and 49b can be engaged with or unscrewed from the screw shaft 51. The screw shaft 51 is connected to the fixing member 32 through a bearing.
An electric servo motor 50 is attached to one of the fixed members 32 so as to be rotatable.

Piston rods 30a, 3 of cylinders 29a, 29b
By advancing Qb, the split nut 49a149b can be engaged with the screw shaft 51.

When the electric servo motor 50 is driven in this state, the screw @51 rotates, and the female threaded member 49 made up of the split nuts 49a and 49b moves in the axial direction together with the box 28, and the cylinder 5.6 The piston rod 7 moves back and forth.

Piston rods 30a of cylinders 29a, 29b,
30b is moved backward, the split nut 49a149b can be disengaged from the screw shaft 51, so that when the cylinder 5.6 is activated, the screw member 49 moves forward and backward together with the piston rod 7.

The reason why the female screw member 49 is engaged with the screw shaft 51 is to move the plasticizing screw 3 backward by the operation of the electric servo motor 50 during the plasticization metering process, and the female screw member 49 is removed from the screw shaft 51. During the injection process, cylinder 5.
This is because the plasticizing screw 3 can be advanced only by the action of 6.

In this embodiment, when retracting the plasticizing screw 3 during plasticization measurement, the screw 3 is mechanically retracted by the electric servo motor 50. Smoothly retreats without being affected by operation delay, resin pressure, etc.

On the other hand, a molten resin pressure sensor 54 is provided to detect the pressure of the molten resin at the tip of the heating cylinder 2. Also,
A load pressure sensor 55 is used to detect the load on the hydraulic motor 4.
is installed in the middle of one hydraulic pipe. The outputs of these sensors 54 and 55 are connected to inputs 1 and 12 of the control circuit 52 via connection lines 53 and 56, respectively. The control circuit 52 contains a preset processing program and executes predetermined calculations based on input signals from the sensors 54 and 55. The output O1 of this control circuit 52 is connected to the electric servo motor 5o via a connection line 57,
The output o2 is connected to the flow layer regulating valve 20 via a connecting line 58. Furthermore, the output o1 is connected to an alarm device 59.

The operation of the injection molding machine with the above configuration will be explained below.

With the piston rod 7 retreating into the cylinders 5 and 6 and the screw 3 moving forward, resin is supplied from the hopper 25 to the base of the screw 3, and the hydraulic motor 4 is rotated by switching the switching valve 15, 18 to move the boat 9. .10, 13, and 14 are all switched to the hydraulic tank 24 side, the resin melted by heating is mixed and plasticized by the rotation of the screw 3, and is sent to the front of the heating cylinder 2. It tries to retreat gradually due to the pressure of

However, at this time, the screw 3 is retracted at a desired retraction speed by the action of the electric servo motor 50, as will be described later. When the screw 3 retreats by a stroke corresponding to the required charging amount, a limit switch (not shown) is activated to stop the rotation and retraction of the screw 3, and the tip of the heating cylinder 2 is filled with plasticized material. is temporarily stored. Next, when the molded product from the previous cycle is taken out of the mold and the mold is closed, the switching valve 15 is switched to send oil to the boat 13, 14, and as the screw 3 advances, the oil is stored at the tip of the heating cylinder. The resin is pressurized and injected into the mold cavity. While the injected resin is being cooled in the mold, the next cycle of plasticizing and melting process is carried out.

In the above process, when the screw 3 is beginning to regress, the control circuit 52 inputs the detection signals of the molten resin pressure sensor 54 and the load pressure sensor 55, and performs a predetermined operation based on these values. , a control signal for the backward speed of the screw 3 is sent to the electric servo motor 50,
A control signal for the rotational speed of the screw 3 is supplied to each of them.

If the screw retraction speed is too slow compared to the screw rotation speed, the frictional resistance between the screw 3 and the heating cylinder 2 or the f! pm resistance, cylinder 5
．． This is because the retreat of the screw 3 is prevented by the advancement of the piston rod 7 (movement to the right in Fig. 1) and the relaxation of the sliding resistance of the rotating shaft of the hydraulic motor unit 4. When the pressure of the molten resin inside the tip of the heating cylinder 2 becomes higher than a predetermined threshold, the control circuit 52 supplies a screw retraction speed control signal to the electric servo motor 50. Electric Nervo Motor 5o is 1IIIIII! The threaded shaft 51 is rotated by a rotation m corresponding to the signal supplied from the one circuit 52, and the female threaded member 49 moves in the axial direction of the threaded shaft 51 accordingly. As a result, the piston rod 7 is able to move past the screw 3.

At this time, the molten resin pressure inside the tip of the heating n2 becomes a positive pressure close to, for example, 2 to 3 kg/cv, or 0 kg/cv, and the screw 3 is adjusted so that the screw retreating resistance force becomes negative. Control the retraction speed. Of course, the screw 3 is directly operated via the screw shaft 51, the female thread member 49, and the piston rod 7 only by the electric servo motor 5o without applying back pressure to the screw 3.

The control circuit 52 sends a screw retraction speed control signal to the electric servo motor 50 when the molten resin pressure drops below a predetermined threshold due to air absorption from the nozzle 1 when the screw retraction speed is too fast compared to the screw rotation speed. supply

The electric servo motor 50 rotates the screw shaft 51 at a rotational speed according to a signal supplied from the control circuit 52, and the diagonal member 49 moves in the axial direction of the screw shaft 51 accordingly. As a result, the piston rod 7 moves the screw 3.

On the other hand, if resin is no longer supplied to the base of the screw 3 due to a lack of resin material in the hopper or a bridging phenomenon, the load on the hydraulic motor 4 decreases, and this is detected by the load pressure sensor 55. In response to this detection signal, the control circuit 52 sends a signal to the flow rate regulating valve 20 to stop the screw from retracting and rotating, and also causes the alarm 59 to issue an alarm indicating an abnormality.

To help better understand the above control operation, the retraction operation of the screw 3 will be explained in detail below.

Figures 2 and 3 are relationship diagrams in which the vertical axis represents the pressure of the molten resin stored in front of the screw, and the horizontal axis represents the screw back pressure or the screw retreat resistance force due to the action of the electric motor. 2 shows the case of a conventional injection molding machine, and FIG. 3 shows the case of the injection molding machine according to the present invention.

4 and 5 are relationship diagrams in which the vertical axis represents the resin pressure in the screw groove, and the horizontal axis represents the position of the screw within the heating cylinder 2. FIG. 5 shows the case of a molding machine according to the present invention.

As is clear from Figures 2 and 3, in the past, the adjustment range of resin pressure was P (depending on the type of resin, but
For ordinary thermoplastic resin, for example, P-20 to 30 kg
/Cv. However, in the case of the present invention in which the backward driving force of Screw 3 is controlled by detecting the molten resin pressure and the load pressure of the hydraulic motor, the resin pressure adjustment range starts from zero. It will be enlarged as follows. That is, like the conventional method using back pressure, the backward resistance force applied to the screw is added to the positive range, and in the present invention, the backward resistance force applied to the screw is negative. In other words,
It can be used to assist in retreating.

As a result, stable plasticization can be achieved even for resins that have caused pulsations, reductions, or stops in the screw retraction speed under conventional plasticization control.

Moreover, if this is seen in terms of the change in resin pressure within the screw groove during the plasticizing process, it becomes as shown in FIGS. 4 and 5. In each figure, the right side is the hopper 25 side, and the left side is the tip of the screw 3. Also, in Figure 4,
Curve L1 is the curve in Fig. 5 when there is a screw back pressure, curve @L2 is the curve when there is no screw back pressure, curve L4 is the curve when there is a retreating resistance force applied to the screw, and curve L4 is the external force acting on the screw. That is, when the retreating resistance force is 0, the curve Lt according to the present invention is of course the curve when the force is supported in a direction that supports the retreating of the screw.

The material supplied from the hopper 25 must overcome the resin pressure in the screw groove and be transferred to the front of the screw 3. In the figure, the farther the resin pressure rises from the hopper 25 side and the lower the resin pressure, the more the resin Easy to transport.

In the case of the present invention shown in FIG. 5, the curve L5 can be used, and it can be seen that the resin can be transferred more easily than in the conventional case shown in FIG. That is, since the aforementioned pulsations, decreases, and stops in the retraction speed of the screw 3 are all caused by the weak propulsive force acting on the resin in the feed zone, these problems can be solved by obtaining the performance of the curve Ls. .

Furthermore, the relationship between the load pressure of the hydraulic motor 4 and the retraction speed of the screw 3 is considered as follows. In an injection molding machine, the screw 3 does not rotate continuously, but rotates and stops repeatedly. Even when the screw is not rotating, thermal energy is applied to the resin in the slurry 3, increasing its temperature, and the viscosity increases accordingly. decreases, so when plasticizing starts, hydraulic motor 4
load pressure is low. On the other hand, since new resin is constantly supplied from the hopper while the screw is rotating, the resin temperature inside the screw 3 decreases and the viscosity increases accordingly.
At the beginning of the process of the plasticization meter, the load pressure of the hydraulic motor 4 gradually increases. In addition, as the screw 3 rotates, the screw itself moves back while transferring the molten resin to the front part of the screw 3, so in the latter half of the plasticization meter process, the hydraulic motor 4
The load pressure of decreases. When the hydraulic motor 4 rotates at a low load pressure, less mechanical energy is applied to the molten resin. If the retraction speed of the screw is reduced in order to compensate for this, the time for the resin to pass through the screw 3 becomes longer than when the load pressure of the hydraulic motor 4 is high. In this way, based on the relationship of screw load pressure x resin passage time - mechanical energy applied to the resin, the load pressure of the screw 3 is detected by the load pressure sensor 55, and the screw is adjusted so that the energy per unit volume is constant. Since the receding speed of the plasticized resin material is determined by the retraction speed, variations in the temperature and dispersion state of the plasticized resin material are reduced.

Furthermore, if control of the number of rotations of the screw is incorporated at the same time as controlling the retraction speed of the screw, the range of molding conditions can be further expanded.

[Effect] In the present invention, when retracting the plasticizing screw during plasticization measurement, an electric motor such as an electric servo motor mechanically plasticizes the resin through a screw mechanism in accordance with the pressure of the molten resin at the tip of the heating cylinder. By retracting the melting screw, it is possible to control the pressure of the molten resin flowing into the tip of the heating cylinder so that it does not become a negative pressure and is slightly lower than Oka/C'.
The plasticizing screw retracts smoothly without being affected by subtle oil pressure fluctuations and pulsations, operational delays due to compression of hydraulic oil, resin pressure, etc. Therefore, stable plasticization of the resin is always achieved and injection products of consistent good quality are easily obtained.

[Brief explanation of the drawing]

FIG. 1 shows a plasticizing control device for an injection molding machine according to the present invention.
A vertical cross-sectional view and a circuit diagram showing the embodiment, FIGS. 2 to 5 are diagrams for explaining the difference in operation between the prior art and the present invention, and FIG. 2 is a resin pressure diagram in the prior art; Figure 3 is a resin pressure diagram in the present invention, Figure 4 is a resin pressure diagram in the screw groove in the prior art, Figure 5 is a resin pressure diagram in the screw groove in the present invention, and Figures 6.7 are screw mechanisms. FIG. 6 is a ■-VI line diagram in FIG. 7, and FIG. 7 is a ■--■ line diagram in FIG. 6. 2... Heating cylinder, 3... Screw, 4... Hydraulic motor, 5.6... Indexing cylinder, 7... Piston rod, 11.15.18... Switching valve, 20. ...Flow control valve, 23...Hydraulic pump, 49...Female thread member,
50... Electric servo motor, 51... Screw shaft, 52
...Control circuit, 54.55...Sensor, 59...
Alarm device patent applicant: Ube Industries, Ltd. $2 Figure 3 Screw 1! Figure 6 Figure 7

Claims (2)

[Claims] (1) A resin pressure sensor that detects the pressure of the molten material at the tip of the heating cylinder as an electrical signal during the plasticizing process, an electric motor whose rotation amount is determined by the supplied control signal, and a plasticizing screw that controls the rotation speed of this electric motor. and a means for directly converting the amount of movement of a hydraulic piston that reciprocates, and a detection signal of the resin pressure sensor, and based on this, the retraction speed of the plasticizing screw is determined so that the pressure of the molten material at the tip of the heating cylinder is negative pressure. A plasticizing control device for an injection molding machine, comprising: a control circuit that supplies a control signal to the electric motor so as to be able to control the plasticization within a range of not becoming 0 kg/cm^2 and approximately 0 kg/cm^2. (2) The means for converting the rotational speed of the electric motor into the amount of movement of the hydraulic piston that reciprocates the plasticizing screw includes a screw shaft provided integrally with the output shaft of the electric motor in parallel with the reciprocating direction of the hydraulic piston; It consists of a female threaded member that is screwed onto a threaded shaft and is attached integrally with the hydraulic piston, and the female threaded member is a half-split member that can be screwed into or unscrewed from the threaded shaft. A plasticization control device for an injection molding machine according to claim 1, which has a structure of: