JPH02252517A - Purging method for injection molding machine - Google Patents

Abstract

PURPOSE:To greatly reduce a time required for purging and resin amount and to completely remove residual resin adhered to the inner surface of a heating cylinder by discharging resin remaining in the cylinder, and then idling a screw for a predetermined period of time. CONSTITUTION:After a controller 18 charges in a stroke of about 20% of a metering full stroke as the degree of a value of a back pressure at the time of a normal molding cycle in a state that a hopper shutter 8 is closed, a screw 6 is moved forward at a high speed to be molded, and executed, for example, repeatedly in 1-3 cycles. Thus, resin in a screw groove is completely eliminated at a certain time point, the screw 6 starts idling in a state that no resin is disposed between the crests of the threads of the screw 6 and the inner surface of a heating cylinder 1. When the screw 6 is idled, the screw 6 is so-called tiltably rotated at its supporting point as a center, the crests of the threads of the screw 6 and the inner surface of the cylinder 1 are frictioned each other to effectively peel the old resin film adhered to the inner surface of the cylinder 1.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a purging (resin change, color change) method in an in-line screw type injection molding machine, and in particular, the present invention relates to a method for purging (resin change, color change) in an in-line screw type injection molding machine, and in particular, the present invention relates to a method for purging (resin change, color change) in an in-line screw type injection molding machine. The present invention relates to a purging method for an injection molding machine that is effective in removing.

[Prior Art] When purging is performed such as changing resin or color due to a change in product type, it is necessary to completely remove the previous resin remaining inside the heating cylinder. It is important to completely remove the resin adhering to the inner circumferential surface of the nozzle and the outer circumferential surface of the screw. That is, if a white molded product, a transparent molded product, etc. are molded after using a colored resin, the previous resin may not be completely removed.

Colored areas occur in these areas, impairing the appearance of the product.

It would be very inefficient to remove the screw from the heating cylinder and manually remove the residual resin after each purging process, so conventionally, the following purging method was generally used. Ta. That is, new resin is continuously supplied from the hopper to the rear of the heating cylinder, and the back pressure (the force that resists the screw backward force generated by the pressure of the molten plasticized resin) is increased to rotate the screw near its forward limit. , the resin is transferred to the nozzle side by the feeding action of the screw, and the resin is melted and plasticized by a known plasticizing mechanism, and the resin is continuously transferred from the nozzle to the
The previously used resin that remained or adhered to the inside of the heating cylinder was discharged and removed.

[Problem M to be solved by the invention] However, in the above-mentioned conventional purging method, it takes time for purging and the resin is continuously discharged during this time, so the amount of resin for purging is limited. There was also a problem in terms of bulk and cost. Furthermore, there was also the problem that it was quite difficult to completely remove the previously used adhering resin.

In other words, as a result of observation by the inventors of the present invention, as shown in FIG. It has been found that it is extremely difficult to remove the residual resin 51 that has adhered to the inner circumferential surface of the heating cylinder 50 by the conventional method. Note that the reason why a large amount of resin tends to adhere to the inner circumferential surface of the heating cylinder 50 is that the roughness of the inner circumferential surface of the heating cylinder 50 is rougher than that of the outer circumferential surface of the screw 52 in order to improve the transferability of the resin. This is thought to be due to the fact that the inner circumferential surface of the heating cylinder 50 reaches the highest temperature due to external heating from the band heater, and the resin is likely to become "scorched". Furthermore, in the figure, the gap between the inner circumferential surface of the heating cylinder 50 and the maximum outer diameter part (thread outer diameter part) of the screw 52 is exaggerated, but in reality, D=0. The residual resin 51 attached to the inner peripheral surface of the heating cylinder 50 has a film thickness of several to several tens of micrometers.

Therefore, a technical problem to be solved by the present invention is to solve the above-mentioned problems of the prior art, and its purpose is to significantly reduce the time and amount of resin required for purging, and to An in-line screw type injection molding machine with excellent economic efficiency that can completely remove residual resin attached to the inner circumferential surface of the heating cylinder, thereby completely eliminating previously used resin inside the heating cylinder in a short time. The object of the present invention is to provide a purging method.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides a purging method for an in-line screw type injection molding machine in which a screw is disposed in the heating cylinder so as to be rotatable and movable back and forth. After the resin remaining inside is discharged, the screw is allowed to idle for a predetermined period of time.

In the present invention, preferably, before the idling stroke of the screw, the back pressure is increased while new resin is supplied to the rear part of the screw in the heating cylinder, and the screw is rotated near the forward limit, so that the resin is discharged from the nozzle. By continuously discharging the resin, the previous resin remaining in the heating cylinder is roughly discharged from the nozzle, and the new resin is supplied to the rear of the screw in the heating cylinder, resulting in a charge stroke of several tens of percent. and subsequent injection for multiple cycles; a process in which the supply of new resin into the heating cylinder is stopped; and a process in which the screw is forcibly retracted to the retraction limit without rotating, and then the screw is moved forward for high-speed injection. and a process in which charging of several 10% of the charge stroke and subsequent injection are performed for one cycle or more, and after the idling process of the screw, new resin is supplied to the rear part of the screw in the heating cylinder. However, at least a process is provided in which charging with a charge stroke of several 10% and subsequent injection are repeated for multiple cycles.

[Operation When copsing, for example, close the hopper shutter, completely remove the previously used resin in the hopper (hereinafter referred to as old resin), clean the inside of the hopper, and then clean the new resin to be used next. A new resin (hereinafter referred to as new resin) is put into the hopper and prepared for purging.

Next, the hopper shutter is opened to supply new resin to the rear of the screw in the heating cylinder, and in this state, the back pressure is made higher than the normal charging stroke, and the screw moves its axial position to the forward limit. The screw is continuously rotated, for example, for about 30 seconds while being held nearby. As a result, the new resin is cross-wired, melted and plasticized and transferred forward (towards the screw tip) by the thread feeding action of the screw, and the molten resin is continuously discharged from the nozzle (druling, takinagashi), and the old resin is The resin is generally discharged from the heating cylinder in the form of extruded new resin.

Next, the back pressure is set to the value during a normal molding cycle, and the charge is made with a stroke of, for example, about 20% of the full metering stroke (due to the rotation of the screw and the retreat of the screw due to the molten resin pressure stored on the tip side of the screw). After melting and plasticizing/metering), the screw is moved forward at high speed to perform injection, and this is repeated, for example, 4 to 5 cycles.By repeating this charging and injection, the old resin remaining in the heating cylinder is subjected to a cleaning action. is discharged.

Next, the hopper shutter is closed to stop the supply of new resin, and then the screw is forcibly retreated by a full stroke without rotation, and then advanced at high speed to the forward limit position to inject the molten resin. be done. In this process, the hard-to-remove old resin adhering to the inner peripheral surface of the nozzle is effectively removed by the high-pressure, high-speed molten resin.

Next, with the hopper shutter closed, the back pressure is set to about the value during a normal molding cycle, and after charging is performed at a stroke of, for example, about 20% of the full metering stroke, the screw Injection is performed by moving the screw forward at high speed, and this is repeated, for example, for 1 to 3 cycles, so that the resin in the screw groove is almost completely exhausted at a certain point.

The screw begins to idle with no resin interposed between the threaded top of the screw and the inner circumferential surface of the heating cylinder. As is well known, the screw is cantilever-supported and long, and the gap between the threaded top of the screw and the inner circumferential surface of the heating cylinder is minute, so when the screw is idling, it loses its support point. At the center point M, a "misosuri rotational movement" is performed, and the thread crest of the screw rubs against the inner circumferential surface of the heating cylinder, and the old resin film that has adhered to the inner circumferential surface of the heating cylinder is effectively peeled off. .

This idling period is to prevent metal-on-metal wear.

For example, it will take about 10 to 30 seconds. (Note that if the resin is present between the threaded crest of the screw and the inner circumferential surface of the heating cylinder, there is no possibility that the threaded crest of the screw and the inner circumferential surface of the heating cylinder will come into contact with each other due to the centering action of the resin.

) Thereafter, the hopper shutter is opened and new resin is supplied, and as before, for example 2
After charging with a stroke of about 0%, the screw is advanced at high speed to perform injection, and this is done for example 4 to 5 times.
By repeating the cycle, the old resin that was peeled off in the previous process is discharged together with the new resin.

In each of the above steps, the old resin that remains or adheres to the inside of the heating cylinder can be completely removed and discharged to the extent that it does not pose a practical problem. If a full stroke backward and high speed forward movement without rotation is required, and you want to be more careful,
After this, 2 to 3 cycles of charging with a stroke of about 20% and injection with high-speed advancement of the screw are performed. Even including this last step, the time required for purging is 1/3 compared to the conventional method described above.
In addition, the amount of resin required for purging can be reduced as much as possible.

[Example 1] The present invention will be explained below using an example shown in FIGS. 1 to 5.

FIG. 1 is an explanatory diagram showing a mechanical section of an injection device of an injection molding machine and structures related thereto.

In FIG. 1, reference numeral 1 denotes a heating cylinder, and its rear end side is fixed to a headstock 2 via a mounting plate 3, and the headstock 2 is held by a support mechanism (not shown).

4 is a band heater wrapped around the outer circumference of the heating cylinder 1;
Reference numeral 5 denotes a nozzle attached to the tip of the heating cylinder, and a band heater 4 is also wound around the outer periphery of the nozzle 5. 6
is a screw disposed in the heating cylinder 1 so as to be able to rotate and move forward and backward, and as is well known, a feed zone, a compression zone, and a metering zone are formed from the rear end side to the front end side. ing.

7 is a hopper for supplying resin material to the rear part of the screw 6 in the heating cylinder 1, and the resin material is supplied from the hopper 7 to the headstock 2 and the material supply port 2a bored in the heating cylinder 1; It is introduced into the heating cylinder 1 via 1a. A hopper shutter 8 closes or opens the lower a of the hopper 7 during material supply. The hopper shutter 8 is selectively controlled to be in a closed or open state by an electromagnetic actuator 9 comprising, for example, an electromagnetic plunger, and the electromagnetic actuator 9 is driven based on commands from a control device to be described later. In addition, 10 is a hopper shutter 8
The shutter sensor 10 is a shutter sensor composed of, for example, a limit switch, which detects the closed/open state of the shutter, and the detection information of the shutter sensor 10 is sent to a control device to be described later.

Reference numeral 11 denotes a rotational drive source connected to the rear end of the screw 6, and although an electromagnetic motor is used in this embodiment, it can also be replaced by a hydraulic motor. FIG. 2 is an explanatory view showing the connection structure of the rear end of the screw 6. In the figure, reference numeral 12 denotes a connection member that rotates integrally with the output shaft (not shown) of the rotary drive source 11. A short-span spline groove forming portion 6a at the rear end of the screw 6 is fitted into the spline groove forming hole 12a, whereby the connecting member 12, that is, the output shaft of the rotational drive source 11 and the screw 6 rotate together. It looks like this. The spline groove forming portion 6a is held immovably in the axial direction with respect to the connecting member 12 by screwing a semi-annular presser plate 13.13 as shown in FIG. 3 to the connecting member 12. has been done.

As described above, in the in-line screw type injection molding machine, the screw 6 has a cantilever support structure in which the short span portion at the rearmost end (the spline groove forming portion 6a in this embodiment) is held. The outermost circumference of the screw 6, that is, the top surface of the thread, and the inner circumferential surface of the heating cylinder 1 are usually set to have a clearance of about 0.5 m+w. 1. In a normal molding cycle, the thread crest of the screw 6 and the inner circumferential surface of the heating cylinder 1 are aligned due to the alignment effect of the resin interposed between the thread crest of the screw 6 and the inner circumferential surface of the heating cylinder 1. do not come into contact with each other, and the screw 6 rotates without causing the free end side to become eccentric (without performing a "slip rotational movement"). However, if the screw 6 is rotated without the resin intervening between the thread crest of the screw 6 and the inner circumferential surface of the heating cylinder 1 (idling), the screw 6 will center around the short-span support at its rearmost end. As a result, the so-called "miso-suri rotational motion" as shown exaggeratedly by the two-point #1 line in FIG. Because it is minute, the top of the screw thread and the inner circumferential surface of the heating cylinder rub against each other.

In FIG. 1, reference numeral 14 denotes a forward and backward drive source for the screw 6, which advances the screw 6 during the injection stroke, controls back pressure during the charging stroke, or forcibly moves the screw 6 backward. ing. In this embodiment, the forward and backward drive source 14 is composed of a hydraulic cylinder, and the tip of its piston rod 14a is attached to the casing of the rotational drive source (motor) 11, thereby causing the piston rod 14a to At the same time, the rotary drive source 11 and the screw 6 move back and forth in unison. In addition, in the embodiment, the forward and backward drive source 14
Although it is made up of a hydraulic cylinder, it is also possible to replace it with a hydraulic motor or an electromagnetic motor by adding an appropriate rotation-linear motion conversion mechanism.

15 is an injection stroke sensor, and in this embodiment,
For example, it consists of an encoder that rotates in conjunction with a binion that meshes with a rack member 16 that moves back and forth integrally with the rotational drive source 11, and the measurement information from the injection stroke sensor 15 is sent to a control device that will be described later. This control device controls the position (stroke) of the screw 6,
Speed is becoming more recognized. Reference numeral 17 denotes an injection pressure sensor consisting of a pressure head or the like attached to the forward/reverse drive source (hydraulic cylinder) 14. Information measured by the injection pressure sensor 17 is transmitted via an A/D converter (not shown), etc., as will be described later. The control device recognizes the injection pressure and back pressure.

18 is a control device consisting of a microcomputer that controls the entire injection molding machine, and a ROM that stores various I10 interfaces, main programs, fixed data, etc.
, R for reading and writing various flags and measurement data, etc.
A M is equipped with a μCPU (Micro Central Processor Unit), etc., which takes charge of overall control, and controls the normal molding process based on a molding condition control program created in advance. It is designed to perform purging control. In addition, the control device fil! 18 is the driver 19.2
0 to an electromagnetic actuator 9 and a rotary drive source 11
Further, the forward and backward drive source 14 is controlled via the driver 21 and the control valve 22, respectively.

In the above structure, during a normal molding cycle, the resin material supplied from the hopper 7 to the rear part of the screw 6 in the heating cylinder 1 is transferred to the screw 6 as is known in the art.
While being kneaded by the rotation of the screw, the mixture is transferred forward by the screw feeding action, and is heated by the heating cylinder 1.
The resin material is melted and plasticized by the frictional heat generated by the rotation of the screw 6 between the resin materials and between the resin material and the metal surface.

Then, as the molten resin is stored on the tip side of the screw 6, the screw 6 retreats while the back pressure is controlled, and when the molten resin equivalent to 1 shot 1 is stored on the tip side of the screw 6 (at the end of measurement) ), the rotation of the screw 6 is stopped. After that, at the injection start timing after a predetermined time, the screw is advanced and the molten F! is discharged from the nozzle 5. A resin is injected into the mold cavity (not shown).
Filled.

The molding process in the above order is continuously repeated under the control of the control device 18, and the control device 18 controls the injection stroke sensor 5. Pressure sensor 17
The rotary drive source 11, the forward/backward drive source 14, etc. are drive-controlled while referring to measurement information from each sensor.

Now, after continuous molding with the new resin (old resin) is completed, an automatic purging operation as described in the next step is executed in order to perform molding with a different new resin (new resin). This automatic purging operation will be explained in detail below with reference to FIG.

First, in purging, the controller 18 is instructed to close the hopper shutter 8 by, for example, a key manual means (not shown), and the hopper shutter 8 is closed by the electromagnetic actuator 9. Subsequently, the old resin that has been used so far in the hopper 7 is completely removed and the inside of the hopper 7 is cleaned, and then the new resin to be used next is put into the hopper 7 to prepare for purging.

Next, when the control device 18 is made to recognize the purging preparation state by key manual means (not shown), the control device 18
starts executing the automatic purging operation, and first drives the electromagnetic actuator 9 to open the hopper shutter 8 as shown in FIG. 5(,). As a result, new resin is supplied to the rear part of the screw 6 inside the heating cylinder 1.

Subsequently, the control device 18 drives and controls the one-rotation drive source 11 to rotate the screw 6, and also controls the forward and backward drive source 14.
is driven and controlled to set the back pressure higher than the normal charging stroke (back pressure P1), so that the axial position of the screw 6 is maintained near its forward limit. This allows the fifth
As shown in Figure (b), by the screw feeding action of the screw 6.

The new resin is mixed, melted and plasticized and transferred forward (toward the screw tip), and the molten resin is continuously discharged from the nozzle 5 (druling, dripping), extruding the old resin into the new resin. It is generally discharged from inside the heating cylinder 1. This process is executed approximately 30 times, which is much shorter than the time required by the conventional method (approximately 30 minutes).

In FIG. 5, A indicates the forward limit position of the screw 6, C indicates the backward limit position of the screw 6, and B indicates the 20% charge stroke position (20% backward position of the screw 6) with respect to the metered full stroke. are shown respectively.

Next, the control bag fi18 causes the rotary drive source 11 to rotate the screw 6, and also causes the forward and backward drive source 14 to set the back pressure to the value at the normal molding cycle (back pressure P2), After charging (melt plasticization and metering by rotating the screw 6 and retracting the screw due to the molten resin pressure stored on the tip side of the screw 6) with a stroke of, for example, about 20% of the full metering stroke, the screw 6 is Stop rotation. Thereafter, the control device 18 immediately controls the forward and backward drive source 14 to move the screw 6 forward at high speed to perform injection. As shown in FIG. 5(c), 20% charging and high-speed injection are repeated for one cycle, for example, four to five cycles.

By repeating the above 20% charge and high-speed injection, the old resin remaining in the heating cylinder 1 is cleaned and discharged, and the old resin remaining in the thread groove of the screw 6 is effectively contained in the new resin. is discharged. In addition, in the process shown in FIG. 5(e), the reason why the charge amount is not 100% but several lO% (20% in this example) is as follows.
This is based on the fact that through experiments conducted by the inventors of the present application, it was found that there is no difference in cleaning effect between the case of 100% charge amount and the case of 10% charge amount.
By doing this, the amount of resin used can be saved considerably compared to the case where the charge amount is 100%.

Subsequently, as shown in FIG. 5(d), the control device 18 closes the hopper shutter 8 using the electromagnetic actuator 9 to stop the supply of new resin.

Thereafter, as shown in FIG. 5(,), the control device 18 causes the forward/backward drive source 14 to forcibly move the screw 6 backward by a full stroke without causing any rotation, and then immediately moves the screw 6 back. is advanced at high speed to the forward limit position, and the molten resin is injected. In this process of FIG. 5(e), the nozzle 5
The old resin adhering to the inner peripheral surface of the machine is effectively removed by the high-pressure, high-speed molten resin. (In addition, if the temperature of the band heater 4 attached to the nozzle 5 described above is set 20 to 30 degrees Celsius higher than the normal set temperature, the resin attached to the inner circumferential surface of the nozzle 5 can be effectively removed. is larger.) Then, as before, as shown in FIG. 5(f), with the hopper shutter 8 still closed.

The control device 18 sets the back pressure to about the value during a normal molding cycle, performs charging at a stroke of about 20% of the metered full stroke, and then advances the screw 6 at high speed to perform injection. Repeat 1 to 3 cycles. As a result, the resin in the screw groove is almost completely exhausted at a certain point, and the screw 6 starts to idle without any resin intervening between the thread crest of the screw 6 and the inner circumferential surface of the heating cylinder 1. screw 6
When the screw rotates idly, the screw 6 performs a so-called "disc rotation motion" centering on its support point (see Fig. 4), as described above, and the thread crest of the screw 6 and the heating cylinder 1
The old resin film adhering to the inner circumferential surface of the heating cylinder 1 shown in FIG. 6 is effectively peeled off. This idling period lasts approximately 10 to 30 seconds, for example, in order to prevent wear between metals.

Subsequently, as shown in FIG. 5(g), the control device 18 operates the hopper shutter 8 using the electromagnetic actuator 9 to restart the supply of new resin.

After that, as shown in FIG. 5(h), the control device 18 repeats, for example, 4 to 5 cycles of charging with a stroke of about 20y1 for the metered full stroke and subsequent high-speed injection. Let it run. As a result, the old resin that was peeled off in the previous process is discharged together with the new resin.

In each of the above steps, the old resin remaining or attached inside the heating cylinder 1 is completely removed and MI
: However, if you want to be more complete, you can perform the full stroke backward and high-speed forward strokes without the rotation of the screw 6 described above as shown in Figure 5), and be even more careful. If the fuel is inserted, charging of 20% stroke and injection by high-speed advancement of the screw 6 are further performed for 2 to 3 cycles as shown in FIG. 5(j).

In this example, the time required for purging can be reduced to about 1/3 compared to the conventional method described above, even including the step shown in FIG. It was confirmed that it can be removed and discharged. Furthermore, the amount of resin required for purging can be reduced as much as possible compared to the conventional method.Although the present invention has been described in detail with reference to illustrated embodiments, it is clear to those skilled in the art that the amount of resin required for purging can be reduced within the spirit of the present invention. It goes without saying that various modifications are possible.

[Effects of the Invention] As described above, according to the present invention, the time required for purging and the amount of resin can be significantly reduced, and the residual resin attached to the inner peripheral surface of the heating cylinder, which was difficult to remove in the past, can be reduced. can be effectively removed and discharged.

It is possible to provide a purging method for an injection molding machine that can completely eliminate the previously used resin in a short time and is highly economical, and has great industrial value.

[Brief explanation of drawings]

1 to 5 relate to one embodiment of the present invention, in which FIG. 1 is an explanatory diagram showing the mechanical part of an injection device of an injection molding machine and related members, and FIG. 2 is a rear end portion of a screw. FIG. 3 is a plan view showing a presser plate, and FIG. 4 is an explanatory view exaggerating the movement of the screw when the screw is idling. FIG. 5 is an explanatory diagram schematically showing each step of the automatic purging operation, and FIG. 6 is an explanatory diagram showing resin remaining or attached to the inner peripheral surface of the heating cylinder. 1...Heating cylinder, 1a...Material supply port, 2...Head stock, 3...
Mounting plate, 4...Band heater, 5...
Nozzle, 6...Screw, 6a...
Spline groove forming part, 7...Hopper, 7a.
...Material supply opening, 8...Hopper shutter. 9... Electromagnetic actuator, 10...
Shutter sensor, 11...Rotational drive source, 12.
...Connection member. 12a...Spline groove forming hole, 13...
... Pressing plate, 14... Forward and backward drive source, 14a.
... Piston rod, 15 ... Injection stroke sensor, 16 ... Rack member, 17 ...
... Injection pressure sensor, 18 ... Control device,
19, 20, 21... Driver, 22...
...Control valve. Figure 2 Figure Figure 6 Figure 5 cg>

Claims (4)

[Claims] (1) In a purging method for an in-line screw type injection molding machine in which a screw is arranged in a heating cylinder so that it can rotate and move forward and backward, the screw is idled for a predetermined period of time after the resin remaining in the heating cylinder is discharged. A purging method for an injection molding machine, characterized in that: (2) A purging method for an injection molding machine according to claim 1, wherein the idle rotation period of the screw is 30 seconds or less. (3) In claim 1, before the idle stroke of the screw, (a) supplying new resin to the rear part of the screw in the heating cylinder and increasing back pressure to rotate the screw near the forward limit; (b) A process in which the previous resin remaining in the heating cylinder is roughly discharged from the nozzle by continuously discharging resin from the nozzle; (c) a process in which the supply of new resin into the heating cylinder is stopped; and (d) a process in which the screw is forcibly retracted to the retraction limit without rotating. and (e) a step of performing one or more cycles of charging with a charge stroke of several 10% and subsequent injection. Machine purging method. (4) In claim 1, after the idling stroke of the screw, new resin is supplied to the rear part of the screw in the heating cylinder, and charging with a charge stroke of several 10% and subsequent injection are repeated for multiple cycles. A purging method for an injection molding machine, comprising at least a step.