JPH0226720A - Purging in injection apparatus of injection molding machine - Google Patents

Abstract

PURPOSE:To attempt to improve cleaning effect of a resin and to shorten a purging time and to attempt to reduce a necessary amt. of the resin by rotating periodically a screw in the forward and reverse direction and performing a relative vibration of the screw and a heating cylinder in the shaft direction when purging is performed. CONSTITUTION:When purging is performed, a resin material fed from a hopper 5 is changed to a resin material to be used newly, which is fed in a heating cylinder 1. In this instance, a screw 7 is placed at a forwarded position. At this state, an operation controlling means 23 starts to drive a forward and reverse rotation of the first motor 9 at a specified cycle of the forward and reverse rotation, a specified time ratio of the forward and reverse rotation and specified speeds of the forward rotation and the reverse rotation. At the same time, the operation controlling means 23 drives the second motor 10 at a specified speed in the retreating direction of the screw 7 and a composite movement wherein the screw 7 is finely vibrated with a high speed is performed in parallel. Therefore, the resin material is effectively and uniformly kneaded and the cleaning effect is improved by receiving complicated forces contg. the vibrational energy from a plurality of directions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a purging method for changing resin materials, changing colors, etc. in a screw-type injection device of an injection molding machine.

[Prior Art] In this type of screw-type injection device, as is well known, the resin material supplied from the hopper into the heating cylinder is kneaded by the unidirectional rotation of the screw inside the heating cylinder while being kneaded along the screw groove. and is sent to the tip of the heating cylinder.

Then, the temperature of the resin material increases due to the heat transferred from the heating cylinder heated by the band heater and the friction heat generated between the resin materials and between the resin material and the metal surface due to the kneading action of the screw, and the resin material is plasticized and melted. It has become.

By the way, in the injection device of this type of injection molding machine, in order to perform purging such as changing the resin material or changing the color, the resin material to be used next is newly supplied from the hopper into the heating cylinder, and the rotation of the screw and the purging are performed. Purging work was performed by repeating free shots until the previous resin material disappeared from inside the heating cylinder.

[Problems to be Solved by the Invention] By the way, in the plasticizing mechanism of resin using external heating and simple unidirectional rotation of the screw as described above, it takes a long time to completely discharge the previous resin material by the above-mentioned barging process. In particular, when changing resin from black resin to white resin or from colored resin to transparent resin, a large amount of resin material is required for purging and it takes a lot of time. there were.

The above-mentioned problems are serious in production sites that carry out high-mix, low-volume production where changing the type and color of resin materials is frequently required, and puts pressure on the actual operating time of injection molding machines.

This becomes a major hindrance when trying to reduce product costs.

Therefore, the 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 improve the cleaning effect of the resin during purging and shorten the purging time. It is an object of the present invention to provide a purging method for an injection device of an injection molding machine, which can reduce the amount of resin required for purging.

[al! [Means for Solving the Problems] The above-mentioned object of the present invention is to knead and plasticize a resin material by rotating a screw in a heating cylinder, and to rapidly advance the screw by an injection cylinder to infuse the molten resin into a mold. In an injection device of an injection molding machine that injects into the mold, the screw is periodically rotated in forward and reverse directions, and the screw and the heating cylinder are caused to vibrate relative to each other in the axial direction during purging for changing resin materials, changing colors, etc. , achieved by a purging method.

[Function] As described above, the present invention prevents the resin material from being cross-wired by periodically rotating the screw in the forward and reverse directions and causing relative vibration between the screw and the heating cylinder during purging.
Since the resin is plasticized, the resin (molten resin and unmolten resin) in the molten boule zone (flow area) between the inner wall of the heating cylinder and the outer circumference of the screw is effectively subjected to back-and-forth motion and vibrational energy. The previous resin material that adhered to the inner wall of the heating cylinder and the inner surface of the screw nozzle is quickly removed and cleaned by the new resin material. In particular, it was confirmed that the resin material adhering to the screw trough and the resin material adhering to the inner surface of the nozzle, which were conventionally difficult to remove, were effectively removed.

In other words, although detailed analysis of the behavior of the resin material in the flow region is difficult, the screw rotates in the direction of arrow X in Fig. 2 (
(forward rotation), a propelling flow Q1 toward the nozzle direction Y based on the rotary transport action of the screw and a back pressure flow Q2 toward the nozzle direction based on the pressure difference between the front and rear of the screw are generated, and both Q1 and Q2 It is said that due to the combined effect of the above, a lateral flow Q3 is generated in a plane substantially perpendicular to the thread of the screw, and a leakage flow Q4 is also generated. In reality, these four types of flows do not occur separately, but are combined into a complex flow that causes crosstalk and plasticization.

By the way, in the present invention, the screw is rotated in forward and reverse directions periodically, so when the screw is reversed, a synthetic flow (not shown) that is different from the above-mentioned forward rotation is generated, and by repeating forward and reverse rotation, the molten resin is The resin is kneaded more effectively and uniformly, and the cleaning effect of the resin is enhanced. Moreover, in the present invention.

During the forward and reverse rotation of the screw, the screw and heating cylinder are vibrated relative to each other in the axial direction, so using the molten resin as a vibration medium, the resin adhering to the inner wall of the heating cylinder, screw, and nozzle is removed by vibration energy. I can do it. Furthermore, the molten resin that has been given vibrational energy is subjected to even more complex forces from multiple directions, and together with the forward and reverse rotation of the screw, the molten resin is more effectively and evenly kneaded and cleaned. The effects will continue to improve.

Therefore, resin adhering to the troughs of the screw and the inner surface of the nozzle is effectively removed.

Note that the arrows in the left region in Fig. 2 very schematically indicate that the resin vibrates in parts A, B, and C (the entire area), and in reality, when the screw rotates forward, the The flow shown in the right region of 2 and the vibration shown on the left are combined, and when the rotation is reversed, the flow and vibration due to the rotation of the screw (not shown) are combined, creating a complex crosstalk, flow, and heat generation plasticization mechanism. I would like to be understood as what is being done.

[Example code] The present invention will be explained below with reference to illustrated embodiments.

FIG. 1 is an explanatory diagram showing an injection device of an injection molding machine according to an embodiment of the present invention. In the figure, ▪ is a heating cylinder, and a band heater 2 is wrapped around the outer periphery of the cylinder, and a nozzle 3 is attached to the tip thereof. 4
is the head 1- which holds the rear end portion of the heating cylinder 1.
It is a member integrated with a base member of an injection device (not shown), and is provided with an opening 6 for guiding the resin material supplied from the hopper 5 into the heating cylinder 1. Reference numeral 7 denotes a screw installed in the heating cylinder 1 so as to be rotatable and movable in the axial direction, and from the right side to the left side in the drawing, a feed zone, a compression zone, and a metering zone are formed as known in the art. .

Reference numeral 8 denotes a support body held on this base member of an injection bag (not shown), 9 a first electric servo motor for charging (hereinafter referred to as the first motor 9) attached to the support body 8, and 10 a support body. A second electric servo motor for injection (hereinafter referred to as second motor 10) attached to motor 9. lO
Although not shown in the figure, there is a built-in encoder for rotation detection.

The rotation of the first motor 9 is caused by the output shaft 1 of the first motor 9.
1, a gear 13 that meshes with the gear 12, and a ball spline body 1 that rotates integrally with the gear 13.
4, and is further transmitted to the screw 7 whose rear end is fixed to the charge drive shaft 15 via the charge drive shaft 15 which is spline-coupled to the ball spline body 14. That is, the screw 7 is driven to rotate in the forward and reverse directions by the forward and reverse rotation of the first motor 9.

Further, the rotation of the second motor 10 is controlled by the rotation of the second motor 10.
A gear 17 is fixed to the output shaft 16 of the output shaft 16, and a gear 18 is meshed with the gear 17. Nut body 1 that rotates integrally with the gear 18
9, the rotation of the nut body 19 is converted into a linear motion of the injection drive shaft 20 screwed to the nut body 19, and the rotation of the nut body 19 is transmitted to the coupling body 21 coupled to the injection drive shaft 20. It is adapted to be transmitted as a linear motion to the coupled drive body 22. The charge drive shaft 15 is held in the drive body 22 so as to be rotatable only, and the charge drive shaft 15 and the screw 7 are held by the drive body 22 so as to be rotatable.
moves in a straight line back and forth. That is, by the rotation of the second motor 10, the screw 7 is moved between the forward injection position shown in FIG. It is also adapted to be subjected to axial vibrational motion. Furthermore, this second motor 10 also controls back pressure control.

Although it is simplified in the first drawing, the Vw connecting body 21 is provided with an injection pressure sensor.

23 is an arithmetic control means consisting of a microcomputer;
Various ■/○ interfaces, ROM that stores the main control program and fixed data, etc., RAM that reads and writes various flags and input data, etc., and μ that manages overall control.
CPU (micro central processor unit)
etc., and drives and controls the first motor 9 and the second motor 10 as described later. Although not shown, the arithmetic control means 23 exchanges data with the external storage means as necessary, and similarly displays the results of arithmetic processing on a display as necessary.

24 is an input means such as a keyboard switch, and the input means 24 allows the operator to input to the calculation control means 23,
Resin material name, grade number, charging completion position, back pressure,
In addition, setting information such as the type of screw to be used is input.

At the time of purging, the arithmetic control means 23 determines the forward rotation speed, reverse rotation speed, normal rotation period, and reverse rotation period of the screw 7 using these setting information and a calculation table stored in advance as a case study in its own ROM or external storage means. The ratio, the period of forward and reverse rotation, the frequency and amplitude of the screw 7, etc. are calculated. Then, the calculation control means 23 uses this calculation result and the sensor group of the injection device (for example, the encoders of the first and second motors 9 and 10, the injection pressure sensor, the screw 7
Detection information SL, S2, etc. from the position detection sensor, etc.)
. . . Based on the SN, a control signal is sent to the driver circuits 26 and 27 via the D/A converter 25, and the driver 2
The first motor 9 is driven by six circuits, and the second motor 10 is driven by a driver circuit 27.

In the above configuration, during purging, the resin material supplied from the hopper 5 is changed to a newly used resin material, and the resin material is supplied into the heating cylinder l. At this time, the screw 7 is placed in the forward position shown in the first figure. Then, in this state, the first arithmetic control means 23 operates the first motor 9.
, for example, a predetermined forward/reverse rotation period as shown in Fig. 3,
Forward/reverse rotation [fi is started at a predetermined forward/reverse rotation period ratio and a predetermined forward/reverse rotation speed. As is clear from FIG. 3, there are more periods of forward rotation (rotation in the direction of sending the resin material to the tip of the screw 7) than periods of reverse rotation, and the forward rotation speed is greater than the reverse rotation speed. Although the screw 7 repeats forward and reverse rotation, the forward rotation has a superior transfer action, so the resin material supplied from the hopper 5 is kneaded and melted along the grooves of the screw 7 and sent to the tip of the screw 7.

At the same time, the arithmetic control means 23 drives the second motor 10 at a predetermined speed in the direction in which the screw 7 retreats, and at the same time causes the screw 7 to perform a complex motion of vibrating at high speed. As a result, the screw 7 begins to retreat in accordance with the amount of molten resin that has begun to be stored at its tip.

When the reaction force from the molten resin stored at the tip of the screw reaches a predetermined pressure due to the rotation of the screw 7 (at time T1 in FIG. 4), the calculation control means 23 activates the second motor 10 to reduce the reaction force. In order to keep the back pressure constant against the
The screw 7 is caused to maintain its vibrating motion while controlling the backward speed of the screw 7, and the first motor 9 is caused to maintain forward and reverse rotation as shown in FIG. 3 described above. As a result, the screw 7 vibrates and rotates forward and backward under a constant back pressure condition, and the molten resin is stored at the tip of the screw, until the retracted position of the screw 7 reaches a predetermined position (12 in Fig. 4). time)
In other words, the molten F stored at the tip of the screw 7
! When the amount of resin A reaches one shot, the backward movement, which is a combination of forward and reverse rotation of the screw 7 and vibration, is stopped. However, the calculation control means 23 causes the second motor 10 to continue the vibration of the screw 7 for a predetermined time at the above-mentioned position where the screw 7 has retreated to the home position.
As a result, the previous resin material adhering to the inner surface of the nozzle 3 is removed. After that, the vibration of the screw 7 is stopped, and the second motor 1o is activated to rapidly advance the screw 7.
Perform blank injection of molten resin. And heating cylinder 1
This operation is repeated until 11 layers of resin are completely exhausted.

By the way, during the above-mentioned barging process, the screw 7
performs a compound motion that periodically repeats forward and reverse rotations accompanied by vibrations. For this reason, as described in the [Function] section above using Fig. 2, the resin material is not only kneaded effectively and highly uniformly, but also subjected to complex forces from multiple directions, including vibrational energy. Enhances cleaning action. Therefore, the previously used resin adhering to the inner wall of the heating cylinder 1, the screw 7, and the inner surface of the nozzle 3 is effectively cleaned and removed by the new resin, and the resin can be completely removed in a shorter time with a smaller amount of resin than before. It was confirmed that purging could be performed. In particular, it has been confirmed that the resin adhering to the troughs of the screw 7 and the resin adhering to the inner surface of the nozzle 3, which were previously difficult to remove, can be reliably removed.

In the above embodiment, the forward and reverse rotation of the screw 7 is controlled by the first motor 9, that is, the first electric servo motor, and the vibration drive control, back pressure control, and injection operation control of the screw 7 are controlled by the second motor. The motor 10, that is, the second electric servo motor is used to perform each operation, but the screw 7
Forward and reverse rotation control is performed by a hydraulic motor driven and controlled by a servo valve, and vibration drive control, back pressure control, and injection operation control of the screw 7 are performed by a hydraulic cylinder driven and controlled by a servo valve. Good too. Also,
In the embodiment, the screw 7 is vibrated, but the heating cylinder 1 may be vibrated. A possible modification of this is possible.

[Effects of the Invention] As described above, according to the present invention, the cleaning action of the resin during purging is significantly improved, making it possible to shorten the purging time and reduce the amount of resin required for purging. , a purging method for an injection device of an injection molding machine can be provided, and its industrial value is great.

[Brief explanation of the drawing]

The drawings all relate to one embodiment of the present invention; Fig. 1 is an explanatory diagram of an injection device of an injection molding machine, Fig. 2 is an explanatory diagram extremely schematically showing the behavior of the resin in a flow region, and the third diagram is an explanatory diagram of the injection device of an injection molding machine. FIG. 4 is an explanatory diagram showing the forward and reverse rotation cycle of the motor for driving the motor in the forward and reverse directions. FIG. 4 is an explanatory diagram showing the relationship between back pressure and screw position. 1... Heating cylinder, 2... Band heater, 3... Nozzle, 5... Hopper,
7... Screw 9... 111th dynamic servo motor (first motor), 10... Second electric servo motor (second motor), 15...・Charge drive shaft, 20... Injection drive shaft, 23...
- Arithmetic control means, 26, 27...driver circuit.

Claims (1)

[Claims] In an injection device of an injection molding machine, a resin material is kneaded and plasticized by rotation of a screw in a heating cylinder, and the screw is rapidly advanced by an injection cylinder to inject molten resin into a mold. In an injection device for an injection molding machine, the screw is periodically rotated in forward and reverse directions during purging such as material change, color change, etc., and the screw and the heating cylinder are vibrated relative to each other in the axial direction. Purging method.