JPH0345324A - Running method for injection molder for flow molding - Google Patents

Abstract

PURPOSE:To make smooth and sure filling possible in response to the shape of various molded items by a method wherein resin in an injection cylinder is filled in a cavity by changing the rotational frequency of a screw and the back pressure applied to the screw in a plurality of steps. CONSTITUTION:The rotational frequency setters N1 - N4 of a screw and its timers T1 - T3, which set the changing-over timing of rotational frequencies, are equipped in the rotational frequency setting section 23 of the screw, which is connected to a proportional solenoid flow control valve 21. And back pressure setters BP1 - BP4, which set the back pressure applied to the screw 10 and its timers T11 - T13, which set the changing-over timing of back pressures, are equipped in the back pressure setting section 24 of the screw, which is connected to a proportionally controlling pressure control valve 22. Further, at the flow molding of molded item, the rotational frequencies set on the rotational frequency setters N1 - N4 and the back pressures set on the back pressure setters BP1 - BP4 are successively changed-over by the timers T1 - T3 and T11 - T13. Further, the rotational frequency and back pressure of the screw may be changed-over by the positions of the screw set on position setters S1 - S3 and S11 - S13.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention allows the resin in the injection barrel to be transferred into the mold by rotating the screw while applying back pressure to the screw in the injection barrel. The present invention relates to a method of operating an injection molding machine for flow molding (intrusion) to fill a cavity.

[Conventional technology]

In general, in the injection molding method for synthetic resins, it is a method to eliminate molding defects such as sink marks, voids (bubbles), flow marks (annual ring-like striped patterns), and welds in thick inner molded products, or to compensate for insufficient injection capacity. A flow molding method is used as the method. This flow molding method involves filling part or all of the cavity in the mold with resin by rotating a screw inside the injection cylinder, then filling the resin with normal injection, and applying holding pressure to obtain a molded product. It is something.

[Problem to be solved by the invention]

By the way, the above-mentioned flow molding method belongs to a special molding method, and although it is a difficult molding method in terms of molding technology, the conditions for screw rotation and back pressure during the flow molding process in a flow molding injection molding machine are , only one stage is prepared for each, there is a lack of freedom in setting conditions, and there is a problem that it is difficult to obtain a molded product of desired quality.

The present invention was made in view of the two circumstances, and its purpose is to freely select the screw rotation and back pressure applied to the screw during the flow mold inking process, and to reduce the pressure inside the cavity. The injection molding machine for flow molding can be used to flexibly mold various molded products and can obtain molded products of the desired quality. The purpose is to provide a method.

[Means to solve the problem]

In order to achieve the above object, the present invention changes the rotational speed of a screw provided in the injection cylinder and the back pressure applied to the screw in multiple stages, thereby causing the resin in the injection cylinder to be released by the screw. It is used to fill the cavity within the mold.

[Function] In the method of operating the injection molding machine for flow molding of the present invention, when the cavity in the mold is filled with resin by rotating the screw with back pressure applied, the inside of the mold is By appropriately changing the screw rotation speed and back pressure according to the state of the flowing resin, molding defects are prevented and the resin is reliably filled into the cavity.

〔Example〕

Hereinafter, the present invention will be explained in detail based on FIGS. 1 and 2.

FIG. 1 shows an example of an injection molding machine for flow molding for carrying out the method of the present invention. In this figure, reference numerals 1 and 2 refer to a fixed mold attached to a fixed plate 3 and a movable plate, respectively. It is a moving mold installed in 4.

Then, this movable mold 2 approaches the fixed mold 1,
They are provided so that they can be separated freely, and a cavity 5 for product molding is formed between both molds 1.2 when the molds are clamped.

Further, the tip of an injection cylinder 7 is fitted into the injection port 6 of the fixed platen 3, and the injection port 6 and the cavity 5 are communicated with each other by a sprue runner 8. Part 1. hand,"
At the top of the base end of the bipedal injection tube 7, resin is injected into the injection tube 7.
A hopper 9 for feeding k is arranged. Furthermore, the injection tube 7
A screw 10 is inserted into the inside thereof, and the base end of this screw 10 is connected to a rotating shaft 13 of a hydraulic motor 12 attached to a support plate 11. Furthermore, a cylinder 14 is disposed at the base end of the injection tube 7, and the tip of the piston rod 15 of the cylinder I4 is attached to the support plate 11.

Then, by moving the piston rod 15 of the cylinder 14 described in - back and forth, the support plate II and the hydraulic motor 12 are moved back and forth.
At the same time, the screw 10 moves backward and forward inside the injection cylinder 7. Further, a pinion 17 is engaged with the rack 16 attached to the biped support plate II, and a detector 18 for detecting the position of the screw 10 is connected to the pinion 17.

” - At the end of the cylinder 14 on the support plate 11 side, there is a 3
The A boat of the position switching valve 19 is connected, and the ht+tank T is connected to the end of the cylinder I4 on the fixed platen 3 side. At one end of the hydraulic motor 12, the 3
A boat B of the position switching valve 19 is connected, and an oil tank T is connected to the other end of the hydraulic motor 12. Also,
A proportional electromagnetic flow control valve 21 is connected to the C boat of the 3-position switching valve 19 and is connected to a proportional electromagnetic flow control valve 21 which is supplied with an operation M from a pressure source 20, and a proportional control valve 21 is connected to the D boat of the 3-position switching valve I9. A pressure control valve 22 is connected, and an oil tank T is connected to the proportional control pressure horn control valve 22. When the three-position switching valve 19 is in the neutral position, the B boat and the D boat are communicated with each other, and the A boat and the C boat are cut off. The configuration is such that the A boat and the D port and the B boat and the C boat are communicated with each other by energizing the solenoid +9b, while the A boat and the D port are communicated with each other.

Further, a screw rotation speed setting section 23 is electrically connected to the proportional electromagnetic flow control valve 21, and this screw rotation speed setting section 23 includes a rotation speed setting device for setting the screw rotation speed. NlN2. N3. and a timer T1.
I2゜I3 and a position setting device Sl, S2. which sets the position of the screw. S3 is provided. Further, a back pressure setting section 24 is electrically connected to the proportional control pressure control valve 22, and this back pressure setting section 24 includes a back pressure setting device BPI for setting the back pressure to be applied to the screw 10; BP2
．． BP3. BF2 and these back pressure setting devices BPI-BP
Timers Tll and TI2.4 set the timing to sequentially change the back pressure set by TI2. T13 and position setters Sll, SI2, which set the screw positions. S13 is provided. Furthermore, the symbol SO is a position setting device that sets the retracted position of the screw IO in the metering process that normally follows the injection and pressure holding processes.

When carrying out the method of the present invention using a flow molding injection molding machine configured like a two-legged machine, the solenoid +9b of the 3-position switching valve 19 is energized immediately after mold clamping is completed, so that the 3-position switching valve 19 is energized. The A port and D boat, and the B boat and C boat of the switching valve 19 are communicated with each other. As a result, the flow rate of the hydraulic oil supplied from the hydraulic source 20 is controlled by the proportional electromagnetic flow control valve 2I, and is sent to the hydraulic motor 12 via the 3-position switching valve 19 to rotate the hydraulic motor 12. A screw 10 connected to a rotating shaft 13 of a hydraulic motor 12 rotates, and the molten resin in the injection cylinder 7 is injected into the cavity 5 through the sprue runner 8 in the fixed mold l.

In this case, the proportional electromagnetic flow control valve 21 is controlled according to the screw rotation speed set in the rotation speed setting device Nl until the time set in advance in the timer T1 of the screw rotation speed setting unit 23. As a result, the screw lO rotates at the rotational speed set to the rotational speed N+, and as a result, the molten resin injected from the injection cylinder 7 is filled into the sprue runner 8. Next, when the time set in the timer T1 has elapsed, the screw 10
is changed to the screw rotation speed set in the rotation speed setting device N2, and the molten resin is supplied into the mold at this screw rotation speed until the time set in the timer T2 elapses. As a result, the molten resin passes from the sprue runner 8 through the entrance (gate) of the cavity 5 and reaches the inside (the position indicated by reference numeral 25 in FIG. 1). Subsequently, after the time set in the timer T2 has elapsed, the timer T
3, the screw 10 is controlled by the screw rotation speed set in the rotation speed setting device N3, so that the molten resin flows through most of the interior of the cavity 5 (indicated by reference numeral 26 in FIG. 1). Further, after the time set in the timer T3 has elapsed, the screw rotation speed is changed to the screw rotation speed set in the rotation speed setting device N4, and the remaining portion in the cavity 5 is filled with the molten resin. .

On the other hand, in the filling process described in item 1, the 3-position switching valve 19
Solenoid +9b of 3-position switching valve 19 is energized, and A of 3-position switching valve 19
By communicating between the boat and the D port, the cylinder I
When the hydraulic oil in 4 exceeds the set pressure of the proportional control pressure horn control valve 22, it flows out from the end of the cylinder 14 on the support plate 11 side, and the hydraulic oil in the 3-position switching valve +9. It is returned to the oil tank T through the proportional control pressure control valve 22. As a result, the set pressure is applied as back pressure to the rotating screw 10 via the piston rod 15° support plate II of the cylinder 14 and the rotating shaft 13 of the hydraulic motor 12.

For example, until the time when the molten resin is filled into the sprue runner 8 (the time set in the timer Tll), the screw lO is controlled by the back pressure set on the back pressure setting device BPI, and then the molten resin flows near the gate. During the passage (time set in timer TI2), the back pressure setting device BPI
By setting a back pressure lower than the back pressure set in the back pressure setting device BP2, the molten resin is gradually supplied into the mold while retracting the screw 10. As a result, molten resin is filled near the gate at an extremely low speed and under low pressure.
Molding defects such as flow marks are reliably prevented. Next, after the molten resin is supplied into the cavity 5 (after the time set in the timer TI2 has elapsed), the back pressure is increased to the pressure set in the back pressure setting device BP3, so that it reaches the end of the cavity 5. In the process of filling the molten resin, back pressure is applied to the screw 10 so that the screw 10 does not retreat. Filling of the cavity 5 is completed when the time set in the timer TI3 has elapsed. Next, the back pressure setting device BP4i applies pressure to the cavity 5 with the set back pressure and fills it with molten resin, but since the cavity 5 has already been filled, the pressure of the molten resin rises and the screw retreats. I'll go.

During this retraction, when the screw position coincides with SO, the screw rotation is stopped, the immediate injection process is started, and a holding pressure is applied to the cavity 5 (the solenoid 1 of the 3-position switching valve 19
9b and energizes the solenoid 19a).

In this way, after filling the cavity 5 with molten resin by the flow molding method and maintaining some pressure by normal injection, the inside of the mold is cooled. Next, after cooling of the molded product in the mold is completed, the molds 1 and 2 are opened and the molded product is taken out.

When the molded product is molded as described above, the timer TI-T3. T
By I l-Tl 3, the rotation speed setting device N1~
N 4 , by changing the rotational speed of the screw IO set in the back pressure setting devices BPI to BP4 and the back pressure applied to the screw 10, it is possible to control the properties of the resin or the cavity, such as performing ultra-low-pressure, low-speed filling of molten resin near the gate. The resin filling operation according to the structure of No. 5 can be performed smoothly, molding defects will not occur, and molded products of desired quality can be reliably obtained.

In addition, when performing more advanced hydraulic control, "bipedal proportional electromagnetic flow control valve 21. A servo valve may be used in place of the proportional pressure control valve 22. Furthermore, each setting device N1-N of the screw rotation speed setting section 23 and the back pressure setting section 24
/1. BPI~BP4S1~S3. SII-S13. Each timer T1-T3. The number of TII to T13 is not limited to this embodiment, and it is sufficient that the screw rotation speed and back pressure can be changed in multiple stages.

Further, FIG. 2 shows a second embodiment of the present invention, and this second embodiment is composed of the proportional electromagnetic flow control valve 21 and the proportional control pressure control valve 22 of the first embodiment shown in FIG. Instead, two 3-position switching valves 303I, three manually set flow rate adjustment valves 32, 33, 34 and a pressure control valve 35, which are switched and controlled by these 3-position switching valves 30.31.
36° and 37°. When the 3-position switching valve 30 is in the neutral position, the 3-position switching valve 19
When the B boat of the 3-position switching valve 19 and the first flow rate regulating valve 32 are communicated with each other, and the solenoids 30a30b of the 3-position switching valve 30 are energized, the B-boat of the 3-position switching valve 19 and the 2nd flow regulating valve 32 are connected. The third flow rate regulating valves 33 and 34 are configured to communicate with each other. Further, when the three-position switching valve 31 is in the neutral position and the solenoids 31a and 31b are in the excited position,
D boat of 3-position switching valve 19 and each pressure control valve 3536.
37 are communicated with each other.

After the mold clamping is completed, the solenoid + of the 3-position switching valve I9 is
9b is energized and the A and D ports and the B and C ports of the 3-position switching valve 19 are connected to each other, the timer sequentially switches the 3-position switching valves 30 and 3 into communication with each other.
] to the neutral position, the excitation position of solenoids 30a and 31a, and the excitation position of solenoids 30b and 31b,
Hydraulic oil supplied from hydraulic pressure #20 or each flow rate adjusting valve 32.33°3 in turn via each 3-position switching valve 1930.
4, the flow rate is adjusted and sent to the hydraulic motor 12 to rotate the hydraulic motor 12 (screw 10), and when the hydraulic oil in the cylinder 14 exceeds the set pressure of each pressure control valve 35, 36, 37, each 3 Via the position switching valve 19.31, the oil is returned to the oil tank T through each pressure control valve 35, 36, 37 in turn, and is transferred manually to the rotating screw 10 in advance. Back pressure is applied according to the set pressure. As a result, in the same manner as in the first embodiment, the screw 1 during the flow molding process
The rotational speed of 0 and the back pressure applied to the screw 10 are appropriately changed to optimal values, and products of desired quality can be obtained by flexibly responding to various molded products.

In each of the above embodiments, the screw rotation speed and back pressure are switched by a timer, but the position setters Sl, S2. It may be switched by the screw position set by S3, Sll, S12, and S13.

In this case, the moving position of the screw detected by the detector 18 is input to the rotation speed setting section 23 and the back pressure setting section 24, and the position of the screw is set in advance by the position setting device 5l-8.
When the position set at 3,5ll-813 is reached, the screw rotation speed and back pressure are changed to correspond to the position, and the screw IO is automatically controlled.

〔Effect of the invention〕

As explained above, the present invention changes the rotational speed of the screw provided in the injection cylinder and the back pressure applied to this screw in multiple stages, so that the resin in the injection cylinder can be moved into the mold by the screw. Since the resin is to be filled into the cavity of the mold, the screw rotation speed and back pressure can be appropriately changed according to the state of the resin flowing in the mold to smoothly and reliably fill the resin into the cavity. In addition, for example, it is possible to fill resin at extremely low speed and low pressure near the gate, and subsequent resin filling can be done relatively quickly, which prevents molding defects and shortens molding cycle time. Moreover, it can be flexibly adapted to the shapes of various molded products, and molded products of desired quality can be easily obtained. Furthermore, since it is possible to set the back pressure commensurate with the filling resistance, it is possible to reduce the load on screw-related parts, and it is possible to mold the resin without applying unnecessary high shearing force.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment/example of the present invention;
The figure is a circuit diagram of a hydraulic control section showing a second embodiment of the present invention. l...Fixed mold, 2...Movable mold, 5...Cavity, 7...Injection tube, 10...Screw 21...
・Proportional electromagnetic flow control valve, 22... Proportional control pressure control valve, 30° 31... 3 position switching valve, 3'2, 33.3
4...Flow rate adjustment 6 Valve adjustment, 35. 36.・・Pressure control valve, 1-N 4・・Rotation speed setting device, BPI-BF2 ・・Back pressure setting device.

Claims (1)

[Claims] While applying back pressure to the screw provided in the injection cylinder,
In the method of operating an injection molding machine for flow molding, in which the resin in the injection cylinder is filled into a cavity in a mold connected to the injection cylinder by rotating the screw, the rotation speed of the screw and the A method of operating an injection molding machine for flow molding, characterized by filling resin into a cavity by changing back pressure applied to a screw in multiple stages.