JPH06143345A - Discharging method of residual material of screw preplasticating injection molder - Google Patents

Abstract

PURPOSE:To shorten the purging operation for changing material and prevent the seizure of a plunger or the like due to the stacking of aged residual material by a method wherein the residual material in a plasticating part is discharged through communicating passages, a gap and a nozzle hole by rotating a screw continuously. CONSTITUTION:Under the state that the plunger 14 of an injection part is held at its dwelling position so as to leave a gap 34 between the plunger and the front wall 11 of an injection cylinder 10, a screw 31 in a plasticating part is rotated continuously. Further, a first process, in which the residual material in the plasticating part 3 is discharged through communicating passages 35 and 15 between the plasticating part 3 and the injection part, the gap 34 and a nozzle hole 19, is equipped. Next, in a second process, the backward and forward actions of the plunger 14 by its maximum stroke is performed at least once. Thus, the sediment accumulated onto the inner wall of the injection cylinder 10 is discharged at the backward motion of the plunger 14, while the residual material in the injection cylinder 10 is discharged through the nozzle hole 19 at the forward motion of the plunger.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw pre-plastic injection molding machine, and more particularly to a technical means for promptly discharging old resin in an injection device when changing its material (including changing color). .

[0002]

2. Description of the Related Art A screw pre-plastic injection molding machine has a structure in which a plasticizing section having a screw and an injection section having a plunger are separately provided and are connected by a communication passage.
The applicant of the present invention, in the screw pre-plastic injection molding machine of the above structure, the screw is provided to be rotatable and axially drivable, and in the plasticizing and measuring step, the screw is slightly retracted to the front wall of the plasticizing cylinder. A ball valve or a check valve is used in the communication passage by opening the communication passage opened and sending the molten material to the injection part, and advancing the screw in the injection process to close the communication passage at the tip of the screw. Instead, an injection molding machine has been proposed in which the molten material is prevented from flowing back to the plasticized portion during injection (see Japanese Patent Laid-Open No. 3-97518).

Generally, a hydraulic cylinder is used as a drive device for the plunger, and the molten resin sent from the plasticizing part to the injection part is measured by the amount of retreat of the plunger, and then the plunger is advanced to mold the material into a mold. Fill the inside of the cavity. At the time of injection, the pressure of the hydraulic cylinder is switched to the holding pressure immediately before the plunger reaches the forward end regulated by the front wall of the injection cylinder, and a slight amount of molten material remains on the tip end side of the plunger of the injection cylinder. A pressure-holding process that applies pressure to the material is provided.

On the other hand, the plunger is fitted in the injection cylinder with a small clearance required for its sliding, but the injection cylinder after passing through the plunger which advances while applying a high pressure to the molten material at the time of injection. The molten material adheres and remains in the form of a thin film on the inner peripheral surface. The remaining molten material flows down along the inner peripheral surface of the injection cylinder and forms a pool of molten material in the lower portion of the inner wall of the injection cylinder that is thicker than the play between the injection cylinder and the plunger. When the plunger retracts in the next metering process, part of this molten resin returns to the front of the plunger through the clearance between it and the injection cylinder, but part of it remains behind the cylinder hole as the plunger retracts. It is pushed out (on the side opposite the nozzle). The extruded molten material may be gradually deposited every time the injection cycle is repeated, and may be thermally deteriorated or carbonized by the subsequent heat transfer from the heater.

In the conventional material change in the screw pre-plastic injection molding machine, the plunger is retracted to the metering setting position, the screw is rotated, and the molten material remaining in the plasticizing cylinder is sent to the injection cylinder. Repeat the operation of advancing the plunger to discharge the molten material from the injection nozzle (purging) multiple times to discharge the residual resin as much as possible, and then use a resin such as a purge material or polypropylene to plasticize the cylinder and inject it. The cylinder, its communication passage, and the injection nozzle hole were cleaned.

[0006]

However, since the conventional material change in the screw pre-plastic type injection molding machine is performed by the above-mentioned procedure, the purging is repeated many times and the amount of the remaining material is in-line type injection molding. There was a problem that it took a very long time because it was more than the number of machines. Also, if the molten material that was pushed out to the rear of the injection cylinder by the plunger that moves backward at the time of metering and remains deposited, it will be carbonized and hardened by the heat transfer from the heater, and in some cases it will become powdery. Therefore, there is a problem in that a clearance between the injection cylinder and the plunger gets into the clearance to hinder the smooth sliding of the plunger, and in extreme cases, the plunger is eccentric to cause galling with the injection cylinder.

Therefore, the present invention shortens the purging work when changing the material in the pre-plastic type injection molding machine, and completely discharges the material in the injection cylinder to prevent the generation of the aging of the material, and thus the injection. An object is to prevent galling between the cylinder and the plunger.

[0008]

According to the method for discharging residual material of the present invention, a screw 31 is rotated in a plasticizing cylinder 30 to knead and plasticize the material, and a plasticizing portion is used. The injection unit 1 for injecting the melted material with the plunger 14 is separately provided, and the plasticization unit and the injection unit are connected by the communication passages 35 and 15 that communicate the front ends of the plasticization cylinder 30 and the injection cylinder 10. In the residual material discharging method of the screw pre-plastic injection molding machine, the screw 31 is continuously held by holding the plunger 14 at a pressure holding position leaving a gap 34 between the front wall 11 of the injection cylinder 10 and the tip of the plunger 14. By rotating, the plasticizing part 3
It is characterized by comprising a first step of discharging the residual material of (3) through the communication passages 35, 15, the gap 34 and the nozzle hole 19.

After the first step, the screw 31 which has stopped rotating is advanced in the axial direction to close the communication passage 35 at the tip of the screw, and the retracting and advancing operations of the maximum stroke of the plunger 14 are performed at least once. By performing the second step, the deposit accumulated on the inner wall of the injection cylinder on the side opposite to the nozzle of the plunger 14 is discharged to the outside of the injection cylinder during the backward movement, and the residual material in the injection cylinder is discharged from the nozzle hole 19 during the forward movement. Is preferred.

After the first step or the second step,
Next, the plunger 14 is moved backward to the measured position of the molded product to stand by, the screw 31 is rotated for a predetermined time to feed the molten material into the injection cylinder, and then the plunger 14 is advanced to the forward end to move the molten material in the injection cylinder. The purging operation of ejecting from the nozzle hole 19 is repeated a plurality of times.

[0011]

First, in the first step, the molten residual material in the plasticizing cylinder 30 delivered by the continuously rotating screw 31 is melted by the melting pressure of the communicating passages 35 and 15, the front wall 11 of the injection cylinder hole and the plunger. The tip 16 and the nozzle hole 19 are vigorously passed so as to be washed out. The material remaining in the plasticizing cylinder 30 is discharged by the first step, and the plasticizing cylinder 30, the screw 31, and the communication passages 35 and 15 are cleaned.

When the plunger 14 is retracted to its maximum stroke end in the next second step, the communication passages 35, 1
5 and the molten material remaining in the nozzle hole 19 is sucked into the injection cylinder 10, and the step C at the rear end of the retracting plunger 14 picks up the deteriorating material deposited on the inner wall surface of the injection cylinder 10. When the vehicle moves backward and reaches the backward end, the injection cylinder 1 starts from the rear end of the injection cylinder 10.
Discharge to the outside. Maximum stroke S of plunger 14
The retracted end at ₀ is set at a position where the rear end of the plunger 14 slightly projects from the rear end of the injection cylinder 10.

Next, the plunger 14 is advanced from the retracted end until the tip 16 thereof comes into contact with the front wall 11 of the injection cylinder hole, and the material sucked into the injection cylinder 10 at the time of retreating the plunger and at the end of the first step described above. The material remaining in the gap K between the plunger 14 and the front wall 11 of the injection cylinder hole is discharged from the nozzle hole 19.

That is, in the second step, the plunger 14 reciprocates in the injection cylinder 10 with no load at a stroke S ₀ larger than the stroke S ₁ which is normally used, so that the plunger 14 moves to the inner wall surface behind the injection cylinder when the plunger is retracted. The deposited and deteriorating material is the injection cylinder 10.
The material in the injection cylinder 10 is discharged to the outside and almost all of the material in the injection cylinder 10 is discharged from the nozzle hole 19 when moving forward.
The material remaining in the injection cylinder 10 after the second step is extremely small.

In the third step, when the viscosity of the material is high and the residual material in the apparatus is not sufficiently discharged by the first and second steps alone, or a resin or ceramic material containing a large amount of glass fiber is molded. After that, when the hard substance contained in the glass fiber or the ceramic remaining in the apparatus is discharged, a cleaning action of sticking and discharging the residue due to the viscosity peculiar to the resin is performed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A screw pre-plastic injection molding machine according to the present invention will be described with reference to the plasticizing apparatus and injection apparatus shown in FIG. 3 and the relationship between the injection cylinder and the plunger in the injection section shown in FIG.

The screw blubber type injection molding machine comprises a plasticizing unit consisting of a plasticizing section 3 and a driving section 4 thereof, and an injection unit consisting of an injection section 1 and a driving section 2 thereof. A heater is wound around the plasticizing cylinder 30 of the plasticizing unit 3 and the injection cylinder 10 of the injection unit 1.

The rear end of the plasticizing cylinder 30 is connected to the drive unit 4 via a connecting casing 32. Drive unit 4
Comprises a rotary drive 40 such as an electric or hydraulic motor and a cylinder 41 for axially driving the screw 31 inserted in the plasticizing cylinder 30. In the cylinder 41, a piston is provided so as to be rotatable relative to the screw 31 and relatively immovable in the axial direction, and the screw 31 and the rotary drive body 40 are relatively rotatable and unrotatable by a spline at the axial center portion of the piston. Are connected so that they can move relative to each other (see above-mentioned Japanese Patent Laid-Open No. 3-97518, FIG. 1).

A hopper port 33 is provided on the front side of the drawing sheet of the connecting casing 32 so as to penetrate the upper wall of the base end portion of the injection cylinder 10. As the screw 31 rotates, the material is supplied from the hopper port 33 so as to be scooped into the spiral groove of the screw 31, and is melted by heat transfer of the heater and internal heat generated by compression and kneading of the material by the rotation of the screw 31. The plasticized and melted material flows to the tip side of the screw 31. The screw 31 is pushed toward the base end side by the reaction force of the molten material, and the plasticizing cylinder 30
Forming a slight gap 34 with the front wall of the communication passage 35,
15 is opened. The molten material flows through the gap 34 and the communication passages 35 and 15 and is sent to the injection unit 1. When the measurement of the molten resin is completed in the injection unit 1, the rotation of the screw 31 is stopped, the hydraulic pressure is supplied into the cylinder 41 to move the screw 31 forward, and the tip of the screw 31 is brought into contact with the front wall of the plasticizing cylinder 30. The communication passage 35 that is in contact with and open is closed.

On the other hand, a nozzle 18 is attached to the tip of the injection cylinder 10 of the injection section 1 via a nozzle holder 17 having a communication passage 15 and a nozzle hole 19. At the time of injection, the entire injection device advances and the nozzle 18 is pressed against the spool port of the mold through the opening 51 provided in the fixed platen 50 of the mold clamping device. A plunger 14 is slidably fitted in the cylinder hole 12 of the injection cylinder 10, and an injection chamber is formed between the front wall 11 of the injection cylinder hole and the tip 16 of the plunger. The plunger 14 is connected to the ram 23 of the drive unit 2 via the shaft 13 and the joint 24, and a step C having a slightly larger diameter on the plunger 14 side is formed between the plunger 14 and the shaft 13. ing.

The base end of the injection cylinder 10 is connected to the main body casing 46 of the drive unit 2 and the end plate 25 via the connection casing 45, and the cylinder 20 having the ram 23 fitted therein is provided inside the drive unit 2. An injection oil chamber 21 and a return oil chamber 22 for moving the ram 23 back and forth are formed in the cylinder 20. The moving amount of the ram 23, that is, the moving stroke of the plunger 14 is determined by the linear scale 26 connected to the joint 24 side of the ram 23 by the connecting tool 27.
Measured at.

A window A is provided below the base end side of the injection cylinder 10 (the back side of the drawing), and is formed between the rear end of the plunger 14 and the shaft 13 when the plunger 14 retracts with the maximum stroke. The step C projects into the opening of the window A (imaginary line in FIG. 2). Further, the main body casing 46 is provided with a window B that also serves as a passage for the linear scale connector 27. In order to prevent damage to the hydraulic device and electric device of the drive unit 2 due to heat, and to avoid thermal deformation of the drive unit 2 and thermal deterioration of the lubricant of the sliding unit, the heating heater wound around the injection cylinder 10 is used. It is important to suppress the heat transferred to the drive unit 2 as low as possible, and for this purpose the casings 45, 4
6 are provided with cavities 28 and 29 for improving air circulation. When there is no strength problem, casing 4
It is further desirable to make 5,46 with a metal having a low thermal conductivity.

Next, the states of plasticizing, metering, and holding pressure of the screw pre-plastic injection molding machine constructed as described above are shown in FIG.
Will be described in detail.

The molten material plasticized in the plasticizing cylinder 12 flows into the injection cylinder 10 through the communication passages 35 and 15. At this time, only a slight back pressure is applied to the injection oil chamber 21, and the pressure of the molten material causes the plunger 14 to move to the forward end position 14 in the normal molding cycle.
The retreat is started from a. When the plunger 14 retracts to the stroke S ₁ corresponding to the volume of the molded product, the linear scale 26 shown in FIG. 3 detects this retracted amount, and the molten resin is measured.

When the measurement is completed, the rotation of the screw 31 is stopped, and then the screw 31 advances to close the communication passage 35 at its tip. Then, pressure oil is supplied to the injection oil chamber 21 of the drive unit 2 of the plunger 14, and the ram 23 advances to inject the molten resin in the injection cylinder 10 from the nozzle hole 19 into the mold. When the tip 16 of the plunger reaches the advance end 16a in the molding cycle, the front wall 1 of the injection cylinder hole 1
The pressure-holding step is started with a gap K left between 1 and the tip 16 of the plunger. This pressure holding step is an important step for sufficiently filling the resin into the cavity of the mold.

In the injection step, when the plunger 14 advances to the pressure holding position 14a, the peripheral edge of the tip 16 of the plunger moves forward so as to reach the injection cylinder hole 12, and the molten resin in the injection cylinder 10 is pressurized. Nozzle hole 19
It is pushed out into the mold through and the plunger 1
4 and the inner circumference of the injection cylinder 10 are pushed into a slight gap, and the injection cylinder 10 after the plunger 14 has passed through
The molten material is attached to the inner peripheral surface of the in a thin film form. The thin film molten material hangs down along the peripheral surface of the injection cylinder hole 12 and forms a pool on the bottom surface of the injection cylinder hole 12.

Next, when the screw 31 rotates again and the molten resin flows into the injection cylinder 10 side, the plunger 14 retreats, but a step C is formed between the shaft 13 and the plunger 14. Therefore, the stepped portion C moves backward while drenching the thin-film molten resin adhering to the injection cylinder hole 12, particularly the pool of molten resin formed at the bottom of the injection cylinder hole 12, and the molten portion picked up at the stepped portion C. The resin is collected little by little on the rear side of the injection cylinder 10 and naturally falls from the window A when the amount thereof increases. The dropped molten resin is received by a receiving tray (not shown).

The maximum stroke S ₀ of the plunger 14 is
The stroke S ₁ in a normal molding cycle is shorter than the maximum stroke S ₀ , although it is determined by the length of the return oil chamber 22 formed in the cylinder 20 of the ram 23. Further, the molten resin remaining in the gap K on the front wall 11 side of the injection cylinder hole at the time of holding pressure merges with the molten resin flowing in in the next plasticizing and metering step, and is eventually injected. However, a part of the molten resin that has been drawn by the step C at the rear end of the plunger 14 and accumulated at the rear of the injection cylinder hole 12 is naturally discharged from the window A, but by continuing the molding cycle for a long time, It is gradually accumulated and deteriorates due to the heat from the heater that keeps the temperature of the injection cylinder 10, and further ages and carbonization proceeds.

Next, a method of discharging the residual material in the screw pre-plastic injection molding machine as described above will be described in detail with reference to FIG. In the method shown in FIG. 1, the material is exchanged in three steps in which the drawing purge purge is the first step, the full stroke empty purge is the second step, and the standby purge is the final third step. Each of these steps can also be performed independently and individually. This series of steps is programmed and is performed in sequence by sequence control.

At the completion of the molding process, the entire plasticizing / injecting apparatus is in the retracted position, and the nozzle 18 is retracted from the opening 51 of the fixed platen 50. In the drawing barge which is the first step of material change, the plunger 14 is located at the pressure holding position having the gap K between the plunger 14 and the front wall 11 of the injection cylinder hole.
That is, it is held at the forward end 14a of the plunger 14 during the molding cycle. Then, without supplying the material from the hopper port 33, the screw 31 is continuously rotated to melt the material remaining in the plasticizing cylinder 30, and the molten material is passed through the communication passage in the same manner as in the ordinary plasticizing and metering process. Three
It is sent to the injection unit 1 from Nos. 5 and 15. Injection cylinder 10
Since the communication passage 15 is open to the front wall 11 of the injection cylinder hole and the tip 16 of the plunger is held at the pressure holding position 16a, the molten resin flowing from the communication passage 15 passes through the gap K and is discharged to the nozzle. It flows into the hole 19 and is discharged from the nozzle 18. In this draw ring purge, the resin discharged from the plasticizing cylinder 30 cleans the wall of the resin flow passage that continues from the screw 31 to the communication passages 35 and 15. In this drawing purge, the rotation speed and rotation time of the screw 31 are set by a program, the rotation time is up, and the rotation of the screw 31 is stopped.

In the next full stroke purge, after the rotation of the screw 31 is stopped, the plunger 14 is retracted to its maximum retracted end 14b, and the maximum stroke S ₀ from this retracted end causes the front wall 11 of the injection cylinder hole to move. And a motion of advancing until it abuts. This plunger 14
During reciprocation with the maximum stroke of the nozzle hole 19 and some or all of the resin in the communication passages 35 and 15 is sucked into the injection cylinder 10, and the nozzle hole 19 and the air sucked into the injection cylinder 10 Is exhaled from. By performing such an operation as many times as set in the program, the resin remaining in the communication passages 35 and 15, the injection cylinder hole 12 and the nozzle hole 19 is washed away by the air flow and cleaned. Further, in this full stroke purge, as shown in FIG. 2, the step C between the plunger 14 and the shaft 13 moves from the front Ca position to the rear Cb position,
Since the inside of the hole 12 is dredged, the injection cylinder hole 12
The defective molten material deposited on the peripheral surface of the injection cylinder will be picked up and discharged from the injection cylinder hole 12 through the window A, and almost no material will remain in the injection cylinder hole 12. In this full stroke purge,
The forward speed, the backward speed, and the number of reciprocations of the plunger 14 are set in the program, and the reciprocating operation of the plunger 14 a predetermined number of times is automatically executed according to the program.

In the next standby purge, the plunger 1
4 is retracted to the metering position in the next molding step and temporarily stopped, and the screw 31 is rotated for a certain period of time to pour the next molding resin or a resin such as a purge agent or polypropylene into the injection cylinder 10 and stop due to time-up. The screw 31 is advanced to close the communication passage 35 at the tip of the screw 31, and the plunger 14 is advanced to discharge the molten resin in the injection cylinder 10 from the nozzle hole 19. In this standby purge, the standby time of the plunger 14 (rotation time of the screw) and the total number of repetitions are set in the program. In this standby purge,
In addition to the plasticizing cylinder 30, the screw 31, the injection cylinder 10 and the plunger 14 that have been cleaned by purging in the previous first and second steps, the communication passages 35, 15
Then, the inside of the nozzle hole 19 is replaced with a new material at an early stage.

As described above, in the material change of the screw pre-plastic injection molding machine, the material in the plasticizing cylinder 30 is discharged in the first step, and the material in the injection cylinder 10 is discharged in the second step. In the third step, new material is supplied and discharged, and old material is converted to new material promptly.

[0034]

As described above, according to the method of the present invention, the discharge and cleaning of the resin in each of the plasticizing cylinder and the injection cylinder individually provided in the plasticizing section and the injection section are independently performed. Since it is carried out in separate steps, the residual resin in each cylinder can be almost eliminated, and the residual resin can be promptly discharged from the inside of the screw pre-plastic injection molding machine. Thus, for example, during molding
By performing the drawing purge and the full stroke purge as in the step and the second step, it is possible to completely discharge the defective molten material, and particularly to prevent damage due to galling of the plunger or the injection cylinder.

Furthermore, as described above, since the inside of each cylinder can be cleaned in a separate process until the inside of each cylinder becomes empty, even if a new material is introduced, the inside of each cylinder is quickly replaced with a new material. Can occupy,
Even when the resin is changed or the color is changed, the old resin does not remain and the time can be speeded up. It is possible to improve the quality and shorten the molding preparation time.

[Brief description of drawings]

FIG. 1 is a flowchart showing steps of the present invention.

FIG. 2 is a partial cross-sectional view showing the operation of the main part in the process of the present invention.

FIG. 3 is a schematic plan view of an injection device and its plasticizing device.

[Explanation of symbols]

 3 Plasticizing part 10 Injection cylinder 11 Front wall 14 Injection plunger 15 Communication passage 19 Nozzle hole 30 Plasticization cylinder 31 Screw 34 Gap 35 Communication passage

Claims (3)

[Claims] 1. A plasticizing part for kneading and plasticizing a material by rotating a screw in a plasticizing cylinder and an injection part for injecting a molten material plasticized by the plasticizing part with a plunger are separately provided. In the method of discharging residual material of a screw pre-plastic injection molding machine, wherein the plasticizing section and the injection section are connected by a communication path that connects the front ends of the plasticizing cylinder and the injection cylinder to each other, the plunger is connected to the front wall of the injection cylinder. A first step of discharging the residual material of the plasticizing portion through the communication passage, the gap and the nozzle hole by continuously rotating the screw while holding the screw at a pressure holding position with a gap left between the plunger tip and the plunger tip is provided. A method for discharging residual material from a screw pre-plastic injection molding machine, which is characterized in that 2. A screw whose rotation is stopped is advanced in the axial direction to close the communication passage at the tip of the screw, and the maximum stroke of the plunger is retreated and the forward movement is performed at least once. The second step of discharging the deposit accumulated on the inner wall of the injection cylinder on the side opposite to the nozzle to the outside of the injection cylinder and discharging the residual material in the injection cylinder from the nozzle hole during forward movement. Method for discharging residual material from screw pre-plastic injection molding machine. 3. The first step or claim 2 according to claim 1.
After the second step described, the plunger is retracted to the next measured position of the molded product and made to stand by, the screw is rotated for a predetermined time to feed the molten material into the injection cylinder, and then the plunger is advanced to the forward end and injected. The purging operation of discharging the molten material in the cylinder from the nozzle hole is repeated a plurality of times, and the method of discharging the residual material of the screw pre-plastic injection molding machine according to claim 1 or 2.