JPH08103923A - Preplasticating injection molding machine and injection molding method - Google Patents

Abstract

PURPOSE: To prevent the variation of an injection amount by reversely feeding resin to a space formed in the injection screw channel at the right of a resin introducing inlet at the time of injection. CONSTITUTION: An injection unit 2 has a seal ring 17 which is engaged movably along the threads of an injection screw 15 inserted into a heating cylinder 23 and rotatably engaged with the right side of a resin introducing inlet 18 provided at the side of the cylinder 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pre-plastic type injection molding machine for performing rubber and plastics in separate devices for plasticizing and injection, and more particularly to a machine using an injection device having a screw built therein.

[0002]

2. Description of the Related Art One of the inventors has proposed the above-mentioned Jitsuko Sho 59.
-5556 discloses the idea of a basic pre-plastic injection molding machine. This device has two features as compared with a conventional pre-plastic injection machine.

The first is related to plasticization and backflow prevention of resin. In the plasticizer, the diameter of the tip portion is set to d1 and is made larger than the diameter d2 of the rear flight portion, and the diameters d1 to d
The plasticizing screw has a tapered shape with the diameter reduced to 2 and the inner diameter corresponds to the outer diameter of the plasticizing screw.
It is composed of a plasticizing cylinder having a step and a step. The screw is allowed to rotate and slightly reciprocate in the plasticizing cylinder.

At the time of plasticizing, the resin supplied from the hopper is plasticized by the screw groove of d2 part of the screw and transferred to the tip side of the screw, but external force is applied to bring the screw and the taper part of the plasticizing cylinder close to each other. , Shearing force is applied to the resin passing through the tapered portion. The resin that has been plasticized and melted in the d2 thread groove is still melted in the tapered portion and becomes a uniform plasticized state. Further, at the time of injection, the screw and the tapered portion of the plasticizing cylinder are brought into contact with each other to prevent the resin flowing back from the injection device. Since this apparatus does not have any valves for preventing backflow, it is characterized by the fact that there is almost no resin retention area peculiar to the valves and that there is no resin retention due to the self-cleaning action.

The second is the injection device,
The injection device has an injection screw fitted in a heating cylinder so as to be rotatable and reciprocally movable. Then, the resin plasticized by the plasticizer and pressure-fed is received, the injection screw is rotated, and the received resin is sequentially transferred to the resin pool at the tip end and injected, so that the resin is not allowed to stay.
In other methods using the injection piston, the resin injected first tends to be extruded last, and the resin injected first tends to stay in the heating cylinder for a long period of time, improving this. The purpose is.

[0006]

FIG. 2 shows a state in which the injection device of the prior art completes the charge of the resin and starts the injection. The resin injected from the resin injection port 57 is
Rotate the injection screw 54 and send it to the resin reservoir 53,
The injection screw 54 itself is pushed by the resin in the resin pool at the same time as the injection screw 54 is rotated and retracted, and stopped at the position where the charging is completed. In this case, the screw groove 56 on the right side of the resin injection port 57 is not always filled with the resin. That is, the injection screw has the function of rotating and transferring the resin to the tip, but the screw groove 56 moved to the right of the resin injection port 57 does not replenish the resin from the outside, so the resin transferred to the tip is Traces can become spaces.

Because of this state, the injection screw 54
When the injection is carried out by advancing the
5 may flow back into the space of the screw groove 56, and the injection amount may decrease, which may cause variations. A mechanism is required to prevent this from happening and to maintain the characteristics of the injection device that incorporates the injection screw. The present invention is an invention relating to more detailed parts of the injection molding machine disclosed in JP-B-59-5556.

[0008]

In order to solve this problem, it is necessary to provide a mechanism for preventing the resin from flowing back into the space formed in the screw groove on the right side of the resin injection port. We propose to install a seal ring to prevent resin backflow. This is a cylindrical seal ring with a hole in the center and a twist groove attached to the outer periphery of the hole so that the thread groove root diameter of the injection screw and the flight part fit, and the injection screw is inserted in the hole in the center. The outer diameter is provided in the heating cylinder immediately to the right of the resin injection port so as to be rotatable together with the injection screw in the heating cylinder.

[0009]

[Function] The cylindrical seal ring, which has the center hole fitted to the injection screw on the right side of the resin injection port of the heating cylinder and whose outer diameter is rotatable in the heating cylinder, prevents the resin from being injected during injection. Prevents reverse flow into the space created in the thread groove on the right side of the resin injection port. Further, the seal ring is caught by the flight portion of the injection screw and is rotated in accordance with the rotation of the screw, and can be rotated along the twist of the injection screw even with respect to the linear movement at the time of injection.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a pre-plastic injection molding machine. Fixed mold 11 attached to fixed plate 13 and movable plate 1
The movable die 10 attached to No. 2 shows a closed state.
A mold clamping cylinder (not shown) can be opened when the molded product is taken out. The injection device 2 can be operated such that the injection device 2 and the plasticizing device 1 are simultaneously moved by a shift cylinder (not shown) to press the nozzle 14 against the fixed mold 11, or the nozzle 14 is moved backward to separate the nozzle 14. Heating cylinder 23
An injection screw 15 is inserted therein so that it can move forward and backward and rotate. A resin injection port 18 for injecting the plasticized resin from the plasticizing device 1 is provided on the side of the heating cylinder 23.

A seal ring 17 is rotatably provided on the right side of the resin injection port 18. The drive shaft 25 on the right side of the injection screw 15 is received by the bearing device 24 and is connected to the piston rod of the injection cylinder 4 via the housing part of the bearing device 24. Also bearing device 2
The shaft of No. 4 is connected to the oil motor 20, and the rotational force of the oil motor 20 is transmitted to the injection screw 15.

Inside the plasticizing cylinder 33 of the plasticizing device 1, a screw 32 having a tip end 34 having a diameter d1 and another portion having a diameter d2 is fitted. Tip 34 of screw 32
Is changed from d1 to d2, a taper portion 35 is formed, and the plasticizing cylinder 33 also has a tapered step portion. The right drive shaft 30 of the screw 32 is received by the bearing device 29, and is connected to the piston rod of the screw moving cylinder 3 via the housing part of the bearing device. The shaft of the bearing device is connected to the oil motor 31, and the rotational force of the oil motor 31 is transmitted to the screw 32.

The resin plasticized by the plasticizing device 1 is injected into the injection device 2 from the resin injection port 18 through the resin passage 19. Since the plasticizing device 1 and the injection device 2 are separate devices and are connected by the resin passage 19, the resin passage 19 may become long depending on the arrangement of both devices. Although not shown, the plasticizing cylinder 33, the resin passage 19,
A band heater is wound around the heating cylinder 23 to keep the resin in a molten state, and the temperature is adjusted.

The internal structure of the screw moving cylinder 3 will be described with reference to FIG. The piston rod 50b on the right side of the piston rods extending to both of the pistons 50 has a part that is thinly constricted, and an auxiliary piston 49 having a width narrower than the interval of the constriction 50a is fitted and the outer diameter is fitted to the screw moving cylinder 3. I am fit. The oil chamber 27 formed between the piston 50 and the auxiliary piston 49 has an effective area equal to that of the other chamber 2
It is larger than 6, 28.

Next, returning to FIG. 1, the external hydraulic circuit will be described. Of the two variable pumps 37 and 38, the variable pump 37
The riff valve 40 and the solenoid valve 6 are connected to the discharge port.
The outlet of the solenoid valve 6 is connected to each of the two ports of the oil motor 20. This is because the injection screw 15 is normally rotated when the solenoid 6a is excited, and the reverse rotation is performed when the solenoid 6b is excited. The injection screw 15 can be either a right-hand screw or a left-hand screw. Regardless of whether it is right or left, the rotation that should proceed in the direction of the resin pool 16 is called forward rotation, and the rotation away from the resin pool 16 is called reverse rotation. The rotation that is not sufficient to distinguish the rotation directions will be simply referred to as rotation. The variable pump 38 has a relief valve 41 and solenoid valves 5, 7, 8, 9 connected to its discharge port. The solenoid valve 5 has its outlet connected to the oil chambers 21 and 22 of the injection cylinder 4 and has the purpose of moving the injection cylinder 4 forward and backward.

The outlet of the solenoid valve 7 is the screw moving cylinder 3
Indirectly connected to the oil chambers 26 and 28 of the
The purpose is to move the screw moving cylinder forward and backward. The pressure reducing valve 42 connected to the connection port of the oil chamber 26 holds the oil pressure in the oil chamber 26 at a set value when the pressure on the pump side is high, and the pressure on the pump side when the pressure on the pump side is lower than the set value. Is introduced into the oil chamber 26 as it is. The throttle valve 45 at the connection port of the oil chamber 28 has the function of narrowing and narrowing the passage of the operating oil, and the sequence valve 44 prevents the operating oil from passing to the oil chamber 28 when the pressure on the pump side is lower than the set value. Arrest,
When the pressure on the pump side is higher than the set value
Has the effect of introducing into.

The check valves 43 and 46 have a function of returning the hydraulic oil discharged to the tank 47 via the electromagnetic valve 7 when the volume of the oil chamber 26 or 28 is reduced. The solenoid valve 8 passes through a passage 48 formed in the piston rod 50b of the piston 50 when the solenoid 8 is excited, and an oil chamber 27 provided with an auxiliary piston 49 incorporated in the screw moving cylinder 3 is provided.
The purpose is to introduce hydraulic oil into the oil chamber to expand the oil chamber 27.
The solenoid valve 9 is a variable pump 38 when the solenoid 9 is excited.
Is connected to the oil motor 31 and the oil chamber 22 of the injection cylinder 4 is connected to the back pressure relief valve 39.

The operation will be described with reference to the operation table of FIG.
In plasticizing, the solenoids 7b, 8 and 9 on the plasticizing device 1 side are excited, and the variable pump 38 drives the oil motor 31 to rotate the screw 32. The resin that has been put into the hopper 36 and has been plasticized is plasticized in the plasticizing device 1, passes through the resin passage 19 and the resin injection port 18 from the outlet of the tip, and the injection device 2
Sent to. At this time, the same hydraulic pressure is depressurized and introduced into the oil chamber 26 by the pressure reducing valve 42, and the pressure of the oil chamber 26 is controlled to apply a force to the screw 32 in the direction of narrowing the gap of the taper portion 35. This force shears the resin passing through the tapered portion 35. However, due to such a mechanism, if the tapered portion 35 directly contacts with each other, the metals may come into contact with each other and seizure may occur. Therefore, pressure oil is also introduced into the oil chamber 27 to prevent contact of the taper portion 35 so that the minimum gap can be secured without contact.

On the injection device (2) side, the solenoid 6b is excited to drive the oil motor 20 with the variable pump 37. This reverses the injection screw 15 and transfers the resin received at the resin injection port 18 to the resin reservoir 16 at the tip. The injection screw 15 is retracted by the pressure as the resin is transferred to the resin reservoir 16. The oil chamber 22 of the injection cylinder 4 is connected to the back pressure relief valve 39 through the electromagnetic valve 9 since the switching of the electromagnetic valve 9 is completed. The oil chamber 22 is contracted by the retreat of the injection screw 15, and the hydraulic oil is pushed out and passes through the relief valve 39. Therefore, the back pressure of the injection screw 15 can be adjusted by the relief valve 39.

When a certain amount of resin is accumulated in the resin reservoir 16, it is detected at the position of the injection screw 15 and the plasticization is completed. In preparation for the next injection, the plasticizing screw 32 is retracted and the taper portion 35 is brought into contact. This operation is performed by exciting the solenoid 7b. After the contact is completed, the solenoid 7b is demagnetized.

In the next injection step, the solenoids 5a and 6a are excited. A variable pump 38 is installed in the oil chamber 22 of the injection cylinder 4.
Of the pressure oil is introduced, and the injection screw 15 is advanced. At the same time, the variable pump 37 drives the oil motor 20 to rotate the injection screw 15 in the forward direction. And plasticizing device 1
On the side, the generated resin pressure is received by the taper portion 35 to prevent backflow. Since the force generated at the tip 34 is large, there is a risk of damaging the surface of the taper portion 35. To alleviate this, the solenoid 7a is excited and the oil pressure of the variable pump 38 is also introduced into the oil chamber 28 of the screw moving cylinder 3. ing.

Now, FIG. 3 is a detailed view of the heating cylinder portion of the injection device 2. The injection screw 15 is configured so that the whole has the same pitch and the same root diameter F. The pitch L is made larger than the outer diameter E of the flight part, and the injection screw 1
The feature of 5 is that the component force of rotation is easily applied to the seal ring 17 during the linear movement of 5. On the right side of the resin injection port 18 of the heating cylinder 23, there is provided a seal ring 17 having a structure in which the injection screw is fitted in the central portion and at the same time the outer diameter portion can rotate in the heating cylinder 23. The seal ring 17 prevents backflow of resin into the right-hand thread groove. However, the leaked resin is discharged from the discharge chamber 60 and the discharge hole 61 to the outside. FIG. 4 shows the shape of the seal ring 17. Since the pitch L of the injection screw 15 is increased as described above, even when the injection screw 15 moves straight, the seal ring 17 is given a rotational force by fitting along the screw thread. However, the seal ring 17 rotates, but the lower the rotation speed is, the better in order to prevent resin burning and seizure of metal parts. For example, during plasticization, the injection screw 15 rotates to transfer the resin forward. At the same time, the resin moves backward due to the pressure at which the resin is transferred to the resin reservoir 16. Therefore, the rotation speed of the seal ring 17 becomes lower than the rotation speed of the injection screw 15.

In injection, the solenoid 5a is excited to advance the injection cylinder 4, but at the same time the solenoid 6 is moved.
The injection screw 15 is also normally rotated by exciting a. The rotation speed N (rev / sec) at this time is L (mm / rev) for the screw groove pitch of the injection screw and S for the injection speed.
(Mm / sec), N = S / L is calculated to obtain N. The calculation utilizes the calculation mechanism in the controller. The variable in this case is S, and when the operator of the machine sets the injection speed S when the machine condition is set, N is obtained from the internal calculation mechanism and a signal is automatically output to the variable pump 37. Due to this rotation, the seal ring 17 hardly rotates, but a slight difference in the number of rotations caused by an operation delay peculiar to the hydraulic system causes the seal ring 17 to rotate and absorb an error.

FIG. 5 is a detailed view of the plasticizing device 1. During plasticization, the solenoid 9 is excited to rotate the screw 32 and plasticize the resin supplied to the hopper 36. By switching the solenoid valve 9, the oil chamber 22 of the injection cylinder 4 can be connected to the relief valve 39 to apply back pressure to the oil chamber 22 during resin charging. At the same time, the solenoid 7b is excited to introduce hydraulic oil into the oil chamber 26 of the screw moving cylinder 3. The screw 32 is pulled to the right and a force is applied so as to narrow the tapered portion 35. A shearing force is applied to the resin thus plasticized and transferred to the tip 34 of the screw 32 to further plastically melt the resin. The pressure reducing valve 42 has the purpose of adjusting the pressure in the oil chamber 26 and changing the shearing force applied to the resin.

When the resin is plasticized in the above operation, the resin does not exist in the taper portion 35 due to the initial plasticization or the lack of the resin in the hopper 36, the metal contact is caused while rotating, and the taper is generated. There is a concern that the surface of the portion 35 will be damaged. Therefore, when plasticizing, the solenoid 8 is excited at the same time, and the oil chamber 2
It is necessary to introduce hydraulic oil into 7. Originally, the piston 50 moves to the right side by the action of the oil chamber 26, and the taper portion 35 comes into contact with it as it is, but when the working oil is introduced into the oil chamber 27 having a larger effective area than the oil chamber 26, the auxiliary piston 49 becomes constricted. The screw 32 is pushed back to the left by a distance that moves within the interval of 50a. By adjusting the interval between the constrictions 50a and the width of the auxiliary piston 49, the taper portion 3 is used during plasticization.
The size is regulated so that the minimum distance t is maintained even when 5 comes closest without contacting.

Next, a mechanism for preventing backflow of the resin by the taper portion 35 provided on the plasticizing screw 32 at the time of injection will be described. When injecting the solenoid 7 in advance
b is excited to retract the plasticizing screw 32, and the taper portion 35 is kept in contact. This is a measure to prevent the resin from flowing backward due to the delayed sealing. After confirming the contact of the taper portion 35, the solenoids 5a and 6a are excited to advance the injection screw 15 while rotating it forward. Heating cylinder 23
Although the resin in the resin reservoir 16 is compressed and injected into the cavities in the molds 10 and 11, the resin pressure P reaches a maximum value of 2188 kg / cm ² .

The resin pressure P passes through the resin injection port 18 and the resin passage 19 and is applied to the tip 34 of the plasticizing screw 32 to push the screw 32 to the right to seal the taper portion 35. The force on the tip 34 becomes ^{P × π (d1) 2/} 4. If this force is received only by the taper portion 35, the area of the taper portion 35 is approximately π (d1 ² −d2 ² ) / 4. Therefore, the surface pressure ν generated in the taper portion 35 is ν = P
(D1) ² / (d1 ² −d2 ² ) For realistic consideration, if d1 = 60 mm and d2 = 40 mm, ν = 3
It is 938 kg / cm ² , and it can be seen that the taper portion 35 is extremely burdened.

In order to solve the above problems, normally, the solenoid 7a is excited at the time of injection to introduce the working oil used for injection into the oil chamber 38 of the screw moving cylinder 3 so that about half of the force applied to the tip 34 is applied. It is received by the screw moving cylinder 3. In this case, ν is 2188 kg / cm ^{2, which} is about half. The sequence valve 44 connected to the inlet of the oil chamber 28 has the purpose of relaxing the above surface pressure ν to an appropriate value. Explaining this purpose in FIG. 7, the graph is a graph showing the relationship between the hydraulic pressure and the surface pressure ν of the taper portion 35. The oil pressure is calculated as 0 to 175 kg / cm ² . In the figure, the dotted line A shows the case without the help of the screw moving cylinder 3, and the solid line B shows the case with the help of the screw moving cylinder 3.

Here, for example, if the set value of the hydraulic pressure is set to 100 kg / cm ² by the sequence valve 44, the hydraulic pressure becomes 0 to 1
In the case of 00 kg / cm ^{2, although} the sequence valve 44 is closed and the solenoid 7a is energized, the screw moving cylinder 3 does not assist, and as the hydraulic pressure increases, ν
Moves up the dotted line A to the right and moves to C point at 2250 kg / cm
² is the highest value. When the hydraulic pressure exceeds 100 kg / cm ² and the sequence valve 44 opens, the screw moving cylinder 3 generates a force and ν shifts from point C to point D. Hydraulic pressure is 100 ~
175 kg / cm is between ² real line moves to the upper right of point D, 2 ν when the highest value 175 kg / cm ² hydraulic
It becomes 188 kg / cm ² . The reason why the screw moving cylinder 3 is not used from the beginning is that the resin leaks easily when the force acts so as to weaken the sealing force of the taper portion due to the subtle difference between the resin pressure and the hydraulic pressure at the time of injection. This is because the surface pressure ν of the portion 35 is increased within a range where it is not damaged to enhance safety.

The purpose of the throttle valve 46 connected in series with the sequence valve 44 is as follows. In the above description, the resin pressure generated in the resin reservoir 16 at the time of injection is transmitted through the resin injection port 18 and the resin passage 19 and reaches the tip 34 of the screw 32 in the plasticizer 1. However, the transmission is delayed due to the viscosity of the resin. The same hydraulic pressure of the variable pump 38 that was used for injection at the same time to the oil chamber 28 of the screw moving cylinder 3 of the plasticizing device 1 in order to prevent the reverse flow of the resin at the taper portion 35 but to alleviate the surface pressure of the taper portion 35. Have been introduced.

However, hydraulic pressure is transmitted quickly and resin pressure is applied to the tip 3
In some cases, the force of the screw moving cylinder 3 may be generated earlier than when it reaches 4. Especially when a high pressure is generated at the start of injection, there is no force generated at the tip 34, so that the tapered portion 3
5 opens and resin backflow occurs. Because of this problem, throttle valve 4
Reference numeral 5 is for delaying the transmission of hydraulic pressure by narrowing the hydraulic passage.

[0032]

The seal ring 17 is provided between the injection screw 15 of the injection device 2 and the heating cylinder 23 to prevent the resin from flowing back to the right-hand thread groove of the resin injection port 18, thereby stabilizing the injection amount, Accurate injection is possible. In addition, the amount of resin retained inside was significantly reduced compared to the piston extrusion type injection device.

Further, the seal ring 17 is the injection screw 15
It is rotatably provided as it moves forward and backward, but it is better not to rotate it as much as possible in consideration of image sticking. According to the invention of the present application, the injection screw 15 is normally rotated at the time of injection,
The control is performed so that the seal ring 17 hardly rotates. At the time of plasticizing, the injection screw 15 is reversed to transfer the resin, but at the same time, the injection screw 15 moves backward as the resin accumulates in the resin pool 16, so that the rotation of the seal ring 17 can be reduced at this time as well. There is an advantage.

If the taper portion 35 of the plasticizing device comes into contact with the plasticizing device while rotating, the taper portion 35 will be damaged. To prevent this, an auxiliary piston 49 is incorporated in the screw moving cylinder 3 to form an oil chamber. 27 is provided,
By selectively introducing hydraulic oil into the oil chamber 27, the taper portion 35 has a mechanism capable of maintaining the minimum clearance t. This prevents the taper portion 35 from being damaged by metal contact. ing.

Besides, the oil chamber 28 of the screw moving cylinder 3
By connecting the sequence valve 44 whose set pressure is set to 100 kg / cm ² to the connection port of and introducing hydraulic oil into the oil chamber 28 through this sequence valve 44, the surface pressure ν of the taper portion 35 can be made as high as possible, However, even at the maximum, the resin pressure is reduced to about half of the maximum value when it is received only by the taper portion 35 to prevent resin leakage and damage to the surface of the taper portion 35.

Similarly, the throttle valve 45 is provided at the connection port of the oil chamber 28.
The time delay in which the resin pressure at the time of injection reaches the tip 34 can be delayed by the throttling effect of the throttle valve 45 even in hydraulic pressure to match the timing. Therefore, the tapered portion 35 does not open and the injection amount is stabilized.

The combination of the injection device 2 with the seal ring 17 for injecting while rotating with the injection screw 15 of the present invention and the plasticizing device 1 for plasticizing by rotating the screw 32 and having the backflow prevention mechanism. The described pre-plastic injection molding machine does not necessarily have to be this combination, and the injection device 2 with the seal ring 17 that injects while rotating with the injection screw 15 does not have a backflow prevention function, and only the screw rotation is used. It goes without saying that it is also possible in a pre-plastic injection molding machine in combination with a plasticizing device for plasticizing. However, in this case, it is necessary to install a rotary or ball type resin check valve in the middle of the resin passage 19.

[Brief description of drawings]

FIG. 1 is a pre-plastic injection molding machine according to the present invention.

FIG. 2 Inside a heating cylinder according to the prior art

FIG. 3 Internal heating cylinder according to the invention

[Figure 4] Seal ring appearance

[Fig. 5] Details of plasticizer

[Fig. 6] Hydraulic circuit operation table

FIG. 7 is a graph of the surface pressure ν of the taper portion 35 against the hydraulic pressure.

[Explanation of symbols]

 1 plasticizing device 2 injection device 3 screw moving cylinder 4 injection cylinder 15 injection screw 16 resin reservoir 17 seal ring 18 resin injection port 19 resin passage 23 heating cylinder 32 screw 33 plasticizing screw 34 tip 35 taper part 49 auxiliary cylinder 50 piston 50a Constriction

Claims (4)

[Claims] 1. A plasticizing device for plasticizing a resin by a rotating action of a screw, or a plasticizer having a function of preventing backflow of a resin by plasticizing by rotating a screw (32) and retreating the screw (32). From any of the plasticizing devices (1) and the injection device (2) that receives the plasticized resin from the plasticizing device and injects the resin into the mold by the forward / backward movement and rotation of the injection screw (15). In this pre-plastic injection molding machine, the injection device (2) is movably fitted along the threads of the injection screw (15) inserted in the heating cylinder (23), and the heating cylinder is (23) A pre-plastic injection molding machine characterized in that it has a seal ring (17) rotatably fitted to the right side of a resin injection port (18) provided on a side portion. 2. The calculation function in the controller according to claim 1, based on the screw pitch L (mm / rev) of the injection screw (15) in the injection device and the injection speed S (mm / sec) set by the machine operator. An injection method of a pre-plastic injection molding machine, characterized in that N = S / L is calculated using the above method, and injection is performed while the screw is normally rotated at N (mm / rev) rotations. 3. A plasticizing device (1) having a function of plasticizing by rotation of a screw (32) and preventing backflow of resin by retreating of the screw (32), and the plasticizing through a resin passage (19). An injection device (2) that receives the plasticized resin from the device (1) and injects the resin into the mold (10, 11) by the forward and backward movement and rotation of the injection screw (15).
In a pre-plastic injection molding machine consisting of the above, the piston (50) in the screw moving cylinder (3) of the plasticizing device (1) is provided with a thin neck (50a) in a part of the piston rod (50b). , The constriction (50
An auxiliary piston (49) having a width narrower than that of (a) is fitted, and an oil chamber (27) is provided between the auxiliary piston (49) and the piston (50) so that the hydraulic oil is rotated when the screw (32) is rotated by plasticization. Is introduced to expand the oil chamber (27) and ensure a minimum interval (t) even when no resin is present in the taper portion 35, a pre-plastic injection molding machine. 4. The sequence valve (4) according to claim 3, wherein the connection port of the oil chamber (28) of the screw moving cylinder (3) is connected.
4), or a throttle valve (45), or the sequence valve (4)
4) A pre-plastic injection molding machine having a hydraulic circuit having a configuration in which a serial circuit of 4) and a throttle valve (45) is connected to the outside.