JPH0880549A - Prepla-type injection molding machine - Google Patents

Abstract

PURPOSE: To keep the rate of injection constant by practically negligibly reduc ing a back flow of resin into the space created within the groove of an injection screw at the right side of resin inlet during injection. CONSTITUTION: This injection molding apparatus 2 is inserted with an injection screw 15 having the cross section of a screw groove reduced as being from the tip end 15a to the rear part 15b, and the space is made small which is created in the screw groove at the right side of the resin inlet 18 during injection.

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 reducing the reverse flow of the resin into the space formed in the screw groove on the right side of the resin injection port as much as practically negligible. . In order to solve the above problems, it is proposed to use an injection screw whose thread groove cross-sectional area gradually decreases as the distance from the tip increases. This injection screw
Since the screw thread portion that has moved backward while charging while plasticizing and has moved to the right of the resin injection port is a portion far from the tip of the injection screw, the thread groove cross-sectional area is small.

[0009]

The screw groove of the injection screw that has moved to the right side of the resin injection port of the heating cylinder has a small cross-sectional area. Therefore, even if there is a space in the resin existing between the screw grooves, the space is extremely small. The backflow of the resin when it becomes small and is injected is reduced to such an extent that there is no problem in use.

[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.

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. Further, the shaft of the bearing device 24 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.

Returning to FIG. 1, the external hydraulic circuit will be described. Of the two variable pumps 37 and 38, the variable pump 3
The riff valve 40 and the electromagnetic valve 6 are connected to the discharge port of the valve 7. The outlet of the solenoid valve 6 is connected to the oil motor 20, and when the solenoid 6 is excited, the oil motor 20 rotates the injection screw 15. The variable pump 38 has a relief valve 41 and solenoid valves 5, 7, 8, 9 connected to its discharge port. The outlet of the solenoid valve 5 is 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 charged into the hopper 36 is plasticized in the plasticizing device 1, and is sent to the injection device 2 through the resin passage 19 and the resin injection port 18 from the outlet at the tip. 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, the tapered portion 35
If is directly contacted 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 6 is excited to drive the oil motor 20 with the variable pump 37. As a result, the injection screw 15 is rotated and the resin received at the resin injection port 18 is transferred 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. Injection cylinder 4
Since the switching of the solenoid valve 9 is completed, the oil chamber 22 is connected to the back pressure relief valve 39 through the solenoid valve 9. 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 solenoid 5a is excited. The pressure oil of the variable pump 38 is introduced into the oil chamber 22 of the injection cylinder 4, and the injection screw 15 is moved forward. Then, on the side of the plasticizer 1, the generated resin pressure is received by the taper portion 35 to prevent backflow. Since the force generated at the tip 34 is large, it may damage the surface of the tapered portion 35. To alleviate this, the solenoid 7a is excited and the hydraulic 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. In the injection screw 15, the root diameter of the screw gradually increases from the tip portion 15a to the rear portion 15b, and conversely, the cross-sectional area of the screw groove gradually decreases from the tip portion 15a to the rear portion 15b. The screw pitch of this injection screw 15 is the same over the entire length. In this figure, the right side of the resin injection port 18 is close to the rear portion 15b, the cross-sectional area of the screw groove is small, and the space generated during plasticization is small. Therefore, even if the injection cylinder 15 is advanced to perform injection, the backflow into the space is slight.

FIG. 5 is a detailed view of the plasticizing device 1. During plasticization, the solenoid 9 is excited to rotate the screw 32 by the oil motor 31 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. Pressure reducing valve 4
2 has the purpose of adjusting the pressure in the oil chamber 26 to change the shearing force applied to the resin.

When the resin is plasticized in the above operation, the resin does not exist in the tapered portion 35 due to the initial plasticization or the lack of the resin in the hopper 36, and the metal contact occurs while rotating to cause the taper. 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 solenoid 5a is excited and the injection screw 1
Move 5 forward. The resin in the resin reservoir 16 of the heating cylinder 23 is compressed and injected into the cavities in the molds 10 and 11, but the resin pressure P is 2188 k at the maximum value.
It can be as ^high as g / 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 during 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, when 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 that the sealing force of the taper portion is weakened due to the subtle difference between the resin pressure and the hydraulic pressure delay during 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, the hydraulic pressure is transmitted quickly and the 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.

In the above-mentioned "Means for Solving the Problems", it has been proposed that the injection screw has a shape in which the thread groove cross-sectional area gradually decreases as the distance from the tip increases.
According to this proposal, the injection screw 17 shown in FIG. 4 is an injection screw in which the pitch of the thread groove gradually narrows according to the distance from the tip. Needless to say, this problem can be achieved by replacing the injection screw 17 with the injection screw 15 inserted into the injection device 2.

[0032]

The injection screw 15 of the injection device 2 has the tip 1
The effective area of the screw becomes smaller from 5a toward the rear portion 15b. Due to such a shape, when the injection screw 15 is charged and retracted due to plasticization, as for the thread groove portion that has moved to the right side of the resin injection port 18 on the side portion of the heating cylinder 23, the thread portion is not covered with the resin. Although there is a space, since the thread groove cross-sectional area is small, the space is also small, and the backflow of resin due to injection does not pose a problem.

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, a 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.

According to the present invention, the injection device 2 incorporating the injection screw 15 in which the cross-sectional area of the thread groove decreases as the distance from the tip increases, the plasticization by the rotation of the screw 32 and the resin retraction by the backward movement of the screw 32. Although the description has been given of the pre-plastic injection molding machine in which the plasticizing device 1 having the function of blocking the backflow is combined, the injection device 2 does not necessarily have to be this combination, and the injection device 2 is plasticized by the screw rotation without the backflow blocking function. It goes without saying that it is also possible in a pre-plastic type injection molding machine in combination with a plasticizing device for carrying out. 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 The inside of a heating cylinder incorporating an injection screw according to the present invention in which the root diameter of the thread groove changes.

FIG. 4 is the interior of a heating cylinder incorporating an injection screw with variable pitch of the thread according to the invention.

[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 injection screw 18 resin injection port 19 resin passage 23 heating cylinder 32 screw 33 plasticizing screw 34 tip 35 taper portion 49 auxiliary cylinder 50 piston 50a Constriction 50b piston rod

Claims (1)

[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 the pre-plastic injection molding machine, the injection screw in which the root diameter of the screw gradually increases from the tip portion (15a) to the rear portion (15b) in the heating cylinder (23) of the injection device (2). (15) Or
Alternatively, a pre-plastic injection molding machine is characterized in that an injection screw (17) having a pitch of a thread groove gradually reduced from the front end (17a) to the rear part (17b) is inserted.