JPH08238558A - Hydraulic device for die clamping - Google Patents

Abstract

PURPOSE: To enable the pressure boosting operation even at the time of operating the die opening by connecting the outlet of a pressure boosting oil in a booster cylinder and piston device to a hydraulic passage between a hydraulic pressure source and a die clamping and die opening change-over valve. CONSTITUTION: The outlet piping in a small diameter cylinder 49 of the booster cylinder and piston device 39 is connected to the hydraulic passage 17. The hydraulic pressure from the hydraulic pressure source 1 is supplied to the die clamping and die opening change-over valve 19 through the hydraulic passage 17. The die clamping and die opening change-over valve 19, and a high speed die clamping and die opening change-over valve 29 are operated, and the piston rod 11 in a die clamping cylinder device 3 is advanced/retreated to execute the die clamping/die opening. The booster cylinder and piston device 39 has a large diameter cylinder chamber 53 and the small diameter cylinder chamber 49, and the boosted hydraulic pressure is generated in the small diameter cylinder chamber 49. Since the boosted hydraulic pressure is supplied to the hydraulic passage 17, the boosting operation is executed at the time of die clamping and that of die opening.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold clamping hydraulic device used for a mold clamping device of a die casting machine or an injection molding machine.

[0002]

A mold clamping device for a die casting machine or an injection molding machine has a double-acting mold clamping cylinder device that reciprocates a moving die plate with respect to a fixed die plate. Mold clamping and mold opening are performed by switching the supply of hydraulic pressure to the first cylinder chamber and the second cylinder chamber provided on both sides.

As a mold clamping cylinder device, Japanese Patent Laid-Open No. 2-21
As shown in Japanese Patent No. 1965, a device having a pressure increasing ram device is known. In this mold clamping cylinder device, the pressure boosting ram device is directly connected to the first cylinder chamber for mold clamping, and during the mold clamping operation, the pressure boosting ram device performs a pressure boosting action on the first cylinder chamber, Increase the mold clamping force.

[0004]

In the above-described conventional mold clamping cylinder device with the pressure increasing ram device, since the pressure increasing ram device is directly connected to the first cylinder chamber for mold clamping, the pressure increasing pressure is increased. The ram device exerts a pressure increasing action only during the mold clamping operation. Therefore, when the mold is opened, the pressure increasing function of the pressure increasing ram device cannot be obtained, the mold opening force may be insufficient, and the mold opening time cannot be shortened.

Further, since the pressure increasing ram device is provided in the mold clamping cylinder device, the mold clamping cylinder device becomes complicated and large in size, and the installation of the mold clamping cylinder device is restricted.

The present invention has been made in view of the above-mentioned problems, and the pressure-increasing ram device effectively acts not only during the mold clamping operation but also during the mold opening operation without complicating the structure.
A pressure increasing effect is generated during the mold clamping operation and the mold opening operation, and the machine cycle time is shortened by shortening both the mold clamping operation time and the mold opening operation time without increasing the amount of oil supplied from the hydraulic pressure source. The purpose of the present invention is to provide a mold clamping hydraulic device capable of improving the operating rate.

[0007]

In order to achieve the above-mentioned object, a mold clamping hydraulic device according to a first aspect of the present invention is characterized in that a movable die plate is reciprocally moved by a mold clamping cylinder device with respect to a fixed die plate. A mold clamping hydraulic device configured to perform clamping and mold opening, in which a hydraulic pressure source and a mold clamping / mold for switching pressure oil supply to the first cylinder chamber and the second cylinder chamber of the mold clamping cylinder device are switched. An open switching valve, a stepped piston member having a small-diameter piston portion and a large-diameter piston portion, and a cylinder member that receives the stepped piston member, and the small-diameter piston portion is formed by the stepped piston member and the cylinder member. A small diameter cylinder chamber serving as a pressure receiving surface, an intermediate cylinder chamber having a stepped portion between the small diameter piston portion and the large diameter piston portion as a pressure receiving surface, and the large diameter piston portion serving as a pressure receiving surface. Diameter cylinder chamber and a small diameter cylinder chamber connected to an oil passage between the hydraulic pressure source and the mold clamping / mold opening switching valve; It has the intermediate cylinder chamber and a pressure increase control valve for controlling the supply and discharge of pressure oil to and from the large diameter cylinder chamber.

In order to achieve the above object, the mold clamping hydraulic device according to claim 2 reciprocates the movable die plate by the mold clamping cylinder device with respect to the fixed die plate to perform mold clamping and mold opening. A mold clamping hydraulic device configured to perform a mold clamping / mold opening switching valve that switches a hydraulic pressure source and pressure oil supply to the first cylinder chamber and the second cylinder chamber of the mold clamping cylinder device. And a stepped piston member having a small-diameter piston portion and a large-diameter piston portion, and a cylinder member that receives the stepped piston member, and the small-diameter piston portion serves as a pressure receiving surface by the stepped piston member and the cylinder member. An accumulator chamber, an intermediate cylinder chamber whose pressure receiving surface is the stepped portion between the small diameter piston portion and the large diameter piston portion, and a back whose pressure receiving surface is the large diameter piston portion. An accumulator chamber that defines a chamber and connects the accumulator chamber to an oil passage between the hydraulic pressure source and the mold clamping / mold opening switching valve, and the intermediate cylinder chamber of the accumulator with the pressure increasing mechanism. And a pressure increase control valve for controlling supply and discharge of pressure oil.

According to a third aspect of the present invention, there is provided a mold clamping hydraulic system according to the first or second aspect, wherein the intermediate cylinder chamber is responsive to the hydraulic pressure in the oil passage and the hydraulic pressure is equal to or more than a predetermined value. A relief valve for connecting the drain is provided.

[0010]

In the hydraulic system for mold clamping according to claims 1 and 2, the small-diameter cylinder chamber of the pressure-increasing cylinder / piston device, which is the pressure-increasing ram device, or the accumulator chamber of the accumulator with the pressure-increasing mechanism is formed from the mold clamping / mold opening switching valve. It is connected to the oil passage on the hydraulic pressure source side, and since this oil passage is the pressure oil supply passage for the mold clamping cylinder during both the mold clamping operation and the mold opening operation, the booster ram device operates during the mold clamping operation. In both of the mold opening operation, the pressure increasing action is performed.

In the mold clamping hydraulic device according to the third aspect, when the hydraulic pressure in the oil passage exceeds a predetermined value, the intermediate cylinder chamber is drain-connected by the hydraulic relief valve, and the pressure boosting ram device automatically performs the pressure boosting action. Start.

[0012]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a first embodiment of a mold clamping hydraulic device according to the present invention. This mold clamping hydraulic device includes a hydraulic power source 1
And a double-acting mold clamping cylinder device 3.

The mold clamping cylinder device 3 has a first cylinder chamber 7 for mold clamping on one side of the piston member 5 and a second cylinder chamber 9 for mold opening on the other side of the piston member 5. 1
1 is drivingly connected to a toggle mechanism (not shown) for mold clamping and mold opening, and the piston rod 11 moves to the right in the figure to perform the mold clamping, and moves to the left to perform the mold opening.

The hydraulic pressure source 1 includes an oil passage 13, a check valve 15,
The oil passage 17 is connected to the port a of the mold clamping / mold opening switching valve 19. Check valve 15 is oil passage 13 rather than oil passage 17
Allow only the flow of pressure oil.

The mold closing / mold opening switching valve 19 is a three-position type electromagnetic switching valve, and has a first switching position in which port a is closed and both ports c and d are connected to drain port b, and port a. A second switching position connecting port c to port d connecting drain port b and a third switching position connecting port a to port d connecting port c to drain port b, When the solenoids 21 and 23 are both stationary, they switch to the first switching position, when the solenoid 21 operates, to the second switching position, and when the solenoid 23 operates, to the third switching position.

The port c of the mold closing / mold opening switching valve 19 is the oil passage 2
5, the port d is connected to the first cylinder chamber 7, and the port d is connected to the port b of the high speed mold clamping / mold opening valve 29 by the oil passage 27.

The high-speed mold clamping / mold opening valve 29 is a three-position type electromagnetic switching valve, and has a first switching position where port a is closed and port c is connected to port b, and port c is connected to port a. And a third switching position for connecting the port b to the drain port d and a third switching position for connecting the port a to the drain port d and connecting the port b to the port c. Any of these switches to the first switching position in the steady state of non-operation, to the second switching position when the solenoid 31 operates, and to the third switching position when the solenoid 33 operates.

The port a of the high speed mold clamping / mold opening valve 29 is the oil passage 3
5 is connected to the oil passage 25, and the port c is connected to the second cylinder chamber 9 by the oil passage 37.

A small diameter cylinder chamber 49 of a pressure boosting cylinder / piston device 39, which is a pressure boosting ram device, is connected to the oil passage 17. The boost cylinder / piston device 39 has a stepped piston member 45 having a small diameter piston portion 41 and a large diameter piston portion 43, and a cylinder member 47 that receives the stepped piston member 45.
And the cylinder member 47, the small diameter cylinder chamber 49 having the small diameter piston portion 41 as the pressure receiving surface, the intermediate cylinder chamber 51 having the step portion between the small diameter piston portion 41 and the large diameter piston portion 43 as the pressure receiving surface, and the large diameter piston portion 43. Is defined as a large-diameter cylinder chamber 53 having a pressure receiving surface.

The intermediate cylinder chamber 51 is connected to the port c of the pressure increase control valve 57 by the oil passage 55, and the large diameter cylinder chamber 5
3 is connected to the port d of the pressure increase control valve 57 by the oil passage 59.

The pressure increasing control valve 57 is a three-position type electromagnetic switching valve, and has a first switching position for connecting the port a to the ports c and d and a port for connecting the port a to the port c. Has a second switching position for connecting the drain port b to the drain port b, and a third switching position for connecting the port a to the port c and the port d to the drain port b.
When any of the three is stationary, it switches to the first switching position, when the solenoid 61 operates, it switches to the second switching position, and when the solenoid 63 operates, it switches to the third switching position. The port a of the pressure increase control valve 57 is connected to the oil passage 13 by the oil passage 65.

Piston rod 11 of mold clamping cylinder device 3
A limit switch 66 is provided in the middle of the movement route of. The limit switch 66 is switched by the pistun rod 11 as the pistun rod 11 moves forward to a predetermined forward position, and the pressure increasing region is set.

Next, the operation of the mold clamping hydraulic device having the above-described structure will be described.

In the standby state before the start of mold clamping, the piston member 5 of the mold clamping cylinder device 3 is located at the retracted position (the position on the left side in the figure), and the stepped piston member 45 of the pressure boosting cylinder / piston device 39. Is located at the initial position (the position on the right side in the figure), and all of the mold clamping / mold opening switching valve 19, the high-speed mold clamping / mold opening valve 29, and the pressure increase control valve 57 are in the first switching position. .

In this state, when a control device (not shown) outputs a mold clamping start signal, the solenoid 21 is first excited and the mold clamping / mold opening switching valve 19 is switched to the second switching position. As a result, pressure oil (line hydraulic pressure) from the hydraulic pressure source 1 is supplied to the first cylinder chamber 7 of the mold clamping cylinder device 3 in a state where the second cylinder chamber 9 of the mold clamping cylinder device 3 is drain-connected, and the pistun rod 11 moves forward and mold clamping is started.

Next, when the control device outputs a high-speed mold clamping start signal, the solenoid 31 is excited and the high-speed mold clamping / mold opening valve 29.
Switches to the second switching position. As a result, the second cylinder chamber 9 of the mold clamping cylinder device 3 is connected to the oil passage 25,
A run-around circuit is established and high-speed mold clamping is performed.

Thereafter, when the limit switch 66 performs a switching operation by advancing the piston rod 11 to a predetermined advancing position, the solenoid 31 is demagnetized and high-speed mold clamping /
The mold opening valve 29 returns to the first switching position, the run-around circuit is released, and in this state, the solenoid 61 is excited and the pressure increase control valve 57 switches to the second switching position.

As a result, the pressure boosting cylinder / piston device 3
The intermediate cylinder chamber 51 of 9 is drain-connected, the stepped piston member 45 of the pressure boosting cylinder / piston device 39 is moved forward, and the hydraulic oil of the small diameter cylinder chamber 49 is communicated with the first cylinder chamber 7. Discharge to 17. As a result, the pressure increasing action is performed on the first cylinder chamber 7.

Here, the pressure receiving area of the piston member 5 in the first cylinder chamber 7 of the mold clamping cylinder device 3 is Aa, the pressure receiving area of the small diameter piston portion 41 is Ab, and the large diameter piston portion 4 is large.
If the pressure receiving area is 1 and the line oil pressure is Pl, the line oil pressure Pl is increased with an area ratio (Ac / Ab).

Therefore, assuming that the output required for mold clamping is F, F = Pl · Aa when the pressure boosting action is not performed, whereas when the pressure boosting action is performed, F = P
l · Aa (Ab / Ac), compared to the case where the pressure receiving area Aa of the piston member 5 is not increased by (A
b / Ac) can be reduced.

Further, the mold clamping speed Vo when the pressure increasing action is not performed is Vo when the pump discharge amount is Q (constant).
= Q / Aa, on the other hand, the mold clamping speed Vb when the pressure increasing action is performed is Vb = Q / Aa (Ab / A
c). As a result, when the pressure increasing action is performed, the mold clamping speed becomes (Ab
/ Ac) times faster.

When the mold is opened, the solenoid 23 is excited to switch the mold closing / mold opening switching valve 19 to the third switching position, and the solenoid 33 is excited to energize the high speed mold clamping / mold opening valve 29 to switch the third position. The first cylinder chamber 7 of the mold clamping cylinder device 3 is switched to the position and the first cylinder chamber 7 of the mold clamping cylinder device 3 is drain-connected so that the pressure oil (line hydraulic pressure) of the hydraulic pressure source 1 is transferred to the second cylinder chamber 9 of the mold clamping cylinder device 3.
Is supplied to. As a result, the pistun rod 11 moves backward and the mold opening is started.

At this time, the solenoid 61 is continuously excited, the pressure increasing control valve 57 is at the second switching position, and the intermediate cylinder chamber 51 of the pressure increasing cylinder / piston device 39 is drain-connected, so that the pressure increasing cylinder is The stepped piston member 45 of the piston device 39 moves forward and discharges the pressure oil in the small diameter cylinder chamber 49 to the oil passage 17 communicating with the second cylinder chamber 9. As a result, the second cylinder chamber 9
A pressure increasing action is performed on.

Due to this pressure increasing action, as in the case of mold clamping,
Compared to when pressure boosting is not performed (Ac / Ab)
A large mold opening force can be obtained. In addition, the mold opening speed is (Ac / Ab) times faster than when the pressure increasing action is not performed.

After the mold opening is completed, the solenoids 23 and 33 are both demagnetized, and the mold clamping / mold opening switching valve 19 and the high speed mold clamping / mold opening valve 29 both return to the first switching position. Also solenoid 63
Is excited, and the pressure increase control valve 57 is switched to the third switching position. As a result, the large-diameter cylinder chamber 53 is drain-connected and the pressure oil is supplied from the hydraulic pressure source 1 to the intermediate cylinder chamber 51, and the stepped piston member 4 of the pressure boosting cylinder / piston device 39 is supplied.
5 returns to the initial position. When this operation is completed, the solenoid 63 is demagnetized, the pressure increase control valve 57 returns to the first switching position, and stands by for the next mold clamping operation.

FIG. 2 shows a second embodiment of the mold clamping hydraulic device according to the present invention. 2, parts corresponding to those in FIG. 1 are designated by the same reference numerals as those in FIG. 1 and their description is omitted.

The second embodiment is a modification of the first embodiment. In this embodiment, the pressure increase control valve 67 is a two-position solenoid switching valve, and the solenoid 69 is energized. If not present, the intermediate cylinder chamber 51 is closed and the large diameter cylinder chamber 53 is connected to the hydraulic pressure source 1 when the solenoid 69 is energized. The drainage connection is made to the large-diameter cylinder chamber 53 to connect the intermediate cylinder chamber 51 to the hydraulic power source 1.

A relief valve 71 is connected to the intermediate cylinder chamber 51. The relief valve 71 is given a hydraulic pressure in the oil passage 17 as a pilot pressure, and when the hydraulic pressure exceeds a predetermined value, the relief valve 71 opens to connect the intermediate cylinder chamber 51 to the drain.

In this embodiment, the boost control valve 67 is switched to the second switching position only when the stepped piston member 45 of the boost cylinder / piston device 39 is returned to the initial position, and is otherwise increased. The pressure control valve 67 is switched to the first switching position. Other than that, the same functions as those of the first embodiment described above.

Therefore, at the time of mold clamping, when the hydraulic pressure in the oil passage 17 becomes equal to or higher than a predetermined value due to the progress of mold clamping with the pressure increase control valve 67 switched to the first switching position, the relief valve 71 is activated. By opening the valve, the intermediate cylinder chamber 51
Is drain-connected, and the pressure boosting cylinder / piston device 39 automatically starts the pressure boosting action on the first cylinder chamber 7.

When the mold is opened and the hydraulic pressure in the oil passage 17 communicating with the second cylinder chamber 7 exceeds a predetermined value, the relief valve 71 is opened and the intermediate cylinder chamber 51 is drain-connected. The pressure increasing cylinder / piston device 39 increases the pressure in the second cylinder chamber 9.

FIG. 3 shows a third embodiment of the mold clamping hydraulic device according to the present invention. Note that, also in FIG. 3, the portions corresponding to those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and the description thereof will be omitted.

In this embodiment, an accumulator 81 with a pressure increasing mechanism is used as a pressure increasing ram device. The accumulator 81 with a pressure increasing mechanism has a stepped piston member 87 having a small diameter piston portion 83 and a large diameter piston portion 85.
And a cylinder member 89 that receives the stepped piston member 87, and the stepped piston member 87 and the cylinder member 89 form an accumulator chamber 91 having the small diameter piston portion 83 as a pressure receiving surface, a small diameter piston portion 83, and a large diameter piston. Intermediate cylinder chamber 93 having a pressure receiving surface at a step with the portion 85
And a large-diameter piston portion 89 as a pressure receiving surface to define a back pressure chamber 95 having a sealed structure and filled with N2 gas under pressure. The accumulator chamber 91 is connected to the oil passage 17 by an oil passage 97.

The pressure-increasing control valve 99 is composed of a two-position type electromagnetic switching valve. When the solenoid 101 is not energized, the pressure increasing control valve 99 is located at the first switching position and the intermediate cylinder chamber 93 is closed by the oil passage 17. When the solenoid 93 is energized, the intermediate cylinder chamber 93 is drain-connected to the second switching position.

The pressure-increasing control valve 67 is switched to the first switching position when returning the stepped piston member 83 of the accumulator 81 with pressure-increasing mechanism to the initial position, and to the second switching position during the pressure-increasing operation. Switch.

In this embodiment, at the time of mold clamping, the pressure increase control valve 67 is switched to the second switching position so that the intermediate cylinder chamber 93 is drain-connected and the accumulator 81 with the pressure increasing mechanism is set to the first position. A pressure increasing action is performed on the cylinder chamber 7.

Even when the mold is opened, the pressure increase control valve 67 is switched to the second switching position, so that the intermediate cylinder chamber 9
Accumulator 81 with pressure boosting mechanism connected to drain 3
Perform a pressure increasing action on the second cylinder chamber 9.

As a result, also in this embodiment, the accumulator 81 with the pressure increasing mechanism works effectively both when the mold is clamped and when the mold is opened.

FIG. 4 shows a fourth embodiment of the hydraulic apparatus for mold clamping according to the present invention. Incidentally, in FIG. 4, the portions corresponding to those in FIG. 3 are designated by the same reference numerals as those in FIG. 3, and the description thereof will be omitted.

The fourth embodiment is a modification of the third embodiment. In this embodiment, the relief valve 7 in the second embodiment is used.
The relief valve 103 equivalent to 1 is connected to the intermediate cylinder chamber 93. The relief valve 103 is given a hydraulic pressure in the oil passage 17 as a pilot pressure, and when the hydraulic pressure reaches or exceeds a predetermined value, the relief valve 103 opens to connect the intermediate cylinder chamber 93 to the drain.

The pressure increase control valve 105 is composed of a check valve which allows only the flow of pressure oil from the oil passage 17 toward the intermediate cylinder chamber 93.

In this embodiment, at the time of mold clamping, when the hydraulic pressure in the oil passage 17 becomes a predetermined value or more due to the progress of mold clamping, the relief valve 103 is opened to open the intermediate cylinder chamber 93.
Is drain-connected, and the accumulator 81 with a pressure increasing mechanism automatically starts the pressure increasing action on the first cylinder chamber 7.

When the hydraulic pressure in the oil passage 17 communicating with the second cylinder chamber 7 becomes a predetermined value or more during mold opening, the relief valve 71 is opened and the intermediate cylinder chamber 93 is drain-connected. The accumulator 81 with a pressure increasing mechanism increases the pressure of the second cylinder chamber 9.

In the above, the present invention has been described in detail with respect to a specific embodiment, but the present invention is not limited to this, and various embodiments are possible within the scope of the present invention. It will be apparent to those skilled in the art.

[0056]

As can be understood from the above description, according to the mold clamping hydraulic device of the present invention, the accumulator of the small diameter cylinder chamber of the pressure increasing ram device, that is, the pressure increasing cylinder / piston device or the accumulator with the pressure increasing mechanism. The room is clamped
It is connected to the oil passage on the hydraulic pressure source side of the mold opening switching valve, and the pressure boosting ram device exerts a pressure increasing function both during the mold closing operation and during the mold opening operation. The shortage can be resolved,
Further, both the mold clamping operation time and the mold opening operation time can be shortened without increasing the amount of oil supplied from the hydraulic power source.
As a result, the machine cycle time can be shortened and the operation rate of the die casting machine or injection molding machine can be improved. Further, the mold clamping cylinder device can be downsized.

When the oil pressure in the oil passage for supplying the pressure oil to the mold clamping cylinder device becomes equal to or higher than a predetermined value, the intermediate cylinder chamber is drain-connected by the relief valve, so that the pressure increasing ram device has a pressure increasing action. Since it is automatically started, the boosting start control of the boosting ram device is always appropriately performed according to the operating state of the mold clamping cylinder device without requiring a special switch or sensor.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of a hydraulic device for mold clamping according to the present invention.

FIG. 2 is a hydraulic circuit diagram showing a second embodiment of the mold clamping hydraulic device according to the present invention.

FIG. 3 is a hydraulic circuit diagram showing a third embodiment of the mold clamping hydraulic device according to the present invention.

FIG. 4 is a hydraulic circuit diagram showing a fourth embodiment of the mold clamping hydraulic device according to the present invention.

[Explanation of symbols] 1 hydraulic power source 3 mold clamping cylinder device 7 first cylinder chamber 9 second cylinder chamber 15 check valve 19 mold clamping / mold opening switching valve 29 high speed mold clamping / mold opening valve 39 pressure boosting cylinder / piston Device 41 Small diameter piston part 43 Large diameter piston part 45 Stepped piston member 47 Cylinder member 49 Small diameter cylinder chamber 51 Intermediate cylinder chamber 53 Large diameter cylinder chamber 57 Pressure increase control valve 66 Limit switch 67 Pressure increase control valve 71 Relief valve 81 Pressure increase Accumulator with mechanism 83 Small diameter piston part 85 Large diameter piston part 87 Stepped piston member 89 Cylinder member 91 Accumulator chamber 93 Intermediate cylinder chamber 95 Back pressure chamber 99 Pressure increase control valve 103 Relief valve 105 Pressure increase control valve

Claims (3)

[Claims] 1. A mold clamping hydraulic device configured to reciprocate a movable die plate with respect to a fixed die plate by a mold clamping cylinder device to perform mold clamping and mold opening, wherein a hydraulic pressure source and the mold clamping A mold clamping / mold opening switching valve for switching the supply of pressure oil to the first cylinder chamber and the second cylinder chamber of the cylinder device, a stepped piston member having a small diameter piston portion and a large diameter piston portion, and the stepped portion A small diameter cylinder chamber having a cylinder member for receiving a piston member, the small diameter piston portion serving as a pressure receiving surface by the stepped piston member and the cylinder member, and a step portion between the small diameter piston portion and the large diameter piston portion. Is defined as a pressure receiving surface, and a large diameter cylinder chamber having the large diameter piston portion as a pressure receiving surface is defined, and the small diameter cylinder chamber is defined by the hydraulic pressure source and the mold clamping / mold. A pressure boosting cylinder / piston device connected to an oil passage between the open switching valve and a pressure booster for controlling supply / discharge of pressure oil to / from the intermediate cylinder chamber and the large diameter cylinder chamber of the pressure boosting cylinder / piston device. A hydraulic device for mold clamping, which has a control valve. 2. A mold clamping hydraulic device configured to reciprocate a movable die plate by a mold clamping cylinder device with respect to a fixed die plate to perform mold clamping and mold opening, wherein a hydraulic pressure source and the mold clamping A mold clamping / mold opening switching valve for switching the supply of pressure oil to the first cylinder chamber and the second cylinder chamber of the cylinder device, a stepped piston member having a small diameter piston portion and a large diameter piston portion, and the stepped portion An accumulator chamber having a cylinder member that receives a piston member, the stepped piston member and the cylinder member having the small diameter piston portion as a pressure receiving surface, and a step portion between the small diameter piston portion and the large diameter piston portion. An intermediate cylinder chamber that serves as a pressure receiving surface,
A back pressure chamber having the large-diameter piston portion as a pressure receiving surface is defined,
An accumulator with a pressure increasing mechanism connected to the oil passage between the hydraulic pressure source and the mold clamping / mold opening switching valve, and supply / discharge of pressure oil to / from the intermediate cylinder chamber of the accumulator with a pressure increasing mechanism. And a pressure increasing control valve for controlling the. 3. The relief valve according to claim 1, further comprising a relief valve that responds to the oil pressure of the oil passage and connects the intermediate cylinder chamber to the drain when the oil pressure is equal to or higher than a predetermined value. Hydraulic system for mold clamping.