JPH0452031Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a mold opening/closing mechanism in an injection molding machine in which the mold is opened and closed by a hydraulic cylinder.

[Prior Art] Conventionally, it has been pointed out that this type of mold opening/closing mechanism has a drawback in that the mold opening/closing operation cannot be performed smoothly due to fluctuations in the load resistance applied to the hydraulic cylinder during mold opening/closing. Ta. Therefore, recently, a system has been developed that eliminates the influence of load resistance fluctuations from the operation of the hydraulic cylinder by applying an appropriate amount of back pressure to the return path of the hydraulic cylinder, thereby solving the above drawbacks. An example of this will be explained below with reference to FIG.

In FIG. 3, reference numeral 1 denotes a movable platen, and 2 a fixed platen, and a pair of molds (not shown) are attached to mutually opposing surfaces of the movable platen 1 and the fixed platen 2, respectively. An end plate 4 connected to the fixed plate 2 by a tie bar 3 is provided on the left end side of the movable plate 1.
and the movable platen 1 are connected via a toggle mechanism 5. The center portion of the toggle mechanism 5 is connected to a piston rod 6a of a hydraulic cylinder 6 fixed to the end plate 4, and the movable platen 1 is brought close to and separated from the fixed platen 2 by reciprocating movement of the piston rod 6a. The pair of molds are then opened and closed.

Ports 6b and 6c of the hydraulic cylinder 6 are connected to load-side ports A and B of a solenoid valve 7, respectively. Pump side port P of this solenoid valve 7
is connected to a tank T via an oil supply path 8, and by a hydraulic pump 9 and a pressure compensation type flow control valve 10 arranged in the oil supply path 8, a pump side port P of the solenoid valve 7 is connected to a tank T. The hydraulic oil inside the T is
The flow rate is controlled and supplied. Further, the return side port R of the solenoid valve 7 is connected to the tank T via a return path 11.
A counterbalance valve 12 is disposed in the return path 11, and the hydraulic oil discharged from the return side port R of the solenoid valve 7 is discharged when the pressure exceeds the set pressure of the counterbalance valve 12. Only the tank T is returned to the tank T.

In the mold opening/closing mechanism as described above, the solenoid valve 7
By energizing either one of the soleids 7a, 7b, the hydraulic oil pumped from the hydraulic pump 9 is supplied to either the port 6b, 6c of the hydraulic cylinder 6, and the piston rod 6a is thereby moved forward or backward. The mold is opened and closed,
In this case, the mold opening/closing speed is the pressure compensated flow control valve 1
Controlled by the opening degree of 0.

Then, the hydraulic cylinder 6 during the mold opening/closing operation.
The influence of variations in load resistance on the operation of the mold is eliminated by the action of the counterbalance valve 12, and the mold opening and closing operations are always carried out smoothly.

That is, when the mold is opened and closed, mechanical friction resistance such as the toggle mechanism 5 and hydraulic oil pressure in the return path of the hydraulic cylinder 6, that is, back pressure act as load resistance on the piston rod 6a of the hydraulic cylinder 6. Considering the case where there is no counterbalance valve 12 and the return path of the hydraulic cylinder 6 is open to atmospheric pressure, the load resistance increases greatly at the start of operation due to fluctuations in static and dynamic frictional resistance, and after the start of operation. It will decrease rapidly.

Under such circumstances, especially when the pressure compensation type flow control valve 10 is throttled down and the mold opening/closing speed is set in a low speed range, an increase in back pressure due to the movement of the piston rod 6a cannot be expected, so the load resistance, i.e. The influence of fluctuations in mechanical frictional resistance becomes more pronounced, and the driving speed of the piston rod 6a increases when the piston rod 6a overcomes static friction and starts operating, and the pressure compensated flow rate regulating valve 10 responds to this change. As a result, the supply of hydraulic oil is reduced, and the drive speed soon becomes zero.
As a result of this repeated operation, a stick slip occurs in the piston rod 6a.
The mold opening/closing operation becomes a discontinuous operation.

However, in the mold opening/closing mechanism described above, since the counterbalance valve 12 is disposed in the return path connected to the return side port R of the solenoid valve 7, the hydraulic cylinder 6 always has the counterbalance valve 12 on its compression side. It is driven with a back pressure equivalent to the set pressure applied. Therefore, even if the frictional resistance suddenly decreases after the piston rod 6a starts operating, back pressure will still remain in the piston rod 6a of the hydraulic cylinder 6 as a load resistance, thus preventing the driving speed of the piston rod 6a from increasing rapidly. . Therefore, the hydraulic cylinder 6 is always driven continuously regardless of the opening degree of the pressure compensation type flow control valve 10.
The mold opens and closes smoothly at all times.

[Problem to be solved by the invention] By the way, the conventional mold opening/closing mechanism described above is excellent in that the mold opening/closing operation is performed smoothly, but the counterbalance valve 12 provided in the return path 11 is It has been pointed out that it is expensive, has a large and bulky exterior, and cannot be installed as a compact unit for hydraulic equipment.

This idea was developed against this background, and it is possible to eliminate the influence of load resistance fluctuations from the hydraulic cylinder operation and perform mold opening/closing operations without using an expensive and large counterbalance valve. The purpose of the present invention is to provide a mold opening/closing mechanism for an injection molding machine that can be smoothly operated.

[Means for Solving the Problems] This invention provides a mold opening/closing mechanism for an injection molding machine in which the molds are opened and closed by moving at least one of a pair of molds facing each other using a hydraulic cylinder. A check valve is provided in the return path of the hydraulic oil discharged from the hydraulic cylinder, which allows the hydraulic oil discharged from the hydraulic cylinder to pass only when the pressure thereof is equal to or higher than the lower limit load pressure of the hydraulic cylinder. The above-mentioned problem is solved by forming a restriction hole in the valve body of the stop valve, through which the flow of the hydraulic oil is restricted and passed through.

[Function] In the above configuration, the check valve disposed in the return path allows the hydraulic oil discharged from the hydraulic cylinder to pass only when the pressure thereof is equal to or higher than the lower limit load pressure of the hydraulic cylinder. A back pressure higher than the lower limit load pressure of the hydraulic cylinder acts on the return path of the hydraulic cylinder.

Then, a small amount of the hydraulic fluid discharged from the hydraulic cylinder is discharged through the throttle hole opened in the valve body of the check valve, so the sensitivity of the valve body of the check valve becomes dull and the lower limit of the hydraulic cylinder This prevents back pressure pulsations caused by the valve body being driven to follow the pressure of the hydraulic oil, which fluctuates slightly near the load pressure.

Note that the lower limit load pressure of the hydraulic cylinder referred to herein is the back pressure necessary to drive the hydraulic cylinder without being affected by fluctuations in mechanical frictional resistance during mold opening/closing operations.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2. In this embodiment, only the counterbalance valve in the conventional mold opening/closing mechanism described above is changed, and the same components are denoted by the same reference numerals and their explanations will be omitted.

As shown in FIG. 1, the mold opening/closing mechanism of this embodiment has a check valve with a throttle hole (hereinafter abbreviated as check valve) in a return path 11 connecting the return side port R of the electromagnetic valve 7 and the tank T. ) 13 is provided. As shown in FIG. 2, this check valve 13 includes an inlet 15 and an outlet 16 formed at both ends of a valve body 14;
Poppet (valve body) inserted inside the valve body 14
17 is a so-called in-line type check valve arranged in a straight line, and the inlet 15 is connected to the return path 11.
The outlet port 16 is connected to the solenoid valve 7 side, and the outlet port 16 is connected to the tank T side (see FIG. 1).

The poppet 17 is fitted into the inner hole 14a of the valve body 14 so as to be slidable in the axial direction, and has a flow path 17 inside thereof that opens toward the outlet 16.
a is formed, and the flow path 17a has a plurality of through holes 17
It communicates with the outer peripheral surface side of the poppet 17 via b. The end surface 17c of the poppet 17 on the inlet 15 side is formed into a conical shape and can be brought into close contact with the seat surface 14b of the valve body 14, so that the hydraulic oil flows from the outlet 16 toward the inlet 15. flow is regulated.

In addition, the poppet 17 and the inner hole 14a of the valve body 14
A spring 19 is stretched between the poppet 18 and the retaining ring 18, which is inserted into the poppet 1.
7, its end surface 17c is the seat surface 14 of the valve body 14.
It is designed to be held in close contact with b. The spring 19 is connected to the end surface 1 of the poppet 17.
7c against the seat surface 14b is determined to be equal to the value obtained by multiplying the lower limit load pressure of the hydraulic cylinder by the pressure receiving area of the poppet 17, and therefore, the hydraulic oil flowing from the inlet 15, When the pressure of the hydraulic oil discharged from the hydraulic cylinder 6 exceeds the lower limit load pressure of the hydraulic cylinder 6, the poppet 17 is moved toward the outlet 16 against the spring 19, and the end surface 17c is moved away from the seat surface 14b. separated, thereby allowing the return path 11
are connected and hydraulic oil is discharged.

Further, a throttle hole 17d is formed in the center of the end surface 17c of the poppet 17. The diameter of this throttle hole 17d is selected so that a back pressure equal to or higher than the lower limit load pressure acts, and when the end surface 17c of the poppet 17 and the seat surface 14b are in close contact with each other, the inlet 1
A small amount of hydraulic oil is allowed to flow out from the outlet 5 to the outlet 16.

However, in the mold opening/closing mechanism configured as above, like the conventional mold opening/closing mechanism described above,
By appropriately switching the excitation of the solenoids 7a and 7b of the electromagnetic valve 7, the piston rod 6a of the hydraulic cylinder 6 is moved forward or backward to open and close the mold. Due to the action, the pressure compensated flow control valve 1
It is always performed smoothly regardless of the opening degree of 0.

If the opening degree of the pressure compensated flow rate regulating valve 10 is small, the driving speed of the piston rod 6a is slow and the flow rate of the hydraulic oil discharged from the hydraulic cylinder 6 is also small.
is closed, and discharge of hydraulic fluid from the hydraulic cylinder 6 is restricted. When the discharge of hydraulic oil is regulated, the hydraulic oil is compressed by the operation of the piston rod 6a, and when the pressure exceeds the set pressure of the tension spring 19 of the check valve 13, the hydraulic oil is compressed by the operation of the piston rod 6a. The poppet 17 of the stop valve 13 opens and discharges into the tank T. Then, as soon as the back pressure falls below the set pressure of the check valve 13 due to discharge of the hydraulic oil, the return path 11 is immediately closed by the poppet 17 of the check valve 13.

In such a state, the back pressure in the hydraulic oil return path 11 repeatedly opens and closes the poppet 17 across the set pressure of the tension spring 19 of the check valve 13, causing pulsations in the back pressure applied to the hydraulic cylinder 6. This is not preferable for stable operation of the piston rod 6a.

However, in this embodiment, the end surface 1 of the poppet 17
A throttle hole 17d is formed in 7c to maintain a back pressure higher than the lower limit load pressure, and a small amount of discharged hydraulic oil from the hydraulic cylinder 6 is discharged from the throttle hole 17d to the tank T, increasing the back pressure. act to make it happen. Therefore, the pulsation of the back pressure applied to the hydraulic cylinder 6 is suppressed, and the pressure compensation type flow regulating valve 10
Even if the degree of opening is small, the drive speed of the hydraulic cylinder 6 is kept constant and the mold opening/closing operation is performed smoothly.

Note that when the opening degree of the pressure-compensated flow rate regulating valve 10 is large, the driving speed of the piston rod 6a is fast, so the pressure of the hydraulic oil increases quickly with the operation of the piston rod 6a, and furthermore, the operation of discharging the hydraulic oil is delayed. Since the flow rate of oil is large, the poppet 17 is driven largely and kept almost open, so no back pressure pulsations occur, and the back pressure in the hydraulic cylinder 6 is adjusted by the back pressure adjustment effect caused by the movement of the poppet 17 itself. is kept constant.

As described above, in this embodiment, the poppet 1
By arranging the check valve 13 in which the throttle hole 17d is formed in the return path 11 from the hydraulic cylinder 6, no matter how the opening degree of the pressure compensation control valve 10 is set, the hydraulic cylinder 6 can be driven with back pressure corresponding to a constant lower limit load pressure applied at all times, thereby eliminating the influence of fluctuations in load resistance from the operation of the hydraulic cylinder 6.

Therefore, according to this embodiment, the mold opening/closing operation can be performed smoothly without using an expensive and large counterbalance valve.

In this embodiment, the case in which the check valve is an in-line type is explained, but the mold opening/closing mechanism of the present invention is not limited to this, and can of course be implemented even when a stacked check valve is used. .

In addition, the lower limit load pressure of the hydraulic cylinder depends on the operating characteristics of the hydraulic cylinder itself such as the cylinder diameter and rod diameter, the discharge pressure of the hydraulic pump, or the movable platen 1.
It naturally changes depending on the mechanical friction resistance of the toggle mechanism 5, so it cannot be determined unconditionally, but in the case of this example, it is set at about 5 kg/cm ² , which is almost sufficient. The effect was confirmed. Also,
If the lower limit load pressure is set extremely high, the driving force of the hydraulic cylinder will be impaired, so the upper limit is
It is preferable to set it at about 10Kg/cm ² .

[Effect of the invention] As explained above, in this invention, the hydraulic oil discharged from the hydraulic cylinder is placed in the return path of the hydraulic oil discharged from the hydraulic cylinder at a pressure higher than the lower limit load pressure of the hydraulic cylinder. A check valve is provided to allow passage of the fluid only in the case of A back pressure equal to or higher than the lower limit load pressure of the hydraulic cylinder can be constantly applied to the compression side of the cylinder, and the sensitivity of the valve element can be dulled to prevent the valve element from being driven frequently near the lower limit load pressure of the hydraulic cylinder. It is possible to prevent back pressure pulsations caused by

Therefore, according to the present invention, the mold opening/closing operation can be performed smoothly without using an expensive and large counterbalance valve.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a schematic configuration of an embodiment of the present invention, Fig. 2 is a sectional view showing the structure of a check valve in an embodiment of the invention, and Fig. 3 is a mold opening/closing diagram in a conventional injection molding machine. FIG. 3 is a diagram showing a schematic configuration of the mechanism. 6... Hydraulic cylinder, 11... Return path, 13
... Check valve with throttle hole (check valve), 17... Poppet (valve body), 17d... Throttle hole.

Claims (1)

[Claims for Utility Model Registration] In a mold opening/closing mechanism of an injection molding machine in which at least one of a pair of molds disposed facing each other is moved by a hydraulic cylinder to open and close the molds, the mold is discharged from the hydraulic cylinder. A check valve is provided in the return path of the hydraulic oil, which allows the hydraulic oil discharged from the hydraulic cylinder to pass only when the pressure thereof is equal to or higher than the lower limit load pressure of the hydraulic cylinder, and a valve body of the check valve is provided. A mold opening/closing mechanism for an injection molding machine, characterized in that a throttle hole is opened through which the flow of hydraulic fluid is regulated by the valve body after being throttled.