JPH046888Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention is used in an injection molding machine that controls injection speed using a flow control valve that adjusts the amount of oil. The present invention relates to an injection molding machine equipped with an injection abnormality detection device that prevents loading conditions.

(Prior art) An injection molding machine is equipped with an injection cylinder that moves an injection screw forward and backward, and after rotating the injection screw in a heating cylinder by driving a hydraulic motor to knead resin, the resin is injected into a mold. It is designed to be filled by injection.

Since the injection speed has a large effect on the quality of the molded product, it is necessary to control it. For this reason, speed control is performed by restricting the flow rate using a flow control valve to obtain an injection speed corresponding to a desired set value.

However, in order to overcome the resistance and advance the screw to fill the mold with resin, it is common practice to keep the set pressure of the relief valve provided in the primary circuit at the highest pressure during injection filling. .

Therefore, if an abnormality occurs during injection, the discharge pressure of the hydraulic pump increases to the highest setting pressure of the relief valve, and the driving force of the pump becomes maximum.

(Problem that the invention aims to solve) Therefore, when an injection abnormality occurs, the injection pressure reaches the maximum pressure and pressure oil escapes from the safety relief valve, causing the hydraulic pump's electric motor to run continuously, causing overload and waste. It ended up consuming a lot of electricity.

For this reason, there is a method to unload the hydraulic pump by detecting when the injection pressure has increased to a certain level, but this simply detects the injection pressure and temporarily sets the relief valve set pressure at the start of injection. There was a problem in that the peak pressure that exceeded the limit was mistakenly recognized as an injection abnormality.

Therefore, in order to determine that the injection is abnormal, it is necessary to detect that this state continues for a certain period of time after the set pressure of the relief valve reaches a predetermined maximum pressure.

In view of these circumstances, the present invention uses a flow rate detection means to detect the amount of oil from the electromagnetic relief valve that has reached a predetermined set pressure. The purpose of this system is to detect an injection abnormality, switch to a low-pressure, low-flow injection pressure, and prevent the pump motor from overloading, thereby providing a low-cost injection molding machine that is smaller and more energy efficient.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an injection molding machine that controls the injection speed by adjusting the flow rate of oil supplied from a hydraulic pump with a flow control valve. An electromagnetic relief valve connected to the secondary side pipe line of the control valve and capable of setting a predetermined maximum pressure of the primary injection pressure is provided, and a flow rate detection means is connected to the secondary side of the electromagnetic relief valve. An abnormality detection device that outputs a signal from the flow rate detection means to switch the pressure of the electromagnetic relief valve to a predetermined low pressure when the flow rate exceeding the set pressure of the valve differs from the set flow rate value of the flow rate detection means. It is characterized by being comprised of an injection molding machine equipped with

(Function) With this configuration, the flow rate of the oil from the hydraulic pump is controlled according to the valve opening determined by the input current proportional to the set speed of the flow control valve. In the event of an abnormality, the injection pressure will reach the maximum pressure set in the relief valve due to an increase in flow resistance, and when the oil escapes from the electromagnetic relief valve to the tank, it will flow into the flow rate detection means.

When the flow rate of this oil reaches the set flow rate value of the flow rate detection means, a signal is output and the injection pressure is switched to the low-pressure, low-flow rate injection secondary pressure, which prevents the hydraulic pump's electric motor from running continuously, preventing overload. Prevent the condition.

As a result, it has become possible to replace the electric motor of the hydraulic pump with one that is smaller than the conventional size.
It is possible to downsize the device and save energy. In addition, by quickly detecting an abnormal injection state, the cause of molding defects can be eliminated at an early stage.

(Example) Embodiments of the present invention will be described based on the drawings.

In Fig. 1, reference numeral 1 denotes a variable discharge rate pump that changes the discharge rate of oil fluid, and the discharge rate of this pump 1 is designed to be variable depending on the magnitude of the pressure acting on port a or port b. .

The variable discharge amount pump 1 has its discharge amount controlled by the pilot pressure of the discharge amount control valve 2, and
to output oil liquid. The pipe line 3 is connected to an electromagnetic proportional directional flow control valve 4, and a relief valve 5 is connected to the pipe line 3, which maintains the oil pressure of the pipe line 3 at a predetermined set pressure and cuts the peak value of the primary side pressure of the flow control valve 4. The hydraulic pressure is provided in a side passage of the tank 6, and when hydraulic pressure exceeding a set value is supplied, it returns to the tank 6.

On the tip side of the conduit 7 on the secondary side of the flow control valve 4,
A 4-port 3-position electromagnetic switching valve 9 for moving the piston of the injection cylinder 8 forward and backward is provided, and an electromagnetic relief valve 10 for setting the injection pressure is provided in a side passage of the pipe line 7 to the highest pressure of the primary injection pressure. is provided.

A flow switch 11 as a flow rate detection means is connected to the secondary side of the electromagnetic relief valve 10, and the oil flowing into the flow switch 11 is returned to the tank. Here, if the flow rate flowing out from the relief valve 10 exceeds a flow rate value set per predetermined unit time, an electric signal is output and the injection pressure is switched to the secondary injection pressure. An injection abnormality detection device 12 is constituted by the relief valve 10 and flow switch 11 provided in the side passage.

Incidentally, the flow switch 11 is configured so that the oil leaking from the electromagnetic relief valve 10 flows into the flow switch 11 through an opening of a regulating valve 14 provided in a flow path 13, as shown in FIG. However, when the secondary side pressure of the flow control valve 4 reaches the maximum setting pressure of the electromagnetic relief valve 10, a large amount of oil flows from the electromagnetic relief valve 10, so the flow rate flowing into the flow path 13 increases. Oil flows into the side passage of passage 13 and piston 1
Press 5. As a result, the permanent magnetic body 16 embedded in the piston 15 moves, and the reed switch 1
The structure is such that the contact point 7 is switched to output an electric signal to issue an alarm and switch to the secondary injection pressure.

Next, the operating state of this embodiment will be explained.

The primary pressure P ₁ and the secondary pressure of the flow control valve 4 are
Assuming P ₂ , when the opening degree of the flow control valve 4 is maximum, the oil flows through the flow control valve 4 without resistance.
P ₁ ≒ P ₂ .

In this state, the pressure acting on the left and right valves c and d of the discharge amount control valve 2 is the pilot pressure of the pipe line 7 on the valve c.
P ₂ is applied, and the pilot pressure P ₁ of line 3 is applied to valve d. Therefore, the left and right valves have the same pressure, but valve c
Since the side is pressed by the spring 18, the discharge amount control valve 2 is offset toward the valve c side.

As a result, the pilot pressure P ₁ in the pipe line 3 acts on the a port of the variable discharge rate pump 1 via the pilot passage 20 and the discharge rate control valve 2, and also acts on the b port via the pilot passage 21. However, the pressure on the a port side acts due to the pressing force of the spring provided at the a port, and the variable pump 1
The rotor is eccentrically moved in the P direction in FIG. 1 to increase the discharge amount.

Furthermore, if we decide to throttle the flow rate from the flow rate control valve 4, P ₁ > P ₂ , so the pilot pressure P ₁ at valve d of the discharge rate control valve 2 becomes greater than the pilot pressure P ₂ at valve c. The discharge amount control valve 2 is offset to the valve d side.

Therefore, the pilot pressure _P1 flowing through the pilot passage 20 is returned to the tank 6 via the throttle valve in the discharge amount control valve 2, so that the pilot pressure at port a becomes atmospheric pressure.

As a result, since the pilot pressure at the b port is maintained at _P1 , the pressure on the b port side acts this time to eccentrically move the rotor of the variable pump 1 in the Q direction and reduce the discharge amount.

In this way, the amount of oil discharged from the variable discharge amount pump is controlled by the flow rate control valve 4.

From the above-mentioned effects, in the event of an injection abnormality due to causes such as clogging of the mold gate, disconnection of the heater in the heating cylinder, or incorrect operation of the set speed, the secondary side pressure P ₂ of the flow control valve 4 will reach the maximum level of the electromagnetic relief valve 10. The pressure becomes higher than the set pressure, and the variable discharge amount pump 1 is always maintained at the maximum discharge amount.

Therefore, the maximum load is applied to the variable pump for a long time, and the pump's electric motor becomes overloaded.

However, if the flow rate exceeds the flow rate setting value of the flow switch 11 (30 to 50% of the maximum discharge amount of the variable pump),
If the fluid flows out from the electromagnetic relief valve 10, an electric signal from the flow switch 11 issues an alarm, and the secondary injection pressure can be switched to a low pressure and low flow rate.

Therefore, according to this embodiment, an injection abnormality is detected early and an overload of the motor is prevented, so that a smaller motor than the one selected based on the safety factor of a conventional pump is enough to deal with the problem. can.

In this embodiment, a variable discharge rate pump is used to control the injection speed using a flow rate control valve, but the present invention can also be implemented with a constant discharge rate pump.

Further, although the flow switch shown in FIG. 2 is used as the flow rate detection means, other means may be used to detect the flow rate.

(Effects of the Invention) As is clear from the above explanation, the present invention detects the amount of oil from the electromagnetic relief valve that has reached a predetermined set pressure using a flow rate detection means, and when the flow rate exceeds the predetermined set pressure, the pressure is reduced.・By installing an injection abnormality detection device that switches to a low flow rate injection pressure, it correctly determines injection abnormalities and prevents overload of the pump motor. The capacity of the electric motor can be reduced, making injection molding machines cheaper and more energy efficient.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram illustrating the operating state of an embodiment of the present invention, and FIG. 2 is a schematic sectional view illustrating the operation of a flow switch, which is an embodiment of the flow rate detection means in FIG. 1. 1...variable discharge amount pump, 4...flow control valve,
10... Electromagnetic relief valve, 11... Flow switch, 12... Injection abnormality detection device.

Claims (1)

[Scope of Claim for Utility Model Registration] In an injection molding machine that controls the injection speed by adjusting the flow rate of oil supplied from a hydraulic pump with a flow control valve, An electromagnetic relief valve capable of setting a predetermined maximum pressure of the primary pressure is provided, and a flow rate detection means is connected to the secondary side of the electromagnetic relief valve, so that the flow rate exceeding the set pressure of the electromagnetic relief valve is detected as described above. An injection molding machine comprising an abnormality detection device that outputs a signal from the flow rate detection means to switch the pressure of the electromagnetic relief valve to a predetermined low pressure when the set flow rate value of the flow rate detection means is reached.