JPS6127710Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a reversal prevention device for an injection molding machine that prevents the screw from rotating in the opposite direction due to the reaction force of the injection during the injection process of molten resin.

To explain the conventional device with reference to FIG. 1, during the rotation process of the screw 3, the switching valve 4 moves the spool 6 to the left by the excitation of the solenoid a, and the pressure oil from the pump 5 flows as indicated by the solid line. As shown by the arrow, the flow flows from port P through port A to hydraulic motor 2, causing screw 3 to rotate.

Then, as the screw 3 rotates, the molten resin is sent to the tip of the screw 3, and the piston 7 is pushed back to the right, so that the oil in the front chamber 1' of the injection cylinder 1 passes from port B, through bypass 14, and through port T. It is returned to tank 9.

In the injection process, by excitation of solenoid b,
The spool 6 moves to the right, and the pressure oil passes from port P to port B and enters the front chamber 1' of the injection cylinder 1, as shown by the dotted arrow, and pushes the piston 7 to the left, causing the screw 3 to melt the molten resin. Inject.

However, at this time, port A and port T are in communication. Since the screw 3 has a torsion angle α corresponding to the lead angle of the screw 3, the reaction force of the injection of the molten resin causes the screw 3 to rotate in the opposite direction to the direction in which the molten resin is sent to the tip. Rotational force is generated.

Therefore, since the port A and port T communicate with each other, the oil in the flow path 8 on the inflow side of the hydraulic motor 2 escapes from the port A to the tank 9 via the port T, and flows into the hydraulic motor 2. will rotate in the opposite direction.

As described above, if the screw 3 rotates in the opposite direction during injection of molten resin, the amount of injection becomes unstable, which adversely affects the dimensional accuracy and appearance of the injection molded product.

The present invention attempts to overcome these drawbacks with an extremely simple device.

This will be explained with reference to FIG.

Reference numeral 4 denotes a directional switching valve for switching the drive of the injection cylinder 1 and the hydraulic motor 2.

The port A is the flow path 8 and the inlet port I of the hydraulic motor 2, the port B is the front chamber 1' of the injection cylinder 1,
Port P is connected to pump 5, port T is connected to tank 9,
Connect each.

Land 13 and land 1 are on spool 6 of the same valve.
3' is formed and moves leftward or rightward by energizing solenoid a and solenoid b.

A bypass 14 is also formed in the valve body. When the spool 6 moves to the left by the solenoid a, the ports P and A communicate with each other, and the ports B and T communicate with each other via the bypass 14.

When solenoid b moves to the right, port P and port B are communicated, and port A remains closed by the wide land 13' of spool 6, so port A and port T are not communicated.

In other words, the width of the land 13' is set to be long so that the land 13' of the spool 6 closes the port A only when the port P and the port B communicate with each other.

O is the outlet of the hydraulic motor 2, 11 is the tank,
1'' is the rear chamber of the injection cylinder 1, 12 is the tank, 1
0 is a relief valve, and indicates the width of the land 13'.

Its effects will be explained.

When the solenoid a of the directional control valve 4 is energized, the spool 6 moves to the left, and the oil from the pump 5 passes from the port P to the port A, as shown by the solid arrow, and passes through the flow path 8 to the hydraulic motor 2. The motor rotates, and this rotation rotates the screw 3.
The molten resin is sent to the tip of the screw 3. The reaction force pushes back the piston 7, and the front chamber 1'
The oil flows from port B of directional valve 4 to bypass 14.
, and is returned to the tank 9 through port T, which is the same as in the conventional device.

Next, solenoid b of the directional control valve 4 is energized,
The spool 6 moves to the right, and the pressure oil from the pump 5 passes from port P to port B as indicated by the dotted arrow, flows into the front chamber 1' of the injection cylinder 1, advances the screw 3, and injects the molten resin. .

And due to this advancement of Sukuriyu 3, Sukuriyu 3
is rotating in the opposite direction to normal rotation.

However, in order for the screw 3 to rotate in the reverse direction, the hydraulic motor 2 sucks oil from the tank 11, flows this oil from the delivery side port O to the delivery side port I, and then uses the flow path 8 to switch the direction. It is necessary to flow from port A of valve 4 to tank 9 via port T.

However, since the land 13' of the spool 6 is formed wide, the port A is closed by the land 13' at this time, and the flow of oil from the port A is blocked.

Therefore, since the hydraulic motor 2 cannot rotate in reverse, even if the piston 7 is moved forward by the pressure oil, reverse rotation of the screw 3 due to the reaction force can be completely prevented.

In this way, the present invention does not cause instability in the injection amount due to reversal of the screw during the injection process of molten resin, and it is possible to obtain an injection molded product with a stable injection amount and good dimensional accuracy. .

Moreover, this device can achieve its purpose with an extremely simple device of widening the width of the land of the spool.

[Brief explanation of the drawing]

FIG. 1 is a front view of a conventional device, and FIG. 2 is a front view of the present device. 1...Injection cylinder, 2...Hydraulic motor, 4...
...Directional switching valve, 5...Hydraulic pump, 6...Spool, 13'...Land, A, B...Port.

Claims (1)

[Scope of utility model registration request] In an injection molding machine in which driving of an injection cylinder 1 and a hydraulic motor 2 is switched by one directional control valve 4,
When switching between port A leading to the hydraulic motor 2 of the directional control valve 4 and port B leading to the injection cylinder 1 using the spool 6, the hydraulic pump 5 connects the port B and the injection cylinder so that pressure oil flows to the injection cylinder 1. The screw reversal prevention device has a land 13' of the spool 6 having a wide width so that when the port A communicating with the hydraulic motor 2 is closed by the land 13' of the spool 6.