JPH0771813B2 - Backflow prevention device for injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a backflow prevention device provided at the tip of a screw of an in-line screw injection molding machine.

(Prior Art) A conventional check valve will be described with reference to FIGS. 2 and 3. The check valve 20 has a small diameter of a screw head 22 fitted on the inner diameter surface of a barrel 25 and attached to the tip of a screw 21. Part 22
A cylindrical shape having an inner diameter surface such that a sufficient gap 23 is formed between a and a predetermined interval between the conical portion 22b of the screw head 22 and the spacer 24 attached to the tip surface of the screw 21. It is only possible to move back and forth in the axial direction. Further, the claw 26 provided at the left front end portion of the check valve 20 in the drawing is engaged with the recess 27 provided in the conical portion 22b of the screw head so that the screw 21 and the check valve 20 rotate together. In addition, a plurality of protrusions 20a are provided on the front end, and when the top surface A of the protrusion 20a abuts on the conical portion 22b of the screw head, the conical portion 22b of the screw head and the plurality of protrusions are formed. A gap 28 sandwiched by the portion 20a is formed, and a gap 23 formed between the screw head small diameter portion 22a and the gap 28, and between the rear end surface B of the check valve 20 and the spacer 24. The gap S formed in the above is connected to form a resin flow passage.

With the above configuration, when the screw 21 rotates during the plasticizing process, the resin material that has been melted and transferred from the right upstream side of the screw 21 in the figure pushes the check valve 20 to the left front side of the figure. As a result of being brought into contact with the conical portion 22b of the screw head, the resin material flows in the resin flow passage as indicated by the arrow a,
It is accumulated in front of the screw head 22. Next, when the predetermined accumulated amount is measured, the plasticizing process ends, and the screw 21 which is in the backward limit to inject the measured resin material advances to the left in the figure, and the check valve 20 turns the screw head.
It will be pushed by the resin accumulated in front of 22,
The space S formed by the backward movement of the rear end surface B and the surface of the spacer 24
And the resin passage is closed.

(Problems to be solved by the invention) However, in this conventional device, the operation of closing the gap S of the check valve 20 at the time of injection is extremely unstable.
It depends on the frictional resistance with the inner diameter surface or the viscosity of the resin. Especially when the gap S is large, the closing operation is unstable. Therefore, the unstable operation of the check valve 20 causes variations in the amount of resin to be injected, often adversely affecting the quality of the molded product.

The present invention eliminates the backflow prevention valve 20 which becomes an unstable element of the above-mentioned resin flow path closing operation, and can perform the backflow prevention operation accurately and surely and instantly even if the clearance S between the screw head and the flow path of the screw is large. An object of the present invention is to provide a backflow prevention device for an injection molding machine.

[Structure of Invention]

(Means for Solving the Problems) In order to achieve the above object, in the present invention, a barrel provided with a heater for heating resin and a screw having a screw head attached at its tip are internally inserted therein. In a backflow prevention device provided on the screw of an in-line screw type injection resin machine, a resin flow hole having an outer diameter approximately equal to the inner diameter of the barrel is formed in the longitudinal direction, and a forward / backward movement is made by a predetermined distance with respect to the screw shaft tip surface. And a connecting member that is fitted into a screw through hole formed in the screw axial direction and has one end locked to the screw head and the other end loosely fitted in a through hole formed at a right angle to the screw through hole. A backflow prevention device for an injection molding machine, which includes a shaft attached to a shaft and a drive device that moves the shaft back and forth through the connecting member to move the screw head forward and backward to open and close the predetermined distance. Provide the storage.

(Operation) In the device of the present invention, the shaft engaged with the screw head for opening and closing the resin flow path between the screw head and the screw end is fitted into the screw to force the shaft. Since the resin flow passage is opened and closed by opening and closing the resin flow passage, the gap S between the screw head and the screw flow passage can be increased to form a large resin flow passage to the front portion of the screw head during measurement. In the injection state, the resin flow path can be closed instantly and accurately.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a screw, which has a through hole 2 having a step in the central axis direction and a through hole 3 provided at a right angle to the through hole, and a rear end on the side opposite to the screw head is connected to a connecting plate 4. It is connected to the attached screw rotation drive motor 5.

Reference numeral 6 is a barrel having a nozzle hole 7 at the left end in the figure, and is provided with an injection cylinder 9 for inserting the screw 1 and the screw head 8 rotatably and axially forward and backward, and externally moving the screw 1 forward and backward. There is. The screw head 8 has a small-diameter shaft portion 10 inserted into a hole 11 at the front end of the screw so as to be able to move forward and backward. It has a shape and has a plurality of through holes 12 that serve as a plurality of resin flow paths in the axial direction.

A shaft 13 is fitted into the through hole 2, one end of which is locked to the screw head small-diameter shaft portion 10, and the other end of which has a space for advancing and retracting with respect to the through hole 2 formed at right angles to the through hole 2. It is connected to the holding connecting member 14 in a T-shape. Both ends of the connecting member 14 are attached to the connecting plate 4 and are connected to the tip of a rod 16 of a cylinder 15. When the rod 16 advances and retracts, the screw head 8 advances and retracts via the connecting member 14 and the shaft 13, and resin of the screw head is used. The resin flow path b is opened and closed by bringing the flow hole 12 and the front end C surface of the screw 1 into contact with each other. When the connecting member 14 and the tip of the rod 16 of the cylinder 15 are connected, the screw 1 is mounted in a fitted state in which the rotation of the screw 1 cannot be prevented.

Next, the operation will be described. When the screw 1 is in the state shown in FIG.
When the screw rotates, the resin will move to the screw head 8 and the screw front end C.
It begins to be stored in the chamber on the nozzle hole 7 side in front of the screw head 8 via the resin flow hole 12 through the gap E between the.
As the resin is stored, the pressure causes the screw 1
Retreats to the right in the figure, retracts the connecting plate 4 at the rear of the screw 1, and retracts the piston rod 17 of the injection cylinder 9 attached to the connecting plate 4 to the right.

When a predetermined metering operation is completed and pressure oil is supplied to the rod side of the cylinder 15 to move the rod 16 to the right immediately before starting the injection, the screw head 8 moves to the right in the figure via the connecting member 14 and the shaft 13. Immediately retreating, contacting the front surface C of the screw 1 and closing the resin flow hole 12 of the screw head, the resin in the flow path b is trapped and the reverse flow becomes impossible, and the reverse flow of the resin can be completely prevented.

Further, if the parallel length portion of the large diameter portion D of the screw head 8 is configured to have about 1/2 of the inner diameter of the barrel 6, backflow from the outer peripheral portion of the screw head 8 is also restricted, and the backflow prevention effect is further improved. You can

〔The invention's effect〕

According to the present invention, the check valve is not mechanically used but the screw head is mechanically advanced and retracted in the screw direction to perform the check valve operation, so that the check valve operation can be performed instantaneously and accurately and reliably. As a result, the amount of resin injected is uniform and stable molded products can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of an apparatus showing an embodiment of the present invention, FIG. 2 is a diagram showing a relationship between a conventional screw head and a check valve, and FIG. 3 is an axial sectional view of FIG. 1 ... screw, 2 ... through hole, 6 ... barrel, 8 ...
Screw head, 12 …… Resin flow hole, 13 …… Shaft, 15 ……
Cylinder.

Claims (1)

[Claims] 1. A barrel provided with a heater for heating resin,
In a backflow prevention device provided in the screw of an in-line screw type injection molding machine in which a screw with a screw head attached at the tip is inserted, a resin flow hole is provided in the longitudinal direction with an outer diameter approximately equal to the barrel inner diameter. The screw head is formed so as to advance and retreat a predetermined distance with respect to the tip end surface of the screw shaft, and is inserted into a screw through hole formed in the screw axial direction so that one end is locked to the screw head and the other end is penetrated by the screw. A shaft attached to a connecting member loosely fitted in a through hole formed in a direction perpendicular to the hole; and a drive device for moving the shaft back and forth through the connecting member to move a screw head forward and backward to open and close the predetermined distance. Backflow prevention device for injection molding machines.