JPH0320103Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a backflow prevention device for an injection molding machine used for plastic injection molding.

(Prior Art) A conventional backflow prevention device for an injection molding machine will be explained based on FIG.

A nozzle 2 is attached to the tip of the cylinder 1, a screw 3' is housed inside the cylinder 1 so as to be movable back and forth and rotatable, and a heater 4' is attached to the outer periphery of the screw 3'. A screw head 5' consisting of a screw head main body 5'a and a shaft portion 5'b is attached to the threaded portion at the tip of the screw 3', and a male screw threaded at the rear end of the shaft portion 5'b. A pusher 6' is fitted into a shaft portion 5'b between the tip end surface of the screw 3' and the annular side surface of the screw head body 5'a. The pusher 6' has a cylindrical shape, and an outwardly inclined surface 6'a is formed on the outer periphery of the rear end. The backflow prevention ring 7' also connects the cylinder 1 with a gap that can form an annular molten resin flow path A between it and the pusher 6'.
It is installed so that it can move back and forth inside. The rear end of the backflow prevention ring 7' is formed with an inwardly inclined surface 7'a that can match the outwardly inclined surface 6'a of the pusher. Therefore, the backflow prevention ring 7' retreats,
When the inward and outward inclined surfaces 7'a and 6'a come into close contact, the molten resin flow path A is blocked.

Next, the operation of such a backflow prevention device will be explained.

The screw 3' inside the cylinder 1 is rotated by a rotating machine (not shown), and the resin is transferred to the tip of the screw 3' while being heated, melted, and kneaded. In this case, the molten resin passes through the molten resin flow path A and accumulates in the front surface of the screw head body 5'a, that is, in the internal space B of the nozzle 2. When the pressure of the molten resin stored here increases, this pressure causes the screw 3' to move backward while rotating, and when the amount of backward movement reaches a set value, the backward movement is stopped by operating a limit switch or the like. , complete the resin plasticization and metering process. Next, the injection process begins, and when the screw 3' is advanced by the action of a hydraulic cylinder or the like attached to the rear thereof,
The resin stored in the internal space B of the nozzle is injected to the outside from the through hole 2a of the nozzle 2 and attempts to flow back toward the rear of the screw 3' via the molten resin flow path A. However, at this time, the ring 7' retreats due to resin pressure on the front end surface 7'b of the backflow prevention ring 7', and both the inward and outward inclined surfaces 7'a and
6'a are in close contact with each other, the molten resin flow path A is blocked, and backflow of the molten resin is prevented.

(Problems to be Solved by the Invention) Incidentally, injection molding may be performed by rapidly changing the injection speed of the resin from high speed to low speed during the injection process.

In such a case, when the speed of the screw 3' decreases, the backflow prevention ring 7' moves toward the screw head body 5'a due to inertia, and until then they come into contact with each other to prevent the resin from flowing back. There was a problem that the two inward and outward inclined surfaces 7'a and 6'a, which had been attached to each other, were separated. For this reason, until both inward and outward inclined surfaces 7'a and 6'a come into contact again and block the molten resin flow path A, a backflow of resin occurs, and this backflow amount is not constant. Additionally, the amount of molten resin filled into the mold cavity during the injection process fluctuated, making the quality of the molded product unstable.

(Means for Solving the Problems) In order to solve the above problems, the present invention mechanically fixes the backflow prevention ring to the screw during the injection process, and during the plasticizing process when the screw is rotating. This is a backflow prevention device for an injection molding machine that keeps a backflow prevention ring in a free state relative to the screw to open a molten resin flow path, and its configuration is as follows.

A short cylindrical part and a rear part that are integrally or integrally provided on the screw head side of the screw of an injection molding machine and have a guide groove formed of an inclined groove in the same direction as the flight of the screw and a circumferential groove connected to the inclined groove. A pusher having an outwardly inclined surface formed at an end thereof; and a pusher movably fitted onto the shaft of the screw head between the pusher and the screw head body; A molten resin flow path is formed on the inner peripheral surface thereof, and an internal thread running in the same direction as the flight of the screw and a pin that protrudes inward and engages with the guide groove of the presser metal are provided on the inner peripheral surface, and an inward facing screw provided on the rear end surface is provided. A backflow prevention device for an injection molding machine includes a backflow prevention ring whose sloped surface abuts the outward sloped surface of the presser metal and blocks the resin flow path.

(Function) In the plasticizing and metering processes where the screw of the injection molding machine is rotating, the backflow prevention device ring
The molten resin that is guided by the pin that engages with the guide groove of the pusher moves toward the screw head main body, and is sent by the screw into an annular molten resin flow formed between the screw head and the screw head shaft. It collects in the front part of the screw head body through the passage. In this case, the pin is located in an inclined groove.

In the injection process, the backflow prevention ring is rotated and retreated in the direction of rotation of the screw during metering due to the resin pressure applied to the front surface of the backflow prevention ring and the front surface of the internal thread, and the pin is inserted into the inclined groove. and into a circumferential groove connected thereto. At this time, the inwardly inclined surface provided on the rear end surface of the backflow prevention ring comes into contact with the outwardly inclined surface of the pusher to block the resin flow path and prevent the resin from flowing back.

In this manner, during the injection process, the anti-reflux ring is mechanically secured to the screw by the pin located in the circumferential groove.

(Example) An example of the backflow prevention device for an injection molding machine according to the present invention will be described based on FIGS. 1 and 2.

1 is a cylinder of an injection molding machine, and 2 is a nozzle. 3 is a screw having a flight 3a, and arrow C indicates the direction of rotation of the screw 3.
Reference numeral 5 denotes a screw head, and the screw head main body 5 is provided with a plurality of grooves 5a' as resin flow paths.
a and a shaft portion 5b. The shaft portion 5b is usually fixed to the tip of the screw 3 by screwing.
Reference numeral 6 denotes a presser metal, which is provided integrally or integrally with the screw head 3 at a distance from the screw head main body 5a, and is composed of an outwardly inclined surface 6 and a short cylindrical portion 6b connected thereto. The short cylindrical portion 6b is provided with a guide groove 6c, which is opened at the end face and consists of an inclined groove 6c' inclined in the same direction as the flight 3a of the screw, and a circumferential groove 6c'' connected thereto. Reference numeral 7 denotes a backflow prevention ring, which is movably fitted onto the screw head shaft 5b between the screw head main body 5a and the pusher 6, and prevents molten resin from flowing between the screw head main body 5a and the pusher 6. A flow path A is formed on the rear end surface of the backflow prevention ring 7.
An inwardly inclined surface 7a is provided which contacts the outwardly inclined surface 6a of the presser metal and blocks the molten resin flow path A, and the inner peripheral surface is provided with an internal thread 7b in the same direction as the flight 3a of the screw. A pin 7d that protrudes and engages with the guide groove 6c is provided. The relationship between the pin 7d and the guide groove 6c will be explained. During the plasticizing/metering process in which the screw 3 is rotating in the direction of arrow C, the backflow prevention ring 7 is rotated in the direction opposite to arrow C by the resin pressure from the back and moves toward the screw head main body 5a. , the pin 7d is located in the inclined groove 6c', is located in the circumferential groove 6'' during the injection process, and is rounded to a groove width that does not interfere with the contact between the inward and outward inclined surfaces 7a, 6a. A circumferential groove 6c' is formed.

Next, the effect will be explained.

In the plasticizing/metering process, the molten resin reaches the molten resin flow path A by the rotation of the screw 3 in the same way as in the conventional example, and flows into the groove 5a' of the screw head and the tip surface of the backflow prevention ring 7. The liquid is sent to the internal space B of the nozzle 2 through the gap between the screw head 5a and the screw head 5a. Even when the tip end surface of the backflow prevention ring 7 is in contact with the annular surface of the screw head 5a, the pin 7d remains within the inclined groove 6c'.

During the injection process, when the screw 3 is advanced in the same manner as in the conventional example, the resin accumulated in the internal space B of the nozzle 2 is transferred to the through hole 2 of the nozzle 2.
The molten resin is injected from a into the cavity of a mold (not shown) and tries to flow back toward the rear of the screw 3 through the molten resin flow path A, and the backflow prevention ring 7 is pushed toward the pusher 6 and the internal thread The screw 3 is rotated in the same direction as the rotation direction arrow C by the resin pressure acting on the pin 7b, and the pin 7d is guided by the inclined groove 6c' and enters the circumferential groove 6c''.At this time, the backflow prevention ring The inwardly inclined surface 7a contacts the outwardly inclined surface 6a of the pusher to prevent the molten resin from flowing back.

When the screw 3 moves back and forth, the backflow prevention ring 7 is restrained by the screw 3 by the pin 7d and moves back and forth, and when the screw 3 starts rotating in the direction of arrow C in the plasticizing and metering process. ,
The pin 7d moves to the inclined groove 6c', and the inward inclined surface 7a and the outward inclined surface 6a are separated, and the molten resin is sent to the molten resin flow path A.

In this way, the pin 7d reciprocates within the guide groove 6c during the plasticizing/metering process and the injection process, so the molten resin does not accumulate and solidify within the guide groove 6. .

(Effects of the Invention) As understood from the above explanation, the backflow prevention device for an injection molding machine according to the present invention has the following effects.

(b) During the injection process, the backflow prevention ring is locked to the screw, so even if the injection molding speed is changed, there is no substantial movement relative to the pusher, ensuring a stable injection amount. This made it possible to perform precise injection molding control.

(b) During the injection process, the inner thread of the backflow prevention ring is also subjected to resin pressure, so the movement of the backflow prevention ring is quick and the time required for it to come into contact with the pusher metal, the so-called sealing time, is shortened.

(c) Furthermore, in the plasticizing/metering process, the inner thread gave the resin a kneading effect similar to that of a screw, and had the secondary effect of improving the degree of kneading.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of the backflow prevention device for an injection molding machine according to the present invention, FIG. 2 is a sectional view of the main part, and FIG. 3 is a sectional view of a conventional backflow prevention device for an injection molding machine. It is a diagram. 1... Cylinder, 2... Nozzle, 3... Screw, 3a... Flight, 5... Screw head, 5a... Screw head body, 5b... Shaft, 6... Push metal, 6a... Outside Direction inclined surface, 6b...
...Short tube part, 6c...groove, 6c'...slanted groove, 6c'...
...Circumferential groove, 7...Backflow prevention ring, 7a...
Inward slope, 7b... (same direction as flight)
Internal thread, 7d... pin, A... molten resin flow path.

Claims (1)

[Scope of utility model registration request] A short cylindrical part and a rear part are provided integrally or integrally on the screw head side of the screw of an injection molding machine and form a guide groove consisting of an inclined groove in the same direction as the flight of the screw and a circumferential groove connected to the inclined groove. A pusher having an outwardly inclined surface formed at an end thereof; and a pusher movably fitted onto the shaft of the screw head between the pusher and the screw head body; A molten resin flow path is formed on the inner peripheral surface thereof, and an internal thread is provided on the inner circumferential surface thereof in the same direction as the flight of the screw, and a pin that protrudes inward and engages with the guide groove of the pusher metal. A backflow prevention device for an injection molding machine, comprising a backflow prevention ring whose sloped surface abuts the outward sloped surface of the presser metal and blocks the resin flow path.