JPH04119812A - Back flow preventive device for screw - Google Patents

Abstract

PURPOSE:To move a nonreturn ring in the backward direction by forming a tapered surface for converting relative rotation between a screw head and the nonreturn ring into the axial movement of the nonreturn ring. CONSTITUTION:A pawl is projected and formed forward to a nonreturn ring 12, and the pawl 15 is housed in the large diametral section of a screw head 11 while a groove 17 having width enabling relative rotation between the screw head and the nonreturn ring is formed. A tapered surface 16 being slid and contacted with one part of the screw head and backward shifting the nonreturn ring by turning the screw heed in the direction opposite to the time of metering is shaped to the pawl. Accordingly, the nonreturn ring is pushed forward by the pressure of a resin during a time when the screw head is revolved and metering is conducted, but one part of the screw head is moved along the tapered surface when a screw 4 is rotated in the opposite direction before metering is completed and injection is started, thus backward shifting the nonreturn ring 12, then abutting the nonreturn ring against a seal ring 3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a screw backflow prevention device.

(Prior art) Conventionally, a molding material heated and fluidized in a heating cylinder is injected into a mold under high pressure, cooled and solidified or hardened therein, and then the mold is opened to take out the molded product. In such an injection molding machine, a screw is disposed in a heating cylinder so as to be rotatable and movable back and forth, and molten resin is injected by the screw.

Therefore, a screw head for pushing out the molten resin is provided at the tip of the screw, and is attached to the screw with an internal lock.

FIG. 3 is a sectional view of a screw head portion of a conventional injection molding machine.

In the figure, 1 is a screw head, which has a large diameter part 1a and a small diameter part 1b. Reference numeral 2 denotes a check ring for preventing backflow of resin, and is disposed so as to surround the small diameter portion 1b. 3 is a seal ring that contacts when the check ring 2 is retreated; 4 is a screw; 5 is a heating cylinder; and 6 is a molten resin.

When the screw 4 moves forward and fills the resin into the mold, the resin 6 is then melted, plasticized, and stored at the tip of the screw head 1, ie, metered, prior to the next shot. In this measurement, the screw 4 is driven by a drive system (not shown) and retreats, and at this time, the resin 6 dropped and supplied from the hopper, that is, the material supply port, is transferred to the screw 4.
As it rotates, it moves forward in the groove 4a and melts in the heating cylinder 5, and is stored in front of the screw 4.

The pressure of the resin 6 in the heating cylinder 5 that occurs as it melts becomes a reaction force against the screw 4, and this reaction force causes the screw 4 to
is now moving backwards.

The resin 6 thus stored in front of the screw 4 is then injected into the mold from a nozzle (not shown) by pushing the screw 4 forward by the drive system.

Here, a part of the resin 6 is transferred to the screw 4 due to the reaction force of the injection force applied when being injected into the mold.
It flows backward through the groove 4a.

In order to prevent this, a check ring 2 is provided at the front end of the screw 4. In order to prevent the check ring 2 from coming off the screw 4, a screw head 1 separate from the screw 4 is formed, and the screw 4 has a female thread 4b, and the rear end of the screw head 1 has a male thread. A screw 1a is formed and both are screwed together. The outer diameter of the screw head 1 is made larger than the inner diameter of the check ring 2 to prevent the check ring 2 from coming off.

(Problem to be Solved by the Invention) However, in the screw backflow prevention device configured as described above, as the screw 4 moves to the left in the figure at the start of injection, the resin moves relatively to the right. Since the check ring 2 is closed by the viscous friction of the resin at this time, the timing differs depending on the state of the resin and the like.

Therefore, the amount of resin flowing backward changes, causing variations in the filling amount, making it impossible to produce a homogeneous molded product.

The present invention solves the problems of the conventional screw backflow prevention device described above, and provides a screw backflow prevention device that can reliably close the check ring before injection and reduce variations in the amount of resin filled. The purpose is to provide.

(Means for Solving the Problems) To solve the problem, the present invention provides a screw, a seal ring fixed to the front end of the screw, a large diameter portion and a small diameter portion formed to protrude further forward from the seal ring, and a large diameter portion and a small diameter portion. and a check ring that surrounds the small diameter portion and is movable back and forth, and that comes into contact with the seal ring and blocks the flow of resin when it moves rearward during injection, etc. are doing.

The check ring has a claw protruding forward, and the large diameter portion of the screw head accommodates the claw and allows relative rotation between the screw head and the check ring. A groove is formed having a width of .

Furthermore, the claw is formed with a tapered surface that slides into contact with a portion of the screw head and moves the check ring backward by rotating the screw head in a direction opposite to that during metering. There is.

(Function) According to the present invention, as described above, the screw includes a screw, a seal ring fixed to the front end of the screw, and a screw that protrudes further forward from the seal ring and includes a large diameter portion and a small diameter portion. It has a head, and a check ring that surrounds the small diameter portion and is movable back and forth, and that comes into contact with the seal ring and blocks the flow of resin when it moves rearward during injection or the like. .

Therefore, during injection, the check ring moves back and comes into contact with the seal ring to prevent the resin from moving backward. During metering, the check ring moves forward and hits the screw head, and the resin supplied between the screw and the heating cylinder is melted and moved forward. Then, it passes through the gap between the seal ring and check ring and is sent to the front of the screw rad.

Further, the check ring has a claw that projects forward, and the large diameter portion of the screw head accommodates the mold and allows relative rotation between the screw head and the check ring. a groove is formed in the mold having a width that is in sliding contact with a portion of the screw head;
By rotating the screw head in a direction opposite to that during metering, a tapered surface is formed that moves the check ring backward.

Therefore, while the screw is rotating and metering, the check ring is pushed forward by the pressure of the resin, but if the screw is rotated in the opposite direction after metering is complete and before injection begins, A portion of the screw head moves along the tapered surface, and as a result, the check ring moves rearward and comes into contact with the sole ring.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a state diagram of the screw backflow prevention device of the present invention during metering, and FIG. 2 is a state diagram of the screw backflow prevention device of the present invention immediately before injection.

In the figure, 11 is a screw head, 12 is a check ring for preventing backflow of resin, 3 is a sole ring that comes into contact when the check ring 12 retreats, and 4 is a screw.

The check ring 2 has a plurality of claws 15 extending forward in the circumferential direction, one rising portion 15a of the master mold 15 extends in the axial direction, and the other rising portion 15b has a tapered surface 16. It is formed.

On the other hand, on the surface of the large diameter portion 11a of the screw head 11 facing the check ring 12, a plurality of grooves 17 are formed in the circumferential direction at positions corresponding to the molds 15. There is.

The groove 17 is wider than the mold 15, and allows the screw head II and check ring 2 to rotate relative to each other. Note that 19 is a recess formed in a portion other than the portion where the pawl 15 is formed, and forms a resin flow path when the check ring 12 and the large diameter portion 11a of the screw head 11 come into contact.

In the screw backflow prevention device configured as described above, when the screw 4 moves backward while rotating in the direction of arrow A during metering, the rising portion 15a on the side surface of the groove 17 comes into contact. At this time, since the screw 4 retreats, the check ring 12 moves toward the large diameter portion 11a and comes into contact with the screw head 11.

The melted resin sent around the screw 4 during measurement is
It passes through the gap between the seal ring 3 and the check ring 12, passes inside the check ring 12, and passes through the recess 19 to the front of the screw Rad II.

After metering is completed, the screw 4 is temporarily stopped just before injection, and then the screw 4 is rotated in reverse at a low speed.

At this time, the screw 4 and the check ring 12 rotate relative to each other and come into contact with the side surface of the groove 17 of the screw head 11 and the rising portion 15b of the mold 15.

At this time, the corner 21 of the groove 17 and the tapered surface 16 come into contact. As the relative rotation between the screw 4 and the check ring 12 progresses, the corner 21 moves along the tapered surface 16, and as a result, the check ring I2 moves in the direction of arrow C.

In this way, the check ring 2 is brought into contact with the seal ring 3, sealing is established between the two, and injection is started in this state, so that variations in the amount of filling are reduced.

Note that the present invention is not limited to the above embodiments,
Various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

(Effects of the Invention) As described above in detail, according to the present invention, the check ring has a claw protruding forward, and the large diameter portion of the screw head accommodates the mold, and the screw A groove having a width that allows relative rotation between the head and the check ring is formed, and the upper hoist is in sliding contact with a portion of the screw head to provide a groove between the screw head and the check ring. Since it forms a tapered surface that converts the relative rotation of A portion moves, thereby allowing the check ring to move rearwardly.

[Brief explanation of the drawing]

Fig. 1 is a state diagram of the screw backflow prevention device of the present invention during metering, Fig. 2 is a state diagram of the screw backflow prevention device of the present invention immediately before injection, and Fig. 3 is a screw head of a conventional injection molding machine. FIG. 3... Seal ring, 4... Screw, 11...
Screw head, lla...Large diameter part, 12...Check ring, 15...Claw, 16...Tapered surface, 17...
-Groove, 21...corner. Patent applicant: Sumitomo Heavy Industries, Ltd. Sub-agent Patent attorney: Makoto Kawagoi (2 others) Figure ■ Figure 5b

Claims (1)

[Claims] (a) a screw; (b) a seal ring fixed to the front end of the screw; (c) a seal ring that protrudes further forward from the seal ring and that extends from the large diameter portion and the small diameter portion. (d) a check ring that surrounds the small diameter portion and is movable back and forth and comes into contact with the seal ring when moved rearward to prevent the flow of resin; (e) The check ring has a claw protruding forward; (f) the large diameter portion of the screw head accommodates the claw, and (g) the pawl is in sliding contact with a portion of the screw head to rotate the screw head in a direction opposite to that during metering; A screw backflow prevention device characterized by forming a tapered surface that moves a check ring backward.