JPH0763996B2 - Backflow prevention device for injection molding machine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backflow prevention device for an injection molding machine, and more particularly, when the molten resin is plasticized and metered, it is backfilled by a resin pressure during injection and filling. Backflow prevention of the injection molding machine that prevents the backflow of the molten resin from the mold by narrowing or closing the resin flow passage with a slight momentum of the valve body by combining the resin with the axial movement of the valve body and the rotational movement. Regarding the device.

[Prior Art] Generally, when a molten resin flows into a mold from a barrel by a screw using an injection molding machine, a part of the molten resin flows backward to the screw side so that the measured molten resin can efficiently flow in. It is configured to prevent trying.

Regarding such a conventional check valve, FIG. 8 and FIG.
To explain with reference to the drawings, the check valve 14 is inserted into the inner diameter surface of the barrel 24, and a sufficient gap 20 is formed between the small diameter portion 18a of the screw head 18 attached to the tip of the screw 16. It has a cylindrical shape with an inner diameter surface, and can advance and retreat in the axial direction by a predetermined distance between a conical portion 18a of the screw head 18 and a spacer 22 attached to the tip surface of the screw 16. Further, the claws provided at the left and right front end portions of the check valve 14 in the figure
26 is engaged with a concave portion 28 provided in a conical portion 18b of the screw head so that the screw 16 and the check valve 14 rotate together, and a plurality of protrusions 14a are provided at the front end, When the top surface Q of the portion 14a abuts on the conical portion 18b of the screw head, a void portion 30 is formed which is sandwiched between the conical portion 18b of the screw head and the plurality of protrusions 14a. A gap 20 formed between the small-diameter portion 18a and the gap portion 30, and a gap S formed between the rear end surface R of the check valve 14 and the spacer 22 communicate with each other to form a resin flow passage. There is.

With the above configuration, when the screw 16 rotates during the plasticizing process, the resin material that has been melted and transferred from the right side upstream of the screw 16 in the figure pushes the check valve 14 to the left front side in the figure. As a result of being brought into contact with the conical portion 18b 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 18. Next, when the predetermined accumulated amount is measured, the plasticizing process ends, and the screw 16 which is in the backward limit for injecting the measured resin material moves forward to the left in the figure, and the check valve 14 turns the screw head.
It will be pushed by the resin accumulated in front of 18,
The gap S formed by the backward movement of the rear end surface R and the surface of the spacer 22
And the resin flow passage is closed.

[Problems to be Solved by the Invention]

However, in this conventional device, the operation of closing the clearance S of the check valve 14 at the time of injection is very unstable and takes time, and it depends on the frictional resistance with the inner diameter surface of the barrel 24 or the viscosity of the resin, and especially when the clearance S is large. The closing movement is more unstable. Therefore, the unstable operation of the check valve 14 causes variations in the amount of resin to be injected, which often adversely affects the quality of the molded product.

Therefore, an object of the present invention is to restrict or block the resin flow passage by a combination of the axial operation and the rotational operation of the valve body due to the resin pressure at the time of injection into the valve chamber provided between the screw tip and the nozzle. By doing so, it is an object of the present invention to provide a backflow prevention device for an injection molding machine in which the backflow prevention operation by the valve can be performed accurately, surely, and quickly.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the backflow prevention device of the injection molding machine according to the present invention, when the molten resin is plasticized by the rotation of the screw and is injected and filled into the mold after weighing. In the backflow prevention device of the injection molding machine that closes the reverse flow of the valve by the axial or circumferential movement of the valve, a valve chamber is formed between the screw tip and the nozzle, and the shaft is fixed to the screw tip in this valve chamber. Then, a plurality of groove portions are provided on the outer circumference of the shaft body at a predetermined interval, and a valve body made of an annular member and having a plurality of groove portions engraved at a predetermined distance is provided on the inner circumference of the shaft body. It is characterized in that it is fitted with the shaft body so as to be rotatable and forward and backward, and the groove portions are throttled or closed by the rotational movement of the valve body by the resin pressure at the time of injection.

In this case, a gap is formed in the circumferential direction in the engaging portion between the valve body and the shaft body, and the valve body is rotated within the range of this gap to communicate or close the groove portion of the shaft body and the groove portion of the valve body, respectively. It is preferable to configure so that

Further, it is preferable that the resin contact surface on the exit side end surface of the annular member is configured to be an inclined surface.

[Action]

According to the backflow prevention device of the injection molding machine according to the present invention, after the molten resin is plasticized and measured by the rotation of the screw, the valve is rotationally operated by the resin pressure at the time of injection filling into the mold, thereby Restriction or blockage of the resin flow passage can be effectively achieved.

〔Example〕

Next, a backflow prevention device for an injection molding machine according to the present invention will be described in detail below with reference to the accompanying drawings.

For convenience of description, the same parts as those of the conventional structure shown in FIGS. 8 and 9 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 is a sectional view showing an essential part of an embodiment of a backflow prevention device for an injection molding machine according to the present invention, and is designated by reference numeral 32.
Indicates the nozzle provided at the tip of barrel 24.
A through hole 32a for injecting a molten resin material is formed on the central axis of 32.

At the tip of the screw 16 fitted into the inner diameter surface of the barrel 24, a screw head 18, which is a shaft, is attached so that the conical portion 18b faces the through hole 32a of the nozzle 32. Further, a sufficient space is formed between the small diameter portion 18a of the screw head 18 and the inner diameter surface of the barrel 24, whereby a cylindrical valve body 42 is formed.

Further, in the valve chamber 40, the small diameter portion 18a of the screw head 18 attached to the tip of the screw 16 is provided with groove portions 18c at predetermined intervals in the axial direction, and an engaging portion is provided at a step portion with the small diameter portion. A pair of recesses 28 are cut.

The small-diameter portion 18a is provided with a groove portion 34a axially formed on the inner peripheral surface thereof with the same gap as the groove portion 18c, and a pair of claws 38 engageable with the pair of concave portions 28 at the injection end portion so as to project. A valve body 42 made of an annular member is fitted so as to be rotatable and movable back and forth.

Further, the outer circumference of the valve body 42 is slidably fitted on the inner circumference surface of the barrel 24 as well, thereby basically forming a backflow prevention device.

The valve body 42 can move back and forth within the range of the gap S in the axial direction between the stepped portion of the screw head 18 and the end portion G of the spacer. In this case, even if the recess 28 of the screw head 18 and the claw 26 of the annular member 34 move until the annular member 34 comes into contact with the spacer 22 side, the engaged state is secured. Further, the top surface Q of the protrusion 36 of the annular member 34 is the screw head.
In the state of being in contact with the stepped portion of 18, the void portion 30 is formed between the plurality of protrusions 36 of the annular member 34 and the stepped portion of the screw head.

Further, as is clear from FIG. 2 and FIG. 3, the small diameter portion 18a of the screw head 18 and the annular member 34 fitted to the small diameter portion 18a are fitted to the fitting portion, respectively, each having an arcuate cross section in the axial direction. The portions 18c and 34a are provided at predetermined intervals in the circumferential direction. The circulation portion 18c on the side of the small diameter portion 18a is formed so as to be shorter than the entire length of the annular member 34, and this groove portion is formed in the annular member 34.
When it is on the front side (exit side), it is completely covered by this annular member. Further, the circulation portion 34a on the side of the annular member 34
Has an opening only on the side of the spacer 22 which is one end thereof, and communicates with the gap S formed between the spacer 22 and the rear end surface R of the annular member 34. Therefore, when the annular member 34 is at the forward end position, that is, when the top surface Q of the protrusion 36 is in contact with the stepped portion of the screw head 18, the gap S side passes through the flow portions 18c and 34a and further the protrusion 36. Through hole of the nozzle 32 through the void 30
A resin flow passage is formed in communication with the 32a side.

In this case, an inclined surface 36a is formed on one side surface that is in the same direction as the plurality of protrusions 36 of the annular member 34, and the pressure at the time of injecting the resin material is the inclined surface after the plasticizing step described later.
It acts on 36a to rotate the annular member 34 (see FIG. 4).

Before the injection process is started, the claw 38 of the annular member 34 is engaged with the recess 28, and in this case, a gap δ is formed in the circumferential direction between the recess 28 and the claw 38 (see FIG. 3). The resin flow passages 18c and 34a are in communication with each other.

In this case, the groove cross-sectional shape of the flow passage is not limited to the circular arc groove, and may be any positional relationship that allows communication or interruption when the annular member rotates by δ in the circumferential direction.

Next, the operation according to the present invention will be described below. In FIG. 1, the resin plasticized by the rotation of the screw 16 flows into the flow passage 34a of the annular member 34 from the gap S, and then flows into the flow passage 18c communicating with each other along the arrow a. Further, the resin flows through the void portion 30 (see FIG. 4) communicating with the flow passage 18c and is accumulated in the nozzle through hole 32a in front of the screw head 18.

As shown in FIGS. 2 and 3, the screw head
When 18 rotates together with the screw 16 in the direction of arrow D, one side surface of the claw 38 of the annular member 34 abuts on one side surface of the recess 28 of the screw head 18, and the claw 38 has a play in the circumferential direction δ with respect to the recess 28. They are engaged with each other, and in this case, the flow passages 18c and 34a are in communication with each other.

Next, when the injection process is started at the end of the plasticizing process, the injection resin flows backward and flows in the direction of arrow b, and the resin pressure P shown in FIG.
Acts on the inclined surface of the protrusion 36 of the cylindrical member 34.

This resin pressure P rotates the annular member 34 in the circumferential direction by the component force Pr in the circumferential direction applied by the inclined surface 36a, and moves the annular member 34 in the direction of the resultant force F (see FIG. 4). ).

Therefore, the force of the resin pressure causes the cylindrical member 34 to δ in the circumferential direction.
Rotate only (in the direction opposite to the arrow D), and each of the flow passages 18c, 34
After a is squeezed, each is in a shielded state.

The rotation of the annular member 34 causes the resin flow resistance from the screw head 18 side to the screw 16 side to increase as the flow passage portion between the grooves 18c and 34a is sandwiched.
The closing speed of is increased at an accelerating rate, and the valve body is closed in a short time.

In this case, the respective flow passages 18c, 34a are finally closed by the rotating force of the annular member due to the angle of the inclined surface, the resin pressure, the flow rate, etc. As shown in the figure, the rear end surface R of the annular member 34 and the end surface G of the spacer 22 are blocked.

〔The invention's effect〕

As described above, the backflow prevention device for the injection molding machine according to the present invention is provided with the valve chamber between the screw tip and the nozzle, and the valve body which is rotatable by the action of the resin pressure is provided in the valve chamber. The resin flow passage can be configured to be throttled or closed by a combination of the axial movement and the rotational movement of, so that the injection resin amount can be accurately controlled, so that the injection accuracy is improved and a precise molded product can be obtained. it can.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part showing an embodiment of the backflow prevention device according to the present invention, FIG. 2 is a sectional view taken along the line BB in FIG. 1, and FIG. 3 is a view taken in the direction of arrow Z in FIG. FIG. 4 is an external view of an essential part showing an embodiment of the backflow prevention device according to the present invention, FIG. 5 is a sectional view taken along line CC of FIG. 7, FIG. 6 is a view taken in the direction of arrow Y of FIG. FIG. 8 is a cross-sectional view of an essential part showing a state when the backflow prevention device is closed, FIG. 8 is an external view showing a conventional backflow prevention device, and FIG. 9 is a cross-sectional view of an essential part of the conventional backflow prevention device. 14 …… Check valve, 14a …… Projection 16 …… Screw, 18 …… Screw head 18a …… Small diameter part, 18b …… Cone shaped part 18c …… Flow passage, 20 …… Gap 22 …… Spacer, 24 ...... Barrel 26 …… Claw, 28 …… Concave 30 …… Gap, 32 …… Nozzle 32a …… Through hole, 34 …… Annular member 34a …… Flow passage, 36 …… Projection 36a …… Sloping surface, 38 …… Claw 40 …… Valve chamber, 42 …… Valve F… Consequent force, G …… Spacer end face P …… Resin pressure, Pr …… Circumferential force Q …… Projection top surface, R …… Rear end face S …… Gap

Claims (3)

[Claims] 1. A backflow prevention device for an injection molding machine, wherein a molten resin is plasticized by rotation of a screw, and a backflow at the time of injection filling into a mold after metering is blocked by axial or circumferential movement of a valve. A valve chamber is formed between the tip and the nozzle, a shaft is fixed to the screw tip in the valve chamber, a plurality of groove portions are provided at predetermined intervals on the outer circumference of the shaft, and the groove is made of an annular member and at predetermined intervals on the inner circumference. By providing a valve body with a plurality of grooves engraved with, the valve body engages with a part of the shaft body and is fitted in the shaft body so as to be able to rotate and advance and retreat, and the valve body rotates due to resin pressure during injection. A backflow prevention device for an injection molding machine, wherein each of the groove portions is narrowed or closed. 2. A gap is formed in the circumferential direction in the engagement portion between the valve body and the shaft body, and the valve body is rotated within the range of the gap so that the groove portion of the shaft body and the groove portion of the valve body communicate with each other. Alternatively, the backflow prevention device for an injection molding machine according to claim 1, which is configured to be closed or squeezed. 3. The backflow prevention device for an injection molding machine according to claim 1, wherein the resin contact surface of the injection side end surface of the annular member is an inclined surface.