JPH07144349A - Back flow preventing valve of screw - Google Patents

Abstract

PURPOSE:To prevent the damage of the valve disc of a back flow preventing valve by forming the protruding part engaged with the recessed part of a screw head to the valve disc and setting the shape of the protruding part so that the ratio of the height of the protruding part and the radius of curvature of the root part of the protruding part to a specific value to reduce the concn. of tensile stress in the circumferential direction of the valve disc. CONSTITUTION:Protruding parts 12 protruding in an axial direction are formed to one end part of the valve disc 11 of a back flow preventing valve 10 at two places and each of them is formed so that the ratio of the height (h) thereof and the radius rhoof curvature of the root part thereof is rho/h>=0.4. The valve disc 11 can be allowed to advance and recede between a spacer 5 and a screw head 3 and, at the time of plasticization, a molten resin passage is opened and, at the time of injection, the valve disc is pushed by the molten resin in front of the head 3 to be brought into contact with the spacer to close the passage and back flow is prevented. At this time, the molten resin in the valve disc 11 is enhanced in pressure by the advance of a screw 2 and tensile stress is generated in the circumferential direction at every injection. Therefore, the conc. stress of the protruding parts due to the tensile stress generated in the root parts of the protruding parts is suppressed to a low value to prevent the damage of the valve disc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a check valve provided on the tip side of a screw of an injection molding machine.

[0002]

2. Description of the Related Art Conventionally, as a check valve of a screw,
The one described in Japanese Patent Publication No. 4-39412 is known.

The check valve 1 is, as shown in FIG.
It has a valve body 4 which is provided between the screw 2 and the screw head 3 and is capable of advancing and retracting in the axial direction. When the screw head 3 moves forward to come into contact with the screw head 3, the molten resin passage is opened and the screw 2 moves backward to move the screw The molten resin passage is closed when it comes into contact with the spacer 5 provided at the tip. A convex portion 7 that engages with the concave portion 6 of the screw head 3 is formed on the screw head 3 side of the valve body 4,
The valve body 4 has a structure capable of rotating together with the screw head 3.

[0004]

However, in the above-described check valve 1, when the convex portion 7 of the valve body 4 is engaged with the concave portion 6 of the screw head 3 to rotate, the rotational torque of the screw 2 is the same as that of the valve body 4. Since it is received by the convex portion 7, the stress concentrates on the convex portion 7. Further, during the injection process, the molten resin filled in the valve body 4 is pushed by the screw 2 to become a resin pressure, and a tensile stress is repeatedly generated in the circumferential direction in the valve body 4 due to the resin pressure. The repeated tensile stress may damage the convex portion 7. Therefore, the convex portion 7 is enlarged or the number is increased to reduce the stress, but the molding is performed with a high injection pressure. In this case, there was a problem that the convex portion 7 was broken in a short period of time.

In view of the above, the present invention has an object to provide a check valve having a valve body which is not damaged.

[0006]

SUMMARY OF THE INVENTION A check valve according to the present invention for solving the above-mentioned problems of the prior art forms a convex portion on a screw head side of a valve body, the convex portion engaging with a plurality of concave portions of the screw head, The shape of this convex portion is such that the ratio of the height h of the convex portion to the radius of curvature ρ of the root of the protrusion is ρ / h ≧ 0.4.

[0007]

In the above check valve, the convex portion of the valve body is engaged with the concave portion of the screw head. Then, the rotational torque of the screw is transmitted to the convex portion and the molten resin filled in the valve body is pressed by the forward movement of the screw, so that tensile stress acts in the circumferential direction in the valve body. However, the stress concentration is reduced to a predetermined value by determining the shape of the convex portion so that the ratio of the height h of the convex portion to the radius of curvature ρ of the root of the convex portion is ρ / h ≧ 0.4. , Prevent damage.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the check valve according to the present invention is shown in FIG.
2 and FIG. 2, the same parts as those of the conventional technique will be omitted.

The valve body 11 of the check valve 10 has a cylindrical shape and is provided with two protrusions 12 projecting in the axial direction at one end in the axial direction at two 180 ° intervals.

In the convex portion 12, the ratio of the height h of the convex portion 12 to the radius of curvature ρ of the root portion of the convex portion 12 is ρ / h ≧.
It is set to 0.4. The valve body 11 is provided between the tip of the screw 2 and the screw head 3.
Further, in the outer peripheral corner of the screw head 3 on the valve body 11 side,
Recesses 13 with which the protrusions 12 of the valve body 11 are engaged are formed at two positions at 180 ° intervals. A spacer 5 is fixed to the tip end side of the screw 2. And the valve body 11
Makes it possible to move back and forth between the spacer 5 and the screw head 3.

Since the check valve 11 is constructed in this way, the molten resin passage is opened during the plasticizing process, and the molten resin flows to the screw head 3 side. Then, during the injection process, the valve element 11 is pushed back by the molten resin accumulated in front of the screw head 3 to move to the spacer 5 side,
The valve body 11 abuts the spacer 5 to close the molten resin passage, preventing the molten resin from flowing back to the screw 2 side. Further, at this time, since the molten resin is filled in the valve body 11, the resin pressure increases as the screw 2 moves forward, and tensile stress is generated in the valve body 11 in the circumferential direction each time it is injected.
At this time, the stress is concentrated on the root of the projection 12, but the height h of the projection 12 and the radius of curvature ρ of the root of the projection 12 are selected so that ρ / h ≧ 0.4. Therefore, the stress at the root is maintained at a lower predetermined value. Since the convex portion 12 of the valve body 11 is engaged with the concave portion 13 of the screw head 3 during resin measurement, the valve body 11 is rotated as the screw 2 is rotated.
Also rotates. The magnitude of stress concentration is expressed by stress concentration coefficient = tensile stress generated at root of convex portion / tensile stress generated at flat portion, and the larger the value, the lower the fatigue strength.

Table 1 shows that 10 kgf is measured in the circumferential direction of the valve body 11.
It shows the result of analyzing the stress concentration factor of the root portion of the convex portion 12 when a tensile stress of / mm ² is generated by using the finite element method. 1
It was found that the stress concentration coefficient becomes constant when ρ / h ≧ 0.4, affected by the height h of 2 and the radius of curvature ρ of the root of the convex portion 12.

[0013]

[Table 1]

[0014]

As described above, the check valve for a screw according to the present invention forms a convex portion on the screw head side of the valve body which engages with a plurality of concave portions of the screw head, and the shape of the convex portion is Since the ratio of the height h of the convex portion to the radius of curvature ρ of the root portion of the convex portion is set to ρ / h ≧ 0.4, the convex portion due to the tensile stress generated at the root portion of the convex portion due to the pressure of the molten resin filling. The stress concentration of can be suppressed to a predetermined low value.

According to the result of the durability test, the durability which is more than three times that of the conventional one can be maintained, so that an excellent effect that the valve body always operates normally without being damaged can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an injection unit of an injection molding machine.

FIG. 2 is a sectional view of a valve body of the check valve.

FIG. 3 is a side view of a conventional injection unit.

[Explanation of symbols]

 2 screw 3 screw head 5 spacer 10 check valve 11 valve body 12 convex portion 13 concave portion

Claims (1)

[Claims] 1. A molten resin passage is provided between a screw tip of an injection molding machine and a screw head, the molten resin passage is opened during the plasticizing process to allow the molten resin to pass to the screw head side, and the molten resin passage is formed during the injection process. In a check valve for preventing the backflow of the molten resin to the screw side by closing the valve, the check valve has a convex portion that engages a plurality of concave portions of the screw head on the screw head side. To form
The check valve of the screw is characterized in that the shape of the protrusion is such that the ratio of the height h of the protrusion to the radius of curvature ρ of the root of the protrusion is ρ / h ≧ 0.4.