JPH031238Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an improved structure of a tunnel gate provided for pouring molten resin into a product molding part (cavity) in an injection mold.

(Prior Art) An injection mold is provided with a gate for injecting molten resin material injected from a cylinder into a product molding section. There are various types of gates, but tunnel gates (also called submarine gates) are known as gates that are configured so that the resin inside the gate and the molded product are automatically separated from each other when the mold is opened. There is.

FIG. 3 shows an example of a conventional tunnel gate structure. In the figure, 7 is a fixed mold, 5 is a movable mold, 2 is a runner provided on the mold dividing surface 8, and 3 is a product forming section.The fixed mold 7 has a runner 2 and a product forming section 3. A tunnel gate 1 for communication is provided diagonally with respect to the product forming section 3. Therefore, the inner wall surface of the tip of the tunnel gate 1 in the mold opening direction (direction of arrow A in FIG. 3) intersects the wall surface 3a of the product molding section 3 at an acute angle θ ₁ , and mold clamping direction (arrow in Fig. 3)
The inner wall surface on the A′ direction) crosses the wall surface 3a at an obtuse angle θ ₂ . The shape of the opening on the tip side of the tunnel gate 1 is as shown in FIG.
b, and circular arc portions 1c, 1d connecting both ends of the straight portions 1a, 1b.

In the injection mold having the above configuration, when the movable mold 5 separates from the fixed mold 7 in the direction of arrow A, the cured resin in the product molding section 3, runner 2, and tunnel gate 1 moves in the direction of arrow A along with the movable mold 5. Therefore, the cured resin in the product molding section 3, that is, the molded product, is automatically cut from the cured resin in the tunnel gate 1 as the movable mold 5 moves in the direction A.

(Problem to be solved by the invention) In this case, since the angle θ ₁ between the molded product and the cured resin in the tunnel gate 1 is acute on the A-direction side of the cut portion, shear stress is applied. However, since the angle θ ₂ between the molded product and the cured resin in the tunnel gate 1 is obtuse on the A′ direction side of the cutting part, no shearing stress is applied and the cutting quality is poor. . Therefore, on the A′ direction side of the cutting part, gate marks such as scratches are noticeable on the surface of the molded product due to poor gate cutting, resulting in poor appearance.In addition, as shown in FIG. Department
There is a problem in that peeling occurs on the A′ direction side, leading to molding defects. In addition, in FIG. 5, 10 shows the cured resin in the runner 2, 11 shows the cured resin in the tunnel gate 1, and 9a shows the peeled part generated in the molded product 9.

Further, when cutting the molded product 9 and the cured resin 11, there is a problem that a large amount of resin scum is generated due to poor gate cutting, and this resin scum adheres to the surface of the molded product 9. The problem caused by this defective gate cutting becomes more noticeable as the obtuse cross-sectional section 12 at the tip end of the tunnel gate 1 becomes rounder due to long-term use, and it is necessary to deal with this problem in a surface hardening process.

The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a tunnel gate structure that can prevent molded product defects caused by gate breakage defects.

(Means for Solving the Problems) The means of the present invention to achieve this technical problem is that in an injection mold in which a tunnel gate is provided diagonally with respect to the product molding part, a protrusion is formed on the inner wall at the tip of the tunnel gate. is provided so that during injection molding, this protrusion forms a notch at the connecting portion between the molded product and the cured resin within the tunnel gate. The notch forming protrusion is provided on the inner wall portion of the tunnel gate on the side forming an obtuse angle with respect to the product molding part.
The tip of the protrusion is formed to have a V-shaped cross section, and the angle of the tip is set to be an acute angle, preferably in the range of 40 degrees to 60 degrees. This is because if the tip angle is set within this angle range, a high notch effect can be obtained. The protrusion is formed in a band shape along the linear portion of the tunnel gate opening shape, and one side of the protrusion is provided so as to constitute a part of the wall surface of the product molding section.

(Function) In this way, if the notch forming protrusion is provided at the corner of the inner wall of the tunnel gate that forms an obtuse angle with the wall surface of the product molding part, when the resin hardens, the obtuse angle of the connecting part between the molded product and the resin in the tunnel gate will be reduced. A notch is carved on the side where the mold is formed, and when the mold is opened, shearing stress concentrates on the notched part. Therefore, shear stress will proceed to the connecting part from both sides of the acute angle section of the tunnel gate and the notch forming protrusion opposite to the acute angle section, which will cause damage to the molded product and the tunnel gate. The internally cured resin is separated from each other extremely smoothly, preventing defects such as poor cutting and peeling.

(Example) An example of the present invention will be described below based on the drawings. Components that are the same as those shown in FIG. 3 are given the same reference numerals.

In Fig. 1, 1 is a runner 2 and a product (here, an automobile bumper made of modified polypropylene).
The plate thickness T is 4 to 6 mm. ) A tunnel gate that communicates with the molding section 3, and the tunnel gate 1 is provided so as to extend diagonally with respect to the product molding section 3. Product molding section 3 of tunnel gate 1
As shown in Fig. 2, the opening on the side is formed into a substantially rectangular shape with straight parts 1a and 1b parallel to each other, and in particular, the corner angles on both sides of the straight part 1a are 90 degrees, unlike the conventional one. is set to . The surface of the inner wall on the tip side of the tunnel gate 1 on the mold opening direction A side forms an acute angle θ ₁ with the wall surface 3a of the product molding section 3, and the surface of the inner wall on the tip side of the tunnel gate 1 on the side of the mold closing direction A' The surface forms an obtuse angle θ ₂ with respect to the wall surface 3a of the product forming section 3.

Mold clamping direction of the inner wall end of tunnel gate 1
On the A' side, a protrusion 4 having a V-shaped cross section is provided in a strip shape parallel to the straight portion 1b. This protrusion 4 is provided to form a V-shaped notch at the connection point between the cured resin (molded product) in the product molding section 3 and the cured resin in the tunnel gate 1 during molding. Angle θ ₃ of the top end of the V-shaped protrusion 4
is set at around 50 degrees here, but even if it is set within the range of 50 degrees to 90 degrees, a sufficient notch effect can be expected at the above-mentioned joint location.

With the above configuration, when the movable mold 5 moves in the direction A to open the mold in the injection molding process, the tunnel gate 1 The shear stress from the cross-sectional acute angle part 6 on the A-direction side of the opening end and the cross-section V
The shear stress from the top end of the letter-shaped protrusion 4 travels along the shortest path from both sides of the joint. As a result, the molded product and the cured resin inside the tunnel gate 1 are effectively separated from each other and become sharp. Therefore, after the molded product is divided, almost no gate marks remain on the surface of the molded product, and peeling does not occur as in conventional molded products.
In addition, in the example, if the inclination angle θ ₄ of the wall surface 3a of the product molding section 3 with respect to the mold opening direction A is further reduced, the sharpness of the dividing section becomes even better, so that the gate marks on the surface of the molded product are further reduced. It becomes less noticeable and the appearance quality is further improved.

In the embodiment, both side surfaces of the protrusion having a V-shaped cross section are formed as flat surfaces, but the inner surface of the protrusion opposite to the product molding part does not necessarily need to be formed as a flat surface, and may be formed as a curved surface.

Furthermore, in the above embodiment applied to a resin product with a plate thickness T = 4 to 6 mm, the product plate thickness t near the gate is
If the thickness is set to be thinner than other parts, for example, t=3.5 mm or less, the resin near the gate will harden quickly, and the gate can be cut more easily.

(Effects of the invention) As described above, according to the invention, a notch forming protrusion is provided on the inner wall on the tip side of the tunnel gate, and a mold opening is formed at the obtuse angle side of the joint between the molded product and the resin in the gate. Since it is configured to produce a time notch effect, the sharpness of this part is significantly better than before. Therefore, the tunnel gate marks left on the surface of the molded product are less noticeable compared to conventional molded products, and the appearance of the molded product is significantly improved. Furthermore, as the cutting quality of the connecting portion improves, the occurrence of peeling on the surface of the molded product is prevented. Furthermore, since the amount of resin residue remaining on the molded product when the gate breaks is considerably smaller than in the past, product defects due to resin residue can be effectively prevented.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a tunnel gate structure according to an embodiment of the present invention, and FIG. 2 is an enlarged view in the direction of arrows showing the shape of the tip opening of the tunnel gate in FIG. 1.
FIG. 3 is a cross-sectional view showing an example of a conventional tunnel gate structure, FIG. 4 is an enlarged view in the direction of arrows showing the shape of the tip opening of the tunnel gate in FIG. 2, and FIG.
FIG. 2 is a perspective view showing a peeled portion of a molded product obtained by the method shown in the figure. 1...Tunnel gate, 3...Product molding section, 4
……protrusion.

Claims (1)

[Scope of utility model registration request] In a tunnel gate formed to communicate obliquely with the product molding section, a notch is provided at the connecting portion between the molded product and the resin in the tunnel gate on an inner wall forming an obtuse angle with the wall surface of the product molding section at the tip of the tunnel gate. A tunnel gate structure for an injection mold, characterized by having a projection formed therein.