JPH04238010A - In-mold gate cutting method in thermoplastic plastic injection molding - Google Patents

Abstract

PURPOSE:To provide a gate cutting method, in which gate cutting can be performed with comparatively small force and the removal of plastic material solidified in a gate is very easy, in a gate cutting operation, through which the thermoplastic plastic material solidified in the gate is cut and removed after the thermoplastic plastic material is injected through a runner and the gate in a cavity for molding. CONSTITUTION:Under the condition that skin layer 10 is formed before the plasticity of molten plastic material 9 in a cavity 3 is completely lost, a gate cutting pin 7 is advanced so as to cut a gate. After the cutting of the gate, the cooling and solidification of the plastic material is proceeded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for obtaining a molded product by injection molding a thermoplastic material into a mold, in which a molten thermoplastic material is injected from a runner into a cavity through a gate. When solidified,
This relates to a method of obtaining a molded product by cutting the plastic material solidified in the sprue and the plastic material (molded product) solidified in the cavity, which are connected by the plastic material solidified in the runner and gate. .

0002

2. Description of the Related Art FIG. 6 is a schematic cross-sectional view showing a conventional plastic injection mold. The mold in this example is
A cavity 3 is formed between a cavity block 1 and a core block 2 by combining them.

Molten thermoplastic material is press-fitted from a sprue 4 and is injected into the cavity 3 from a gate 6 via a runner 5.

[0004] When the molten plastic is cooled, it solidifies,
A molded product is formed in the cavity 3, and this molded product is taken out from the mold in a state in which the plastic solidified in the gate 6, the plastic solidified in the runner 5, and the plastic solidified in the sprue 4 are connected.

[0005] Therefore, the portion corresponding to the gate 6 must be cut using nippers or a hot knife, which requires a great deal of labor.

Furthermore, if a precise shape is required, the cut portions must be manually finished, which further increases the number of man-hours required.

[0007] Cutting using a robot, applying vibration, cutting using a laser beam, etc. are theoretically possible, but the equipment costs are high and daily maintenance is not easy. Because it is not, it is not practical.

[0008]

A method shown in FIG. 7 can be considered as a method for automatically or semi-automatically cutting a gate portion within a mold.

A gate cut pin 7 is provided opposite the gate 6 and can be driven vertically in the figure.

[0010] thermoplastic in cavity 3;
When the thermoplastic in the gate 6 is solidified, the gate cut pin 7 is driven upward in the figure to cut the gate. Reference numeral 8 in the figure is a sprue ejector pin for discharging the solidified sprue 4, which is connected to the gate cut pin 7 (not shown) and is driven together in the vertical direction in the figure.

However, the prior art gate cutting method shown in FIG. 7 has the following difficulties.

[0012] The molten plastic material press-fitted into the mold is mainly deprived of heat by the mold, and is cooled and solidified. Therefore, the molten plastic material in contact with the mold is rapidly cooled and a hard skin layer is formed along the inner surface of the mold.

[0013] Since the above skin layer is formed, it is not easy to cut the vicinity of the gate 6 with the gate cut pin 7. That is, it is not easy to shear a resilient, solidified plastic material sandwiched between hard skin layers.

Furthermore, if an attempt is made to forcibly cut the solidified plastic material at this gate portion, an isolated fragment (an individual fragment that is not connected to either the molded product or the solidified plastic material in the runner) is produced; Another problem is that it is not easy to remove these isolated fragments.

The present invention was made in view of the above-mentioned circumstances, and allows gate cutting to be performed with a relatively small force.
Moreover, it is an object of the present invention to provide a gate cutting method in which removal of cut members is extremely easy.

[0016]

[Means for Solving the Problems] In order to achieve the above object, an in-mold gate cutting method according to the present invention includes a method for cutting a runner and a gate into a cavity formed between a cavity block and a core block. In the method of cutting the gate portion after injection molding the thermoplastic material in a molten state through the injection molding method, a skin layer is formed at a portion where the plastic material injected into the cavity is in contact with the cavity block, and While the inside of the plastic material has not yet lost its plasticity, a gate cut pin placed opposite to the gate is advanced to cut and separate the plastic material inside the gate and the plastic material inside the cavity. Along with urging,
The skin layer formed in the gate and the skin layer formed in the runner are connected without cutting, and when the thermoplastic plastic solidified in the runner is removed from the cavity block together with the sprue, the runner The method is characterized in that the skin layer within the gate connected to the skin layer formed within the gate is removed together.

[0017]

[Operation] According to the above method, a. The inside other than the skin layer still has plasticity (semi-fluid state),
Since the gate cut pin is advanced, the resistance against the gate cut pin is mainly due to the reaction force that cuts the thin skin layer and the flow resistance that cuts the semi-fluid plastic material, and does not require a large force.

b. The skin layer formed within the gate is separated from the part and remains connected to the solidified plastic material within the runner and sprue, which can be removed along with the sprue. It's easy. In practice, when the sprue is removed with the sprue injector pin 8 shown in FIG. 7, the skin layer formed within the gate is removed along with it.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 5 are process diagrams schematically depicting one embodiment of the method of the present invention.

FIG. 2 shows the state before the injection process, and 3
is a cavity, 5 is a runner, and 6 is a gate. A gate cut pin 7 is arranged to face the gate 6 and is driven in the vertical direction in the figure.

When the molten plastic material 9 is injected in the state shown in FIG. 2 above, the state shown in FIG. 3 is obtained.

Next, as shown in FIG. 4, a thin, hard skin layer 10 is formed along the surface where the molten plastic material 9 contacts the cavity block 1 and the core block 2.

In this state, that is, in a state where the parts other than the skin layer 10 have not yet completed solidification and have fluidity (have plasticity), the gate cut pin 7 is advanced as shown in FIG. and the skin layer 1 formed within the gate 6
0 is sheared away from the skin layer formed within the cavity 3. Since the skin layer 10 is thin, the shearing force required is not large.

During this operation, the molten plastic material 9 separates without any significant resistance. At this time,
Since the molten plastic material in the gate 6 has fluidity, there is no risk of it becoming isolated fragments, and it flows into the runner 5 and is removed.

After cooling and solidifying the molten plastic material 9 in the state shown in FIG. 1, when the gate cut pin 7 is retreated downward in the figure, the state shown in FIG. 5 is achieved. That is,
The molded product in the cavity 3 is separated from the solidified plastic material in the gate 6 and becomes a nearly completed product.

The skin layer formed within the gate 6 (indicated by a chain line) is connected to the skin layer formed within the runner 5 (indicated by a chain line).

Since the plastic material solidified in the runner 5 is connected to the plastic material solidified in the sprue (not shown), the gate 6 is connected to the plastic material solidified in the sprue (not shown).
The solidified plastic material inside (consisting primarily of the skin layer) is automatically removed together with the solidified plastic material within the runner 5.

[0028]

Effects of the Invention As explained above, the method of the present invention involves injection molding of a molten thermoplastic material into a cavity formed between a cavity block and a core block via a runner and a gate. After that, in the method of cutting the gate part, a skin layer is formed in the part where the plastic material injected into the cavity is in contact with the cavity block, and the inside of the plastic material has not yet lost its plasticity. in,
A gate cut pin disposed opposite to the gate is advanced to cut and separate the plastic material in the gate and the plastic material in the cavity, and also to separate the skin layer formed in the gate and the plastic material in the runner. When the thermoplastic plastic solidified in the runner is removed from the cavity block along with the sprue, the thermoplastic plastic is connected to the skin layer formed in the runner without cutting. Since the skin layer within the gate is removed at the same time, the gate can be cut with a relatively small force, and the cut member is extremely easy to remove.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of the method of the present invention,
The state in which the gate cut pin is advanced is depicted.

FIG. 2 similarly depicts the state before molten plastic is injected into the cavity 3 from the gate 6.

FIG. 3 also depicts the situation immediately after the molten plastic material 9 has been injected into the cavity 3. FIG.

FIG. 4 similarly depicts a state in which the molten plastic 9 has been cooled and a skin layer 10 has been formed.

FIG. 5 similarly depicts a state in which the gate cutting pin 7 is retreated after finishing the gate cutting.

FIG. 6 is a schematic cross-sectional view of a mold shown for explaining a gate cutting method according to the prior art.

FIG. 7 is a sectional view for explaining a conventional mold having a structure including a gate cut pin and its problems.

[Explanation of symbols]

1 Cavity block 2 Core block 3 Cavity 4 Sprue 5 Runner 6 Gate 7 Gate cut pin 8 Sprue ejector pin 9 Molten plastic material 10 Skin layer

Claims (1)

[Claims] Claim 1: A method of injection molding a molten thermoplastic material into a cavity formed between a cavity block and a core block via a runner and a gate, and then cutting the gate portion. , a skin layer is formed where the plastic material injected into the cavity is in contact with the cavity block,
And, while the inside of the plastic material has not yet lost its plasticity, a gate cutting pin disposed opposite to the gate is advanced to cut the plastic material inside the gate and the plastic material inside the cavity. At the same time, the skin layer formed in the gate and the skin layer formed in the runner are connected without cutting, and the thermoplastic plastic solidified in the runner is removed from the cavity block along with the sprue. An in-mold gate cutting method for thermoplastic plastic injection molding, characterized in that, when doing so, a skin layer in a gate connected to a skin layer formed in the runner is removed together with the skin layer in the gate.