JP2000000852A - Plastic molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plastic molding formed into a disk-like shape such as a plastic gear or the like moldable with a high dimensional accuracy. SOLUTION: The plastic molding comprises a first disk 13 formed into a disk-like shape, a thinner second disk 14 than the disk 13 and expanded concentrically with the disk 13 from an outer periphery of the first disk 13, a thicker third disk 14 than the disk 14 and expanded concentrically with the disk 13 from an outer periphery of the disk 14, and a plurality of gates 17 arranged at an equal interval on a surface of the disk 14 to be finally removed in such a manner that base ends of the gates 17 protrude from the surfaces of the disks 13 and 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc-shaped plastic molded product, and is particularly suitable for application to plastic gears requiring high dimensional accuracy.

[0002]

2. Description of the Related Art Plastic molding is advantageous when mass-producing complicated shapes, and is self-lubricating, quiet, or lightweight in the case of gears that do not require much mechanical strength. In this respect, there are many advantages as compared with gears formed by metal cutting.

[0003] Such a plastic molded product is molded by melting a plastic material into a mold, and cooling and solidifying the plastic material in the mold. The molding accuracy is affected by molding. Shrinkage. In order to accurately mold a plastic molded product, it is necessary to uniformly shrink the plastic material. Specifically, the plastic material must be uniformly filled in a mold so that pressure is uniformly applied.

As a conventional plastic gear, one disclosed in Japanese Patent Application Laid-Open No. 8-132542 is known. When a gate is located on a disk portion, an annular groove is formed on the outer peripheral side of the gate to form a plastic material. The flow was controlled.

[0005]

SUMMARY OF THE INVENTION Japanese Patent Application Laid-Open No. H8-13254
In the conventional plastic gear disclosed in Japanese Patent Publication No. 2 (1993) -1995, although an annular groove is formed on the outer peripheral side of the gate, the flow of the plastic material flowing from the gate cannot be sufficiently controlled, and the plastic material cannot be controlled depending on the distance from the gate. A material filling time difference occurs, and as a result, a shape that should be a perfect circle becomes a polygonal shape corresponding to the number of gates, and there is a disadvantage that a meshing error, particularly, a one-pitch meshing error increases.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a disc-shaped plastic molded product such as a plastic gear which can be molded with high dimensional accuracy.

[0007]

According to the present invention, there is provided a plastic molded product comprising: a first disk portion having a disk shape;
A second disk portion which extends concentrically with the first disk portion from the outer periphery of the disk portion and has a smaller thickness than the first disk portion; and a second disk portion which is concentric with the first disk portion from the outer periphery of the second disk portion. A third disk portion that is wider than the second disk portion and is disposed at equal intervals on the surface of the second disk portion, and the base ends of a plurality of gates that are finally removed are connected to the third disk portion. It is characterized in that it protrudes from the surfaces of the first disk portion and the third disk portion.

According to the present invention, the molten plastic material flows from the base end of the gate into the cavity of the mold corresponding to the second disk portion. In this case, the base end of the gate protrudes from the surfaces of the first and third disk portions.
That is, since the gate length is set to be long, the plastic material fills the entire cavity of the mold corresponding to the second disk portion before flowing into the mold cavity corresponding to the first and third disk portions. It flows in a diffuse state throughout. When the plastic material flows into the mold cavities corresponding to the first and third disk portions, the second
The cavity of the mold corresponding to the disk portion acts as a flow path resistance to suppress the flow of the plastic material in the radial direction, and diffuses it in the circumferential direction to flow to an unfilled portion or a low pressure portion.

That is, the flow of the plastic material into the mold cavities corresponding to the first and third disk portions is as follows:
Starting from the entire circumference of the mold cavity corresponding to the second cavity portion, the plastic material is filled with uniform pressure into the entire mold cavity corresponding to the first and third disk portions.

In this manner, the plastic material filled in the entire cavity is cooled and solidified, and the gate is cut off from the second disk portion when the mold is opened to take out the plastic molded product.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a plastic molded article according to the present invention, a plurality of projections which are arranged on the back surface of a second disk portion so as to be in line with a gate and which are finally removed together with the gate project. There may be.

The front and back surfaces of the second disk portion may be recessed from the front and back surfaces of the first and third disk portions, respectively.

[0013] The first disk portion may further include a cylindrical boss portion, and the first disk portion may extend concentrically with the boss portion from an outer periphery of the boss portion.

The plastic molded product may be a gear having a tooth surface formed on at least one of the inner periphery of the first disk and the outer periphery of the third disk.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a plan view of an embodiment in which a plastic molded product according to the present invention is applied to an external gear.
And FIG. 2 showing a cross-sectional structure taken along the line II-II of FIG. 2. However, the present invention is not limited to such an embodiment, and is applied to technologies in other fields including similar problems. be able to.

The plastic gear 11 in the present embodiment
A boss 12 having a cylindrical shape to which a rotating shaft (not shown) is integrally fitted, a circular first disk portion 13 extending from the outer periphery of the boss portion 12 in the radial direction, and a first disk portion 13 And an annular third disk portion 15 extending radially from the outer periphery of the second disk portion 14 and an annular second disk portion 14 extending radially from the outer periphery of the third disk portion 15. A tooth surface 16 having a predetermined pitch is formed on the outer circumference, and functions as an external gear as a whole.

In this case, a spline or serration may be formed on the inner periphery of the boss portion 12 so as to be spline-fitted or serrated-fitted to a rotating shaft (not shown).

The surfaces of the first disk portion 13 and the third disk portion 15 are on the same plane, and their back surfaces are also on the same plane, and have the same thickness. In contrast,
The thickness of the second disk portion 14 is
3 is set to be thinner than the thickness of the third disk portion 15, and is recessed from the front surfaces of the first disk portion 13 and the third disk portion 15 and also recessed from the back surfaces of the first disk portion 13 and the third disk portion 15. It has become. In other words, the second disk unit 14 is connected to the first disk unit 13
It is formed as an annular groove separating the disk portion 15.

A plurality of gates 17 finally removed from the plastic gear 11 are arranged at equal intervals on the surface side of the second disk portion 14 and protrude from the surfaces of the first disk portion 13 and the third disk portion 15. It is elongated. In this embodiment, a plurality of projections 18 which are finally removed from the plastic gear 11 together with the gates 17 are arranged on the back surface of the second disk portion 14 so as to be aligned with the respective gates 17. The gate 17 and the projection 18 have a diameter of, for example, about 0.5 mm so that the gate 17 and the projection 18 are automatically separated from the molded second disk part 14 when the mold for molding the plastic gear 11 is opened. It has very thin dimensions.

When such a plastic gear 11 is injection-molded, a molten plastic material is used for the gate 17.
Flows into the cavity of the mold corresponding to the second disk portion 14 from the base end of the mold. In this case, the base end of the gate 17 is the first
The plastic material protrudes from the surfaces of the disk portion 13 and the third disk portion 15, that is, the gate length is set to be long, so that the plastic material is
Prior to flowing into the mold cavity corresponding to the disk portion 15, the protrusion 18 is aligned with the gate 17.
And flows in a diffused state over the entire cavity corresponding to the part and the cavity of the mold corresponding to the second disk part 14. When the plastic material flows into the cavities of the mold corresponding to the first disk portion 13 and the third disk portion 15, the cavity of the mold corresponding to the second disk portion 14 becomes a flow path resistance, and It suppresses the flow along the radial direction, diffuses it in the circumferential direction, and flows to an unfilled portion or a low pressure portion.

That is, the flow of the plastic material into the mold cavities corresponding to the first disk portion 13 and the third disk portion 15 starts from the entire circumference of the mold cavity corresponding to the second cavity portion 14, and The material is filled into the entire cavity of the mold corresponding to the first disk portion 13 and the third disk portion 15 at a uniform pressure.

In this way, the plastic material filled in the entire cavity is cooled and solidified, and when the plastic gear 11 is taken out by opening the mold, the gate 17 and the projection 18 are separated from the second disk portion 14. .

In order to manufacture such a plastic gear 11, a polyacetal resin heated to 180 ° C.
Inject into the cavity corresponding to the plastic gear 11 of the mold kept at 0 ° C. at an injection speed of 15 mm / sec.
As a result of molding while keeping the pressure at 8 MPa, it was found that the meshing error of the obtained plastic gear 11, especially the one-pitch meshing error, could be improved as compared with the conventional one.

[0024]

According to the plastic molded product of the present invention,
A plurality of gates to be finally removed are arranged at equal intervals on the surface of the second disk portion, which is located between the first and third disk portions and has a smaller thickness than the first and third disk portions, and the base ends of these gates are Since the gate length is set long so as to protrude from the surfaces of the first disk portion and the third disk portion, the plastic material fills the entire area of the second disk portion before the first and third disk portions are filled with the plastic material. As a result, the first and third disc portions are filled with a plastic material. As a result, a disc-shaped plastic molded product having high dimensional accuracy can be obtained. It is effective when you do.

[Brief description of the drawings]

FIG. 1 is a plan view of an embodiment in which a plastic molded product according to the present invention is applied to an external gear.

FIG. 2 is a sectional view taken along the line II-II in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Plastic gear 12 Boss part 13 1st disk part 14 2nd disk part 15 3rd disk part 16 Tooth surface 17 Gate 18 Projection part

Claims (7)

[Claims] A first disk portion having a disk shape; and a second disk portion extending from the outer periphery of the first disk portion concentrically with the first disk portion and having a smaller thickness than the first disk portion.
A disk portion, and a third disk portion that extends concentrically with the first disk portion from the outer periphery of the second disk portion and is thicker than the second disk portion. A plastic molded product, wherein base ends of a plurality of gates that are arranged at equal intervals and that are finally removed protrude from surfaces of the first disk portion and the third disk portion. 2. A plurality of projections, which are arranged on the back surface of the second disk portion so as to be in a straight line with the gate and which are finally removed together with the gate, protrude. The plastic molded product according to the above. 3. The front surface and the back surface of the second disk portion are recessed from the front surface and the back surface of the first disk portion and the third disk portion, respectively. Plastic molded products. 4. The apparatus according to claim 1, further comprising a cylindrical boss portion, wherein the first disk portion extends concentrically with the boss portion from an outer periphery of the boss portion. A plastic molded article according to any one of the above. 5. A gear having a tooth surface formed on an outer periphery of the third disk.
A plastic molded article according to any one of the above. 6. A gear having a tooth surface formed on an inner periphery of the first disk.
A plastic molded article according to any one of the above. 7. An inner periphery of said first disk and said third disk.
The plastic molded product according to any one of claims 1 to 4, wherein the gear is a gear having tooth surfaces formed on the outer periphery of the disk.