JP2000346176A - Plastic molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reduction of the roundness of a plastic molded product having a circular ring part in the external periphery by a reinforcing rib part formed in radial shape. SOLUTION: This molded product comprises a boss part 12 formed in cylindrical shape, disk parts 13 spread to a radial direction outer side from the external periphery of this boss part 12, a plurality of spoke parts 15 protruded from a surface of this disk part 13 to be spread radially from the boss part 12, a rim part 14 surrounding these spoke parts 15 and disk parts 13, and rib parts 16 protruded to a radial direction inner side from the internal periphery of this rim part 14 to be extended along a lengthwise direction of the boss part 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical boss portion, a disk portion extending radially outward from the outer periphery of the boss portion, and a plurality of radially extending bosses projecting from the surface of the disk portion. The present invention relates to a plastic molded product having a spoke portion and a rim portion surrounding the spoke portion and the disk portion, and is particularly suitable for gears.

[0002]

2. Description of the Related Art Plastic molding is advantageous when mass-producing complicated shapes, and in the case of gears that do not require much mechanical strength, such as lubrication and quietness, There are many advantages compared to gears made by metal cutting.

[0003] Such a conventional plastic gear has a cylindrical boss located at the center, a rim located concentrically with the boss located on the outer peripheral side, and a spoke connecting the boss and the rim. Generally, the rim has spokes extending radially from the boss to the surface of the disk from the rim to the surface of the disk, and a tooth surface is formed on the outer periphery of the rim. In addition to the plastic gears, when a disk-shaped rotationally symmetric object is plastic-molded, rib portions for reinforcement are often formed radially on the disk portion.

[0004]

Generally, a plastic molded article is formed by melting a plastic, filling the mold, and cooling and solidifying the plastic in the mold. It is molding shrinkage that affects the accuracy of this plastic molded product. In order to accurately mold the plastic gear as described above, it is necessary to uniformly shrink the plastic in the mold, but the presence of the rib prevents uniform shrinkage, and as a result, the rim portion in contact with the rib portion Is drawn inward in the radial direction, and the roundness of the pitch circle is reduced.

[0005] For this reason, it is conceivable to suppress such inconvenience by densely arranging a large number of rib portions. However, increasing the number of rib portions is limited, and the existence of the rib portions is limited. However, since the resistance at the time of mold release is increased, the processing accuracy may be rather reduced.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a plastic molding which has a rim portion reinforced with radially formed rib portions on its outer periphery and which can maintain high roundness and obtain high processing accuracy. To provide goods.

[0007]

According to the present invention, there is provided a plastic molded product comprising: a cylindrical boss; a disk extending radially outward from an outer periphery of the boss; and a boss projecting from a surface of the disk. A plurality of spoke portions radially extending from the portion, a rim portion surrounding the spoke portion and the disk portion, and a rib protruding radially inward from an inner periphery of the rim portion and extending along a longitudinal direction of the boss portion. And a part.

[0008] According to the present invention, the shrinkage of the spoke portion in the radial direction during molding is reduced by the presence of the rib portion, so that the roundness of the rim portion is favorably maintained. Further, the rib portion does not extend to the boss portion, so that an increase in release resistance from the mold during molding is minimized.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In a plastic molded product according to the present invention, a spoke portion may be one in which both radial ends are connected to a boss portion and a rim portion. Also,
The ribs are preferably located between the joints between the rim and the individual spokes. Further, the plastic molded product according to the present invention may be a gear having a tooth surface formed on an outer periphery of a rim portion.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a plastic molded product according to the present invention is applied to an external gear will be described in detail with reference to FIG. 1 showing its appearance and FIG. The present invention is not limited to such an embodiment, and can be applied to other technologies that should be included in the concept of the present invention described in the claims of this specification.

[0011] The plastic gear 11 in the present embodiment
A cylindrical boss portion 12 to which a rotating shaft (not shown) is integrally fitted; a circular disk portion 13 extending radially from the outer periphery of the boss portion 12;
And a plurality of rims 14 (in the illustrated example, 12 projecting from the surface of the disk portion 13 and extending radially from the boss portion 12 between the rim portion 14 and the boss portion 12).
The rim comprises a plurality of (12 in the illustrated example) rib portions 16 protruding radially inward from the inner periphery of the rim portion 14 and extending along the longitudinal direction of the boss portion 12. A tooth surface 17 having a predetermined pitch is formed on the outer periphery of the portion 14,
The whole functions as a plastic gear 11. The plastic gear 11 in this embodiment has a tip circle diameter of 3
A helical gear having a diameter of 6 mm and a module of 0.5, and a reinforcing annular portion 18 having a smaller diameter than the rim portion 14 is formed concentrically with the boss portion 12 from the surface of the disk portion 13 opposite to the rim portion 14. Have been.

In this embodiment, the shape of the rib portion 16 in FIG. 1 is formed in a rectangular shape. However, the present invention is not limited to this, and there is no problem if the rib portion 16 is formed in a semicircular shape or a polygonal shape. Further, these shapes and sizes do not need to be all the same, and may be changed according to the shrinkage characteristics at the time of molding. Further, in the present embodiment, the radially outer end portions of the spoke portions 15 and the rib portions 16 are alternately formed on the inner periphery of the rim portion 14, but between the joining portions of the rim portions 14 and the individual spoke portions 15 A plurality of rib portions may be formed respectively. The end faces of the spokes 15 and the ribs 16 and the end faces of the boss 12 and the rim 14 are flush with each other. Boss part 12
And lower than the end face of the rim portion 14.

When the plastic gear 11 is formed, the spoke portion 15 is moved by the heat shrinkage to form the disk portion 1.
3 together with the radially inner side, that is, toward the boss portion 12 side, the rim portion 14 having the tooth surface 17 formed on the outer periphery,
The contraction amount is large in the portion where the spoke portion 15 is in contact,
The diameter of the pitch circle close to this portion is reduced, which adversely affects the roundness.

In this embodiment, however, the ribs 1 projecting from the inner periphery of the rim 14 between the spokes 15 are provided.
6, the rib portions 16 of the rim portion 14 are formed.
As a result, the amount of heat shrinkage at the portion where the plastic gear 11 comes into contact also increases, so that heat shrinkage occurs substantially uniformly over the entire circumference of the rim portion 14, and the roundness of the pitch circle diameter of the plastic gear 11 is favorably maintained. be able to.

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.
When the plastic gear 11 was molded while being held at a pressure of 8 MPa, the resulting meshing error of the plastic gear 11, in particular, the one-pitch meshing error was 3 times smaller than the one-pitch meshing error of the conventional plastic gear having no rib portion 17 molded under the same conditions.
It has been found that the pitch error of the conventional plastic gear is 15 μm, and the pitch error of the plastic gear 11 in this embodiment is 12 μm.

[0016]

According to the plastic molded product of the present invention,
Since the rib portion protruding inward in the radial direction from the inner periphery of the rim portion and extending along the longitudinal direction of the boss portion is formed, radial shrinkage of the spoke portion during molding is reduced by the rib portion. The roundness of the portion is maintained well, and a high-precision plastic molded product can be obtained.

Moreover, since the rib does not extend to the boss unlike the spoke, an increase in the resistance to release from the mold during molding of the plastic molded article can be minimized.

[Brief description of the drawings]

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

FIG. 2 is a cutaway sectional view illustrating the structure of the plastic gear illustrated in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Plastic gear 12 Boss part 13 Disc part 14 Rim part 15 Spoke part 16 Rib part 17 Tooth surface 18 Reinforcing ring part

Claims (4)

[Claims] A cylindrical boss portion; a disk portion extending radially outward from an outer periphery of the boss portion; a plurality of spoke portions projecting from the surface of the disk portion and radially expanding from the boss portion; A plastic molding comprising: a rim portion surrounding the spoke portion and the disk portion; and a rib portion protruding radially inward from an inner periphery of the rim portion and extending along the longitudinal direction of the boss portion. Goods. 2. The plastic molded product according to claim 1, wherein said spoke portion has both ends in the radial direction connected to said boss portion and said rim portion. 3. The plastic molded product according to claim 1, wherein the rib portion is located between joining portions of the rim portion and the individual spoke portions. 4. The plastic molded product according to claim 1, wherein the plastic molded product is a gear having a tooth surface formed on an outer periphery of the rim portion.