JPH11325220A - Plastic molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the circularity of a plastic molding having an annular portion on the outer periphery with the contraction of a reinforcing rib radially formed. SOLUTION: A plastic molding includes a cylindrical boss 12, a first disc 13a enlarged radially outside from the outer periphery of the boss 12, a first rib 16 protruded from the surface of the first disc 13a and enlarged radially from the boss 12, a shock absorbing portion 15 encircling the first rib 16 and the first disc 13a, a second disc 13b enlarged radially outside from the outer periphery of the shock absorbing portion 15, a second rib 17 enlarged radially from the shock absorbing portion 15 and an annular portion 14 encircling the second rib 17 and the second disc 13.

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 rib portion and an annular portion surrounding the rib 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.

FIG. 3 shows an example of such a conventional plastic gear. That is, a conventional general plastic gear includes a cylindrical boss portion 1 located at the center, an annular portion 2 located at the outer peripheral side and concentric with the boss portion 1, and the boss portion 1 and the annular portion. Disk part 3 that connects part 2 and boss part 1
In general, there is provided a rib portion 4 extending radially on the surface of the disk portion 3 from the ring portion 2 to the ring portion 2, and a tooth surface 5 is formed on the outer periphery of the ring portion 2. 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 adversely affects the accuracy of the plastic molded product. In order to accurately mold a plastic gear as shown in FIG. 3, it is necessary to uniformly shrink the plastic in the mold. Ring part 2 in contact with
Is drawn inward in the radial direction, and the roundness of the pitch circle is reduced.

For this reason, it is conceivable to suppress such a problem by arranging a large number of the rib portions 4 densely. However, increasing the number of the rib portions 4 is limited, and the rib portions 4 are limited. The presence of results in an increase in resistance at the time of mold release, so that the processing accuracy may be rather reduced.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a plastic which has an annular portion reinforced with radially formed ribs on its outer periphery and which can maintain high roundness and obtain high processing accuracy. It is to provide a molded article.

[0007]

According to a first aspect of the present invention, there is provided:
A cylindrical boss portion, a first disk portion extending radially outward from an outer periphery of the boss portion, and a plurality of first rib portions projecting from the surface of the first disk portion and radially extending from the boss portion; A first annular portion surrounding the first rib portion and the first disk portion, a second disk portion extending radially outward from an outer periphery of the first annular portion, and protruding from a surface of the second disk portion; A plastic molded product comprising: a plurality of second rib portions extending radially from the first annular portion; and a second annular portion surrounding the second rib portion and the second disk portion. .

According to a second aspect of the present invention, there is provided a boss having a cylindrical shape, a disk extending radially outward from an outer periphery of the boss, a boss protruding from the surface of the disk, and radially extending from the boss. In a plastic molded product having a plurality of ribs extending in a direction, and an annular portion surrounding the ribs and the disk, a cushioning portion for relaxing shrinkage of the ribs in a radial direction during molding is provided by the ribs. Is formed in the middle of the process.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the plastic molded product according to the first embodiment of the present invention, this may be a gear. Further, the first rib portion and the second rib portion may not be arranged in a straight line.

In the plastic molded product according to the second aspect of the present invention, this may be a gear. Further, the buffer portion may be concentric with the annular portion.

[0011]

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 the appearance and FIG. However, the present invention is not limited to such an embodiment,
The present invention can be applied to technologies in other fields that include similar problems.

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;
3 as a second annular portion of the present invention surrounding the outer peripheral edge of the disk portion 3, and projecting from the surface of the disk portion 13 between the annular portion 14 and the boss portion 12, the annular portion 14 and the boss. The first annular portion 1 of the present invention is concentric with the portion 12.
4, a plurality of first rib portions 16 that straddle the buffer portion 15 and the boss portion 12 and protrude radially from the boss portion 12 to the surface of the disk portion 13; 15 and a plurality of second rib portions 17 that radiate from the buffer portion 15 to the surface of the disk portion 13 so as to straddle the ring portion 14 and have a tooth surface with a predetermined pitch on the outer periphery of the ring portion 14. 18 are formed, and function as the plastic gear 11 as a whole.

In this embodiment, the first rib portion 16 and the second rib portion 17 are set so as not to be linearly aligned in the radial direction, and the disk portion 13 on which the first rib portion 16 is formed is formed.
Corresponds to the first disk portion 13a of the present invention,
The portion of the disk portion 13 where the rib portion 17 is formed corresponds to the second disk portion 13b of the present invention.

The thickness of the buffer portion 15 in the radial direction (the thickness in the left-right direction in FIG. 2) is set smaller than the thickness of the individual rib portions 16 and 17 in the circumferential direction. If the required strength is satisfied, the thickness of the ribs 16 and 17 should be 1
/ 2 is sufficient. The height of the buffer 15 from the surface of the disk 13 is set higher than the height of the first and second ribs 16, 17 from the surface of the disk 13.

When the plastic gear 11 is formed and contracted, the first and second rib portions 16 and 17 contract in the radial direction, respectively. For this reason, the second
In the portion where the rib portion 17 is in contact, the second rib portion 1
7 is affected by shrinkage. The portion of the boss 12 where the first rib 16 abuts is also pulled radially outward under the influence of the contraction of the first rib 16. In the present embodiment, the buffer unit 15 includes the first and second buffers.
It functions to absorb the shrinkage of the ribs 16 and 17.

[0016] Plastic gear 1 requiring high processing accuracy
In order to further reduce the influence of the contraction of the first and second rib portions 16 and 17 on the one tooth surface 18, the first rib portion 16 and the second rib portion 17 are linearly aligned in the radial direction. In this way, the difference in diameter between the portion of the annular portion 14 where the second rib portion 17 is in contact and the portion where the second rib portion 17 is not in contact, that is, the error of the pitch circle 19 is reduced, and the trueness of the plastic gear 11 is reduced. The roundness can be improved.

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 maintaining the pressure at 8 MPa, it was found that the meshing error of the obtained plastic gear 11, especially the meshing error of one pitch, could be improved as compared with the conventional one.

[0018]

According to the plastic molded product of the present invention,
Since the first annular portion is formed between the first rib portion and the second rib portion connecting the boss portion and the second annular portion, the first rib portion and the second rib portion contract in the radial direction during molding. Is reduced by the first annular portion, so that the roundness of the second annular portion is favorably maintained, and a highly accurate plastic molded product can be obtained.

Further, since the buffer portion is formed in the middle of the rib portion connecting the boss portion and the annular portion, the shrinkage of the rib portion in the radial direction during molding is reduced, and the roundness of the annular portion is reduced. A well-maintained, high-precision plastic molded product can be obtained.

[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 sectional view taken along the line II-II in FIG.

FIG. 3 is a plan view of a conventional plastic molded product to which the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Plastic gear 12 Boss part 13 Disk part 13a 1st disk part 13b 2nd disk part 14 Ring part 15 Buffer part 16 1st rib part 17 2nd rib part 18 Tooth surface 19 Pitch circle

Claims (6)

[Claims] 1. A boss portion having a cylindrical shape, a first disk portion extending radially outward from the outer periphery of the boss portion, and a plurality of first bosses projecting from a surface of the first disk portion and radially extending from the boss portion. A first rib portion, and a first rib portion surrounding the first rib portion and the first disk portion.
An annular portion; a second disk portion extending radially outward from an outer periphery of the first annular portion; and a plurality of second ribs projecting from a surface of the second disk portion and radially extending from the first annular portion. And a second portion surrounding the second rib portion and the second disk portion.
Plastic molded article characterized by having an annular portion. 2. The plastic molded product according to claim 1, wherein the plastic molded product is a gear. 3. The plastic molded product according to claim 1, wherein the first rib portion and the second rib portion are not arranged in a straight line. 4. A boss portion having a cylindrical shape, a disk portion extending radially outward from an outer periphery of the boss portion, a plurality of rib portions projecting from the surface of the disk portion and radially extending from the boss portion, In a plastic molded product having a rib portion and an annular portion surrounding the disk portion, a buffer portion for relaxing shrinkage of the rib portion in a radial direction during molding is formed in the middle of the rib portion. Plastic moldings. 5. The plastic molded product according to claim 4, wherein the plastic molded product is a gear. 6. The plastic molded product according to claim 4, wherein the buffer portion is concentric with the annular portion.