JPH09166199A - Injection molded gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection molded gear made of plastic in a shape wherein lightening is effected on a disc part from both surface sides and a high-precise shape size is provided. SOLUTION: A rim 2 formed at a tooth part 1 and a concentrically arranged boss 3 are integrally formed through a disc part 4. A plurality of gate parts 6 through which a molten material is injected on a concentric circle is arranged on one surface of the disc part 4. The thickness of the rim 2 is thickmost at a connection part between the disc part 4 and an outside diameter part and gradually decreased toward above and below. Further, the thickness of the disc part 4 is thickmost in the position of the gate part 6 and gradually decreased in the direction of an outside diameter part and in the direction of an inside diameter part. The thickness of the outside diameter part is thicker than that of the rim 2 at a connection part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic injection-molded gear in which a rim and a shaft portion are integrated via a disc portion and teeth are formed on an outer peripheral surface of the rim.

[0002]

2. Description of the Related Art First, a conventional example of this type of gear will be described with reference to FIGS. FIG. 9 is a plan view of a conventional example, and FIG. 10 is a sectional view thereof. A cylindrical rim 12 having a tooth portion 11 formed on the outer peripheral surface thereof and a boss 13 which is also concentrically provided are integrated via a disc portion 14. Four gate marks 15 are concentrically formed on one surface of the disk portion 14. The wall thickness of the rim 12 and the wall thickness of the disk portion 14 are uniform and both are the same.

When manufacturing this gear, a molten plastic material is injected into the mold through the gates 16 provided at the positions of the gate marks 15, respectively. The injected molten material initially flows radially around the gate 16 position,
Eventually, as a whole, it will flow toward the outer diameter direction and the inner diameter direction of the disk portion 14. The molten material that has flowed in the outer diameter direction fills the cavities of the tooth portion 11 and the rim 12, and the molten material that has flowed in the inner diameter direction has the boss 13.
The inside of the cavity will be filled. Then, it is cooled and solidified, and released from the mold to obtain a gear as shown.

[0004]

It is known that in such an injection molding process, a shrinking action more or less acts at the time of solidification by cooling, which influences formation of a predetermined shape. The contraction degree generally increases as the inner pressure decreases as the distance from the gate increases, and if the inner pressure is the same, the thicker the wall, the larger the solidification with a delay from the solidification. Therefore, as in the above-mentioned conventional example, in the case of a gear having a shape in which the disk portion is thinned from both sides, and the thickness of the rim and the thickness of the disk portion are the same, as shown in FIG. In the area shown by a circular dashed line in FIG. 1, that is, the connection area between the rim and the disk portion, the solidification is delayed more than the surrounding area, and the area shrinks largely in the gate direction.
As a result, the shapes of the tooth portion and the rim are distorted as shown by the chain double-dashed line in FIG. In addition, the disk portion may be twisted due to other factors. Therefore, it has been very difficult to manufacture high-precision spur gears and helical gears.

The present invention has been made to solve the above problems, and its purpose is to:
An object of the present invention is to provide a plastic injection-molded gear which has a shape in which the disk portion is thinned from both sides and whose shape and dimension can be obtained with high accuracy.

[0006]

In order to achieve the above object, the present invention provides a cylindrical rim that is integrated with a plurality of teeth on its outer peripheral surface and an axial portion of the rim that has an outer diameter. In a plastic injection-molded gear, which comprises a disc portion connected to a shaft portion at an inner diameter portion and connected to a substantially middle portion, and one surface of the disc portion is provided with an injection portion of a molten material on substantially concentric circles, The thickness of the disk portion, the thickness on each concentric circle is the same, the thickness on the concentric circle provided with the injection portion is formed so as not to be thinner than the thickness on other concentric circles, The thickness of the rim is smaller than the thickness of the outer diameter portion of the disc portion, and the connecting portion with the outer diameter portion is maximum and is formed to be thinner as the distance increases.

Further, preferably, in the plastic injection-molded gear of the present invention, the wall thickness of the disk portion is made substantially uniform, or is gradually reduced from the injection portion toward the outer diameter portion. Or it is formed so as to be gradually thinned. Further, preferably, in the plastic injection-molded gear of the present invention, the disc portion is formed in a stepped shape at a predetermined radial position so that the outer diameter portion and the inner diameter portion have different surfaces. .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The mode for carrying out the present invention will be described with reference to the five examples shown in FIGS. Since each embodiment is different only in the shape and has the same basic configuration, the reference numerals of the respective parts are, in principle, the same reference numerals, and the different reference numerals are used only for particularly necessary parts.

First, the first aspect of the present invention will be described with reference to FIGS.
An embodiment will be described. FIG. 1 is a plan view of this embodiment, and FIG. 2 is a sectional view thereof. A cylindrical rim 2 having a tooth portion 1 formed on the outer peripheral surface thereof and a boss 3 provided concentrically are integrated via a disc portion 4. On one surface of the disk portion 4, four gate marks 5 in which the molten material is injected are formed concentrically. The thickness of the rim 2 is as shown in FIG.
As can be seen from the above, it is formed so that it is thickest at the connecting portion with the outer diameter portion of the disc portion 4 and becomes thinner as it goes up and down. Further, the wall thickness of the disk portion 4 is the same as the position of the gate 6 into which the molten material is injected, and has a uniform thickness.

The manufacturing method of this gear is the same as that of the conventional gear described above. That is, when a molten material of plastic is injected into the mold from each gate 6, the injected molten material initially flows radially around the injection point, but eventually, as a whole, in the outer diameter direction of the disk portion 4. The molten material flowing in the inner diameter direction and the outer diameter direction fills the cavities of the teeth 1 and the rim 2, and the molten material flowing in the inner diameter direction fills the cavity of the boss 3. afterwards,
After cooling and solidification, the mold is released to complete a gear with the shape shown in the figure.

The gear of the present embodiment, in other words, the cavity of the mold for manufacturing the gear of the present embodiment has such a shape, and therefore, in each portion that affects the shape of the tooth portion 1. It is possible to make the degree of shrinkage uniform. That is, since the rim 2 is thickest in the connecting portion with the outer diameter portion of the disc portion 4 and gradually thinned in the vertical direction, it is located far from the gate 6. However, sufficient pressure is applied to the upper and lower ends to prevent the degree of contraction at those positions from increasing.
In addition, since the wall thickness of the rim 2 at the connection portion is smaller than the wall thickness at the gate position, it is possible to continue to apply a holding pressure to the connection portion without the gate position solidifying first. The degree of shrinkage at the connecting portion is not increased. Therefore, it is possible to manufacture the rim 2 and thus the tooth portion 1 into a desired shape.

Next, a second embodiment of the present invention will be described with reference to FIG. Although FIG. 3 is a sectional view, as can be seen from a comparison with FIG. 2, this embodiment is different from the first embodiment only in the cross-sectional shape of the disk portion 4. Therefore, the planar shape of this embodiment is substantially the same as that of FIG. In this embodiment, the thickness of the disk portion 4 is thickest at the position of the gate 6 and becomes thinner toward the outer diameter portion and the inner diameter portion. And the thickness of the outer diameter part is
It is thicker than the wall thickness of the rim 2 at the connecting portion.

Since this embodiment has such a shape, even when the diameter of the disk portion 4 is increased, the gate position is greater than the outer diameter portion of the disk portion 4 as compared with the case of the first embodiment. Is hard to be solidified first, and it is possible to keep sufficient pressure from the outer diameter portion and the inner diameter portion of the disc portion 4 to the gate position, so that the disc portion 4 is not twisted and the shape accuracy is high. A good gear can be manufactured. In the present embodiment, the wall thickness of the disk portion 4 is reduced from the position of the gate 6 toward the outer diameter portion, but it is formed so as to be gradually reduced from a predetermined diameter position. Can obtain the same effect.

A third embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a plan view of this embodiment, and FIG. 5 is a sectional view thereof. Also in the case of this embodiment, the shape of the disk portion 4 is different from that of the first and second embodiments,
The other shapes are substantially the same as those of the above-described embodiments. The disc portion 4 of the present embodiment includes an upper first disc portion 4A having an inner diameter portion, a lower second disc portion 4B having an outer diameter portion, and a step portion 4C therebetween. The gate trace 5 is formed on the first disk portion 4A.

Then, the thickness of the first disk portion 4A, the second
The thickness of the disc portion 4B and the thickness of the stepped portion 4C are uniform, but the thickness of the first disc portion 4A is the largest and the thickness of the stepped portion 4C and the second disc portion 4B becomes smaller in this order.
The wall thickness of the rim 2 and the relationship between the wall thickness of the rim 2 and the wall thickness of the second disk portion 4B are substantially the same as those in the first embodiment. In this embodiment, the disk unit 4 is thus divided into two parts.
Due to the stepped shape, it is possible to obtain a gear that is robust in comparison with the thickness of the disk portion 4.

Next, a fourth embodiment of the present invention shown in FIG. 6 will be described. The present embodiment is different from the third embodiment only in the cross-sectional shape of the disk portion 4. Therefore, the planar shape of this embodiment is similar to that of FIG. In this embodiment, the thickness of the disk portion 4 is thickest at the position of the gate 6 of the first disk portion 4A, and becomes thinner toward the outer diameter portion and the inner diameter portion. And
Regarding the relationship between the wall thickness of the outer diameter portion of the second disc portion 4B and the wall thickness of the rim 2 at the portion connected to the second disc portion 4B, the wall thickness of the outer diameter portion is formed larger. The disk portions 4 of the gears shown in the third and fourth embodiments are both two-stepped, but if the stepped portions on the outer diameter side are thinner, those disk portions 4 will have three steps. The shape may be more than a step.

Finally, a fifth embodiment of the present invention shown in FIGS. 7 and 8 will be described. 7 is a plan view of this embodiment, and FIG. 8 is a sectional view taken along the line AA of FIG. In each of the embodiments described so far, a boss for fitting with another shaft component is formed as the shaft portion of the gear, but in this embodiment, another bearing is used as the shaft portion. The rotary shaft 7 supported by the parts is integrally formed. Since the rotating shaft 7 is hollow, the top plate portion 8 is formed at one end portion and four ribs 9 are formed inside in consideration of strength and / or shape accuracy. Regarding the other points, the description of the third embodiment can be applied to this embodiment as it is, and therefore the description is omitted to avoid duplication.

Although the rotary shaft 7 is formed hollow in the present embodiment, when the rotary shaft 7 may be thin, such as when the gear is small, the present invention does not need to be hollow. The result of is obtained. Further, the rotary shaft 7 in this embodiment is
Although it has been shown that it is rotatably supported by the outer diameters of the upper and lower ends, the lower end of the rotary shaft 7 may be supported by another shaft member at the inner diameter except for the rib 9. Further, by doing so, a gear having a cantilever structure with only the lower end portion may be formed. Furthermore, it is not necessary to provide the top plate portion 8 on the rotary shaft 7. When the top plate portion 8 is not provided and the rotary shaft 7 is long, it is possible to pull out the mold pieces inside the rotary shaft 7 from both sides of the rotary shaft 7 when the mold is opened. It will be possible.

Further, in each of the above-mentioned embodiments, the positions of the gates 6 are arranged on the one surface of the disk portion 4 in the same circumference and at equal intervals, but the arrangement is strictly made. It does not have to be evenly spaced, and may be slightly deviated.

[0020]

As described above, according to the present invention, an injection-molded gear having a disk portion whose both sides are thinned can be accurately formed into a desired shape without being deformed by contraction during molding. can do.

[Brief description of the drawings]

FIG. 1 is a plan view of a first embodiment of the present invention.

FIG. 2 is a sectional view of the first embodiment of the present invention.

FIG. 3 is a sectional view of a second embodiment of the present invention.

FIG. 4 is a plan view of a third embodiment of the present invention.

FIG. 5 is a sectional view of a third embodiment of the present invention.

FIG. 6 is a sectional view of a fourth embodiment of the present invention.

FIG. 7 is a plan view of a fifth embodiment of the present invention.

FIG. 8 is a sectional view taken along line AA of FIG. 7;

FIG. 9 is a plan view of a conventional example.

10 is a cross-sectional view of the conventional example shown in FIG.

[Explanation of symbols]

 1, 11 Tooth portion 2, 12 Rim 3, 13 Boss 4, 14 Disc portion 4A 1st disc portion 4B 2nd disc portion 4C Step portion 5, 15 Gate mark 6, 16 Gate 7 Rotation shaft 8 Top plate portion 9 Rib

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuyuki Sakamaki 1-30-30 Namiki, Kawaguchi City, Saitama Enplus Corporation

Claims (5)

[Claims] 1. A cylindrical rim having an outer peripheral surface integrated with a plurality of teeth, and a disc portion having an outer diameter portion connected to a substantially intermediate portion in the axial direction of the rim and an inner diameter portion connected to the shaft portion. And a plastic injection-molded gear in which one surface of the disc portion is provided with a molten material injection portion on substantially concentric circles, wherein the disc portion has a same thickness on each concentric circle. And formed so that the thickness on the concentric circle on which the injection portion is provided is not thinner than the thickness on other concentric circles, and the thickness of the rim is the thickness of the outer diameter portion of the disc portion. An injection-molded gear made of plastic, characterized in that it is thinner than the outer diameter part, and is thinned as the connection part with the outer diameter part is maximized and further away. 2. The plastic injection-molded gear according to claim 1, wherein the disk portion is formed to have a substantially uniform wall thickness. 3. The plastic injection molding according to claim 1, wherein the disk portion is formed so that the wall thickness thereof gradually decreases from the injection portion toward the outer diameter portion. gear. 4. The plastic injection according to claim 1, wherein the disk portion is formed so that the wall thickness thereof gradually decreases from the injection portion toward the outer diameter portion. Molded gear. 5. The disc portion is formed in a stepped shape at a predetermined radial position so that the outer diameter portion and the inner diameter portion have different surfaces. The injection-molded gear made of the plastic described.