JP2000127205A - Plastic gear and molding thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for molding a plastic gear capable of keeping accuracy and rigidity. SOLUTION: In a plastic gear molding method, a thin-walled part is provided between the gear shape part 14 of an outer peripheral part and a center part and a rib 18 is arranged to this thin-walled part and a plastic gear 30 having an R-shape is molded to the connection part of the rib 18 and the gear shape part 14. In this case, the inside of the R-shape is molded into a hollow shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic gear requiring high rigidity and high precision, and a method for molding the same.

[0002]

2. Description of the Related Art Conventionally, in the case of a gear molded product made of plastic, a molded product having a solid tooth shape cannot be formed because sink marks are generated, and it is necessary to remove lightening. Therefore, rigidity for preventing deformation at the time of engagement has been maintained by providing a rib shape that supports the tooth shape.

[0003]

However, when the molded article has a rib shape, the thickness of the entire molded article tends to be uneven, and it is difficult to maintain the accuracy. Further, when the rib shape is pursued to maintain the accuracy, the thickness of the rib shape has to be reduced.

[0004] For the above reasons, it is necessary to increase the number of ribs in order to increase the rigidity at the time of engagement. It causes trouble.

Accordingly, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a plastic gear capable of maintaining accuracy and rigidity, and a method of molding the same.

[0006]

Means for Solving the Problems The above-mentioned problems are solved,
In order to achieve the object, a method of molding a plastic gear according to the present invention includes a lightening portion between a gear-shaped portion and a central portion of an outer peripheral portion, and disposing a rib in the lightening portion,
A method of forming a plastic gear for forming a plastic gear having an R shape at a connection portion between the rib and the gear shape portion, wherein the inside of the R shape is formed into a hollow shape.

Further, in the method for molding a plastic gear according to the present invention, the inside of the R-shape is molded into a hollow shape by flowing gas inside the R-shape.

In the method of molding a plastic gear according to the present invention, the gas is supplied into the cavity from a gate for injecting resin into a cavity of a mold for molding the plastic gear. Features.

Further, in the method for molding a plastic gear according to the present invention, a plurality of the gate portions are arranged at positions where the circumference of the gear is equally divided.

Further, the plastic gear according to the present invention has a lightening portion between a gear-shaped portion on an outer peripheral portion and a central portion, a rib is arranged in the lightening portion, and the rib and the gear-shaped portion are provided. A plastic gear having an R-shape at a connection portion with the portion, wherein the inside of the R-shape is molded into a hollow shape.

Further, in the plastic gear according to the present invention, by flowing gas inside the R shape,
It is characterized in that the inside of the R shape is formed in a hollow shape.

Further, in the plastic gear according to the present invention, the gas is supplied into the cavity from a gate for injecting a resin into a cavity of a mold for molding the plastic gear. .

Further, in the plastic gear according to the present invention, a plurality of the gate portions are arranged at positions equally dividing the circumference of the gear.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described. Before that, an outline of the present invention will be described.

In the present invention, in a plastic gear molded article having a rib for supporting a tooth shape, an R-shape is provided at a joint portion between the tooth shape portion and the rib portion in order to improve rigidity at the time of meshing of the teeth. Here, due to the presence of the R-shaped portion, the thickness becomes non-uniform, and the accuracy deteriorates.
By injecting gas into the shape part and making it hollow, the contraction rate of the joint between the tooth shape part and the rib is suppressed, the same shape as the other tooth shape part is maintained, and the accuracy of the entire tooth shape is maintained .

Further, by providing a gas channel through which the gas flows in the R-shaped portion, the gas injection molding can be performed, and the precision of a molded product which requires precision in the radial direction such as a gear molded product can be reduced. Enables sustained molding methods.

Hereinafter, description will be made with reference to the drawings.

FIGS. 1A and 1B are views showing the shape of a gear before the present invention is implemented. FIG. 1A is a plan view of the gear as viewed from above, and FIG. It is the side view which made the cross section seen from.

In FIG. 1, a gear 10 has a central portion 12
And a cylindrical gear-shaped portion 14 on the outer periphery are connected to a flange portion 16 extending in the horizontal direction by ribs 18 and 20. Eight ribs 18 are formed so as to divide the circumference equally, and four ribs 20 are formed so as to equally divide the circumference. The central portion 12 and the gear shape portion 14 are formed with lightening portions 22 and 24 for making the thickness of the molded product uniform.

On the upper surface of each of the four ribs 20, a mold gate 26 is located, and from this gate 26, molten resin is introduced into a mold cavity having a shape matching the shape of the gear 10. Be injected.

Next, a method of forming a gear according to an embodiment based on the shape shown in FIG. 1 will be described.

First, the shape of the molded product shown in FIG. 1 is deformed, and a deformation amount when a constant load is applied is obtained assuming a shape having twelve thin ribs as shown in FIG.

Next, consider adding an R-shape to the portion B in FIG. 2, that is, the connecting portion between the rib 18 and the gear-shaped portion 14. Points P1, P2, P for each shape
FIG. 3 shows the amount of deformation at 3.

From the results shown in FIG. 3, the shape of the portion B is R = 2.0.
It can be seen that the rigidity is improved by 5% with respect to the conventional shape at the time of mm.

However, in the case of the R shape at this time, in the case of normal molding, a difference in shrinkage due to uneven thickness occurs, and accuracy is not obtained. Therefore, injection of gas during molding is considered.

In order to guide the gas to a desired portion, a gas flow path for facilitating the gas flow, that is, a gas channel is required. The setting location and shape of the gas channel will be described below.

The gas tends to flow into a place where the plastic resin easily flows. That is, it flows to the place where the pressure difference of the resin in the cavity occurs.

As a means for confirming the ease of resin flow, a method based on simulation calculation is appropriate, and the description will be made accordingly.

FIGS. 4 and 5 are diagrams showing the results of simulation calculation of the distribution of the resin flow. In this figure, it is shown that the lighter the color, the easier the resin flows. The portion where the resin easily flows has a property that gas is easily introduced. Here, means for positively flowing gas into the rib shape is considered.

Specifically, referring to the portion of FIG. 4 where the resin easily flows, it is considered to add an R shape to the portion where the gas easily flows, that is, the portion where the gas channel is easily formed. The gas is injected into the cavity from the gate 26 together with the molten resin. As the gas, an inert gas such as nitrogen is used.

First, from the flow results in the cross-sectional shape of FIG. 5, it can be expected that gas channels are likely to be formed at the positions indicated by the thick lines in FIGS.

As described above, it is necessary to add a shape similar to the R shape added to the joint portion between the tooth portion and the rib portion for improving rigidity at a position where the gas channel shown in FIGS. 5 and 6 is easily formed. Think.

The R shapes are set at the positions shown by the thick lines in FIGS. 5 and 6 so that the gas is positively flowed.
We aim to maintain accuracy. That is, the inside of the R shape is made hollow by gas.

Incidentally, reference numeral 30 in FIG. 6 denotes a plastic gear of this embodiment to which an R shape is added.

The shape of the plastic gear described above is applied to the range of the shape shown in FIG.

The size of the added R shape is set in the range of R1 to R5 depending on the thickness of the tooth bottom.

As an example applied this time, POM is used as a material, and various conditions are as shown in FIG.

As a result of molding the plastic gear under these conditions, a plastic gear having high accuracy and high rigidity was able to be molded.

It should be noted that the present invention can be applied to a modification or modification of the above embodiment without departing from the gist thereof.

[0040]

As described above, according to the present invention, a plastic gear having high accuracy and high rigidity can be formed.

[0041]

[Brief description of the drawings]

FIG. 1 is a view showing a shape of a plastic gear before embodying the present invention.

FIG. 2 is a view showing a state in which an R shape is added to a connection portion between a rib and a gear shape portion.

FIG. 3 is a diagram showing a deformation amount with respect to a load due to a difference in R shape.

FIG. 4 is a diagram showing a distribution of resin flow.

FIG. 5 is a cross-sectional view showing a distribution of resin flow.

FIG. 6 is a view showing a shape of a plastic gear of one embodiment.

FIG. 7 is a diagram showing a range of a shape of a plastic gear.

FIG. 8 is a view showing molding conditions of a plastic gear of one embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Gear 12 Central part 14 Gear shape part 16 Flange part 18,20 Rib 22,24 Lightening part 26 Mold gate

Claims (8)

[Claims] An outer peripheral portion has a lightening portion between a gear-shaped portion and a central portion, a rib is disposed in the lightened portion, and an R-shaped portion is formed at a connecting portion between the rib and the gear-shaped portion. A method for molding a plastic gear for molding a plastic gear having the following, wherein the inside of the R shape is molded into a hollow shape. 2. The method according to claim 1, wherein the inside of the R shape is formed into a hollow shape by flowing a gas inside the R shape. 3. The plastic gear according to claim 2, wherein the gas is supplied into the cavity from a gate for injecting a resin into a cavity of a mold for molding the plastic gear. Molding method. 4. The plastic gear molding method according to claim 3, wherein a plurality of the gates are arranged at positions where the circumference of the gear is equally divided. 5. An outer peripheral portion has a lightening portion between a gear-shaped portion and a central portion, a rib is disposed on the lightened portion, and an R-shaped portion is formed at a connecting portion between the rib and the gear-shaped portion. A plastic gear, characterized in that the inside of the R shape is formed into a hollow shape. 6. The plastic gear according to claim 5, wherein the inside of the R shape is formed into a hollow shape by flowing a gas inside the R shape. 7. The plastic gear according to claim 6, wherein the gas is supplied into the cavity from a gate portion for injecting a resin into a cavity of a mold for molding the plastic gear. . 8. The plastic gear according to claim 7, wherein a plurality of the gate portions are arranged at positions equally dividing the circumference of the gear.