JPS6347563A - Plastic molding gear - Google Patents

Abstract

PURPOSE:To improve mechanical accuracies including a space deflection and an intermeshing pitch error or the like, by shifting each position of symmetrical ribs, and installing an axial metal relief hole in an arm part of a part where the rib is coupled with a rim part. CONSTITUTION:A shaft clamping boss part 5 is clamped to a shaft 7 with knurling 10, while an arm part 8 is installed in the circumference, and furthermore a rim part 2 and a gear 3 are installed in the circumference. Symmetrical ribs 4 and 6 differing in each position are installed in this arm part 8, and furthermore an axial metal relief hole 1 is installed in a part where these ribs 4 and 6 are coupled with the rim part 2, molding all of them as one body. And, torque out of the gear 3 is transmitted to the shaft 7 via the rim part 2, the arm part 8 and a clamping boss part 5, but since this arm part is thin, occurrence of a mold cavity lowering strength and draw deformation in the central direction of a gear shaft direction central part 9 both are preventable and, what is more, unequalization in central direction contraction of these reinforced ribs 4 and 6 is also relieved. Thus, such a plastic molding gear that is more than the five grade of mechanical accuracy is securable inexpensively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gear of a speed reducer connected to a small mold, and particularly to a structure suitable for improving the accuracy of a plastic molded gear.

[Conventional technology]

Numerous examples of plastic molded gears are well known.

[Problem that the invention seeks to solve]

There are generally two methods for manufacturing gears for reduction gears: a cutting method using a hobbing machine, etc., and a plastic molding method. The former generally makes it possible to obtain highly accurate gears, and can also be applied to steel gears that require strength. However, in terms of productivity, it is significantly inferior to the latter manufacturing method. Although plastic molded gears have very high productivity, they have the drawbacks of inferior precision and lower strength than steel gears. This is because the molding shrinkage rate of plastic is large, and if the tooth width is made large to increase the strength of the gear, cavities will occur and the required strength will not be obtained.Therefore, the wall thickness of the arm part, etc. must be made thinner. It will disappear forever. Normally, ribs are provided to reinforce this thin part. When ribs are provided, the cross-sectional wall thickness of the arm part becomes uneven, the molding shrinkage rate becomes uneven, and the shrinkage toward the center of the gear part varies, resulting in deformation of the gear. However, there is a problem in that the meshing pitch error accuracy and the tooth groove runout accuracy of the gears, which greatly affect noise, are significantly lowered.

An object of the present invention is to obtain a highly accurate plastic molded gear for a reduction gear.

[Means for solving problems]

The above purpose is to shift the position of the left and right ribs.

This is achieved by providing an axial relief hole in the arm section where the rib joins the rim section.

[Effect]

During plastic molding, shrinkage stress is generated toward the center, and if ribs or the like are present, that part becomes thicker, which delays hardening and causes uneven shrinkage, which ultimately reduces the mechanical precision of the gear.

When the left and right rib positions are mismatched, the wall thickness can be made more uniform without reducing the rib effect compared to when the rib positions are matched.
The shrinkage rate and residual stress are made uniform, and strain in the gear part can be alleviated.

Furthermore, by providing a relief hole for the connecting part of the rim of the rib, the cross-sectional area of the connecting part becomes smaller, which equalizes the curing time, reduces the shrinkage tensile force toward the center, and allows for high-precision gears. can get.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

A shaft fastening boss part 5 is fastened to a shaft 7 provided with a knurling 10, an arm part 8 is provided on the outer periphery of this shaft fastening boss part 5, a rim part 2 and a gear 3 are provided on the outer periphery of this arm part 8, and the arm The portion 8 is provided with left and right ribs 4 and 6 whose positions do not match, and furthermore, the portion where the rib 4.6 connects with the rim portion 2 is provided with an axial meat relief hole 1 in the arm portion 8,
All of these are integrally molded.

The torque transmitted to the gear 3 is transmitted to the rim portion 2° and the arm portion 8. It has a structure in which it is transmitted to the shaft 7 via the shaft fastening boss portion 5.

The arm portion 8 has a thin wall and is reinforced by ribs 4 and 6 in order to prevent the occurrence of cavities that would significantly lower the strength and sinkage deformation of the central portion 9 in the axial direction of the gear toward the center.

According to this embodiment, it is possible to alleviate the non-uniform contraction in the center direction due to the ribs 4.degree. 6, which is necessary for reinforcement, so that a highly accurate gear can be obtained.

〔Effect of the invention〕

According to the present invention, a plastic molded gear with mechanical accuracy of grade 5 or higher in terms of tooth groove runout, meshing pitch error, etc. can be obtained, and the price is about 1/3 or less compared to a cutting gear.

[Brief explanation of drawings]

1 to 4 show an embodiment of the present invention, in which FIG. 1 is a left side view showing the arrangement of ribs and meat relief holes, FIG. 2 is a cross-sectional view of the upper part of FIG. FIG. 3 is a right side view of the same, and FIG. 4 is a sectional view of the upper part B in FIG. 1. 1...Meat relief hole, 2...Rim part, 3...Gear,
4... Left side rib, 5... Shaft fastening boss part, 6... Right side rib, 7... Shaft, 8... Arm part, 9... Gear axial direction center part, 10... Knurling.

Claims (1)

[Claims] 1. A gear integrally molded with plastic on a rim, an arm integrally molded with the rim on the inner circumferential side thereof, and a fastening boss part integrally molded with the arm part to the gear shaft; In a gear assembly in which an arm for connecting a rim and a boss is provided with radial reinforcing ribs in the outer circumferential direction on the left and right sides of the arm, the positions of the left and right ribs do not match on the left and right, and A plastic molded gear characterized in that, in the rim connecting portion, an axial relief hole is provided in the arm portion to partially disconnect the arm portion from the rim portion.