JPH0435139Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention relates to a mold for molding plastic gears used in the train of a watch. This invention relates to a mold for forming plastic gears used in the wheel train of an analog electronic watch driven by a motor.

[Prior Art] In an analog electronic timepiece driven by a step motor, the rotor is driven to step intermittently, and the rotor moves intermittently between the rotor pinion and the meshing gear. A ticking sound occurs.

As a measure to prevent or suppress the generation of this ticking sound, for example, German Published Patent No. 2263430,
BACKGROUND OF THE INVENTION Gears having a structure as disclosed in Japanese Patent No. 2419189 or Japanese Patent No. 2425495 are known. This is achieved by forming elastic arms extending in the radial direction through slits in the gear, and protruding teeth on the same plane at the tip of each elastic arm, so that the elastic arm rotates relative to the axis of the gear. By elastically displacing in the direction, the impact at the time of meshing is absorbed. Gears for this purpose are generally molded using soft plastic such as polyacetal or polyester elastomer in order to further improve shock absorption.

[Problem to be solved by the invention] The plastic gears with a known special structure are very effective in preventing the sound and absorbing shocks that occur when the rotor is stepped in steps. The gears used are generally of fairly small diameter, and the width of the slit is accordingly very small.
Moreover, since such gears are driven with low torque, the meshing efficiency cannot be reduced, and therefore, unlike ordinary plastic parts, it is virtually impossible to adopt too large a draft angle. For this reason, as mentioned above, soft plastics are sometimes used as materials, which tend to be difficult to separate from the mold during injection molding, and the pull-out resistance during molding causes the elastic arms to There was a problem in that it was deformed.

Therefore, an object of the present invention is to provide a gear molding die that prevents deformation of the molded product and allows smooth release of the molded product when ejecting the plastic gear from the mold. There is a particular thing.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a first mold provided with a cavity corresponding to a plurality of elastic arms extending in the radial direction; A second mold is provided, which faces the mold and is provided with a cavity corresponding to a tooth portion protruding radially from the tip of the elastic arm. The facing surface of the first mold and the second mold is the separation surface of the mold, and the side end surface forming the cavity corresponding to the elastic arm of the first mold has the first elastic arm. In order to enable smooth release from the second mold, a relatively large draft angle is provided compared to the side end surface constituting the cavity corresponding to the teeth of the second mold.

[Examples] Hereinafter, details of the present invention will be explained along with examples shown in the accompanying drawings.

Figures 1 and 2 show a plastic gear integrally injection molded using a gear mold according to the present invention, and the plastic gear is made of soft plastic such as polyacetal or polyester elastomer. There is. The plastic gear has an elastic arm 2 having teeth 1.
A pinion 3 and shaft ends 4 and 5 are provided.

The elastic arm 2 is formed to extend in the radial direction by forming a slit 6 from the outer periphery toward the center. and each elastic arm 2
Due to the presence of the slits 6 between the gears, the gears can be elastically displaced in the rotational direction (circumferential direction) of the gears, thereby absorbing the impact during meshing. The tooth portion 1 is formed on one side (upper surface in FIG. 1) of the tip of each elastic arm 2 so as to protrude in the radial direction from the tip surface of the elastic arm 2. That is, as can be clearly understood from FIG. 1, the tooth portion 1 and the elastic arm 2 are at different levels when viewed from the side.

In order to injection mold a plastic gear having the above-mentioned structure, the following innovations have been made to the mold.

In FIG. 3, numeral 7 is a stationary mold plate as an example of a first mold constituting a mold for molding plastic gears, and 8 is a movable mold plate as an example of a second mold. The opposing surfaces of the two serve as the separation surface 9 of the mold. The templates 7 and 8 have a cavity 7a corresponding to the elastic arm 2 and a cavity 8 corresponding to the tooth 1 shown in FIGS.
a are formed respectively. Of course, although not shown in the drawings, the templates 7 and 8 also include cavities and shaft ends 4 corresponding to the pinion 3 and shaft ends 5.
Needless to say, each has a corresponding cavity. As shown in FIG. 4, side end surfaces 8b, 8b forming the cavity 8a
In order to maintain a predetermined meshing efficiency of the teeth 1 (see Figures 1 and 2), the draft angle is kept extremely small.
b and 7b are provided with a necessary and sufficient draft angle so that the elastic arm 2 (see FIGS. 1 and 2) can be smoothly released from the mold plate 7. In other words, according to the gear mold having the structure of the present invention, it is possible to provide different appropriate draft angles to each of the mold plates 7 and 8 for injection molding plastic gears. . As a result, when pulling out the molded plastic gear from the mold,
Since the easily deformable elastic arm 2 can be smoothly released from the mold plate 7, the elastic arm 2 is not bent accidentally.

[Effects of the invention] The present invention having the above-described configuration provides a first mold with a cavity corresponding to a plurality of elastic arms extending in the radial direction, and a second mold with a cavity facing the first mold. , a cavity corresponding to the teeth protruding in the radial direction from the tip of the elastic arm is provided, the facing surface of the first mold and the second mold is used as the separation surface of the mold, and the elasticity of the first mold is The elastic arm is attached to the side end surface forming the cavity corresponding to the arm, so that the elastic arm can be smoothly released from the first mold. Since a large draft angle is provided, when the plastic gear as a molded product is extracted from the mold, the plastic gear can be smoothly released from the mold, thereby preventing deformation of the plastic gear.

[Brief explanation of the drawing]

Fig. 1 is a side view showing the left half of a plastic gear integrally injection-molded using the gear molding die according to the present invention, Fig. 2 is a plan view of the same plastic gear, and Fig. 3 is the same as above. FIG. 4 is an enlarged sectional view taken along the line of FIG. DESCRIPTION OF SYMBOLS 1... Teeth, 2... Elastic arm, 7... First mold, 7b... Side end surface forming a cavity corresponding to the elastic arm of the first mold, 8... Second mold , 8b... side end surface forming a cavity corresponding to the teeth of the second mold, 9... separation surface.

Claims (1)

[Scope of Claim for Utility Model Registration] A first mold provided with a cavity corresponding to a plurality of elastic arms extending in the radial direction; and a second mold provided with a cavity corresponding to the teeth protruding in the direction, and the facing surface of the first mold and the second mold is a separation surface of the mold, The side end surface of the cavity corresponding to the elastic arm of the first mold is provided with the teeth of the second mold so that the elastic arm can be smoothly released from the first mold. A relatively large draft angle is provided compared to the side end surface constituting the cavity corresponding to the cavity. A gear molding die characterized by: