JPS6056095B2 - Injection molding method for slip gear bodies for watches - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an injection molding method for a slip gear body for a timepiece, and particularly for an injection molding method for a slip gear body for a timepiece, which is comprised of a shaft portion and a gear portion that is slip-coupled thereto. It is related to.

Prior Art A method for injection molding a slip gear body for a watch is disclosed in which a metal rotary wheel is fixed to a mold, and a shaft portion that is slip-coupled with the rotary wheel is injection molded using molten synthetic resin.

However, in this conventional method, since the rotary wheel is made of a metal member, manufacturing costs are high in order to maintain processing accuracy, and the rotary wheel must be accurately mounted on the mold during injection molding of the shaft. The disadvantage was that injection molding required a lot of time and labor.

For this reason, in recent years, it has been considered that both the shaft part and the gear part that is slip-coupled to the shaft part are injection molded from molten resin, and various resins have been used from the viewpoint of whether good slip torque can be obtained. That was tested.

Here, the slip torque refers to the coefficient of friction of the gear part with respect to the shaft part, the shrinkage rate of the gear part after molding, and the shrinkage rate of the gear part after molding.
This value is determined by the combination of the radius from the center of the shaft to the slip surface of the shaft. When using amorphous resins such as ABS resin (acrylonitrile butadiene styrene) and PS (polystyrene), the molding shrinkage rate is 0.2.
% to 0.8%, good slip torque can be obtained, but the mechanical strength is low and easy to break, so it cannot be used as a material for gear parts.

In addition, if the same material (for example, nylon 6) is used for the shaft and gear, the static friction coefficient of the gear against the shaft is too large, making it unsuitable as an injection molding material for slip gear bodies for watches. . Therefore, it has been confirmed that the following synthetic resins are suitable for the shaft portion and the gear portion. In other words, the material for the shaft must have wear resistance, high mechanical strength, and a higher melting temperature than the material for the gear, and for this purpose hard synthetic resins such as polyacetal and polycarbonate are required. is suitable. In addition, the material used for the gear part has a melting temperature lower than that of the material for the shaft part, has a relatively low shrinkage rate during the cooling process after the injection process, and has the strength to perform the rotation transmission function. , conditions such as a low coefficient of friction against the shaft are required, and for this purpose polyester elastomer,
Soft synthetic resins such as polybutylene terephthalate and nylon are suitable. However, simply selecting the materials for the shaft and gear parts in this way will result in problems, even if the gear parts are molded from synthetic resin with a low molding shrinkage rate.
Distortion occurs on the circumferential surface of the shaft that comes into contact with the gear, resulting in excessive slip torque.

In other words, when the molten resin is injected into the mold from the nozzle, the temperature of the circumferential surface of the shaft that comes into contact with the gear increases due to the shear heat generation phenomenon, and the circumferential surface of the shaft is pressed by the injection pressure. As a result, the circumferential surface of the shaft portion is deformed. The circumferential surface of the shaft that comes into contact with the gear becomes a slip surface, so if the circumferential surface of the shaft is deformed, it will no longer be possible to slip smoothly. That is, during one rotation of the gear part relative to the shaft part, there are parts where the frictional force is small and parts where it is large, resulting in a drawback that the overall slip torque becomes excessive. Purpose of the Invention The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to provide an injection molding method for a slip gear body for a watch that can be molded easily at low cost and with high precision. be.

Structure of the Invention In order to achieve the above object, the present invention injection molds a gear part made of a soft synthetic resin that is irremovably and slipably coupled to a shaft part made of a hard synthetic resin by an engaging part. In an injection molding method for a slip gear body for a watch, molten soft synthetic resin is injected through a gate placed near the tooth on the gear surface of the gear part, and a plurality of circles are formed between the gate and the shaft part. The injection direction is changed by injection direction conversion elements arranged in the circumferential direction, and injection is performed from around the gear part, and near the slip surface of the shaft part, molding is performed with molten resin whose temperature has decreased, and the shape of the shaft part is It is characterized by preventing temperature deformation.

Example Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a mold suitable for the injection molding method for a slip gear body for a watch according to the present invention. The shaft portion 12 having the rounded portion 10 as shown in FIG.
Injection molded from hard synthetic resin such as polyacetal.

As shown in FIG. 2, an engagement convex portion 18 is formed on the slip surface 14 of the shaft portion 12 for non-separably and slipably coupling with a gear portion 16 which will be injection molded later. The size of the engaging convex portion 18 is preferably such that the shaft portion 12 can be forcibly removed from a mold (not shown) during injection molding of the shaft portion 12. This is because, if the shaft portion 12 were molded using a mold using a slide core, the slide core would cause unevenness on the slip surface 14 of the shaft portion 12, and the slip torque would become excessive due to the unevenness. It is. Then, in the mold clamping process, the shaft part 12 is fixed to templates 20 and 22, and in the injection process, a soft synthetic resin such as molten nylon is injected into these templates 20 and 22, thereby forming the gear part 16 by injection molding. will be held.

In this case, the gate 24 serving as the injection port for the molten resin is arranged near the toothed portion 28 of the geared portion 26 of the geared portion 16, as shown in FIG. Further, between the gate 24 and the shaft portion 12 in the template 22, a plurality of injection direction changing elements 30 are arranged in the circumferential direction in order to change the injection direction of the molten resin injected from the gate 24. Ori,
In this embodiment, the injection direction changing element 30 is formed integrally with the template 22 so as to pass through the gear surface 26 of the gear portion 16 .

When the molten resin is injected from the gate 24, the molten resin bounces off each injection direction changing element 30 as shown by the arrows in FIG. Injection is performed from

As a result, in the vicinity of the slip surface 14 of the shaft portion 12, molding is performed using the molten resin whose temperature has decreased, and temperature deformation of the shaft portion 12 can be prevented as described later. In addition, as shown in FIG. 3, it is preferable that the injection direction changing elements 30 mentioned above have elements of the same shape arranged at equal intervals, so that the gear part 1 during injection molding can be
The shrinkage ratio of No. 6 is uniform throughout, and the optimum slip torque can be obtained. Further, one of the plurality of injection direction changing elements 30 is connected to a gate 24 as shown in FIG.
It is preferable that the molten resin be placed on a straight line connecting the shaft portion 12 and the molten resin, so that the molten resin is sufficiently injected around the gear portion 16 and then injected toward the periphery of the shaft portion 12. will be exposed. A mold suitable for the injection molding method of the present invention has the above configuration, and the injection molding method will be explained below.

First, in the mold clamping process, the shaft part 1 which has been injection molded in advance
2 are fixed to templates 20 and 22.

In this way, in this embodiment, since the shaft portion 12 is injection molded in advance from hard synthetic resin, there is no need to precision machine the gear portion made of metal material in advance as in the conventional method, which reduces manufacturing costs. I can do it. In addition, in this embodiment, the shaft portion 12 is easily fixed to the templates 20 and 22;
Since there is no need to fix the gear part as in the conventional method, the mold clamping process can be completed in a short time. Next, in the injection process, molten soft synthetic resin is injected into the mold plates 20 and 22 through the gate 24.

At this time, the molten resin injected from the gate 24 bounces off the plurality of injection direction conversion elements 30 as shown by the arrows in FIG. 3, and the injection direction is changed. will be held. After the molten resin is filled around the gear portion 16, the molten resin is injected toward the periphery of the shaft portion 12. As a result, the molten resin whose temperature has increased due to the shear heat generation phenomenon described above is
The temperature decreases slightly by the time it reaches the circumference of shaft part 1, and therefore
In the vicinity of the slip surface 14 of No. 2, molding is performed using a molten resin whose temperature has decreased, and temperature deformation of the shaft portion 12 can be prevented.

Next, in the cooling process, the molten resin injected into the templates 20 and 22 is cooled and solidified, and then in the mold opening process, the templates 20 and 22 are separated from each other, and then in the ejection process, the shaft part 12 and the gear A slip gear part consisting of section 16 is projected as a product.

In the above-mentioned embodiment, the engagement convex portion 18 for slip coupling with the gear portion 16 is formed on the slip surface 14 of the shaft portion 12, but as shown in FIGS. 4 and 5, It is also possible to form an engagement recess 32 in the slip surface 14 of the shaft portion 12.

Further, as shown in FIG. 6, the slip surface 3 of the shaft portion 12
4 may be formed in an inclined shape and a locking portion 36 may be provided on the upper portion of the slip surface 34.

In this case, the shaft portion 12 and the gear portion 16 are slidably connected by the slip surface 34, and are prevented from coming off by the locking portion 36. In each of the embodiments described above, a hard synthetic resin such as polyacetal is used as the injection molding material for the shaft portion 12, but fluorine powder may be mixed into this, thereby making the shaft portion 12 The coefficient of friction between the gear portion 16 and the gear portion 16 can be reduced. Effects of the Invention As explained above, according to the present invention, the shaft portion and the gear portion are each injection molded using an optimal synthetic resin, and the injection direction of the molten resin is changed to prevent temperature deformation of the shaft portion. , a trowel for easily molding a slip gear body for a watch at low cost, with high precision, and an optimum slip torque for the slip gear body can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a mold suitable for the injection molding method of a slip gear body for a watch according to the present invention, and FIG.
3 is a plan view of FIG. 1, FIG. 4 is a sectional view showing other slip coupling means for the shaft and gear parts, and FIG. 5 is an enlarged view of the vicinity of the slip surface shown in FIG. 4. FIG. 6, which is an enlarged view of the vicinity of the slip surface, is a cross-sectional view showing other slip coupling/coupling means for the shaft portion and the gear portion. 12...Shaft portion, 14...Slip surface, 16
... Gear part, 18... Engagement convex part, 20, 22.
...template, 24...gate, 26...
... Gear surface, 28 ... Teeth, 30 ... Injection direction conversion element, 32 ... Engagement recess, 34 ...
...Slip surface, 36...Locking part.

Claims (1)

[Claims] 1. In an injection molding method for a slip gear body for a watch, in which a gear part made of a soft synthetic resin is irremovably and slipably coupled to a shaft part made of a hard synthetic resin by an engaging part, The soft synthetic resin is injected from a gate placed near the tooth on the gear surface of the gear, and the injection direction is controlled by a plurality of injection direction changing elements arranged circumferentially between the gate and the shaft. A slip for a watch, characterized in that the molten resin is converted and injected from around the gear part, and molding is performed with molten resin at a lower temperature in the vicinity of the slip surface of the shaft part, thereby preventing temperature deformation of the shaft part. Injection molding method for gear bodies.