JPS6153212B2 - - 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, particularly for an injection molding method for a slip gear body for a timepiece, which comprises a shaft portion and a gear portion that is slip-coupled thereto. It is related to.

PRIOR ART There is a well-known injection molding method for slip gear bodies for watches, in which a metal rotary wheel is fixed to a mold, and a shaft portion that is slip-coupled to the rotary wheel is injection molded using molten synthetic resin. It is disclosed in Publication No. 55-29828.

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-connected to the shaft part are injection molded using molten resin, and various resins have been used from the viewpoint of whether good slip torque can be obtained. That was tested. Here, slip torque is a value determined by a combination of the coefficient of friction of the gear against the shaft, the shrinkage rate of the gear after molding, and the radius from the center of the shaft to the slip surface of the shaft. It is.

ABS resin (acrylonitrile, butadiene,
When using amorphous resins such as (styrene) or PS (polystyrene), the molding shrinkage rate is small at 0.2% to 0.8%, so good slip torque can be obtained, but the mechanical strength is low and it is easy to break. Therefore, it cannot be used as a material for gear parts.

Furthermore, if the same material (for example, 6 nylon) 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 materials for the shaft and gear parts in this way will cause distortion on the peripheral surface of the shaft part that comes into contact with the gear parts, even if the gear parts are molded from synthetic resin with a low molding shrinkage rate. This resulted in a drawback that the slip torque became excessive.

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. Since the peripheral surface of the shaft that comes into contact with the gear becomes a slip surface, if the peripheral 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 provides an injection molded 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 the injection molding method for slip gear bodies for watches, molten high-temperature soft synthetic resin is injected from a gate placed near the teeth on the gear face of the gear part, and is injected into the vicinity of the slip face of the shaft part in advance. Due to the protrusion formed integrally with the template and the injection direction changing elements arranged in the circumferential direction between the gate and the shaft of the template, large injection resistance is applied, and the injection direction near the slip surface of the shaft is To extend the time it takes to reach
The soft synthetic resin is injected and molded from around the gear portion first, and the molten resin at a lower temperature is molded near the slip surface of the shaft portion, thereby preventing temperature deformation of the shaft portion. do.

Embodiments Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 shows an embodiment of a mold suitable for the injection molding method of a slip gear body for a timepiece according to the present invention.

A shaft portion 12 having a pinion portion 10 as shown in FIG. 1 is injection molded in advance from a hard synthetic resin such as polyacetal. Slip surface 1 of shaft portion 12
4 includes an engaging convex portion 1 for non-releasably and slippably coupling with the gear portion 16 to be injection molded later.
8 is formed. The size of the engagement convex portion 18 is
A suitable size is such that the shaft portion 12 can be forcibly removed from a mold (not shown) during injection molding of the shaft portion 12. That is, if the shaft part 1
2 is molded using a mold using a slide core, the slip surface 14 of the shaft portion 12 has unevenness due to the slide core, and the slip torque becomes excessive due to the unevenness.

Then, in the mold clamping process, the shaft portion 12 is attached to the mold plate 2.
0 and 22, and injection molding of the gear portion 16 is performed by injecting molten soft synthetic resin such as nylon into these mold plates 20 and 22 during the injection process. In this case, the gate 24 serving as the injection port for the molten resin is connected to the gear portion 1 as shown in FIG.
It is arranged near the tooth portion 28 on the gear surface 26 of No. 6. Further, in the vicinity of the slip surface 14 of the shaft portion 12, protrusions 30 and 32 are previously formed integrally with the mold plates 20 and 22, respectively. Then, the molten resin injected from the gate 24 from a nozzle (not shown) via the spool and runner is temporarily applied to the slip surface of the shaft portion 12 by the protrusions 30 and 32 as shown by arrows (solid lines) in FIG. Injection into the vicinity of the gear portion 14 is prevented, and injection is first performed around the gear portion 16. As a result,
In the vicinity of the slip surface 14 of the shaft portion 12, molding is performed using molten resin at a reduced temperature.
As will be described later, temperature deformation of the shaft portion 12 can be prevented.

Furthermore, the gate 24 and the shaft portion 12 in the template 22
In order to change the injection direction of the molten resin injected from the gate 24, a plurality of injection direction changing elements 34 as shown in FIG. In the example, the injection direction changing element 34 is formed integrally with the template 22 so as to pass through the gear face 26 of the gear part 16 .

The molten resin injected from the gate 24 is temporarily prevented from being injected into the vicinity of the slip surface 14 of the shaft portion 12 by the protrusions 30 and 32, but if the molten resin is injected into the vicinity of the slip surface 14 of the shaft portion 12 Even if an attempt is made to do so, the injection collides with each injection direction converting element 34 and bounces off as shown by the arrow (dotted line) in FIG. 2, and the injection direction is changed to ensure injection from around the gear portion 16.

Note that, as shown in FIG. 2, it is preferable that the injection direction changing elements 34 mentioned above have elements of the same shape arranged at equal intervals, thereby reducing the shrinkage rate of the gear part 16 during injection molding. It becomes uniform throughout, and optimal slip torque can be obtained. Further, one of the plurality of injection direction changing elements 34
As shown in FIG. , injection will be performed toward the periphery of the shaft portion 12.

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 a mold clamping step, the shaft portion 12, which has been injection molded in advance, is fixed to the mold plates 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. Furthermore, in this embodiment, it is only necessary to fix the shaft part 12 to the mold plates 20 and 22, and there is no need to fix the gear part as in the conventional method, so that the mold clamping process can be completed in a short time. .

Next, in the injection process, molten soft synthetic resin is injected into the templates 20 and 22 through the gate 24. At this time, the molten resin injected from the gate 24 is temporarily prevented from being injected into the vicinity of the slip surface 14 of the shaft portion 12 by the protrusions 30 and 32, as shown by arrows (dotted lines) in FIG. Even if the resin is injected into the vicinity of the slip surface 14 of the shaft portion 12, it hits the plurality of injection direction changing elements 34 and rebounds, as shown by arrows (solid lines) in FIG. 2, and the injection direction is changed. Therefore, the injection is first performed around the gear part 16, and after the molten resin is filled all around the gear part 16, it is injected toward the slip surface 14 of the shaft part 12.

As a result, the temperature of the molten resin whose temperature has increased due to the above-mentioned shear heat generation phenomenon decreases slightly by the time it reaches the periphery of the shaft portion 12, and therefore, the temperature of the molten resin that has decreased near the slip surface 14 of the shaft portion 12 cannot be molded. As a result, 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 body consisting of section 16 is ejected as a product.

In the above-mentioned embodiment, the slip surface 14 of the shaft section 12 is formed with an engagement protrusion 18 for slip coupling with the gear section 16, but the slip surface 14 of the shaft section 12 is formed with an engagement recess. It is also possible to form

It is also possible to form the slip surface 14 of the shaft portion 12 in an inclined shape and provide a locking portion at the upper part of the slip surface 14. In this case, the shaft portion 12 and the gear portion 16 are slidably connected by the slip surface 14, and are prevented from coming off by the locking portion.

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 also be mixed into this, thereby forming the shaft portion 12. The coefficient of friction between the gear portion 12 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 by staggering the injection timing of the molten resin to prevent temperature deformation of the shaft portion, A slip gear body for a timepiece can be easily molded at low cost with high precision, and an optimum slip torque can be obtained for the slip gear body.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a mold suitable for the injection molding method for a slip gear body for a timepiece according to the present invention, and FIG. 2 is a plan view of FIG. 1. 12... Shaft portion, 14... Slip surface, 16...
Gear portion, 18... Engaging convex portion, 20, 22... Template, 24... Gate, 26... Gear surface, 28...
Tooth portion, 30, 32...Protrusion portion.

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 gear part is The molten high-temperature soft synthetic resin injected from the gate located near the tooth on the gear surface is applied to a protrusion that is preliminarily formed integrally with the template near the slip surface of the shaft, and The injection direction changing elements arranged circumferentially between the gate and the shaft in the template receive a large injection resistance, and the time taken to reach the vicinity of the slip surface of the shaft is extended. A watch characterized in that injection and molding are performed around the gear part first, and molding is then performed with molten resin at a lower temperature near the slip surface of the shaft part, thereby preventing temperature deformation of the shaft part. Injection molding method for slip gear bodies.