JPH0356885B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming a bearing directly mounted on a plastic base plate (hereinafter referred to as a plastic base plate).

Conventionally, in analog clocks, the part on which gears, bridges, calendar parts, etc. are mounted is called the main plate, and the material used is metal, generally brass.
However, manufacturing such a metal main plate requires a lot of machinery, tools, personnel, space, and man-hours, so it has been a long-held dream of the watch industry to drastically streamline the process. As a means to make this dream a reality, we thought of using highly productive thermoplastics to manufacture the main plate, which previously required many processes, in a single process called ``injection molding.'' Based on this idea, a plastic base plate for mechanical watches was developed several years ago, but it was not widely used due to various drawbacks such as durability and reliability.
However, today, with the introduction of quartz watches, improvements in plastic materials, and the demand for inexpensive watches, plastic plates have once again come to the fore. Moreover, in the case of quartz electronic watches,
Unlike mechanical watches, the lateral force from the mainspring is not applied to the bearings through the gears, and the gears simply transmit rotation, so bearings installed directly on the plastic base plate can also be sufficiently durable and can be used advantageously. It became.

As mentioned above, a bearing structure directly installed on the plastic base plate became possible and rationalized. but,
As shown in Fig. 1, the bearing structure has a structure in which an oil reservoir 2 and a shaft hole 3 are simultaneously molded on a plastic base plate 1, and the oil reservoir 2 is located opposite to the side on which the gear is mounted. It will be formed on the side. Therefore, in the mold for forming the plastic base plate 1, the mold structure for forming the above-mentioned straight hole is a small diameter pin (140 to 160μ) for forming the shaft hole.
and a protrusion (both not shown) for forming the oil reservoir part 2 are divided into upper and lower molds. Therefore, when finishing the mold, it takes time to adjust the abutment between the small diameter pin and the protrusion in order to prevent burrs from appearing during molding, and if the abutment is too strong, the fine Breakage and cracking of the diameter pins occur, resulting in a decrease in yield, and further disadvantages include a decrease in machine engagement ratio and an increase in mold repair time.

In addition, even if the adjustment of the abutment between the small diameter pin and the protrusion is well done, as the number of production increases during mass production, burrs 4 will occur in the shaft hole as shown in Figure 2, which will reduce the reliability of the watch. It had the disadvantage of causing problems.
An object of the present invention is to provide a plastic base plate with good productivity by devising a bearing structure in order to eliminate the above-mentioned drawbacks. The gist of the present invention for achieving the above object is to mold a plastic base plate forming at least a bearing, leaving a thin film forming a substantially blind hole at the bottom of the shaft hole constituting the bearing, The thin film has a thick part in the center, and a connecting part between the thick part and the vicinity of the bottom of the shaft hole, which is thinner than the thick part and narrower in width than the thick part. , the thin film is removed after the bearing is molded to form a through hole.

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 3 is a sectional view of the bearing according to the present invention, and as shown in section A, when the plastic base plate 1 is formed, a thin film 5 is also formed between the shaft hole 3 and the oil reservoir 2 at the same time. From the perspective of the mold structure, the thin film 5 during molding
The fact that is formed means that the small diameter pin and the protrusion for forming the bearing do not abut, but there is a gap corresponding to the thin film 5.

Therefore, no time is required for adjusting the mold, and breakage and shattering of small diameter pins do not occur.

FIG. 4 is an enlarged view of part A in FIG. 3, and the cross-sectional shape of the thin film 5 has a relatively rigid thick part in the center, and a connecting part 6 connecting the thick part to the inner periphery of the bottom of the shaft hole.
is formed. The thickness of the thin film 5 in the connecting portion 6 is approximately 50 to 100 μm, and the thick portion is approximately 4 to 5 times that of the connecting portion 6. Further, the length of the connecting portion 6 should be about the same as the thickness in consideration of processing variations, but the smaller the length, the better because it will not leave any burrs. If it is too long, there will be a lot of burrs left behind when it is pushed down.

In order to form the thin film 5 having the above shape, it is sufficient to make the small diameter pin somewhat shorter than the shaft hole, and to form a concave shape in the protrusion for forming the oil reservoir 2. Of course, the protrusion of the thick portion of the thin film 5 may be located inside the shaft hole.

Since the shape of the thin film 5 is formed by a thick part and a connecting part 6 that is thinner than the thick part, when the thin film 5 is pushed down with a jig 7 or a gear shaft, the thick part is not cut and only the connecting part 6 is cut. If the length of the connecting portion 6 is appropriately selected, the shaft hole can be formed with almost no burrs remaining in the shaft hole.

FIG. 5 shows the state in which the thin film 5 is dropped by the jig 7. That is, the shaft hole 3 is formed without abutting the small diameter pin, and then the thin film 5 at the bottom is pushed down to form a through hole, and the jig 7 is not used, and the gear shaft is directly inserted into the gear shaft when assembling the gear train. It is also possible to drop the thin film. In any case, by dropping the thin film 5, a through hole is formed and a bearing is formed.

As described above, according to the present invention, by creating a structure in which the small diameter pin of the mold and the protrusion do not come into contact with each other when forming the bearing on the plastic base plate, a thick part is formed in the center of the bottom of the shaft hole.
Since we have formed a connection part around the periphery that is thinner and narrower than the thick part, even if you press it with a shaft that is thin and has a sharp tip like a clock, the thin film will only be cut at the connection part, and the thick part will not be cut. Since the burr can be removed while leaving the shape intact, the burr can be easily removed and the through hole can be formed without any effect on the rotation of the shaft of the timepiece wheel train. Moreover, there is no need for mold adjustment time, and molding yield is improved.
Significant effects were obtained, including a significant improvement in machine operating rates and a reduction in mold repair time.

[Brief explanation of drawings]

1 and 2 are a sectional view and a plan view showing a conventional bearing structure, FIG. 3 is a sectional view of the bearing structure of the present invention, FIG. 4 is an enlarged view of section A in FIG. 3, and FIG. 5 FIG. 2 is a cross-sectional view illustrating a method for removing a thin film. 1... Plastic base plate, 2... Oil reservoir, 3... Shaft hole, 5...
Thin film.

Claims (1)

[Claims] 1. At least a plastic base plate on which a bearing is formed has a thick part in the center so that the bottom of the bearing hole constituting the bearing is a substantially blind hole; Forming a thin film between the inner wall of the bottom of the hole and having a connecting portion having a thickness thinner than the thick wall portion and a width narrower than the wall thickness of the thick wall portion,
A method for forming a bearing in a plastic base plate, characterized in that after forming the bearing, the thin film is removed to form a through hole.