JPH0790571B2 - Method for manufacturing hollow cylindrical molded product made of synthetic resin - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a synthetic resin hollow cylindrical molded product using a high pressure gas injection technique.

[0002]

2. Description of the Related Art There are various functional parts to be driven which have a disk or cylindrical shape. When manufacturing disk-shaped functional parts such as gears and pulleys with synthetic resin,
A method is used in which a molten synthetic resin is injected into a molding chamber of a mold, cooled, solidified, and then taken out from the mold. In the production of such synthetic resin gears and the like, the cooling time is proportional to the square of the wall thickness, so that the average wall thickness is reduced by removing the wall except for the necessary portions to improve the productivity.

However, in the case of a cylindrical body, for example, a functional part such as a roll, it is very difficult to lighten the outer peripheral surface of the cylinder, or it may not be possible to lighten it at all. Therefore, in order to manufacture the roll, the material is cut or
Although a method is used in which a material is wound around a shaft and thermocompression-bonded and then the surface is polished and finished, there is a problem that the work becomes complicated. Moreover, various problems such as a decrease in processing accuracy occur due to an increase in temperature accompanying the processing.

For this reason, after the molten synthetic resin is injected into the molding chamber (cavity) formed in the mold, an inert high-pressure gas such as nitrogen gas or argon gas is injected into the molten resin in the cavity. A high-pressure injection molding method has been developed in which a molten synthetic resin is pressed against the mold surface of the cavity by its internal pressure to produce a hollow synthetic resin molded article. However, even if the high-pressure injection molding method is directly applied to the production of the synthetic resin roll, uneven thickness occurs on the outer peripheral surface, the center of rotation and the center of gravity do not match, and the rotation function is hindered. As a result, there is a problem that the degree of cooling is partially different and thus the roundness is reduced, and the uneven thickness causes a longer cooling time and lower productivity.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to make a hollow cylinder made of synthetic resin having a uniform outer peripheral surface and a high roundness, and having excellent rotation performance in which the center of gravity and the center of rotation are substantially coincident with each other. It is intended to provide a method for manufacturing a molded product.

[0006]

A method of manufacturing a synthetic resin hollow cylindrical molded product according to the present invention comprises a molten synthetic resin in a cylindrical molding chamber formed in a mold with a central axis extending vertically. And injecting high-pressure gas from the bottom of the molding chamber into the unsolidified molten synthetic resin in the molding chamber to form a cylindrical hollow portion and the unsolidified molten synthetic resin And a step of solidifying the molten synthetic resin after pressing it against the inner surface of the molding chamber.

Examples of the hollow cylindrical molded product include rollers. As the synthetic resin, any synthetic resin that can be injection-molded can be used, and examples thereof include polyacetal, ABS resin, polyamide resin (for example, nylon), polycarbonate, and polyphenylene ether. .
Further, a composite synthetic resin in which an inorganic material such as glass or carbon is mixed can be similarly used. As the high-pressure gas, an inert gas such as nitrogen gas or argon gas can be used.

[0008]

According to the present invention, after the molten synthetic resin is injected from the bottom of the molding chamber into a cylindrical molding chamber having a central axis extending vertically in the mold, the molten synthetic resin is injected from the bottom of the molding chamber. High-pressure gas is injected into the unsolidified molten synthetic resin in the molding chamber. By the injection of the high-pressure gas, a cylindrical hollow portion is formed in the unsolidified molten synthetic resin in the molding chamber, and the unsolidified molten synthetic resin is uniformly pressed against the inner surface of the molding chamber. Then, by solidifying the molten synthetic resin, it is possible to manufacture a synthetic resin hollow cylindrical molded product whose outer peripheral surface has a uniform thickness. Such a hollow cylindrical molded product has a high roundness and has an excellent rotation performance in which the center of gravity and the center of rotation are substantially aligned. Further, when the high-pressure gas is injected in the solidification step, the wall thickness can be made uniform, so that the cooling time in the solidification step can be shortened and the productivity of the synthetic resin hollow cylindrical molded product can be remarkably improved.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. Example FIG. 1 is a cross-sectional view showing a mold for manufacturing the synthetic resin roll of this example. Reference numeral 1 in the drawing denotes a rectangular mold body that is divided in the vertical direction. A cylindrical molding chamber (cavity) 2 is formed in the mold body 1 such that a central axis thereof extends in the vertical direction. In addition, on the upper and lower sides of the cavity 2, small-diameter columnar portions 3a and 3b which serve as bearings are formed. A spool 4 is opened in the mold body 1,
The spool 4 is connected to the bottom of the cavity 2 through a runner 5 and a gate 6. High pressure gas introduction pipe 7
Is inserted from the bottom of the mold body 1 into the small-diameter cylindrical portion 3b at the bottom of the cavity 2.

Next, a method of manufacturing the roll will be described with reference to FIGS. First, as shown in FIG. 2, the polyacetal 8 melted at 190 ° C. is passed through the spool 4, runner 5 and gate 6 of the mold body 1 into the cavity 2 formed in the mold body 1 at a pressure of, for example, 600 kg / cm ² . It fired at. At this time, as shown in FIG. 2, the molten polyacetal 8 was injected so as to form an unfilled portion 9 in the upper portion of the cavity 2.

Next, high pressure nitrogen gas is introduced into the high pressure gas introduction pipe 7
Through the bottom of the cavity 2 into the unsolidified molten polyacetal in the cavity 2. At this time,
As shown in (1), a cylindrical hollow portion 10 was formed in the unsolidified molten polyacetal, and the unsolidified molten polyacetal was uniformly pressed on the inner surface of the cavity 2. Then, by solidifying the molten polyacetal, a roll 12 made of polyacetal having bearing portions 11a and 11b at the top and bottom was manufactured.

The roll 12 taken out from the mold body 1
Had a uniform wall thickness, especially the outer peripheral surface, and had an extremely high roundness. In addition, when the rotation performance of the obtained roll 12 was examined, it was confirmed that the roll 12 smoothly rotated because the center of gravity was substantially coincident with the rotation center.

Comparative Example FIG. 4 is a sectional view showing a mold for manufacturing a synthetic resin roll of a comparative example. Reference numeral 21 in the figure denotes a rectangular mold body that is divided in the vertical direction. A cylindrical molding chamber (cavity) 22 is formed in the mold body 21 such that the central axis thereof extends in the horizontal direction. The cavity 2
On the left and right of 2, small-diameter cylindrical portions 23a,
b is formed. The mold body 21 has a spool 2
4 is opened, and the spool 24 is communicated with the left end of the cavity 22 through a runner 25 and a gate 26. The high-pressure gas introduction pipe 27 is inserted from the left side surface of the mold body 21 into the small-diameter cylindrical portion 23a on the left side surface of the cavity 2.

Next, a method of manufacturing the roll will be described with reference to FIGS. First, as shown in FIG. 5, the polyacetal 28 melted at 190 ° C. is filled with the spool 2 of the mold body 21.
4, 600 kg inside the cavity 22 formed in the mold body 21 through the runner 25 and the gate 26.
It was injected at a pressure of / cm ² . At this time, as shown in FIG. 5, the molten polyacetal 28 was injected so as to form an unfilled portion 29 at the upper and right ends of the cavity 22.

Next, the high pressure nitrogen gas is introduced into the high pressure gas introduction pipe 2
The solidified molten polyacetal in the cavity 22 was injected from the left end of the cavity 22 through 7. At this time, as shown in FIG. 6, a cylindrical hollow portion 30 was formed in the unsolidified molten polyacetal and the unsolidified molten polyacetal was pressed against the inner surface of the cavity 22. Then, by solidifying the molten polyacetal, a roll 32 made of polyacetal having bearing portions 31a and 31b at the top and bottom was manufactured.

A roll 32 taken out from the mold body 21.
In particular, since the cylindrical hollow portion 30 formed at the time of injecting the high-pressure nitrogen gas was deformed and the unsolidified molten polyacetal was pressed unevenly against the inner surface of the cavity 22, the wall thickness of the outer peripheral surface was particularly large. It was partially non-uniform. As a result, since the degree of shrinkage of the molten polyacetal in the solidification process was larger at the thicker portion, the roundness was lowered. Further, the solidification time was about three times longer than that in the above-mentioned embodiment. Furthermore, when the rotation performance of the obtained roll 32 was examined, the center of gravity did not coincide with the center of rotation, and smooth rotation was not performed.

In the above-mentioned embodiment, an example of manufacturing a roll using polyacetal as a synthetic resin has been described, but the same applies to other synthetic resins such as polyamide resin (eg nylon), polycarbonate and polyphenylene ether. It was possible to produce rolls with an effect.

[0018]

As described above in detail, according to the present invention, the outer peripheral surface is made of a synthetic resin having a uniform thickness, a high roundness, and an excellent rotation performance in which the center of gravity and the center of rotation are substantially coincident with each other. A method for manufacturing a hollow cylindrical molded product can be provided.

[Brief description of drawings]

FIG. 1 is a sectional view showing a mold for manufacturing a roll according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the manufacturing process of the roll according to the embodiment of the invention.

FIG. 3 is a cross-sectional view showing the manufacturing process of the roll according to the embodiment of the invention.

FIG. 4 is a cross-sectional view showing a mold for manufacturing a roll of a comparative example.

FIG. 5 is a cross-sectional view showing a roll manufacturing process in a comparative example.

FIG. 6 is a cross-sectional view showing a roll manufacturing process in a comparative example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Mold main body, 2 ... Molding chamber (cavity), 4 ... Spool, 5 ... Runner, 6 ... Gate, 7 ... High pressure gas introduction pipe, 8
... Molten polyacetal, 10 ... Hollow part, 11a, 11b
... Bearing part, 12 ... Polyacetal roll.

Claims (1)

[Claims] 1. A step of injecting a molten synthetic resin from a bottom portion of the molding chamber into a cylindrical molding chamber having a central axis extending in a vertical direction in a mold, and a high-pressure gas is injected from a bottom portion of the molding chamber. A step of injecting into the unsolidified molten synthetic resin in the molding chamber to form a cylindrical hollow portion, pressing the unsolidified molten synthetic resin against the inner surface of the molding chamber, and then solidifying the molten synthetic resin. A method for manufacturing a synthetic resin rotation function component, which is characterized in that