JPH08267566A - Production of plastic vent pipe - Google Patents

Abstract

PURPOSE: To produce a plastic vent pipe having almost uniform wall thickness in both end parts and central part thereof. CONSTITUTION: A cylindrical plastic straight pipe is heated and softened to be subjected to bending processing by using a mold to produce a plastic vent pipe 2. This method has a process forming the plastic straight pipe wherein the cross sections of the outer and inner peripheral surfaces of both end parts are a circular shape having the almost same center and almost uniform wall thickness and the cross sections of the outer and inner peripheral surfaces of a central part have circular shapes having different centers and one of them is made larger than the other one of them in wall thickness and a process bending the thick-walled part of the central part of the plastic straight pipe as the back wall part 23 of the plastic vent pipe 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a plastic bend pipe used in a bent portion of a pipe such as a water and sewer pipe and a cable protection pipe for power transmission.

[0002]

2. Description of the Related Art Bend pipes made of plastic are used for bent portions of pipes such as water and sewer pipes and cable protection pipes for power transmission. As a conventional method for manufacturing a plastic bend pipe, for example, one described in Japanese Patent Laid-Open No. 4-193524 is known. In this way,
First, in order to prevent distortion of the cross-sectional shape and wrinkles during molding, a straight plastic pipe is filled with sand, rubber, etc. and heated. Next, the heat-softened plastic straight tube is pressure-molded using a mold having a predetermined radius of curvature and a bend angle. Then, the formed pipe is cooled and taken out from the mold to obtain a bend pipe.

As another conventional method for manufacturing a plastic bend pipe, the one described in Japanese Patent Laid-Open No. 6-79775 is known. This method is a method of manufacturing a bent pipe by bending a heat-softened plastic straight pipe using a mold as in the above-mentioned conventional technique, and the plastic straight pipe has an outer peripheral surface and an inner surface. This is a method in which the cross section of the peripheral surface is circular with different centers and one is made thicker than the other side, and this thick portion is bent as a back portion of the plastic bend pipe.

[0004]

In the above-mentioned prior art, the former method for manufacturing a plastic bend pipe disclosed in Japanese Patent Laid-Open No. 4-193524 discloses a back meat outside a central axis of a bent bend pipe. There was a problem that the wall thickness of the part became thinner than the wall thickness of the inner belly part, and the wall thickness standard of the pipe was deviated.

Further, in the case of the latter method of manufacturing a plastic bend pipe disclosed in Japanese Patent Laid-Open No. 6-79775, the thick wall portion of the plastic straight pipe which is the back wall portion of the plastic bend pipe is not formed in the central portion. Similarly, the thin portion of the straight plastic pipe that is pulled from both sides to become the abdominal portion of the plastic bend pipe is compressed from both sides at the central portion and made thicker, and the back portion and the abdominal portion are formed. The thicknesses of and can be made substantially equal, and can be kept within a predetermined standard.

However, at both ends of the straight plastic pipe, both the thick and thin portions are pulled or compressed only from one side, so that the change in the wall thickness is smaller than that in the central portion, and bending is performed. There was a problem that the initial thickness deviation was left at both ends of the plastic bend pipe, and the thickness of the pipe was out of the standard. An object of the present invention is to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide a method for manufacturing a plastic bend pipe in which the wall thicknesses at both ends and the center are substantially uniform.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and a cylindrical plastic straight pipe is heated and softened, and is bent by using a die to obtain a predetermined shape. In a method of manufacturing a plastic bend pipe having a bend angle of, the outer peripheral surface and the inner peripheral surface of both ends are made to have a circular and substantially uniform wall pressure with substantially the same center, A step of forming a plastic straight pipe having a circular cross-section with different centers and one of which is made thicker than the opposite side, and bending the thick part of the central part of the plastic straight pipe as the back wall part of the plastic bend pipe A method of manufacturing a plastic bend pipe including the step of:

In the above-described method for manufacturing a plastic bend pipe, the back wall portion of the plastic bend pipe means a portion where the outer peripheral portion of the plastic bend pipe is convex. The portion where the outer peripheral portion on the opposite side of the back meat portion is concave is referred to as a belly meat portion.

As a mold used in the bending process of the present invention, the mold surfaces at both ends are made straight without R, and only the central part is rounded with R, and both ends of this mold are formed. Installed both ends where the wall thickness of the plastic straight pipe is uniform,
A method of manufacturing a plastic bend pipe may be performed in which a thick portion of the plastic straight pipe is installed in a central portion of a die having R to be a back wall portion of the plastic bend pipe and bending is performed.

[0010]

The operation of the plastic bend pipe of the present invention is as follows.
The outer and inner peripheral surfaces of both ends have a circular shape with approximately the same center and have a substantially uniform thickness, and the outer peripheral surface and the inner peripheral surface of the central portion have circular centers with different centers, and one of them is from the opposite side. It includes the steps of forming a thick plastic straight pipe and bending the thick portion of the central portion of the plastic straight pipe as a back wall portion of the plastic bend pipe.

During this bending process, the thick portion of the central portion of the plastic straight pipe, which is the back wall portion of the plastic bend pipe, is pulled from both sides to reduce the thickness, and similarly, the thick portion of the plastic bend pipe and the abdominal portion of the plastic bend pipe. The thin portion of the central portion of the plastic straight pipe is compressed from both sides to be thickened so that the thickness of the back portion and the thickness of the abdominal portion can be made substantially equal, and can be set within a predetermined standard.

On the other hand, at the time of the bending process, since the back meat portion and the belly meat portion at both ends of the plastic straight pipe are simply pulled or compressed from one side respectively, the change in the wall thickness is small as compared with the central portion, Moreover, since both ends are originally made to have a uniform thickness, it is possible to make the thickness substantially uniform. As a result of the above, in the method for manufacturing a plastic bend pipe of the present invention, the wall thicknesses at both ends and the center can be made substantially uniform.

Further, both ends of the mold used for bending are straightened without R, and a mold surface with only R at the center is formed. The both ends of which the thickness is made uniform are installed, and the thick part of the plastic straight pipe is installed in the center of the R-shaped mold so as to become the back part of the plastic bend pipe and bent. Then, since no bending force is applied to both ends of the straight plastic pipe, a uniform thickness is maintained, the central part is thin-walled, the thin-walled part is thickened, and the back and belly parts are thickened. The wall thickness is made uniform. As a result, it is possible to obtain a plastic bend pipe having a more uniform thickness at both ends and the center.

[0014]

Embodiments of the present invention will now be described with reference to the drawings. 1 and 2 show an embodiment of the present invention, in which FIG. 1 (a) is a cross-sectional view of a plastic straight pipe, (b) is a vertical cross-sectional view taken along line XX of FIG. ) Is (a)
It is a longitudinal cross-sectional view taken along line YY of the drawing. FIG. 2 is a longitudinal sectional view of a plastic bend pipe manufactured by bending the straight plastic pipe of FIG.

Reference numeral 1 is a straight plastic pipe, and 2 is a plastic bend pipe. This plastic straight pipe 1 is made of a hard vinyl chloride resin and is composed of end portions 11 and 11 and a central portion 12, and the end portion 11 has an outer peripheral surface and an inner peripheral surface as shown in FIG. The cross section is circular with the same center 13 and has a uniform wall thickness. As shown in FIG. 1C, the central portion 12 has a circular shape in which the center 13 of the outer peripheral surface and the center 14 of the inner peripheral surface are different, and the lower portion is a thick portion 12a and the upper portion is a thin portion 12b. ing. Since the outer peripheral surface of the plastic straight pipe 1 has a circular shape having the same center 13, it has a uniform outer shape without steps.

The above plastic straight pipe 1 is disclosed in JP-A-5-1.
It was manufactured by a molding device using a "thickness adjusting mechanism of a synthetic resin pipe extrusion molding device" described in Japanese Patent No. 6205. This plastic straight pipe 1 has an outer diameter of 147.5.
mm, length 1250 mm, end 11 length 150 mm
The thickness of each part of the end part 11 and the central part 12 (mm)
Are shown in (Table 1).

[0017]

[Table 1]

Further, as shown in FIG. 1, markings 15 and 15 are drawn along the longitudinal direction at four places on the outer peripheral surface of the plastic straight pipe 1.

Next, a method for producing the plastic bend pipe 2 by bending the above plastic straight pipe 1 will be described below. First, a filler or the like is filled in the plastic straight pipe 1 shown in FIG. 1 and heated to a temperature at which bending can be performed. This temperature depends on the plastic material used, and for example, in the case of the above-mentioned hard vinyl chloride resin, it is heated to 100 to 120 ° C.

After that, in order to obtain the plastic bend pipe 2 having a predetermined shape shown in FIG. 2, the mold surface of the mold is made to match the outer peripheral surface shape of the plastic bend pipe 2, and the plastic is directly attached to the mold. Set tube 1. The plastic bend pipe 2 has end portions 21, 21 and a central portion 22.
And the end portion 21 is straight and the central portion 22
Has a bend angle 27 of 45 ° and a radius of curvature 26 of the center line 25 of 1180 mm.
And have.

When setting the heat-softened plastic straight pipe 1 in the mold, the marking 15 shown in FIG.
Using as a guide, the thick portion 12a of the central portion 12 of the plastic straight pipe 1 is set to be the back portion 23 of the plastic bend pipe 2, and pressure molding is performed for a predetermined time. After that, the plastic bend pipe 2 is obtained by cooling with water or the like and releasing from the mold. The wall thickness (mm) of each part of the plastic bend pipe 2 thus obtained is shown in (Table 2).

[0022]

[Table 2]

As shown in (Table 2), the wall thickness of the pipe end portion 21 is the same as that before bending, but the wall thickness of the central portion 23 is
The thickness of the back meat part 23 is reduced by -0.5 mm, and the thickness of the belly meat part 24 is +
0.6mm thicker, resulting in tube end 21 and center 2
The wall thicknesses of 2 are made almost equal, and both are within the standard value of the wall thickness.

As described above, according to the method for manufacturing the plastic bend pipe 2 of this embodiment, both ends of the die surface of the die used for bending are straightened without R, and only the central portion is R. Both ends 11 of the plastic straight pipe 1 having uniform wall thickness are provided at both ends of the mold, and the plastic straight pipe 1 is attached to the center of the mold with R.
The thick-walled portion 12a is installed so as to become the back-walled portion 23 of the plastic bend pipe 2 and is bent.

Therefore, both ends 1 of the straight plastic pipe 1
In Nos. 1 and 11, since no bending force was applied, the initial uniform thickness was maintained. On the other hand, in the central portion 12 of the straight plastic pipe 1, the thick-walled portion 12a is pulled from both sides to be thinned, and the thin-walled portion 12b is compressed from both sides to be thickened to form the back-walled portion and the belly-walled portion. The wall thickness can be made almost equal. As a result, in the plastic bend pipe 2 obtained in this embodiment, both end portions 21 and the central portion 22 are made uniform in wall thickness and can be accommodated within a predetermined standard.

[0026]

According to the method for manufacturing a plastic bend pipe of the present invention, both ends of the plastic straight pipe are made to have a substantially uniform thickness, and one of the central portions is made thicker than the opposite side. Since the meat part is bent as the back part of the plastic bend pipe, it is possible to prevent the thickness of both ends and the center part of the plastic bend pipe from becoming uniform and out of specification. Bend tubes can be manufactured.

Further, in the plastic straight pipe used in the method for manufacturing a plastic bend pipe of the present invention, the thickness of both ends is made uniform, and only the curved portion of the central part is unevenly thickened, so that the warp is prevented. Less likely to occur and easy to handle.

[Brief description of drawings]

1 is an embodiment of the present invention, in which (a) is a cross-sectional view of a straight plastic pipe, (b) is a vertical cross-sectional view taken along line XX of (a), and (c) is (a). ) Is a vertical cross-sectional view taken along the line YY of the drawing.

FIG. 2 is a vertical cross-sectional view of a plastic bend pipe manufactured by bending the plastic straight pipe of FIG.

[Explanation of symbols]

 1 Plastic straight pipe 2 Plastic bend pipe 23 Back meat part 27 Bend angle

Claims (1)

[Claims] 1. A method for manufacturing a plastic bend pipe having a predetermined bend angle by heating and softening a cylindrical plastic straight pipe and bending the same using a mold, wherein an outer peripheral surface and an inner peripheral surface of both end portions are manufactured. A straight plastic pipe whose surface has a circular shape with approximately the same center and has a substantially uniform thickness, and the outer peripheral surface and the inner peripheral surface of the central portion have different centers and one of which is thicker than the opposite side. A step of forming
A method for manufacturing a plastic bend pipe, comprising a step of bending the thick portion of the central portion of the plastic straight pipe as a back wall portion of the plastic bend pipe.