JP3147940B2 - Core material for bending plastic pipe and bending method using the core material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a core material for bending a plastic pipe useful for manufacturing a bent plastic pipe, and a bending method using the core material.

[0002]

2. Description of the Related Art When a gas pipe, a water supply pipe or a sewage pipe is constructed by using a plastic pipe, a bent plastic section is used to construct a bent portion.

[0003] A general method of manufacturing this curved plastic tube is to enclose a heating fluid in a plastic straight tube, then form the plastic tube containing the fluid by heating and softening it with a metal mold, and after cooling, cool the tube. This is a demolding method (see Japanese Patent Publication No. 58-18890).

By the way, as the pipe is bent, tensile strain in the axial direction of the pipe acts outside the neutral bending surface, and compressive strain in the axial direction of the pipe acts on the inner side of the neutral bending plane. In addition, as a result of uneven stress acting in the circumferential direction of the pipe due to compression, flattening of the pipe cross section is unavoidable (the pipe inner diameter decreases in the bending direction, and the pipe inner diameter decreases in the direction perpendicular to the bending direction). Increase).

Therefore, conventionally, a fluid filler such as sand is put in a plastic tube before bending the plastic tube with a mold (Japanese Patent Application Laid-Open No. 53-19385, Japanese Patent Publication No. 58-1983).
No. 1888), and a flexible core material is inserted to suppress the flattening of the pipe.

[0006]

However, when a fluid filler such as sand is used, the flattening of the cross section of the pipe causes the sand to loosen in the direction in which the inner diameter of the pipe increases, so that the cross section of the sand is loosened. Resistance to shape change cannot be expected very much.
Therefore, some flattening (about 5%) is inevitable,
In terms of fluid transport, there is a problem in terms of flow rate, pressure loss, and the like, and in the case of a low-pressure fluid, partial turbulence is likely to occur in a bent portion. In addition, fluid fillers such as sand can hardly be expected to function as an inner mold because the cross section easily changes, and wrinkles and whitening are likely to occur on the pipe surface in the portion where the occurrence of the compression strain is remarkable, That has led to a reduced appearance.

On the other hand, when a flexible core material such as rubber is used, if a soft core material is used, the core material is easily deformed. Failure occurs. On the other hand, when a hard core material is used, when the plastic tube into which the core material is inserted is bent, the frictional resistance acting between the core material and the plastic tube becomes large, and after the bending, It becomes difficult to pull out the core material, and the wear of the core material becomes remarkable. At the time of pulling out, for example, an operation such as pulling one end of the core material with a winch and hitting the other end with a hammer through a push rod or the like is required. In addition, the bending reaction force of the core material also increases, making it difficult to pressurize with a mold.

The present invention focuses on the above-mentioned conventional problems, and makes it easy to apply pressure by a metal mold when bending a plastic tube, to prevent the plastic tube from flattening, and to form a core material from the plastic tube. It is a common object to provide a core material that can be easily pulled out and a method of bending a plastic pipe using the core material.

[0009]

According to a first aspect of the present invention, there is provided a core material for bending a plastic pipe, wherein a flexible thin plate having a hollow portion and a substantially circular cross section is provided. The core material body is formed by laminating as described above, and a tube made of an elastic body and capable of injecting a fluid is provided in a hollow portion of the core material body.

In the bending method according to the second aspect of the present invention, the core material is inserted into a plastic tube, and then the tube provided in the hollow portion of the core material body is expanded. The plastic tube is bent under heating while sliding between the thin plates of the core body.Then, the tube is shrunk, and the core material is removed from the bent plastic tube. It is a method of pulling out.

[0011]

In the method for bending a plastic pipe using a core material according to the first aspect, the tube provided in the hollow portion of the core material body is expanded and pressed against the wall surface of the hollow portion.
The plastic pipe can be bent in a state where the core material body and the plastic pipe are sufficiently adhered to each other.

In this method, the plastic pipe is bent while sliding between the thin plates of the core material body.
By this sliding, the tensile force acting outside the bending neutral surface of the core body and the compressive force acting inside the bending neutral surface are reduced. Accordingly, since the bending reaction force of the core material body is reduced, the plastic tube can be bent and formed with a small pressure, and the cross section of the core material body can be maintained substantially in the original shape.

Furthermore, in this method, the core material is pulled out from the bent plastic tube after the tube is contracted, so that the resistance at the time of pulling out the core material does not increase, and the bending reaction force of the core material body is reduced. As the size becomes smaller, the frictional resistance between the core material and the plastic tube becomes smaller, and the drawing can be performed with a smaller force than in the conventional case.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below in detail with reference to FIGS.

First, the structure of a core 1 for bending a plastic pipe will be described with reference to FIGS. FIG.
FIG. 2 is a plan view showing the bending core material 1, and FIG.
3 is a sectional view taken along the line III-III in FIG.
1 is a core material body, 12a and 12b are binding rings, 13a and
13b is a bolt, 14a and 14b are nuts, 15 is a tube, and 16 is an air introduction tube.

The core body 11 is formed by laminating a plurality of flexible thin plates 1A to 1L so as to have a hollow portion 111 and have a perfect cross section. Further, through holes 112 are formed at both ends of the core material body 11 so as to penetrate all the thin plates 1A to 1L.

The binding rings 12a and 12b are made of thin plates 1A to 1A.
It is provided at both ends of the core material body 11 so as to bind 1 L. In addition, each binding ring 12a, 12b has
A through-hole 121 that matches the through-hole 112 of the core body 11 is formed.

The bolts 13a and 13b are connected to the through-hole 112 of the core body 11 and the through-hole 1 of each of the binding rings 12a and 12b.
21 and the nuts 14a and 14b
It is screwed to 3a, 13b. The bolt 13a has a hollow shaft. This hollow shaft
For example, it is formed by cutting threads on the outer periphery of a steel pipe.

The tube 15 is provided in the hollow portion 111 of the core body 11 and is connected to an air compressor 17 via an air introduction pipe 16. The tube 15 is made of an elastic material such as rubber.

The piping of the air introduction pipe 16 inside the core material main body 11 has a communication passage 113 formed by cutting out some of the thin plates 1A to 1L so as to connect the cavity 111 and the through hole 112. And the hollow shaft of the bolt 13a. Further, a three-way valve 18 is provided in the middle of the air introduction pipe 16.
It is possible to switch between a side where the tube 15 and the compressor 17 are connected and a side where the tube 15 is released to the atmosphere.

The through-hole 112 of the core material body 11 and the through-hole 121 of the binding rings 12a, 12b are formed as elongated holes longer in the length direction than the width direction of the core material 1, and are provided with bolts 13a, 13b. And thin plates 1A-1 with nuts 14a and 14b
Even when L is fastened, the thin plates 1A to 1L can slide with respect to each other within a predetermined length in the length direction.

Therefore, it is preferable to use the thin plates 1A to 1L that are easily slippery and do not thermally deform at the temperature in the plastic pipe at the time of bending (typically 45 ° C.). For example, olefin-based plastics, particularly ultra-high molecular weight polyethylene, high / medium density polyethylene, and the like are preferable. However, when a resin or metal with low slip is used, lubricating oil or a lubricant may be applied. In addition, each thin plate 1A
The thickness of 〜1 L varies depending on the material thereof, the diameter of the core material 1 and the like, but is usually preferably 2 to 3 mm.

Next, based on FIG. 4 to FIG.
A method of bending the plastic pipe 2 using the method will be described.

When the plastic pipe 2 is to be bent, first, the plastic pipe 2 is heated to near the softening temperature, and the core material 1 is inserted into the heated plastic pipe 2. When inserting the core material 1 into the plastic tube 2,
In advance, the bolt 13b and the nut 14b and the binding ring 12
b is removed, and the core material body 11 is inserted into the plastic tube 2 from the end from which they have been removed. Then, after inserting the core material main body 11 into the plastic tube 2, the binding ring 12b is attached to the end of the core material main body 11, and the bolt 13b and the nut 14b are fastened. (See FIG. 4). That is, the core material 1 has an outer diameter substantially equal to the inner diameter of the plastic tube 2 and a length longer than the length of the plastic tube 2.

Next, after confirming that the three-way valve 18 has been switched to the side where the tube 15 and the air compressor 17 are connected, the air compressor 17 is operated, and the three-way valve 18 is provided in the hollow portion 111 of the core body 11. Air is injected into the tube 15. The air is injected until the tube 15 expands and is pressed against the wall surface of the cavity 111.

Thereafter, the plastic tube 2 into which the core material 1 has been inserted is bent using a mold 6 at a predetermined bending radius and bending angle while sliding between the thin plates 1A to 1L. The plastic tube 2 is formed by, for example, hooking a wire 7 on each of the bolts 4 and pulling the wire 7 with a winch 8 in the direction in which the wire 7 is to be bent (see FIG. 5).

Next, the plastic tube 2 is cooled and solidified by flowing cooling water into the mold 6, and when the plastic tube 2 is solidified, the operation of the air compressor 17 is stopped and the tube 15 is released to the atmosphere. Three-way valve 18 on the side to be
Is switched to release the air in the tube 15. The air does not need to be completely removed from the tube 15;
What is necessary is just to shrink to such an extent that 5 does not press against the wall surface of the cavity 111.

After the mold is released, the core 1 is pulled out of the plastic tube 2. When pulling out the core material 1 from the plastic pipe 2, the bolt 13b, the nut 14b and the binding ring 12b are removed from the core material body 11, and the bolt 13
a is pulled with a winch or the like, and the core material body 11 is collectively pulled out from the plastic tube 2.

By these operations, the bending of the plastic tube 2 is completed.

Next, the operation of the first embodiment will be described.

According to the method for bending a plastic pipe 2 using the core material 1 according to the first aspect, the hollow portion 11 of the core material body 11 is formed.
1 is expanded so that the tube 15 provided in the hollow portion 1 is expanded.
11 when pressed against the wall of the core material body 11
The thin plates 1 </ b> A to 1 </ b> L are spread in the laminating direction and act in a direction in which the thin plates 1 </ b> A to 1 </ b> L adhere to the inner surface of the plastic tube 2. Therefore, the plastic tube 2 can be bent in a state where the core material body 11 and the plastic tube 2 are sufficiently adhered to each other. As a result, the cross section of the core material body 11 can be maintained in a substantially original true circle, and wrinkles and whitening on the surface of the plastic tube 2 can also be prevented.

In this method, since the plastic pipe 2 is bent while sliding between the thin plates 1A to 1L of the core body 11, the sliding causes the plastic pipe 2 to be more bent than the bending neutral surface of the core body 11. The tensile force acting on the outside and the compressive force acting on the inside of the neutral bending surface are reduced. Therefore, since the bending reaction force of the core material body 11 is reduced, the plastic tube 2 can be bent and formed with a small pressure, and the cross section of the core material body 11 can be maintained in a substantially original perfect circle. it can. In addition, it is possible to prevent wrinkles and whitening from occurring on the surface of the plastic tube 2.

Further, in this method, after the tube 15 is contracted, the core material 1 is removed from the bent plastic tube 2.
, The resistance when the core material 1 is pulled out does not increase, and the frictional resistance between the core material 1 and the plastic pipe 2 decreases as the bending reaction force of the core material body 11 decreases, Withdrawal can be performed with a smaller force than before.

The through-holes 112 formed at both ends of the core body 11 and the through-holes 121 formed in the binding rings 12a and 12b are formed as long holes longer in the length direction than the width direction of the core material 1. So that these through holes 112, 1
The thin plates 1A to 13A are bolted by bolts 13a and 13b.
1L sliding is hindered, and conversely bolts 13a, 13b
Can be prevented from being cut off.

Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific structure is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. Are also included in the present invention.

For example, in the embodiment, the method of bending the plastic resin tube 2 having a perfect circular cross section has been described. However, in the case of bending the plastic tube 2 having an oval shape, a core material having an oval cross section may be used. Bending can be performed by the same processing method.

In the embodiment, the tube is expanded by injecting air. However, water, fine particles or the like may be used instead of air.

[0038]

As described above, in the plastic pipe bending method using the core material according to the first aspect, the tube provided in the hollow portion of the core material body is pressed against the wall surface of the hollow portion. In addition, the plastic pipe can be bent in a state where the core material body and the plastic pipe are sufficiently adhered to each other. Therefore, the cross section of the core material main body is kept substantially in the original shape, the flattening of the plastic pipe is prevented, and
The occurrence of wrinkles and whitening on the surface of the plastic tube is also prevented.

Moreover, in this method, the plastic pipe is bent while sliding between the thin plates of the core body, so that this sliding causes a pulling force acting outside the bending neutral surface of the core body. And the compressive force acting on the inner side of the bending neutral surface is reduced, and the bending reaction force of the core material main body is reduced. As a result, the plastic tube can be bent with a small pressure, and the workability is improved.

Further, in this method, the core material is pulled out from the bent plastic tube after the tube is shrunk, so that the resistance at the time of pulling out the core material does not increase, and the bending reaction force of the core material body is reduced. As the size becomes smaller, the frictional resistance between the core material and the plastic tube becomes smaller, and the drawing can be performed with a smaller force than in the conventional case. That is, workability is improved and wear of the core material is reduced.

[Brief description of the drawings]

FIG. 1 is a plan view showing a core material for bending a plastic pipe according to a first embodiment.

FIG. 2 is a diagram of FIG. 1;

FIG. 3 is a diagram of FIG. 1;

FIG. 4 is a side view showing a state where a core material is inserted into a plastic tube.

FIG. 5 is a view showing a state where a plastic pipe is bent.

FIG. 6 is a diagram showing a state in which a core material is pulled out of a plastic tube.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Core material 1A-1L thin plate 11 Core material main body 111 Hollow part 15 Tube 2 Plastic tube

Claims (2)

(57) [Claims] 1. A core material main body is formed by laminating a flexible thin plate having a hollow portion and having a substantially circular cross section, and a hollow portion of the core material body is formed of an elastic body, and is formed of a fluid. A core material for bending a plastic pipe, characterized by being provided with a tube capable of injecting the same. 2. After inserting the core material according to claim 1 into a plastic tube, a tube provided in a hollow portion of the core material body is expanded and pressed against a wall surface of the hollow portion, and then the core material body is formed. The plastic tube is bent under heating while sliding between the thin plates, and then the tube is shrunk,
A method for bending a plastic pipe, comprising extracting a core material from the bent plastic pipe.