JPH08141658A - Method for bending polyvinyl chloride-coated steel tube - Google Patents

Abstract

PURPOSE: To prevent wrinkles on the internal bending part inside a polyvinyl chloride- coated steel tube from generating by compressing a part to be bent and the neighborhood into an oblong circular cross-section and bending the part along the face of external circumference of a bending die at the same time. CONSTITUTION: A forth part 3b of a straight polyvinyl chloride-coated(PVC) steel tube 3 is tightened and clamped with a receiving part 5a and a moving part 5b of a clamp holder 5, and a core metal 8 is pressed inside the tube with a prescribed pressure. The forth part 3b of the PVC steel tube 3 is tightened further with the clamp holder 5, and the part to be bent is compressed with a pressure holder 6 and a bending die 7. A semi circular grooves are installed on the pressure contact faces with the PVC-coated steel tube 3 of the clamp holder 5 and the bending die 7, The cross-section of the semi circular groove is made in a little oblong circular shape, so the part to be bent of the PVC-coated steel tube 3 and the neighborhood are compressed in a little oblong circular cross-section and these are bent along the face of external circumference of the bending die 7 at the same time, therefore, the cross-section of the part to be bent 3b of the PVC-coated steel tube 3 is bent so as to be made in an almost real circular shape. Therefore, the defective goods of the PVC-coated steel tube are hardly generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for bending a vinyl chloride steel pipe in which a vinyl chloride pipe portion is closely adhered to at least the inside of the steel pipe portion, and the bent portion of the curved vinyl chloride steel pipe has a substantially circular cross section. The present invention relates to a method for bending a vinyl chloride steel pipe which holds and does not cause cracks or wrinkles on the inner vinyl chloride pipe during bending at a low temperature.

[0002]

2. Description of the Related Art Rigid polyvinyl chloride (PVC) pipes are
It is widely used because of its good chemical resistance, but it cannot withstand high pressure as its diameter increases, and it cannot generally be used in a high temperature environment of 70 ° C or higher. In order to avoid such an essential defect of the PVC pipe, a PVC steel pipe, which is a two-layer pipe made of PVC and steel, has been proposed in recent years, which has higher pressure resistance and mechanical strength than a hard PVC pipe, and can be It is used for piping such as air conditioning equipment in condominiums.

The PVC steel pipe in which the PVC pipe is adhered at least to the inside of the steel pipe portion can be applied to a wider range of applications than the PVC pipe, but is a composite pipe made of a dissimilar material of PVC and iron and easily bent by warm working. I can't. For this reason, in the case where a pipe of PVC steel pipe has a curved portion, conventionally, in most cases, an elbow portion having a two-layer structure is separately manufactured and connected to a straight PVC steel pipe.

[0004]

The elbow portion described above is very expensive and the connecting work with the pipe end is complicated,
Water leakage or corrosion may occur from the connecting portion between the elbow portion and the PVC steel pipe. On the other hand, if the PVC steel pipe is directly bent, the cross section of the bent portion of the PVC steel pipe is likely to be deformed into an elliptical shape, and cracks and wrinkles are generated in the inner PVC pipe portion, and the PVC pipe portion and the outer steel pipe portion are It is easy to cause delamination between and.

The present inventor has conducted various experiments for bending a PVC steel pipe, and as a result, it has already been disclosed in Japanese Patent Application No. 6-1.
No. 75911 is proposed, and the method of the present invention is an improvement thereof. Therefore, an object of the present invention is to provide a method for bending a PVC steel pipe in which a bent portion of the curved PVC steel pipe maintains a substantially perfect circular cross section. Another object of the present invention is to provide a method for bending a PVC steel pipe in which cracks and wrinkles do not occur in the inner PVC pipe portion during bending even in a low temperature period such as severe winter.

[0006]

In order to achieve the above object, the bending method according to the present invention, as shown in FIGS. 1 and 2, fits a PVC pipe portion 2 inside a steel pipe portion 1 by fitting it. It may be applied to the PVC steel pipe 3 to be made, and may be a three-layer pipe (not shown) in which the PVC pipe portion is fitted / adhered to the outside of the steel pipe portion, if desired. The steel pipe part 1 used is generally a carbon steel pipe, but a stainless steel pipe or the like may be used. Further, as the PVC pipe portion 2, a polyethylene pipe, a polypropylene pipe or the like can be applied. Steel pipe part 1 and PVC pipe part 2
Generally, the two are fitted together and then brought into close contact with an adhesive.

In the steel pipe bending apparatus 4 for carrying out the method of the present invention, the bent portion 3 a of the straight PVC steel pipe 3
The front portion 3b is tightened by the clamp holder 5 (FIG. 2), and the bent portion is compressed by the pressure holder 6.
The pressure holder 6 sandwiches the PVC steel pipe 3 together with a bending die 7 having an outer circumference corresponding to the bending radius of the PVC steel pipe 3. The clamp holder 5, the pressure holder 6, and the bending die 7 are provided with a semicircular groove on the surface that comes into pressure contact with the PVC steel pipe 3, and the cross section of the semicircular groove is a slightly horizontally long circular shape (FIGS. 4 and 5).
See reference).

During bending, the mandrel 8 is pushed from the rear side of the PVC steel pipe 3 into the pipe, and the heater 1 is inserted into the mandrel.
The inner PVC pipe portion 2 can be heated by wiring 0. The mandrel 8 has, for example, a displaceable disk portion 12 connected by a wire or a rivet to the tip of a cylindrical body 11, and a heater is also embedded in the disk portion. Instead of burying the heater, hot air may be blown from the mandrel 8 and the hot air may be blown to the PVC pipe portion 2 inside. The diameter of the mandrel 8 is
As shown in FIGS. 2 and 3, it is usually preferable that the inner diameter of the PVC steel pipe 3, that is, the inner diameter of the PVC pipe portion 2 is smaller by about 2 mm.

In the method of the present invention, instead of the cored bar 8 or together with the cored bar, a filling material such as warm water 13 (FIG. 6) may be pressure-filled inside the PVC steel pipe 3. The hot water 13 is charged, for example, by attaching a blind flange 14 to one end of the PVC steel pipe 3, arranging the PVC steel pipe vertically, and injecting the hot water 13 under pressure, and after the hot water injection, a blind flange at the other end of the steel pipe. Close 15 Such fillers may be heated silica sand, PVC chips, metal particles such as lead, iron powder, zinc powder, aluminum powder, soft brazing filler metals, steel belts and the like. Instead of these fillers, hot air may be blown onto the PVC pipe portion 2 to heat the bent portion of the pipe portion, and then the PVC pipe portion 2 may be bent.

Normally, when the bent portion 3 a of the PVC steel pipe 3 is bent along the outer peripheral surface of the bending die 7, the slide holder 17 is pushed forward and the PVC steel pipe 3 is pushed backward toward the clamp holder 5. The rearward-pressing operation member of the PVC steel pipe 3 may be a hydraulically-operated chuck 18 as shown in the figure, or a pair of clamp holders for grasping the rear end portion of the PVC steel pipe 3 or a rear end protrusion of the slide holder 17 may be attached to the PVC.
The structure may be such that it is locked to the rear end surface of the steel pipe 3.

[0011]

In the bending method of the present invention, the clamp holder 5, the pressure holder 6 and the bending die 7 have semi-circular grooves having a slightly oblong circular shape, so that the bent portion 3a of the PVC steel pipe 3 and its vicinity are a slightly oblong circular shape. While compressing into a cross section, the P
The VC steel pipe is bent along the outer peripheral surface of the bending die 7. By this bending process, the bent portion 3a of the PVC steel pipe 3 is curved so that its cross-section has a slightly small diameter but a substantially perfect circle. The extent to which the bent portion 3a has a small diameter is 60 mm in diameter.
The PVC steel pipe 3 has a thickness of about 2 mm, which is only about 5 mm at maximum, so there is no practical problem.

Further, in the bending method of the present invention, the core metal 8 is pushed into the inside of the PVC steel pipe 3 at the time of bending, or hot water 13 or the like is pressurized and filled. The mandrel 8 that has been pushed in has a PV inside by wiring the heater 10 inside.
Heats the C pipe 2 to allow PVC in low temperatures such as the harsh winter
When the bent portion 3a of the steel pipe 3 is bent along the outer peripheral surface of the bending die 7, the inside PVC pipe portion 2 is prevented from cracking or wrinkling.

[0013]

EXAMPLES Next, the present invention will be explained based on examples.
The method of the present invention is applied to a PVC steel pipe 3 as illustrated in FIGS. 1 to 3, and in the PVC steel pipe, the PVC pipe portion 2 is fitted inside the carbon steel pipe portion 1 and adhered by an adhesive.
In this case, a three-layer pipe in which the PVC pipe portion 2 is further fitted and brought into close contact with the outside of the steel pipe portion 1 is also applicable. PVC steel pipe 3
Is generally for air conditioning pipes or water supply pipes, and the carbon steel pipe portion 1 has, for example, a diameter of 60.5 mm and a thickness of 4 mm, and the PVC pipe portion 2 has a diameter of 52.5 mm and a thickness of 1.5 mm.

The steel pipe bending apparatus 4 for carrying out the method of the present invention is provided with a bending die 7 of a substantially circular plane which is rotatably installed and has an outer periphery corresponding to the bending radius of the PVC steel pipe 3. An annular semicircular groove 21 is provided on the outer peripheral surface (see FIG. 5). The bending die 7 is provided with a notch 22 in a part of its outer periphery, and the receiving portion 5a of the clamp holder 5 is fitted and fixed thereto. As is apparent from FIG. 4, the clamp holder 5 is composed of a rectangular flat receiving portion 5a having semicircular grooves 23 and 24 on opposite surfaces and a movable portion 5b, and the side surface of the receiving portion is of the bending die 7. Located on the diameter pass line. The clamp holder 5 can clamp the steel pipe front portion 3b together with the receiving portion 5a by pressing the movable portion 5b toward the PVC steel pipe 3 by a hydraulic mechanism (not shown).
The clamp holder 5 is fixed to the bending die 7 and is rotated together with the bending die by an appropriate rotating mechanism.

As shown in FIG. 1, the pressure holder 6, which is a slightly horizontally long rectangular plane, is in a rest state of the apparatus (FIG. 2).
, The PVC steel pipe 3 is sandwiched with the bending die 7 on the front surface adjacent to the movable portion 5b of the clamp holder 5 and provided with the semicircular groove 25. In the clamp holder 5, the pressure holder 6, and the bending die 7, the semicircular grooves 21, 23, 24, and 25 provided on the surfaces that come into contact with the PVC steel pipe 3 are
As is clear from FIG. 4 and FIG. 5, the cross section has a slightly oblong circular shape. These semi-circular grooves, for example,
If the horizontal diameter is 60.5 mm, the vertical diameter is set to 58 mm.

On the other hand, the slide holder 17 is linearly slidable and is arranged in the vicinity of the pressure holder 6, and its front end face 28 extends substantially tangentially to the bending die 7 when viewed from above. The fixing block 29 for preventing the buckling of the PVC steel pipe 3 is arranged at a position facing the slide holder 17 when seen from a plane, and can be moved in the axial direction of the PVC steel pipe 3 and fixed at a predetermined position. A semicircular groove corresponding to the outer circumference of the PVC steel pipe 3 is formed on the front end surface 28 of the slide holder 17 and the inner surface of the corresponding portion 30 of the block 29.

The mandrel 8 having a substantially cylindrical shape as a whole has a disk portion 12 connected to the tip of a cylindrical body 11 by a wire, and the disk portion can be displaced during bending. In the mandrel 8, the nichrome heater 10 is wired inside the cylindrical body 11 and the disk portion 12, and when the nichrome heater 10 is pushed into the PVC steel pipe 3, the PV inside
The C tube part 2 can be heated. The core 8 has a diameter of 47.5, for example.
mm, which is smaller than the inner diameter of the PVC steel pipe 3, that is, the inner diameter of the PVC pipe portion 2 by 2 mm. A link bar 33 connected to the rear end of the mandrel 8 parallel to the axial direction passes through the chuck 18 and is connected to a hydraulic cylinder (not shown) that operates parallel to the axial direction of the PVC steel pipe 3. Further, the hydraulically operated chuck 18 that holds the rear end of the PVC steel pipe 3 pushes the PVC steel pipe 3 toward the clamp holder 5 when bending the bent portion 3 a along the outer peripheral surface of the bending die 7.

In the method of the present invention, when the PVC steel pipe 3 is bent, the front portion 3b of the linear PVC steel pipe 3 is clamped by the receiving portion 5a of the clamp holder 5 and the movable portion 5b, and then the mandrel 8 is attached. The PVC steel pipe 3 is pushed into the pipe from the rear side with a predetermined pressure. With the PVC steel pipe 3 held horizontally, the front part 3 of the PVC steel pipe 3 is clamped by the clamp holder 5.
b is further tightened, and the pressure holder 6 and the bending die 7
The compressed portion 3a is compressed with. As a result, PVC steel pipe 3
The front portion 3b and its vicinity are compressed into a slightly oblong circular cross section, for example, the horizontal diameter becomes 60.5 mm and the vertical diameter becomes 58 mm.

After that, the clamp holder 5 and the bending die 7 are rotated in the arrow direction of FIG. 3, and the bent portion 3 a of the PVC steel pipe 3 is bent along the outer peripheral surface of the bending die 7. At this time, the bent portion 3a of the PVC steel pipe 3 bends along the outer peripheral surface of the bending die 7 while being compressed into a slightly laterally long circular cross section. Further, the slide holder 17 is pushed forward, and the PVC steel pipe 3 is pushed backward to the pressure holder 6 by the hydraulically operated chuck 18. As a result, the PVC steel pipe 3 has a curved portion 3a having a diameter of 58 mm and a slightly smaller cross section, but is curved so as to have a substantially perfect circle.

In this bending method, the cored bar 8 is pushed into the PVC steel pipe 3 during bending. The inner PVC pipe portion 2 is heated by the heater 10 inside the mandrel.
As a result, when the bent portion 3a of the PVC steel pipe 3 is bent along the outer peripheral surface of the bending die 7 in a low temperature period such as a severe winter, cracks and wrinkles do not occur in the inner PVC pipe portion 2. The heater 10 may not be used in the summer when the temperature of the working environment becomes high.

In the modification shown in FIG. 6, in place of the core metal 8, warm water 13 at about 80 ° C. is pressurized to 10 to 30 Kg / cm ² by a pressure pump (not shown), and PVC is used.
The inside of the steel pipe 3 is filled. The filling of the warm water 13 is, for example, P
A blind flange 14 is attached to one end of the VC steel pipe 3 to
After arranging the C steel pipe vertically, hot water 13 is injected under pressure, and after the hot water injection, the blind flange 15 at the other end of the steel pipe is closed and then returned horizontally. In addition to warm water 13, such fillers include heated silica sand, PVC chips, metal particles such as lead, iron powder, zinc powder, aluminum powder, soft brazing filler metal,
Steel belts can be used.

When hot water 13 is pressure-filled inside the PVC steel pipe 3 during bending, the inner PVC pipe portion 2 is heated to about 50 to 60 ° C. by the pressurized hot water, and the PVC pipe portion 2 is made into a steel pipe. Since it is pressed toward the portion 1, the bent portion 3a
In, the PVC pipe part 2 is prevented from peeling from the steel pipe part 1. Moreover, in the low temperature period such as severe winter, PVC steel pipe 3
When the bent portion 3a of B is bent along the outer peripheral surface of the bending die 7, cracks and wrinkles are prevented from occurring in the PVC pipe portion 2 on the inside.

[0023]

In the bending method according to the present invention, the clamp holder, the pressure holder and the bending die have semi-circular grooves having a slightly oblong circular shape. This compresses the bent part of the PVC steel pipe and its vicinity into a slightly oblong circular shape,
The PVC steel pipe is bent along the outer peripheral surface of the bending die, and the bent portion of the PVC steel pipe is curved so as to have a substantially circular shape.
Therefore, when the bending method of the present invention is used, when the PVC steel pipe is bent at an arbitrary angle, the cross section of the bent portion always keeps a perfect circle, and the PVC steel pipe is prevented from being crushed. As a result, the wall thickness reduction rate of the steel pipe portion in the bent portion of the PVC steel pipe is small, wrinkles are prevented from being generated in the inner curved portion of the inner vinyl chloride pipe portion, and the mechanical strength of the obtained PVC steel pipe is increased.

Further, in the bending method according to the present invention, the core metal is pushed into the inside of the PVC steel pipe, or hot water or the like is pressurized and filled so that the PVC pipe portion is not peeled off during bending. The mandrel pushed in heats the inner PVC pipe portion by wiring a heater inside the mandrel, and
The steel pipe is prevented from being crushed, and the PVC pipe portion inside is prevented from being cracked or wrinkled in a low temperature period such as winter. Therefore, when the bending method of the present invention is applied, PV
The number of defective C steel pipes is reduced, and the running cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic plan view showing a steel pipe bending apparatus for carrying out the method of the present invention.

FIG. 2 is a schematic vertical sectional view showing the steel pipe bending apparatus of FIG.

FIG. 3 is a schematic vertical sectional view similar to FIG. 1, showing a state in which a PVC steel pipe is bent by the steel pipe bending apparatus of FIG. 1.

FIG. 4 is a side view showing a receiving portion and a movable portion of the clamp holder.

FIG. 5 is a partial lateral cross-sectional view of a side surface of the pressure holder and a bending die.

FIG. 6 is a schematic vertical sectional view showing a modified example of the method of the present invention.

[Explanation of symbols]

 1 Steel Pipe Part 2 PVC Pipe Part 3 PVC Steel Pipe 3a Bent Part 5 Clamp Holder 6 Pressure Holder 7 Bending Type 8 Mandrel 10 Heater 17 Slide Holder

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B32B 15/08 102 A 9349-4F

Claims (5)

[Claims] 1. A vinyl chloride steel pipe in which a vinyl chloride pipe portion is fitted inside a steel pipe portion, and a vinyl chloride pipe portion is fitted and closely adhered to the outside of the steel pipe portion as well, if desired. The front part of the bent part is clamped by the clamp holder and the bent part is compressed by the pressure holder. The clamp holder, the pressure holder and the bending die are provided with a semi-circular groove on the surface that comes into pressure contact with the vinyl chloride steel pipe. Due to the slightly horizontally long circular cross section, the bent part of the vinyl chloride steel pipe and its vicinity are compressed into a slightly horizontally long circular cross section and bent along the outer peripheral surface of the bending die. Bending method of vinyl chloride steel pipe that bends so that the cross section of the pipe becomes almost circular. 2. A vinyl chloride steel pipe in which a vinyl chloride pipe portion is fitted inside a steel pipe portion, and a vinyl chloride pipe portion is also fitted and closely adhered to the outside of the steel pipe portion if desired. By tightening the front part of the bent part with a clamp holder and compressing the bent part with a pressure holder, push the mandrel into the pipe from the rear side of the vinyl chloride steel pipe and wire the heater inside the mandrel. A method for bending a vinyl chloride steel pipe that prevents cracking of the vinyl chloride pipe when the inner portion of the vinyl chloride pipe is heated and the bent portion of the vinyl chloride steel pipe is bent along the outer peripheral surface of the bending die in a low temperature period. 3. A mandrel to be pushed into a vinyl chloride steel pipe has a displaceable disc portion connected to the tip of a cylindrical body with a wire or a rivet, and a heater is also embedded in the disc portion. Bending method described. 4. A vinyl chloride steel pipe in which a vinyl chloride pipe portion is fitted inside a steel pipe portion, and a vinyl chloride pipe portion is also fitted and closely adhered to the outside of the steel pipe portion, if desired. Tighten the front part of the bent part with a clamp holder and compress the bent part with a pressure holder, and pressurize and fill hot water inside the vinyl chloride steel pipe to heat the inner vinyl chloride pipe part. A method for bending a vinyl chloride steel pipe, which prevents cracking of the vinyl chloride pipe portion when the bent portion of the vinyl steel pipe is bent along the outer peripheral surface of the bending die. 5. A blind flange is attached to one end of a vinyl chloride steel pipe, the vinyl chloride steel pipe is vertically arranged, hot water is injected under pressure, and the blind flange at the other end of the steel pipe is closed after hot water injection. The bending method according to claim 4.