JPH0819821A - Method for bending plastic steel pipe - Google Patents

Abstract

PURPOSE:To prevent a crack and the occurrence of the wrinkle of a plastic pipe part by pushing a mandrel after filling a packing material into the plastic steel pipe, and at the time of bending, pushing the plastic steel pipe toward a clamp stand. CONSTITUTION:A packing material such as quartz sand 8, etc., is filled inside a plastic steel pipe 3 into which a plastic pipe part is inserted on the inside surface of a steel pipe and is made to adhere closely to the steel pipe. The tip of the pipe 3 is clogged by the spot welding of a steel plate 23, and a mandrel 9 is pushed into the pipe 3. In a bending device 4, the front part 3c of the pipe 3 is held by tightening it by a clamp stand 10. The rear part 3c of the pipe is put between a slide stand 6 and a bending die 7, and the rear end part of the pipe is held by the chuck 11 of a hydraulic operation. A part 3a to be bent of the pipe 3 is bent along the outer peripheral surface of the bending die 7 by rotating the clamp stand 10 and the bending die 7. At that time, the slide stand 6 is pushed out forward, and the pipe 3 is pushed toward the clamp stand 10 by the chuck 11. Consequently, at the time of bending work, stripping- off between the layers of a steel pipe part and a plastic pipe part can be prevented.

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 plastic steel pipe in which a plastic pipe portion is closely adhered to the inner surface of the steel pipe portion, and a plastic steel pipe in which cracks and wrinkles do not occur in the plastic pipe portion inside when bending Regarding the bending method.

[0002]

2. Description of the Related Art Rigid polyvinyl chloride pipe (PVC pipe)
Has very good chemical resistance and is easy to connect, and is now widely used as a water pipe and an industrial pipe. Since this kind of PVC pipe generally cannot withstand high pressure and high temperature of 70 ° C or higher, the PVC pipe is fitted into the inner surface of the steel pipe portion and closely adhered to improve the pressure resistance and mechanical strength of the large diameter PVC pipe. There is an aged PVC steel pipe.

The PVC pipe is adhered to the inner surface of the steel pipe P
Although VC steel pipes can be applied to a wider range of applications than simple PVC pipes, they cannot be easily bent by heat forming. For this reason, in the case where the pipe of the PVC steel pipe has a curved portion, conventionally, an elbow portion having a two-layer structure is manufactured separately, and this is 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. However, when the PVC steel pipe is directly bent, cracks and wrinkles are likely to occur in the inner PVC pipe, and the PVC pipe and the outer steel pipe portion are likely to be separated from each other.

The present inventor has conducted various experiments for bending various types of plastic steel pipes including PVC steel pipes, and as a result, cracks and wrinkles do not occur in the inner plastic pipe portion and The bending method that does not peel off is completed. Therefore, it is an object of the present invention to provide a method for bending a plastic steel pipe, in which cracks and wrinkles do not occur in the inner plastic pipe portion and delamination between the steel pipe portion and the plastic pipe portion can be prevented.

[0006]

In order to achieve the above object, the bending method according to the present invention is, as shown in FIG. 1, a plastic steel pipe in which a plastic pipe portion 2 is fitted into and closely adhered to the inner surface of a steel pipe portion 1. 3 is applied (see FIG. 3).
The steel pipe part 1 used is generally a carbon steel pipe, but a stainless steel pipe or the like may be used. The plastic pipe portion 2 is generally a PVC pipe, but a polyethylene pipe, a polypropylene pipe, a polyamide pipe, an ABS resin pipe, or the like is also applicable. The steel pipe portion 1 and the plastic pipe portion 2 are generally fitted together and then brought into close contact with an adhesive.

The steel pipe bending apparatus 4 for carrying out the method of the present invention comprises a bent portion 3 a of a linear plastic steel pipe 3.
The rear portion 3b is sandwiched by the slide base 6 and the bending die 7 on the outer periphery corresponding to the bending radius. Bending die 7 generally has a generally circular plane as shown, but it could be a fan plane with only the required perimeter. The slide base 6 and the bending die 7 are provided with semi-circular grooves corresponding to the outer peripheral surface of the steel pipe on the surface contacting the plastic steel pipe 3. A block 5 for preventing buckling of the plastic steel pipe 3 may be arranged at a position facing the slide base 6.

At the time of bending, the filling material 8 may be packed into the plastic steel pipe 3 and the packing material 8 may be lightly pushed into the pipe. As the filler 8,
Besides general silica sand, plastic chips, metal particles such as lead, iron powder, zinc powder, aluminum powder, soft brazing material, and steel belt may be used. After filling the filling material 8 and closing the steel pipe tip, the mandrel 9 is pushed into the pipe from the rear side of the plastic steel pipe 3. As shown in FIG. 3, it is generally preferable that the diameter of the mandrel 9 is smaller than the inner diameter of the plastic steel pipe 3, that is, the inner diameter of the plastic pipe portion 2 by about 2 mm. The mandrel 9 is preferably in the form of a series of discs connected by a wire, and is preferably a bendable cannonball shape as a whole, and may be a bendable bellows shape or an integral cannonball shape.

Next, the front part 3 c of the bent portion 3 a of the plastic steel pipe 3 is clamped by the clamp base 10. The plastic steel pipe 3 has, for example, a carbon steel pipe portion having an outer diameter of about 60 mm and a thickness of 3.5 to 4.5 mm and a thickness of 1.5 to 2.5 mm.
It is preferable to closely adhere the PVC pipe portion, and if the carbon steel pipe portion has a predetermined thickness or less, wrinkles are likely to occur during bending.
The plastic steel pipe 3 can be bent similarly even if its outer diameter is changed to some extent. Although not shown, the clamp base 10 may be a pair of gripping mechanisms provided with an appropriate hydraulic mechanism, and the clamp base 10 can rotate around the bending die 7 together with the bending die by an appropriate rotating mechanism.

When the bent portion 3 a of the plastic steel pipe 3 is bent along the outer peripheral surface of the bending die 7, the slide base 6 is pushed forward and the plastic steel pipe 3 is pushed backward toward the clamp base 10. This pushing force is, for example, 1.5 to 2.5 m in thickness for a carbon steel pipe part having a thickness of 3.5 to 4.5 mm.
It is preferable to set the plastic steel pipe 3 in which the PVC pipe portion of m is adhered to about ² to 5 t / cm ² . The pushing member for pushing the plastic steel pipe 3 may be the hydraulically actuated chuck 11 as shown, or a pair of clamp members for holding the trailing end portion of the plastic steel pipe 3 or the trailing end projection of the slide base 6 may be made of plastic. 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 plastic steel pipe 3 is pushed toward the clamp base 10 during bending, and the pushing force can be set relatively high by filling the inside of the plastic steel pipe 3 with the filling material 8. When the plastic steel pipe 3 is pushed toward the clamp base 10 with an appropriate pressure during bending, the reduction rate of the wall thickness of the steel pipe portion 1 in the bent portion 3a of the plastic steel pipe 3 is significantly reduced, and the steel pipe portion 1 and the plastic pipe portion It is possible to prevent delamination from the layer 2.

Further, in the bending method of the present invention, the filling material 8 is packed inside the plastic steel pipe 3 at an appropriate pressure so that the plastic pipe portion 2 of the plastic steel pipe 3 is not crushed during bending. Since the packed filling material 8 is also present around the cored bar 9 pushed into the inside of the pipe, when the bent portion 3a of the plastic steel pipe 3 is bent along the outer peripheral surface of the bending die 7, the cored bar 9 is It does not come into direct contact with the inner plastic pipe portion 2 and cracks and wrinkles do not occur in the plastic pipe portion.

[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 and 3, and in the PVC steel pipe, the PVC pipe portion 2 is fitted into the inner surface of the carbon steel pipe portion 1 and adhered with an adhesive.
PVC steel pipe 3 is generally used for water supply pipes, and carbon steel pipe portion 1
Is, for example, diameter 60.5 mm, thickness 4 mm, PVC pipe 2
Has a diameter of 52.5 mm and a thickness of 2 mm.

The steel pipe bending apparatus 4 for carrying out the method of the present invention includes a bending die 7 having a substantially circular flat surface rotatably installed.
And a semicircular groove corresponding to the outer circumference of the PVC steel pipe 3 is formed on the outer peripheral surface 15 of the bending die (see FIG. 3). The slide base 6 is linearly slidable and is arranged in the vicinity of the bending die 7, and an inner end surface 16 thereof extends substantially tangentially to the bending die 7 when viewed from a plane. Also on the inner end surface 16 of the slide base 6,
A semicircular groove corresponding to the outer circumference of the PVC steel pipe 3 is formed.

The fixed block 5 for preventing the buckling of the PVC steel pipe 3 is arranged at a position facing the slide base 6 when seen from a plane, and the PVC steel pipe 3 is also provided on the inner surface 17 of the block.
Forming a semi-circular groove corresponding to the outer periphery of. Block 5 is
It can be fixed in place by changing the position of the PVC steel pipe 3 in the axial direction.

The clamp base 10 is arranged adjacent to the slide base 6 in the rest state (FIG. 1) of the apparatus, and is pressed toward the PVC steel pipe 3 by a hydraulic mechanism (not shown), so that the bending die 7 is pressed. Steel pipe front part 3 with corresponding part 18
It is possible to tighten c. Semicircular grooves corresponding to the outer circumference of the PVC steel pipe 3 are formed on the inner surfaces 19 and 20 of the clamp base 10 and the corresponding portion 18. The clamp base 10 is a pair of gripping mechanisms provided with an appropriate hydraulic mechanism, and the clamp base 10 rotates around the bending die 7 together with the bending die by an appropriate rotating mechanism.

The mandrel 9 which is entirely in the shape of a bullet is made up of a series of discs 22 whose centers are connected by a wire, and is entirely bendable during bending. The diameter of the mandrel 9 is 46.5 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. Although not shown, the link 21 connected to the rear end of the mandrel 9 parallel to the axial direction is
And is connected to a hydraulic cylinder that operates parallel to the axial direction of the PVC steel pipe 3. Further, the hydraulically operated chuck 11 that holds the rear end of the PVC steel pipe 3 pushes the PVC steel pipe 3 toward the clamp base 10 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 bending the PVC steel pipe 3, silica sand 8 as a filler is packed inside the PVC steel pipe, and the packing pressure of the silica sand 8 is, for example, 0.8 g / cm ^2.
It is preferably about the same. After the silica sand 8 is packed in the PVC steel pipe 3 and the tip of the steel pipe is closed by spot welding of the iron plate 23, the mandrel 9 is pushed into the pipe from the rear side of the PVC steel pipe 3 with a predetermined pressure.

In the bending device 4, the front part 3 c of the straight PVC steel pipe 3 is clamped and clamped by the clamp base 10. Further, it is necessary to sandwich the steel pipe rear portion 3b between the slide base 6 and the bending die 7 and further to hold the rear end portion of the PVC steel pipe 3 by the hydraulically operated chuck 11.

After this, the clamp base 10 and the bending die 7
2 is rotated in the direction of the arrow in FIG. 2 to bend the bent portion 3a of the PVC steel pipe 3 along the outer peripheral surface of the bending die 7. At this time,
The slide base 6 is pushed forward, and the PVC steel pipe 3 is pushed backward toward the clamp base 10 by the hydraulically operated chuck 11. This pushing force has a diameter of 60.5 mm and a thickness of 4 m.
It is about 4.0 t / cm ² for a PVC steel pipe 3 having a m carbon steel pipe part 1 and a 2 mm thick PVC pipe part 2.

In the method of the present invention, PVC is used during bending.
Even if the rear end of the steel pipe 3 is pushed by the chuck 11, the PV
The rear portion 3b of the C steel pipe is protected by the block 5 and the slide base 6 so that it does not buckle. The silica sand 8 is packed inside the PVC steel pipe with an appropriate pressure, and the mandrel 9 is present inside the rear portion 3b, so that the PVC pipe portion 2 of the PVC steel pipe 3 is not crushed or peeled. Further, at the time of bending, the shell-shaped mandrel 9 is deformed as shown in FIG. 2, so that the inner peripheral surface of the PVC pipe portion 2 is not damaged,
It is also easy to pull out the cored bar 9 from the PVC steel pipe 3 after bending.

Further, the pushing force in the method of the present invention is
Generally, it is larger than the force for pulling and bending the PVC steel pipe 3 with the clamp base 10 and the bending die 7. As a result, the thickness reduction rate of the outside of the steel pipe portion 1 in the bent portion 3a of the PVC steel pipe 3 is significantly reduced, and delamination between the steel pipe portion 1 and the plastic pipe portion 2 can be prevented.

[0023]

The bending method according to the present invention pushes the plastic steel pipe toward the clamp base during bending. When the plastic steel pipe is pushed toward the clamp base with an appropriate pressure during bending, the wall thickness reduction rate of the steel pipe portion in the bent portion of the plastic steel pipe becomes small, and the delamination between the steel pipe portion and the plastic pipe portion is prevented. Therefore, when the bending method of the present invention is used, the plastic steel pipe itself can be easily bent without connecting the elbow portion of the two-layer structure, and the mechanical strength of the manufactured plastic steel pipe is increased.

Further, in the bending method according to the present invention, the filling material is packed into the inside of the plastic steel pipe with an appropriate pressure so that the plastic steel pipe is not crushed during bending. When the bent part of the plastic steel pipe is bent along the outer peripheral surface of the bending die due to the filled packing material, the core metal does not directly contact the inner plastic pipe part and the plastic pipe part is cracked or wrinkled. Will not do. Therefore, when the bending method of the present invention is used, the number of defective plastic steel pipes is reduced, and the accuracy of the bending device can be maintained for a long time to reduce the running cost.

[Brief description of drawings]

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

FIG. 2 is a schematic vertical sectional view similar to FIG. 1, showing a state in which a plastic steel pipe is bent by the steel pipe bending device of FIG.

FIG. 3 is a partial cross-sectional view taken along the line AA of FIG.

[Explanation of symbols]

 1 Steel pipe part 2 Plastic pipe part 3 Plastic steel pipe 3a Bending part 6 Slide stand 7 Bending die 8 Filler 10 Clamp stand

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location // B32B 1/08 Z 7415-4F

Claims (3)

[Claims] 1. A plastic steel pipe in which a plastic pipe portion is fitted into and closely adhered to the inner surface of the steel pipe portion, wherein a rear portion of the straight plastic steel pipe is bent from a bent portion to a slide base and a bending die having an outer periphery corresponding to a bending radius. With the sandwich,
After filling the inside of the plastic steel pipe with a filler, the core metal is pushed into the inside of the pipe from the rear side of the pipe, the front part of the bent part of the plastic steel pipe is fastened with a clamp stand, and the bent part of the plastic steel pipe is bent. A bending method that pushes the slide base forward and pushes the plastic steel pipe backward toward the clamp base when bending along the outer peripheral surface. 2. A plastic steel pipe in which a polyvinyl chloride pipe having a thickness of 1.5 to 2.5 mm is brought into close contact with a carbon steel pipe portion having a thickness of 3.5 to 4.5 mm, and a force for pushing the plastic steel pipe toward the clamp base. The bending method according to claim 1, wherein is set to about ² to 5 t / cm ² . 3. A mandrel pushed into a plastic steel pipe is a series of discs connected by wires and is in the form of a bendable shell, and a filler made of silica sand is a mandrel pushed into the steel pipe. The bending method according to claim 1, wherein the bending method is interposed between the outer peripheral surface of the and the inner peripheral surface of the plastic pipe portion.