JPH0938726A - Method for bending steel pipe and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of bending a steel pipe which prevents the lowering of a pipe strength without impairing the appearance of the pipe at the time of bending the steel pipe for structural use and to provide a device therefor. SOLUTION: Both ends of the steel pipe 1 to be worked are closed with blind covers 2 and a pressurized liquid supplying valve 3 providing a pressure gage 4, pressure control valve 5 and an air vent valve 4 is fitted to this blind cover and the pressurized liquid is supplied from this supplying valve to pressurize the inner part of the pipe to a prescribed pressure. Successively, the bending work is started by three pieces of rolls and the elevated pressure generated by deforming the pipe cross section on the way of this working is controlled with the pressure control valve and the pressure in the pipe is held constant to execute the working. By this method, the pipe is worked with good precision while restraining a flattening rate and the appearance as the structural material is not impained and further, the strength of the pipe is not lowered and the excellent bent steel pipe can easily be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-roll bending method and bending apparatus for a medium diameter steel pipe used for structural purposes.

[0002]

2. Description of the Related Art Conventionally, the methods conventionally used for bending steel pipes are roughly classified into (1) cold bending with three rolls, and (2) a fixed bending die is used and pressed against it. There are three types: bending by bending and (3) hot bending by heating (high-frequency heating, etc.) a steel pipe.

The main use is to use small-diameter pipes with a small working diameter. When bending a large number of pipes of the same shape, die bending is used. For small- to medium-diameter pipes, the working diameter is large. When bending, perform cold bending with three rolls, and use hot bending when bending a small diameter beyond the limit of cold bending or when bending a medium to large diameter pipe. are doing.

Many steel pipes used for structural purposes have a small diameter to a medium diameter of 80 to 400 A and a wide range of working diameters depending on the structure. This internal hot bending causes deformation of the pipe. The flattening ratio is low, but the cost is high. Therefore, cold bending with three rolls is mainly used.

FIG. 3 shows an example of a cold bending method using three rolls. In this method, as shown in (a), three hourglass-shaped rolls 22a to 22c are arranged in an isosceles triangle shape, the two rolls 22a and 22b forming the base are fixed, and the roll 22c at the apex position is fixed. The steel pipe 21 is movable in a direction perpendicular to the bottom side, and the steel pipe 21 to be processed is sandwiched between the steel pipe 21 and the roll 22c, which is rotated in the forward and reverse directions while pressing the roll 22c, to reciprocate the steel pipe 21 as shown in FIG. Bending is performed on a curve having a diameter of.

[0006]

By the way, when performing the bending work with the three rolls, when the cold bending work is carried out with a small working radius, for example, a working radius within 10 times the pipe diameter, as shown in FIG. As shown in FIG. 4 showing the details of the portion A, wrinkles 23 are generated on the inner surface side of the pipe, and a crease 24 is formed at the boundary between the rolled and machined portions, resulting in an extreme shape change.

This change in shape shows the flatness of the pipe shown in FIG. 5 [indicating the flatness of the pipe with respect to the nominal diameter, {(long diameter D
_max -minor diameter D _min ) / nominal diameter D} × 100 (%)], but if this flatness ratio exceeds 5%, the appearance will be extremely deteriorated. It was not preferable in terms of strength such as deterioration.

The present invention provides a method and apparatus for bending a steel pipe, which maintains its roundness when bending the pipe, does not impair the aesthetics of the pipe, and prevents deterioration of the pipe strength.

[0009]

According to the processing method of the present invention, both ends of a steel pipe to be processed are closed by a blind lid, and a pressure gauge, a pressure adjusting valve and an air bleeding valve are provided on the blind lid on the one end side. A liquid supply valve is attached, the pressurized liquid is supplied from the supply valve, and when the pressure in the pipe reaches a predetermined pressure, the supply of the pressurized liquid is stopped, and then bending is started by three rolls. A method for bending a steel pipe is characterized in that the pressure increase caused by the deformation of the cross section is adjusted by the pressure control valve to keep the internal pressure of the pipe constant, and then the steel pipe is bent.

In the above bending method, water or water containing a rust preventive agent is used as the pressurized liquid.
In this case, as the pressurizing liquid, use water or an aqueous liquid in which an additive is added to water, an oil-based liquid such as mineral oil or vegetable oil, ethylene glycol, or other liquid chemical compound liquid. You can In short, if it is a liquid, it works as the pressurized liquid of the present invention. However, water is preferable from the viewpoint of economy and ease of handling, and an aqueous solution containing a rust preventive is most preferable.

The processing apparatus of the present invention comprises a pressurized liquid supply valve equipped with a pressure gauge, a pressure adjusting valve and an air bleeding valve, and the valve is attached to the blind lid of the steel pipe to be processed to bring the inside of the pipe to a predetermined pressure. A steel pipe bending apparatus characterized by pressurizing and adjusting a pressure increase caused by deformation during pipe processing by a pressure adjusting valve to maintain a constant pipe internal pressure.

In the present invention, the steel pipe to be cold-bended by the three rolls is a structure called a normal medium diameter pipe having a minimum of 80 A, a plate thickness of 2.8 mmt to a maximum of 400 A, and a plate thickness of about 19.0 mmt. It is a steel pipe.

According to the method for bending a steel pipe of the present invention, a pressurized liquid having a predetermined pressure is supplied into the pipe during bending, and the pipe is pressed by the internal pressure of the pressurized liquid against the force of deformation of the pipe during processing. In order to prevent the deformation, it is more effective to prevent the deformation by increasing the applied internal pressure as much as possible. For that purpose as well, it is preferable that the pipe diameter, wall thickness, and yield strength are as high as possible.

However, when bending a pipe, it is very difficult to perform the work while maintaining the complete shape before the work, so that the appearance of the pipe after the work is not deteriorated and the strength of the pipe is significantly affected. Empirically as a range not given 3.
Flatness up to about 5% is acceptable. Therefore, when the pipe is deformed during processing and the pressurized liquid is compressed, and the abnormal high pressure occurs in the pipe, the pipe may be destroyed. By letting it escape, the internal pressure of the pipe is kept within a normal pressure range, and the pipe is prevented from being broken.

As the pressure applied to the internal liquid at the time of this processing, JIS G05 which defines the test pressure at the time of the water pressure test of the pipe is used.
82 or JIS G0583 as a basis, pressurization is performed based on the following formula 1. It should be noted that according to the following calculation formula, as the pipe diameter increases, the plate thickness naturally increases, so that the pressure becomes almost constant, but it is practically preferable to pressurize in the range of 70 to 100 kg / cm ² .

[0016]

[Equation 1] Where P: test pressure (kg / cm ² ), t: pipe thickness (mm), D: pipe outer diameter (mm), s: yield point or 60% of the minimum yield strength (kg / cm ^2). ).

The blind lid in the above processing apparatus is not particularly limited as long as it has a structure capable of withstanding the above-mentioned pressing force. In addition to the flange structure generally used for pipe joining, the blind lid is attached to the pipe end surface by welding. ， Screw on the pipe end face and screw in the cap that is a blind lid ， Install a plurality of wedges on the outer peripheral face of the pipe end, and attach tie bolts to the bite fittings that have a sloped surface that slide-matches the sloped surface of this wedge. , Tighten the blind lid with the tie bolts, etc.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An example of a steel pipe bending apparatus of the present invention will be described below with reference to FIG.

This bending apparatus is composed of a pressurized liquid supply valve 3 equipped with a pressure gauge 4, a pressure adjusting valve 5 and an air bleeding valve 6, and this valve 3 is provided with a blind lid 2 of a steel pipe 1 to be processed.
It is attached to the drum-shaped rolls 22a to 22c of the cold-rolling apparatus using the three rolls shown in FIG.

In this case, when the pressurized liquid such as water is supplied from the pressurized liquid supply valve 3, in order to completely eliminate the residual gas in the pipe, if necessary, a blind lid on the other end side of the steel pipe 1 to be processed. Two
If the air bleeding valve 6a is further attached to a, air bleeding can be facilitated and more complete air bleeding in the pipe can be performed.

As an example of attaching the blind lid to the steel pipe 1 to be processed, in addition to a commonly used flange structure, FIG.
A method for attaching the blind lid 1 directly to the pipe end surface by fillet welding 11 shown in (a), and a screw 12 is cut on the pipe end surface to show a cap 13 which is a blind lid, as shown in FIG. 2 (b). 2C, a plurality of wedges 14 are attached to the outer peripheral surface of the pipe end, and a tie bolt 16 is attached to a biting fitting 15 provided with a sloped surface that slide-matches the sloped surface of the wedges. There is a method such as mounting and tightening the blind lid 2 with a tie bolt through the packing 17, but it may be appropriately selected in consideration of the diameter and wall thickness of the steel pipe to be processed and the pressure applied to the pipe.

In this way, the inside of the pipe is pressurized to a predetermined pressure,
The pressure rise due to the deformation that occurs during pipe working is performed by adjusting the pressure with a pressure control valve to keep the pressure inside the pipe constant while resisting the deformation stress and minimizing the work deformation.

[0023]

EXAMPLE FIG. 6 shows the relationship between the tube size (A) and R / D (bending radius / tube outer diameter) when the present invention is applied.
It is a drawing showing the minimum bending radius. In this case, when the value exceeds 125A, the value of R / D slightly increases, that is, the minimum bending radius tends to increase.
The bending radius can be reduced until / D = 5.

FIG. 7 shows R / D (bending radius / outer diameter of pipe) of STK400 material of 250 A pipe having a plate thickness of 7, 8, 9 (mm) and 8 mm thickness when water pressure is applied. Is a diagram showing the relationship between the flatness ratio (%) and the flatness ratio (%). In this case, the flatness ratio can be reduced when the bending radius is large and the pipe sheet thickness is large. When added, the flatness can be further reduced.

FIG. 8 shows 250 of STK400 material as in FIG.
R / D (bending radius / outer diameter) and the amount of deformation due to tube breakage (mm) when water pressure is applied to a tube with a thickness of 7, 8, 9 (mm) and an 8 mm thickness using the A tube It is a drawing showing the relationship of, the flatness can be reduced when the bending radius is large and the tube sheet thickness is large similarly to the above,
Further, when a predetermined water pressure is applied to the pipe, the crack can be further reduced.

FIG. 9 is a drawing showing the relationship between the internal pressure of the pipe and the flatness of the pipe when the R / D is set to 7.5, 10, 12, and 15 for a pipe of 250 A and a plate thickness of 8 (mm). And
If the R / D is large, that is, the bending radius is large, the flatness ratio can be naturally reduced, but in this example, even if the R / D is 7.5, the flatness is within the range of the pipe pressure of 70 to 100 kg / cm ² described above. The rate can be suppressed to 3.5% or less.

[0027]

As described above, according to the method and apparatus for bending a steel pipe of the present invention, the steel pipe to be processed is closed with a blind lid, and the blind lid is provided with a pressure gauge, a pressure adjusting valve and an air bleeding valve. The pressurizing liquid supply valve is attached, and the pipe is bent while supplying the pressurizing liquid of a predetermined pressure into the pipe, and the internal pressure of the pressurizing liquid is resisted against the force that the pipe is deformed during processing. Has the effect of preventing the deformation of the tube. For example, as shown in the above embodiment, the flatness and the crack can be reduced when the bending radius is the same, and the bending radius can be reduced when the flatness and the crack are suppressed. Therefore, the bent steel pipe can be obtained by a simple method without being impaired in the aesthetic appearance as a structure by accurately processing the pipe and reducing the strength of the pipe.

[Brief description of drawings]

FIG. 1 is a drawing showing a configuration example of a steel pipe bending apparatus of the present invention.

2 (a), (b), and (c) are drawings showing an example of how to attach a blind lid to a steel pipe to be processed.

FIG. 3 is a plan view showing a state in which wrinkles and cracks (A portion) are generated by the three rolls, (a) is a state before bending, and (b) is a state in which a defect is generated after processing. is there.

FIG. 4 is a drawing showing the details of the constriction (A part) of FIG. 3;

FIG. 5 is a diagram illustrating a flatness of a pipe.

FIG. 6 is a drawing showing the minimum bending radius in the relationship between the tube size and R / D when the present invention is applied.

FIG. 7: R for various plate thicknesses and water pressure applied to the pipe
6 is a drawing showing the relationship between / D and flatness.

FIG. 8: R for various plate thicknesses and water pressure applied to the pipe
It is the figure which showed the relationship of the amount of deformation by / D and a crack.

FIG. 9 is a drawing showing the relationship between the internal pressure of a pipe and the flatness of the pipe when R / D is variously changed.

[Explanation of symbols]

 1 Worked Steel Pipe 2, 2a Blind Lid 3 Pressurized Liquid Supply Valve 4 Pressure Gauge 5 Pressure Adjustment Valve 6, 6a Air Bleed Valve 11 Fillet Welding 12 Threaded Part 13 Cap 14 Wedge 15 Biting Metal Fitting 16 Tie Bolt 17 Packing 21 Worked Steel Pipe 22a-22c Bending roll 23 Wrinkles 24 Constriction

Claims (3)

[Claims] 1. A steel pipe to be processed is closed at its both ends with a blind lid, and a pressure gauge, a pressure adjusting valve, and a pressurized liquid supply valve equipped with an air bleeding valve are attached to the blind lid on one end side, and a pressure is applied from the supply valve. When the pressure liquid is supplied and the inside of the pipe reaches a predetermined pressure, the supply of the pressure liquid is stopped, and then the bending process is started by the three rolls. A method for bending a steel pipe, characterized in that the pressure is regulated by a regulating valve, and the pressure inside the pipe is kept constant for processing. 2. The method for bending a steel pipe according to claim 1, wherein water or water containing an anticorrosive agent is used as the pressurized liquid. 3. A pressurizing liquid supply valve comprising a pressure gauge, a pressure adjusting valve and an air bleeding valve, the valve being attached to a blind lid of a steel pipe to be processed so as to pressurize the inside of the pipe to a predetermined pressure for pipe processing. An apparatus for bending a steel pipe, characterized in that the pressure increase caused by the deformation at the time is regulated by a pressure regulating valve to keep the pressure inside the pipe constant.