JPH0373371B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an on-line method for straightening bends in an electric resistance welded tube manufacturing line.

(Conventional technology) The general equipment outline of the ERW pipe manufacturing line is explained in Section 7.
As shown in the figure. That is, a roll forming machine 1 forms a flat plate into a mold with a nearly circular cross section, a welding machine 2 melts the plate ends, and a squeeze roll 3 removes molten steel and simultaneously joins the plate ends. Thereafter, the welded part is heat treated in a seam heat treatment device 4, reduced to a predetermined outer diameter in a sizing mill 5, and then processed into one or two stages of Turk's heads 6.
The conventional method is to correct the bends in order to produce straight steel pipes.

However, in reality, as the outer diameter of steel pipes becomes smaller, curved steel pipes are manufactured.
As in the publication, a rotary straightening machine installed offline is used to straighten the steel pipe. Since this rotary straightening machine transports the steel pipe while rotating, it is not possible to increase the transport speed, resulting in low productivity. Moreover, since the cross section of the steel pipe is easily crushed during straightening, when the plate thickness/outside diameter (t/D) of the steel pipe is small, the leveler effect is produced in the circumferential direction due to the crushing of the cross section, rather than the steel pipe being repeatedly bent in the longitudinal direction. The tube circumference increases and the length decreases. Further, when t/D is large, the cross section of the steel pipe is difficult to collapse, so that repeated bending in the longitudinal direction is performed well and the length becomes long. Due to this phenomenon, the length may be insufficient and the product may fall short of specifications. Such offline rotary straightening machines have deficiencies in terms of productivity, operability, and the like.

(Problems to be Solved by the Invention) The present invention aims to provide an extremely advantageous method for straightening the bending of an electric resistance welded pipe, which straightens the bending of a steel pipe online, enables stable straightening, and improves productivity. purpose.

(Means for Solving the Problems) In order to overcome the above-mentioned defects, the current situation is to install a Turk's head on the exit side of a sizing mill to manufacture straight steel pipes.

However, if the drawing process is applied at the final stage of the sizing mill, the slight deformation applied at the Turk's head will leave bending deformation in the steel pipe.In general, materials in a plastic state will not tolerate the addition of a small amount of stress. It is clear from the basic principle that deformation occurs easily. The third part is a schematic explanation of this basic principle.
It is a diagram. In other words, let's consider the bending deformation of a beam from the basis of the idea. In the state A in FIG. 3A, the bending deformation remains within the elastic range, and the bending stress distributed within the beam at that time is indicated by diagonal lines. However, in the unloaded state B, the residual stress distribution becomes zero and no bending deformation remains. In state A of (b), bending deformation has progressed further and yielding has occurred from the surface layer to a certain plate thickness. In this case, residual stress remains in the unloaded state B, and bending deformation remains. Therefore, a fairly large force is required to transform from state A to state B. Furthermore, state A in C indicates a state in which the shape is bent due to stress in the longitudinal direction, but in state A of unloading, the residual stress distribution becomes zero and no bending deformation remains. Even if a slight bending deformation (within the elastic range) is applied to state A, the stress distribution will be superimposed as shown by the dotted line because the material has already yielded. This non-uniform stress state leaves residual stress and bending deformation in the unloaded state B. Contrary to the case of deforming from state A to state B, plastic deformation can be applied only by applying a slight bending deformation from state C to state D. This indicates that a material in a plastic state can undergo slight elastic deformation. The function of the Turk's head on the outlet side of the sizing mill is considered to be the same as in the state shown in Fig. 3D. Since the condition 2 is quite unstable, it is impossible to completely straighten all the bends in the steel pipe with one stage of Turkshead. This is the 34th Plastic Working Union Lecture Proceedings (1983-11),
This is also clear from the results of experiments to suppress bending deformation by installing pinch rolls on the exit side of the sizing mill for ERW pipes. On the other hand, installing two levels of Turk's heads was aimed at stabilization. However, as shown in FIG. 4, it is impossible to correct all bends by appropriately selecting the pass line of the first stage of the Turk's head for the final stage of the sizing mill. In other words, since the sizing mill applies a restriction to the steel pipe, the slightest disturbance causes bending deformation, so the steel pipe that comes out of the sizing mill has various bends. Not only the amount of bending may be different, but also the direction of bending may not be uniform. In such cases, even if the pass line of the first stage of the Turk's head shown in FIG. 4 is set to an appropriate value, the bending may sometimes be promoted rather than corrected. Therefore, the first stage of the Turk's head matches the pass line with the last stage of the sizing mill (the pipe centers match).
In order to apply new plastic deformation to correct the bend, it is necessary to appropriately set the pass line of the second stage of the Turk's head. Therefore, in order to remove the bend in the pipe at the exit side of the sizing mill, at least three stages of Turk's heads must be installed on the exit side of the final stage of the sizing mill, as shown in FIG. Furthermore, Fig. 6 shows a bending moment-curvature diagram, and curves 1, 2, and 2 with different initial curvatures,
In No. 3, the difference in residual curvature is reduced by bending and unbending once, but the difference in residual curvature is further reduced by bending and unbending twice and three times. Therefore, if there are large variations in the bending of the pipe coming out of the sizing mill, in order to manufacture straight steel pipe while keeping the roll position of the Turk's head fixed, a minimum of three Turk's heads should be installed, and preferably five. It is necessary to install several steps.

Previously, one or two stages of Turk's heads were installed on the exit side of the sizing mill to straighten the bent steel pipe coming out of the sizing mill.
As described above, since plastic deformation (drawing) is applied by the sizing mill, the straightening operation becomes unstable with a one-stage or two-stage Turk's head, which has the disadvantage that the purpose cannot necessarily be achieved.

The present invention advantageously overcomes these drawbacks. That is, the present invention is to correct any bends in the steel pipe coming out of the sizing mill to manufacture straight steel pipes. This method of straightening the bend of an electric resistance welded pipe is characterized in that three or more stages of heads are installed, the sizing function and the repetitive bending function are separated, and the bend is corrected by applying repeated bending using the Turk's head.

Next, the present invention will be described in detail based on examples.
Figure 2 shows the conventional method in which two stages of Turk's heads are installed for a 139.0φ x 4.35 t steel pipe, and the method of the present invention (in which five stages of the final stage 1 of the sizing mill and the Turk's head are installed) as shown in Figure 1. ). In the conventional method, few pieces passed the standard bending value of 8 mm/12 m or less, and the bends were removed using an off-line straightening machine, but with the method of the present invention, most of the pieces passed the standard value.

(Effect of the invention) By doing so, the present invention completely separates the drawing process of the sizing mill and the straightening function of bending and unbending of the Turk's head, making it possible to manufacture stable and straight steel pipes. .

[Brief explanation of drawings]

Figure 1 shows an example of the method of the present invention, and is an explanatory diagram of equipment in which five stages of Turk's heads are installed on the outlet side of a sizing mill. Figure 2 is a diagram showing a comparison between the method of the present invention and the conventional method. Figures A, B, C, and D are diagrams showing that bending deformation can be achieved with a small force during plastic deformation using an example of bending a beam. Figure 5 is an explanatory diagram of equipment with three stages of Turk's heads installed on the outlet side of the sizing mill, Figure 6 is a bending moment-curvature diagram showing the principle of bending correction, and Figure 7 is an electric resistance welded pipe. FIG. 2 is a diagram showing an outline of a manufacturing line. 1... Roll forming machine, 2... Welding machine, 3... Squeeze roll, 4... Seam heat treatment device, 5...
Sizing mill, 6...Turkshead.

Claims (1)

[Claims] 1. In the production line for electric resistance welded pipes, three or more stages of Turk's heads are installed on the exit side of the sizing mill, the sizing function and the repetitive bending function are separated, and the Turk's heads are used to apply repeated bending to correct the bending. A method for straightening the bending of an ERW tube.