JPH06134581A - Manufacture of electric resistance welded tube - Google Patents

Abstract

PURPOSE:To prevent the generation of lap butt by a simple method without requiring a big equipment investment by working both side edges of the tip of strip steel into a tapered shape obtained from the peripheral length of squeeze rolls in advance. CONSTITUTION:The side ends corresponding to both side edges 1a and 1b of the tip of the strip steel 1 are notched by cutting or machining in advance so as to formed into a tapered shape along a cut line. The drawing quantity S shows the variation of the peripheral length of an open pipe in front and in rear of the squeeze rolls and since it is coincident with the crossing quantity of edges 1a and 1b at both sides at the time of generating lap butt, when it is reduced above values of the width W and S at the tip of the strip steel 1, the edges 1a and 1b at both sides are not joined to each other even if these are bitten into the squeeze rolls, hence lap butt is not generated. Accordingly, the tip loss length of the strip steel 1 can be reduced and the product yield is improved greatly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electric resistance welded steel pipe, and more particularly to a method for preventing lap butting of an edge portion of an electric resistance welded steel pipe.

[0002]

2. Description of the Related Art Generally, in the production of electric resistance welded steel pipe, as shown in FIG. 3, a strip-shaped steel strip (hereinafter, referred to as strip steel) 1 guided by a guide roll 2 is sequentially cylindrical by a plurality of breakdown rolls 3. Fin pass roll 4
Is subjected to reduction in the circumferential direction to stably form the seam edge, and finish-molded into the open pipe 1A having a predetermined size and shape, and the seam guide 5 adjusts the center of the seam. From the contact tip 6 to a circular shape by upsetting welding with a squeeze roll 7 and then cutting a weld bead portion with a bead cutting device 8 and the like, and then a predetermined outer diameter and length. ERW steel pipe 1B having is manufactured.

By the way, in the case of manufacturing a so-called medium diameter electric resistance welded steel pipe having a diameter of 6 inches or more without performing the band welding of the strip steel, the strip steel 1 is formed on the fin pass roll 4 as shown in FIG. 4 (a). 4C and the cage roll 4b, in the process of being formed into a cylindrical shape, a left-right edge 1a, 1b may have a height difference Δh due to an asymmetrical shape as shown in FIG. 4B. This phenomenon is considered to be caused by bending of the strip steel 1 and misadjustment of the forming roll. However, if this height difference Δh occurs, the squeeze roll 7
In front of a, as shown in Fig. 4 (c), the open pipe 1A
It appears as a front-back difference Δa of the tip end of, and causes the following problems.

That is, the squeeze roll 7 used in the manufacture of medium-diameter electric resistance welded steel pipe is usually a pair of right and left squeeze rolls as shown in the four roll type of FIG. 5 (a) or the five roll type of FIG. 5 (b). Since the roll 7a is configured by combining the upper squeeze roll 7b or the lower squeeze roll 7c, if the front-back difference Δa of the open pipe 1A is large as described above, as shown in FIG. When being bitten by 7, the edge 1a that protrudes forward with respect to the traveling direction hits the upper roll of the squeeze roll 7b first and is pushed down.

At this time, the rear side edge 1b does not hit the upper side roll at the same time as the front side edge 1a, so that the height position thereof does not change, and therefore both side edges 1a, 1b.
There will be a step between the two. Due to this step, when passing through the squeeze roll 7, as shown in FIG. 6 (b), the edge 1a on the pushed-down side slips under the other edge 1b, and the so-called lap abutting portion is formed. 9 will be formed.

Therefore, such a lap abutting portion 9
When a problem occurs, a notch 10 as shown in FIG.
It is common to start the welding of the edge portion after the heights of a and 1b are aligned.

[0007]

However, if the above-mentioned notch 10 is made, the welding start point will be delayed rearward, and the length of the unwelded portion at the tip of the open pipe 1A will be delayed accordingly. Becomes longer, which causes a problem that the yield of products is deteriorated. As one of means for preventing such lap butting, for example, Japanese Patent Publication No. 60-33586 discloses a squeeze roll in which a squeeze roll housing is circumferentially rotated with respect to a squeeze roll stand in accordance with the size of the lap. A method of matching the center of the space with the abutting position of the edge part is disclosed, but if this method is applied to manufacturing equipment for medium-diameter ERW steel pipes with a large diameter, it will cost a huge amount of money to modify the roll stand, etc. It requires space and cannot be a realistic solution.

Further, Japanese Laid-Open Patent Publication No. 1-210175 discloses a means for obtaining a position adjustment amount of a squeeze roll that eliminates a step between edges based on a temperature difference between both edge portions immediately before welding. There is a drawback that it cannot be applied to the tip of the open pipe, which is the part where heating by (1) has not started. The present invention has been made in view of the above problems of the prior art, and of an electric resistance welded steel pipe capable of preventing the occurrence of lap butting by a simple method without requiring a large capital investment. It is intended to provide a manufacturing method.

[0009]

According to the present invention, when a medium-diameter size electric resistance welded steel pipe is manufactured using a strip-shaped steel sheet, both side edges of the tip end portion of the strip-shaped steel sheet are preliminarily obtained from the circumference of a squeeze roll. It is a method of manufacturing an electric resistance welded steel pipe, which is characterized in that it is processed into a shape. The tapered shape is L>
It is desirable that (1/2) S and 0.1 ≧ tan θ ≧ 0.05 be satisfied. Here, L is the cutting distance from the side end of the front end of the strip-shaped steel sheet, S is the amount of reduction of the circumferential length of the squeeze roll, and θ is the cutting angle.

[0010]

[Operation] According to the present invention, as shown in FIG.
Since the side end portions corresponding to the edges 1a and 1b on both sides of the tip end are cut or cut in advance so as to form a taper shape along the cut line 11, it is possible to prevent the lap butting. Will be possible.

Here, the cutting distance L from the side end portion at the tip portion is 1 / the reduction amount S of the circumferential length of the squeeze roll.
Explaining the reason why the value is set to be larger than 2, the reduction amount S represents the amount of change in the circumferential length of the open pipe before and after the squeeze roll, and coincides with the amount of intersection of the edges 1a and 1b on both sides when lap butting occurs. Therefore, if the width W at the tip of the strip steel 1 is shortened to the value of S or more, the edges 1a and 1b on both sides are not joined even if they are bitten into the squeeze roll, so that the lap butting is also possible. It will not happen.

The reason why the angle θ formed by the cut line 11 and the lateral line of the steel strip 1 is limited to the range of 0.1 ≧ tan θ ≧ 0.05 is shown in FIG. 1 when tan θ is larger than 0.1. Buckling may occur at the time of passing through the squeeze roll at the part A, and if tan θ becomes smaller than 0.05, the unwelded part of the strip steel 1 becomes too long, impairing the yield improvement effect of the product. Because.

[0013]

Example When manufacturing a 20-inch ERW pipe using a strip steel having a plate thickness of 6.5 mm and a width of 1595 mm, the following two experiments were conducted to confirm the effect of the present invention. [Experiment 1] First, tan θ was set to three levels of 0.15, 0.1 and 0.05, and the edge was cut with a gas cutter before the start of bending.
It cut so that the cutting distance L might be 45 mm, 30 mm, and 15 mm. As a result, when tan θ was 0.15, buckling occurred at a position 300 mm from the tip corresponding to point A, and normal welding could not be performed. When tan θ was 0.10 and 0.05, no lap butting occurred. [Experiment 2] Next, with tan θ set to 0.10, the edge was cut by using an edge cutting machine by milling and gradually changing the cutting allowance. The loss length at the tip of the steel strip for various plate thicknesses at this time is shown by the ● mark in FIG. For comparison, the loss length obtained by the conventional method in which the edges were not cut is also shown by a circle in the figure.

As is apparent from this figure, it is understood that the loss length according to the present invention example can be reduced by about 0.5 m as compared with the conventional example.

[0015]

As described above, according to the present invention,
The edges corresponding to the edges on both sides of the steel strip are pre-cut to prevent the occurrence of lap butting, which makes it possible to reduce the loss length of the steel strip leading to improved product yield. Greatly contribute.

[Brief description of drawings]

FIG. 1 is a plan view showing a strip steel to which the method of the present invention has been applied.

FIG. 2 is a characteristic diagram showing the relationship between the plate thickness and the loss length at the tip of the steel strip.

FIG. 3 is a schematic view showing a manufacturing process of a conventional electric resistance welded steel pipe.

4 (a), (b) and (c) are explanatory views showing a process of forming a steel strip into a cylindrical shape.

FIG. 5 is a front view showing an example of the configuration of a squeeze roll used for manufacturing a medium-diameter electric resistance welded steel pipe.

6 (a) and 6 (b) are explanatory views of a mechanism of occurrence of lap butting.

FIG. 7 is an explanatory diagram of a conventional countermeasure for lap butting.

[Explanation of symbols]

 1 Strip Steel (Strip Steel Strip) 1A Open Pipe 1B ERW Steel Pipe 3 Breakdown Roll 4 Fin Pass Roll 5 Contact Tip 7 Squeeze Roll 9 Lap Butt 11 Cut Line

Claims (2)

[Claims] 1. When manufacturing a medium-diameter electric resistance welded steel pipe using a strip-shaped steel sheet, both side edges of the front end portion of the strip-shaped steel sheet are processed into a taper shape previously obtained from the circumference of the squeeze roll. ERW steel pipe manufacturing method. 2. The taper shape is L> (1/2) S
2. The method for manufacturing an electric resistance welded steel pipe according to claim 1, wherein 0.1 ≧ tan θ ≧ 0.05 is satisfied. Here, L is the cutting distance from the side end of the front end of the strip-shaped steel sheet, S is the amount of reduction of the circumferential length in the squeeze roll, and θ is
Is the cut angle.