JPS58173025A - Prevention method of forming flaw in case of forming welded steel pipe - Google Patents

Abstract

PURPOSE:To prevent forming flaws and penetrater of weld zone by sticking protective sheet on a steel strip or steel plate during forming process when manufacturing a steel pipe by forming a steel strip or steel plate successively into a cylindrical form and welding edges to each other. CONSTITUTION:A steel strip 2 that passed through an entry device 1 goes through forming processes of a break down roll 3, a side roll 4, and a fin pass roll 5 to produce an open pipe and edges are butt welded by a welding machine. Then, it is corrected by a sizing roll 7 and cut to obtain a product. Protective sheet 8 is stuck on one side or both sides of the steel strip that arrives at the roll 3 to allow stripping off, and formed into an open pipe through forming process. Then, just before arriving at the welding machine 6, the sheet is stripped off from the open pipe and welded. The sheet 8 is PVC adhesive sheet etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing forming flow during forming of welded steel pipes, and in particular, a method for peeling off a protective sheet formed on a forming surface before welding so as not to cause any inconvenience during welding work. This is a proposal for a method characterized by effectively preventing molding flow.

rW welded steel pipes include electric resistance welded steel pipes and UOE steel pipes, among which the former is formed into a cylinder by sequential forming using forming rolls arranged in rows, while the latter is formed into a cylinder by stepwise pressing through a mold. A common manufacturing method is to mold the blade into a shape, and then weld the two edges together.

The above-mentioned molding process often causes molding flow such as scratches on the contact surface with rolls, molds, etc., that is, the molding surface. Moreover, if a large amount of water or lubricant is used to prevent such forming flow, some of it will remain attached to the edge, so if resistance welding is performed as is, a defect called penetration will occur in the joint, leading to quality deterioration. There was a problem.

Conventionally, this problem has been prevented by 1) wiping off the adhering water and oil or blowing it off with compressed air immediately before welding, and 2) impregnating the surface of forming rolls with resin or polymerizing soft alloys. becomes softer than the material,
■Also, the surface of the forming roll etc. is coated with T soil 0□, Ti
The molded bottom has been prevented by impregnating the surface with N or applying hard chromium plating to harden the surface, but in addition to not achieving the expected effect, maintenance is time-consuming and expensive. It had the disadvantage of being bulky.

This invention was developed with the aim of overcoming the drawbacks of the conventional forming flow prevention technology described above, and involves sequentially forming steel strips or steel sheets into a cylindrical shape using rows of IW rolls or presses to form edge surfaces. When making a welded steel pipe by welding through the butt forming process, a protective sheet is first pasted on one or both sides of the copper strip or steel plate before the above forming, and then after the forming is completed and before welding. This is a technique in which a welded steel pipe without a formed bottom is obtained by peeling off the protective sheet. The details of the configuration will be explained below.

Fig. 1 is a diagram of an electric resistance welded steel pipe manufacturing apparatus (d) suitably used in carrying out the present invention.
After passing through breakdown rolls 8, side rolls 4, and fin pass rolls 5 to form an open pipe, the edges are butt-welded using a high-frequency welder 6, and then straightened by sizing rolls 7 and sent to a cutter. The product is then cut into a predetermined length.

In the above-mentioned pipe forming process (hereinafter referred to as the forming process), the present invention applies a removable protective sheet 8 to one or both sides of the steel strip 2 that passes through the entry process and reaches the breaker down roll 8 in advance, The structure is characterized in that after it is formed into an open pipe on a forming stand, the protective sheet 8 is peeled off from the open pipe just before it reaches the welding machine 6 and welded.

The reason why the protective sheet 8 is removed before reaching the welding machine 6 as described above is that if the protective sheet 8 is applied to the welding machine 6 with the protective sheet 8 attached, it is certainly effective in preventing molded bottoms, but This is because the heat generated causes the protective sheet 8 to shrink and stick to the surface of the steel pipe in a diffused state, causing inconveniences such as smoke generation in subsequent processes such as upper post annealing, which requires time and effort to remove.

The protective sheet used in the above sense may be a sheet made of synthetic resin such as vinyl chloride or polyethylene, as well as cloth or paper, but preferably one that can withstand the pressure of roll forming without tearing. A sheet of vinyl chloride is suitable as the material. Furthermore, while the adhesive used in association with the protective sheet 8 has a strong adhesion force during forming, it is necessary that no adhesive residue remains on the steel pipe when it is peeled off. When applying the protective sheet 8, it is preferable to use a pressure-sensitive adhesive sheet with an adhesive coated on one side of the sheet in advance, in order to simplify the process of applying the protective sheet 8.

The protective sheet 8 can be applied at any time before starting the forming process, but it has been found that it is best to apply the protective sheet 8 just before forming, as if it is applied too early, the adhesive force will be too strong and it will be difficult to peel it off. .

In the illustrated example, the sheet pasting machine 9 for the protective sheet 8 is placed in front of the forming stand if, and the sheet peeling machine IO is placed immediately after the fin pass roll 5, so that the peeled protective sheet 8' is placed on the sheet outside the line. This is an example in which winding is performed by winding fill.

The above examples are all about electric resistance welded steel pipes, but U
The present invention can also be applied to other welded steel pipes such as OEJ pipes.

As explained above, according to the present invention, the formed bottom of the welded steel pipe is not seen at all, and it has been found that it works effectively to prevent penetrators in the welded portion, so that high quality products can be manufactured with a high yield.

[Brief explanation of the drawing]

FIG. 1 shows an electric resistance stitch suitable for carrying out the method of the present invention. s
FIG. 2 is a front view of an i-tube manufacturing device. ■...Entry device 2...Steel strip 8...Breakdown roll 4...Side roll 5...Fin pass roll 6...Welding machine 7...Sizing roll 8.8'...・Protective sheet 9... Sheet pasting machine 1
0... Sheet stripping @@ 1.1... Sheet winding machine.

Claims (1)

[Claims] 1. When making a welded steel pipe by sequentially forming a steel strip or steel plate into a cylindrical shape using rolls or presses arranged in rows and welding the steel strip or steel plate through a forming process in which the edges are butted, first, prior to the above-mentioned forming, an 8g strip or A method for preventing forming flow during forming of welded steel pipes, which comprises applying a protective sheet to one or both sides of a steel plate, and peeling off the protective sheet after forming and before welding.