JPH08267150A - Production of metallic welded tube - Google Patents

Abstract

PURPOSE: To prevent the occurrence of flaws on surface and to produce a welded tube with high quality by a Die-draulic forming method. CONSTITUTION: A forming die 20 formed with a through-hole 22 whose diameter is made smaller from the inlet side toward the outlet side by 20 to 30 deg. taper angel is used, a plate-shaped metallic strip 1 is passed through the through-hole 22 and formed in a cylindrical shape that both end parts of the width direction are abutted on each other, then both end parts of the width direction are subjected to but welding to produce a welded tube 1c. Since the taper angle is regulated to 20 to 30 deg., the drawing force applied on a forming die 20 during forming is decreased and the occurrence of flaws on the surface of the forming die and the metallic strip 1 can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a welded pipe having no surface flaw by a die draw forming method.

[0002]

2. Description of the Related Art In the production of welded pipes, a roll forming method is generally employed in which a metal strip is bent in the width direction with a product curvature to form a tubular shape, and both ends in the width direction are welded. In the roll forming method, as shown in FIG. 1, forming rolls or cage rolls 2 each having a plurality of calibers are arranged in tandem along a running line of the metal strip 1. Both ends 1a in the width direction of the metal strip 1 are sequentially bent. The metal strip 1 formed in a tubular shape is held by the seam guide rolls 3 or the squeeze rolls 4, for example, the abutting portions 1b at both ends are welded by the welding torch 5, and delivered as a welded pipe 1c. When changing the diameter of the welded pipe 1c to be manufactured by the roll forming method, all of the forming rolls or cage rolls 2, seam guide rolls 3, squeeze rolls 4 and the like correspond to the outer diameter of the welded pipe 1c to be manufactured. You need to replace it with something. Moreover, since there are at least 20 or more roll sets that need to be replaced corresponding to one type of outer diameter, it takes a lot of labor and a long time to replace the rolls.

Since the pipe making line is stopped when the rolls are replaced, the production efficiency of the equipment is reduced. Further, since it is necessary to stock a large number of rolls corresponding to the outer diameter of the welded pipe to be manufactured, the economical burden is large and a space for storing the rolls is required. Further, if there is a setting error in some of the roll positions of each roll set, the twist of the welded pipe 1c and a step difference in the abutting portion 1b are likely to occur. The step generated in the abutting portion 1b makes the welding conditions unstable and causes defects such as deterioration of the bead shape and insufficient penetration. As a result, particularly in the manufacture of small-diameter pipes, high accuracy is required for the installation position of each roll group, and the labor and work time required for roll replacement is further increased.

As a pipe forming method in which the roll exchange is simplified,
A die draw forming method in which a tubular formed body is formed at once from a metal strip by drawing using a forming die is introduced in Japanese Patent Publication No. 39-18657. As shown in FIG. 2, the die draw forming method uses a molding die 7 in which a through hole 6 whose diameter is sequentially reduced along the running direction of the metal strip 1 is formed. When the metal strip 1 passes through the through hole 6, the metal strip 1 is curved in the width direction from both end portions 1a following the diameter of the through hole 6 and has a predetermined outer diameter at the parallel portion 8 having the smallest diameter on the exit side of the through hole 6. And is sent out as a tubular body having a shape corresponding to the welded pipe to be manufactured. The formed metal strip 1 is annealed using a non-oxidizing furnace by high frequency induction heating after the butt portions 1b are sequentially welded. In addition, Japanese Patent Publication No. 4-18925 discloses a series of production lines in which a welded pipe produced in this manner is subjected to corrugation processing and continuously subjected to bright heat treatment in a non-oxidizing gas atmosphere. The die draw forming method is a method in which the flat metal strip 1 is pulled out from the through hole 6 on the entry side of the forming die 7 and formed into a tubular shape, so that the equipment cost is significantly lower than that of the roll forming method. Further, even when the outer diameter of the welded pipe 1c to be manufactured is changed, it is only necessary to prepare a die corresponding to the outer diameter of the welded pipe 1c, so that the production efficiency is not reduced.

[0005]

When the metal strip is bent by the die draw forming method, both side edge portions 1a of the metal strip 1 first come into contact with the through holes 6 of the molding die 7. While the forming is progressing inside the through hole 6, the bending moment in the width direction during forming is the smallest at both side edge portions 1 a of the metal strip 1. Therefore, the both side edge portions 1a of the metal strip 1 are drawn into the tapered portion of the through hole 6 until just before the parallel portion 8 of the through hole 6 with almost no bending work. That is, the both side edge portions 1a of the metal strip 1 slide on the tapered surface on the side of the through hole 6 just in contact with the tapered surface on the side of the through hole 6 with a high surface pressure. If molding is continued for a long time in this state, a flaw is generated on both side edge portions 1a of the metal strip 1 and a portion of the tapered surface on the entrance side of the through hole 6 with which the both side edge portions 1a of the metal strip 1 contact is damaged. The life of the molding die 7 is shortened. Further, when the metal powder that has fallen off from the flaws generated on both side edge portions 1a of the metal strip 1 is accumulated inside the molding die 7, it may cause surface flaws on the metal strip 1. Therefore, in the die draw forming method, it is required to interrupt the molding work and frequently care for the molding die 7.

When the friction between the molding die 7 and the metal strip 1 is reduced, the generation of flaws on the surfaces of the molding die 7 and the metal strip 1 is suppressed. The present inventors have found that it is effective to apply a lubricant to the lower surface of the metal strip that comes into contact with the forming die 7, that is, the entire surface on the outer surface side of the welded pipe 1c, on the basis of such a premise. I applied. As the lubricant, for example, a solution having a composition of 50.5% of polyether polyol, 10.5% of higher alcohol, and 39.0% of anticorrosive active agent, diluted with water is used. However, even when the molding is performed while applying the lubricant, the flaws may still occur on the surfaces of the molding die 7 and the metal strip 1.
The present invention has been devised to solve such a problem, and by using a molding die having a through-hole with a regulated taper angle, it is possible to suppress flaws generated on the molding die and the surface of the metal strip. In addition, it is an object of the present invention to suppress the cost increase of the molding die and to manufacture a high-quality welded pipe having no surface flaw.

[0007]

In order to achieve the object, the method for producing a metal welded pipe of the present invention is provided with a through hole having a taper angle of 20 to 30 degrees from the inlet side to the outlet side, the diameter of which is reduced. Using a forming die, a flat metal band is passed through the through hole to form a tubular shape having both ends in the width direction butted together, and then both ends in the width direction are butt-welded. In the pipe making line according to the present invention, for example, the equipment configuration shown in FIG. 3 is adopted. The metal strip 1 unwound from the uncoiler is sent out as a welded pipe 1c via the lubricant applying device 10, the forming die 20, the wiping device 30, and the welding device 40. The lubricant applying device 10 pumps the water-soluble lubricant 12 contained in the tank 11 into a pump 13
Is pumped up to the coating tank 14. A coating roll 15 is rotatably immersed in the coating tank 14. The water-soluble lubricant 16 sent to the coating tank 14 is coated on the surface of the metal strip 1 by the coating roll 15. Excessive amount of lubricant attached to the metal strip 1 is wiped off the surface of the metal strip 1 by the elastic roll 17 arranged on the downstream side of the coating roll 15.
After being received by the recovery tank 18, it is returned to the tank 11.

The metal strip 1 coated with the lubricant is molded by a molding die 20 into a cylindrical shape having a predetermined outer diameter.
As the molding die 20, as in the conventional case, the die body 2
A die having a through hole 22 formed in 1 is used.
The through hole 22 has a taper whose diameter decreases from the inlet side to the outlet side, and has a parallel portion 23 having a minimum diameter corresponding to the outer diameter of the welded pipe 1c to be manufactured near the outlet side. The through holes 22 formed in the molding die 20 have 20 to 20 holes.
It is preferable to have a taper angle of 30 degrees. If the taper angle of the through hole 22 is appropriate, the forming die 20 and the metal strip 1
Generation of flaws on the surface is suppressed. However, if the taper angle is less than 20 degrees or more than 30 degrees, the drawing force applied to the molding die 20 increases, and even if a lubricant is used, many metal bands 1 and the inner surface of the molding die 20 after molding have a large number. Surface flaws occur. As a result, the cost of the forming die 7 increases, and the production yield of good welded pipes also decreases.

The metal strip 1 formed into a predetermined cylindrical shape by the forming die 20 is immediately sent to the wiping device 30. That is, by wiping off the lubricant adhering to the surface of the metal strip 1 with the wiping device 30 before drying,
The lubricant is efficiently removed and is not brought into the welding device 40 on the downstream side. Next, the metal strip 1 is sent to the welding device 40, both ends in the plate width direction are butt-welded, and sent to the lower step as the welded pipe 1c. In this way, when the metal strip 1 is fed into the molding die 20 whose taper angle is regulated and is molded, the metal strip 1 is molded into a good tubular shape without the occurrence of surface flaws. As a result, a high quality welded pipe 1c is manufactured, and it is not necessary to frequently replace the forming die 20.

[0010]

【Example】

Example 1: As the metal strip 1, a plate thickness of 0.7 mm and a plate width of 3
A 0.7 mm austenitic stainless steel plate was prepared. A solution having a composition of 50.5% polyether polyol, 10.5% higher alcohol and 39.0% rust inhibitor was used as lubricant. Concentrate this lubricant with water to 15
A water-soluble lubricant 16 diluted to volume% was prepared, and 20 liters of the lubricant was stored in the tank 11. The forming die 20 is made of tungsten carbide and has through holes 22 having a diameter of 35 mm on the inlet side and a diameter of 10 mm on the outlet side with taper angles of 20 degrees, 22 degrees, and
Five kinds of dies formed at 25 degrees, 27 degrees and 30 degrees were used. In each case, a composite film of titanium carbide and titanium nitride was formed on the inner surface of the through hole 22 by a chemical vapor deposition method. The water-soluble lubricant 16 was applied to the entire lower surface of the metal strip 1 unwound from the uncoiler by the application roll 15, and the excess lubricant was removed by the elastic roll 17. And pipe making speed 4m /
The metal strip 1 is fed into the forming die 20 in a minute, and both side edges 1
It was formed into a tubular shape in which b was butted. The formed cylindrical metal strip 1 was sent to the wiping device 30 to wipe off the lubricant adhering to the surface. After heating and drying the metal strip 1 by the heater 35, the butt portion was TIG welded using the welding torch 43 while supplying the shielding gas at a flow rate of 10 liters / minute. The obtained welded pipe 1c was of high quality with no surface defects. Further, the molding die 20 had no surface flaw.

Comparative Example 1: Forming die 20 has a taper angle of 18
A welded pipe 1c was manufactured under the same conditions as in Example 1 except that the through holes 22 were formed at regular intervals. When the obtained welded pipe 1c was observed, many defects were found on the surface. Further, a flaw is also generated on the tapered surface of the molding die 20, and the parallel portion 23
A trace of the metal strip 1 burned in the vicinity was observed. Comparative Example 2: Through-hole 2 with a forming die 20 at a taper angle of 33 degrees
2, except that the welded pipe 1c was formed under the same conditions as in Example 1.
Was manufactured. When the obtained welded pipe 1c was observed, as in Comparative Example 1, many defects were found on the surface. A flaw was also generated on the tapered surface of the molding die 20, and a trace of the metal band 1 seizing near the parallel portion 23 was observed.

Summarizing the above results, as shown in FIG. 4, when the taper angle of the through hole 22 formed in the molding die 20 is in the range of 20 to 30 degrees, the molding die 20 is formed.
It was also confirmed that a good welded pipe 1c was produced without causing a flaw on the surface of the metal strip 1. Further, when the pulling force applied to the molding die 20 during molding was measured,
As shown in FIG. 5, the pull-out force tended to decrease in the taper angle range of 20 to 30 degrees. On the other hand, when the taper angle was less than 20 degrees or more than 30 degrees, the drawing force was increased. Due to this increase in pulling force, Comparative Examples 1 and 2
It is considered that surface flaws occurred in the welded pipe 1c and the molding die 20 as shown in FIG.

[0013]

As described above, in the present invention, when a metal strip is formed into a tubular shape by the die draw forming method and both ends in the plate width direction are welded to manufacture a welded pipe, the welded pipe is inserted from the inlet side. By using a molding die in which a through hole that reduces in diameter at a taper angle of 20 to 30 degrees toward the exit side is formed,
The pulling force applied to the forming die is reduced, and the metal strip can be formed into a tubular shape without causing surface defects. As a result, high quality welded pipe is produced. In addition, since the generation of surface flaws in the molding die is suppressed, it is not necessary to frequently replace the molding die, and the manufacturing cost can be reduced.

[Brief description of drawings]

[Figure 1] Pipe making line adopting the conventional roll forming method

FIG. 2 Molding die used in die draw forming method

FIG. 3 Pipemaking line according to the present invention

[Fig. 4] Appropriate range of taper angle of the through hole formed in the molding die

[Fig. 5] Relationship between taper angle and drawing force applied to forming die

[Explanation of symbols]

1: Metal strip 1a: Both side edges 1b: Butt portion 1
c: Welded pipe 20: Forming die 21: Die body 22: Through hole 23: Parallel part

Claims (1)

[Claims] 1. A taper angle of 20 to 50 from the entrance side to the exit side.
A forming die having a through hole whose diameter becomes smaller at 30 degrees is used, and a flat metal band is passed through the through hole to form a tubular shape in which both ends in the width direction are butted against each other. A method for manufacturing a metal welded pipe by butt welding.