JPH06154849A - Production of square electric resistance welded tube - Google Patents

Abstract

PURPOSE:To prevent brittle fracture with a small electric power. CONSTITUTION:A belt-like steel coil member 11 is heated by a combusion furnace (batch type furnace) 12 using a fossil fuel. The heated band steel coil member 11 is formed in a round tube forming process 14. Before the process 14, the steel coil member 11 is heated in a heating process 13. The edge of the round tube body formed in the forming process 14 is heated in an edge- heating process 15, then butt-welded in a high frequency process 16 to form the electric resistance welded tube. The electric resistance welded tube is heated in a heating process 17, then formed in the square tube in a square tube forming process 18.

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 pipe, particularly a rectangular electric resistance welded pipe.

[0002]

2. Description of the Related Art Heretofore, cold forming has been used to manufacture a rectangular tube. First, a thick plate is formed into a channel shape by a press as shown in FIG. 3A to obtain a pair of molded bodies 1 and 2, and the molded bodies 1 and 2 are butted to each other to form a square shape, and then as shown in FIG. 3B. Then, the formed bodies 1 and 2 are joined by the submerged arc welding method to form a rectangular tube.

Second, as shown in FIG. 3C, after a thick plate is semi-formed into a channel shape by a press, the edges of the joints are high-frequency welded while roll-forming, thereby forming a rectangular pipe.

Third, as shown in FIG. 4, the strip steel coil material 5
Is continuously formed into a circular tube shape at the round forming section 6 and the edges of the seams are subjected to high frequency welding at the high frequency welding section 7 and then formed into a square tube at the corner forming section 8 while cold. It is a measure. The formed rectangular tube is cut into a predetermined length by a cutting device (not shown).

[0005]

As described above, in the case of manufacturing a conventional rectangular tube, the thick plates are strongly bent while cold to form the molded bodies 1 and 2, so that the corner portions are work hardened. Caused deterioration of strength and toughness. In addition, for example, a thick rectangular pipe having a wall thickness of 22 mm or more or an arcuate curvature R of the corner portion is reduced to 3.5 t or less (t is the wall thickness of the pipe) to reduce the working degree of the corner portion. If raised, brittle fracture begins to partially occur, which makes it unsuitable for use in columns of high-rise buildings, which is the main application of rectangular tubes (columns).

Therefore, if the corner portion is processed by hot or warm forming, there is no problem in production, but in order to put hot or warm forming in-line, the furnace length for raising the temperature should be close to 100 m. As a result, the area occupied by the factory site must be increased, and the waste of energy and cost for heating the entire plate to process the corners becomes a problem. In the case of high frequency electric resistance welded pipe welding, if the hot and warm forming of the corner part is made in-line to maintain productivity, the normal production scale will be 100,000 tons / month, so the temperature rise The energy required for this is a heat source equivalent to 100,000 KW level (86 million Kcal / H), and even if induction heating is used to reduce the space, it is difficult to obtain the power supply itself, making it practical. poor. The reason why the above amount of electric power is necessary is as follows. That is, it is already known that in order to obtain good welding characteristics in high frequency electric resistance welded pipe, a good welding result cannot be obtained unless the line (welding) speed is 10 m / min or more. There is a problem that the amount of electric power becomes the above when calculated in consideration of the speed of more than a minute.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a rectangular electric resistance welded pipe capable of manufacturing a rectangular pipe that does not cause brittle fracture with a small amount of electric power.

[0008]

In order to achieve the above object, the present invention provides a first preheating step of preheating a strip steel coil member to a temperature below the transformation point of the steel, and preheating in this first preheating step. Forming the coil member into a round tubular body, a second preheating step of preheating the edge portion of the round tubular body formed in this step, and a round tubular body preheated in the second preheating step. A process of welding the edge parts with each other at high frequency to make a round electric resistance welded pipe, a heating process of heating the electric resistance welded pipe made in this process so that it can be warm-formed into a square pipe, and this heating It is characterized by comprising a step of warm forming the electric resistance welded tube heated in the step into a rectangular tube and a step of cutting the rectangular tube formed in this step. The heat applied to the electric resistance welded pipe in the heating step is set to the recrystallization temperature.

[0009]

[Operation] The strip steel coil member is preheated in the first preheating step. Then, the coil member is formed into a round tubular body in a forming process.
After the edge portion of the round tubular body is preheated in the second preheating step, the edge portions of the round tubular body are welded at a high frequency to form a round electric resistance welded pipe. Then, in the heating step, the electric resistance welded pipe is heated to warm-form the rectangular pipe, and the rectangular pipe is cut at regular intervals.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, 11 is a strip steel coil member, and this coil member 11 is preheated in a batch furnace 12 to a temperature below the A _C3 transformation point of steel. The batch furnace 12 uses a combustion furnace that uses fossil fuel to reduce costs. Reference numeral 13 is a heating step for performing controlled supplemental heat by induction heating or the like. This step 13 is a temperature (450 ° C.) near the outlet in the next round tubular forming step.
The following) is to supplement heat so that it does not drop too much.
14 is a step of forming the coil member into a round tubular shape, and the forming temperature in this forming step 14 is a recrystallization temperature of 450 ° C.
It is performed in the range of 650 ° C. The round tubular body formed in the forming step 14 has a band edge of 750 before the high frequency welding step 16.
It is heated in the edge preheating step 15 by induction heating or the like to a temperature range of ℃ to 900 ℃. After that, high-frequency welding process 16
Then, the band edges are welded to each other to form a round electric resistance welded pipe.

The formed circular electric resistance welded pipe is heated again in a heating step 17 such as induction heating, and then 450 ° C. to 650 ° C.
At the (recrystallization temperature), a warm rectangular tube forming step 18 by circular forming is gradually formed into an angular tube. At the time of this forming, the temperature of the forming inlet is supplemented by the heating step 17 before the inlet of the forming roll so that the temperature can be maintained at 450 ° C. or higher at the final forming point of the rectangular tube forming step 18.

The above circular forming is shown in FIGS.
This is done as in D. That is, in FIG. 2A, the radius is R
₂ shows a cross section of a ₀ electric resistance welded pipe. This electric resistance welded pipe is first formed in the process of FIG. 2B so as to have a large radius of curvature R ₁ and a small radius of curvature R _2, and then sequentially as shown in FIGS. 2C and 2D. The large radii of curvature R ₁ ', R ₁ "at the sides are successively larger, and the smaller radii of curvature R ₂ ', R at the corners are larger.
_{The 2} "is formed into a rectangular tube by shaping it so that it becomes smaller.
In the step of FIG. 2D, for example, R ₂ "= αt (α: 3.5-
2.5, t: wall thickness).

Next, the operation of the above embodiment will be described. The coil member 11 is first preheated in the batch furnace 12 and then placed in the process. The preheated coil member 11 is heated in a heating step 13 and then formed into a round tubular body in a round tubular forming step 14. This round tubular body is welded at the edges of the joints in the high frequency welding process 16 to form a circular electric resistance welded pipe. Before the high frequency welding process 16, the edge is welded so that the welding is performed well. In the preheating step 15, the edge of the round tubular body is heated. Then, the round electric resistance welded tube is formed into a square tube by warm forming in a square tube forming step 18. The formed rectangular tube is cut into a predetermined length in a cutting step 19.

[0014]

As described above, according to the present invention,
The following effects can be obtained.

(1) By preheating both edges to be butt-welded, it is possible to obtain a sound high-frequency welding process for a thick-walled pipe and a healthy electric resistance welded pipe even at a line speed significantly lower than 10 m / min. Therefore, it is possible to manufacture a thick-walled rectangular pipe by the electric resistance welded pipe welding method without requiring a large amount of electric power for hot or warming for warm forming.

(2) As a heat source for heating the strip steel coil member, an off-line combustion type can be used, so that it can be realized in a narrow space. This can significantly reduce the cost.

(3) Since the heating step and the preheating step are performed using electric power such as induction heating, controllability and reproducibility are obtained, and stability is greatly improved.

(4) It becomes possible to prevent the deterioration of the structure and strength of the corner portion (corner portion) due to the square tube molding. Efficiently manufacturing high-quality thick-walled rectangular steel pipes with strength and soundness at the corners by the electric resistance welded pipe manufacturing method, including cases where the radius of curvature of the corners is smaller than the wall thickness of the pipes. You can

[Brief description of drawings]

FIG. 1 is a manufacturing process explanatory view showing an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the embodiment.

3A and 3B show a method for manufacturing a rectangular tube of a conventional example, where A is a perspective view before welding by the first method, B is a perspective view after welding,
FIG. 3C is a perspective view after press molding by the second method.

FIG. 4 is an explanatory view of a manufacturing process of a conventional rectangular tube.

[Explanation of symbols]

 11 ... Strip steel coil member 12 ... Batch furnace 13 ... Heating step 14 ... Round tubular forming step 15 ... Preheating step 16 ... High frequency welding step 17 ... Heating step 18 ... Square tube forming step

Claims (2)

[Claims] 1. A first preheating step of preheating a strip steel coil member to a temperature below a transformation point of steel, a step of forming the coil member preheated in the first preheating step into a round tubular body, and this step For preheating the edge of the round tubular body formed by
A preheating process, a process of welding the round tubular body preheated in the second preheating process at a high frequency to make an electric resistance welded pipe, and warm forming the electric resistance welded pipe made at this process into a rectangular pipe. Characterized by comprising a heating step of heating as much as possible, a step of warm forming the electric resistance welded tube heated in the heating step into a rectangular tube, and a step of cutting the rectangular tube formed in this step Method for manufacturing rectangular electric resistance welded pipe. 2. The method for manufacturing a rectangular electric resistance welded pipe according to claim 1, wherein the heating applied to the electric resistance welded pipe in the heating step is performed within a recrystallization temperature range.