JPH08238578A - Production of thick and small-diameter electric resistance welded tube - Google Patents

Abstract

PURPOSE: To provide a process for producing a thick and small-diameter electric resistance welded tube which is increased in thickness while its diameter is reduced by a forging machine. CONSTITUTION: This process for producing the electric resistance welded tube by roll forming a steel strip having a prescribed width and subjecting the formed steel strip to high-frequency welding comprises pushing the steel tube after welding into a rotary forging machine which has >=4 pieces of dies and is adjusted in the taper angle of the dies to <=20 deg., thereby increasing its thickness while reducing its diameter. As a result, the production of the thick electric resistance welded tube having less deviation in the thickness is made possible.

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 a small diameter ERW steel pipe having a large thickness.

[0002]

2. Description of the Related Art Generally, when a thick-walled steel pipe is manufactured by an electric resistance welded steel pipe, as shown in FIG. 5, a thick steel strip having a thickness close to the final thickness is roll-formed by several stages of forming stands to form a tubular shape. After that, it is welded at a high frequency and made to have a predetermined outer diameter wall thickness with a sizer. This method is the most efficient and highly productive method for manufacturing steel pipes and is widely used, but the ratio t / D of thickness t to outer diameter D is 10% or more. However, there are various problems that hinder the efficiency and productivity. Further, there is a limit to the manufacturable t / D due to the roll forming property on the molding stand. For this reason, attempts have been made to invent a new roll forming method and solve these problems, for example, Japanese Patent Laid-Open No. 5-30.
As described in Japanese Patent No. 9422, a new roll forming method of the former breakdown is proposed.

[0003]

As described above, a method of an electric resistance welded steel pipe in which a steel strip having a thickness close to the final thickness is roll-formed by several stages of forming stands to form a tubular shape and then welded at high frequency. In the case of manufacturing a thick-walled steel pipe, if the ratio t / D of the thickness t to the outer diameter D is 10% or more, there are various problems, which hinders efficiency and productivity. Also, t / D that can be manufactured from the roll forming property on the molding stand
Has a limit.

In order to solve these problems, (1) a roll forming method and (2) a thickening method by squeezing after manufacturing a pipe have been studied. In the former roll forming method, the edge part of the plate cannot be bent sufficiently in the initial stage, and in order to bend while restraining the whole in a state of being in a tubular shape in the latter stage, not only it cannot be bent sufficiently, There is also a new problem of increasing the thickness of the edge portion. In the latter method of increasing the thickness by squeezing after pipe production, squeeze rolling by a roll is usually performed, but this requires tension and is not efficient because of a small amount of thickness increase.

Therefore, in order to solve the above-mentioned problems when manufacturing a thick-walled pipe in an electric resistance welded steel pipe, the present invention pushes it into a rotary forging machine in a thickening method by reducing after pipe production, and increases the diameter while reducing the diameter. The purpose is to produce a thick-walled electric resistance welded steel pipe by making it thick.

[0006]

The object of the present invention, which achieves the above object, is to provide a method for producing an electric resistance welded pipe in which a steel strip having a predetermined width is roll-formed and high-frequency welded. In, the production of thick-walled small-diameter ERW steel pipe characterized by having 4 or more dies after welding and pushing into a rotary forging machine with a taper angle of 20 ° or less to increase the wall thickness while reducing the diameter. On the way.

Hereinafter, the present invention will be described in detail. FIG. 1 shows the manufacturing process of the present invention. In the conventional process, as shown in FIG. 5, a steel strip having a predetermined width is continuously inserted into a forming roll, and a tube is roll-formed and then high-frequency welding is performed. After that, the tube was slightly squeezed with a standard roll to make it a perfect circle, but there was almost no increase in wall thickness. Therefore, as shown in FIG. 1, tubular roll-forming, high-frequency welding, and standard shaping are performed, followed by rotary forging. At this time, the drawing with the standard roll is made to be a perfect circle, but since it is the rotary forging that finally makes a perfect circle, the standard roll may be omitted.

Next, a general rotary forging is shown, and its structure is shown in FIG. One or several spherical punches 1 are rotated around the die 2, and the die is also an object (tube).
Push the object while rotating it around 3. As a result, the object is reduced in diameter to a predetermined shape to measure the thickness increase. At this time, the most important thing is dimensional accuracy. Such general rotary forging generally has poor dimensional accuracy, particularly thickness accuracy, and also has poor surface quality. This is basically due to forging. The biggest point to solve these problems is the shape of the die. When the number of dies is small, the uneven thickness increases, and when the number of dies is large, the equipment cost increases and the cost becomes a problem. Therefore, the number of dies is set to 4 or more, and the taper angle of the die shown in FIG. 3 is set to 20 ° or less.

As shown in FIG. 4, the optimum condition exists because the uneven thickness decreases as the number of dies increases, and the uneven thickness increases as the taper angle of the die increases. The number of dies is 4, The taper angle of the die is 20 °. However, even if the number of dies is increased, the uneven thickness is reduced. Further, the lower the taper angle of the die, the less the uneven thickness, so it was set to 20 ° or less. However, the optimum condition is equipment cost,
It goes without saying that the cost can be reduced. Thus, the present invention, by pushing in a rotary forging machine having four or more dies in the thickening method by drawing after tube production and having a die taper angle of 20 ° or less, and increasing the thickness while reducing the diameter, It became possible to manufacture thick ERW steel pipes.

[0010]

EXAMPLES Table 1 compares the conventional method and the method of the present invention with a size of φ42.7 × t8.0. In order to reduce the uneven thickness, which is not possible by the conventional tube manufacturing method or the conventional rotary forging machine method, if the method and conditions as shown in Table 1 are used, the uneven thickness can be obtained. It is possible to manufacture a few thick ERW steel pipes. In the evaluation, the case where the uneven thickness is 15% or less and the surface properties are good was evaluated as ◯.

[0011]

[Table 1]

[0012]

As described above, in the case of the conventional method,
When the ratio t / D between the thickness t and the outer diameter D is 10% or more, there are various problems, which hinders efficiency and productivity. Also, it can be manufactured from the roll forming property on the molding stand.
/ D has a limit, and even in the thickening method by pipe drawing, uneven thickness has conventionally been generated. On the other hand, by applying the method of the present invention, it is possible to manufacture a thick-walled electric resistance welded steel pipe with less uneven thickness, and to provide a manufacturing method extremely advantageous in industry.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of the present invention,

FIG. 2 is a diagram showing a rotary forging machine,

FIG. 3 is a diagram showing a taper angle of a die,

FIG. 4 is a diagram showing the relationship between the number of dies, the taper angle of the dies, and the uneven thickness;

FIG. 5 is a diagram showing a conventional manufacturing process.

[Explanation of symbols]

 1 Punch 2 Die 3 Object (tube) 4 Die taper angle

Claims (1)

[Claims] 1. A method of manufacturing an electric resistance welded pipe in which a steel strip having a predetermined width is roll-formed and high-frequency welded, and after the welding, rotary forging having four or more dies and having a taper angle of 20 ° or less. A method for manufacturing thick-walled small-diameter electric resistance welded steel pipe, which comprises pushing into a machine to increase the wall thickness while reducing the diameter.