JPH08238579A - Production of extremely thick and small-diameter electric resistance welded tube - Google Patents

Abstract

PURPOSE: To provide a process for producing an extremely thick and small- diameter electric resistance welded tube having good dimensional accuracy. 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 >=10 pieces punches and >=4 pieces of dies, thereby increasing its thickness while reducing its diameter. As a result, the production of the extremely 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, in the case of producing a thick-walled steel pipe with an electric resistance welded steel pipe, as shown in FIG. 4, a thick-walled steel strip close to the final thickness is roll-formed by several stages of forming stands to form a tubular shape. After that, they are 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. 5-309.
As described in Japanese Laid-Open Patent Publication No. 422, 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 drawing and then increases the diameter while reducing the diameter. By thickening, the purpose is to manufacture a thick-walled electric resistance welded steel pipe with high dimensional accuracy.

[0006]

The object of the present invention, which achieves the above object, is to provide a method for manufacturing an electric resistance welded pipe in which a steel strip having a predetermined width is roll-formed and high-frequency welded. After welding, the method for producing an extra-thick small-diameter electric resistance welded steel pipe is characterized in that it is pushed into a rotary forging machine having 10 or more punches and 4 or more dies to increase the wall thickness while reducing the diameter.

Hereinafter, the present invention will be described in detail. FIG. 1 shows the manufacturing process of the present invention. In the conventional process, a steel strip having a predetermined width is continuously inserted into a forming roll as shown in FIG. 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 number of punches and dies. If the number of punches and dies is small, the uneven thickness increases, and if the number of punches and dies is large, the equipment cost increases and the cost becomes a problem. Therefore, the number of punches is 10 or more and the number of dies is 4
Make more than one.

As shown in FIG. 3, the uneven thickness decreases as the number of punches and dies increases, but there is an inflection point where the number of dies is 4 regardless of the number of punches. Reduction rate of uneven thickness is reduced. On the other hand, the reduction rate of uneven thickness decreases as the number of punches increases, but it is better that the number of dies is smaller in consideration of cost. Therefore, the number of dies is four, which is the inflection point, and the number of punches is 1 due to uneven thickness accuracy.
0 or more. However, even if the number of dies is increased, the uneven thickness is reduced. However, it goes without saying that the optimum conditions can reduce equipment costs and costs. As described above, according to the present invention, in the thickening method by drawing after the pipe is manufactured,
By pushing into a rotary forging machine with 4 or more punches and 4 or more dies and increasing the thickness while reducing the diameter,
It has become possible to manufacture extremely 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 was 15% or less and the surface quality was 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 an industrially extremely advantageous manufacturing method.

[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 the relationship between the number of punches and dies and uneven thickness,

FIG. 4 is a diagram showing a conventional manufacturing process.

[Explanation of symbols]

 1 Punch 2 Die 3 Object (tube)

Claims (1)

[Claims] 1. 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, and after welding, the steel strip is pushed into a rotary forging machine having 10 or more punches and 4 or more dies, A method for manufacturing an extra-thick, small-diameter ERW steel pipe, characterized by increasing the wall thickness while reducing the diameter.