JP2636683B2 - Manufacturing method of seamless steel pipe - Google Patents

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 seamless steel pipe by a Mannesmann mandrel mill method.

[0002]

2. Description of the Related Art A seamless steel pipe is manufactured by a Mannesmann mandrel mill method. A round steel slab of a material is heated in a rotary hearth heating furnace, and then drilled with a drilling machine to form a raw pipe. The bar is inserted in a skewered shape and rolled to a predetermined size in a single pass by a mandrel mill consisting of 7 to 9 stands. After rolling, the mandrel bar is pulled out of the tube. After the pipe is cut with a hot saw, the bad shape of the pipe end (fins, biting out or crushing when pulling out the mandrel bar, etc.)
It is reheated in a reheating furnace, is subjected to descaling by high-pressure water, and is subjected to a reduction in outer diameter and a slight reduction in wall thickness by a stretch reducer composed of multiple stands to be finished to required product dimensions. Thereafter, the tubes are cooled on a cooling bed, cut to the required length by a cold saw and sent to a refining line.

[0003] In the production of a seamless steel pipe by the Mannesmann mandrel mill method, fins, biting, or crushing at the time of mandrel bar pulling out at the rear end of the pipe by mandrel mill rolling are difficult to load into a reheating furnace, or In order to inhibit the biting ability with the stretch reducer,
It has been cut by a hot saw. Also, at the final stage, the thick part of the pipe end is cut by a cold saw.

[0004]

In the production of a seamless steel pipe by the above-mentioned Mannesmann mandrel mill method, after the mandrel bar is pulled out of the pipe, a portion having a poor pipe end shape is cut as a crop loss with a hot saw, and then the product is produced. Not only does the pipe yield deteriorate, but also the number of processing steps for crop processing is required.

An object of the present invention is to provide a seamless steel pipe manufactured by the Mannesmann mandrel mill method in which a mandrel mill rolls a fin, bite out at the rear end of the pipe, or collapses at the time of pulling out a mandrel bar. It is an object of the present invention to provide a method of manufacturing a seamless steel pipe which can eliminate the obstruction of the charging property or the biting property by a stretch reducer, omit the hot saw, and improve the pipe production yield.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object. As a result, a one-stand three-roll sizer was installed in front of the reheating furnace inlet, and the fins, biting out, or crushing at the time of mandrel bar pulling out at the rear end of the pipe during mandrel mill rolling were pressed down to the outer diameter of the mandrel mill rolling. This eliminates the difficulty of charging the reheating furnace or biting by the stretch reducer, and improves the pipe production yield by charging the reheating furnace without cutting the crop with a hot saw. We have determined what we can do and arrived at this invention.

That is, the present invention relates to a method of manufacturing a seamless steel pipe by the Mannesmann mandrel mill method,
Manufacture of seamless steel pipe characterized in that fins generated by elongation rolling by a mandrel mill, crushing, and crushing allowance at the time of burst ripping are pressed down to the outside diameter of the mandrel mill by a three-roll sizer and charged into a reheating furnace. Is the way.

[0008]

In the present invention, the fins generated during elongation rolling by the mandrel mill, the crushing at the time of bursting and burst ripping are pressed down to the outer diameter of the mandrel mill by a three-roll sizer and charged into the reheating furnace. In addition, the obstruction of charging into the reheating furnace or the bite by the stretch reducer is eliminated, and the deviation of the rotation speed control is reduced.
Become. As a result, poor pipe end wall thickness in the refining process after the stretch reducer is suppressed by the fin of the pipe at the rear end by a three-roll sizer, biting, and holding down of a crushing allowance at the time of burst ripping, and the pipe production yield is improved. Further
Then, increase the thickness of both pipe ends during stretch reducer rolling.
But not cut with a hot saw according to the invention.
The yield can be improved because it can be left as a crop fee.

The method of the present invention has a great effect on a thin tube having a wall thickness of 3.5 to 8.0 mm after the mandrel mill rolling, which has a large fin at the rear end of the tube during the mandrel mill rolling and a large bite.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In manufacturing a seamless steel pipe of the Mannesmann mandrel mill system, as shown in FIG.
After charging the round slab 1 into the rotary hearth heating furnace 2 and heating, the slab 1 is pierced and rolled by the piercing machine 3, and then the mandrel bar 5 is inserted into the raw tube 4 by the shell inserter and rolled by the mandrel mill 6. The mandrel bar 5 was pulled out by a burst ripper to obtain a tube 7 having an outer diameter of 198 mm, a wall thickness of 6.5 mm, and a length of 28400 mm. The pipe 7 has a fin generated by rolling at the end by the mandrel mill 6, biting, and a crushing allowance at the time of burst ripping are pressed down to a mandrel mill rolling outer diameter by a three-roll sizer 8, and then the reheating furnace 9. After charging and reheating, the scale on the surface is removed with a descaler and the outer diameter is reduced with a stretch reducer 10.
mm, a wall thickness of 5.68 mm, and a length of 91230 mm, and cooled on a cooling floor. Next, the product was cut into required dimensions using a cold saw (not shown) to obtain a product seamless steel pipe. As a comparative example, as shown in FIG. 2, the fins generated by rolling the end of the pipe 7 by the mandrel mill 6, and the crushing allowance at the time of burst ripping are reduced to the outer diameter of the mandrel mill by a three-roll sizer 8. Instead of pressing down, except cut as a crop with a hot saw,
The tube was produced under the same conditions as in the method of the present invention, and cooled in a cooling bed. Next, the product was cut into required dimensions using a cold saw (not shown) to obtain a product seamless steel pipe. About the obtained product seamless steel pipe, the cut length was measured as a pipe rear end crop. The result is shown in FIG.

As shown in FIG. 3, the length cut as a pipe rear end crop was 800 mm in the case of the method of the present invention, whereas the length cut as a pipe rear end crop was 1100 mm in the conventional example. As compared with the method of the present invention, the crop loss was longer by 300 mm, and it was confirmed that the yield of the pipe of 300 mm in length was improved by the method of the present invention as compared with the conventional example.

[0012]

As described above, according to the method of the present invention, in the production of a seamless steel pipe of the Mannesmann mandrel mill type, a fin formed by mandrel mill rolling is provided with a three-roll sizer before the reheating furnace. By suppressing the crushing allowance at the time of biting and burst ripping to the outer diameter of the mandrel mill, the hot saw can be omitted, and the pipe production yield can be improved.

[Brief description of the drawings]

FIG. 1 is a manufacturing process diagram showing the concept of the Mannesmann mandrel mill method of the present invention.

FIG. 2 is a manufacturing process diagram showing the concept of a conventional Mannesmann mandrel mill system.

FIG. 3 is a graph showing the crop length of the pipe rear end of the method of the present invention and the conventional example in Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Round steel slab 2 Rotating hearth heating furnace 3 Drilling machine 4 Raw tube 5 Mandrel bar 6 Mandrel mill 7 Tube 8 Sizer 9 Reheating furnace 10 Stretch reducer

Claims (1)

(57) [Claims] 1. A method for producing a seamless steel pipe by a Mannesmann mandrel mill method, wherein fins generated by elongation rolling by a mandrel mill, crushing at the time of bursting and bursting at the time of burst ripping are reduced to a mandrel mill rolling outer diameter by a three-roll sizer. A method for producing a seamless steel pipe, comprising holding and charging into a reheating furnace.