JPH09220603A - Manufacture of thick-wall seamless steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly efficiently manufacture a thick-wall seamless steel tube having the highly precise dimension of an outside diameter by restricting the variation of outside diameter by a plug mill, controlling the temp. of a stock tube to a prescribed range at the front of a sizer mill and reducing the total draft by a sizer mill. SOLUTION: A cast slab 7 is heated in a heating furnace 1, formed into a hollow stock tube by a piercer mill (piercer) and reduction of thickness and expansion of the outside diameter are executed by an elongator mill 3. Rolling of prescribed passes is executed at the draft to the outside diameter within the range of 1-1.5% per pass by a plug mill 4 and rolling is executed at the total draft to the outside diameter within the range of 1-3% by a sizer mill 6. Then, at the front of the sizer mill 6, the temp. of the tube stock is kept at the range of 900-950 deg.C. In this way, the thick-wall seamless steel tube is manufactured highly precisely in high yield.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a method for hot working a seamless steel pipe, and more particularly to a method for hot working a thick seamless steel pipe.

[0002]

2. Description of the Related Art FIG. 1 is a diagram showing an example of a manufacturing facility (rolling line) for a Mannesmann type seamless steel pipe in hot working. As shown in FIG. 1, in manufacturing a conventional seamless steel pipe in general hot working, a square or round slab 7 is heated in a heating furnace 1, and a piercer mill (piercing machine) 2 is used to form a hollow shell. Forming, expanding the outer diameter by reducing the wall thickness by the elongator mill 3, rolling by the plug mill 4 to a predetermined product thickness, polishing by the reeler mill 5, and rolling by the sizer mill 6 to the predetermined outer diameter. It consists of processes.

When a thick seamless pipe is manufactured by the above-mentioned manufacturing equipment, a thick pipe has a considerably larger cross-sectional area than a thin pipe having the same outer diameter, and therefore has the same length and the same outer diameter. As compared with the thin-walled tube, the material of larger volume is required, and the equipment cost for heating the material and its equipment becomes enormous.

Japanese Unexamined Patent Publication No. 63-149004 discloses a method for producing a seamless steel pipe which solves such a problem (hereinafter referred to as "prior art document"). Since the equipment capacity (motor load) of the reeler mill 5 and the sizer mill 6 is exceeded, the prior art document proposes a method of finishing the product with a predetermined outer diameter by the elongator mill 3 (hereinafter referred to as "conventional method 1"). Further, when the equipment capacity of the reeler mill 5 is not exceeded, a method of finishing to a predetermined product outer diameter by the reeler mill 5 has been proposed (hereinafter referred to as "conventional method 2"). None of the conventional methods described above is a method in which neither the plug mill 4 nor the sizer mill 6 is used, or only one of them is used.

[0005]

In the case of rolling to a predetermined product size by the elongator mill 3 and reeler mill 5 as in the conventional methods 1 and 2, these mills 3 and 5 use barrel rolls. Therefore, the JIS standard outer diameter tolerance of general piping or the outer diameter tolerance that is generally exchanged with customers (customers), the overall length and end of the pipe satisfy the nominal outer diameter ± 0.5%. There is a problem that it is not possible to manufacture an excellent product that satisfies the dimensional accuracy that can be achieved. Further, even if it can be manufactured, there is a problem that the yield is extremely low and the cost is high, which is economically disadvantageous.

Therefore, an object of the present invention is to solve the above problems and to manufacture thick-walled seamless steel pipes with high precision and high yield without remodeling conventional manufacturing equipment that has been generally used. To provide a method that can.

[0007]

According to the present invention, a slab is heated by a heating furnace, the slab is pierced by a piercing machine to form a raw pipe, and the raw pipe is sequentially rolled by an elongator mill, a plug mill and a sizer mill. In the plug mill, a predetermined pass rolling is performed at an outer diameter reduction rate within a range of 1 to 1.5% per pass, and a total outer diameter reduction rate within a range of 1 to 3% is performed in the sizer. It is characterized in that it is rolled and the temperature of the shell is maintained in the range of 900 to 950 ° C. in front of the sizer mill.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the manufacturing facility for the Mannesmann type seamless steel pipe shown in FIG. 1 can be used, but the reeler mill 5 is not used. The slab 7 is heated in the heating furnace 1, formed into a hollow shell by a piercer mill (piercing machine) 2, the wall thickness is reduced by the elongator mill 3, the outer diameter is expanded, and the plug mill 4 achieves a predetermined product wall thickness. Roll and then roll to size with a sizer mill 6. The temperature control of the raw pipe on the front surface of the sizer mill 6 is performed by the reeler mill 5 (in the present invention, the reeler mill is not used, but it is provided in the existing seamless steel pipe manufacturing facility).
This is performed by using a descaler (not shown) arranged on the front surface of the machine or on the front surface of the sizer mill 6. And in this invention, the rolling conditions in a plug mill and a sizer mill, and the temperature conditions of the raw pipe rolled in a sizer mill are prescribed | regulated as follows.

In the plug mill, the outer diameter reduction rate per pass should be limited to the range of 1 to 1.5%.
The reason is that the clearance angle θ shown in FIG. 2 is set in the range of 25 to 30 °. FIG. 2 is a diagram for explaining the plug caliber. By limiting the clearance angle θ to the range of 25 to 30 °, the outer diameter accuracy of the product is ± 0.5 without causing flaws on the outer surface of the pipe.
% Can be secured. If θ is less than 25 °, the outer surface will be scratched by the flange. On the other hand, when θ exceeds 30 °, the protrusion of the flange becomes large and lap-shaped flaws occur. Moreover, since the outer diameter variation of the material before the Sizer mill rolling is set to 0 to less than 1%, the reeler mill is not used,
In this plug mill, rolling is performed for 3 or 4 passes at an outer diameter reduction rate of 1 to 1.5% per pass. Further, in order to remove the non-circle generated in the process before the plug mill rolling, the outer diameter reduction rate per pass in the plug mill is required to be 1 to 1.5%. By performing such rolling, the circularity of the shell becomes 1.5% or less.

Here, the non-circularity is expressed as follows. Non-circularity: (Outer diameter of the manufactured steel pipe with the largest outer diameter-Outer diameter of the manufactured steel pipe with the smallest outer diameter) / Target steel pipe outer diameter In the sizer mill, the total outer diameter reduction Rate 1-3%
Should be limited to The reason is described below. In the production of seamless steel pipe, rolling with a sizer mill is carried out in order to obtain a predetermined highly accurate product outer diameter. Conventionally, in this sizer mill, the total outer diameter reduction ratio is usually 6 to
10% is adopted. On the other hand, in the present invention, in order to reduce the motor load of the sizer mill, the total outer diameter reduction rate is set within the range of 1 to 3% as described above.
In order to manufacture a product having a highly accurate outer diameter, it is necessary to have an outer diameter accuracy of 1.5% or less in the non-circularity by rolling in a plug mill.
This is achieved by setting the outer diameter reduction rate per pass to 1 to 1.5%. In addition, the product outer diameter accuracy ±
In order to achieve 0.5%, it is necessary to reduce the total outside diameter reduction rate in the sizer mill to 1 to 3% and to perform rolling. The motor load of a general sizer mill is about 200 kW, and if the capacity is about this, the wall thickness / outer diameter ratio is 0.
In the case of 12 or more products (thick-walled steel pipe), if the total outer diameter reduction ratio exceeds 3%, rolling is impossible, and even if rolling is possible, the probability is low. On the other hand, the total outer diameter reduction rate is 1
If it is less than%, the outer diameter of the product becomes smaller than a predetermined value due to the effect of heat shrinkage. From the above, the total outer diameter reduction rate of the sizer mill should be limited to 1 to 3%.

Maintaining the temperature of the tube on the front side of the sizer mill within the range of 900 to 950 ° C. is to reduce the variation of the outer diameter variation due to the thermal contraction of the outer diameter due to the temperature and minimize the influence. Is. The control of the temperature range may be performed by using the descaler arranged on the front surface of the reeler mill or the front surface of the sizer mill, as described above.

[0012]

Next, the present invention will be described with reference to embodiments. Using the seamless steel pipe manufacturing equipment shown in FIG. 1, thick wall seamless steel pipes having the following dimensions were manufactured by the method of the present invention. The temperature control of the tube in front of the sizer mill was carried out by a descaler arranged in front of the sizer mill. For comparison, thick-walled seamless steel pipes having the same dimensions were manufactured by the above-mentioned conventional methods 1 and 2 (conventional method 1: standardization method by elongator mill, conventional method 2: standardization method by reeler mill).

Product dimensions of seamless steel pipe: φ406.4 × 6
0t × 6000l where φ: Outer diameter t: Wall thickness l: Overall length Dimension unit: mm Outside diameter tolerance of seamless steel pipe: ± 0.5% And outside diameter tolerance of seamless steel pipe: ± 0.5% The number of defective outer diameter defects and outer diameter fluctuations was examined. The number of products manufactured was 30 each. The result is shown in FIG.
At the same time, the rolling time (number of extraction seconds) per seamless steel pipe production was investigated. FIG. 4 shows the results.

As can be seen from FIG. 3, in the conventional method 1, the number of defective pieces was as many as 13, and in the conventional method 2, although it was one piece, a trip occurred and as a result, only two pieces were rolled. On the other hand, in the present invention, the desired seamless steel pipe was produced and the number of defective pipes was as small as one.

As can be seen from FIG. 4, the conventional method 1 had a long rolling time of 243 seconds and the conventional method 2 had a long rolling time of 175 seconds. On the other hand, in the present invention, the rolling time per rolling was 58 seconds, which was significantly shorter than that of the conventional methods 1 and 2.

From the above results, it is understood that according to the present invention, a high-quality thick-walled seamless steel pipe can be efficiently manufactured with a high yield.

[0017]

As described above, according to the present invention, the fluctuation of the outer diameter of the material is suppressed by the plug mill, the temperature of the raw pipe on the front surface of the sizer mill is suppressed within a predetermined range, and the total outer diameter reduction by the sizer mill is performed. Since the manufacturing method for thick-walled seamless steel pipes was configured by reducing the ratio, thick-walled seamless steel pipes with highly accurate outer diameter dimensions can be manufactured with high efficiency, and conventional general seamless steel pipe manufacturing Since the equipment can be used, it is economically advantageous without investing in equipment, and thus brings about an industrially useful effect.

[Brief description of drawings]

FIG. 1 is a diagram showing a facility for manufacturing a seamless steel pipe.

FIG. 2 is a diagram illustrating a plug caliber.

FIG. 3 is a graph showing a comparison between the present invention and a conventional method regarding outer diameter defects and outer diameter fluctuations.

FIG. 4 is a graph showing a comparison between the present invention and a conventional method in terms of rolling time per piece.

[Explanation of symbols]

 1 Heating Furnace 2 Pier Samill (Punching Machine) 3 Elongator Mill 4 Plug Mill 5 Reeler Mill 6 Sizing Mill 7 Cast Piece

Claims (1)

[Claims] 1. A method comprising heating a slab with a heating furnace, piercing the slab with a perforator to form a raw pipe, and rolling the raw pipe sequentially with an elongator mill, a plug mill and a sizer mill. Predetermined pass rolling is performed at an outer diameter reduction ratio within a range of 1 to 1.5% per pass, rolling is performed at a total outer diameter reduction ratio within a range of 1 to 3% in the sizer mill, and At the front surface of the sizer mill, the temperature of the tube is set to 900-95.
A method for manufacturing a thick-walled seamless steel pipe, characterized by maintaining the temperature within a range of 0 ° C.