JPS61140317A - Control method of rolling of mandrel mill - Google Patents

Abstract

PURPOSE:To perform rolling without producing defects or poor rolled parts in the bulged part of a pipe stock, by using a bulge-width sensor, etc. and measuring the real bulge-width to set it within a proper range. CONSTITUTION:A dectection signal, detected by a bulge-width sensor 40 arranged at the outlet side of the prescribed stand of a mandrel mill 30, is analyzed by a bulge-width measuring instrument 41 and is transmitted to a host operator 42. The operator 42 compares the actual bulge-width Bx with the allowable upper limit of bulge-width Ba and the allowable lower limit of bulge- width Bb, to transmit the adjusting rolling-reduction of each stand to a rolling reduction controller 38 when the real bulge-width Bx is not contained within a range of allowable bulge-widths Ba-Bb, thereby controlling the drive of rolling reduction screws 36. Further, the rotational speed of adjusting roll of each stand, capable of setting the bulge-width Bx within said range Ba-Bb, is transmitted to a roll rotational-speed controller 39, to control the drive of a main motor 37 of each stand.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to rolling control of a mandrel mill in which a plurality of side movable roll stands are successively arranged and a hollow shell into which a mandrel bar is inserted is stretched and rolled. Regarding the method.

[Prior Art] In general, the manufacturing process of seamless steel pipes includes a drilling process for making holes in a round bar material, a stretching process for thinning and stretching the perforated hollow tube, and a finishing rolling machine for the stretched and rolled process. It consists of three steps: a finish rolling step to reduce the tube to a predetermined outer diameter. That is, as shown in FIG. 2, the raw material round bar 11 is heated to a predetermined temperature in a rotary hearth type heating furnace 12, and is then pierced and rolled by a Mannesmann piercer 13 to form a hollow shell 1.
It becomes 4. Since this hollow tube 14 is thick and short, it is stretched to reduce its thickness by a mandrel mill 15 serving as a stretching and rolling mill. The mandrel mill 15 has a hollow tube 1
This is a rolling mill that performs elongation and rolling with a mandrel bar 16 inserted into the roll stand 4, and usually consists of 7 to 8 roll stands. Each roll stand has two sets of hole-shaped rolls 1
7, and the rotational axes of the grooved rolls 17 are arranged 90 degrees apart from each other in a plane perpendicular to the rolling axis between adjacent roll stands. These grooved rolls 17 are driven independently for each roll stand, and their rolling positions can be adjusted. The hollow blank tube 14 is stretched to twice to four times the length by a mandrel bar 15, and becomes a finish rolling mill blank tube 18. Finish rolling machine The raw pipe 18 is reheated in a reheating furnace 19 if necessary, and then finished rolled in a stretch reducer 20 serving as a finishing rolling mill. The stretch reducer 20 reduces the outer diameter of the raw tube by up to 75%, and the surface of the raw tube is shaped by the perfect circular hole roll on the final stand of the stretch reducer 20, resulting in a finished tube 21 with relatively excellent outer diameter dimensional accuracy. is obtained.

[Problems to be Solved by the Invention] By the way, in the mandrel mill 15 described above, if the reduction amount setting and roll rotation speed setting of each roll stand are inappropriate, "outward" from the gap between the upper and lower roll flanges in the intermediate stand. If the bulge width of the bulge part of the raw pipe protrudes from the bulge part is too large or too small, it may cause various internal and external surface defects and poor rolling operations.For example, JP-A-54-126
652 points out the occurrence of ear phlegm due to overfilling (too much) of the raw tube and the occurrence of failure to pull out the core metal due to underfilling (underfilling), and describes a method of controlling to maintain the outer diameter value of the ideal rolling condition. stipulated.

However, according to the research conducted by the inventors, it was found that the above-mentioned ear leaks and failure to pull out the core metal can be prevented by appropriately processing the shape of the roll caliber, especially the corner radius, and the bulge width and It has been found that the correlation between This was recognized. In other words, if the bulge width is too large, the bending deformation of the bulge part of the raw pipe will be severe.
This causes defects such as internal doors in the finish rolling mill raw tube 18 and eventually in the finished tube 21. Further, if the bulge width is too small, it means that excessive tension is acting on the cross section of the raw tube, and a local thin wall portion is produced in the finish rolling mill raw tube 18 and eventually in the finished tube 21.

The object of the present invention is to set the bulge portion of the blank tube within an appropriate range during elongation rolling, and to perform smooth rolling.

[Means for Solving the Problems] The present invention provides a rolling control method for a mandrel mill in which a plurality of side movable roll stands are arranged in an am manner and a hollow tube into which a mandrel bar is inserted is stretched and rolled. Determining the minimum bending radius of the bulge portion that will not cause internal defects in the bulge portion of the raw pipe being rolled in the stand, and predetermining the bulge width corresponding to the minimum bending radius in the predetermined stand as the allowable upper limit bulge width in the predetermined stand. With,
A bulge width that does not cause local overthinning of the bulge portion of the raw pipe during rolling in a predetermined stand is predetermined as the allowable lower limit bulge width in the predetermined stand, and the actual bulge width on the exit side of the predetermined stand is measured; In fact, in order to set the bulge width within the range of the above allowable upper limit bulge width and allowable lower limit bulge width,
At least the rolling reduction amount of the predetermined stand is adjusted, and at least the roll rotation speed of the stands before and after the predetermined stand is adjusted.

[Function] According to the present invention, the actual bulge width of the raw pipe at a predetermined stand is measured during rolling by using a bulge width sensor, etc., and the actual bulge width is set within an appropriate range. It becomes possible to obtain a rolling state that does not cause defects or rolling defects.

[Example] FIG. 3 is a front view showing the rolling state in a predetermined stand of the mandrel mill 30, and FIG. 4 is an enlarged view of the main part of FIG. 3. The raw pipe 31 is subjected to elongation by the upper and lower rolling rolls 32 and the mandrel par 33, thereby creating a bulge portion 34 in which the raw pipe material protrudes from the gap between the roll flange portions of both rolling rolls 32. In Figure 4, B is the bulge width, W is the axial distance M between the center of the roll caliber corner radius and the roll center, Rc is the roll caliber corner radius, G is the roll gap (set value), and a is the mill springback. , Ro is the bending radius of the outer surface of the bulge portion, Rt is the bending radius of the inner surface of the bulge portion, and St is the wall thickness of the raw pipe. The following (1
) holds true. Further, the following equation (2) holds between the bending radius RO of the outer surface of the bulge portion and the bending radius Ri of the inner surface of the bulge portion.

B=2 [W −((Rc+Ro)” −(Rc×G
/2+α/2)-Ro)] ... (1) Ri=
Ro-3t...(2) Shite,
There is the following correlation between the bending deformation state of the bulge portion 34 of the raw pipe 31 in each stand of the mandrel mill 30 and the occurrence of inner surface defects. That is, FIG. 5(A)~
(G) respectively have a bending radius Ri of the inner surface of the bulge portion of 1
1.0mm, 9.0mm, 7. Oram,
5.0mm, 3.5mm, 1.5
FIG. 3 is a state diagram showing a deformed state of the bulge portion 34 when ra+, lam or less. This figure 5 (A) to (G
), the bending radius Ri of the inner surface of the bulge part is 3.5 mm.
It is recognized that a defect called inner thread curvature occurs on the inner surface of the bulge portion 34 under the following conditions.

That is, when rolling the blank tube 31 using a predetermined stand of the mandrel mill 30, it is possible to determine the minimum bending radius Ria of the inner surface of the bulge portion 34 without causing inner surface defects in the bulge portion 34.

Furthermore, since a certain relationship is established between the bending radius Ri and the bulge width B according to the above equations (1) and (2), in the present invention, the bending radius Ri and the bulge width B are When rolling the tube 31, the bulge IIB corresponding to the above minimum bending radius Rfa is calculated in advance from the above equation (4) and (2).
), and the calculated bulge width B is determined as the allowable upper limit bulge width Ba for the predetermined stand.

During rolling of the raw pipe 31 by the mandrel mill 30, if the actual bulge width Bx of the bulge part 34 is larger than the above-mentioned allowable upper limit bulge width Ba, the inner bending radius of the bulge part 34 becomes equal to or less than the minimum bending radius Ria, and the bulge part This will result in a defect on the inner surface of 34. FIGS. 6(A) to 6(C) are diagrams showing the occurrence of inner surface defects during rolling in the mandrel mill 30 consisting of a total of 8 stands, where the horizontal axis represents the wall thickness St of the raw pipe at the exit side of the final stand; The vertical axis is the bulge width B on the exit side of the fourth stand, and Za is the limit line of the allowable upper limit bulge width Ba calculated corresponding to the minimum bending radius Ria=3.5ts. A 0 mark indicates that there is no inner surface defect, and an X mark indicates that there is an inner surface defect. In addition, in Fig. 6 (A), the outside diameter of the inlet side of the raw pipe is 11
0+5I11. Figure 6 (B) shows the rolling results when the exit outside diameter is 90 mm, and Figure 6 (C) shows the rolling results when the input outside diameter of the blank tube is 175 mm and the exit outside diameter is 146 mm. The outer diameter of the inlet side of the raw tube is 207aI11. Exit outer diameter is 180m
This is the rolling result when Il. That is, Fig. 6 (A
) to (C), under all rolling conditions, the raw pipe 31
The actual bulge width Bx of is determined by the minimum bending radius R as described above.
If the width is larger than the allowable upper limit bulge width Ba determined based on ia, it is recognized that defects will occur on the inner surface of the bulge portion 34.

Further, during rolling in each stand of the mandrel mill 30, there is the following correlation between the bulge width B of the bulge portion 34 and the occurrence of local overthinning. That is, FIGS. 7(A) to 7(C) are diagrams showing the occurrence of local overthinning during rolling in a mandrel mill consisting of a total of 8 stands, and the horizontal axis represents the raw tube at the exit side of the final stand. The wall thickness St, the vertical axis is the bulge width B on the exit side of the fourth stand, the 0 mark indicates no local overthinning, and the X mark indicates local overthinning. In addition, Fig. 7 (A) shows the rolling results when the outer diameter of the inlet side of the raw tube is 1 l ha and the outer diameter of the outlet side is 90 mm, and Fig. 7 (B) shows the rolling results when the outer diameter of the inlet side of the raw tube is 175 II m and the outer diameter of the outlet side is 175 II m. Figure 7 (C) shows the rolling results when the outside diameter of the side is 148a+m, and the outside diameter of the entrance side of the raw pipe is 20mm.
This is the rolling result when the outer diameter of the outside diameter is 7 mm and the outside diameter of the exit side is 180 mm. According to FIGS. 7(A) to 7(C), under all rolling conditions, there is a boundary line zb of the allowable lower bulge width Bb that does not cause local overthin parts in the raw tube 31. Is recognized. Therefore, in the present invention, the mandrel mill 3
When rolling the raw pipe 31 using a predetermined stand of 0, the lower limit of the allowable bulge width Bb under the same rolling conditions is determined in advance. When the actual bulge width Bx of the bulge portion 34 is smaller than the allowable lower limit bulge width Bb during rolling of the raw pipe 31, local overthinning will occur.

Therefore, the present invention provides the above-mentioned allowable upper limit bulge width Ba when rolling the raw pipe 31 using a predetermined stand of the mandrel mill 30.
Under the condition where the allowable lower limit bulge width Bb is predetermined, the actual bulge width Bx at the exit side of the predetermined stand is measured, and the actual bulge width B
Let x be the above-mentioned allowable upper limit bulge width B-a and allowable lower limit bulge width B
At least the amount of reduction of the predetermined stand is adjusted so that it is set within the range of b, and at least the amount of reduction of the predetermined stand is
The roll rotation speed of the stands before and after the stand is adjusted.

FIG. 1 is a control system diagram showing one embodiment of the present invention, and FIG. 8 is a flowchart showing the control procedure.

The hollow tube 31 into which the mandrel bar 33 is inserted is attached to the roll 3 provided on each stand of the mandrel mill 30.
After being rolled down sequentially by step 2, finish rolling mill i35
becomes. Here, in each stand, the roll 32 is supported by a roll chock (not shown), and a reduction screw 36
The rolling reduction amount is set by , and the roll rotation speed is set by the main motor 37 . The amount of reduction of each roll 32 by each reduction screw 36 is controlled by a reduction amount controller 38.
It can be adjusted by Further, the roll rotation speed of each roll 32 by each main electric motor 37 can be adjusted by a roll rotation speed controller 39.

A bulge width sensor 40 is disposed on the exit side of a predetermined stand (in this embodiment, the third stand) of the mandrel mill 30. The detection signal of the bulge width sensor 40 is analyzed in the bulge width measuring device 41, and
The actual bulge width Bx of 1 can be measured. The measurement results of this bulge width measuring device 41 are transmitted to the main computing unit 42.

In the main calculator 42, the allowable upper limit bulge width Ba and the allowable lower limit bulge width Bb at a predetermined stand, that is, the exit side of the third stand, of the hollow tube 31 are set as set values of the setter 43. Note that the allowable bulge widths Ba and Bb are as follows:
As mentioned above, it is determined in advance through experiments, etc., and is stored in the form of diagrams or empirical formulas. The main calculator 42 also includes adjustments of the first to final stands necessary to set the actual bulge width Bx at the exit side of the third stand of the hollow tube 31 within the range of the allowable bulge widths Ba and Bb. The rolling reduction amount and the adjustment roll rotation speed are stored in advance.

Therefore, as shown in FIG. 8, the main computing unit 42 compares the actual bulge width Bx with the allowable bulge widths Ba and Bb, and determines that the actual bulge width Bx must be within the range of the allowable bulge widths Ba to Bb. For example, the actual bulge width B× is the allowable bulge width Ba−B
The adjustment reduction amount of each stand that can be set within the range b is transmitted to the reduction amount controller 38, and the reduction screw 36 of the λ stand is transmitted to the reduction amount controller 38.
In addition, the adjustment roll rotation speed of each stand that enables the actual bulge width Bx to be set within the range of the allowable bulge portion Ba-Bb is transmitted to the roll rotation speed controller 39, and the main motor of each stand is 37 is driven and controlled.

According to the above embodiment, the actual bulge width Bx of the raw pipe at a predetermined stand is measured during rolling by using the bulge width sensor 40, and the actual bulge width Bx is set within an appropriate range, so that the bulge portion 34 of the raw pipe is It becomes possible to obtain a rolling state that does not cause defects or rolling defects.

In addition, in the example L, the actual bulge width Bx on the exit side of the third stand
The case where the reduction amount and the roll rotation speed of the first to final stands are adjusted using the above-mentioned method has been explained.
The amount of reduction of the stand and the roll rotation speed of at least the second stand and the fourth stand may be adjusted.

Furthermore, in the above embodiment, the actual bulge width Bx is measured only on the exit side of the third stand, but the actual bulge width B x i is measured on the exit side of multiple or all stands, and Fruit bulge @
In order to set B X i within the range of the allowable upper limit bulge width Bai to the allowable lower limit bulge width Bbi of each stand, the rolling reduction amount and roll rotation speed of each stand may be adjusted comprehensively.

[Effects of the Invention] As described above, the present invention provides a rolling control method for a mandrel mill in which a plurality of side movable roll stands are successively arranged and a hollow shell into which a mandrel bar is inserted is stretched and rolled. The minimum bending radius of the bulge part that will not cause internal defects in the bulge part of the raw pipe being rolled on a predetermined stand is determined, and the bulge width corresponding to the minimum bending radius in the predetermined stand is set as the allowable upper limit bulge width in the predetermined stand. At the same time, the bulge width that does not cause local overthinning or thinning of the raw pipe being rolled at a specified stand is determined in advance as the allowable lower limit bulge width at the specified stand, and the actual bulge width at the outlet side of the specified stand is measured. and adjusting at least the amount of reduction of the predetermined stand so that the actual bulge width is set within the range of the allowable upper limit bulge width and the allowable lower limit bulge width.
In addition, at least the roll rotation speeds of the stands before and after the predetermined stand are adjusted. Therefore, it is possible to set the bulge width of the blank tube within an appropriate range during elongation rolling, and to perform smooth rolling.

[Brief explanation of drawings]

Fig. 1 is a control system diagram showing one embodiment of the present invention, Fig. 2 is a process diagram showing a general steel pipe manufacturing process, Fig. 3 is a front view showing the rolling state by a mandrel mill, and Fig. 4 is a Figures 5(A) to 5(G) are state diagrams showing the state of bending deformation of the bulge, and Figures 6(A) to (C) are enlarged views of the main parts of the figure. Diagram showing the relationship between
0... Mandrel mill, 31... Raw tube, 32...
Rolling roll, 33... Mandrel bar 134... Bulge portion, 35... Finish rolling mill tube, 38... Rolling amount controller, 39... Roll rotation speed controller, 40... Bulge Width sensor, 42... Main computing unit, Bx
... Actual bulge width, Ba ... Allowable upper limit bulge width, Bb
... Allowable lower limit bulge width. Representative Patent Attorney Osamu Shiokawa
Figure 3 Figure 8 East 4 Figure □C+1- Figure 6 (0) Figure 7 (A) Group 7 (B) t Figure 7 ((j

Claims (1)

[Claims] (1) Multiple side-driven roll stands are arranged in succession,
In a rolling control method for a mandrel mill that elongates and rolls a hollow shell into which a mandrel bar is inserted, the minimum bending radius of the bulge that will not cause internal defects in the bulge of the shell during rolling at a predetermined stand is determined, and The bulge width corresponding to the minimum bending radius in the stand is predetermined as the allowable upper limit bulge width in the predetermined stand, and the bulge width that does not cause rolling defects in the bulge portion of the raw pipe being rolled in the predetermined stand is determined in advance as the allowable upper limit bulge width in the predetermined stand. The lower limit bulge width is predetermined, the actual bulge width at the exit side of the predetermined stand is measured, and the reduction amount of at least the predetermined stand is set so that the actual bulge width is set within the range of the allowable upper limit bulge width and the allowable lower limit bulge width. 1. A method for controlling rolling of a mandrel mill, the method comprising adjusting the roll rotation speed of at least the stands before and after the predetermined stand.