JPS59113907A - Rolling method of pipe in reducing mill - Google Patents

Abstract

PURPOSE:To obtain a sufficient effect for eliminating an increase of wall thickness by performing a speed reduction control of the roll peripheral speed of a stand located at the upstream when a prescribed part of the front or rear end of a blank pipe is rolled by prescribed stands located at the upstream and the downstream. CONSTITUTION:In a rolling method of a blank pipe by draw rolling the pipe through a group of rolling rolls consisting of plural stands, the roll peripheral speed of a stand located at the upstream is controlled by speed reduction when a prescribed part of the front or rear end of the pipe is rolled by the prescribed stands located respectively at the upstream and the downstream. Therefore, the responsiveness of a roll driving motor is enhanced to increase rapidly and surely a tension between the stands acting on the front and rear ends of the pipe, thereby a sufficient effect for eliminating the increase of wall thickness is obtained.

Description

[Detailed description of the invention] The present invention relates to a method of rolling a tube in a reducing mill.

Generally, in a seamless steel pipe production line, a raw material heated to a required temperature in a heating furnace is perforated in a piercing rolling machine to obtain a perforated raw pipe, and then the perforated raw pipe is stretched and rolled in an elongation rolling machine. After obtaining the drawn blank tube, it is possible to further reduce and roll the drawn blank tube to a required size in a reducing mill to obtain a thin tube.

The above-mentioned reducing rolling mill is composed of a rolling roll group consisting of multiple stands, and by adjusting the roll rotation speed ratio of each stand, it is possible to control the inter-stand tension applied to the raw pipe during rolling and control its wall thickness. It is said that

By the way, when a raw pipe is reduced and rolled in the above-mentioned reducing mill, the tension acting on the tip of the raw pipe is zero, and from that state the tension increases in the axial direction of the raw pipe, causing the A predetermined tension is reached in the center. In addition, the steady state tension in the center of the tube gradually decreases toward the rear end.
The tension at the rear end of the raw pipe becomes zero. Therefore, the tension acting on the tip side and the rear end 1111 of the raw pipe is:
The tension is smaller than the tension acting on the central portion where steady rolling is performed, and the wall thickness at the tip and rear ends of the blank tube is thicker than other portions and tends to be thickened. The thickened portions that occur at the tip and rear ends of the raw tube are usually cut off as off-gauge crops, causing a decrease in yield.

Conventionally, when a predetermined tip portion or a predetermined rear end portion of a blank pipe is rolled in a predetermined upstream stand and a downstream stand in the traveling direction of the blank pipe, the roll peripheral speed of the downstream stand is accelerated and controlled to roll the tip of the blank pipe. Proposals have been made to alleviate the above-mentioned thickening phenomenon by applying greater tension to the front end or the rear end. However, when the peripheral speed of the roll of the downstream stand is controlled in the acceleration direction in this way, the responsiveness of the roll drive motor becomes slow and a sufficient effect of eliminating thickening cannot be obtained.

The present invention provides a method for rolling a pipe in a reducing mill that can quickly and reliably increase the inter-stand tension acting on the tip and rear ends of a blank pipe and obtain a sufficient effect of eliminating thickening. With the goal.

In order to achieve the above object, the present invention provides a method for rolling a pipe in a reducing mill in which a raw pipe is reduced and rolled by a roll group consisting of a plurality of stands, in which a predetermined tip portion or a predetermined rear end portion of the raw tube is When rolling is performed in the upstream stand and the downstream stand, the roll circumferential speed of the upstream stand is controlled to be decelerated.

First, the basis for establishing the present invention will be explained as follows. That is, when controlling the roll circumferential speed in order to increase or decrease the slack force between stands in a reducing rolling mill, it is desirable from the viewpoint of tension control that the roll circumferential speed changes in a rectangular manner after a control signal is issued. However, in reality, the behavior shown in FIG. 1 occurs due to the inertia of the drive system and the responsiveness of the control system. Here, the response time τ is generally expressed by the following equation (1).

In the above equation (1), ΣGD2 is the sum of the inertia moments of the drive system, N is the rotational speed of the motor, and To is the effective torque. However, the above effective torque T. is expressed by the following equation (2).

T, = ITM-TR-T, l...
(2) In equation (2) above, TM is motor torque,
TR is rolling torque, and TF is friction torque. That is, when accelerating or decelerating the motor from a steady rotation state, the motor torque T1 is the sum of the rolling torque and the friction torque (T
Only the difference between R+TF) is the effective torque TI.

It is involved in acceleration and deceleration work. Therefore, if the motor torque TM is constant (for a normal motor, 20% of the rated output
0%), the effective torque T is larger when decelerating during rolling than when accelerating during rolling, and therefore the response time τ is smaller. That is, by controlling the roll peripheral speed of the upstream stand to reduce the speed during reduction rolling, the tension between the stands can be increased quickly and reliably, making it possible to increase the effect of tension control.

Hereinafter, specific examples of the present invention will be described.

In this embodiment, the total number of stands of the reducing rolling mill 100 shown in FIG. 2 is 24, and the control according to the present invention is performed in the first to tenth stands, and The predetermined length region of the leading end or the trailing end is at most the length 2L defined by the region between two adjacent stands.

First, as shown in FIG. 3, the roll peripheral speeds of the first to tenth stands before the start of rolling are as follows:
The speed Ni (
1+δi).

In addition, in Figure 3, time is taken on the horizontal axis, and the
Changes in roll circumferential speed in the stand, the third stand, and the i-th stand are shown by solid lines, broken lines, one-dot chain lines, and two-dot chain lines, respectively.

Next, when the detector 102 detects that the tip of the raw tube 101 is caught in the i+l-th stand, the controller 1
03, when the roll peripheral speed of the i-th stand as an upstream stand with respect to the ill-th stand is decelerated as follows, the roll peripheral speed of the i-1st stand as an upstream stand with respect to the i-th stand is controlled as follows. Control deceleration so that That is, - due to the above-mentioned deceleration control, the tip end of the raw pipe 101 is Ni+1 (1+
A tension based on a speed difference greater than the speed difference in the steady state width is applied between the stand and the i+1th stand, which is placed on standby for speed increase at δ1+1).

In addition, under the state in which the raw pipe starts to be caught in the second stand and in the state in which it starts to be caught in the 11th stand, there is a stiffness,
Tension control is applied only between the first and second stands and between the tenth and eleventh stands, respectively.

Further, when the detector 102 detects that the rear end of the raw pipe 101 has passed through the i-2nd stand, the controller 103 performs deceleration control like the low of the second stand,
If the roll circumferential speed of the 11th stand is decelerated as follows, the roll circumferential speed of the i-2nd stand will be changed to The speed is increased to return to the original state, and the rolling stock is put on standby for the start of rolling of the subsequent blank pipe. That is, the raw pipe 101
The rear end has a roll circumferential speed, and the speed difference is greater than the speed difference in the steady state between the i+1th stand maintained at the steady speed Ni+1, and the speed difference is greater than the speed difference in the steady state. Tension is applied based on the difference. Note that when the rear end of the raw pipe 101 passes through the 9th stand, the rear end of the raw pipe 101 passes through the 10th to 1st stands.
Tension is controlled only between one stand.

By the way, in the above embodiment, the appropriate speed increase ratio δi to be set for each stand is such that the circumferential speed of the roll is faster than the material over the entire area within the caliber plane formed by the rolling rolls in each stand, causing forward slippage. , set to obtain the maximum tension that can be achieved. As an example, the coefficient of friction between the rolls and the material in each stand constituting a reducing rolling mill is μ, the roll radius is R1, the outside diameter of the blank tube at the entrance and exit sides of the reducing rolling mill is R61hl, and the entrance and exit diameters are R61hl. The wall thickness of the side pipe is to
, tl, the stretch coefficients on the inlet and outlet sides (tensile stress acting on the raw pipe/yield strength of the raw pipe) are 20.21, and the average stretch coefficient as the average value for all stands of the stretch coefficient in each stand is Zm. Then, the following equation (3) approximately holds true.

However, the average stretch coefficient Zm is expressed by the following equation (4).

However, ψ7 in the above equation (4). ψt and ε□ are expressed by the following formulas (51, 161, and (71), respectively.

In the above equation (3), all numbers are known except for jl + zll zm. Also, (7! When considering the first stand, Z (1 = O), so by substituting it into equation (3), Zl can be found, (81M2 stand,
Z is the stretch coefficient Z1 on the exit side of the first stand. Close (
3) Find Zl by substituting it into the equation. (C) If you repeat the calculations in the same manner and proceed with the calculation for one stand at a time, the only independent variable among the above unknowns is t1, and this tl Calculate the above formula (3) by appropriately assuming the value of , calculate the value of tl such that the above formula (31) holds,
If Zl is found based on the calculated 11, the appropriate speed increase ratio δi of the roll circumferential speed that should be set in the i-th stand is the maximum stretch coefficient that Zl can reach.
8) It is expressed by the formula.

! / δi=k・−7・・ (8) gl! Here, k is a constant and is usually 1 (=l). Also, ε
l is expressed by the following formula (9).

As described above, the present invention provides a pipe rolling method in a reducing mill in which a raw pipe is reduced and rolled by a rolling roll group consisting of a plurality of stands, in which a predetermined tip portion or a predetermined rear end portion of the raw tube is connected to a predetermined upstream stand. When rolled at the downstream stand, 01) The peripheral speed of the rolls at the upstream stand is controlled to decelerate, so the responsiveness of the roll drive motor is improved, and the stand which acts on the tip and rear ends of the blank tube. The tension can be increased quickly and reliably, and a sufficient effect of eliminating thickening can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first control state of the roll drive motor, FIG. 2 is a control system diagram showing a reducing rolling mill in which the present invention is implemented, and FIG. 3 is a diagram showing the control state of the roll circumferential speed according to the present invention. FIG. 100...Reducing rolling mill, 101...Material pipe, 10
2...Detector, 103...Controller. Agent Patent Attorney Osamu Shiokawa α2 Figure I1

Claims (1)

[Claims] (1) In a pipe rolling method in a reducing mill in which a raw pipe is reduced and rolled by a group of rolls consisting of a plurality of stands, a predetermined tip portion or a predetermined rear end portion of the raw pipe is rolled in a predetermined upstream stand and downstream stand. A method for rolling a pipe in a reducing rolling mill, which comprises controlling the circumferential speed of a roll in an upstream stand to reduce the speed at which the roll is rolled.