JPH0252563B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of rolling a tube in a reducing mill.

Generally, in the production line of seamless steel pipes,
After the material is heated to the required temperature in a heating furnace and perforated in a perforation rolling machine to obtain a perforated pipe,
After the perforated blank tube is stretched and rolled in a stretching mill to obtain a drawn blank tube, the stretched blank tube is further reduced and rolled to a required size in a reducing mill to obtain a steel pipe.

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, the inter-stand tension applied to the raw pipe during rolling is controlled, and the wall thickness is controlled. It can be controlled.

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. Further, the steady state tension at the center of the raw pipe gradually decreases toward the rear end, and the tension at the rear end of the raw pipe becomes zero. Therefore, the tension that acts on the tip and rear ends of the raw pipe is smaller than the tension that acts on the center where steady rolling is performed, and The wall thickness is thicker than other parts and tends to be thickened. The thickened parts that occur at the tip and rear ends of this raw pipe are
Usually truncated as an off-gauge crop,
This causes 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 as set forth in claim 1 quickly and reliably increases the inter-stand tension acting on the tip of the blank pipe without enlarging the equipment, thereby achieving a sufficient effect of eliminating thickening. The purpose of this method is to reduce the occurrence of defective shapes at the tips of raw tubes and improve the yield rate.

Furthermore, the present invention as set forth in claim 2 quickly and reliably increases the inter-stand tension that acts on the tip and rear ends of the blank pipe without increasing the size of the equipment. The purpose is to reduce the occurrence of defective parts at the tip and rear ends of the raw tube and improve the yield rate by obtaining a sufficient effect of eliminating thickening.

The present invention as set forth in claim 1 provides a method for rolling a pipe in a reducing mill that reduces and rolls a raw pipe by a rolling roll group consisting of a plurality of stands, in which a predetermined portion of the tip of the raw pipe is rolled. Prior to that,
The roll peripheral speed of each stand is set higher than the standard peripheral speed, and when the tip of the raw pipe passes the downstream stand, the roll peripheral speed of the upstream stand relative to the downstream stand is decelerated at a constant deceleration rate, and Control is performed so that the roll circumferential speed of all stands becomes the reference circumferential speed at the time the tip of the tube passes through the final stand to be controlled.

Further, the present invention as set forth in claim 2 provides a method for rolling a pipe in a reducing mill in which a group of rolls consisting of a plurality of stands performs reduction rolling of a stock pipe. Prior to this, the roll circumferential speed of each stand is set higher than the standard circumferential speed, and when the tip of the raw pipe passes the downstream stand, the roll circumferential speed of the upstream stand relative to the downstream stand is reduced at a constant deceleration rate. When the tip of the raw pipe passes through the final stand to be controlled, the peripheral speed of the rolls on all stands is controlled to the reference peripheral speed, and then, when rolling a predetermined portion of the rear end of the raw pipe, Each time the rear end of the blank pipe passes through the upstream stand, the roll circumferential speed of the downstream stand relative to the upstream stand is reduced by a constant deceleration rate compared to the roll circumferential speed of the stand further downstream.

First, the basis for establishing the present invention will be explained.
It is as follows. That is, when performing roll circumferential speed control in order to increase or decrease the tension between stands in a reducing rolling mill, it is desirable for the tension control to change the roll circumferential speed 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 reaction time τ is generally expressed by the following equation (1).

τ=ΣGD ² N/375·T _E (1) In the above equation (1), ΣGD ² is the total moment of inertia of the drive system, N is the motor rotation speed, and T _E is the effective torque. However, the above effective torque T _E is
It is expressed by the following equation (2).

T _E = |T _M −T _R −T _F | …(2) In the above equation (2), T _M is the motor torque, T _R is the rolling torque, and T _F is the friction torque. That is,
When accelerating or decelerating the motor from a steady rotation state,
Only the difference between motor torque T _M and the sum of rolling torque and friction torque (T _R + T _F ) is the effective torque.
T _E is involved in acceleration and deceleration work. Therefore,
When the motor torque T _M is constant (200% of the constant detection force for a normal motor), the effective torque T _E is larger when decelerating during rolling than when accelerating during rolling. , therefore the response time τ becomes small. In other words, when accelerating the motor against the rolling torque T _R , the effective torque T _E is suppressed because the motor torque T _M is suppressed by the upper limit of the motor capacity.
cannot grow beyond a certain limit.
However, when decelerating, the rolling torque T _R can be used as if it were a brake, so the effective torque T _E can be made much larger than when accelerating. Assuming that the motor capacity is 200% on the converter side and 200% on the inverter side, comparing T _E α during acceleration and T _E β during deceleration, the rated
For TMC it will be as follows.

T _E α＝｜2T _MC −T _R −T _F ｜ …(3) T _E β＝｜−2T _MC −T _R −T _F =｜2T _MC +T _R +T _F ｜ …(4) Here, T _R If ≒T _MC and T _F ≒0.1T _MC , T _E α=｜2T _MC −T _MC −0.1T _MC ｜ =0.9T _MC …(5) T _E β=｜2T _MC +T _MC +0.1T _MC = 3.1T _MC …(6) and T _E α/T _E β = 3.44 …(7). That is, by substituting this result into equation (1),
Comparing τα during acceleration and τβ during deceleration, τα / τβ = T _E β / T _E α = 3.44 ...(8), and the response time τα during acceleration is 3 times smaller than the response time τβ during deceleration. It is understood that it will be more than twice as long.

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 quickly and reliably increased, and the effect of tension control can be increased.

Further, there is no need to increase the size of the roll drive motor of each stand, thereby making the equipment more compact and making it possible to suppress a huge investment in equipment.

Hereinafter, specific examples of the present invention will be described. Here, in this embodiment, the total number of stands of the reducing rolling mill 100 shown in FIG. 2 is 24,
The control of the present invention is performed in the first to tenth stands, and the predetermined length region of the tip or rear end of the raw pipe 101 to which the control is applied is defined by the region between two adjacent stands at maximum. The length shall be (2L).

First, the roll circumferential speeds of the first to tenth stands before the start of rolling are the steady speeds during steady rolling in those stands (i), as shown in Figure 3.
It is put on standby at a speed _{N i (} 1+δ _i ) that is increased by an acceleration/deceleration amount δ _i of an appropriate ratio with respect to N i. In addition, in Figure 3, time is taken on the horizontal axis, and the first stand,
The changes in roll circumferential speed at the second stand, third stand, and i-th stand are shown by solid lines, broken lines, and 1, respectively.
It is shown by a dashed dot line and a dashed two dot line.

Next, when the detector 102 detects that the tip of the raw pipe 101 is caught in the i+1st stand, the controller 103 controls the roll peripheral speed of the i-th stand as an upstream stand with respect to the i+1-th stand. is decelerated as N _i (1+δ _i )→N _i (1+δ _i /2), and the roll circumferential speed of the i-1st stand as an upstream stand with respect to the i-th stand is N _i-1 (1+δ _i-1 /2)→N Perform deceleration control as shown in _i-1 . That is, due to the above-mentioned deceleration control, the roll circumferential speed at the tip of the raw pipe 101 is
The _{i-1st stand where N i-} 1 and the roll circumferential speed are
A tension is applied between the stands with the i-th stand which is N _i (1+δ _i /2) based on a speed difference that is larger than the speed difference in the steady state, and the roll circumferential speed is N _i (1+δ _i /2). The tension is generated between the i-th stand whose roll circumferential speed is N _i+1 (1+δ _i+1 ) and the i+1-th stand which is on standby for speed increase, due to a speed difference that is larger than the speed difference in the steady state. is added. In addition, under the state where the raw pipe starts to bite into the second stand and the state where it starts to bite into the 11th stand, between the first and second stands,
Tension control is applied only between the 10th and 11th stands.

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 adjusts the roll circumferential speed of the i-th stand by N _i → N _i (1-δ _i ′/2) The roll peripheral speed of the i-1st stand is controlled as follows: N _i-1 (1-δ _i ′ _-1 /2) → N _i-1 ( 1−δ _i ′ _-1 ), and the roll circumferential speed of the i-2th stand is controlled as N _i-2 (1−δ _i ′)→N _i-2 (1+δ _i-2 ). 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, at the rear end of the raw pipe 101, the roll circumferential speed is
In a steady state, between the i-1st stand where N _i-1 (1-δ _i ′ _-1 ) and the i-th stand where the roll peripheral speed is N _i (1-δ _i ′/2), The i-th stand is applied with tension based on a speed difference greater than the speed difference, and the roll circumferential speed is N _i (1−δ _i ′/2), and the roll circumferential speed is maintained at a steady speed N _{i +1.} A tension is applied between the stand and the (i+1)th stand, which is based on a speed difference that is larger than the speed difference in the steady state.
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 stand.
Tension is controlled only between the stand and the 11th stand.

By the way, in the above embodiment, the appropriate speed increase ratio δ _i to be set for each stand is such that the circumferential speed of the roll is faster than the material over the entire area of 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, let μ be the friction coefficient between the rolls and the material in each stand that makes up the reducing rolling mill, R be the roll radius, and h ₀ and h ₁ be the outer diameters of the blank tubes on the entry and exit sides of the reducing rolling mill. , the wall thickness of the raw pipe on the inlet and outlet sides is t ₀ ,
t ₁ , the stretch coefficients at the entrance and exit sides (tensile stress acting on the raw pipe/yield strength of the raw pipe) are Z ₀ , Z ₁ is the average stretch coefficient as the average value for all stands of the stretch coefficient at each stand. If Z _n , the following equation (3) approximately holds true.

However, the above average stretch coefficient Z _n is as follows:
It is expressed by equation (4).

Z _n = r/t (2-ε _n ) + (1-2ε _n )/r/t
(1−ε _n )−2(ε _n −1)…(4) However, _r , _t , and ε _n in the above equation (4) are calculated according to the following equations (5), (6), and (7), respectively. It is expressed as

_r = ln (t ₀ /t ₁ ) …(5) _t = lnh ₀ −t ₀ /h ₁ −t ₁ …(6) ε _n =1/2 (t ₀ /h ₀ −t ₀ +t ₁ /h ₁ −t ₁ )...(7) In the above equation (3), all numbers are known except for t ₁ , Z ₁ , and Z _n . Also, when considering the first stand (A), Z ₀ = 0, so by substituting it into equation (3), Z ₁
(B) For the second stand, Z ₁ is obtained by substituting the stretch coefficient Z ₁ at the exit side of the first stand as Z ₀ into equation (3), and (C) Repeat the calculations using the same procedure below. If you proceed with the calculation for one stand at a time, the only independent variable among the above unknowns will be t ₁ , and by appropriately assuming the value of t ₁ and calculating the above equation (3), the above (3) Calculate the value of t ₁ such that the formula holds,
If Z ₁ is found based on the calculated t ₁ , then Z ₁ becomes the maximum reachable stretch coefficient. Therefore,
From the material elongation ε _l at this time and the material elongation ε _l ′ at the i-th stand during steady rolling, an appropriate acceleration ratio of the roll circumferential speed to be set at the i-th stand δ _i
is expressed by the following equation (8).

δ _i =k·ε _l /ε _l ′ (8) Here, k is a constant and is usually set to k=1. Further, ε _l is expressed by the following equation (9).

ε _l =t ₀ (h ₀ -t ₀ )/t ₁ (h ₁ -t ₁ )...(9) As described above, the present invention as set forth in claim 1 is a rolling mill consisting of a plurality of stands. In a pipe rolling method in a reducing mill that reduces and rolls a blank pipe by a group of rolls, before rolling a predetermined portion at the tip of the blank pipe, the circumferential speed of the rolls of each stand is set higher than the standard circumferential speed. When the tip of the tube passes through the downstream stand, the roll peripheral speed of the upstream stand relative to the downstream stand is decelerated at a constant deceleration rate, and when the tip of the raw tube passes through the final stand to be controlled, the peripheral speed of all stands is reduced. The circumferential speed of the roll is controlled to be the reference circumferential speed. Therefore, by quickly and reliably increasing the tension between the stands that acts on the tip of the raw pipe without increasing the size of the equipment, and thereby achieving a sufficient effect of eliminating thickening, the tip of the raw pipe can be reduced. It is possible to reduce the occurrence of portions with defective shapes and improve the rate of non-defective products.

Further, the present invention as set forth in claim 2 provides a method for rolling a pipe in a reducing mill that reduces and rolls a raw pipe by a rolling roll group consisting of a plurality of stands, in which a predetermined portion of the tip of the raw pipe is rolled. Prior to this, the roll circumferential speed of each stand is set higher than the standard circumferential speed, and when the tip of the raw pipe passes the downstream stand, the roll circumferential speed of the upstream stand relative to the downstream stand is reduced at a constant deceleration rate. When the tip of the raw pipe passes through the final stand to be controlled, the peripheral speed of the rolls on all stands is controlled to the reference peripheral speed, and then, when rolling a predetermined portion of the rear end of the raw pipe, Each time the rear end of the blank pipe passes through the upstream stand, the roll circumferential speed of the downstream stand relative to the upstream stand is reduced by a constant deceleration rate compared to the roll circumferential speed of the stand further downstream. Therefore, by quickly and reliably increasing the tension between the stands that acts on the tip and rear ends of the raw pipe without increasing the size of the equipment, and thereby achieving a sufficient effect of eliminating thickening, it is possible to It is possible to reduce the occurrence of defective portions at the tip and rear ends of the tube and improve the yield rate.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the 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. It is a line diagram. 100...Reducing rolling mill, 101...Material pipe, 10
2...Detector, 103...Controller.

Claims (1)

[Scope of Claims] 1. In 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, the circumference of the rolls of each stand is The speed is set higher than the reference circumferential speed, and when the tip of the raw pipe passes the downstream stand, the roll circumferential speed of the upstream stand relative to the downstream stand is decelerated at a constant deceleration rate, and the tip of the raw pipe is A method for rolling a pipe in a reducing rolling mill, characterized in that the circumferential speed of the rolls of all stands is controlled to be the reference circumferential speed at the time of exiting the final stand to be controlled. 2. In a pipe rolling method in a reducing mill that reduces and rolls a blank pipe by a group of rolling rolls consisting of multiple stands, before rolling a predetermined portion of the tip of the blank pipe, the circumferential speed of the rolls of each stand is adjusted from the standard circumferential speed. When the tip of the raw pipe passes the downstream stand, the roll peripheral speed of the upstream stand relative to the downstream stand is decelerated at a constant deceleration rate, and the tip of the raw pipe passes through the final stand to be controlled. At this point, the roll circumferential speed of all stands is controlled to be the reference circumferential speed, and then, when rolling a predetermined portion of the rear end of the raw pipe, each time the rear end of the raw pipe passes through the upstream stand, A method for rolling a pipe in a reduction rolling mill, characterized in that the circumferential speed of a roll on a downstream stand relative to the upstream stand is reduced by a constant deceleration rate compared to the circumferential speed of a roll on a stand further downstream.