ISSN 0967�0912, Steel in Translation, 2011, Vol. 41, No. 10, pp. 845–848. © Allerton Press, Inc., 2011.Original Russian Text © R.L. Shatalov, E.A. Maksimov, A.G. Babkin, 2011, published in “Stal’,” 2011, No. 10, pp. 33–36.

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In recent years, Russian consumers have imposedmore stringent quality requirements on rolled metal.The export market is governed by European standards,according to which the tolerances on the strip thick�ness and flatness (planarity) are 1.5–2 times tighterthan in the Russian standards. For existing equipmentand levels of automation, we need to find means ofimproving rolled strip and sheet.

Our ability to minimize the transverse thicknessvariation and maximize the flatness of rolled corro�sion�resistant steel strip depends not only on theequipment and rolling technology employed but alsoon the adjustment of the rolling mill and the scope forregulation of the rolling parameters. On sheet mills,the transverse thickness variation and flatness of stripare regulated by methods such as shaping the rollerbarrels, controlling their thermal convexity, andhydraulic flexure of the roller barrels in four�rollercells. However, these methods have distinct disadvan�tages. For example, the roller profiles are usually opti�mal for a specific type of strip; and thermal regulationof the roller barrels is characterized by considerableinertia. In four�roller cells, the use of counterflexure atthe working rollers and additional flexure at the sup�porting rollers imposes additional load on the bearingsand intensifies barrel wear.

We know that the transverse flexure of the rollersystem in a four�roller cell is determined by parame�ters such as the roller geometry (the barrel and pindiameters of the supporting and working rollers, thedistance between the axes of the adjustment screws);the elasticity of the supporting and working rollers;and the rolling force. In addition, traditional methodsdo not permit complete regulation in the fluctuation ofelastic strain of the roller system over the strip lengthwith change in the rolling force, nonuniform trans�verse wear over the barrel length, abrupt temperaturevariation over the barrel length and strip width, and

nonuniform variation in mechanical properties overthe strip length and width [1].

In reversible rolling with known roller geometry in afour�roller cell (diameter of supporting and workingroller, barrel length, and the distance between the axesof the adjustment screws), the mill may be adjusted forconstant rolling force in each pass by ensuring constanttransverse flexure of the rollers and hence constanttransverse thickness variation of the strip in each pass

(1)

(2)

(3)

where P1, P2, P3, Pn denote the rolling force in differ�ent passes; ΔZ1, ΔZ2, ΔZ3, ΔZn denote the flexure of thecell’s rolling system in different passes; δh1y, δh2y, δh3y,δhny denote the transverse thickness variation of therolled strip in different passes; 1, 2, …, n are the num�bers of the passes in reversible rolling. In reversiblerolling, the relative transverse thickness variation ofthe strip will be the same in each pass if a strict planar�ity condition is satisfied [1]

(4)

where δh0y, δh1y denote the transverse thickness varia�tion of the rolled strip on entering and leaving thedeformation source, respectively; h0, h1 are the mean(over the width) strip thicknesses on entering and leav�ing the deformation source.

We know that, in asymmetric strip rolling, the roll�ing force and the flexure of the roller system, whichaffect the transverse thickness variation and flatness ofthe strip, may be regulated by adjusting the discrep�ancy between the azimuthal velocities of the workingrollers and the tension at the ends of the strip. Adjust�ment of the rolling mill to obtain flat strip may be

P1 P2 P3 Pn const,= = = =

ΔZ1 ΔZ2 ΔZ3 ΔZn const,= = = =

δh1y δh2y δh3y δhny const,= = = =

δh0y/h0 δh1y/h1,=

Adjustment of Rolling Mills to Produce Flatter Steel StripR. L. Shatalova, E. A. Maksimovb, and A. G. Babkinc

aMoscow State Open University, Moscow, RussiabZAO Intrai, Chelyabinsk, Russia

cOAO Chelyabinskii Metallurgicheskii Kombinat, Chelyabinsk, RussiaReceived October 28, 2011

Abstract—A method of rolling�mill adjustment is proposed for the production of flatter strip, with corre�sponding calculations of the rolling conditions. On the basis of such adjustment, combined (symmetric +asymmetric) rolling of corrosion�resistant steel strip has been introduced in the 1700 reversible four�rollermill at OAO Chelyabinskii Metallurgicheskii Kombinat, with improvement in strip flatness.

DOI: 10.3103/S0967091211100202

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SHATALOV et al.

ensured by selecting the discrepancy between the azi�muthal velocities of the working rollers and adjustingthe tension ratio at the ends of the strip so as to obtainconstant metal pressure at the roller per pass, as inEq. (1). To calculate the mean metal pressure at theroller in asymmetric rolling, we use the formula [2, 3]

(5)

where σ0 is the rear ten�sion; h0 is the strip thickness on entering the roller;β = 1.15 is the Lode coefficient; λ, λ0 are the extensioncoefficients in the given pass and the preceding pass;σs0 is the metal’s resistance to deformation on enteringthe deformation source; τ1 = τ0 = τ are the frictionalforces at strip contact with the working rollers; l is thelength of the deformation source; A is a constant char�acterizing the strengthening rate of the metal when theactual strengthening curve is replaced by the lineardependence σs00 isthe metal’s resistance to deformation in the absence ofcold hardening.

The model for W was stated in [2, 3]

In Eq. (5), the longitudinal coordinates of the crit�ical angles for rollers with large and small azi�muthal velocities in asymmetric rolling (as shown inthe figure) may be expressed in the form [2, 3]

(6)

where v1 is the speed of the strip leaving the rollers;vv1 is the larger azimuthal velocity of the workingroller; kv characterizes the discrepancy between theazimuthal velocities of the working rollers in asym�metric rolling [2, 3]

(7)

where v0 is the smaller azimuthal velocity of the work�ing rollers.

The rolling force is determined from the classicalformula

(8)

where B is the width of the strip.

pc βσs0 1 2A 2Aλ0 1–λ0

�����������– 2A λ 1–λλ0 λln���������������–+⎝

⎛=

– 0.5 1 A+( ) λ��⎠⎞ln l

h0 λ2ln

�������������W1 σ0,–+

W1 W1 λ Xγ0* Xγ1* τ l, , , ,( ),=

σs σs00 Aσs00 λλ0 1–( )/λλ0,+=

W 2τ Xγ1* λ1 X

γ1*–λln λ

1 Xγ1*–

λ–+( )=

– 2τ 1 Xγ0*–( ) λ λXγ0*

–ln 1+[ ].

Xγ0* Xγ1*,

Xγ1*Xγ1

l������

v1/vv1( )ln

λln����������������������,= =

Xγ0*Xγ1

l������

kv

( )ln

λln�������������+ ,=

kv vv1/vv0,=

P pcBl,=

For asymmetric rolling, the tension σ1 at the frontis found from the energy balance [2, 3]

(9)

where

The total tension at the front end is

(10)

At present, the planarity of strip rolled on the1700 reversible four�roller cold�rolling mill(OAO Chelyabinskii Metallurgicheskii Kombinat,Mechel group) is regulated by shaping the roller barreland regulating their thermal convexity. The character�istics of the 1700 mill are as follows:

The working rollers rest on two�row roller bearings;a single primary drive is employed; and the rollers arecooled by means of emulsion.

If equipment for counterflexure of the roller systemis absent or of limited ability to regulate the flatnessand transverse thickness variation of the strip, com�bined symmetric and asymmetric rolling of corrosion�resistant steel strip is employed. In asymmetric rolling,a discrepancy is established between the azimuthalvelocities of the working rollers, and the tension at theends of the strip is adjusted. In that case, the systemequalizing the speeds of the working rollers in the1700 reversible four�roller mill at OAO ChelyabinskiiMetallurgicheskii Kombinat is replaced by a systemfor introducing a discrepancy between the azimuthalvelocities of the working rollers. The azimuthal veloc�ities of the rollers and the ends of the strip are mea�sured by means of frequency meters based on the fre�quencies of signals obtained from photodiode sensors.In rolling, the considerable heat liberation in thedeformation source at a strain rate U > 80 s–1, whichmight be lead to buildup on the rollers, is compensated

Diameter, mm:

supporting rollers 1420–1550

working rollers 420–500

Length of roller barrel, mm 1700

Rolling speed, m/s 4–6

Permissible rolling force, MN 30

Type of motor 2P19�67K

Power, kW 2 × 1040

Permissible tension, MN 0.45

Type of coiling�machine motor 2P21�70�12K

Permissible torque, kN m 240

σ1 σ0 βσs00 1 A+( ) λ Aλλ0 1–λλ0

��������������–ln⎝ ⎠⎛ ⎞+=

– 2lτh0 λln�����������W1,

W1 W1 Xγ0* Xγ1* λ, ,( ).=

T1 σ1h1B.=

STEEL IN TRANSLATION Vol. 41 No. 10 2011

ADJUSTMENT OF ROLLING MILLS TO PRODUCE FLATTER STEEL STRIP 847

by more rapid cooling of the roller system and the stripand also by limiting the rolling speed.

The working rollers are shaped so as to remaincylindrical at the bottom with the addition of +0.2 mmat the top. The supporting rollers are cylindrical butwith tapering. The control system for asymmetric roll�ing includes a potentiometer and a pulse specifying thediscrepancy between the azimuthal velocities of theworking rollers, as well as units specifying the azi�muthal velocities of the lower and upper working roll�ers, photopulse sensors measuring the azimuthalvelocities of the lower and upper working rollers, and aunit limiting the torque difference.

In asymmetric rolling, the 1700 reversible four�roller mill is adjusted as follows:

⎯in accordance with the required reduction, theadjustment screws establish the required absolutereduction of the strip;

⎯at the coiling systems, the front and rear end ten�sion of the strip is established;

⎯the potentiometer on the operator’s controlpanel sets the discrepancy between the azimuthalvelocities of the working rollers;

⎯the rolling mill’s primary drive is turned on.In that case, the discrepancy between the azi�

muthal velocities of the working rollers in Eq. (7) isestablished by reducing the azimuthal velocity of thelower working roller, with constant azimuthal velocityof the upper working roller. Tables 1 and 2 present datafor the symmetric and combined (symmetric + asym�metric) rolling of corrosion�resistant steel strip (auste�nitic 12X18H10T steel) on the 1700 reversible four�roller mill at OAO Chelyabinskii MetallurgicheskiiKombinat.

Analysis of Table 1 shows that, in symmetric striprolling, the maximum discrepancy between the rollingforces in the passes is 25%; for the last three passes, thecorresponding figure is 15.7%. Such variation in roll�ing force does not ensure constant transverse flexure of

the roller and transverse thickness variation of thestrip. As a result, the strip will not be flat. In combinedrolling—symmetric rolling (1–6 passes) and asym�metric rolling (last three passes)—the strip thicknessis first reduced from 2.50 to 0.95 mm in symmetricrolling. (This corresponds to reduction εΣ = 62%).Then the reduction is increased to εΣ = 68% by asym�metric rolling, with 1.02 ≤ kv ≤ 1.04 and T1/T0 = 1.35,1.21, and 1.21 in the last three passes. Comparison ofthe total reduction, the discrepancy between the azi�muthal velocities, and the difference in the tensionand the rolling force (Table 2) indicates that the given

R1

α1

τ1Xγ1

h 1

σ1

l

x

α0 R0

τ0 Xγ0

h 0

σ0

v0

v1

1 23 0

Kinematic diagram of the deformation source in asym�metric rolling: Xγ1, Xγ2 are longitudinal coordinates corre�sponding to the critical angles at the rollers with larger andsmaller azimuthal velocities; v0, v1 are the strip speeds onentering and leaving the rollers; α1, α2 are the captureangles at the rollers with larger and smaller azimuthalvelocities; σ1, σ0 are the front and rear tensions; h0, h1 arethe strip thicknesses on entering and leaving the deforma�tion source; R1, R0 are the radii of the rollers with largerand smaller azimuthal velocities; τ1, τ0 are the frictionalforces at contact with the rollers characterized by largerand smaller azimuthal velocities; l is the length of thedeformation source; (1) creep zone; (2) forward�slip zone;(3) zone with opposing frictional forces.

Table 1. Conditions of cold symmetric rolling of 12Х18Н10Т steel strip on the 1700 reversible four�roller mill at OAO Che�lyabinskii Metallurgicheskii Kombinat (initial thickness 2.5 mm; final thickness 0.8 mm; width 1030 mm; T0, T1, front andrear strip tension; v1, rolling speed; εΣ, total relative reduction per pass)

No. h0, mm h1, mm λ εΣ, % v1, m/s kv T0, kN T1, kN P, MN

1 2.50 2.00 1.25 20 1.5 1.00 90 260 16.1

2 2.0 1.65 1.21 34 4.0 1.00 290 290 18.0

3 1.65 1.40 1.18 44 4.0 1.00 260 260 18.9

4 1.40 1.20 1.17 52 4.0 1.00 260 260 20.0

5 1.20 1.05 1.14 58 4.0 1.00 230 230 20.4

6 1.05 0.95 1.11 62 4.0 1.00 210 210 19.7

7 0.95 0.88 1.08 64.8 4.0 1.00 200 200 18.2

8 0.88 0.83 1.06 66.8 4.0 1.00 190 190 19.4

9 0.83 0.80 1.04 68 4.0 1.00 150 14.5 16.7

z

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SHATALOV et al.

discrepancy between the azimuthal velocities and ten�sion difference yield a constant rolling force P/P* =52% in the last three passes, with increase in εΣ from62 to 68%.

Constant rolling force in the last three passes per�mits stabilization of the elastic flexure of the roller sys�tem and the transverse thickness variation of the stripbetween passes (with constant temperature condi�tions) and permits adjustment practically in accor�dance with Eq. (4). This facilitates the production offlatter strip. Combined (symmetric + asymmetric)rolling of corrosion�resistant steel strip on the1700 reversible four�roller mill at OAO ChelyabinskiiMetallurgicheskii Kombinat improves its planarity by10–25%.

CONCLUSIONS

(1) Mathematical simulation permits the develop�ment of combined (symmetric + asymmetric) rollingof strip. A method of rolling�mill adjustment is pro�posed for the production of flatter strip, with corre�sponding calculations of the rolling conditions. In thisapproach, we adjust the discrepancy between the azi�muthal velocities of the working rollers (kv) and the

parameter T1/T0 so as to ensure constant rolling forcein the last three passes during reversible rolling.

(2) Experimental trials show that the rolling forceP/P* = 52% is constant in the last three passes whenreducing the thickness of corrosion�resistant steel stripfrom 2.5 to 0.8 mm on the 1700 reversible four�rollermill at OAO Chelyabinskii Metallurgicheskii Kombi�nat, in conditions where 1.02 ≤ kv ≤ 1.04, T1/T0 = 1.35,1.21, and 1.21, respectively, and the total reduction isincreased from 62 to 68%. This permits decrease in thetransverse thickness variation and improvement instrip thickness.

REFERENCES

1. Grigoryan, G.G., Zheleznov, Yu.D., Chernye, V.A.,et al., Nastroika, stabilizatsiya i kontrol’ protsessatonkolistovoi prokatki (Adjustment, Stabilization, andMonitoring of Thin�Sheet Rolling), Moscow: Metal�lurgiya, 1975.

2. Maksimov, E.A., Reducing the Pressure on the Rollerand the Tension in the Asymmetric Cold Rolling ofStrip, Metallurg, 2010, no. 11, pp. 54–57.

3. Maksimov, E.A., Shatalov, R.L., Boskhamdzhiev, N.Sh.,Proizvodstvo planshetnykh polos pri prokatke (Flat�StripProduction in Rolling), Moscow: Teplotekhnika, 2008.

Table 2. Conditions of cold combined (symmetric + asymmetric) rolling of 12Х18Н10Т steel strip on the 1700 reversible four�roller mill at OAO Chelyabinskii Metallurgicheskii Kombinat (initial thickness 2.5 mm; final thickness 0.8 mm; width1030 mm; mean transverse thickness variation δh0 = 0.03 mm; P*, permissible rolling pressure for the 1700 mill, P* = 30 MN)

No. h0, mm h1, mm λ εΣ, % v1, m/s kv T0, kN T1, kN T1/T0 P P/P*, %

1 2.50 2.00 1.25 20 1.5 1.00 90 260 1 16.1 54

2 2.0 1.65 1.21 34 4.0 1.00 290 290 1 18.0 60

3 1.65 1.40 1.18 44 4.0 1.00 260 260 1 18.9 63

4 1.40 1.20 1.17 52 4.0 1.00 260 260 1 20.0 67

5 1.20 1.05 1.14 58 4.0 1.00 230 230 1 20.4 58

6 1.05 0.95 1.11 62 4.0 1.00 210 210 1 19.7 66

7 0.95 0.88 1.08 64.8 4.0 1.04 200 270 1.35 15.7 52

8 0.88 0.83 1.06 66.8 4.0 1.02 190 230 1.21 15.6 52

9 0.83 0.80 1.04 68 4.0 1.02 140 170 1.21 15.6 52