METALLURGY ABROAD

M O D E R N C O L D - R O L L I N G S T R I P

(UDC 621.771.26)

V. A. L i p u k h i n

Translated from Metallurg, No. 3,

pp. 31-32, February, 1965

hlILLS

Continuous mills with two to six 4-high stands are used for the cold-rol l ing of strip, as well as single stand 4-high reversing mills and mult i rol l mills of various types. The first of these are used for the production of compar-

a t ive ly uniform products in large volumes, and the second for small volumes of production, for rolling special steels, and so on. Multiroll mills are also used for the production of special steels, very thin strip, and foil.

In capi ta l i s t countries, more than 100 continuous wide strip cold-rol l ing mills have been established with a

rol l f lank length of 900 mm and more, and of these 66 are in the USA. The total annual production capaci ty of a l l

the mills is assessed at roughly more than 54 mil l ion tons, of which 35 mil l ion tons is produced on mills established in the USA (about 65%).

Twenty-f ive mills with a total annual production capaci ty of about 13.0 mi l l ion tons (around 25%) have been

established in European countries. Sixteen mills with a total annual production capaci ty of about 6 mi l l ion tons

(about 10~ have been established in the other capi ta l is t countries, and of these 10 mills are in japan.

Roughly, more than 100 reversing wide strip cold-rol l ing mills have been established. The total annual pro- duction capaci ty of these is about 9 mi l l ion tons.

Compara t ive ly few (less than reversing mills) mult i rol l wide strip cold-rol l ing mills have been established, and their production capac i ty is small , since the major i ty of these mills are designed for the rolling of a l loyed steels.

Of a l l the cold- ro l l ing mills, the reversing 4-stand mil l is the most widely distributed (Fig. 1). More than 50 of these mills have been established, and the total annual production capaci ty of these amounts to more than 2(~ mi l - l ion tons (48% of the total production capac i ty of co ld- ro l l ing mills of a l l types). The second place is taken by

5-stand mills, the number of which exceeds 36, and the yearly production capaci ty exceeds l(J mil l ion tons (about 30% of the total production capac i ty of co ld- ro l l ing mills).

The wide distribution of 4-stand mills is explained by the fact that, as distinct from 3-stand mills, they can be used for rolling co ld- ro l led strips over a wide range of thickness dimensions (0.15-0.25 to 2.5-3 ram), whereas on

3-stand mills sheets of thict~less from 0.6-0.8 to 3 mm can be rolled. Four-stand mills can be used not only for

roi l ing thin sheets from carbon steels, but also for rolling t inplate, stainless steel, and sil icon transformer steel sheets,

and so on. Tlte f lank length of the rolls in modern mills is 1370-2030 ram, the diameter of the working rolls 400-

5ff2 ram, and the d iameter of the backup rolls 1346-1524 mm. Thin working roils are used in rolling a l loyed steels and in roll ing t inplate. Rolls with a diameter of 533-572 mm are used for rolling carbon steels.

The roll ing speed on 4-stand mills reaches 25 m/sac. The total power of the motors for the drive to the work- ing rolls and col lar is up to 25,500 kW, the weight of the rolled coils up to 36 tons, and the production capaci ty up to 1,200,000 tons per year.

Five-s tand cold- ro l l ing mills are used for rolling t inplate and especia l ly thin sheet. Tinplate with a thickness from 0.11-0.15 to 0.6 mm is rolled on modern 5-stand mills. The length of the roll f lank on thesemil ls is from 1065 to 1450 ram, and the d iameter of the working roils is from 533-610 mm and of the backup rolls 1346-1422mm. The roll ing speed reaches 37 m/sac. The total power of the main motors to drive the working rolls and coilers is up to 22,000 kW. The weight of the rolled coils is up to 45 tons. In recent times, 5-stand mills have begun to be used for roll ing thin sheet as wall.

In recent t imes, 3-stand mills have been used rarely for rolling thin sheet.

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2

Fig. 1. Layout of a four-stand cold-rol l ing mill . 1) Decoiler; 2) working stands; 3) coiler; 4)bear -

ing rollers; 5) entry guides; 6) del ivery guides; 7 and 8) "bil ly"rollers; 9) rollers measuring tension;

10) x- ray or isotope thickness meters; 11) promotion guards; 12) collectors and jets for supplying emul - sion and cooling water to the rolls.

A special p lace is occupied by the new 3-stand mills for roll ing very thin t inplate. These, and six-stand mills,

have appeared since 1960. At the same t ime, very thin t inplate with a thickness from 0.076 to 0.152 mm also ap- peared in the USA as a result of the compet i t ion with tinned plate from aluminum foil, paper, and glass.

The following methods are known for the production of very thin t inpla te :

1. The roll ing of tinned plate of ordinary thickness with a reduction of 20-50%. However, in fl~is case the

tinned surface of the plate takes on a matte appearance.

2. The simultaneous roll ing of two strips of b lack t inplate. In this case, the internal surfaces of the strip be-

come matte , as dist inct from the outside polished surfaces. Such t inplate is accep tab le for special re-

quirements.

3. Rolling in one go on a six-stand cold-rol l ing mill . However, i t is considered that this method of rolling

very thin t inplate is not very suitable since, with a reduction in the t inplate thickness, the production cap-

aci ty of the mil l is reduced (almost in direct proportion).

4. Rolling on ordinary 5-stand mills. This method is even more unsuitable than the preceding one, since in tllis case i t is necessary to reduce the thickness of the rolled strip on the hot roll ing mill , or to roll the

t inplate in two goes.

5. Secondary rolling of the black t inplate after anneal ing with a reduction of up to 50%. In this case, i t re-

places temper rolling. The tinning of the t inplate is performed in the work hardened condition without an-

nealing. The hardness of such t inplate reaches 80-85 Rockwell units. When very thin soft t inplate is re-

quired, i t is annealed af ter the second roll ing in belt furnaces.

Three or four-stand mills have been set up for the second rol l ing of t inplate. The first 1220-ram 3-stand mil l

(Fig. 2) for rolling very thin t inplate was set up in 1962 at the factory of Johns and Laughlin at All iquippe, USA. The

characmris t ic feature of this mil l is the fact that the first stand in i t is a temper roll ing stand and, moreover, replaces

the tensioning instal lat ion of the e ight - ro l le r type.

The 1200-ram 3-stand mi l l is designed to roll strip with a thickness of 0.5 mm and a width of 457-1067 ram.

The external coil d iameter may be up to 2130 ram, its weight 20.4-26.7 tons by 1 m strip width, the maximum rol l - ing speed 28.4 m/see , the mi l l production capaci ty 13,600 tons/month, the d iameter of the mi l l ' s working rolls

584 mm, and of the backup rolls 1370 ram.

A second 3-stand mil l with rolls having a flank length of 1370 ram, is being prepared for the Inland Steel

Company (USA).

Five 2-stand mills have been set up in the USA. For example , the 1145-mm mil l in the Bethlehem Steel Company's factory in Sparrows Point is designed to roll t inplate with a thickness of 0.22-0.34 mm into very thin tin- p la te of thickness 0.076-0.167 111111 at a rolling speed of up to 28 m/see. The first stand, with working rolls of d iame- ter 560-480 ram, is driven from a 3-armature motor of capaci ty 3350 kW, at 450-900 rpm. The second stand, with working rolls of 610-508 mm diameter , is driven by a motor of 2235 kW,capaci ty, at 450-900 rpm.

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r I,', le ~g, ( I / ~ ~2__k

Fig. 9. Layout of three-stand mil l for rolling very thin sheet. 1) Decoiler; 2) No. 1 temper roll ing stand; 3) No. 2 working stand; 4) No. 3 working stand; 5) coi le t with

bel t wrapper; 6) nip rollers; 7) entry guides; 8) smoothing rollers; 9) del ivery guides;

10) ironing rollers; l l ) r o l l e r s measuring tension; 12) promction guards; 13 and 14)"bi l ly" rollers; 15) entry guides; 1G) x- ray thicka~ess meters; 12) nip rollers; 18) det ivery guides;

19) collectors and jets for cooling water; 20) collectors and jets for strip lubrication.

Six-stand mills appeared in the USA in 1961. A 1320-ram mil l il~ a factory at Indiana tiarbor is designed to roll t inplate of tMckness 0.089-0.6 mm from strip of thickness 1..9-2.8 ram. The width of the strip being rolled is

560-1170 ram, the external coi l d iameter 760-2030 ram, the internal d iameter 420 mm, and the coi l weight up to 28.2 tons.

Two powerful emulsion rec i rcula t ing systems with a total capaci ty of around 76 m a have been instal led to lu-

br icate and cool the rolls. The first system serves the second, third, and fourth stands, and the second system the fiftlt and sixth stands. The rolls in the first stand are cooled with water. The advantage of using two emulsion systems consists in the fact that in the first system, dirt which is on rite strip, is washed off, and the emulsion in the second

system is not therefore contaminated, and this is conducive to obtaining a strip with a c lean surface.

Single stand co ld- ro l l ing reversing mills may be divided according to their purpose into three groups: a) gen- eral purpose mills for rol l ing sheets of carbon steels; b) mills for rolling t inplate and especia l ly thin sheets; c) mills for rolt ing a l loy steels.

The first of these have rolls with a flank length of 2150 ram. The diameters of the working rolls in these mills lies in the range 400- 580 ram, and the d iameter of rite backup rolls is up to 1420 ram, and their maximum peripheral

speed can reach more than 15 m/sec; the total power of the motors driving the working rolls, coilers, and decoilers, is more than ~/000 kW. Mills for roll ing t inplate , and also a l loyed steels, are distinguished by their smal ler dimensions.

The deve lopment of modern continuous and reversing cold- ro l l ing mills with 4-high stands is typified by the following pr incipal features:

1. The increase in the weight of the coils being rolled up to 46 tons. New mills are pla~med for roll ing even heavier coils (up to 60 tons). The increase in the coil weight is achieved by roiling heavy slabs of up to 18 tons and more on t~te hot - ro l l ing mills. With the increase in coil size, i t is a imed to have in the continuous pickling plants

not more than 9-3 welded seams in the enlarged coil, in view of the fact that welded seams need to be rol led on co ld- ro l l ing mills a t a reduced speed (approximate ly up to 8 m/see.) .

9. An increase in the r ig idi ty of working stands by increasing the d iameter of backup rolls to 1624 ram, the cross-section of the mills column to 7100 cm z, and the weight of the frame to 120 tons. The accuracy of roll ing rises with an increase in the r ig idi ty of stands.

3. For the present, no increase in rol l ing speed is observable. The speeds of 6- and 6-stand mills do not ex- ceed 37 m/see , and of 4-stand mills 25 m/see. An increase in rolling speed is held up by the fact that as yet no technica l lubricants have been found which can ensure high roll ing speeds.

4. An increase in the power of the main motors driving the working rolls and coilers.

5. The wide introduction of au tomat ic control of the adjustment of the roll ing m i l l to mainta in constant thickness dimensions in the strip being roiled by means of the au tomat ic adjustment of the screwdowns in the first stands, and by the regulat ion of interstand tension in the strip being rolled in tits last stands.

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Of mult i rol l mills, 20-stand mills have been chiefly used in recent times; the special feature of these is the ex t r eme ly high r igidi ty of the working stand's construction. The system of rolls is contained in a massive solid steel cast or forged frame without blocks and screwdowns, and this is conducive to a reduction in the deformation of the stand under load. As well as this, in connection with the smaller d iameter of the working rolls in comparison with

four-high mills, the pressure of the meta l on the rolls is considerably less in 20-high mills (with the same reductions).

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