US2821492A - Method and apparatus for pickling ferrous strip - Google Patents

Description

Jan. 28,. 1958 A. J. BERDIS I 3 L 9 METHOD AND AmRA-TUS FoR'RIcKLINc FERRQUSL STRIP Filed Feb. 16, 1955 2 Sheets-Sheet 1 I nvvmrcw 7 v ALBERT J. HERD/S his Attorney.

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A. J BERDIS Jan. 28, 1958 METHOD AND APPARATUS FOR PICKLInd FER-ROUSVSTRIP Filed Feb. '16, 1955 2 Sheets-*Sheqo 2 *M/ VENTOR ALBERT J. amp/s AM how his Attorney.

United States Patent lVIETHOD AND APPARATUS FOR PICKLING FERROUS STRIP Application February 16, 1955, Serial No. 488,493 I 3 Claims. 01. 1s4 1's This invention relates to the manufacture of sheet steel and, in particular, to the treatment of hot-rolled steel strip of intermediate gage, preparatory to the coldrolling thereof to final gage. r

' As is well known to those familiar with the steel indu stry, hot-rolled steel strip as coiled at intermediate gage, on leaving the last stand of the finishing train of a continuous hot mill,is covered with a layer of oxide or scale which is tightly adherent to the underlying metal surface. This scale must be removed in .order to permit the re quired surface conditions tobe obtained on further reduction of the strip to final gage by cold-rolling in a continuous cold mill. The pickling operation, however While necessary, is a wholly unmixed evil because of the cost of the equipment required, the mill floor space occupied thereby, the additional handling of the material involved, the cost of the pickling agent consumed and the noxious fumes inevitably accompanying the treatment. Since continuous processing of steel strip at high speed is now conventional, extensive apparatus including a long acid tank, a wash tank and a dryer, with the necessary guide and feed rollers, is required to pickle traveling strip in single ply, and such lines naturally involve heavy capital investment. It is accordingly the object of my invention to increase materially the efficiency of the pickling operation as now carried on, by a simple and relatively inexpensive preliminary treatment of the strip, and thereby substantially reduce the total pickling cost per ton of strip.

In a preferred embodiment of the invention, I subject hot-rolled steel strip, with the hot mill scale thereon, to a combination of tensile and compressive forces sufficient slightly to elongate the strip and produce incipient fractures in the scale layer, thereby facilitating the action of the pickling medium, e. g., a dilute solution of sulphuric acid, when the strip is subsequently immersed therein. More specifically, I subject successive portions of the strip progressively to a substantial tension and a relatively light compression and then pass the strip directly into a pickle line of conventional type. The necessary combination of forces may conveniently be produced by a single-stand cold-rolling mill having a backtension means on the entering side and a forward-tension means on the exit side. The tension means may be friction bridles connected to dynamo-electric machines capable of operating either as generators or motors. A pinchroll stand ahead of the back-tension bridle and another beyond the forward-tension bridle serve, respectively, to pull strip from a looping pit and feed it into the entry end of a pickle line.

A complete understanding of the invention may be obtained from the following detailed description and explanation which refer to the accompanying drawings illustrating the present preferred embodiment. In the drawings:

Figure 1 is a plan view of one embodiment of apparatus suited for carrying out my improved method; and

Figure 2 is a central longitudinal section through the apparatus, with certain parts thereof shown in elevation.

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Referring now in detail to the drawings, hot-rolled strip 10, e. g., low-carbon steel strip from .075" to .125 thick, is pulled from a looping pit 11 through a series of staggered unfolding rolls 12 and a friction brake 13 in the form of a plank drag, by a pair of pinch rolls 14, ahead of which is mounted a billy roll 15. The brake includes a fixed lower frame '16 and an upper frame 17 adapted to be moved toward and from it by fluid-pressure cylinders and pistons 18. Theadjac'ent faces of frames 16 and 17. are lined with wooden planks or blocks which constitute the friction surfaces engaging opposite sides of the strip.

Pinch rolls 14 are connected through the usual spindlesv 19 and pinion stand 20 to a motor 21.

' Pinch rolls 14 are built into a tension bridle 22 including rolls 23 and 24. Roll 23 is journaled in stationary bearings and roll 24in a tiltable frame 25 which may be moved by a fluid-pressure cylinder and piston 251: from the operative position shown, to an out-of-the-way posi tion{ Roll 23 is connected through a pinion stand 23a to a dynamo-electric machine 26 adapted to serve as a motor to drive the roll 23 or as a generator when driven by it.

'. The strip, on leaving the bridle 22, enters a cold-rolling mill 27. As shown, this is a two-high mill of conventional construction. It is fitted with billy rolls 28 on the entry and exit sides, adapted to be frictionally driven by the strip. These rolls drive differential means such as tach-- ometer generators 29 which, in a known manner, indicate the reduction effected by the mill, by a comparison of the speeds of the strip entering and leaving the mill. The mill drive includes a motor 30, pinion stand 31 and spindles 32.

The strip leaving the mill passes through a tension birdle 33 which is substantially a duplicate of bridle 22 but of opposite hand. Corresponding parts of bridle 33 are designated by the same numerals used in describing bridle 22, with a prime afiixed. The strip is delivered from birdle 33 by the pinch rolls 14 thereof into the entrance end of a pickle line indicated by tank 34.

Rolls 12 remove sharp bends from the strip which may be formed as a result of its piling up in the pit. Brake 13 applies a constant but limited drag or back tension to the strip and also smooths out the bends to some extent.

As indicated above, pinch rolls 14 serve to pull strip from pit 11. They then feed it at a constant rate to rolls 23 and 24. It will be readily understood that the resist- :ance offered by the strip accumulated in the pit will be highly variable depending on how the strip is disposed therein, and the load on motor 21 varies accordingly. Thus rolls 14 constitute an equalizer to prevent such variations from passing through to the rest of the system.

By suitable control of the field excitation of machine 21, rolls 23 and 24, under running conditions, are caused to exert a heavy back tension of about 2500 p. s. i., on the strip entering the mill, by regenerative braking. The strip advancing under such tension drives the rolls which operate machine 21 as a generator, returning current to the supply lines or to a load resistor.

Mill 27 has its screw-downs adjusted to efiect only a light draft on the strip, i. e., from 2 to 4%, as indicated by the differential gage-reduction meter mentioned above. The mill screw-downs are operated as necessary, to maintain this reduction substantially constant as the rolling of the strip proceeds.

Bridle 33, by proper excitation of the field of machine 26', exerts a heavy forward tension on the strip leaving the mill, substantially equal to the back tension applied by regenerative action of machine 26 through bridle 22. Thus the overall effect of the apparatus described is to apply heavy tension to successive portions of the strip length and, simultaneously, a relatively light compression. The result of this treatment is to cause an incipient fracture of the scale layers on both sides of the strip. In fact,

, 3' soxne'scale is actually detached in the form of a fine powder. The remainder of the 'scale,"however, remains adherent but is in such condition after being subjected to the combined tension and compression, that complete removal Shy 'picklingis' facilitated to asuflr 'r'nia "degree.

' A'n'indication of]theadvantages gainedfby' km efth'od of myinvention isfoun'd'in the:factTthatitihasImatle it possible to double the 3 output of a: particular pickling, line by, increasing thespeed ofstrip ,tr'a'vel'and,infaddition, has reduced-the acid consumption by about'4 '5%.

As a specific example'bf actual operating; practice, "in processing strip 36'' wide and thick at normals eea, machine 26 deliveredabout'400 'ainpere's -regeurated, machine 26' required about the san'leinpu'tv and rnillfrrlofor 30 consumed aboutf.100 amperes,1all currents'beiijgjat'a voltage of about250. 'The'it'o'taltension' thus'prbdiic'ed was about 8800 pounds'or Z'SQpOunds per inehofwfdth.

Since the"back tension on [the Strip atlfthe .entryq'sidepf- -t he mill is about equal to'thetforward, tension 'onfthezle'xit side, the mill motor supplies all ,the work 'r e'quir'ed t'o effect thellight reduction of the strip gage and tolsupply the losses, in machine 26. .For other widths andfgage s 'of strip, the output of and load on machines, 26 and 26,, respectively,.may vary between -200and 1200 amperes.

The motors 21 and '21 are adjusted to operate sothat only the necessary feeding tension exists in the strip betweenrolls14 andv24 on the entry side 'androlls 24' and 14' on the exit side.

Although;I' have disclosed, herein-thepreferred e'mbo'diment and practice of my invention, 'Ixintendatorcover as well any change or modification" therein which'mayxbe made without departing from the spirit and scope of the invention.

I claim:

1. In a strip-pickling line including an elongated solution tank, the combination therewith of a cold-rolling mill at the entry end of the tank, a back-tension bridle on the entry side of the mill and a forward-tension bridle between the mill and the tank.

2.''In a method of descaling scale-coated ferrous strip, the steps of subjecting the strip to a light reduction in a cold-rolling mill, applying a restraining'tension to the stripentering the mill, applying a forward tension to the strip leaving the mill, the combination of-tensile and compressive 'forces effecting an incipient fracture of the scale, and then substantially immediately introducing the strip into a pickling solution.

3. In a method of descaling scale-coated ferrous strip, the ,steps of passing the strip through a back-tension bridle, a cold-rolling mill and aforward-tension bridle, in'jsuccess'ion, applying substantially equal and opposite tensionsto the strip by said bridles, effecting alight-reduction of the strip in said mill and then'subst antially immediately subjecting the strip to a pickling'solution.

' References Cited inithe file of this patent UNITED STATES PATENTS 1,392,780 Marsh 'Oct.-4, 1921 2,287,380 Klein June 23, 1942 2,359,095 :Elder Sept. 26, 1944 {2,650,888 Pottberg Sept. '1, 1953 2,109,143 :Francis May 24, 1955

Claims (2)

1. IN A STRIP-PICKING LINE INCLUDING AN ELONGATED SOLUTION TANK, THE COMBINATION THEREWITH OF A COLD-ROLLING MILL AT THE ENTRY END OF THE TANK, A BACK-TENSION BRIDLE ON THE ENTRY SIDE OF THE MILL AND A FORWARD-TENSION BRIDLE BETWEEN THE MILL AND THE TANK.

2. IN A METHOD OF DESCALING SCALE-COATED FERROUS STRIP, THE STEPS OF SUBJECTING THE STRIP TO A LIGHT REDUCTION IN A COLD-ROLLING MILL, APPLYING A RESTRAINING TENSION TO THE STRIP ENTERING THE MILL, APPLYING A FORWARD TENSION TO THE STRIP LEAVING THE MILL, THE COMBINATION OF TENSILE AND

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