US2381652A - Continuous strip pickling - Google Patents

Description

Aug. 7, 1945. s. .1. Dls-HAUZI CONTINUOUS* STRIP PICKLING original Filed July 24, 1941 Patented Aug. 7, 1945 2,381,652

uNlTEo STATES PATENT ol-Fici-z CONTINUOUS STRIP -PICKLING Steve J. Dishauzi, Hollidays Cove, W. Va., assign-4 or to National Steel'Corporation, a corporation of Delaware -Original application July 24, 1941, Serial No.

Divided and this application November 11, 1943, Serial No. 509,893

1 Claim. "(Cl.2667) A This invention relates to an improved continuous pickling method tand apparatus for striptransferred to an empty tank through Which the strip has been running, and a fresh pickling solution is mixed 'in ,the tank from which the waste pickling solution was transferred. The present invention is an improvement over that shown in A the patent.

The greatest action of vthe pickling solution takes place in the first tank contacted by the strip. Here the acid of the pickling solution attacksthe oxide on the metal with the greatest vigor. As a result a partially spent pickling solution in this tank can perform a proportion of the pickling comparable to that performed in each of the following tanks containing fresher solution. On the other hand, a fresh pickling solution in this tank would attack the strip with such/vigor that the solution would soon be spent. his

would put no burden on thev subsequent tanks at tained at a reduced level Vand the effect of using new pickling solution is minimized on the operation of the pickling line by such solution being used only in the subsequent tanks where it has less effect. A` further result of this manner of operation is that the minimum speed of the strip is greatly increased. With a plurality of tanks in use and the condition of the solution in the first tank such as necessitates dumping, the speed of the strip is rediiced as this tank is dumped.

Since the waste solution being dumped was having a very slight pickling action on the strip, the

`reduction in speed of the strip at this point need be slight. With a solution which is only partially -spent being transferred from a subsequent tank to theflrst tank, no further reduction in the speed of the strip is necessary. While the subsequent tank is being replenished the speed of the strip can be gradually raised to the maximum for obrst but would throw the burden on these tanks l as the solution in the first tank became spent. The solution in the second tank would then heavily attack the metal afterv the solution in the first tank was spent. Recharging the'iirst tank with fresh pickling solution would again cause the heavy reaction to be transferred to-this tank. When the tanks subsequent to the first tank contained fresh solution, the heavy reaction in the first tank would result in overpickling by the fresh solution in the subsequent tanks. When ,the reaction in the first tank fell off sharply andthe solutionv in the subsequent tanks was partially depleted, underpickling of the strip would result. 'I'hus a sharp rise and fall of the pickling action would follow replenishing and depletion of the solution in the rst tank.

To avoid this situation I have evolved a pickling method in which a partially spent pickling solution is charged to the first tank and the condition of the solution in this tank governs the re'- plenishing of the subsequent tanks. of the reaction in the first tank is thus maine The extent taining satisfactory pickling. Thus, contrary to the systems of the prior art, at no time is a mini.-

mum number of tanks being used with one of the tanks having a spent solution therein.

In order to increase the pickling action of the partially spent solution in the first tank to a max'- imum, I have devised a system for circulatingr the solution using the heating medium. Due to the strip manufacturing process resulting in a hot rolled coil of strip, the center sections on both sides of the strip are not badly oxidized. The

edges of the. strip, however, being exposed in the coil, present heavily oxidized surfaces. By inducing a stream of the pickling solution to impinge upon the edge of the strip along its path through the tank, I have raised the action of the pickling solution at that point to a maximum.

This application is a division of copending application Serial No. 403,902 filed July 24, 1941 now Patent No. 2,334,177'.

'An important object of the present invention is the provision of a method of pickling continuous strip at a high rate of speed and with a minimum Y part of the-present disclosure and in which like reference numerals designate like parts,

Flgure'l is a side elevation, partially in section,

of apparatus capable of carrying out the-method,

.level than the others to make possible gravitational iiow of the pickling solution being transferred. Strip to be pickled is fed by power driven rolls I3 over guide roll I5 into tank I0. The strip passes under weighted rolls I6 located ,at each end of tank I and designed to maintain the strip under the surface of pickling solution I1. Strip Il emerges from tank l0 and passes over guide roll Il' to tank II where it passes under weighted rolls I8 similar to roll I8 through pickling solution I9. Strip I3 emerges from tank I I and goes over guide roll into tank I2 wherein it is maintained under the surface of pickling solution 2I by weighted rolls 22. Strip I3 emerges from tank I2, goes over guide roller 23 and enters tank I3 wherein it is maintained under the surface of pickling solution 23 by weighted rollers 25. Strip I4 emerges from tank I3 and passes under guide roll 28 to further treatment and coil- -ing notV shown. Obviously rolls I8, I8, 22 and could be omitted since gravity would cause strip steel. The acid concentration in the nrst tank .may be somewhat higher or may be suhstantially equal to that in the second tank. When the concentration of iron sulphate in the first tank exceeds about 30%, preparations may be initiated for dumping the solution. After this point is reached no more acid is added to the solution in the first tank so the acid content will the strip to hang in catenary form between the guide rolls I5, I'I', 20, 23 and 28, thus to be guided through each tank.

vReferring to Figures 2 and 3, tank I0 is shown as being comprised of steel side walls 21, endwalls 28 and bottom 29. A liquid tight acid resistant lining 30 is bonded to the walls and bottom of tank I0. A protective lining 3| formed of acid resistant refractory bricks or the likeis placed on the inside of the lining 30. submerged in pickling solution I1 is `the strip metal I4. Steam is used to maintain the pickling solution at the required temperature and steam supply pipes are shown at 32 entering the tank. These steam supply pipes connect with headers 33 which extend along the length of the tank adjacent the side walls and resting on the bottom. Each header 33 has a plurality of jets 33 which are directed at an angle of about 45 so that a stream of steam emitted therefrom will impinge upon the strip metal at its edge. Brackets 35 support header 33 against rotation dueto the weight of .the jets and the reaction of the stream of steam.

Although this str ucture is shown applied to tank I0, the same heating and agitating system can be used in the other tanks.

approach 15 to 20% at time of dumping. De-

pending upon the extent of pickling desired and the speed of the strip metal, concentration of iron sulphate in this tank may be allowed to mount over 35%. When the iron sulphate concentration has reached the desired maximum point, the operator proceeds to dump the solution from this tank. Despite the high concentration of iron ysulphate in the solution being dumped, some pickling action is present; therefore, with this tank emptying, the overall pickling action ofthe line is being reduced andthe strip metal` speed must be reduced slightly so that the increased pickling time will make up for the pickling action lost in tank I0. The operator then transfers the pickling solution from one of the subsequent tanks to the first tank, the subsequent tank chosen being that having thehighest concentration of iron sulphate in the solu-4 tion. A new batch of picklingsolution is then prepared in the subsequent tank from which the solution was transferredI and the speed of the strip metal is simultaneously increased. The solution with the highest iron sulphate concentration is chosen' to be transferred to the first tank because, as mentioned above, the action of the acid'on the strip metal is considerably greaterin this tank. Placing partially spent solution in this tank reduces this action somewhat and at the same time results in the most 4eillcient use of the partially spent solution. The partially spent solution fortified by the addition of acid may be used for the major fraction of a day or more before the metal content becomes too high. Generally speaking, with the low carbonv strip metal and a speed of the strip between 350 and 400 feet per minute, depending on the width of the strip, the concentration of iron sulphate in the first tank is allowed to reach 32 to 40% although a few percent oney way or the other is not critical. While dumping the first tank the speed may be reduced to about 250 feet per minute. In such operations the subsequent tank having n'ext highest concentration of iron sulphate will usually I run between 10% and 20%` iron sulphate. With With the system operating and the metal strip travelling through all the tanks, the actionA of the acid, preferably sulphuric acid, results in the formation of iron sulphate in the pickling solution. Since the oxide and other impurities on the metal strip are heaviest in tank ID3-the action of the acid is greatest here. There would, therefore, be a more rapid production of iron sulphate in this tank where the initial pickling solution in each tank is the same. The operator of the pickling line observes the increase of ironsulphate in the pickling solution of each tank together with the reduction in concentration of acid. The proper concentration of acid'is mainthe addition of acid. It has been found that an strip 36 inches wide, I have found a speed of `375 feet per minute satisfactory and an iron sulphate concentration of about 38% the maximum desirable.

In order to obtain the most efficient action of the partially spent pickling solution in tank I3, I have devised the combined heating and agitating system which makes possible maximum speed of the strip metal with satisfactory pickling. This heating system maintains the solution in all the tanks at about 215 F. Headers 33 and jets 3l are arranged so that the stream of heating .steam ejected into the pickling solution causes acid concentration of v25 to 30% in the first and a stream ci* solution and steam to impinge on the edge portions of the strip metal. It is these pox'- tions that are not properly pickled when satisfactory pickling is not achieved. 'Iv'he hot rolled strip being coiled while still hot. only the edm of the strip are exposed to continued action of atmospheric oxygen to give a heavy oxide coating at this point. Previous Jet systems which merely circulate the pickling solution do not give the assassin 3 same satisfactory results as the present jet systems.

Due to the high temperature used in the present process and the high concentration of iron sulphate and free acid present in tank Il, the

rate of pickling would be very low if it were not for applicants improved agitating means. As the ferrous sulphate concentration approaches saturation, the ferrous sulphate being continually formed by the action of the acid, lt will dissolve less readily in the solution and thus tend to re` I claim:

Apparatus for continuous pickling of strip metal comprising a tankfor holding a body of pickllng solution having a bottom, side walls and end walls, means adjacent theend walls to guide the strip metal through the body cf pickling solution in the tank, a conduit extending along the inside of the tank, jets inthe conduit directed towards points in the tank along which the adjacent edge of the strip metal travels, and a source of heating fluid connected to the conduit for supplying heating iiuid to the'jets under pressure so that heating iiuid emitted from the jets causes a stream of the pickling solution to implnge on the strip metal.

STEVE DISHAUZI.

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