US2650599A - Continuous pickling apparatus - Google Patents

Description

sept. 1, 1953 A l.u T. CAMPBELL CONTINUOUS PIUKLINU APPARATUS 2 Sheets-Sheet l Filed Dec. l5, 1948 Inventor: ZF (4A/PEEL 2 Sheets-Sheet 2 hwenwr: a0/5 7T (4A/05H1,

L. T. CAMPBELL CONTINUOUS PICKLING APPARATUS Sept. l, 1953 Filed Dec. 15, 1948 Patented sept. 1, 1953 CONTINUOUS PICKLING APPARATUS Louis T. Campbell, Pittsburgh, Pa., assignor to United States Steel Corporation, a corporation of New Jersey Application December 15, 1948, Serial No. 65,403

3 Claims.

This invention relates to improved apparatus for the continuous pickling of metallic strip, particularly steel strip.

It is the conventional practice to continuously descale hot rolled strip by passing the strip through a series of tanks containing the pickling soltuion. During its passage through the tanks the strip is supported on rotatable rolls located between the tanks and outside the eonnes of the tanks. The common practice is to drape the v strip over the support rolls, the weight of the unsupported strip between rolls being sufiicient to cause it to hang in a catenary and dip into the solution. To avoid corrosion of the bearings and other unprotected portions of their structure the support rolls are located a considerable distance above the level of the pickling solution. To position the strip laterally during its passage through the tanks, side guides are provided at or immediately ahead of each of the support rolls. The maintenance of such guides is diicult.

Owing to the relatively high position of the support rolls and the method of suspension of the strip in the tanks, there is a substantial volume of solution toward the ends of a tank which must be heated and maintained at the required acid concentration while serving no useful purpose. Thus for a required length i immersion, conventional construction results in an unduly long processing line. Sink rolls have been suggested as the remedy for this condition. This expedient, however, has not been successful since their use exaggerates the problems of strip trackage and the cost of their maintenance is excessive.

Since the pickling process involves the use of hot acid solutions, there is a serious problem in fume control. It is the conventional practice to enclose the tanks with a hood which is directly connected to an exhaust fan or fans. The use of support rolls complicates the design of the hood. Openings must be provided for the roll shafts and for inspection and maintenance. Sealing these openings against leaks is practically impossible. The necessarily elevated position of rolls dictates the shape of the hood and results in creating a considerable space between the level of the pickle bath and the underside of the hood. The net result of the combined conditions is that in attempting to prevent pollution of the atmosphere within the pickle house large volumes of air from the building must be moved through the conventional hood system. This not only requires excessively large fans and power, but the movement of large volumes of air over the surface of the bath has a substantial cooling eiiect on the bath and requires additional. heat to maintain the bath at minimum operating tempearture. The large surface area of the conventional hood also provides greater area from which heat losses by radiation can take place. This further decreases the efficiency of the process.

Exhausting fumes directly from the surface of the bath has the added disadvantage that large qauntities of acid bearing vapors are released into the atmosphere over the pickle house with the result that constant and costly repairs must be made to this and adjacent structures. Moreover, the conventional construction of the pickle tanks and support rolls is such that there are many places at which acid leakage and spillage occurs. This condition shortens the life of the tanks, their supports and foundations.

Accordingly it is an object of the present invention to provide improved apparatus for continuously pickling metallic strip in which the aforementioned objections are overcome.

It is a particular object to provide improved support means for the strip, the use of which permits the provision of an improved cover and an improved fume exhaust system.

These and other objects will be made apparent by the following description when read in conjunction with the attached drawings, in which:

Figures 1 and 1A, when joined together at the dash-dot lines, show a plan view of the tank embodying my invention;

Figures 2 and 2A, when joined together at the dash-dot lines, show a longitudinal sectional View of the tank of Figures 1 and 1A;

Figure 3 is an enlarged sectional view taken on the line III-III of Figure 2;

Figure 4 is an enlarged fragmentary view of the bulkhead of Figure 2;

Figure 5 is a view, partly in section, showing the strip-supporting device;

Figure 6 is an end view of the device of Figure 5; and

Figure '7 is an enlarged sectional view showing the joint between sections of the hood.

Referring more particularly to the drawings which show a specific embodiment of the present invention, a strip S of hot rolled steel is shown entering a pickle tank I over a deflector roll 2 which is located just outside the confines of the tank. The tank l is preferably a single continuous tank of sufficient length to provide the required immersion time at the maximum speed for which the equipment is designed. The tank comprises a steel outer shell protected against corrosion from the pickle bath by a rubber lining 3 which in turn is protected against abrasion by the strip and is thermally insulated from the hot pickle solution by a masonry lining d. rlhe nature and methods of applying the linings to the tank yare well-known and therefore are not described here.

The tank is divided into sections or compartments by masonry bulkheads 5. This facilitates maintenance and permits local repairs to the lining without emptying the whole tank. ylliocated over each of the bulkheads v5 is a strip-supporting device (i formed of a cylindrical rubber roll body 'l secured to a square non-rotatable shaft 8 having a rubber covering over its ends which extend beyond the body l. The vsquare shafts 8 of the supports 6 rest in pockets 9 built into .the brick lining of the tank. The vertical position of ,the pockets is such that the underside of the cylindrical center portion of the supports kt is approximately yat the liquid level 'of the pickling solution in the tank. 'The strip S vpasses Vover each of the supports '6 iin turn and .is suspended in a catenary-like loop between adjacent supports. The Weight of the `unsupported length cf strip between supports is suflcient to maintain this catenary-like shape While the ,str-ip is being pulled through .the tank. To prevent the strip from resting on the bottom of the tank and 'thus being subjected to .unequal pickling conditions, rubber-covered skid supports Vlli are provided at intervals along the bottom .of the tank. After the strip S passes over'the last of the supports '6 located yadjacent the last bulkhead, .it passes under'deflector rolls .H and l2 and hence out of the tank through .squeegee .rolls lf3. That section of the tank in which rolls 4Il Land .l2 are located comprises Va rinse compartment. The deflector rolls I i and til in the .rinsefcompartment serve .to depress the strip below .thesur-aceof the rinse water.

Substantially Vhat sectionalremov-able covers I4 .are provided to conne vsubstantially .all .fumes and steam .into the space immediately above the pickle solution. Thecovers I4 rest upon a gasket l5 located along the `topsurfaces of the masonry klining Thecoversare protected against corrosion by a rubber lining i6. An overlapping joint I1 is provided between sections as shown in Figure 7 to form a seal.

Located along both sides rof -the tankare inverted L-shaped Vducts it. The ends of the horizontal vlegs of 'therducts t3 are'open and form a substantially continuous slot :I9 through which any fumes or steam AWhich-might escape from under the covers I4 l:are Withdrawn. Theopenings I9 are provided with adjustableorince plates 2li whereby the velocity of-airfentering the'ducts can be regulatedand equal -suction Amaintained along the length of the ducts. .Theductoriiice 19 is 1o- Vcated as close `as possible to -the joint made by the cover Id and the gasket I5 at the top-of the tank. The collector ducts -l-8 .farepreferably made in sections .of some convenient Vlength and-each i pipes for heating, Yacid supply lines, etc., are made `as near as possible'tofthe edge of the cover. 'this manner any leaks around such openings oc- 4 cur in the vicinity at which the exhaust system is most eicient.

The pickling tank of the present invention may be supported on a substructure consisting of the equally spaced transverse beams 26 which rest upon the longitudinal beams 2l which in turn are supported at appropriate intervals Iby concrete or masonry piers not shown. The support .structure for the tank is preferably that shown :in my cri-pending application, Serial No. 64,553,

filed December 10, 1948. The side Walls of the lt'ank .l yare s'tiffened by the buck-stays 25.

li? theprogress of the strip through the tank is .stopped .'Eor fanyappreciable time, there is danger of thestrip S being overpickled or otherwise damaged by the action of the acid. To avoid such damage, devices '28 can be provided which inciuoleinovable arms extending through the covers ifi whereby the striprcan be raised out of contact with the acid.

The nature and form .of equipment necessary for handling the strip S into and out of the pickling section described above is Well-known and therefore has not been'described here. Suityable `equipni'en't for performing these operations is shown .in the 4United States .Patent to Wean et al..No.`2,'198,600.

n `operation, the .strip S passes through the successive 'pickling compartments Where its surfaces arefreed of oxideby the action of the acid solution and th'en through the -rinse chamber where the Vfreshly `pickled surface is Washed with cold Water. Fresh acid may vbe lintroduced into the system at a point near the end vof the last pickllng compartment. The addition of fresh acid is preferably continuous, the rate being regulated to maintain a desired uniform concentration in the last compartment. `Water losses may be made up bypermitting a .controlled portion .of

the wash Water in Ithe rinse compartment to overnovv into the last pickling compartment. In this manner a portion of .the Vacid solution .lost by drag-out on .the surface .of the strip may also be recovered. The pickling solution flows from the last compartment towards the first so that the strip is subjected Yto 4cleaner and stronger 'solution as it progresses Vthrough the tank. The Waste pickle liquoris preferably removed near the entry end of the rst compartment Where it is allowed to overiiow through .a standpipe or equivpasses `to the pinch rolls I3 Which remove excess rinse Water. 'The strip may then be further rinsed or otherwise processed, dried and coiled.

The pickling .solution must be maintained hot and this may beaccomplished'by any of several means. IA means which has proven very satisfactory is Venturi-type steam yinjectors which not only produce the necessary heating but also a high degree of turbulence Within the bath which contributes A.to the `efllciency and uniformity of pi'ckling action.

As previously mentioned, .the steam pipes enter the tank through the cover at .a point as close as possible to the 4junction .of the ycover with the top of the tank. Water pipes and acid supply pipes also enter the tank through the cover at this general location.

The steam and acid fumes which were involved during the pickling are confined Within the tank by the substantially flat covers I4. Any steam or acid fumes which may leak at this junction or around the openings in the -cover for the admission of steam, acid or Water lines are drawn into the ducts I3 and conducted out of the building through the exhaust system previously described. The exhaust system in the present invention is not directly connected to the tank cover as is the case in conventional practice. Thus the removal of fumes is accomplished without drawing air through the pickling tank itself.

This permits the maintenance of higher pickling bath temperatures with the use of less heat and. for a given length of pickling bath, markedly increases the production capacity of the equipment.

The use of substantially at covers and an exhaust system which is not directly connected thereto is made possible largely by the improved strip-supporting devices 0. The use of a single continuos tank is also largely attributable to the improved devices 6. The strip-supporting devices 9 do not revolve as do conventional support rollers; the strip merely skids over their rubbercovered surfaces which are maintained lubricated by the pickling solution carried to them by the strip as it passes from one compartment to the next. Since the supports 6 do not revolve, all parts are readily protected from the acid solution by rubber covering. The fact that they do not have to rotate reduces the size of support required. The new supports 6 can therefore be located entirely inside the tank and very close to the solution level therein. Thus dead space at the ends of the tank is considerably reduced and the length of the tank 'can be materially shortened. Furthermore, the need for side guides within the tank is eliminated by the use of the improved supports 6. It is sufficient to laterally position the strip only at it enters the tank.

The cylindrical form of the support 6 is merely a preferred shape which permits a worn supporting surface to be replaced by simply lifting the support out of its normal position, revolving it 99 and reinstalling. The cylindrical form of the support V6, therefore, provides four supporting surfaces which can be used before the support must be replaced or repaired.

Although I have illustrated and described a preferred embodiment of the invention, it will be recognized that changes in the details and arrangement disclosed may be made Without departing from the spirit of the invention or the scope of the appended claims.

I claim:

l. In .apparatus for the pickling of continuous metallic strip, the combination which includes a tank for containing the pckling solution, a

substantially at removable cover on said tank, a non-revolving strip support located entirely Within the confines of said tank above the solution level therein and below said cover, said non-revolving support comprising a cylindrical body of a corrosion-resistant material mounted on a square shaft, the ends of said shaft extending beyond said cylindrical body and being protected by a covering of a `corrosion-resistant material, shaft receiving recesses in the Walls of said tank for engaging said shaft to maintain the support in position, and a fume exhaust system, said exhaust system including horizontally disposed ducts extending substantially the length of and along both sides of said covered tank, said ducts having a substantially continuous fume receiving' opening adjacent the juncture of said cover with said tank.

2. In apparatus for the pickling of continuous metallic strip, the combination which includes a tank for containing the pickling solution, a subsantially flat removable cover on` said tank, a stationary strip support having a smooth convex upper surface, said support positioned entirely within the confines of said tank above the solution level therein and below said cover, and a fume exhaust system separate from said tank, said exhaust system including horizontally disposed ducts extending substantially the length of and along both sides of said tank and characterized by adjustable and substantially continuous fume receiving orifices located adjacent the joint between the cover and the top of said tank.

3. In apparatus for the pickling of continuous metallic strip, the combination which includes a tank for containing the picking solution, a, nonrevolving strip support located entirely within the confines of said tank above the solution level line, said non-revolving support comprising a cylindrical body and a square shaft, the outer surfaces of said shaft and said cylindrical body `being of a corrosion-resistant materiaL, and shaft receiving recesses formed in the tank to engage said shaft and maintain the support in fixed position.

LOUIS T. CAMPBELL.

References Cited in the le Of this patent UNITED STATES PATENTS Number Name Date 31,361 Washburn Feb. 5, 1861 1,175,429 Frese Mar. 14, 1916 1,896,951 Hahn Feb. 7, 1933 1,999,822 Nieman Apr. 30, 1935 2,110,991 Gabrielsen Mar. 15, 1933 2,169,206 Krongold Aug. 8, 1939 2,216,544 True et al. Oct. 1, 1940 2,234,593 Ferm Mar. 11, 1941 2,320,499 Wood June 1, 1943 2,325,158 Wood July 27, 1943 2,356,842 Helmond Aug. 29, 1944

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