Abstract:
A pickling tank for the continuous treatment of a steel strip includes a pickling trough and a recovery tank separated from one another by a linkage that allows for limited movement between the trough and recovery tank. The recovery tank includes a pair of press rollers to remove pickling solution from the steel strip. The linkage includes a chute extending from the trough to the recovery tank to contain the pickling solution while allowing for differences between thermal expansion between the pickling trough and recovery tank. In one embodiment, the chute is coupled to the pickling trough and has a free end inserted into the recovery tank. In a second embodiment, the chute includes two telescoping members extending between the trough and recovery tank.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a system for the continuous treatment of a steel strip in a liquid treating tank. More particularly, the invention is directed to an apparatus for the continuous pickling of a steel strip. 
     BACKGROUND OF THE INVENTION 
     Numerous pickling tanks have been developed for pickling sheet steel in a continuous process. Many of these pickling tanks include a shallow pickling bath where the continuous steel strip is pulled through the bath of pickling acid. Spray nozzles are also used to supply a continuous stream of pickling acid to the steel strip. 
     Many pickling processes use a plurality of pickling tanks arranged in series. The continuous steel strip is carried through each tank in successive stages to attain the desired pickling effect. The pickling tanks typically include a suitable device for removing excess pickling acid from the steel strip as the steel strip is removed from each successive bath. For example, pressing rollers are often used at each end of a pickling tank to guide the steel strip through the pickling acid and remove the excess pickling acid from the strip. An example of this type of pickling tank is disclosed in U.S. Pat. No. 5,800,694 to Starcevic et al. 
     Another example of a pickling tank is disclosed in U.S. Pat. No. 5,566,694 to Pugh et al. The pickling tank includes two end stands spaced apart from each other and secured to a foundation. A trough containing a pickling acid extends between the two stands and is anchored at the center. The stands at each end of the trough include pressing rollers to guide the steel strip. An expandable seal connects each end of the trough with each stand to allow for thermal expansion of the trough relative to the stands. The expandable seal is formed from several spaced apart baffles allowing some movement between the trough and the stand. 
     Recently, there has been an increase in interest in producing pickling tanks made of a synthetic material that are resistant to attack by the pickling acids. However, tanks made from synthetic materials often are not sufficiently strong to contain the weight of the pickling bath and the steel strip. As a result, the pickling tanks can sag and deform due to the weight of the pickling acid and the temperature of the acid bath. In addition, the end chambers of the bath when made from a synthetic material often deform causing leaking of the pickling acid. It is very difficult to control the flow of the pickling acid in these devices because the liquid level in the pickling bath is above the seal between the pickling tank and the end chamber. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a pickling tank for treating a continuous steel strip. More particularly, the invention is directed to a pickling tank assembly having an expandable linkage to prevent leaking of pickling acid. 
     Accordingly, a primary object of the invention is to provide a pickling tank having a sealing assembly for containing the pickling acid. 
     Another object of the invention is to provide a pickling tank having a sealing assembly at each end where the liquid level in the pickling tank is independent of the sealing assembly. 
     A further object of the invention is to provide a pickling tank for a steel strip where the liquid level in the pickling tank can be adjusted independent of the sealing assembly. 
     Another object of the invention is to provide a pickling tank having a pickling trough and a separate pickling acid recovery tank spaced from the pickling trough. 
     Still another object of the invention is to provide a pickling tank having a pickling trough and a pickling acid recovery tank where the recovery tank includes two opposing pressing rollers for removing pickling acid from a steel strip. 
     A further object of the invention is to provide a pickling tank having a pickling trough and a separate pickling acid recovery tank where a primary acid recirculating loop takes place only in the pickling trough. 
     A further object of the invention is to provide a pickling tank having a pickling trough and a pickling acid recovery tank having two opposing pressing rollers and a chute connecting the pickling trough with the recovery tank where the chute allows limited movement between the pickling trough and the recovery tank. 
     Another object of the invention is to provide a pickling tank including a pickling trough and a pickling acid recovery tank coupled together by a chute that is able to accommodate for thermal expansion between the pickling trough and the recovery tank. 
     A further object of the invention is to provide a pickling tank made of a synthetic material that is resistant to corrosion attack by a pickling acid. 
     Another object of the invention is to provide a pickling tank having an overflow tray made of a synthetic material, a pickling trough and a pickling acid recovery tank where the pickling trough is positioned on the tray. 
     A further object of the invention is to provide a pickling tank having a pickling trough, a pickling acid recovery tank having two opposing pressing rollers and a chute having a first end connected to the pickling tank and a second end forming a seal against the rollers. 
     The objects of the invention are basically attained by providing a pickling tank for pickling a continuous strip. The pickling tank comprises a pickling trough for containing a pickling solution. The pickling trough has a bottom wall, a first end wall at a first end of the trough and a second end wall at a second end of the trough. The first end wall has an inlet for the continuous strip and the second end wall has an outlet for the continuous strip. A pickling solution recovery tank has an inlet, an outlet and two opposing pressing rollers positioned in the recovery tank. The recovery tank is spaced from and coupled to the pickling trough. 
     The objects of the invention are further attained by providing a pickling tank for pickling a continuous steel strip. The pickling tank comprises a pickling trough having a pickling bath area with a first end and a second end. The pickling trough is dimensioned for containing a pickling solution. The pickling trough has a pickling solution discharge trough at the first end of the pickling trough for receiving overflow pickling solution from the pickling bath area. A pickling solution recovery tank has two opposing pressing rollers positioned in the recovery tank for removing pickling solution from a steel strip passing through the tank. A chute has a first end coupled to the discharge trough and a second end coupled to the recovery tank. The chute is coupled to the discharge trough and the recovery tank to allow limited movement between the discharge trough and recovery tank. 
     The objects, advantages and salient features of the invention will become apparent to one skilled in the art in view of the following detailed description of the invention, taken in conjunction with the annexed drawings which form a part of this original disclosure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following is a brief description of the drawings in which: 
     FIG. 1 is a partial side elevational view in cross section showing the ends of pickling tanks and a pickling solution recovery tank connected together by a chute; and 
     FIG. 2 is a side elevational view in cross section showing a second embodiment of the invention including two pickling troughs and a pickling solution recovery tank connected together by an expandable chute. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to a pickling tank assembly  10  for treating a continuous strip of steel  40 . The pickling tank assembly  10  of the invention includes a pickling trough  12  and a pickling solution recovery tank  14 . 
     The pickling tank assembly  10  of the invention provides a connection between various components of the assembly for containing the pickling solution while allowing thermal expansion between the various components. The pickling apparatus  10  typically includes several pickling troughs  12  connected together in series for guiding a steel strip  40  through several pickling acid baths. In the embodiments illustrated, two pickling troughs  12  are illustrated. It will be appreciated that the number of pickling troughs can vary depending on the needs of the pickling process. 
     In the embodiment illustrated, two pickling troughs  12  are provided and connected to a single recovery tank  14 . In practice, a recovery tank  14  is positioned at the upstream end of pickling trough  12  for feeding the steel strip through pickling trough  12 . Similarly, a recovery tank  14  is position downstream at a discharge end of each pickling trough  12 . Several pickling troughs can be connected in series and separated by a recovery tank  14 . In a preferred embodiment, each pickling trough is substantially identical. 
     Referring to FIG. 1, pickling trough  12  includes a pickling bath area  16  on a bottom wall  18 . Bottom wall  18  has a generally V-shaped configuration to provide a sufficient depth to the pickling solution as known in the art. Bottom wall  18  has an end  20  defining the end of the bath area  16 . Several legs  22  are coupled to bottom wall  18  to support trough  12 . Pickling trough  12  includes inlets (not shown) for introducing and recirculating a pickling solution as in conventional pickling tanks. The end portion  20  of bottom wall  18  contains the pickling solution at a predetermined level  24  in bath area  16  as shown in FIG.  1 . 
     A discharge trough  26  is provided at each end of pickling trough  12  and at the end of the bath area  16 . Pickling trough  26  includes an inner wall  28 , a bottom wall  30  and an outer end wall  32 . Inner wall  28  in the embodiment shown extends substantially vertically and is coupled to the end  20  of bottom wall  18 . Inner wall  28  extends substantially parallel to supporting legs  22  and assists in supporting trough  12 . Outer end wall  32  is spaced from inner wall  28  and extends substantially parallel thereto for forming an end wall of pickling trough  12 . Discharge trough  26  includes a top wall  34  coupled to inner wall  28 . Top wall  34  is spaced from outer end wall  32  to form an opening  36  into discharge trough  26 . In this embodiment, trough  26  prevents large quantities of pickling solution from entering recovery tank  14 . 
     A guide member  38  is positioned on top wall  34  to guide the steel strip  40  being carried through the pickling trough. Guide member  38  preferably extends the entire width of pickling trough  12  and has a height sufficient to support and guide steel strip  40  and prevent steel strip  40  from contacting inner wall  28  and end  20  of bottom wall  18 . Preferably, guide member  38  has a height to support steel strip above end  20  of bottom wall  18 . As shown in FIG. 1, guide member  38  also has a height sufficient to form a dam and assist in controlling the level and depth of the pickling solution in pickling trough  12 . Preferably, guide member  38  is removable and can be replaced with a different guide member having a different height as needed for adjusting the level of the pickling solution. 
     In preferred embodiments, pickling trough  12  is made from a light weight, synthetic material that is non-reactive and resistant to corrosion attack by the pickling solution. Examples of suitable synthetic materials include polypropylene, polyethylene and polyvinyl chloride. The pickling solution is typically sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, and mixtures thereof as known in the art. 
     In the embodiment illustrated, pickling trough  12  is positioned in an overflow tray  42  having a dimension to contain pickling trough  12 . Tray  42  is preferably made of a synthetic material such as polypropylene and is dimensioned to contain pickling solution that may spill or leak from pickling trough  12 . As shown in FIG. 1, tray  42  has a substantially flat bottom wall  44  and side walls  46 . Support legs  22  of pickling trough  12  preferably rest directly on bottom wall  44  of tray  42 . Tray  42  can also include an outlet (not shown) for recovering and recycling pickling solution. In one embodiment of the invention, pickling trough  12  is fixed to tray  42  and centrally located therein. 
     A steel strip  40  is passed through pickling trough  12  in the direction of arrow A, through the pickling solution  24 , and through an outlet  48  in outer end wall  32 . The pickling solution is drawn along the bath area  16  in the direction of outlet  48  by the movement of the steel strip and overflows into discharge trough  26 . The pickling solution exits discharge trough  26  through an outlet pipe  50  where the pickling solution is regenerated and recycled to the bath area  16 . Preferably, a cover  52  is attached to pickling trough  12  to contain acid vapors. The pickling solution in pickling trough  12  is recirculated and replenished according to standard procedures in the pickling industry. 
     Recovery tank  14  is a separate structure from pickling trough  12  and is spaced from outlet  48  in end wall  32 . Recovery tank  14  includes side walls  54  having an opening  56  in each wall. As shown in FIG. 1, recovery tank  14  is symmetrical so that each side is a mirror image of the other. Two opposing pressing rollers  58  are mounted in recovery tank  14  for guiding steel strip  40  and removing pickling solution from the steel strip passing through recovery tank  14 . A top wall  60  is coupled to side walls  54  and encloses recovery tank  14 . Recovery tank  14  also includes two discharge outlets  62  at a bottom end thereof for recovering pickling solution. Typically, the pickling solution recovered from recovery tank  14  is not recirculated to pickling trough  12 . As shown in FIG. 1, steel strip  40  passes through pickling trough  12  and is guided through a first opening  56  in recovery tank  14  and between rollers  58 . Steel strip continues and is discharged through the opposite opening  56  on an opposite side wall  54  and directed to a second pickling trough. The second pickling trough is substantially identical to pickling trough  12  so that identical components are identified by the same reference number. 
     Recovery tank  14  is connected to pickling trough  12  by a suitable linkage  64  as shown in FIG.  1 . Linkage  64  forms a connection to contain pickling solution in the respective pickling trough while allowing for relative movement between the pickling trough and the recovery tank. Linkage  64  in a preferred embodiment is a chute  66  forming an enclosed path extending from pickling trough  12  to recovery tank  14 . Chute  66  provides a connection between pickling trough  12  and recovery tank  14  to contain the pickling solution and compensates for movement between pickling tank  12  and recovery tank  14  due to thermal expansion from changes in temperature. 
     In the embodiment of FIG. 1, chute  66  includes a first end  68 , coupled to outer end wall  32  of pickling trough  12  and a second end  70  positioned in recovery tank  14 . First end  68  of chute  66  includes a flange  72  that is preferably fixed to outer end wall  32 . Second end  70  extends through opening  56  in side wall  54  of recovery tank  14  and is able to float freely with respect to side wall  54 . Preferably, second end  70  of chute  66  includes a radially extending flange  74  having a dimension greater than opening  56  to prevent pickling solution from splashing outwardly through opening  56 . An identical chute  66  connects recovery tank  14  with the downstream trough  12 . 
     In preferred embodiments, chute  66  is positioned at an incline with the second end  70  higher than first end  68 . Positioning chute  66  at an incline enables pickling solution draining from steel strip  40  to drain back into pickling trough  12  instead of flowing toward recovery tank  14 . Therefore, only small amounts of pickling solution are carried into recovery tank  14 . 
     As shown in FIG. 1, end wall  32  includes an overflow trough  76  adjacent outlet  48 . Overflow trough  76  includes an end wall  78  spaced from outer end wall  32  of trough  12  and includes a substantially U-shaped recess  80  to accommodate chute  66 . A bottom wall  82  is coupled to end wall  78  and inclined toward outer end wall  32 . A drain opening  84  is provided in outer end wall  32  adjacent bottom wall  82  of overflow trough  76  to allow pickling solution to drain into discharge trough  26 . In this manner, pickling solution that may pass between chute  66  and outlet  48  is collected in overflow trough  76  and recycled to the pickling trough  12 . 
     Recovery tank  14  includes a similar overflow trough  86  coupled to each side wall  54  at openings  56 . Overflow trough  86  includes an end wall  88  extending parallel to side wall  54  and a bottom wall  90  inclined toward side wall  54 . A recess  92  is dimensioned to receive chute  66 . A drain opening  94  is formed inside walls  54  to drain pickling solution into recovery tank  14 . An annular shield  96  extending radially outward from chute  66  is provided in overflow trough  86  to prevent pickling solution from passing through recess  92 . A similar shield  98  is coupled to chute  66  and positioned in overflow trough  76 . 
     As shown in FIG. 1, a vertical dividing plate  63  is positioned below press rollers  58  and extends to a bottom wall  65  of recovery tank  14 . Dividing plate  63  and press rollers  58  separate recovery tank  14  symmetrically into an upstream side and a downstream side and directs recovered pickling solution to an outlet  62  on either the upstream side or downstream side. In this manner, pickling solution from the upstream side can be isolated from the pickling solution from the downstream side. 
     In operation, several pickling troughs are assembled in series with a recovery tank positioned between the troughs. A continuous steel strip is passed through guide rollers into the pickling trough and passes through the pickling solution. The steel strip then passes through the chute to the recovery tank where the pressing rollers remove any remaining pickling solution. The steel strip continues through a chute at the outlet end of the recovery tank to the next pickling trough. 
     Referring to FIG. 2, a pickling tank assembly  100  in a second embodiment of the invention is illustrated. Pickling tank assembly  100  includes pickling troughs  12 ′ and a recovery tank  14 ′. Pickling trough  12 ′ and recovery tank  14 ′ are similar to the embodiment of FIG. 1 so that identical components are identified by the same reference number with the addition of a prime. Pickling tank  100  differs from the embodiment of FIG. 1 by the linkage  102  connecting trough  12 ′ with recovery tank  14 ′. 
     Pickling tank assembly  100  uses press rollers  58 ′ as dam rollers to increase the depth of the pickling solution and the length of the bath area  16 ′. Pickling tank assembly  100  is particularly suitable for high speed pickling processes that are able to treat a steel strip above 150 meters per minute. 
     Linkage  102  in the embodiment of FIG. 2 forms a conduit between trough  12 ′ and recovery tank  14 ′. A collar  104  is connected to outer wall  32 ′ surrounding outlet  48 ′. A flange  106  is connected to an outer end of collar  104  and extends radially outward. A chute  108  is coupled to flange  106  and extends through opening  56 ′ into recovery tank  14 ′. In embodiments of the invention, chute  108  can have a square, rectangular or circular cross-section. 
     Chute  108  is an expandable member having a first telescoping section  110  and a second telescoping section  112 . First section  110  has a first end  114  with a flange  116  for coupling with flange  106 . First section  110  has a second end  118  coupled to second section  112 . 
     Second section  112  has a first end  120  coupled to second end  118  of first section  110  and a second end adjacent press rollers  58 ′. First end  120  of second section  112  includes a slot  124  extending longitudinally through second section  112 . Slot  112  is dimensioned to accommodate second end  118  of first section  110 . As shown in FIG. 2, second end  118  of first section  110  slides longitudinally within slot  124 . Preferably, second end  118  of first section  110  forms a fluid-tight seal in slot  124 . 
     Second end  122  of second section  112  has curved surfaces  113  that are shaped to conform to the contour of press rollers  58 ′. Preferably, second end  122  forms a liquid seal between chute  108  and press rollers  58 ′. 
     In the embodiment of FIG. 2, chute  108  forms fluid-tight connections between trough  12 ′ and press rollers  58 ′ to contain the pickling solution. Press rollers  58  form a dam to contain the pickling solution in chute  108  and in pickling trough  12 ′. Outlet  50 ′ of discharge trough  26 ′ can be closed partially to increase the depth of the pickling solution to level  126  above guide member  38 ′. As shown in FIG. 2, the level of the pickling solution  126  is above the bottom portion of chute  108 . Thus, the effective length of the pickling bath extends from the press rollers  58 ′ through chute  108  and through the entire length of pickling trough  12 ′. Pickling trough  12 ′ includes an overflow outlet  128  to maintain a desired level of the pickling solution in pickling trough  12 ′. 
     As in the previous embodiment, the steel strip  40 ′ is fed through pickling trough  12 ′ through the bath area  16 ′. The steel strip  40 ′ exits the outlet end of pickling trough  12 ′ and passes through chute  108  to press rollers  58 ′. Steel strip  40 ′ passes between rollers  58 ′ and through chute  108  on the opposite side of recovery tank  14 ′ to the next pickling trough  12 ′. The second section  112  of chute  108  forms a seal box against the rollers  58 ′ to substantially prevent the pickling solution from passing between adjacent pickling troughs. In the embodiment illustrated, chute  108  includes telescoping sections to allow for movement between trough  12 ′ and recovery tank  14 ′ in a longitudinal direction with respect to chute  108 . In further embodiments, chute  108  can include two sections connected together by an expandable bellows structure to allow longitudinal movement between the two sections of the chute. 
     While several embodiments have been chosen to illustrate the invention, it will be appreciated that various modifications can be made without departing from the scope of the invention as defined in the appended claims.