US2628924A

US2628924A - Method of cleaning strip

Info

Publication number: US2628924A
Application number: US759158A
Authority: US
Inventors: Samuel S Johnston; John E Elswick
Original assignee: National Steel Corp
Current assignee: National Steel Corp
Priority date: 1947-07-05
Filing date: 1947-07-05
Publication date: 1953-02-17
Anticipated expiration: 1970-02-17

Description

Feb. 17, 1953 s. s. JOHNSTON ETAL ,6 8,

I METHOD OF CLEANING STRIP Filed July 5, 1947 ii .Zl! =2? l INVENTOR. SAMUEL 6'. Jamsro/v. N 7 BY JOHN E. ElSW/CK.

Patented Feb. 17, 1953 METHOD OF CLEANING STRIP Samuel S. Johnston and John E. Elswick, Steubenville, Ohio, assignors to National Steel Corporation, a corporation of Delaware Application July 5, 1947, Serial No. 759,158

This invention relates to a method of cleaning strip and is primarily concerned with progressively and substantially completely removing residual electroplating electrolyte containing electrolytic salts from continuously moving electroplated strip.

The present invention will be described more particularly in connection with the removal of residual tin electroplating solution from electr lytically' tinplated ferrous metal strip, but the present invention is not limited.- thereto and is applicable for removing other electrolytes from strips of other metals. The principles of the present invention may he applied to cleaning, for example, electrolytically cleaned, pickled or anodically polished metal strip having residual electrolytic solution on its surface.

In the present day practice of electroplating ferrous metal strip with tin, the strip is moved continuously through or across the electroplat ing cells at a high rate of speed, The higher the speed, the greater the quantity of strip plated in unit time. Many electroplating lines are operated today at speeds of about 1,000 to 1,506 feet per minute. As the strip leaves the last electroplating cell, it is subjected to a washing treatment to remove the electrolyte dragged out of the last electroplating cell. The washed strip after being dried usually is heated to reflow or flowbrighten the tin on the strip surface. The washing treatment supposedly removes allof the electrolyte. A customary treatment of the strip has been to pass the strip first through a pair of wringer rolls to reduce the quantity of electroplating sclution on the. strip and then through a bath to wash off the residual, electrolyte. In some installations, the strip from this bath is further washed with sprays before being passed. between a final pair of wringer, rolls to remove the excess liquid. Solution. from the bath. has been returned to the electroplating. cells to make up the liquid. lost from the electroplating cells and to save the electrolytic salts removed from the strip by the bath.v

We have discovered that this cleaning of the strip as practiced heretofore, does not, contrary to the, general opinion, remove all of the electrolytic salts- It has been found that, especially at the high speeds of 1,000 to 1,500 feet per minute,.such a large quantity of strip passes. through the bath that the bath. contains a sufficiently large amount of salts to prevent cleaning of the strip. The bath merely slightly dilutes the residual solution. It also has been discovered that passing the strip from the bath through water sprays and then through wringer rolls as prac- 7' Claims. (Cl. 134-45) ticed heretofore does not completely remove the residual electrolytic salts. Apparently, the wringer rolls leave a thin film of liquid on the strip and the wash water or sprays merely dilute this liquid to a limited extent. As a result, the strip is not substantially thoroughly cleaned of the residual salts.

Accordingly, the primary object of the present invention is to provide an improved method of substantially completely removing all of the residual electrolyte solution from strip.

Another object of the present invention is to provide a method of more nearly completely flushing the residual electrolyte off of the strip.

A further object of the present invention is to provide more complete mixing of the wash water with the residual electrolytic solution on the strip to dilute the solution.

Another object of the present invention is to pass strip through a series of sprays and wringer rolls so arranged that the residual electrolyte is substantially completely removed by a combination of flushing the electrolyte off thestrip and ore hfl ugh mixing of the decreased quantity of residual electrolyte with the wash water to increase the dilution eifect of the wash water.

In accordance with our invention, the, strip from the final electroplating cell is repeatedly subjected to sprays of fresh wash Water and is repeatedly passed between wringer rolls to remove the major portion of the liquid on the strip. The strip and sprays are so arranged that the sprays of wash water are directed downwardly against the strip. By this arrangement, the water from the sprays spreads laterally both across and. along the surface of the strip to provide .a more thorough. flushing off of the residual electroplating salts. After each surface of the strip .has been sprayed with wash water, the'strip is'wrung by passing it between wringer rolls so that a greater degree of dilution of. the residual solution is obtained as a result of a more thorough mixing of the liquids. Fresh water is used in these sprays;

These and other objects and advantages will become more apparent from the following detailed description, taken with the accompanying drawings, in which:

Figure 1 is a plan view of apparatus embodying the features of the present invention; and,

Figure 2 is a sectional view taken along line 2-2 of Figure 1.

Referring to the drawings, a strip II] which is being. progressively and continuously withdrawn from the electroplating cell (not shown) is passed through a first pair of wringer rolls H and [2 which remove most but not all of electroplating solution dragged from the electroplating cell. The present invention is not limited to any particular means for moving the strip along its path of travel through the washer, although it is preferable to rotate the wringer rolls by a suitable drive means of the type customarily used in mills for rotating rolls. The speed of strip is high and may, for example, be about 1,000 to 1,500 feet per minute. The higher the speed the greater the amount of solution that is dragged out of the electroplating cell by the moving strip.

The wringer rolls H and I2 are rotatably mounted and one or both of these wringer rolls may be formed of metal or rubber coated metal. The rolls H and i2 remove most but not all of the electroplating solution so that a thin film of solution remains on the strip. Strip l moves from these wringer rollsthrou h a wash tank I4. Two similar rolls i5 and I6 are rotatably mounted in the tank to hold the moving, strip below the surface of the liquid in the tank. The strip I9 when it leaves tank It drags out a considerable quantity of the wash liquid and is passed positioned on opposite sides of the strip and are connected to a water supply pipe 22 which is in turn connected to source of fresh wash water. Each apertured pipe l9 and 2H directs a water spray 23 against the corresponding surface of the strip 10. The sprays 23 dilute the liquid on the strip so that the liquid on the strip will contain a smaller percentage of salts than the bath in tank M.

The tank I4 is provided with an outlet connection 24 which preferably communicates with the electroplating cells so that the liquid in tank Hi can be used to replace at least part of the liquid lost from the cells by drag out and other causes. By using the bath liquid from tank It to replace the liquid lost from the cells, a large portion of the electroplating salts removed from the strip by the bath in tank M are recovered. The amount of solution dragged out of the last electroplating cell is so large that recover of at least part of the salts is an important economic advantage. The sprays 23 are located so that the excess liquid which contains some of the electrolytic salts and which falls away from or flows back along the strip will be deposited in the tank M, Preferably, the rate of flow of the sprays 23 is approximately equal to the rate of flow of solu tion from tank I l to the electroplating cells.

The sprays 23 dilute the solution on strip 16 to a limited extent but do not remove all of the salts so that the film left on the strip after the strip passes through wringer rolls I1 and I9 contains an appreciable quantit of salts. The strip I9 moves from the wringer rolls I1 and 18 through a rinsing apparatus shown generally at 26. The rinsing apparatus 26 includes a collector tank 21, a rotatable guide roll 28 and three pairs of similar wringer rolls 29, 3G and 3|, respectively, which may or may not be driven by any one of the usual roll driving means. Six similar

apertured pipes

32, 33, 34, 35, St and 3? preferably are sprays of hot water.

are each connected to water supply pipe 22 for discharging sprays of fresh wash water against the surfaces of the strip as will be more fully hereinafter described.

The strip it passes from wringer rolls I? and i8 beneath guide roll 23 and then moves horizontally past the water spray 3i issuing from apertured pipe 32. The spray 31 is directed downwardly against the top surface 38 of strip Ill. The strip iii passes beneath and then up and around the horizontal, bottom wringer roll 29 before passing between the wringer rolls so that the bottom surface 39 of the strip is uppermost when the strip passes beneath spray 40 discharged from pipe 33. After passing between wringer rolls 29, the strip passes up and around the upper wringer roll 29 and then downwardly beneath lower wringer roll 30. As the strip passes pipe 34 the surface 38 is again uppermost and the spray il from this pipe is directed downwardly against the top surface 38 of the strip. The strip It then move between wringer rolls 30 in a rearward direction and the bottom surface 39 is again uppermost as the strip moves past spray 42 discharged from pipe and directed downwardly against surface 39 of the rearwardly moving strip. The strip next travels between wringer rolls 39 which remove the excess liquid and then passes around upper roll 30 and forwardly and downwardly beneath the lower wringer roll 3!. The top surface 38 is uppermost when the strip moves past spray 43 discharged from the apertured pipe 36. Before the strip [9 passes rearwardly between wringer rolls 3| and while surface 39 is uppermost, the spray 44 from pipe 3"! is directed downwardly onto surface 39. After the strip passes between rolls 3|, it is free of or substantially free of all electrolytic salts dragged out of the electroplating cell and after being dried, the strip can be heated in the usual manner to flow-brighten the tin coating and produce a better grade of electrolytic tinplate.

The sprays in the final rinsing apparatus 26 The water is fresh, that is, the water has not been previously used to wash the strip and contains no salts from the electroplating solution. The water may contain the usual small amount of metals and impurities normally present in the water supply for mills. The water sprays 31', 40, 4|, 42, 43 and 44 are each directed downwardly against the strip while the

corresponding surface

38 or 39 is uppermost. With this arrangement, the wash water spreads laterally over the strip and clings to the strip so that the wash water does a much better job of flushing off the residual thin film of electrolyte left on the strip after it has been wrung by the preceding pair of wringer rolls. In addition, as each spray is directed downwardly against the strip, the wash water from the sprays clings to the moving strip and does not quickly fall away from the strip. Consequently, as the moving strip starts to pass around each lower wringer roll or starts to pass between each pair of wringer rolls, the wash water which is clinging to the strip piles up ahead of the wringer roll at the nip of the roll. This water which is piled up ahead of each wringer roll between the wringer roll and the surface just sprayed is in a highly turbulent state so that the wash water is thoroughly mixed with the residual film of saltcontaining solution left on the strip by each pair of preceding wringer rolls. This thorough mixing increases the dilution of the residual, contam'inated film of liquid: on. the strip and more thoroughly cleans the strip.

The tank 21 is provided with. anoutlet. 45 -com,- municating with a sewer or other place of disposal. The outlet 45 is of such a size that the strip l.0-' does not pass through a bath in tank 21. The excess wash water containing. some electrolyte falls free of the. strip and does not recontaminate the strip. The clean strip which we obtain would not be obtainedifa bath were maintained in tank 21 of sufficientdepth so that the strip passed through the bath. as it does in the reclaimed or cell-replenishingv bath in tank I14.

In practice, for example, it has been found that the strip ID as it enters the three stand, rinsing apparatus 26, will have a film of liquid on its surface containing about 1,000 parts per million of solids. After passing through the rinsing apparatus 26, the liquid film on the strip will contain only about 200 parts of total solids per million parts, or only about 15 parts per million more than the solids in the wash water which in this instance contained about 185 parts per million of solids. Reducing the amount of solids in the liquid film on the strip so that the film contains less than only 25 parts per million of solids more than number of parts per million of solids in the fresh wash water is both unusual and highly desirable as the final, flow-brightened sheets will not be appreciably contaminated with residual salts from the electrolytic cells.

We claim:

1. In the process of removing a solution of electroplating salts from a moving metal strip electroplated with metal, the steps of directing the strip along a predetermined path with one surface uppermost and directing a stream of fresh wash water downwardly ontosaid one surface, changing the direction of strip travel and positioning the other surface uppermost and directing a stream of fresh wash water downwardly onto said other surface, and thereafter passing the strip between wringer rolls.

2. In the process of removing a solution of residual electroplating electrolyte from continuously moving metal strip electroplated with metal,

the steps of passing the electroplated strip having such a solution thereon through a first bath, passing the strip from the bath and wringing the strip, arranging the wrung strip with one surface uppermost and directing fresh wash water onto the uppermost surface, arranging the strip with the other surface uppermost and directing fresh wash water onto this other uppermost surface, and wringing the strip to remove the excess liquid and leave a thin film of liquid on each surface of the strip.

3. In the process of removing a solution of residual electroplating electrolyte oontaining electrolytic salts from, continuously moving metal strip electroplated with metal, the steps of passing the electroplated strip having such a solution thereon through a first bath, passing the strip from the bath and wringing the strip, arranging the wrung stripwith one surface uppermost and directing fresh wash water onto the uppermost surface, arranging the strip with the other surface uppermost and directing fresh wash water onto this other uppermost surface, and wringing the strip to remove the excess liquid and leave a thin film of liquid on each surface of the strip, the liquid of said film containing less than 25 parts per million of electrolytic salts in excess of that carried in the wash water.

4. In the process of progressively removing residual electroplating electrolytecontaining electrolytic salts from. continuously moving: metal strip electroplated. with: metal, the steps comprising passing the strip from. an; electroplating cell through a first rinse bath, passing the strip up wardly from the bath and spraying the strip withother surface uppermost, and applying a spray of fresh wash water against the other surface while uppermost and before passing between the wringer rolls.

5. In the process of progressively removing electroplating solution from metal strip electroplated with metal continuously moving through three coplanar horizontal pairs of upper and lower, wringer rolls, the steps comprising directing the strip forwardly beneath the lower wringer roll of the first pair of a first surface of the strip uppermost, directing the strip rearwardly between the first pair of wringer rolls with the other second surface uppermost, directing the strip around the upper wringer roll of the first pair and then forwardly and downwardly beneath the lower roll of the second pair with the first surface uppermost, directing the strip about the lower roll and then rearwardly between the second pair of wringer rolls with the second surface uppermost, directing the strip upwardly about the upper roll of the second pair of rolls and then forwardly and downwardly beneath the lower roll of the third pair of rolls with the first surface uppermost, directing the strip upwardly about the lower roll and then rearwardly between the third pair of wringer rolls with the second surface uppermost, directing a spray of wash water downwardly against the first surface each time it is uppermost before it passes beneath a lower roll, and directing a stream of fresh wash water onto the second surface each time it is uppermost and prior to passing between each pair of wringer rolls.

6. The process of removing electroplating electrolyte containing electrolytic salts from moving metal strip electroplated with metal comprising the steps of supporting and moving the strip; alternately washing the strip from fresh water and removing excess liquid from the strip by passing it between wringer rolls at least three diiferent times, each washing operation including positioning the moving strip with one surface uppermost and directing a stream of fresh water against said uppermost one surface, positioning the moving strip with the other surface uppermost and directing a stream of fresh water against said uppermost other surface, and then passing the strip between the wringer rolls; and collecting and removing the wash water away from the strip whereby the strip is not contaminated with removed electrolyte.

7. The process of removing electroplating electrolyte containing electrolytic salts from horizontal metal strip electroplated with metal moving along a path comprising the steps, of passing the strip from the plating cell through wringer rolls to remove some of the residual electroplating electrolyte; passing the strip through an aqueous reclamation bath to wash the strip and remove some residual electrolyte; subjecting the strip to repeated washing and wringing operations, each operation including directing the strip along a path with first one surface uppermost and then the other surface uppermost, directing a Water spray downwardly against each surface while in the uppermost position so that the water spray flows over the strip, and wringing the strip after both surfaces have been sprayed; and removing sprayed water from the vicinity of the strip and preventing recontamination of the strip.

SAMUEL S. JOHNSTON. JOHN E. ELSWICK.

8 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 517,566 Eyre Apr. 3, 1894 1,544,506 Tytus June 30, 1925 1,626,439 Voegeii Apr. 26, 1927 2,314,369 Reed Mar. 23, 1943 2,342,266 Gessner Feb, 22, 1944 2,372,599 Nachtman Mar. 17, 1945 2,377,550 Hall June 5, 1945

Claims

1. IN THE PROCESS FOR REMOVING A SOLUTION OF ELECTROPLATING SALTS FROM A MOVING METAL STRIP ELECTROPLATERD WITH METAL, THE STEPS OF DIRECTING THE STRIP ALONG A PREDETERMINED PATH WITH ONE SURFACE UPPERMOST AND DIRECTING A STREAM OF FRESH WASH WATER DOWNWARDLY ONTO SAID ONE SURFACE, CHANGING THE DIRECTION OF STRIP TRAVEL AND POSITIONING THE OTHER SURFACE UPPERMOST AND DIRECTING A STREAM OF FRESH WASH WATER DOWNWARDLY ONTO SAID OTHER SURFACE, AND THEREAFTER PASSING THE STRIP BETWEEN WRINGER ROLLS.