US2307928A - Process and apparatus for cleaning metal - Google Patents

Description

Jan. 12, 1943.

G. B. HoGABooM PROCESS AND APPARATUS FOR CLEANING METAL 2 Sheets-Sheet l Filed Feb. 24, 1959 650,965 Hoo/1 @oo/W.

lNVENTOR ATTORNEYS Jan. 12, 1943. G. B. HoGABooM PROCES AND `APPARATUS FOR CLEANING METAL 2 Sheets-Sheet 2 Filed Feb. 24. 1959l G50/@af #oaxaca/W.

ATTORN EYS.

Patented Jan. 12, 1943` UNITED STATE s PATENT OFFICE raocEs-s Arm APPARATUS Foa eLEANnve.A

i METAL George B. Hogaboom,

or to Hanson-Van Matawan, N. J.,acorpor ati `Application February 24,1

s calms., (ci.

The temperature can be controlled because the In the usual process of electrolytic cleaning of metal, the metal is passed through, or hung in,A

a tank containing, an alkaline solution and'is cathodically connected in an eiectriecircuit supl plied with current at 6 to l2 vol/ts. This produces a current density of at least 10 amp/sq. ft.

and causes avigorous evolutionof hydrogen gas f cn the cathode. The improvement in the cleansing action over straight cleaning is believed to be due to sevral "causes, including the formation of free alkali at the cathode, the lmechanical action ofthe hydrogen bubbles on the surface' of the cathode tending. to lift the oilfllm and to assist in its emulsiflcation. and the agitation of the solution, caused by the/evolution of gas, whichl constantly brings fresh solution to the cathode surface. Y

A primary/'object of my invention is to render the electrolytic cleaning process more rapid and efficient byfsu'pplementing theV effects of the usual process by /a vigorous mechanical action brought about by throwing a forceful stream of cleaning solutionl against the metal. 'I'he cleaning action is accelerated by the impact of the Y solution,.which physically tears away the dirt as it is loosened by the dissolving and electrolytic l action.A At the same time the dissolving action j becomes more rapid, due to the continuous sup'- ply o f new solution to the metal surface and its greater pressure against the metal surface.

A number of difficulties areencountered in electrolytic vcleaning tanks as now operated. In

the first place the cleaning is carried out in a tank which is constantly accumulating the dirt from the metal, leading to the danger of rey contamination of the metal from the scum in the tank. i A

In the second place, there is a gradual rise in the polarization voltage at the anodes, which is only partially corrected by making the anodes in' the form of grids of very large surface.

In the thirdplace, the temperatur-cof thevcleaning solution'cannotbe properly controlled. This temperature should be somewhat below the boiling point for best results, preferably about 180 F. The current generates heat, leading to boiling of the solution. which cannot be controlled, because the large anodes choking the tank do not permit eiective use of cooling coils.

These and other difficulties are .overcome by my invention. lThe cleaning operation is carried out in a cleaning chamber,` to which cleaning solution is supplied from a reservoir and from which it constantly flows out, carrying with it the dirt removed from the metal. This removes the danger oi the clean metal being soiled by an accumulation of dirty scum. The violent agita tion of the solution in the cleaning Vchamber keeps the anode surfaces clean and prevents a continuous rise in the polarization voltage.

'4 diately carried of! be vgoverned by electrolytlc cleaning apparatus in'- accordanceV 4shown in the accompa Newnruain, conn., assun- Winkle-Munning Company,

n of New Jerseyass, semi No. zsass f zul-141) hold a cooling coil and the immereservoir is 'free to heat generated by the electric current to discharging from the cleaning chamber, the used solution. being replaced by solution from the reservoir at the controlled temperature..

The invention is .well suited to the cleaning of metal strip, Vthecleaning chamber, in this case, being arranged so it to streams olf-cleaning solution. The cleaning solution can be allowed to escape from the cleaning chamber through the same gates by l which the metal strip enters and leaves.

In electrolytic cleaning the cathodic cleaning is sometimes followed much shorter duration, posit upon the metal from in the cathodic treatment for instance, where a dethe cleaning solution must be removed before electroplatlng. In accordance with my in- Because of the greater eflocienoy of the, cleim-A ingprocess according to my invention, the appaf ratus required for the same'work can be smaller. Where it is a question of treating strip which is running at a certain speed determined by other units of a combination of apparatus, the length of space required for the electrolytic cleaning can'be considerably shortened.

While I have mentioned particularly the use of an alkaline cleaning bath, the invention is also applicable to electrolytic pickling and bright dipping.

The invention reference to two illustrative forms of apparatus nylng drawings, wherein Fig. 1 lis a longitudinal vertical section of an with my invention; A v

Fig. 2 is a vertical cross section of the samel apparatus on the line 2--2 of Fig. 1;

l; and

Fig.l fi is a vertical longitudinal section of another forrn of apparatus in accordance with my invention.

In the apparatus shown in Figs. 1 .to 3 a tank i' is provided as 'a reservoir for alkaline cleaning solution 3, which may the tank are Varranged.

known formulas. Above the reservoir by the solution l that the strip will enter and v` leave it through gates and will be subjected in by anodic treatment ofl the duration of treatment can Any' will be explained ni detail by a Fig. 3 is a detail section on the line 3 -3 of Fig. l

be of any of thewell- 'l a series of cleaning chambers 5,1, 9 and |I, etc.,

ment,though`fewer may be employed if desired. As indicated by the break in the apparatus illus-A trated in Fig. 1, it may be considerably longer and the number of cleaning chambers corre- I3.` Each cleaning chamber iscomposedl ottwo i box-shaped members ,I and I1 providedwith horizontal ilanges i9, 2|, 23,"25,'2129, 3| and. 33.' The ilanges 21 `and 29 and the ilanges 3| and those shown being only a part of the fun cemple- Vspondingly greater. This apparatus is designed -ior cleaning continuous strip metal indicatedl at The metal strip I3 is continuously ied through the cleaning chambers by the pairs of rollers |03, |85, |01, |09, III, H3. Cleaning Solution `generator through the positive busbar to the 33 are separated by sheets of insulating material j 35, since in this particular apparatus the'upper half o! the cleaning chamber is to be electrically 4 `charged oppositely tothe lower half. -The two halves are clamped together by bolts 31 having metal washers 33 bearing upon washers 4I of lx1-.- sulating material, which protect the bolts 31 tromcontact with the' ilanges 29 and 33;, At the bridge clamps 45, and lock nuts 41.

upper half I5 of the first cleaning chamber, thence through the cleaning solution to the upper side of the metal strip I3, 'The current leaves the lower lside of the metal strip and passes through -the cleaning solution to the lower half I1 of the cleaning chamber, from whichv it returns through lead 91 and bus bar 9| to the -generator.

42o p upper end the bolts have nuts 43 bearing upon The space 49 between llanges I9 and 2| constitutes an entrance gate through which the metal moves into the cleaning chamber and the space 5I between ilanges 23 and 25 constitutes an exit gate from lwhichfthe metal leaves the cleaning chamber. `Within these spaces are buttons or At the second cleaning chamber the current from thepositive bus bar 89 goes to the lower half I1 of the cleaning chamber, thence upward through the solution, the metal strip, and the solution again to the upper half I5 of the cleaning chamber, from which it returns through lead 991 to the negative bus bar 9|. Thus in the successive cleaning chambers the currentilows alternately downward and upward, and both surfaces oi the metal strip receive cathodic treatment-and anodic treatment. The current is conribs 53 of insulating material, to hold the metal j strip I3 out-of contact with the metal parts of the cleaning chamber.'

The bottom half of the cleaning chamber is fixed by screws 55 to channel bars 51 extending across the tank. The channelbars are supported by insulating posts 59 upon flanges 6I secured to the side walls o! the'tank I. Screws 63 x the channel bars to the insulatthe insulating ing posts 59 and screws 65 secure 1 posts to the flanges 6I.

Within each hal! of each cleaning chamber is y a pipe B1 provided with a longitudinal slot or se- Vries of perforations'at 69 to emit a stream of,

cleaning solution directed against the upper and lower sides of the metal strip I3'. The cleaning p solution is supplied through pipes 1| connected by nipples 13 and sections of hose 'I5 to the pipes nected by a pipe 9| to the inside oi' the tank I. A,

in the tank I is a cooling coil 85 supplied with coolant from a refrigerator unit 81.

Running along the series of 'cleaning chambers are bus bars 89and 9| connected respectively to the positive and negative poles of a generator 93. The positive bus bar'89 is connected by a lead 95 to the upper half I5 of the ilrst cooling chamber, while the negative bus bar 9| is connected by a lead 91 to the lower half I1 of the first cleaning chamber. The connections are reversed at the second cleaningchamber, where the upper hall i5 is connected by a lead 99 to the negative bus bar lli and the lower haii i1 is connected by a lead lill to 'the positive bus bar till. The connections are thus alternated through the series of cleaning chambers.

Pairs of rollers lud, |95, lill, las, lil and feed or support the metal strip I3 through the series of cleaning chambers. The pair ci? rolls-rs iII has the additional function of stripping the cleaning solution from the metal strip heitere it passes beyond the end wall of the tank i.

'The apparatus operates in the following manner:

centrated principally across the spacesbetween flanges I8 and 2| and acnges l23 and 25, but some of the current also passes through other parts of the cleaning chamber. In the course of its travel through the cleaning chamber the metal strip I3 is subjected to the streams of cleaning solution issuing from the pipes 61 and the cleaning action due to solution and electrolytic activity isV thus accelerated by the mechanical action l of the streams of cleaning solution. The cleaning solution flows out of the cleaning chambers through the gates 49 andv 5I from which it falls into the reservoir I. This solution therefore constantly carries out of the cleaning chambers the dirtv and grease removed from the metal. The

insulating strips v35 extend into the cleaning 81, and by a pipeV 'I1 to the pressure side of a u pump 19. The suction side of the pump is' conlter press 83 may be Inserted in the pipe 11 to f remove solids from the cleaning solution. Withchambers close to the edges of the metal strip I3 to guide the strip and to prevent short-circuiting of the electric current around' the strip. There is considerable heat evolved in the cleaning chambers, ,much of which is'carried to the reservoir with the returning cleaning solution and is absorbed by the refrigerating coils 85.

-The escape of cleaning solution from the cleaning chambers is controlled by the spacing of the flanges I9 and 2I andthe anges 23 and 25, as

v well as by the shape and size of the insulating buttons or ribs y53.

In the form oi. apparatus shown in Figs. l-3 the metal receives the same periods of anodic and cathodic treatment, since in one cleaning chamber the upper side of the metal strip is being treated cathodically while the lower side s is being subjected to anodic treatment and in the next cleaning chamber the conditions are reversed. A`It is sometimes desirable to make the duration of one kind of treatment longer than the other, particularly to give a longer cathodic treatmentthan anodic treatment. The apparatus shown in Fig. a is designed for this purpose. il. reservoir lib has mounted on it a ce.-

l thodic cleaning chamber H21 and an anodic cleaningr chamber |29, the manner of mounting the cleaning chambers on the reservoir being the same as before. In this case both the upper and lower halves of the cleaning chamber |21 are connected by leads lili to the positive bus bar while both halves of the anodic cleaning chamber |28 are connected by leads |33 to the negative bus bar 9|. Thus the current travels from the positive bus bar through the leads |3| and the upper and lower walls of cleaning chamber |21 through the cleaning solution to the strip |3, and longitudinally through the strip into cleaning chamber |29,where it passes through the cleaning solution to the upper and lower walls of the cleaning chamber |29 and through leads |33 to the negative bus bar 3|. The portion cf the metal strip I3 in the cleaning chamber |21 is therefore a cathode, while the portion in cleaning chamber |29 is an anode. The chamber |21 in this case is, for example, five times as long as the chamber |29, thus' giving a eathodic treatment of, for instance, ten seconds and an anodic treatment of two seconds. In order to compensate for the greater electrode surface in chamber |21 than in chamber |23 there may be provided a shunt connection |35 with a rheostat |31.` This shunt connection makes contact with the strip I3 by a brush |39 and is connected at its other end to lead |33. Conforming to the greater length of chamber |21 there are provided ve jet pipes 61 above and five below the strip I3. If desired, the single long cathodic cleaning chamber |21 could be replaced by a number of short cleaning chambers giving a total length equal to the one long one.

Aside from the differences noted the second form of apparatus is the same as the rst, having the same means for circulating the cleaning tion. These have not been shown in the drawings.

For electrolytic pickling and bright dipping an apparatus similar to that shown in Fig. 4 may be used, but with separate tanks under the two cleaning chambers. The pickling and bright dipping may be carried out as described in the patent to Hogaboom and King No. 1,865,470. The two chambers should be so proportioned that the metal can be given a treatment of 60 to 90 sec,- onds in the nrst chamber and from 4 to 12 seconds in the second chamber. The circuit should be arranged as shown in Fig. 4, so that the metal will be cathodic in the firstl chamber and anodie in the second; The acid bath for the first chamber is preferably a sulphuric acid solution of 32 B. and is maintained at a temperature of 140" F. In the second chamber a 46 B. solution of sulphuric acid and a temperature not higher than 60 F. are preferred. The concentrations and temperatures may, however, be varied within the boundaries described in the aforesaid Patent No. 1,865,410. A currentof 10 to 150 amperes per square foot of cathode surface may beused 4in the rst chamber, and in thesecond chamber a current of 25 to 200 amperes per square foot of anode surface, depending upon the temperature of the solution.

While the term cleaning solution generally denotes an alkaline detergent bath, in the following claims it is 4to be construed in the broader sense of any electrolytic solution having a capacity for cleaning metal under the influence of an electric current.

I claim:

1. Apparatus for cleaning the surfaces of metal strip, comprising a cleaning chamberV provided lwith entrance and exit gates for the strip to bounded by opposed electroconductive surfaces of large area provided with means for insulating the strip therefrom, means for applying cleaning solution to both sides of the strip in the cleaning chamber in opposed forceful transverse streams and thereby flushing the cleaning solution over the strip and out through said gates, and means for establishing an electric circuit passing through the surface of the strip and the cleaning solution in contact therewith.

2. Apparatus for-cleaning the surface of metal strip, comprising means forming a cleaning chamber completely enclosed except for two gates for entrance and exit of the strip by longitudinal movement. means for applying cleaning solutionl to both sides of the strip in the cleaning chamber in opposed forceful transverse streams, whereby to hush cleaning solution over the st rip in said chamber and out through said gates, and means for establishing an electric circuit passing through the surface of the strip and the solution in contact therewith. Y

3. In apparatus for cleaning continuous metal strip, a cleaning chamber comprising closely spaced electroconductive surfaces of large area provided with insulating means for spacing and guiding the strip between said surfaces, means for forcing opposed streams of cleaning'solution against the opposite sides of the strip and through the spaces between said electroconductive surfaces and the two sides of the strip, and means.

for establishing an electric circuit passing through the surface of the continuous strip and the cleaning solution in contact therewith.

4. A method of electro-cleaning metal strip which comprises passing the strip longitudinally through the interior of an approximately closed cleaning chamber by way of restricted entrance and exit `gates extending longitudinally of the strip, supplying cleaning solution to the interior of said cleaning chamber in` opposed forceful transverse streams directed against the opposite faces of said strip within the interior of said cleaning chamber and thereby expelling a stream of cleaning solution from the cleaning chamber along each face of the strip by way of at least one of said restricted gates through which said strip is longitudinally passing, and passing electric current between each face of the vstrip and the cleaning solution in contact therewith.

5. Apparatus for electro-cleaning metal strip which comprises an approximately closed housing forming an interior cleaning chamber of relatively large volume with relatively restricted entrance and exit gates fo rthe metal strip in passing through said chamber, -means for continuously feeding the metal strip through said cleaning chamber and gates, means for delivering cleaning solution into said interior cleaning chamber in the form of opposed forceful streams against the opposite faces of the metal strip passing therethrough, means for spacing the metal strip from the walls of said entrance and exit gates to provide passageways along the two faces of said strip for the escape of cleaning solution from'the interior cleaning chamber outwardly through said gates, and means for passing electric current between the cleaning solution and strip.

' GEORGE B. HOGABOOM.

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