US2174722A - Process of electrolytic cleansing - Google Patents

Description

Patented Oct; 3,1939

UNITED STATES PATENT OFFICE rnoonss or rmijr izify'rro CLEANSING Ferdinand Artur Herrmann, Leipzig Germany No Drawing. Application November 14, 1935, Se-

rial No. 49,709. Renewed March 14, 1939 1 Claim. (Cl. 204-1) The present invention relates to an electrodetermined or ascertained high current density, lytic method for the cleansing of metals, parthe H2804 concentration always being less than ticularly such asare in the form of wires, ribbons 250 g/l and the current density always being and the like, so as to prepare the same for subsehigher than 20 amperes per square decimeter,

5 quent coating or plating. the determined or ascertained current-density 5 One of the'objects of the invention is to conand the determined or ascertained acid-concentinuously clean for an extended length of time tration being mutually related (inversely) and annealed iron wire and also hard drawn steel or also related to the time of exposure of any spot iron wire which has a firmly adherent oxide coaton the travelling wire to the Sulphuric acid bath l0 ing upon its surface by means of an electrolytic Solution, and t0 the Prevailing Conditions 0 cleaning method in which the said iron or steel temperat re. The d ned high Current de wire forms the anode. sity is such that enough oxygen is liberated over It has heretofore been proposed. in the patent nearly the entire anode surface as to mechaniliterature to clean wire, preliminarily to apcally effect the loosening and detaching of the i5 plying a. metal coating thereto, by running the iron-oxide film from the iron or steel wire and wire continuously through a solution containing clean the wire. sulphuric acid and through which solutio an Unlessthe concentration of the sulphuric acid electric current passes to the wire as an anode. In e Current density be P p y determined said patent literature, it has also been proposed W relation to o e another, and t0 t e t me Of to clean ferrous articles by passing current of a xposure of the wire and the prev i n eondi- 20 I density higher than 20 amperes per square decii n f te p r e. the n n proc w uld meter through a solution containing less than 250 nevertheless soon lose its cleaning effectiv ne grams per liter sulphuric acid to the article as an or soon exhaust the available current supp y anode, but without specific reference therein to even thellgh e ulp ac d C n trat o o th length of th leaning time nd/o to the the bath be below 250 g/l and the current density 25 durability or longevity of the process when apbe higher than 20 amps./sq.dcm.

plied to the cleaning of wire running continuously The numerical figures for a determined conthrough the bath, or. to the necessary Conditions centrationof sulphuric acid and for a determined therefor. current density in any concrete case are obtained I am unaware that any process of anodically y following the en r l e f decreasing i so cleaning wire, ribbons, and the like, which are the HSO4 concentration and increasing the cur i run Continuously through the cleaning solution, rent-density, the shorter the time the travelling and which are partially soluble in the cleaning W re s e p d to t bath, the H2804 e0ncentra solution, such as iron wire in the sulphuric acid n being in every case below 250 /l and the solution, has ever been heretofore known or current density, in every case, above 20 35 used which was satisfactory in respect to the ampS-/Sq- The pe d of the wire determines durability or longevity of the process, to the uni-. the time o exp re a given le of ba formity and reliability of the cleaning action With a given length and Size of a h d a over extended periods of time; to the adherence iven w rep nd t kin into unt the of after-applied coatings (as, for instance, thickprevailing conditions of temperature, a suphuric 40 zinc coatings produced either electrolytically or ac d conce t ation for t e bath (be 250 /l) by dipping in molten zinc); to the requirements and a current density (above 20 amps/Sodom), of a reasonable cost; or to the requirements of s selec ed, being guided by t general rule above synchronous operation in line with .the line of ed; process is n p in p ti n, nd

machinery in a modern continuous wire-processthe evolution of oxygen on the wire and the rise 45 ing plant. The limitations and insufliciencies of in temperature of the bath watched. If the ourthe processes of the prior art hereinabove set rent density is insufficient to maintain an oxy forth are obviated by the process of the present cover on nearly the entire length of the wire in invention, as hereinafter more fully described. t e. bath Or to e the q ed Cleaning e According to the present invention, iron or the current density must be raised, and if the 50 steel wires, ribbons, or the like, are cleaned by temperature of the bath continues to rise, then running them in extended lengths, as anodes, the concentration of the sulphuric acid in the continuously through an unheated e ectrolytic bath must be lowered as often as required 'to bath of dilute sulphuric acid having a deterarrive at a solution concentration which has a 65 mined or ascertained H2SO4 concentration at a conductance (or resistance) required to limit the flow of current to a current density which will give a copious evolution of oxygen over nearly the entire length of the wire and also produce the required cleaning effect, at a temperature at which the solution stabilizes when heated by the aforesaid required current.

If the wire or the like has thereon scale or grease, or other extraneous matter, especially if in considerable quantity, the wire or the like is preferably preliminarily treated in any of the well-known ways to remove suchniatter, or. the greater part thereof, as by running it through pickling solutions, degreasing solutions, etc. 7

A critical study of the conditions within the solution while it is being operated for effecting cleaning, reveals that bubbles of oxygen do not appear on thewire (anode) immediately on the wire entering the electrolytic solution, and that there is a time interval (variable with the operating conditions) between the time the wire enters the solution and the time it becomes fully covered, while in the solution, with the oxygen bubbles. The length of the wire within the electrolytic cleaning solution may therefore be envisaged as comprising two portions,one, a portion where it lacks an oxygen-gas cover, and another portion where it is covered with oxygengas. Now the length, within the solution, of the portion of the wire which lacks the oxygen cover depends not only on the interval between the time the wire enters the bath and the time when the wire becomes covered with oxygen gas, under a given set of conditions, but also on the speed of movement of the wire through the cleaning-bath, The speed of movement of the wire should preferably remain constant, and needs to where the cleaning is one stage or step inthe train or series of operations for the continuous processing of wire. With the speed of the wire determined and the total length of the wire within the solution fixed by the size of the equipment it follows that the length of that portion of the wire which is subjected to thecleaning action of the gas, and which is covered'with oxygen-gas, will depend on the time interval required for the oxygencovering to form. The longer this time interval, the shorter the length of the wire undergoing cleaning action, and hence the less complete the cleaning. Iron or steel, however, is chemically dissolved from that portion of the wire within the bath which lacks the oxygen-cover.

The efiect of the dissolved iron (FeS04) is to change the resistance of the solution. If the concentration of sulphuric acid in the bath is above 250 g/l the ferrous sulphate'resulting from the chemical action of the sulphuric acid solution on the iron or steel wire always causes a net decrease of the resistance, with the result that the current density will increase inversely, proportionally. Proporfionally with the increase in current density there will also be a larger amount of electrical energy dissipated in the bath, the net result of which will be a rise in decrease of the resistance and the spiral increase in current density, and thus causing the limit of the electric generator capacity to be rapidly reached. Moreover, by reason of the changes taking place in the solution, the whole process is. made variable, irregular and uncertain. I Even below a sulphuric acid concentration of 250 g/l the efiect of iron going into solution may The chemical be likewise unless checked by a corresponding increase in resistance through the selection of a concentration to suit the current density.

- The effect of increased temperature of the solution on the effectiveness of the process can be demonstrated with a laboratory experiment. For instance, with a solution containing 80 g/l H2304 and a bath temperature of about 20 C., the evolution of oxygen will set in after 2 or 3 seconds after the circuit is completed. At 30 C. and with the same current density, it will take 10 seconds before the oxygen evolution begins, At 40 C., it will be more than 60 seconds before oxygen is liberated.

The importance of the time element in continuous cleaning operation under actual industrial conditions is quite obvious when one considers that 80 f. p, m. is not regarded as a very high speed in a wire galvanizing plant and that the length of the cleaning bath for economical reasons is usually held at approximately 20 ft. This allows only 15 seconds for the cleaning operation It follows that the time it takes for the oxygen to appear should be only a small fraction of .the 15 seconds if the cleaning efliciency is to be high. If, however, after say 24 hours operation, the temperature of the bath has increased so that, as in the above example, it would take 10 seconds for the oxygen to appear (whereas it took only 2 seconds at the start), it is evident that conditions which are set to produce effective cleaning at one bath temperature will not be efiective when such an increase of bath temperature occurs as is contrasted in the examples given above.

By employing above 20 amps./sq.dm. current densities which will produce copious amounts of oxygen over nearly the entire submerged surface to be cleaned, so that the chemical dissolving action of the solution is retarded and a powerful mechanical cleaning action is obtained, and by diluting the solution having a concentration 5 lower than 250 g/l sulphuric acid, to such an extent that the temperature of the bath will stabilize under the employed conditions of current density and temperature, the cleaning effectiveness of the bath will be greatly prolonged and the useful life of the solution extended for a long period of continuous use.

Cooling of the bath in any well known manner, as by running cold-water through coils immersed in the bath, may be practiced, to thereby stabilize the temperature of the bath at a low level against the heat generated by the current flow, to diminish the chemical action of the solution on the wire, and to counteract the rise in conductance due to the temperature factor.

The high current density is essential to operation with a dilute and cold solution thereby insuring an ample evolution of oxygen to effect a thorough cleaning and to greatly retard the dissolving action of the acid solution on the wire (anode). As the speed of the wire is increased, the current density must beincreased while the concentration of the sulphuric acid should be decreased,

Water and sulphuric acid are supplied to replenish the portions of the solution lost by gasformation and escape and dragou't, in such man ner as to not increase the conductivity of the solution. In practice the maintenance of the solution at a constant hydrometer reading will sufiice.

It is to be understood that in the use of the process a cathode should be chosen which is not afiected by, or soluble in, sulphuric acid.

or the cleaning effectiveness to any harmful extent.

The essential feature or features of this invention reside in so selecting and correlating the conditions of wire-speed, length of wire exposed in the solution, temperature, concentration, and current density for an acid solution in an electrolytic cleaning process in which an object chemically soluble in the solution, as iron or steel, is run continuously through the solution while current passes thereto as an anode, that the dis-.

solving of the metal will be retarded and a rapid liberation of oxygen be efiected, and that the working condition of the electrolyte will remain substantially unchanged for a long period of constant use,

A reference is made herein to my abandoned application Serial No. 445,225, April 17, 1930.

What is claimed is:

In a process for cleaning iron or steel wire. ribbons and the like in which initially unheated sulphuric acid of concentrations below 250 grams per liter areused, in which the wire travels'continuously at a substantial speed through the bath and in which the wire is directly connected as an anode to a current source, the anode current density being high enough to liberate oxygen over nearly the entire submerged anode surface, that improvement for prolonging the useful life of the bath with respect to its uniformity and reliability of cleaning action over extended periods of continuous operation which comprises correlating and controlling the current density, wire speed, temperature, and concentration of the acid bath in a manner that the concentration of acid is always maintained less than 250 grams per liter and the current density is always higher than 20 amperes per square decimeter, the tem perature isrstabilized at a moderate increase over the initial temperature and the wire speed isnot less than that of a continual wire processing operation, and compensating for increase of temperature due to heating efiects of the current in the bath which tend to render the cleaning operation variable, irregular and uncertain by decreasing the concentration of acid in the bath and for increase in wire speed or both speed and temperature increase by decreasing concentration of acid in the bath while increasing the