US2615840A

US2615840A - Electrolytic method to remove rust

Info

Publication number: US2615840A
Application number: US87261A
Authority: US
Inventors: Chapman Alfred Arthur Grahame
Original assignee: Individual
Current assignee: Individual
Priority date: 1947-06-06
Filing date: 1949-04-13
Publication date: 1952-10-28
Anticipated expiration: 1969-10-28
Also published as: CH278602A; BE482434A; LU29036A1; GB693951A; DE814231C; FR1022302A

Description

lA.-A. G. CHAPMAN ELEcTRoLYTIc METHOD To REMOVE RUST Oct. 28, 1952 Filed April Ls. 1949 GRAHAME CHAPMAN .fev/fm `lus ATTORNEY;

- I INVENTOR 4 ALFRED ART' Oct. 28, 1952 A. A. G. CHAPMAN 2,615,840

ELECTROLYTIG METHOD TO REMOVE RUST Filed April 13. 1949 I 4 Sheets-Sheet 2 A/7a 25. A INVENToR /7 ALFRED ARrHuRGRAHAME CHAPMAN /1/5 ATTORNEYS. l

Oct. 28, 1952 A A. G. CHAPMAN ELECTROLYTIC METHOD To REMOVE Rus'r 4 Sheets-Sheet 3 Filed April 13. 1949 INVENTOR BY MWA a@ his ATTORN EYS.

Oct. 28, 1952 A. A. G. CHAPMAN 2,615,840

ELECTROLYTIC METHOD TO REMOVE RUST Filed April 13. 1949 4 Sheets-Sheet 4 FIG. le.

INVENTR A LFRED ART H U R GRAHAME CHAPMAN www. @www f5 ATTORNEYS.

Patented Oct. 28, 1952 ELECTROLYTIC METHOD TO REMOVE RUST Alfred Arthur Grahame Chapman, London, England Application April 13, 1949, Serial No. 87,261 In France June 6, 1947 11 Claims. (Cl. 204-141) This invention relates to processes and compositions for treating articles to remove rust and other deposits from metallic articles. It relates particularly to processes and compositions for removing rust from ferrous metals and surface coatings, such as, carbonaceous deposits, cement, paint, enamel, and other materials from the surfaces of ferrous metals, copper, lead and their alloys.

Many processes are already known for removing rust from ferrous metals and for scouring and cleaning metals in general. Some of these processes involve electrolytic treatment of the article. Usually, the part to be treated is used as an electrode contact with a solution of various compounds, such as, phosphates, iiuorides and the like. While these prior processes are capable of removing rust and other deposits from metallic articles, they do not produce a perfectly clear or clean surface nor are they capable of removing rust from the small interstices in the articles.

The present invention provides a method and a composition whereby articles of substantially any size can be cleaned and freed from rust to such an extent that the surfaces of the article are rendered clean and shiny in appearance, even though the part may have been rusted or corroded to such an extent that it appeared to be useless.

The process and the cleaning composition have the characteristic of acting so completely on corroded or rusted surfaces as well as such great penetrating power that, for example, a nut which has rusted solidly to a bolt is cleaned sufliciently that it can be easily unscrewed after the treatment.

The process is applicable to the treatment of many kinds of devices, such as, machine tools, typewriters and other devices which have become corroded or rusted to such an extent, as, for example, by immersion in water over a long period of time. Frequently, such devices can be placed in a usable condition by treatment in accordance with the present invention Without disassembly and reassembly.

In accordance with the present invention, the article to be cleaned or freed from rust, after being scoured and rinsed in hot water, is used as a cathode in an electrolytic bath which consists essentially of an aqueous solution of an alkali metal hydroxide, an alkali metal cyanide, one or more alkali metal halides, a suitable peptizing salt, such as, for example, an alkali metal metasilicate or an alkali aluminate and a wetting agent, such as sulfated fatty alcohols or lsulfonated products.

In addition to the basic components of the bath, as described above, the bath may be benetted by the addition of small quantities of alkali metal zincates or stannates. These materials, when combined with the other components used, form a very thin coherent ilm on the surface of the article when it has been cleaned or de-rusted, this thin lm providing corrosion resistance in the article when it is stored.

The relative proportions of the various components of the solution depend upon various factors, and, in particular, on the speed with which it is desired t0 carry out the derusting or rustremoving operation, on the quantity and nature of the rust or other deposit to be removed. Inasmuch as some parts may have deposits of varying characteristics, these deposits may have to be removed simultaneously. The composition of the bath must be such that it can be used for such purposes within relatively wide limits controlled chiefly by economic conditions and the cost of the necessary chemicals.

The treatment of the article is preferablyl effected at ambient temperature at a low continuous voltage and a relatively high current density. The part to be cleaned is immersed in the electrolyte as the negative pole or cathode of the circuit while the bath is vigorously stirred, as, for example, by the introduction of air under pressure into the lower part of the vat. After this initial treatment, the current is reversed and electrolysis is continued with the article as an anode for a period of time equal to about 1/5 of the time during which electrolysis was carried forward with the part as a cathode.

A better understanding of the present invention may be had from the following description and by reference to the accompanying drawings, in which:

Fig. 1 is an elevation of the treatment vat, part of which has been removed to show the inside arrangement.A

Fig. 2 is a plan view corresponding to Fig. 1.

Fig. 3 shows on a larger scale the arrangement, inside of the vat, of the anodes and of the air-inlet pipe, as well as the arrangement of the bus bars arranged outside and connected with the other pole of the source of current.

Fig. 4 is an end view of one of the terminals connecting the connecting cables with the bus bars arranged outside of the vat.

Fig. 5 is a view, partly in elevation and partly in section of the part shown on Fig. 4.

Fig. 6 shows the end of a connecting cable provided with a terminal part which fits onto the terminals and members which connect with Fig. 9 is an end view of the part shown onV Fig. 8.

Fig. 10 is an elevation view with the ends shown in section of a bar fastened above the vat, and making it possible to suspend on same the light-weight objects to be treated. v

Figs. 11 and 12 are an elevation view and a plan view of a basket intended to receive the small parts to be treated.

Fig. 13 shows in vertical section a portion of the scouring vat provided with a gas heating device. v. v

Fig. 14 is a section along XIV- XIV of Fig. 13.

Fig. 15 is an elevation of the general installation. 4

Fig. 16 is a plan view of the same installation.

The parts to be derusted are first of all carefully scoured in order to enable the electrolyte to wet all the portions of the part.- This scouring, like all the other operations of the process, is carried out in a vat of suitable dimensions, made of any material capable of withstanding the action of the liquids it is to contain. The scouring may be effected in a hot solution of caustic soda to which a wetting agent of the sulfated alcohol or sulfonated oil type may be added. The vat containing this solution is heated to about 80 C., the bath being constantly stirred during the operation. A 40 per cent solution of caustic soda is satisfactory for the cleaning operation, although solutions of varying concentrations may be used.

After the part has remained .from fifteen to thirty minutes in the scouring bath, the part is rinsed with hot water for five to ten minutes in a vat similar to the scouring vat and then it is immersed in the derusting bath. The derusting bath is susceptible to considerable variation depending upon the conditions. of use, but preferably the components thereof should be present in about the proportions indicated in the following table.

Table I Alkali metal hydroxide 2f tok 31/2 lbs/gal. Alkali metal metasilicate or aluminate 2to 4 oz./ga1. Alkali metal cyanide 3 to 12 oz./gal. Alkali metal fluoride l 1A; to 2 oz./gal. Alkali metal chloride 1 to 8 oz./gal.

Wetting agent (sulfated fatty alcohol or sulfonated products) le to 14 oz./gal.

In addition to the above components, the 'solution may include alkali metal stannate or zincate, l to 3 oz./gal.

The preferred bath is about a 30 Baume solution but it will be understood that the concentration will vary depending upon the variation in proportions of the components as set forth in the table.

During the use of this solution, its composition will vary, so that it is necessary, from time to time, to replenish certain ofthe components of the bath as. will be explained hereinafter.

When the water available for the .making of the solution is hard Water, it may be desirable to soften it by adding to same a suitable softening agent, such as sodium metaphosphate, in a proportion which is not to exceed l kg. per 900 liters of solution.

The action of the several components of the bath combinato produce a most eicient rustremoving operation permitting the process to be carried forward at considerable speed and at a reasonable current density. Each of the components of the bath serves a useful purpose, and they act together as a group in such a way as to provide in thetreated article a clean, shiny Surface.

The alkali metal hydroxide, for example,

A sodium hydroxide, is necessary in order to provide a solution of low electrical resistivity, thereby permitting the use of substantial current densities. It also acts to remove grease by emulsilication or saponification. It provides a solution of substantially constant pH value, and, when electrolyzed, produces a copious evolution of hydrogen and oxygen which facilitate the removal of scale or rust from the article by their mechanical action.

The alkali metal cyanide, for example, sodium cyanide, is beneficial in the removal of thin films of oxide, especially on non-ferrous articles. It also has the advantages of providing a solution of low polarization and thereby facilitates the rate of scale penetration and rust removal.

The alkali metal chloride acts as a strong peptizer and therefore facilitates scale removal. Also, the chloride ion is a very active agent tending to promote scale penetration and the regeneration of the various types of salts used in the process. It also has a strong depolarizing effect.

The alkali metal ,uorida for example, sodium uoride, is similar in its action to the sodium chloride but is even more reactive so that the effects produced by the chloride ion are enhanced by the presence of the fluoride.

The sodium silicate or aluminate is used on account of its peptizing action, that is to say, at the time of the electrolysis, the one of the agents used decomposes, giving an element which remains in semi-colloidal form-silica, silicon hydroxide or silicio acid in the case of silicate, aluminum hydroxide in the case of aluminate, which element acts mechanically as an abrasive when it is dispersed in the solution.

The wetting agent which is preferably a sulfonated oil type of compound or a sulfated alcohol, improves the penetrating power of the solution so that the composition tends to penetrate even into most minute crevices or intersticcs in the article, thereby facilitating the removal of rust or other unwanted surface impurities from the article. `It also has a tendency to decrease the danger of a back E. M. F. in the .solution during electrolysis since it decreases the surface tension of. the liquid and thereby enables the gases produced to pass readily from the solution. The wetting agent must, of course, not be affected by the presence of nascent oxygen and hydrogen inthe bath, it must be stable at the high pH value of the solution and it must be efficient and have a long operating life.

The main purpose of the sodium phosphate is to soften hard waters `and to maintain the calcium and magnesium salts in solution While permitting the best possible dissolutionv of the chemical products used.

While the part to be derusted is utilized as `a cathode, in addition to the mechanical action due to the formation of hydrogen on the surface of the metal (which mechanical action tends to detach the largest particles of oxide), the strongly adhering iron oxides may be reduced by the action of nascent hydrogen in accordance with the formula FezOs-l-Gl-IzZFe--HQO so that metal is deposited on the part which adds itself to the anode-cathode transfer, thereby partly replacing the metal lost through oxidation.

The part being treated is electrolyzed for a period from thirty minutes to three hours according to the degree of oxidation of the parts and at a current density between about 3 and 31/2 amperes per square decimeter. When this rst period of the treatment, during which the part to be derusted is used as a cathode, has elapsed, current is reversed and the article is electrolyzed as an anode for a period about one-iifth as long as the previous period.

During this last phase of the derusting, the chlorine ions go directly to the part to be derusted and the last particles of oxide are eliminated by the nascent chlorine which reacts in accordance with the formula To prevent too rapid an attack on the part by the chloride ion, the concentration of the alkaline chloride should not exceed the limits given above. During this phase of treatment, the iron previously deposited by electrolysis may be slightly oxidized, but the oxide formed is immediately dissolved by the cyanide and at the end of the treatment, the parts have a shiny appearance and are perfectly clean. This action of the cyanide partly transforms the alkaline cyanide into complex salts with a base of iron, ferrior ferro-cyanides. thereby making the solution weaker in cyanide so that it is necessary to add cyanide periodically to the bath.

During a rather long period, one year, for example, the electrolytic bath may be maintained at about 30 Baume by adding to same from time to time, either water when the density is too high, or, when the density of the bath is too low, a mixture of suitable salts called regeneration mixture and containing a high percentage of cyanide. The composition of this regeneration mixture may be included within the following limits:

Table I I Preferred Preferred Rango Formula Percent Perec/m5 Caustic soda 42 to 70 55 Sodium cyanide .I 50 to 18 33 Sodium chloride 4 to l0 9. n Sodium iiucridc 2 to 1.5 Sodium metasilicate l to I 1.0 wetting agent 14, to 0.25

All pei-cents on dry basis.

They must stay in the Washing electrolyte but also to bring them to a sufficient temperature to enable them to dry rapidly. They are subsequently immersed in an oil or other similar bath which prevents their being oxidized by the air. A very satisfactory bath consists of a 20% solution of lanolin in kerosene. The parts are subsequently dried and may be used again immediately.

This treatment process has such a complete action that the nuts,l bolts, screws and any assemblies which before treatment could not be loosened and were useless are renovated and may be again used. In many cases, machine tools which as a result of their exposure to weather had become useless and had been seriously dam aged, could be again used without disassembling.

A specific example of the process is as follows: A metallic article, for example, a rusted steel article, is degreased and partially cleaned by introducing it into a bath consisting of a 40 per cent solution of caustic soda heated to a temperature of about and containing a small amount of a suitable wetting agent such las a sulfated fatty alcohol. The part is left in the bath for about twenty minutes while the bath is stirred continuously until it appears that grease and like deposits have been removed from the article. The article is then rinsed for about 5 to l0 minutes in hot Water and then is transferred to an electrolytic bath having the following composition:

Sodium hydroxide 3 lbs. per gal. Sodium metasilicate 3 oz. per gal. Sodium cyanide 7 oz. per gal. Sodium chloride 5 oz. per gal. Sodium fluoride 7/8 oz. per gal. Sulfated fatty alcohol 1/8 oz. per gal. Sodium stannate 1 oz. per gal.

The sodium stannate can be omitted if desired.

The article is connected in an electrical circuit and immersed as a cathode in the electrolytic bath. The article is electrolyzed at a current density of 31A? amperes per square decimeter for a period of about two hours. Atk the end of this treatment, the current is reversed and electrolysis is continued at the same current density, but with the part as an anode for an additional period of about twenty-five minutes. At the end of this period, the current is shut olf and the article is removed, drained and washed in hot water for a sufficient period of time to remove the last traces of the electrolyte and also to heat the article to a sufficiently high temperature to enable it to dry quickly.

The article is then immersed in a bath consisting of a twenty per cent solution of lanolin in kerosene andv subsequently drained, leaving only a thin surface iilm of the solution on the parts for preventing oxidation. y

Articles treated in the manner described above have a clean, bright surface finish and the rust or other deposits are removed so completely that, in many cases, the article can be used immediately without any further treatment.

The process may be practiced with a series of vats of materials resistant vto corrosion or attack by thev above-mentioned chemical agents.

In the drawings, apparatus is disclosed which may be used with excellent results. The vats described hereinafter may advantageously be made of sheets of soft steel, suitably reinforced by angles in accordance with the maximum weight and dimension of the parts to be treated.

Figs. 1 and 2 show a vat which is well suited for the derusting operation proper. Vat l of '7 sheet metal has its sides and the' bottom lb welded together, and it is provided at its -upper part with an edge or flange 2 on which there are fastened wooden rails or supports 3 actingA as insulators to hold the current conductor bars `Il extending around the interior of the top of the vat. Inside the vat a conduit 5 supplied compressed air through descending tubes 6 to headers 'I placed near the bottom of the vat. The headers 'I are provided with nozzles 8 inclined at 45 in both directions.

A copper bracket supported on the rail 3 is connected with one of the poles of the low voltage installation, which includes an inverter capable of allowing the maximum intensity to-pass, and on this part 9 there are fastened the four bus bars 4, of copper, between which there are attached the anodes II formed of plates of soft steel (Fig. 3). The bars and the anodes may be fastened by means of carpenters bolts Ill which extend through the members 3 and the bars 4 which are held at suitable spacing by washers I 2. As can be seen from Fig. 2, the anodes are provided on the four sides of the vat and are spaced a short distance from the walls of the latter, from which they are electrically insulated.

The second pole of the source of the current is connected with the outer bus bars I3 which'extend along one side of the Vat and which support a certain number of connectors I4 which form g connection terminals. These connectors, as shown in Figs. 4 and 5, are made of brass or phosphor bronze and they include a body having two slots I 5 therein which make it possible to receive two of the three bus bars I3. A hole I6 permits each bus bar I3 to be retained in a slot i5 by means of a bolt I D (Fig. 3).

The connectors I4 also include a pipe connection I'I threaded on the outside and bored conically at Ila so as to constitute the female part of the connection. The male part fastened to the current supply cable I8 (Fig. 6) includes a hollow rod made of bronze or brass in which the cable I8 engages, which rod terminates at the other end in a cone I9 which is inserted in the cavity I'Ia of the female part and which is provided, at its portion where its diameter is largest, with a shoulder I9a which serves as a rest for a lock nut with a knurled surface 20.

Similar connections may be used in all meml bers which are to supply the current to be treated.

When the latter are of sufcient dimensions, they may be connected with a suitable pole of the source of current by attaching to same a stirrup or a flange shown in Figs. '7 to 9. The stirrup o f Fig. 7 consists of a U-shaped member, one of the arms of which is provided with a female connection member previously described, and Vof, a V-shaped notch 2l, The other arm is provided with a clamping screw 22.

The connector shown in Figs. 8 and 9 can be fastened to a part being treated by means of a bolt which is screwed into the said part, and it includes the female connection member IT which is integral with a sleeve 2 3 `having a central hole 2t for receiving the fastening bolt, the two parts I1 and 23 being onset so as to receive tbenut 2D of the male part of the connector (Fig. 6).

Above the vat, there may be arranged at a suitable height a certain number of cross-members which may consist, for example, of beams, when the parts to be treated are heavy, the current being fed directly to the parts by means of the stirrups or anges 4just described, or when the to the parts parts are lighter in weight, they may consist of simple round bars 25 of suitable diameter, an example of which is shown on Fig. l0. These bars are provided with welded spacing rings 26. The parts to be treated are suspended on these cross-members by means of hooks, Ss or suitable chains. The rings 26 play an important part when the parts are suspended by means of chains because they prevent the latter from sliding during treatment.

When the parts to be treated are of small` dimensions, they are simply placed in baskets 26 (Figs. 11 and 12) made of steel formed of welded members and provided at their upper part with a hook 2'! and below with a ring 28. In this way, several baskets may be suspended one above the other, so as to utilize the entire height of the vat. It must be noted that the parts being treated must not be too near the plates if which act as anodes. It is necessary to maintain a distance equal to at least .1.0 cm. `between the ancdes and the parts :being treated. It goes without saying that the parts must be carefully cleaned at the points where they are attached to the stirrups or connecting flanges in order to permit an easy passage of the current.

The scouring and rinsing vats of course are not provided with electrolyzing equipment, but they must be capable of being heated in such a manner as to bring the temperature of the liquid to about 80 C.

Figs. 13 and le show an advantageous arrangement for heating of these vats by means of gas. Rows of gas burners 29 are arranged under the metal vat. At a slight distance from the sides Ial of the vat, a sheet metal shell 3S forms with the sides Ia a conduit for the hot gases which 'give off to the walls of the vat, during their scent, a large part of the heat which they con- The general installation may be understood in accordance with the arrangement shown on Figs. l5 and 16. vIn this system, the vats are arranged following each other in an excavation 25 so that the upper edge oi the vats is located approximately one meter above the ground, and, between the vats and the edges of the excavation, floor sections made of latticework make it possible to move all around the vats. The articles to be treated are introduced into a scouring vat 3! and the first rinsing vat 32, both gas heated by means of the rows of burner-s 29. The electrolytic vat or cell is adjacent to the rinsing bath 32. The second rinsing vat 33, which follows the electrolytic Vat or cell, is identical with vats 3l and 32. In view of the fact that the parts remain in

vats

32 and 33 only a short time, it would be possible to-provide for only one vat for the two washing operations. For the sake of most elicient operation of the installation, it is preferable to provide the two vats.

When leaving the rinsing in vat 33, the parts must be dried (drained), for this purpose they may be arranged on a grating 36 below which there is arranged an inclined plate El' connected through a conduit 38 with the vat 33, so that the h quidvwhich drips from the rinsed parts returns directly to vat 33. Protection after treatment is effected in vat 316 and the iinal drying (draining) oiigatiigl Silhsimilar to grating Sd, which is pro- (1 e w1 e same device the drippnguquid. for the recovery of The installation may include a hoistii paratus 40 capable of moving at a suitable llfigeillit above the various treating vats. The bottom of 9. the excavation 35 is advantageously inclined and coated with a waterproof material in order to permit the draining of theA liquids which may spill on same, and in order to facilitate cleaning.

Needless to say, modifications may be made to the process, and the equipment just described, in particular through the substitution of equivalent constructions. Therefore, the form of the invention disclosed should be considered as illustrative and notas limiting the scope of the following claims.

I claim:

1. Amethod of freeing metals from rust, corrosion and the like which comprises immersing a metalvartcle in an electrolyticbath and passing an electric current between an anode in the bath and the article as a cathode, said bath consisting essentially of an aqueous solution of the following compounds:

Alkali metal hydroxide 2 to 31/2 lbs/gal. Alkali metal cyanide 2 to 4 oz./ga1. Alkali metal chloride 1 to 8 oz./gal. Alkali metal fluoride 1/4 to 2 ca /gal. Wetting agent 11g to 14 oz./gal.

and a member of the class consisting of alkali metal metasilicate and aluminate, 2 to 4 ora/gal.

2, A method of freeing metals from rust, corrosion and the like which comprises immersing a metal article in an electrolytic bath and passing an electric current between an anode in the bath and the article as a cathode for a period up to about three and one-half hours, then reversing the direction of loW of current to render the article an anode for about one-lifth the period of time that the article served as the cathode, said bath consisting essentially of an aqueous solution of the following compounds:

Alkali metal hydroxide 2 to 31/2 lbs/gal. Alkali metal cyanide 2 to 4 02./ gal. Alkali metal chloride l to 8 oz./ gal. Alkali metal uoride 1A; to 2 oz./gal. Wetting agent to 14 oz./gal.

and a member of the class consisting of alkali metal metasilicate and aluminate, 2 to 4 02./ gal.

3. A method of freeing metals from rust, corrosion and the like which comprises immersing a metal article in an electrolytic bath and passing an electric current between an anode in the bath and the article as a cathode at a current density between about three and three and one-half amperes per square decimeter, said bath consisting essentially of an aqueous solution of the following compounds:

Alkali metal hydroxide 2 to 31/2 lbs/gal. Alkali metal cyanide 2 to 4 oZ./gal. Alkali metal chloride 1 to 8 oz./gal. Alkali metal fluoride 1A to 2 oz./gal. Wetting agent 11s to 14 oZ./gal.

and a member of the class consisting of alkali metal metasilicate and alumihate, 2 to 4 02./ gal.

4. A method of freeing metals from rust, corrosion and the like which comprises immersing a metal article in an electrolytic bath and passing an electric current between an anode in the bath and the article as a cathode for a period up to about three and one-half hours and at a current density between about three and three and one-half amperes per square decimeter, then reversing the direction of flow of current to render the article an anode for about one-fifth the period of-time that the varticle served as the cathode, said bath consisting essentially of an aqueous solution of the following compounds:

Alkali metal hydroxide 2 to 31/2 lbs/gal. Alkaliimetal cyanide 2 to 4 02./ gal. Alkali metal chloride 1 to 8 oZ./ gal. Alkali metal fluoride 1A; to 2 oz./gal. Wetting agent to i4 oz./gal.

and a' member of the class consisting of yalkali metal metasilicate and aluminate, 2 to 4 02./ gal.

5. The method set forth in claim 1 in which between one and two Ounces of an alkali metal salt oi' the class consisting' of Zncates and stanhates are added per gallon of solution.

6."'A method of 'freeing' metals of surface deposits of rust, corrosion products and other foreign substances, comprising immersing a metallic article in an electrolytic bath maintained at about ambient temperature, passing an electric current between an anode and the article as a cathode at a current density between about 3 and 31/2 amperes per square decimeter for a period of between about one-half and three and onehalf hours, then reversing the current to render the article an anode for a period of about onefifth the duration of the period in which the article acted as a cathode, then removing the article from the bath and washing it, said bath consisting essentially of an aqueous solution 1n about the following proportions per gallon of water:

7. The method set forth in claim 6 in which about one ounce oi' sodium stannate is added to the bath per gallon of water.

8. The method set forth in claim 6' in which about one ounce of sodium zincate is added to the bath per gallon of water.

9. A method of freeing metals of surface deposits o-f rust, corrosion products .and other foreign substances, comprising immersing a metallic article in `an electrolytic bath, passing an electric current between an anode and the article as a cath-ode at a current density'between about 3 and 31/2 amperes per square decimeter for a period of between about .two yand three and one-half h-ours, then reversing the current to render the Iarticle an anode for -a period of about one-fifth the duration of the period in which the article acted as a cathode, then removing the article from the bath and washing it, said bath consisting essentially of an aqueous solution in about the following proportions per gallon of water:

Wetting agent of the class consisting of sulfated fatty alcohols and sulfonated oils 10. A composition to be diluted with water to form an electrolytic Ibath for removal of rust and 11 12 the like frommetal consisting, in about the .fol- REFERENCES CITED lowing proportions of: The following references are of record in the Alkali metal hydroxide lbs-- 2to31/2 le of this patent: Alkali metal Ghiqfidef1vn0h- 1 't0 8 UNITED STATES PATENTS Alkali metal yanide-- '.,OZn` 3110 12 5 Alkali metal uorie oz-. M; to 2 Number Name- Date Wetting agent r, 1 ,oz 3151x314 13241317 Marmo Dec* 9' 1919 l1,528,144, Couesnon Mar. 3, 1925 and a member of the class consisting of 'alkali 1,954,473 Dunn Apr. 10, 1934 metal metasliate and aluminate, 2 to 4 Oz. 10 2,371,033 Deshaw Man 6l 1945 11. The composition set forth in claim 10 containing, in about the following proportion, about OTHER' REFERENCES 1 to 2 oz. of a member 'of the class consisting of The Monthly Review of The American yElecalkali metal stannateand alkali meta1z'inoate. troplaters Society, June 1935, 'pages 4-19- Journal of The Electrodepositors Society," ALFRED ARTHUR GRAHAME CHAPMAN. vol. 7 (1932), pages 157, 158.

Claims

1. A METHOD OF FREEING METALS FROM RUST, CORROSION AND THE LIKE WHICH COMPRISES IMMERSING A METAL ARTICLE IN AN ELECTROLYTIC BATH AND PASSING AN ELECTRIC CURRENT BETWEEN AN ANODE IN THE BATH AND THE ARTICLE AS A CATHODE, SAID BATH CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF THE FOLLOWING COMPOUNDS: ALKALI METAL HYDROXIDE 2 TO 3 1/2 LBS./GAL. ALKALI METAL CYANIDE 2 TO 4 OZ./GAL. ALKALI METAL CHLORIDE 1 TO 8 OZ./GAL. ALKALI METAL FLUORIDE 1/4 TO 2 OZ./GAL. WETTING AGENT 1/16 TO 14 OZ./GAL. AND A MEMBER OF THE CLASS CONSISTING OF ALKALI METAL METASILICATE AND ALUMINATE, 2 TO 4 OZ./GAL.