US2939826A - Method of cleaning ferrous metal objects - Google Patents

Description

mrrronorcmsmommous d L. other, times as; rune wa r 1N0 Drawing. Filed Apr.5,1956,$er.No.;516,250 I f 3 95 1 This invention relates to afmethod 'of'removing scale,

rust or other corrosion products, also certain electroplated surface films and the like from surfaces of ferrous metal articles or alloys thereof. d

It has heretofore been suggested that the surface of an iron or steel article can be cleaned by immersing the article in an aqueous solution of sodium hydroxide and sodium cyanide, and passing an alternating current. through the article to be cleaned, the aqueous solution,

to an electrode. However, the sodium cyanide bath is toxic and accordingly presents special problems both in the operation of the bath and in its ultimate disposal.

Furthermore, the parent metal is subject to attack as iron reacts with alkali cyanide to form alkali ferrocyanide.

Other methods of cleaning iron and steel articles have been proposed, but it is an object of this invention'to provide a method giving radically improved results.

More particularly, it is an object of this invention to provide an improved process which is of a substantially universal nature in removing rust, scale and corrosion products with equal ease. Still another object is to provide a method of cleaning a ferrous metal object wherein the underlying base metal is not attacked and wherein the cleaned metal, after removalffrom the bath, is so conditioned that it resists corrosionand that it can readily be silver soldered, soft soldered electroplated or that othersurface coating operations can be performed once the given a cleaned object is removed from the bathand swill in cold water.

2,939,826 Patented June 7, 1960 ice In accordance with the method of this invention aferrous metalobject is immersed in an aqueous 80111111011.

of sodium hydroxide and an amine, triethanolamine being a preferred example, and an alternating electric current,

is passed through the solution.

' Although the composition of the bath in. accordance with the process of this invention may be varied considerably, the bath must be an aqueous solution of an alkali metal hydroxide such as sodium, potassium or lithium hydroxide or the equivalent. Incorporated into thissolution is a tertiary amino alcohol having nitrogen bonded directly to terminal carbon atoms of three saturated hydrocarbon chains which each have a single OH. group bonded to a carbon atom other than that bonded to the nitrogen and where said chains contain from 2 to 4 carbon atoms.

Still amther ject of this invention is to Provide ant current as distinguished from the direct current of either fixed polarity orperiodic reverse polarity required by most processes of the prior art.

Other processes of the prior art have required the use of a separate chelating or complexingagent for preventing the staining of clean surfaces, and it is another object of this invention to provide an improved process of this kind having the advantage that no such separate chelating or complexing agent is required, this function being performed by the reaction products of the essential ingredients disclosed' 1 Still another object of this invention is to provide a method of this type, using a solution in which the compounds removed from the cleaned metal surface have limited solubility in the bath liquid and tend to settle to the bottom as sludge without interference with the operation of the process.

' Still another object of this invention is to provide a process as referred to above wherein spent ingredients of the processingsolution may inexpensively be regenerated. Other objects and advantages of this invention, including the simplicity and economy of the same, and the ease with which it maybe applied to a variety of ferrous metal-"objects, will further become apparent hereinafter.

When the amine is incorporated into the alkali metal hydroxide solution, the hydrogen atoms of the OH groups are replaced by alkali metal until equilibrium is established between OH and ONa.

The preferred amine in accordance with this invention is triethanolamine, which is readily available and efiicient. Triisopropanolamine is also elfective and falls within the scope of this invention. Mixtures of various amines as defined above may also be used.

The relative proportions of ingredients of the bath may vary within wide limits, but it is preferred to employ a molar ratio of about three moles alkali metal hydroxide permole amine. V

The concentration of thejsolution may vary from as low as 3% alkali metal'hydroxide and 5% triamine in percentages being calculated on a weight basis. The more dilute solutions are suitable for removal of light rust, particularly where time is not of the essence, while the more concentrated solutions provide very rapid cleaning and are particularly suitable for the removal of heavy coatings of mill scale, rust and the like.

The current applied to the bath is an alternating cur rent, preferably sixty cycle current because of its ready availability. However, I have utilized four hundred cycle alternating current and the cleaning effect is greatlyaccelerated by using the higher frequency. Additionally, I have cleaned work in accordance with this process by using in induction field of a high frequency induction heat treating unit, and thus produced almost instant clean? ing. I have also obtained excellent cleaning results using a low voltage secondary transformer having a maximum voltage of about seventeen volts R.M.S.

Although the work is cleaned with optimum economy and efficiency by connecting the work as an electrode,

good cleaning results may be obtained by using a pair of spaced electrodes connected to opposite sides of an AC..

shape of the electrode has considerable bearing upon the efficiency of cleaning. For example, flat electrodes pro-: duce the best results when the work is round, and round electrodes when the work is flat.

*For optimum-results, the work should be placed'at a point substantially midway between the electrodes, and} the electrodes should be placed as far away from the work as is possible, to provide uniform cleaning over the entire surface of the work.

The current density may; similarly be varied within wide limits. Using sixty cycle alternating current, and

be cleaned in less than one-half minute, at which time 'its' appearanceis' thatofa like object made of silver.

Typical objects that were cleaned with this bath were black steel pipe cut in short sections for convenient hanusin'g-two carbon electrodesea'chf meas I i QZ x 6 ,"a; dling, bolts, nuts, and bearings that have been heat current-'in 'excess offfiftyampere's may-be applied; The treated as well as bearings which have become rusted, maximum; current densitymay be" over five; thousand tools such as micrometerspand. gauges and the like which amperes per square footof electrode. Using the work? have become rusted, stee'Fstrapping that is used in shipas one electrode, a, maximum current density of about ping .halesa andZhUndISiandE'PacKageB,nietalfiwhichihas five thousandamp'eres-per square ,foot' may be-employed. been blackened by rust pi'oofing'processes and the like, The current density-'may'be reduced almost to zero, but blackiron screws, and heat treatedehacksaw. bladeswhich cleaning is-mnchslc iwer-. p have beenpai'nt'ed'l A typical example 0% the practice ofEthis' invention. lrniaiecordaneenwitlrmy .inventitm;thei-worlcr;may be follows} I connected direetlyhy externalmeanstomne side of the Ninehnndred m1. of tapgwater are-placed into a onev alternating current line," orth'e two electrodes may be litre glass beaker. grams'sodinm hydroxide and connected one each to the two sides of the line and the ev n y-fiv -gram ri ha lamine re stirre iin n il diswork placed in the bath without external connection, derb n" electrodes, each one meas i g pending,uponthe-curreutinduced inithe work. by thei flow A, are pl in k r in Such a Way of currentbetween, the electrodes. i 1 that opposed surfaces of maximum arealie parallel and a results r m b had by connecting work apart as far as the dlmensions of the beaker allow' directly to one side of the alternating, current line rather; Electric conductors are connected from both electrodes than dependingmpon the: current inducedbycurrent flow to slde of an ahematmg current Power Supply havmg betweenthe: electrodes; for: supplying the energy needed adjustable ouiput of i 10 to 17 volts The for cleaning. However, either arrangement-gives satis side of the power supply s connected to a cable fitted wit factoryilresuns if, time, Power consumption am, a steel clamp at. its terminus, which serves to support p work to be cleaned and toestablish electrical contact. Immortal. i'. I The work to be cleanedis clamped firmly and placed in The; time, @qmredto clFan a'PIeCeIOf d} the bath between the two carbon electrodes, the power f slx'fnches g' the bath at the hlghest cone turned on andwm-k is kept immersedumfl clean. centration which I have'reported 1n the'foregomg-"tahlcr'.

Theprocedure outlinedjabove was followed; usinga, approximately fifteen The Increases variety f i b' h Th foll i abl sets the concentration of triethanolamine-sodium hydroxide reforth the compositions .ofthe specific baths and also the' action compound decreases, but inother baths which L character oftheresultsobtained. 35 have considered satisfactory, the time tocleanv A1 Table MolarRatlo. Molar Wt. Equiv. I Percent;

Bath NIL. i t

. TEA, NaOH, H.011 TEA, NaOH, H.011 Total TEA, NaOH,. H.0H,

80% 0.1. Dist. 80% 0.1-. Dist. CiP'. Dist.

1 3 10, 180 487.5 as 25 a7:

1 a 1,000 1 12.000 18,307.5 1.1 .s 03.3 8-..- 1 U a 2,000 187;5 120 30,000 ,307 .5 .3 19m? Bath No. 1 had a melting point of approximately 220 inch. pipe-six inches longhas run approximately l1.to. 1%.; FL and produced veryrapid cleaning. Bath No. 2 had minutes. v 4 a melting point ofapproximately 170 F, and produced There is apparently no destruction ortdissolution ofl very rapid cleaning. The melting point of bath No. 3 the parent metal by this process, as is -the. case. vvhen-; was below room temperature and baths 3 and 4 gave 55 cyanide solutions are used. Pieces ofsteel left; in the excellent and rapid cleaning. Bath 5 was very satisbath for a considerablelengthof time, (,up; to-fifteenfactory, whilebath No. 6 was satisfactory for very light hours orv more), and then measured by-a'micrometer indie scale andfor a medium Weight coating of rust. Bath cate no measurable, differencein length or width; nor is---- No.'7 was quite slow forremoval of, rust and for most there any weight change once the pieceis. cleanediand: scale. Bath No. 8 was suitable for light rust only and then replacedtin the bath for a considerable length of was very'slow. time such as fifteen, hours or more; 7 a 5 Operatingtemperatures for the bath, at which satis- According to my process, the surfaceof the metah is. factory cleaning takesplace, from the standpoint of surso cleaned thatit has asilver; colored-appearance.andiis face finish, range from 15-20 to 90-100 degrees centiconsiderably morearesistant to .corrosionthan'it would, grade. Excessive time is required at the lower temperahave beenzhad the. scale. been. cleaned .offawith emery: tures, however, and the most satisfactory temperature cloth. It is mybeliefi that thereisachange inthesurrangenliesfrom about 60 degrees on up to boil. face charge in. thetmetalv which is at. leasbpartially=re-- Onespecificusezfor which. this-invention was developed sponsible for this result although thistheory has notbeenn was; to, clean ball and 1 r,ollerbearingcomponents after scientifically established. However, it has; been: estabheat,treat DiLquenchandannealoperations. This-cleanlished thatperfectlyclean metalproducedbymy process ing method is very rapid. in its operation while at the. immersed intap water,.ruststmuch lesstthanmetahwhiclrf same time being very thorough; All recesses, grooves, has. been cleaned by mechanical abrasionand immersed" etQ-,.,a1' .e de-s calcd almost as, rapidly as the outer surfaces. in the, same tap, water: 7 Aflsteel hearing race1 of, .-inch O.D.,- inch I.D., A Although various forms. of this.=.invention have..-bce1r-.'

inch; high; coatedj scale carbonized oil, etc.,. may

referrednto; in. particular. termshereim; it is;.to=.

preciated that various modifications may be resorted to without departing from the scope of this invention. For example, equivalent chemicals and currents may be utilized, and various features may be used independently of the use of others, all without departing from the spirit and scope of this invention as defined in the appended claim.

Having thus described my invention, I claim:

In a method of cleaning a ferrous metal object, the steps which comprise immersing said object in an aqueous solution consisting essentially of .330% alkali metal hydroxide and about .5-47% by weight of a tertiary amino alcohol having nitrogen bonded directly to terminal carbon atoms of three saturated hydrocarbon chains which each have a single OH group bonded to a carbon atom other than that bonded to the nitrogen and where said chains contain from two to four carbon atoms, and subjecting said solution and the object immersed therein to a high frequency induction field by passing alternating current of at least 400 cycles per second through said solution and object.

Potthofi Nov. 27, 1923 Wernlund Aug. 21, 1951