US2440837A - Metal cleaning composition - Google Patents

Description

Patented May 4, 1948 Jen: Shoemaker SenidLNo. 496,50!

team; (01. amiss):

This invention relates. to cine matter an'd to aprocessfoii f solution'fo'r remcvallof oXid "etals' have been treated in. ai niolt 7 It. Hath prising sodium" hydifoxiiiei sodi'llmf liifi'lati preferably containing a? small amount of. siidiiiiii; chloride; I

In my joint application; Serial" 43111168,, fi ed; Febr uary16; 1942" mewatanaon dij' the'refi'si'dis closed the use'ofa'ni o11 salt @1211 am an" alkali metal nyaroxiae all: N trate, and" preferably aismalla V a kali'metal'chloride rtscieamh" "ni'et' Fsinf and particularly f rrous? iiietal crapes process comprises immersing. the. metal articleih the molterisalt bathorithe. tove rhemiqnea coin position; followed by. an immersion iii a diliite mineral acid'sucli ashsiarbcmonbior :SiHfiIILQa-Cid'. In the first step oftlie process, which i'fiiihier'sion, in the molten salt bath orizfanic'limnni itieson the metal surface are oxidized'and} therefore lie-- moved;v and the iiiolgii lio impurities; such a graphite, carbon, and cofiinoundslcfi sulphur; silicon, phosphorus, etc. are conven d into-com pounds which'are readily removed: from themetah surface) in the. dilute acid treatment. Treatment in the aqueous acidsolntion removes all the-im purities from the surface at the metal. and ten-- ears the metaiisurrace clean" aneitrightl Inmy appn atio serraiito, i'z313191gfiiefe Jana my 23, 1943 ev d s s e r mses em ing metal surfaces with protectiigelead alloys immersion of the article in a salt bath de--" scribed above, fonow'ee Ltpby trea -Itment in: a:

dilutev mineral acid, washing or the dilutemineretacid' from the surface otthemetal, and finally coating the metal surfacewith aproteetizvc" 1336i alloy. The salt bath and acidtreatmentstogether: convert the exposed surfaces of the metal pieces into etched matrices having minute foramina or pockets materially depleted of oiddized and nonmetal substances; The etched matrices: oletained have been: found to; form an; exceeclingly strong bond with high-lead alloys when the alloy is suitably applied thereto-; H p I In my joint application Serial No;; 4 3-..12i-," filed: April 10, 1943- (now abandoned), isdisclosed anew type of bearing and a process tor preparinathe new type of bearing in which; acomhinatten; 0t

molten salt and acid treatmentis used-toprepare a bearing back to receive a bearingalloy,

In all of these processes it isnecessalfy totreat; the surface of metal which has-been immersed-in 1 the molten salt bathin an aqt eousacidsolution. This treatment in acid solution is not entirelya ui e na themes cid? to be lietained on the a -t'e'fiifency smftioeofth I efl ect" on meter coating treatmentsi It appearsitliaif' avert" a brief immersio in di'lnte acid resultsonly iii af' remote: oi the oxide former themetal snrface: by the molten saltt- Hath; that some' or the-carbo anegraphitemwhe eta ibntl'below the surface isex i pdserBcausinef the tobesmi-idgm siich aisurfaGe-is nnsiiitahlefof coating operations;- Fiiitthermore; iif-hasbeefi found on certain types of restatemen articles that-even} a brief treat- 7 meat in? dimes sci-d5 results instrong:

ease ior hydro en on the surface or the efiibfittlhieiit" the metal article; and thus for these typesof" rerroh imetar articles the proc- 63S?" mamma -ale; Thehydrogen adsorption tefri'cis to wetiken thehond'between the metal and;

the? coating" alloy; Also, When} the process is used for reparing hearings; the hydrogen adsorption.

' on the bearing backresnltsiina weak band be tween the: bearing metal? alloy; and: the bearing been Inthe case'of treatment of common-meter articles; it has, been foiirid that fairly prolonge treatmentin thedilute'aci'd'isnecessary to'remove" all of the oxide, coatin and this pickling. pro cezinrehas proved"undesirable;

It? is an object; therefore of this. invention" to pid'viidefla procession preparing the surface of mecais foncoatin'g opeigatiorisfby use; of molten salts without use of acid solutions; toremoizethe onee-rayerrqrmearmuh molten Salli balth'.

Anothefobje'ctis 'tiipro'vide'a procession clean,

' ingmetfill 'rti has by" reatment'ma molten. salt,

batl ii comprisn gi sodium hydroxide.- sodium Iiitr'ate; and? plfeirbly Containing a small. alilburlfi of spaiiihi; clilori' e: wimout the subsequent use.

I of dill itemiifiralT'abids...

Another objefit of iriveiitioriis to. pioiiideia processlffoi t costume; fiietala'rticles which the metal? ole ispreparedtofiieiizethefiietalcoat; mg; 155? iii a; molten Salt. bath including; an; alkaliiii'etalhirdiokide and nitrate without the use of he: someone: twemov the oxides from. the; s'fiifac' of; th metalsv after immersion in m' 'm itn salt bath. l l H A ti'otlief olij eel; a new composition of matter suitable; when dissolved in water for removal oi oxides formed on metal. articles which have been immersed in a molten saltz bath comprising an alkali metal h droxide an alkali metal nitrate, and pre' ferably a sm-allamount of an alkali metal chloride; 7 v p r metal? lf his'acid -lias-adeleterious Still another object of my invention is a process for avoiding the use of acid solutions in the preparation of bearings by a process in which the bearing base is first immersed in a molten salt bath, followed by immersion in a molten metal bath for providing the bearing base with a high lead tinning alloy, A

My invention has forfurther objects such adi ditional operative advantages and improvements as may be found hereinbelow.

dilute acid to remove the oxide layers frommetal articles immersed in molten salt baths ifthe 12140111 1.. solution is replaced by an aqueous solution ofa; composition comprising sodium hydroxide, sodi;

. I have found that I may avoid the use of hibited-a dull, dark finish, The metal parts were um borate, sodium cyanide, and in-somecases a small amount of either sulfur or sodium chlolthen immersedin an aqueous bath containing 70 parts sodium hydroxide, 18 parts sodium cyanide, 4 parts powdered borax, 4 parts sulfur, and 4 parts-sodium chloride, made up to about 1.5

specific gravity and heated to 250 degrees F., and

ride, or both. This composition serves the same.

purpose as the dilute acids for removing the oxides and oxidized substances from the surface of the metal, but it has the advantage thatthe solution is alkaline and thereby any possibility of hydrogen adsorption or acid retention on the surfaces of metals is completely avoided.

In general the composition may vary over fairly wide limits. The sodium hydroxide may range from about 50 to about 90 parts, sodium borate from about l to about 10 parts, sodium cyanide from 5 to 46 parts, sulfur from .10 to about' l parts, and sodium chloride from .10 to about 4.

parts. The sodium hydroxide, sodium b orateand sodium cyanide are necessary components of'the mixture, but the composition will operate without the use of sulfuror sodium chloride. However,

the'prese'nce of either of these two substances,"

and preferably both of them, appears to "have a beneficial action'on the composition. f a

O'ne' composition which hasbeen particularly advantageous contains 70 parts sodium hydroxide, 18 parts sodium cyanide, 4 parts powdered borax, 4 parts sulfur, andi parts sodium chloride. This compositionhas been used to treat a wide variety of met rar'uues such as cast iron, spring steel, stainless "steel, and other common ferrou's'metal alloys with goodIsucc'ess.

It has also been used with bro'nt'e, brass, and like alloys successfully.

While I have particularlydescribed the'sodium compounds, it will be obvious to those skilled in the art] that any of the other alkali metal salts, such as potassium or lithium salts; may be used in makin up the composition.

In practice, the composition is ter in a concentration about 8'poundsper gallon of water and heated to a temperature of about 220 -250 degrees F., but of'course below the boiling point of the solution. After the metal articles have been immersed inthemolten salt bath and have been rinsed with wash "water, they are immersed in this aqueous solution for a' period of time sufficient to removethej oxide layer formed in the molten salt bath. The period of immersion will vary over wide limits and will depend'to a considerable extent upon the conditioner the metalsurfaces and the type, of metal beingtreat ed. In general, however, a period of minutes has been found to be satisfactoryin the usuali type of articles. In the case ofthe treatment of bearings to prepare them to receive a tinning alloy, a period of minutes has been found satisfactoryfor the average type of small bearings. It appears that this composition has a dissolving action on the metal oxides and other oxidized substances on the surface of the metals, It is alkaline and has a reducing action to aid in dissolved in wawere maintained in this bath for about 15 minutes.

After this treatment, the oxide layer was removed, and the articles had a metallic appearance, appearing to be ,clean' of all surface impurities. 7 All oxidizable' substances, .including carbon and graphite and compounds of sulfur,

found to be] silicon, phosphorus, etc.'were removed from the surfaces of the metals; These parts were then dipped in a molten lead alloy containing about 90 percent lead, 5 per cent tin, and 5 per cent antimony. The lead alloy, made: a particularly firm bond on.these articles, and were'satisfactory in .all respects, being'free of pinholes, and havingauniformly coated surface. The articles showed no evidence of hydrogen embrittlement as would havebeen found if ana'cid treatment had been used to remove the oxide layer.

In' another specific. example of my invention I'applied my process to certaincast iron parts. These parts presented a. diflicult problem as their surfaces held a' considerable amount of adherent or"i mbedde d"si1ica".. The parts were first immersedfor-five'minutes in the molten saltbath of the same composition as that used in the preceding example, They were then removed, rinsed, and immersed in an aqueous solution of the'same composition described in the preceding example, and maintained at about 2'70 degrees.

for about 20 minutes. Finally, they were taken out, rinsed, and dried; and were found to'be particularly clean and suitable ,for'coating operations. After dipping, the partstin a molten lead alloy containing about 90; per cent lead, about 5 per cent tin,: and about 5 per cent antimony, they acquired a'uniform lead alloy surface free of pinholes and having no rivulets or dewetting. The bond'betweenthe Coating lead alloy and the cast iron was particularly firm.

In still another example of my invention, a cast iron bearing back wa ssubjected to the same treatmentnoted in the "previous example. After the lead alloy surface had been put on the bearing back,- th'eEba'se was coated witha bearing metal c'ontaining'about 1 per centtin, l per cent arsenic, 15 per cent antimony, and the remainder lead, by pouring the-molten bearing alloy on the bearing base to the desired thickness. This bearing was very satisfactory and had a-very high shear strength. -After' the bearing was poured and solidified, it was annealed according tothe ordinary' practice. The bearing prepared in this fashion withstood th'e annealing opera- "tion with-out loosening of the bearing alloy from v, 1 The use of thiscomposition in connectiQn with the" molten salt bath treatment has several advantages. Because it is alkaline there can be no hydrogen adsorption on the surface of the metals, and therefore nohydrogen embrittlement and no deleterious action through retention of a small amount of acid on the surface of the metal. Furthermore, the composition has no tendency to attack the metal itself and therefore it does not expose additional graphite, carbon, or other impurities which are in the metals themselves but beneath the surface of the metal,

Its only action is a reducing action in removing the metal oxides and other oxidizable substances from the surface of the metal.

While I have described my invention hereinabove with respect to particular applications and compositions and noting specific examples of alloys, it will be obvious to those who are skilled in the art that the invention is not limited to the specific examples of practice, but may :be variously practised and employed within the scope of the claim hereinafter made.

What I claim is:

A metal cleaner comprising an aqueous solu- 6 tion of an alkali metal hydroxide, an alkali metal borate, and an alkali metal cyanide, in proportions, by weight, of 50-90 parts, 4-10 parts, and 546 parts, respectively.

HUGH G. WEBSTER.

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

UNITED STATES PATENTS