US2828192A - Method for etching metals - Google Patents

Description

March 25, 1958 w. P. LANGSFELD 2,828,192

METHOD FOR ETCHING METALS Filed Oct. 4, 1954 I 2 Sheets-Sheet 1 INVENTOR.

N SFELD 7 March 25, 1958 w. P. LANGSFELD 2,828,192

METHOD FOR ETCH'ING METALS 2 Sheets-Sheet 2 Filed Oct. 4, 1954' INVENTOR.

w w a. U H

Il /mm I? Lmvasrao flTTORNEY- United States Pa ent 2,828,192 METHOD non ETCHING METALS William P. Langsfeld, Huntington Park, Califi, assignor to Turco Products, Inc., Los Angeles,'Cahf'., a corporation of California Application October 4, 1954, Serial o.460,o12

2 Claims. 01. 41-42 1 This invention relates to improvements in.the chemical etching of metals, and is more particularly concerned with novel procedure and apparatus for the control of foam formed on the surface of the etching bath.

It is known to etch acid soluble metals, such as magnesium, zinc, iron, titanium,'nickel and their alloys with an acid solution such as aqueous nitric acid. It is also known to etch alkali soluble metals such as aluminum and its alloys with a solution having a solvent action on the aluminum or alloy surface, such as a hot aqueous alkali solution, for example, one containing sodium hydroxide. I

One common method of carrying out the etching operation is to immerse the metal partto be etched in an etching bath contained in a tank. However, during the' etching reaction, hydrogen gas is liberated, and this gas, together with entrained water vapor including droplets containing etchant, generally produces a layer of froth or foam on the surface of the etching solution. When the part or work piece being etched is removed from the bath, the froth causes a wavy etch pattern to be superimposed on the etch of the part due to passage thereof through this froth layer. Also, the etchant contained in the entrained vapors above the bath tends to coat and pre-etch the metal part prior tovand during immersion thereof, thereby resulting in a non-uniform final etch pattern. Also, when the part is only partially immersed during the etching period, non-uniform etching takes place in the area of contact of the froth with the exposed surfaces of the work piece.

One object of the invention is to provide novel apparatus and procedure for efficiently etching a metal part.

Another object is the provision of procedure and apparatus for etching a metal part while eliminating or minimizing undesired additional etching caused by stationary contact of the part with the surface froth, or by passage of the part through the surface froth during immersion or removal of the part from the etching solution.

Yet another object is to provide novelapparatus and procedure for controlling the surface froth in an etching bath.

Still another object of the invention is to substantially remove such surface froth from around a part to be etched during immersion thereof in or withdrawal thereof from the bath following the etching operation.

Still another object is to minimize the proportion of en-' trained etching agent in the vapors in the zone above the etching bath.

A still further object is to cool the zone above the etching bath.

Another aim of the invention is to achieve the foregoing objects employing an alkali solution as the'etching agent fortreatment of an aluminum or aluminum alloy part, that is, one composed of aluminum'..as the base metal.

Other objects and advantages willapp'ear from the following description of my invention:

I'have' found that the adverse" effects of 'such'froth or ice immersed in such solution during the etching period, can

be substantially eliminated or to a great extent alleviated by directing a stream. of air or an air blast, preferably containing moisture, at the liquid etching bath surface below the froth line and against the part. Preferably, means in the form of a fan shaped spray nozzle is employed to emit a stream of spray which acts like a knife to sweep away the froth'and to strip adherent etchant from the surface of the part. The air stream destroys the froth around, or in the immediate vicinity of, the part by breaking up the bubbles of foam. The nozzle is preferably positioned a short distance above the surface of the froth and is mounted so that it is inclined downwardly at an acute angle to the liquid surface. In this manner, impingement of the air stream or blast through the froth and against. the metal part while it is partially submerged in the bath during etching, or while such part is passing through the froth, pushes the froth back and restrains it from making contact with the part.

The moisture to air ratio in the moist air stream preferably employed may be adjusted to include the desired amount of moisture in the air blast. For example, the amount of water in the air stream may be small in comparison to the loss of water in .the system by evaporation and chemical reaction in such etching process, wherein water is consumed in the reaction, as in the case for example in etching aluminum with caustic soda. Preferably, the amount of water in the air stream is adjusted to add approximately the water necessary to maintain' solution level as well as the concentration of the etching bath. The presence of water in the air blast tends to prevent any undesired etching in the exposed portionsof the work piece above the bath surface, or any further.

I rise of vapors containing entrained etching agent through such blanket and into the space above the tank. This greatly reduces the extent of undesirable pre-etching which takes place due to coating of the metal surface of the work piece with such entrained etchant while the work piece extends into or is passing through the zone above the bath prior to and during immersion thereof in the bath. It also aids in preventing formation of a coat of etchant solution on the work piece whilebeing withdrawn from the bath. Reduction of the amount of entrained etchant solution above the bath also materially decreases corrosion of overhead tank equipment. Also, by using additional air streams, preferably moist air, the froth orfoam can be controlled over the entire tank surface, and the air stream or streams impinging in a partially lateral direction on the froth layer, direct or sweep the liberated hydrogen gas and entrained etchant vapors to the exhaust outlets at the sides of the tank.

Below is described a novel apparatus for carrying out the invention procedure, taken in connection with the accompanying drawings, wherein:

Fig. l is a cross section in elevation of the invention device; 7 i i Fig. 2 is a plan view of the device of Fig. 1;

Fig. 3 is a fragmentary section in elevation taken on line 3--3 of Fig. 2; j v V j Fig. 4 is essentially an enlarged fragmentary section Patented Mar. 25, 1958 evi Fatal? 0. e re en s a. k, n. ehlme e i ork stes Parts on. he ts. are tehe 'qr; il i e dtq 1 nt atiqn f; DdYQ 9 1mm i imhin a ned nt et ank. he e: he: W rk n e e ar c mposed. an. acid: oluble. met 19!! as, itanium. t mrmer. sta nle s el m n si m z ne tthei ll y e o'l' nt o ut on. hnt e of suiWlEFFiQfiQMPQSifiQI hjeha queeu hitrie, queous hydrofluq e.as de.antlmi V n yq lth j reot lte tal ses/ sst l i. h m ntion e. etehina r. V .7 r r ana utnih enabminum al eyv materia s, lkali o uhlet l ot j que ust slut pn is. mnleyede hte hins an ta kal l uehasl o u n Qrpetas: un, hyd ex e -s dium nh phat g em sh. i e, ke o m xtu s, he eon Pie. ra lya a qd utu ydrex: i e so on s se .v The alkali on ent a nsemployed n. h e, e chin seludonsm w, an e r m 0.1, o 10 normal. Temperature of, thesolutionlin' the etchingtanlg is generally maintainedin a rangesayfrom 100 degrees F. b .ut. boilingd ing, re m n o e e lower temperaturesmay, also be. used. Numeral, 11 represents a layer of frothor foam which forms, on thesurface of the.

liguid intank 10 frornjheetching reaction as previously, pointed out.

Tank, 1Q has I a, hollow. flange, 12 ;disp0sed, aboutthe.

n i e p rip ry. f h nk uf ihe l l ange ormi a trough for. the frothcrfoam. A short.cionduit-130,, communicateswith hq trough 12,,theother, end of,co nv edges. of; the oppositesides 16,and 17 of. tank 1 0i is apaiif. of tracks, or guide channels 18,

A. number of manifolds 22, shown as,,four in Fig. 1,

are suspended in the, upper, portion of, tank 10. The

manifolds 22 are elongated hllowmemberswhich extend almost.acrossthe-entirewidth of the tanlc, each of suchmanifolds, having endwalls 21 and inclined side portions.2 3 .whi ch slope downward and inwardly, at equal anglestolhevertical, as seen in'Fig. 4. The washed,

botto n 25 .of. the manifolds, are, parallel to .each other.

Positioned on the. outer surface. ofeachof the. sloping sides 23 .ofthe .manifoldsisa nozzle 30, preferablyhaving afan shapedcrosssection, with forwardly tapering sides 29,v The, nozzles 30.,are ofawidthsubstantially. coextensive with thelengthofthe manifolds 22, asseenin Fig. 2,-

and are secured by suitable means such; as. bolts (notshoyvn) to sides 23 ,of the manifolds, with the longitudinal axis of the nozzlesparallel' to the longitudinal axis of the manifolds. Nozzles 30 each have a,square integrallug 26 centrally positioned along, the .rear wall 36 thereof,

which lug.,fits into a square aperture;.26.f in the center. of

the,. sloping sides 23 of the manifold, each lug 2 6 having a central aperture 27 .thereinwhichis in alignmentwith an aperturefiljn the, ,rear wall 36 0f the nozzle. charge orificelor slot,32 is centrally positioned in the,

forward. end 37 of thenozzlesii), opposite, apertures 27 and 3 1. It is seenthat the nozzles 30,, that is along.th e transverse. X,--X,axis, .thereof, are inclined at an angle to the, horizontal, axis of; tank, 1tt,,and that such, nozzles are approximately on a level ,with trougl r lz for a, .reason pointed hu X e e Eae z t hemh teld hasa n inlet duction of i nder.pgtess reintes he-man tel s yn fiap peii.

Manifolds 22 e eeh uspende ve he. d t: ehi .1s,: u du es erwt legen -1 gto the with the nozzles 30 positioned thereon 34 centrally connected to the top 24 thereof for intro.

in the tank by means of a pair of double hooked arms 38; the lower hooks 42*of'which are receiveddn ringbolts 39 which are threadedly received in the top of the manifolds. The upper hooks 43 of the arms 38 are looped over a shaft 39 to be supported thereon. A pair of wheels 40 are suitably mounted at the opposite ends of each of shafts 39, said wheels}, being disposed in the pp hannels racks. 8,. for. euid ..d mo m t therein along the top of tank 102 It is thus-seen-that the manifolds nd heir: ssoeiates in ttsa nelurli g nozzles; 3t);- carrhe ovedttghanyt-desi-redpositionnaerosss hetank between the end walls 41 thereof. 7

The w tlttni ees.enme al pa t Aiton xamdejn the form ofaluniinum or aluminum alloy plates, are suspended from suitable-clamptmemhersn lfissupported from rings 48 on ropes or chains 47 in turn controlled by a hoisting mechanism such as a crane, not shown. The maniteld. ssemh ies re. mo ed to e red position fore am 1e, as shoyvn imfiigsd and "2, andth'e metal plates. .4,S,,to beetchjedjareimmersedjvertically in ,the solt1 tion adjacent the, manifold assemblies; Figs; 1 and" 2 show three plate s 451 with again of manifold'asse nblies disposedbetvi eencach; ofj e thr eejp lates. It is obvious, of course, that' the numlpjer of'workpieces' 45f'andthe numherqfman told; Pr v d d hat tj e st. one. j ier ozz es 3018 d e wa d.. a hm t lih rfae ndergp nstet h s, the tank.

n t er- Q. mmerse, heworlqpiec s. pl s 45? inv the etching bath'll', or to remove them from theb'ath} a tream. Q pr ab y; moi t. air tom l manifolds: 22.. s."

ejected frornihe orifice 3 2 ofgnpzzles w against the, sur; face Q o thetp a es, 5.-.

tsnotednhatdhe n .zz e itl)' e.v loe edi a ove,

he urface. 1. a: .th t re h, ,lhyen 1.1,, uch vsu f ace.. .eii;1g,.

i i 591120 4 nez less is desi ned: eemitt re l-y' hi hly, i e s am, 52.-. fr, o ha re sgat elat els, arser r a of pin ement ofttheair:

r arna sa nst the; iaeentt urfae fitl fith plat s 5- Also it is; noted thatfiht rigts or streams: of preferably; moisttair are directed downward at-such anflangle; as to,

sweep the froth back away frQmJhesurfaces, 5i) ofthe P tes, extendin hro h: h i reth ay r; 1,,, il t he plates; are ,statiena yr hertei t rt rei in l w r d t t t dr o htthelfreth ayer, .senthat t-t i rt thiis substantia y prevented r frornrthus. ontcting; heepl test 5:- h is: targeaerifiee; 32;; be; e igned: o ave: a; iz nd. ap epe ntlonr e; esir dw leei y f: r r .-v

In -this manner; surfa s; 6;: ofivp a es; 55 eingm: mersed iruthe; solutionfor etchingmre stripped ofmny entrainedsetchanhdepositednn thet-surfaees thereof especiallysduring :passage through -;the 2011.6:53, above the. etch: ing solution in the tank. nificance; where the: plates 45 {are being; withdrawn from the etching solution' following treatment therein, surfaces; 50 0f Iplates- 45 are stripped-and irinsed of adhering etch: ant by the blasts; of; preferably moist air whichwash: down the platesurfacem-Sfla Also, as to; anyetchant unrinsedfromlthe surfacessoflthe plates 5ft y-the moist; air blasts, the latter will provide the metal surfaces with; a protectivecoating-which will imaterially reduce or halt the action of any residual adhering etchant and prevent. attack by a ny cartrained caustic-etchant in the: vapors abovethe" bathi The ratio ofmoisture in the air streams can; be -varied to produce certain efiects. Thus, for example, sufficient terl may, e. pr nt he. a r. streams, to esult. n

Washing down of the urtacesnfith s rhpi eel tend: 1

ssernblies rnay be varied as desireds lo atecuat b ntn -level bi umen- 12., T e eharees Further, and of particular Sigt tion of any adhering etching agent. This washing phenomenon can be accentuated by still further increasing the amount of moisture in the air streams so long as any undesired dilution of the etching bath is not obtained. If desired, such washing action can be reduced by decreasing the amount of moisture in the air streams and relying on the sweeping effect of the air streams to give the protection against the foam action previously dis cussed. However, it is preferable to have sufficient water in the air streams to give a washing effect and to compensate for water lost in the etching bath.

While the application of the invention has been described above chiefly with respect to passage of a work piece through the froth layer during its immersion into or Withdrawal from the solution, the streams of moist air can be directed against the part while the latter is maintained stationary in the bath during etching, where only a portion of the part is immersed. Under these circumstances the streams of air keep the froth substantially free from contact with the exposed surfaces of the part extending through the layer, as in the case where the part is moving through such layer during immersion in or removal of the part from the etching solution.

Also, the relatively cool streams of air emitted from the nozzles 30 have a lateral pressure component and form a sort of blanket of cool air above the froth layer in tank 10. Since the warm vapors containing entrained etchant and the hydrogen gas evolved in the etching reaction rise from the solution at about atmospheric pressure, such vapors and hydrogen gas are essentially prevented from rising through the streams of air emitted from the nozzles and acting as a blanket, and are swept laterally toward the sides of the tank beneath the air streams from the nozzles, and into suitable outlets such as conduit 13 and the stack 14. This materially cuts down the amount of entrained etchant in the zone above the bath and thus reduces pre-etching of a metal part passing through this zone into the solution, and prevents formation of a residual coat of etchant on the part during removal thereof following etching.

As previously noted, the ratio of water to air in the moist air streams directed against plates 45 may be adjusted to approximately balance the amount of water lost in tank 10. If, however, smaller ratios of water are employed in the air stream or blast, additional water may be added to the tank, as desired, through pipe 55 connected by bracket 56 to the top of the tank. Vapors and hydrogen gas liberated in the reaction and passing with any overflowing froth into pipe 13 and stack 14 are vented therein, and froth dropping into the bottom of the stack is drained therefrom through line 15.

The instant invention is applicable to the etching of any suitable metals including, in addition to aluminum, iron, nickel, magnesium, zinc, titanium stainless steel, etc., and their alloys. Further, it is noted that aluminum and its alloys may be etched in acid solutions such as hydrochloric acid or salts as for example ferric sulfate, as well as alkali solutions.

The following advantages are obtainable according to the invention: (1) control of foam and froth, (2) uniform etching of a metal part in an etching bath containing a froth layer on the surface thereof, (3) directing of the hydrogen gas and entrained etchant fumes to the exhaust equipment, (4) reduction of the amount of entrained etchant, for example, caustic alkali, in the vapors above the etching bath, (5) prevention or reduction of attack by any such entrained etchant on the metal part as aluminum or an alloy thereof, being treated, particularly by washing down of the part by the air streams, (6) cooling of the metal part by the air streams to reduce or stop the action of any etchant unrinsed from the surface of the metal part, (7) cooling of the zone above the bath, and (8) protecting the overhead equipment from the corrosive action of vapors containing entrained etchant.

Of course, it will be understood that the apparatus described herein should be constructed of materials which are substantially inert to attack by the etchant solutions employed, and those skilled in this art will know how to select such materials.

While I have described a particular embodiment of my invention for the purpose of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.

I claim:

1. The process of etching a metal work piece in an etching solution containing a layer of froth on the surface thereof, which comprises passing said work piece through said layer into said solution, etching said work piece in said solution, passing said work piece out of said solution and through said froth layer, and directing a moist air stream from a point above the surface of the froth into said froth at an acute angle to the surface of said solution below the froth line and against said work piece during passage thereof through said froth layer both into and out of said solution.

2. The process of etching a metal work piece in an etching solution containing a layer of froth on the surface thereof, which comprises passing said work piece through said layer into said solution, etching said work piece in said solution, passing said Work piece out of said solution and through said froth layer, and directing a moist air stream from a point above the surface of the froth, into said froth at an acute angle to the surface of said solution below the froth line and against said work piece during passage thereof through said froth layer out of said solution.

I References Cited in the file of this patent UNITED STATES PATENTS 1,081,289 Albert Dec. 16, 1913 2,293,201 Gaebel Aug. 18, 1942 2,347,511 Scarzello et a1 Apr. 25, 1944 2,370,495 Sebell Feb. 27, '1945 2,390,007 Sherman Nov. 27, 1945 2,566,142 Powers Aug. 28, 1951 2,724,918 Triman Nov. 29, 1955

Claims (1)

1. THE PROCESS OF ETCHING A METAL WORK PIECE IN AN ETCHING SOLUTION CONTAINING A LAYER OF FORTH ON THE SURFACE THEREOF, WHICH COMPRISES PASSING SAID WORK PIECE THROUGH SAID LAYER INTO SAID SOLUTION, ETCHING SAID WORK PIECE IN SAID SOLUTION, PASSING SAID WORK PIECE OUT OF SAID SOLUTION AND THROUGH SAID FORTH LAYER, AND DIRECTING A MOIST AIR STREAM FROM A POINT ABOVE THE SURFACE OF THE FROTH INTO SAID FROTH AT AN ACUTE ANGLE TO THE SURFACE OF SAID SOLUTION BELOW THE FROTH LINE AND AGAINST SAID WORK PIECE DURING PASSAGE THEREOF THROUGH SAID FROTH LAYER BOTH INTO AND OUT OF SAID SOLUTION.

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