Workshop Practice Series 11 - Electroplating

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11. Electroplating The techniques of depositing a thin metallic layer on dn object lor decoration, corrosion protection. electrical conductivity, wedr resistance and so on have been known for many years but have been developed and improved to a remarkable extent in the second hali of this century. This book sets out to discuss the principles and practice of those forms of plating most suited to the amateur and small workshop. using relatively simpl and inexpensive equipment to procluce results virtually uncletectable lrom work carried out by major plating concerns. Jack Poyner, a professional involved in all forms of plating for many years, is also a keen model engineer able to recognise the dividing line between what his average fellow enthusiast would consider practical and worthwhile and what is really better leit to experts in the field. The result is a really useful and practical book which will be of value to both dmateur and light industrial users in many diverse fields. ISBN 0-85242-862 -6

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Contents Chap'''' ,

IntrOduction and princip'H 0/ electroplating

Chap'''' 2

Chap'",3 Chapter 4

Chaptet 5

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Chap'''' 6

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Th, el.,nlng of 'he s"bSl,ata Th" "Kt,olyle

EIKtrofOfming and .'ecuopl.ting 0" non..:(lnducto"

EIKt,ol,," .'ea,opll,ing An example and Ihe c;:on,ide.atlorl 0'

.'ectroplating Chapte,9 I"de~

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Th" electrical Supply The e'eo;lropia ling lank

The finishing of aluminium and ill.llor-

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CHAPTER 1

Introduction and Principles of Electroplating Present d.... electropl,tlng h.. become I _II -utabli,heoclll'f. bosed on the an of

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Fig. 4 shaWl In electroplatong 'ank w"h enodes lInd 11 ~lI'hode !Wspendtd in The elect.olvte. Th" ~8lhode i, so Ihaped Ihat it h1l5 "US labelled h'gh current densnv lInd low current den,i'v. In elec · I'opl"ing Ih" component wnh,n Ihe IInge of Ihe currenl densilV la. the Plr' lieul., el«iroIVl" 'hG wmponent may Nove I coa'M. 'ough depol'l bu,1'II in Ih' h'gh current density ,rel Ind Intll 0' no depOsol ,n the low CUfflfl1 dens,ty • r... To Impro ... the depoln V'fOOUI m"ans If. pos"bll. The Inodl in front

CHAPTER 2

The Electrical Supply

elec:t.opllling. and WI\h • bulld·up of I(IlIpe,ienCllhey w>1I not be too d,ffICult

to eccomphll'l. However. mOSI ~ompanenlS are of. srraighlfofWlrd shape and will electroplale qune well when luspended in a bath. The olhe' Imparl.nl shapes in electroplaling are blind holll5. These p'ove difficull, leaY,ng 11"nl .round Ihe hole The best waV 10 ,tdu~e this ploblem ,. to filllh" hole w'th Wlx Or sim,l.!Jr mlle,i.l; IhlS will ,n .ffect "OP eleo;tropllll ' ing in th. holl. but w-II .edtJGe the staining effect On Ih' rompanent.

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Met.,s I .. mllnlv electrodeposiled bV the action of In electrical CUffenl. Direcl current IOC) I. l"lnlilll for electro· dlposition. Alle,nating curren, (AC) will not deposil mel.I •. However, th ..1 Irl vlI,iltiOJll on IlIlrnlting ,yslams which Ire slill bting developed. These methods g,ve .....ooth.. IInd denser metal depotll .nd Ire used in ~in lped,,./Id com~n'."';Iti/ /hrMJ

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.. ' ",pa"ta Itlm il dn"ld. but If you hava Inoogh loom Insldl thl battlry Chlfgll casing. you ean flltha COnl.ol Itlm.lnto thIS. Thin, whin thl Unil i, 0Ieded ... battlry ch •• glr, w,nd Ikct polllmllomlllf knob to fTMlI!mum vohs, maklng ..... thlll 11'11 one .mp meter is shOf1I1d 001 us'ng IhI 5 Imp switch, and you "1 ,e.dy 10 ch••g•. Should you m.ke the control unit IS. sapa.ata item, .. m.mbat 10 connect the ehaui, o. metal casa to tha matsl case o. chaUit of tha battary cha.ge •. F.g. 8 shows thl ci'cuit dl.gr.m which is vlry IImple. The potentJomlt.r is corlOectlld ac.oss tha ootput of lhe battary cha.ge., numbe.1Id 1 and 2 on the diltg.am, and the slidlng .. m 3 taps off the voltlog. I f .equ"IId,.mI is shown on th. voltmlllf

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11 you are electroplating a compon.nt thal .equi••• mo .. than one smp, then th. one .mp .mmete. must be .honlld oot by (IO$'ng the 5 .mp switch S.W. The higher .mpe"gl can then be teld on tne ch.rgar unil'. inllmal ammate •. When you "";sh to electroplata a small

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component 'equiflng than one amp, lu.n th' pOtantiomlte. right down 10 uto put minim ... m voltage In thl cir· cuit, open thl SWItch S ,W.. and with ll'Ie .nodes ami componlnll (cathodes) .I••.,ty in thl electrolytl, connect the control unit OOlput to the (l fot 11 dllV. 10 .... il any 1111" .p-

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pear. For metal 'snh thlt h8" 8 been welded Il'Ie S8mt1 checkmg for leak, Ipplies. For stl,nl"ss ,,"'tenks mike lu" 11 good lIt dipl .nd pickl ••. A typical Ulnk i. iIIu.I,"ed IInd th, fol·

Iowing numbers rei". 10 the' shown 1l_. Check all elactricel contact. on the tenk for he". If hOI. make lure Ihat a beller COnnlClion i. Obt.ined. (Heat dissl' pate. the current). Mak. lure III the sOlutions ere up 10 the requirld volume. If nOllhey a.elopped up wllh clean wale'. or distilled or daioni"d weler. Makl sura III Ihl anodH ..I cleln, and thl eonllct. 10 thl Inodl ba. a'l cl. .n. In all Ihl" lreas Ihl currlnt denSIty will v.ry if Ihere i. I bed CCH'IlIct. Ensur. III 'aetifier alact.icll con· tact5 a .. claln. Removl Ihl anode. and rinse whIn thl Ilact.olyte Is nOI in USI. Cove. th, ellctrolytes with lids whIn nOl In u...

The Cleaning of the Substrate The mOlt imponanl p ..t of thl lIact.o· pl aling P'OCI.. i. Ihl preperatlon and cleaning 01 the substrala. i.e. Ihe SUrfacl of the componlm prior 10 Ihe elact.o· plating Op!lrallon. This Plrt of the p.ocess delefminl' the appearlnce Ind the adhesion Ollhl electroplatee 4in. ~ 3in .• Or perfor.ted zie Ih"l Sin. ~ 600. boughl from you. 10:.

per II.UOn. 25grms pe. ""e. C«N:.nrr.ted Ammonl. 1.880 S.G) 6 fluid oz. pe. gallon. 375ml,. pe. lot ••. W.,..-Io mlk. up to '1I.11on (0' litr.). Le.v. tha eomponenl In the IOlut,on unt,1 th. desirBd sh.d. I, obt.lned. for d •• p bllld.s, h.allh. IOlul'On. bUI nole Ih ' ammonia w\ll lume and lIiv. olf • '''onll smell, Ih ••• fo.e it mutt be w.1I .... ntillted o. done outdoors. In both cases, wh.n IIM COI.ect coloo. ;. obt.ined •• inse in cold w.t .... ttHIn in hOt w"e'. and lelve to h..den olf the leye •. 00 not touch the colou.ed surfac. until h •• dened.

Brown M.k, up Double Nick.1 S,II, O.5oz. pe. 1I.1l0n 311'mS pa' "t ••. COP{H' Sulpllat. 0.5o.r. par lIallon 3grml per lit ••. Pot.mum Clllonte 0.5o.r. pe. 1I.llon 3grms pe. litra. UM Ih.lOlution al6O"C. "",th In Int •• • medlat. scr.tch-bfulhinll to even outlh. colou •. W.Minll off imp.O'I.' Ihe colour Nor. Potassium Chlo •• le i. e powerful oxidisinll Ig.nt, and Ihe pow. d., mull be kept in • well SIOppe/Bd cont.lne •.

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81ue Colou. (P,uivata) M.ke up Sodium OH;/!romlte 0.8o.r. pe. g.11on Sg.ml pe. litre. COfI(;"''''Ied Nitric Acid 3.2 fluid al. pe.

1I.1I0n 2OmJ •• per "tr • . D,uol.... the sodium dichrom.le In ooe IIt.e of Wile •• then add Ihe nlt.ic add car.lully. "i"lnll well in .Iowly The balh ;. ope.. ted at room lemper •• tu.e. Th, immersion time \ 0 to 20 seconds. IrId ...... nt CoIoo r (Pauivete) Mate up Sodium Dichrom't' l00.r. pe. 1I.llon 6Og.ml pe.lit.a C~ntr.red Sulphurit Add 0.511uid oz. pe. 1I.llon 3.Omls. pe. litr. 011101\1. tM sodium dichromat. in th. voluma r~uired. th.n add tM< con· e.nt.ated lulphu.ie acid slowly and ca.elully. Itl.ring continuoosly. Th. baTh i. ope.atad .t .OOm tamper.lu ••. Tha imm ...ion Ilm. is 8to 10 lOCOnd, CARE WiTh nItric acid Ind sulphu.ie acid, IIlov•• , 1101111181 .nd ov...1I1 mUll beWOfn. Th' Iln !WO formulations ' .. pU" pnsiv"a coatinll'•• nd It. left for 24 hoofl la hltden off belo •• funh..- 1,1111. Afta. hafCMning off th.y CIOn be plinted if requ ired. Th" combinl!ion 01 l ine. pluiv"e Ind pllnt olf... llood CO" .0slon '.Iilllnce 10./0"01,11 malals. NICKEL ELECmOLYTES

Nickel off.r. llood corrosion r,"i,"nce whon ,IKt'OpI.,ed on bolh let/oul and non-Ietfoo, ma'.I, .uch as copper .nd .110.... of copper. 1lMI mec.hlnitm of nickel. copper .nd tin .Iectropl.ting 11 thlt """ dg i.e. lICfiflCi.1. A good .11 round nick" .lectroIyt. is " lollows :.

w.tt'. Nickel 38.50z.pe. gallon 240g.ms pe.lil ••. Nk:kal CII/on"de 7.2oz.pe. 1I.llon 45grms per "Ita. Boric Acid 4.80 •. pe, 1IIIIon 3()g.ml per lil, • . To mike up tM< ,Iecuolyt •. w.rm up three qUlrte .. o ltM< 'tOluma 01 w.ter. Idd The w.illhed .mount 01 n,cIt;.lsul· ph"., sti, .•nd WI.m until dissolved . Then add tha weillhed Imount 01 nick.1 chloride. r.pelt until d'ssolved. Finally. ,dd the bo.ic acid, which willt.ke tima to dissolv•. AIt.r '"lh, chemicals Ira in IOlulion, maka UP 10 th. required 't01. ume with W.I .... Th .. p.H thould be checked by wh.t· ...... mean •. papefl O. p.H meter. Tha p.H Ihould be 3_5. It is recommlnded th.t th;. soIUI;On be 'plat.d oot' I1 • Iow curr.nt with tom. scrap lleel pllla IImilar to Th" No.2 zinc alectrolyt., Till . will .emov. th. diSSOlved Imputitias in Ih. nickll Nickel

Sulphlla

alec!ric he.,er ;. und. 1lMI ev."nT clantlTY .. ~' is from 10 •.•.1.104O . ..... or l .oa.dm 104.0. dm' Thi. i, as pr.viously m.ntloned. The pan 01 tM ,.nga chosen il dependant on th. shape of Iha companlnl and the t.~lu.e of th. daposit required. Th. low •• tha Current danSlTy Th. lin •• the daposit. Thi, ,lectrolyt. w ill dapo.il:. 0.OOOlin.(2.5microns) 11 lOa.'" in 15 minutes or o.OOOlin.(2.5micron.) at lOII ... 1. in 5 minUles. Thil electrolyt. gl_ a llood dull 10ft dePOSlI which will polilh up to I hlllh IUllrl. III p.opetli •• 11 •• not lI.eatly Iffected by I wide ch.ng. In p.H, tarn. peratu.a Ind balance 01 ch.mical com. position In tha bath. Wh.n this deposit i, ov.r"lectro_ pI.ted w'lh decorative chrome illllves. plea,inll dull chromo effect. IImilar to the finish on mic.om.t..-. Ind simil•• tool • .

Seml·8rllilht Nickel EIac!.olytl Thl. Is baNd on I Wail's Formulllion with tha .ddition of an orllanic b.illhT· en ••. ulll. Sulphltl 38.~.pe. lIallon Nick" The anod •• uMd in Ihis electrolyte 240g.m. per litre . ..I 41n. ,,4in .•'11lI 01 pure n,cIt;.1. Thelll Nocllel Chloride 7.2oz.pe< ".1I0n 45g.ms can be Obtained Irom .Iectroplatlng PIf'ille .upply hou,,". Thi •• izl 'pproMim" •• BorIC AcId 4.80z..per "lIl1on 3()grm. pe. to tha .nodes uMd on Hull c.J1 Appa •• li"a. 811,1,. How ....... for. 1"lIa Nt·Up bas_ Saccll.n"n. 0.32oz.pe. 1I.,IOn 2.Ogrms keled nlckal.hot o. hoolt;ed Inodes may pe.lit.a. be used. buttha.. eln be •• pens;"'e. Th, alectrolyt. IS m.da up .. for Ihe The ope .. tinll t.mpe.atu.a for this prevloul nick.1 eleclrolyt. (Wall.), but el.c1tolyt. Is 5O'C 113O'FI. with th. addilion at Th. end 01 the Thl hea,inll m.y be accomplished by waillhed .mounl of sacch,"ne. Thil is vllious method •. If • "ainless steel con.tantly "irrBd wh.n wa.m, unlll dis· COntlina. is used, I 1111 ring i. placed IOlvad. Th .. d.ssolulion may t.ka some underneath, If th. con",in.. is Pyrex lime because SI (h~.in.I'I'IOI.-.rv ..,1111.15 o. pI.stic, Ihln.n aqu.rium TYpe ubi • •

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The ..me current deflsity .anges apply lor Ihi. I. for the ptIYious electrolyte. u ~II uthe IImperlluI:l y ./«;t,,:>forming..., In 11 wckmg d'e .1I0wo~ 1I 10 W uHI.

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'rom low m"lmp (JOIn' alloy. N(I1. ,,,.. in"",

mw/lied in 10' e H'Klng Pe ..".,,, Windows, and COMHIlylhen, Iype). The sulphuric acid il Idded ,lowly. Ind stirred con. tinuously. All,. lhe Idditlon ollh. Kid. add the potelllum fluo.rd., slIrrrng con . linuously until dllSOl"rtd. Allow to COOl to .oom tl'll'lperature. Adjust to linll "01. ume wi!h W81er. Use Ihe stripper It room temper.lu... Allow the com . pc>nen15 to '''nd In Ih. ''';PP'' untIl the anodise i, d,llolvtrd off. The info, . mat ion on stripping d.fedive Inodi .. in chapter nine i, IIill rele~enl, but e separe" .Uipper mey be needed, especielly WIth dyed pen" which would colour the !he lnodise pre-trutment This glvtrl e choice.

6). Fo r Itrlpplnt tin trom steel end c:GpJl4f Ind Its ello.,... The lollowing lOIution C4n be used:Meke up:· CopPlr sulphete errsfe/s. 6 Ol, per gal· Ion 50grms per litre. Concentrated sulphuric e"id. 1611.0:.pI. glllon loomls per lit ... Water. to meke up 1 gellon Ho make 1 lit ..), The solulion is used et room tampe'l' ture. All tha listed IItippers can be used in plntic con"i.,..,. lik, pOlylhllne. CARE w ith sulphufic Ind nitr~ Kidl, both .rI corro.i~a. Use goggl •• , glovtr$ Ind OVllralls. Add acid to water. nOI ylce· versa. Watr;h fo. h"1 generated by the f41Ci;On. After .ach Plft 01 the pro' cessing. i,l. belween 1114 cleaners. pickle, bright dip. .ndthe electrolytes. 1

cold wit.. rinse must be carried out Thi' cleans the component.. end stops the .Netion, and pr_nil C4rrv-over 01 the solutions, thus pr_nting conllmi_ nllion. All of the lormuletion. hive I~c!uded ,1I\h' cyanides end chromic ,cld. They hay. "-en mentioned in Ihlle~t. but the '8Ison lor excluding the.. elect.olyles. auch .. silve, end gold. 11 because they COnllln cyanide. You might be eble 10 purd>.SI !h.m from th' VI"OUI IUpply housel. but td>edulee Will il then twisted 10 .n.... '. I rigid

contact. Tt,,, 'e51 of the componen" I',

wired lhe sama. if vou •• e anod .. ing I batch Or I sel of component • • The wired components should hlng Ipp.o_i. ma,ety midway in ,he elllCtfolyll, ..,,,th an allowll'ICfI QlOl.l'. Some allo'(l conUrln alloy con,muanll luch .. mang,...,....!rcon. magnesium and copper. If the.. materials are pr,""nt between 5%-8%. ,hey produce a coIor. t.on o l lhe ..IOdised him. Th. colore"on varies from a brown for mangan,"", for silicon Ind mag ...... um I bluish g.ey.

and for eopper In o"nge yellow To obelin I consistent ,.p.odOKible uniform colour, the easiest and most ,",nomal wily ia to use an orlllnic dye tllat i. soluble in waler. To obtain the re· qui.ed sha de of colou. y",oua con· c,nt.ations of 'he dyes have to be used. A guide is between I IIrm.pe. li,re 10 100,ms pe. lit ... O.1SoB.pe. gallon '0 1.60z•. pe. glllon. This concent.ation will plso yary wilh colou •. ()pe