Preparation of basis metals for plating

PREPARATION

OF BASIS METALS

FOR PLATING

by Earl C. Groshart Consultant,

Seattle

If a plated deposit is to realize its full value on a part. it is absolutely necessary that it have the best possible adhesion to the part. The part must he scrupulously cleaned to achieve any adhesion, but to achieve maximum adhesion. each basis metal must he treated to a y;crie\ of steps that remove all traces of foreign materials and leave it active enough to form metallurgical bonds as well as physical ones. The processes given here are intended to do this on a production basis. Where common producrion solutions can be used. i.e.. \olurions thal can be for more than one metal. they will be specified. It will be assumed that parts reaching the plating department or shop will have been made ready for plating. All machining, grinding. polishing, straightening. and other mechamcal operations should be finished; all heat-treating, thermal aging, and stress relieving should have been accomplished; and all mill scales, rolling scales. or heat treating gales should have been conditioned for easy removal. Other sections of this G~ridrhook (cleaning. pickling, polishing. etc.) provide complete instructions for accomplishing many of these operations.

PRECLEANING Precleaning is designed to remove the bulk of the contamination from the part surface in the least expensive way, thus protecting the more expensive and more important final solutions. It is also the step necessary to provide a part that is clean enough for masking and racking. The first step. which was traditionally done with solvent vapor degreasers, has largely been supplanted by modern solvent/water or alkaline emulsion cleaners hecause of the environmental and health haLards associated with degrea\in g \olvenls. Following cleaning with these emulsions, the parts should be thoroughly rinsed. Alkaline cleaners devoted to the removal of grease, oil, polishing or drawing compounds, grinding and machining coolants. and general shop dirt will work equally as well as aolventa, but should be restricted to those jobs and should not he expected to produce water-break-free surfaces. Heavy rusts and scales muht he removed prior to plating. Pickling. sandblasting, 01 electrocleaners are used. When electrocleaners are used. it is best thal they not be the same solutions used in the general plating lines. Once the bulk of these soils has been removed. the parts should be clean enough to apply any required mackants and to rack.

LOW

CARBON

STEELS

Cleaning Thorough cleaning, either in a strong alkaline soak cleaner (pH above I I) or in an anodically operated electrocleaner, is the first step. The cleaners should be free rinsing and suitably compounded as steel cleaners. The preferred electrocleaner should be operated hot (up to 200°F) with a current density of 50-100 A/f? with a voltage source of6-0 V. Hot soak cleaners may require mild rack or solution movement. Use l-4 minutes for electrocleaning and up to 30 minutes for soak cleaning.

194

Rinsing Rinse preferably in a two-stage rinse in warm (140-I 150°F) water. A fog spray top of the cleaner tank helps to keep the hot solution from drying on the parts before rinsed and can be used to replace evaporation lo\ses. Rinse thoroughly: at thi\ \tagc must have a water-break-free surface, i.e.. a surface where water form\ a \hect breaking over unwet arcas.

over the they are the parts without

Activating Without drying, immerse the parts into an acid solution to remove any light oxides. rust, or scale. A S-10% by weight solution of hydrochloric acid (31%) for S-IS seconds at room temperature is preferred: however. higher concentrations and temperatures arc also usable. A I Oc/ solution of sulfuric acid at room temperature and a I O-20% solution of sulfamic acid arc also excellent activator rolutionh.

Rinse Follow immediately by another rinse. preferably cold water, which can be followed by a warm water rinsr if the parts arc going into a warm plating solution and transfer time is short enough so that they will not dry bcforc being immersed in the plating solution. If plating i\ not immediate. they may be stored in a solution of Z-4 oz/gal of sodium hydroxide or the alkaline cleaner up to several hours. After removal they should be rinsed. given an acid dip, another Irinse. and plate. As an alternative to acid treatment for activation. treat the part in a periodic recerse solution as given under High-Strength Alloy Steels below.

HIGH

CARBON

STEELS

These steels (over 0.35% carbon) require much the same treatment as low carbon steels. but because they have a tendency to form a smut during the pickling operation, an extra step is required to remove it. Also. because the higher carbon steels are used in the hardened condition and under sustained load5 (parts such as springs and lock or bellvillc washers). they must be treated so that they do not become embrittled during the platmg operation.

Stress

Relieving

High carbon steel parts. which have been subjected to any cold working except shot peening or polishing, should be stress relieved prior to plating. accomplished by baking at 350--IOO”F for 0.5-3 hours just prior to the final plating steps.

operations, This can be preparatory

Cleaning Anodically electroclean in free rinsing alkaline solutions using for low carbon steels. Soak cleaning is not recommended for racked in a soak cleaner i\ preferred for bulk parts. Thoroughly rinse.

Oxide

the technique5 established parts; howeve!-. tumbling

Removal

Treat in 10% hydrochloric required to remove the oxides, at 120P140”F for the minimum

acid, without inhibitors. rust, and scales. Alternatively. time can be used.

for

the minimum a 20% solution

length of time of sulfamic acid

195

Smut

Removal

Smut, which may have formed, cleaner can be used, or, if the smut follow\

must be removed. Anodic is light. it will be removed

treatment in the electrolytic in the etch treatment that

Etching Anodically etch in a sulfuric acid solution (up to 70 oz/gal H,SO,) at a temperature below 85°F. The addition of Na,SO, (15-18 or/gal) will help provide a microetch on the harder. high carbon steels. A current density of IOU-400 A/f? for a time not to exceed 2 minutes is sufficient. Thoroughly rinse The periodic rcvcrse treatment shown for highstrength steels i\ an effective alternative.

HIGH-STRENGTH

ALLOY

STEELS

Steels, which have a hardness of Rockwell C 38 or above, are considered high strength must be treated very carefully to prevent hydrogen embrittlement of the steel. Stress relieving of these steels just prior to plating is very important as any cold working of the surface just adds to the embrittlement problem. If no specific baking time and temperature are given for the operation, the following general guide can be used. Stress relieve bake at a temperature SO-75-F below the tempering temperatures (XOO‘F maximum) for the material involved for a time of 3 hours minimurn. If the tempering temperature is not known. bake at 350~400°F for 3 hours minimum. and

Abrasive

Blasting

Technique

The most popular procedure uses dry abrasive blasting of the parts after a suitahlc precleaning for bulk grease. etc. removal and alkaline cleaning. Aluminum oxide, garnet. OIother Gtable nonmetallic abrasives should be used. Plating should be started within 30 minutes of blasting. A IO-30 second dip in 3-S?+ hydrochloric acid (followed by a cold waterrinse) ju\t prior to plating has been helpful in promoting adhesion, providing a mut i\ not formed. Smut< can he treated as for high carbon steels wjhcn rcquircd.

Electrocleaning

Technique

After parts hate been suitably prcclcaned. masked, and I-ached. they can he treated electrolytic cleaner losing periodic reverse current. There are many commercial solution\ are satisfactory or the following formula is suggested. Sodium hydroxide, IO-20 or/gal Trisodium phosphate, S-10 or/gal Glutamic acid (monosodium glutamate). Surfactant. as required to foam smoothly

4-X

in an that

o//gal

This should be operated on a periodic reverse: IO second.\ cathodic-10 seconds anodic: always ending on an anodic cycle. The bath can be operated from room temperarure to 150°F. the warmer temperature heing required to remove heavy scales. Time sill range from 2 to 20 minutes. depending on the amount of scale, oxides. etc. to be removed. This treatment is followed by through rinsing, first in warm water followed by cold water. The part should now be ready to plate. A short dip in a sulfamic acid solution ( I O-I 2 ozlgal) at room temperature will enhance adhesion on those
196

Postplating bath

Thc\e steels will require up to 23 hours used and the hardness of the steel. The

of bahing after plating depending on the plating plating procedures should be followd carefully.

STAINLESS

STEEL

The plating of stainless steel is complexed by the immediate formation ofu pa\\i\r oxide on the cleaned surface. An adherent plating cannot be applied to this pauive film. w a simultaneous activation/plating step is included. The removal for processing soils, polishing compounds. etc.. follows the standard pl-ecleaning steps for steel. Because of the poor conductivity of stainless steels. extl-emel) good rack contact should be made. It i.\ also advisa hle to increase the area of such contacth or to add extra contacts.

Alkaline

Cleaning

Both soak cleaner% and electrolytic cleaners can he ubed. For high chrtrmium slecl\ and highly polished steels, the minimum exposut-c to the high alkalinity and high current dcnslty of steel electrocleaners i\ recommended. as they tend to “frost” a bright finish.

Activation Cathodic treatment of 5 Aifl’ in a room temperature solution of I210 w/gal of sulfuric acid (5.g. I .X) for l-5 minutes, followed by a quick rinse and immediate nickel plate will hc wtisfactory for most trf the IOLV chromium-nickel alloys and the PH hwdenable alloy\. hut the univerwl activation ttwatment is the simuIt;mcou\ acGvation/nicheI strike pl-occdure. known a\ the Wood‘s nickel wihc. The hydrochloric

formula acid

for this need is ~recommcndcd.

not

be

Nickel chloride, I643 orlfal Hydrochloric acid, X-32 11 w/pal Operate at room temper-aturc using Plate. I --I minutes

precise,

nickel

anode\

but

a

and

I:I

tratio

a current

of

nickel

density

chloride

oU 20-200

and

Alli’

The both i\ s~~ccc~\fully ued by starting worh nnodically at 10~1-0 Aif6 for 2 minute\, followed by cathodically treating as shown 111 the formula. Other pl-ocedure\ place the wol-h in the wlution and allou it to \it for a few minutes. then plate. Fcrrou\ chloride ma) be cub\tituted for the nlckcl chloride when it is nece~sxy to reduce the LIX of nickel because ~rf EPA and health wnvderations. This treatment mill leave the stainles\ steel in an active condition. ready 10 recelvc other plating; however, thi\ actibitv will last only a short while and will be lo\t if rinsing and plating do not follow immediately. Rinvx should have a pH below 7, hut no special requirement other than not contaminating the rinw with alkaline solulions is nrcestry. Whcncver pooible. current should be on the part5 v.hrn they are immersed into the plating hath.

ALUMINUM The surface

198

first step in plating aluminum layer and provide a fine etch.

involve\ an alkaline A 1-3 minute imml’r\ion

etch

of the surface in a hot (I 60-l

to remove the 80°F) solution

containing 3 oz/gal of sodium carbonate and second immersion in a 5% solution of sodium

Acid

3 oz/gal hydroxide

of trisodium at 120-140°F

phosphate. or a 30-60 will accomplish this.

Treatments

The alkaline etch will expose many probably leave a light smut on the parts. acid treatments are recommended.

Pure Aluminum Dip

of the alloying elements in the various To remove this and provide an active

alloys surface.

and will various

and the 3000, 5000 Series

in a 50%

solution

of nitric

acid

at room

temperature

fol- 30-60

seconds.

2000 and 6000 Series Etch l-2 minutes a 30-60 second. room

in a hot (180-F), 25% sulfuric temperature. 50% nitric acid

7000 and High

Castings

Silica

Dip in a solution that is three seconds at room temperature.

parts

nitric

acid

acid solution. solution.

and one

part

followed.

hydrofluoric

after

a rinse,

by

acid,

for 30-60

Zincating Following method. which solutions are:

these steps, the most popular method of applying plating is to use the zincate applies an immersion coating of zinc on the cleaned part. Some suggested

I. Sodium hydroxide, I6 oz/gal Zinc oxide, 2.7 o~/gal Sodium potassium tartrate, 6.7 oz/gal Sodium nitrate, 0. I3 &gal Time, 30 second5 2. Sodium hydroxide, 67 oz/gal Zinc oxide, 13 oz/gal Ferric chloride hexahydrate. 0.3 oz/gal Sodium potassium tartrate, I .3 oz/gal Time, 30-60 seconds The double zincate process applies the first zinc coating, followed by an immersion in 50% nitric acid solution to strip the zinc, then the zinc is applied as a second coat. The second coating is much more uniform than the first. Commercial zincate and commercial bronze solutions are aljo very successful. as is immersion into a noncyanide zinc plating tank.

Copper The

Striking zinc

surface

is now

plated

with

copper

from

a low

pH

bath.

One

formula

is:

Copper cyanide, 5.6 oz/gal Sodium cyanide, 6.7 or/gal Sodium carbonate. 4.0 ozlgal Sodium potassium tartrate, 8.0 oz/gal Free cyanide (by analysis), 0.8-2.0 oz/gal Temperature, 120-l 30’F

199

pH, 10.2-10.5 Current density

and

time,

25 A/f?

for 2 min.

then

15 A/f?

for

3 min

An

alternative is to apply electroless nickel in place of the copper. This is c\peci;dly if the final coating is to be electroless nickel. A third alternative for wrought materials is to anodize in a standard chromic acid anodizing bath (10% chromic acid) until the voltage reaches 20 V. Immediatei~ remove. rinse. and ap& electroles nickel using an auxiliary anode to start the plating. themicallv can he treated in a phosphoric acid anodize bath until . .nure (CP) aluminum the voltage starts to rise, then it can he transferred to a chromium bath for direct chromium plating. useful

COBALT Cobalt and its alloys react to plating much as stidnless even after scale conditioning treatments, ia difficult The nickel or ferrous chloride solution shown under following limits, is ~ucccssful in plating cobalt:

forms,

Nickel or ferrous chloride, Hydr~~chl~~ric itcid. X-35

es-70 ozigal

steel and to remove. Stainless

Steel.

The oxide uperatcd

that to the

ozigal

The bath can be opcmted slightly above room temperature, for 5 minutes prior to turning on the anodic current at I00 A/f? the part. Transfer through a quick rinse to the plating solution. go into any cyanide or alkaline solution with the current on Using the sulfuric anodic etch shown under Nickel will cobalt. hut the nickel strike should be used. Cobalt chloride. make up the strike. which can he used with either coh:ht or

COPPER

nickel.

AND

COPPER

up to IOO”F. as a \oak pickle for 24 minutes to strike plate It is generally a eood idea to at low voltage. remove any heavy scale5 from when available. may he used to stainless steel anodes.

ALLOYS

Precleaning Removal of heavy scales. oxides, drawing pickling section of this ~lli~~~b[~~~~. Oil. grease. emulsion cleaner.

Alkaline

lubricants. and organic

etc., is covered elsewhere. in the soils can be removed m ii standard

Cleaning

In gencr& the cleaners used for steel can be used for copper. Soak cleaners with work rod agitation arc satisfactory. although electrolytic cleaning is preferred. Both anodic and cathodic cleaning are satisfactory. Anodic cleaning may cause slight etching of the material. particulurly brnss. if applied for long period& of time. Cathodic cleaning may cause smutting. Commercial cleaner\ are recommended. hut a basic formukl can be used: Sodium Sodium T&odium Wettin&

200

hydroxide. 5-8 oz/gal carbonore. IO- 15 o&gal phos~~hatc, S-15 otlgal agent. 0. I or/pal

Temperature, I40- 160°F Current density, IO-30 A/f? Time, l-3 minutes cathodic;

5-10

minutes

The same solution, with or without small parts that can be tumhled.

anodic

the sodium

hydroxide,

can he used

as a cleaner

for

Activating Solutions of S-1010 by volume of sulfuric acid or IO-20% by volume of hydrochloric acid are commonly used. The solution should be at room temperature; immersion time should he lesh than 30 seconds. The same HCI pickle can be used for steel, but close control of the dissolvrd copper must be observed or it will plate out on the steel, usually as a black powder. Parts to be plated in a fluoborate bath can he dipped in 8-10s by volume fluohoric acid solution, then transferred to the plating bath without riming. Leaded copper will require dipping in a solution containing nitric acid. as the lead will not dissolve in the other acids. A solution containing IO-20% by volume nitric acid and 2-5s by volume fluoboric acid is satisfactory. When %right dipping” is used, the parts may go directly through the rinse to the plating bath. Beryllium copper forms hard-to-remove scales during heat treating operations. Solutions I and 4 under Copper Alloys, found elsewhere, in the pickling section of this G~idehook. will remove these scales and leave the beryllium copper in an active condition.

Striking A copper strike is recommended for the brass alloys. the beryllium alloys. and the alloys containing lead or containing soft solder (such as at joining seams). A nickel strike or thin nickel underplate is also desirable for plating nickel, chromium, or gold and is necessary for rhodium and platinum. Silver requires its own strike, even when copper and nickel have been used. See the individual metal sections elsewhere in this GuidrhooX for solution chemistry and operating conditions.

LEAD Lead cleaner,

and ending

its alloys can be successfully on the anodic cycle. Any

plated standard

by cleaning electrocleaner

in a periodic reverse is satisfactory.

alkaline

Activation 1, Treat for 15-30 seconds in a IO% fluoboric acid solution to which 3-h fl oz/gal of 30% hydrogen peroxide have been added. Rinse and plate. 2. Anodic etch in 4-109 fluoboric acid solution for 5-l 5 seconds at 6 V. Rmse and plate.

MAGNESIUM Magnesium is a difficult-to-plate metal with many varied alloys adding to the complexity of plating. For a successful production operation, process should be tailored to the alloy and form; however, the following work for most alloys.

and several forms, it appears that the general process will

201

Cleaning extra

Soak in a caustic solution caustic work satisfactorily.

with

the pH maintained

at I2 or above.

Steel

soak

cleaners

with

Pickling The

following

For AZ31B

pickles

are recommended:

Alloys

Chromic acid, 45-50 w/gal Nitric acid, 2-3 ozlgal Hydrofluoric acid. 0.5-0.8 oz/gal Room temperature for I-S minutes

For Other

Alloys

Phosphoric acid. Room temperature

I X0-200 w/gal ( 130 minimum) with mild agitation for l-5 minute

immersion

Activator coating

Following pickling. on the surface Phosphoric Ammonium

part\ are activated to prevent oxidation.

acid, 32-3X bifluoride.

oz/gal 7-9 w/gal

in the following

solution.

This

form?

a fluoride

fluorine

Zincate The fluoride of zinc.

will

dissolve

in the following

bath

and be replaced

with

Zinc sulfate, I-I .6 ix/gal as Zn Tetra sodium pyrophosphate, IO-I 2 w/gal as pyrophosphate or Tetra potassium pyrophosphatc. I O-l 2 w/gal as pyrophosphate Temperature, I40- I SO’F for AZ3 I B; l60- 190°F for other-s Mild agitation Immersion time to form a uniform blue-gray coating, l-5 minutes

Copper The

Strike Lint

surface

is now

copper

plated

in the following:

Potassium cyanide, 9.0 a/gal (0.5-l .5 as CN) Cuprous cyanide, 5.5 oa/gal (3.6-3.9 3s Cu) Potassium tluoride. 4 oz/gal (I .0-I .3 as F) pH, 9.6-10.4 Temperature, 130-I JO’F

202

a blue-gray

coating

The bath should be mildly agitated and operated with twice the anode area as part to prevent polarization. Parts should go into the bath with the voltage set at l-2 V and be adjusted quickly to prevent gassing. A Rochelle copper strike has also been used effectively. The copper-plated parts can be plated with whatever metal is required. The noncyanide alkaline coppers, which are replacing many cyanide coppers. have shown to work satisfactorily, but testing before starting a production facility is recommended.

area then now been

MOLYBDENUM Molybdenum temperatures.

Alkaline Any

is plated

to protect

it from

catastrophic

oxidation

when

used

at very

high

Clean electrocleaner

will

be satisfactory.

Soak

cleaners

used

for steel

are also

satisfactory.

Activation Anodic

etch

in the following

solution:

Sulfuric acid. I I8 oz/gul Phosphoric acid, 96 ozigal Current density, 70-80 A/f? Time, 2-3 minutes Room temperature Treatment

is followed

by etching

in the following

soIuGon:

Pota\\ium ferricyanide, 10 or/gal Potassium hydroxide. I.3 o~/gnI Current density. IO0 A/ft’ Time, l-l 3 minutes Temperature, 185°F oz/gal

Strike immediately in a standard H$O,. This can be followed

high chromium bath containing by plating in a chloride nickel

67 oz/gal bath.

CrO,

and 0.67

NICKEL Nickel and high nickel alloys react like stainless steels and can be treated in the same simultaneous activation-nickel stl-iking baths. Anodic etch in 35% sulfuric acid at 20 A/f? t’or IO minute\. followed by 200 Aift’ for 3 minutes, and then treat cathodically for 2-3 minutes at 200 Alft’. This will allow for heavy deposits and simultaneous addition of
203

SILVER Silver and its alloys are very corrosion resistant to atmospheric oxygen. but arc susceptible to tarnish by atmospheric sulfides and nitrates, so they uill have a dark to black appearing tarnish or scale as they emerge t’r‘ronn manufacturing and polishing operation\. Polidlmg conqxwda are removed in the uwal way with alkaline cleancrs and solvent!, (we Precleaning). Electrolytic cleaning (24 V for 1-2 minute\) in a solution of sodium hydroxide oI’S- IO w/gal at room temperature will ~mwe this tarnish. To aid in quick removal. the same solution can be used &arm at 100-120°F. This is lidlowed by a rinse before moving on. Immersion in a 10% solution d 30% by volume hqdropen peroxide \bill remove sil\c~ tarnish and leave the surt’acc platablc.

TITANIUM This rnctal bonds the plate differ-ently and

i\ difficult to plate and with tno\t known mctho&, a thermal treimwnt. to the titanium. i\ necesswy to get atisfactory adhesion. Various alloy\ require tailwed proceswh ah shown.

which react

Cleaning The titamum.

I-S

%mdard Chemically

methods of providing pure (CP) titanium.

wrfxe a water-break-tree hA I JV and -IA I-3Mn. may

This i\ t’ollowed by plntin g chromium. copper from FoIlwing the final plate thickness. the part is baked hours at X00- I ,200‘P.

are ratisfltctorq be trcatcd:

an acid bath, or nickel. in an inert atmosphere

(arpon)

for

l’ot

Cl’ titanium. 3A I -5C‘r. SA I-Xr-2 Mu, hA I -V, can be trcatcd as follow\: Blast clean all alloys with it Iquld slurry of pumice, eluminum oxide. or @ass brads. Grit \ize can be from 100 to 1.250 or any of the pumice flour\, but should only he t~srtl fat tit;mium. Immediately ai’ter blasting. the part\ should be rnckcl or clcctroles\ nichel plated. For ~nall areas. brush plating is satisfactory. Adhesion with thi\ method is \c~-y good. Bahing may not hc quit-cd, c\pccially with bl-ush-plated nichel.

TUNGSTEN

204

Anodic

etch

in the following

Sodium hydroxide, 0.5-2.0 Temperature, 13S-14~5°F Currcnl den\itb ! SO- 125 Time, to remove required To remove

light

scales,

solution

to remove

surface

metal.

acid

at room

oz/gal A/ft9 metal

anodic

and etch

scale in 10%

sulfuric

temperature

at 50 A/f?.

Activate I Treat in a 20-40s solution of hydrofluoric acid at room temperature, using 4-6 V AC. Use either two parts in the solution or a platinum electrode as the second part. Plate immediately in an acid electroplating bath. 2. Treat by anodically etching in a 4 oz/gal potassium hydroxide solution, I20-140-F, for 2-3 minutes. Rinse and then neutralize in a 10% sulfuric acid solution. Strike immediately in a chromium bath, 33 oz/gal, 100: I ratio. This is followed by immersion in a 20% hydrochloric acid solution for 2-S seconds, rinse, and then nickel sulfate strike. The desired metal can now be plated onto the part.

ZINC-

AND

ZINC

ALLOY-BASED

DIE CASTINGS

Zinc castings usually require a number of mechanical operations to smooth the parting lines and the rough cast surfaces, and to repair defective surfaces. This operation may leave greases and buffing compounds burned. caked, and ground into the parts. It is advisable to remove these as soon as possible to prevent etching of the metal. which can occur if compounds are left for long periods in a moist environment.

Precleaning Alkaline emulsifiers can be used with brushes to remove Solvent emulsion cleaning may also need some mechanical compounds. Spray emulsion cleaning is effective.

the heavy assistance

buffing compounds. in removing buffing

Cleaning Anodic electrocleaning mixed alkalies, trisodium than 0. I oz/gal) sodium should be limited to 3045 required if the solutions warm rinse followed by required.

Acid

is recommended. The cleaner solutions should be phocphate, metasilicate, etc., and should contain no hydroxide. Current densities should be 15-30 A/f? seconds for solutions operated at I XO’F. Longer operate at lower temperatures. Rinsing is extremely a cold rime, followed by a second cold rinse. are

made up with (or not more and the time times may be important. A the minimum

Activating

A 2545 second dip in a 0.25-0.50%~ sulfuric acid solution at room temperature should remove smut and zinc oxides, which tend to form in the alkaline cleaners. Again, thorough rinsing is required. All traces of acid should be removed from porous areas and other surface irregularities or the parts will blister at the\e spots after plating.

Copper

Striking

A standard copper strike can be used. At least 0.04 mil should be applied which will be further copper plated and 0. I-O. I2 mil when nickel plate is used.

to castings,

205