2 Eleetroplating and metal finishing

The processes and solutions described in this section are intended to give a general guide to surface finishing procedures. To operate these systems on an industrial scale would normally require recourse to one of the Chemical Supply Houses which retail properietary solutions. This particularly applies to electroplating baths containing brighteners.

32.8 Polishing compositions

The following abrasive powders are used for polishing metal.

ALOXITE

Aluminium oxide made by fusing bauxite. Used for cutting down in the same way as emery.

ALUMINA

Certain grades of alumina are used for polishing stainless steel and chromium. The material is generally used in the form of a composition in which the powder is mixed with stearines or other fats.

EMERY POWDER

Used principally in cutting down and for preliminary operations. It is applied to the mop by means of an adhesive, usually glue. Emery powder is an impure aluminium oxide containing about 50-60% A1,0,, 3040% magnetite and small amounts of ferric oxide, silica, chromium, etc. Emery powder should never be used on magnesium or aluminium components because af the adverse effect on corrosion resistance.

TRIPOLI

A calcined diatomaceous earth used for polishing brass, steel and aluminium. It is used generally in tbe intermediate stages, and is usually compounded with stearines and paraffin wax to make a polishing composition which can be used directly on a mop.

CROCUS POWDER

A polishing composition consisting essentially of ferric oxide, of coarser grade than rouge, used for polishing iron and steel. and also, tin. Usually compounded with stearine and used with a mop or fibre brush.

32-1

32-2 Electroplating and metal finishing

ROUGE

A high-grade ferric oxide supplied in various degrees of fineness. It can be used in the form of a paste directly on to a soft mop or can be made into a composition with stearine. It is used essentially for finishing to obtain a very high polish on gold, silver, brass, aluminium, etc.

BLACK ROUGE

This consists of black oxide of iron and is sometimes used for finishing operations,

GREEN ROUGE

Chromic oxide used for polishing chromium and stainless steel and can be used either in the form of a composition mixed with stearine or as a paste applied directly to the mop.

VIENNA LIME

Used for making the white finish for polishing nickel, etc. It consists of a calcined dolomite and contains about 60% calcium oxide and 40% magnesia.

CARBORUNDUM

Silicon carbide used for low tensile strength materials, e.g. brass, copper, aluminium, etc. and also brittle metals, such as hard alloys and cast irons.

32.2 Cleaning and pickling processes VAPOUR DEGREASING

Used to remove excess oil and grease. Components are suspended in a solvent vapour, such as tri- or tetrachloroethylene. Note: Both vapours are toxic and care should be taken to ensure efficient condensation or extraction of vapours.

EMULSION CLEANING

An emulsion cleaner suitable for most metals can be prepared by diluting the mixture given below with a mixture of equal parts of white spirit and solvent naphtha.

Pine oil 62 g

Triethanolamine 1.2 g Ethylene glycol-monobutyl ether 20 g

Oleic acid 10.8 g

This is used at room temperature and should be followed by thorough swilling.

Table 32.1 ALKALINE CLEANING SOLUTIONS

Composition of solution Temperature Metal to be cleaned ozgal-' g l - ' "F "C Remarks

All common Sodium hydroxide metals (NaOH) 6 37.5 180-200 80-90 For heavy duty other than Sodium carbonate aluminium and (Na,CO,) 4 25.0 zinc, but Tribasic sodium including phosphate magnesium (Na,PO, . 12H,O) 6.2

1.5 Wetting agent

CIeuning and pickling processes 32-3 Table 32.1 ALKALINE CLEANING SOLUTIONS-continued

Composition of solution Temperature Metal to be cleaned ozgal-I gl- ' "F "C Remarks

Aluminium and zinc

Most common metals

Most common metals

Sodium hydroxide Sodium carbonate Tribasic sodium phosphate Sodium metasilicate (PJa,SiO,. 5H,O) Wetting agent

Tribasic sodium phosphate Sodium metasilicate Wetting agent

Tribasic sodium phosphate Sodium metasilicate Wetting agent

Sodium carbonate Tribasic sodium phosphate

Wetting agent

Sodium carbonate Sodium hydroxide Tribasic sodium phosphate Sodium cyanide (NaCN) Sodium metasilicate Wetting agent

2 12.5 4 25.0

2 12.5

2 12.5 1 - 8 0.75

4 25.0 4 25.0 1 0.75 8

2 12.5 4 25.0 1 - 8 0.75

2 12.5

4 25.0

* 1.5 - 1

6 37.5 1 6.25

2 12.5

2 12.5 1 6.25 - 8 0.75

180-200 80-90

180-200 80-90

180-200 80-90

180-200 80-90

Room Room

For medium duty

For light duty

Electrolytic cleaner, 6 V Current density l00/A ft-' (1O/A drn-') Article to be cleaned may be made cathode or anode or both alternately

May be used electrolytically

Table 32.2 PICKLING SOLUTIONS

Composition of solution Temperature Metal to be pickled ozgal-I g l - ' "F "C Remarks

Aluminium For etching (wrought) Sodium hydroxide

(NaOH) 8 56 104-176 40-80

Aluminium Nitric acid, s.g. 1.42 1 gal 11 Room Room (cast and Hydrofluoric acid 1 gal 1 1

Water 8gal 81 wrought) (52%)

Articles dipped until they gas freely, then swilled, and dipped in nitric acid 1 part by vol. to I of water (room temperature)

Articles first cleaned in solvent degreaser. Use polytheile or PVC tanks

Note-: It is almost universal practi- to use an inhibitor in the pickling bath. This ensures dissolution of the scale with practically no attack on the metal. inhibitors are usually of the long chain amine type and often proprietary materiais. Examples are Galvene and Stannine made by ICI.

32-4 Electroplating and metal ,finishing

Table 32.2 PICKLING SOLUTIONS-continued

Composition of solution Temperature Metal to be pickled ozgal-' g l - ' "F "C Remarks

Aluminium and other non- ferrous metals

Copper and copper alloys

Iron and steel

Bright dip Chromic acid Ammonium bifluoride Cane syrup Copper nitrate Nitric acid (s.g. 1.4) Water (distilled) to

Bright dip Phosphoric acid (s.g. 1.69) Nitric acid (s.g. 1.37)

To remove scale Sulphuric acid* Water

Or Sulphuric acid' Sodium dichromate (Na,Cr,O, .2H,O) Water

Bright dip Sulphuric acid* Nitric acid Water Hydrochloric acid

Matt dip Sulphuric acid* Nitric acid (s.g. 1.42) Zinc oxide (ZnO)

Semi-matt dip Sodium dichromate Sulphuric acid* Water

Slow pickle to loosen heavy scale Sulphuric acid' Glue

To remove scale Sulphuric acid*

0.84 oz 0.72 oz 0.68 oz 0.04 oz 4.8 oz 1 gal

8.4 gal 0.6 gal

1 gal 4 gal

1 gal 12 02

4 gal

2 gal 1 gal 1 gal 0.5 oz

1 gal 1 gal 2 lb

3 02 18 oz 1 gal

2 Yo 0.25%

10%

5.2 g

4.2 g 0.25 g 30 ml 1 1

4.5 g

9.41 0.61

11 41

11 75 g

41

21 11 11 25 ml

11 11 2 m g

19 g 114 g 11

- -

-

195 90

195 90

150-170 65-75

70-175 20-75

Room Room

160-180 70-80

Room Room

Room Room

120-180 50-80

Immerse for 15 min. Solution has limited life. AR chemicals and deionized or distilled water should be used

Immerse for several min. Agitate work and solution. Good ventilation necessary. Addition of acetic acid useful with some alloys

After pickling articles can he dipped in sodium cyanide: 40zgal- ' (25gl-') to remove tarnish

This solution leaves a slight passive film which helps to prevent tarnish

If any scale first dip in spent bright dip. Remove stains by dipping in sodium cyanide 4 oz gal- (25 g 1-I)

If the finish is too fine add nitric acid. If too coarse add sulphuric acid

Leave for several hours or overnight

Or hydrochloric acid 10-20%

* Sulphuric acid, pure cornel. grade, s.g. 1.84. Note: It is almost universal practice to use an inhibitor in the pickling bath. This ensures dissolution of the scale with practically no attack on the metal. Inhibitors are usually of the long chain amine type and often proprietary materials. Examples are Galvene and Stannine made by ICI.

Cleaning and pickling processes 32-5 TabUe 32.2 PICKLING SOLUTIONS--continued

Composition of solution Temperature Metal $0 be pickled ozgal-' g l - ' "F "C Remarks

Iron and steel Bright dip conrinued Oxalic acid crystals 4 oz

Hydrogen peroxide 2 oz

Sulphuric acid (10%) 0.02 oz Water to 1 gal

Anode etching Sulphuric acid* 1 gal Water 2 gal

(100 vol.)

25g Room 13 g

0.1 g 11

Room This solution has so far only been used on an experimental basis

11 Not 21 above

75

Not Current density: above 2 0 0 A K 2 25 (20Adm-')

For polished work Sulphuric acid* - Not

above 75

- Not Density must not fall above below 1.61 g 01 25 work will he etched

Magnesium General cleaner and magnesium Chromic acid alloys

16-32 100- Up to 200 b.p.

Up to b.p. films, corrosion

For removal of oxide

products, etc. Should not be used on oily or painted material

Sulphuric acid pickle Sulphuric acid* 3 Yo - Room Room Should be used on

rough castings or heavy sheet only. Removes approx. 0.002 in. in 20-30 s

Nitro-sulphuric pickle Nitric acid Sulphuric acid*

Bright pickle for wrought products Chromic acid Sodium nitrate Calcium or magnesium Iluoride

Brightpickle for castings Chromic acid Concentrated nitric acid (70%) Hydrofluoric acid (50%)

Acetic acid

8% 2 Yo

- Room __

Room

23 4 1 -

150 Room 25 - 3 A

Room Lustrous appearance. Involves metal removal

314 3:

1

235 Room 20

6.2

Room

8 approx.

8 approx.

50 Room approx.

50 Room approx.

Room Special purpose pickles

Room Special purpose pickles

Citric acid

* Sulphuric acid, pure comcl. grade, s.g. 1.84. Note: It is almost universal practice to use an inhibitor in the pickling bath. This ensures dissolution of the scale with practically no attack on the metal. Inhibitors are usually of the long chain amine type and often proprietary materials. Examples are Galvene and Stannine made by ICI.

32-6 Electroplating and metal jnishing

Table 32.2 PICKLING SOLUTIONScontinued

Composition of solution Temperature Metal to be pickled ozgal-' gl- ' "F "C Remarks

Stainless steel To loosen scale Sulphuric acid* 13-30 80-180 130-160 60-70 Use prior to scale Hydrochloric acid 6-20 40-120 removal treatment, for (s.g. 1.16) heavy scales

To remove scale Nitric acid (s.g. 1.4) 32 200 130-150 55-65 Hydrofluoric acid 6 40 (52% HF)

Or Sulphuric acid* 10 60 Room Room Hydrofluoric acid 10 60 Chromic acid (CrO,) 10 60

Bright pickle

(s.g. 1.16) Hydrochloric acid 40 250 140-160 60-70

Nitric acid (s.g. 1.4) 3 22

White matt finish Ferric sulphate 13 80 160-180 70-80 5-15 min [Fex(so4),1 Hydrofluoric acid 6 40 (52% HF)

Zinc and zinc Bright dip alloys Chromic acid (CrO,) 40 250 Room Room 5-30 s. If yellow film

Sodium sulphate 3 19 persists after rinsing ( N a W 4 ) dip in sulphuric acid:

1 floz per gal (6 ml1-I) and rinse again

* Sulphuric acid, pure comcl. grade, s.g. 1.84. Nore: It is almost universal practice to use an inhibitor in the pickling bath. This ensures dissolution of the scale with practically no attack on the metal. Inhibitors are usually of the long chain amine type and often proprietary materials. Examples are Galvene and Stannine made by ICI.

Anodizing and plating processes 32-7

32.3 Anodizing and plating processes Table 32.3 ANODIZING PROCESSES FOR ALUMINIUM Good ventilation above the bath and agitation of the bath is advisable in all cases.

Temp- Current COmpOSiliOfl of SOhtiOn rrature density Time

02 ampft-2 and gal-'g I - ' "F - "C (A dm-2) voltage Cathodes Vat Hangers Remarks

Chromic acid 5-16 30-100 103- 38- Current tl-10 min Tank or Steel Pure Slight agitation is (CrO,), chloride content must not exceed 0.2 g I-', sulphate less than 0.5 g 1-' (After Bengough- Stuart)

Sulphuric acid (sg. 32 200 1.84)

Hard anodizing Hardas process Sul?huric acid

Elosui G X process Oxalic acid (COOH),.2H20

Eloxal WX process Oxalic acid

108 42 con- 0 4 0 V stain- (ex- a h - required trolled increased less hausted) minium by in steps steel voltage. of 5 V Average 5-35 min 3-4 Maintain (0.34.4) at 40 V d.c. 3-5 min

Increase gradually to 50 V 4-5 min Maintain at 50 V

60- 15- 10-20 12-18V Alum- Lead 75 24 (1-2) d.c. 20-40 inium or lined

min lead pla- steel tes (tank if lead lined)

32 200 23- -5- 25-400 40- 41 + 5 (2.540) 120V

d.c.

12.8 80 70 20 10-20 50 V (1- 2) d.c. 30-60

min

12.8 80 75- 25- 20-30 20-60 95 35 (2-3) a s . V 40-

60 min

Lead Lead lined steel

Vat Lead lining lined

steel

Vat Lead lining lined

steel

or This process titanium cannot be used

with alloys containing more than 5% copper

Pure The current alumin- must not ium or exceed 0.2 titanium A l - ' of

electrolyte

Alumi- Agitation nium required. or Gives coating titanium 1-3 thou.

thick

Alum- Oxalic acid pro- inium cesses are more ex- or pensive than sul- titanium phuric acid anodiz-

ing; but coatings are thicker and are coloured.

Alum- inium or titanium

Integral colour Anodizing Kalcoior process

Sulphosalicylic acid 16 100 (3) d.c. 2 M 5 Lead Lead Alum- Aluminium level in Sulphuric acid 0.8 5 72 22 30 25-60 V

min lined inium solution must be steel or maintained between

titanium 1.5 and 3 gl-'

t Period according to degree of protection. Complete cycle normally 40 min

32-8 Electroplating and metal ,finishing

Table 32.4 ANODIZING PROCESSES FOR MAGNESIUM ALLOYS

Tempera- Composition of solution ture Current

density Time 0 2 A ft-a and gal-' g I- ' "F "C (A dm-') voltage Cathodes Vat Hangers Remarks

HAE process Potassium hydroxide Aluminium Potassium fluoride Trisodium phosphate Potassium manganite

Dow 17 process Ammonium bifluoride Sodium dichromate Phosphoric acid 85% H,PO,

Cr 22 process Chromic acid Hydrofluoric acid (G%, H m 4 (85%) Phosphoric acid

Ammonia solution 25- 160- 30 180

19.2 120

1.7 10.4 5.5 34 5.5 34

3.2 20

39 232

16 100

14 88

4 25 4 25

13.5 84

MEL process Fluoride anodize Ammonium 16 100 bifluoride

<95 t 3 5 12-15 90 min Mg Mild Mg Matt hard, brittle, (1.2-1.5) at 85 V alloy steel or alloy corrosion resistant.

approx. for a.c. rubber dark brown 25- ax. Mg or lined 50 pm thick, pre- steel if abrasion resistant ferred d.c. used

160- 70- 5-50 180 85 (0.5-5)

165- 75- 15 205 95 (1.5)

<86 <30 5-100 (0.5-10)

10-100 Mg Mild Mg Matt dark green, min up alloy steel or alloy corrosion to for a.c. rubber resistant, 25 pm 110 V Mg or lined as. steel abrasion or d.c. for d.c. resistant

thick approx.,

12 min - Mild Mg Matt dark green, 380 V steel alloy corrosion as. resistant, 25 pm

thick approx.

30 min Mg Rubber Mg Principally a 120 V alloy lined alloy cleaning process a.c. for ax. to improve pre- Mg or corrosive ferred steel resistance by

for d.c. dissolving or ejecting cathodic particles from the surface

32.4 Electroplating processes

Table 32.5 PLATING PROCESSES ~ ~~

Qperating conditions

Temperature Current density Current efficiency

Metal Type and composition ozgal-' g l - ' "F "C Aft-, Adm-2 % Voltage pH Anodes Vat Remarks

Aluminium

Antimony

Brass

Bronze imitation

Aluminium chloride Lithium aluminium hydride Diethyl ether

Antimony oxide (Sb,O,) Potassium citrate Citric acid

Sodium cyanide (NaCN) Copper cyanide (CuCN) Zinc cyanide (Zn(CN),) Sodium carbonate (Na,CO,) Ammonia (s.g. 0.88) Free cyanide

Zinc Sodium cyanide Copper cyanide Zinc cyanide Rochelle salt (KNaC,H,O, . 4H20) Free cyanide

65 400 2 13 Solvent

7 45 20 130 24 1 so 7.5 4s 4 26 1.2s 1.7 4 26 0.2* 1.5* 2.6 17

5 33 4 26 0.3 2 2 13 0.3 2

60-140 15-60 20 2 100 - - Aluminium

130 55 2s 2.5 - - 3.6 Antimony or carbon

75-100 24-40 3-5 0.3-0.5 60-70 2-3 10.5-11.5 Brass (cathode) (80/20)

cast or rolled

Room for light 2-4 0.2-0.4 - 2-3 - Copper 92% colour, warm for Zinc 8% red colour

Glass sealed

Hard rubber

rubber lined

Steel or rubber lined steel

or

Steel

Operation must be in an atmosphere of nitrogen and the work introduced through a lock. Connections must not spark

Brightener: 2 Ib caustic soda in 4 gal of water

to which is added 1 lb white arsenic. Use 2-4 fl oz gal-' solution (15-30 ml per 100 1).

b 3

g

Free cvanide bv !2 Q

analysis

3 a a

P * 0.2 tl 02 gal-' or 1.5 rnl I - ' . \D

w Y

Operating conditions 6

Temperature Current density Current ",

Table 32.5 PLATING PROCESSES-continued

:: T

r

efJiciency Metal Type and composition ozgal-' gl- ' "F "C Aft-, Adm-, % Voltage pH Anodes Vat Remarks

Bronze Cadmium 4.5 imitation Sodium cyanide 3 -continued Copper cyanide 0.25

Cadmium oxide 2 Sodium carbonate (Na,CO,) 1 Free cyanide

Bronze Potassium cyanide 9 Copper cyanide 4 Potassium stannate (K,SnO,) 5 Potassium hydroxide 1.5 Rochelle salt 6 Free cyanide 3

Cadmium Sodium cyanide 12-15 Cadmium oxide 3-5 Free cyanide 8-10 Addition agents 0.015-2.4

Chromium Bright chrome Chromic acid (CrO,) 72 Sulphuric acid 0.72

29 Room 20 1.5 13 6.5

60 150 65 26 33 10 40 20

75-100 75-90 24-30 20-33

0.1-15 52-66

450 95-110 35-45 4.5

Hard chrome Chromic acid Sulphuric acid

40 250 120-140 50-60 0.4 2.5

2-5 0.2-0.5

u p to u p to 100 10

10-20 1-2

70-150 7-15

200-700 20-70

-

40-50

90

12-15

12

- 2.

maintained by addition rq

of small quantities of cadmium oxide dissolved in sodium cyanide f

2-3 - Copper Steel Cadmium content

Must be kept free of $ bivalent tin. Maintain 5 additions of potassium stannate

- 12.5 Copper Steel

tin content by Q

2-3 13 Cast cadmium - Brightener; Organics (such as dextrin) or metallic (such as nickel

or cadmium balls in a steel cage salts)

4-5 - Tin (7%) Steel lined This solution requires lead with reducing: either boil

antimonial with citric acid lead 7% or 2ozgal-' (12.5gl-') PVC or with tartaric acid

3ozgal-' (18gl-')or with oxalic acid 4ozgal-' (25 gl- ')

5-7 - Tin (7%) Steel lined Reduction as above: lead with citric acid 1 oz gal-'

antimonial lead 7% or acid l tozgal- ' PVC

(6.25 g I-') or tartaric

(9 g 1-') or oxalic acid 2 02 gal-' (12.5 g 1-')

Black chrome Chromic acid Fluosilicic acid

Copper Acid Copper sulphate (CuSO,. 5H,O) Sulphuric acid Phenol

33 220 90 30 150-450 15-45 0.033 0.22

32 200 60-120 16-50 10-200 1-20 95-97 1-3

8.0 50 0.16 1

Through-hole plating

Sulphuric acid 27-30 170-190 Chloride > 15 ppm

Cyanide (strike) Sodium cyanide (NaCN) 3 19 110-140 45-60 10-30 1-3 10-60 6 Copper cyanide (CuCN) 2 13 Sodium carbonate (Na,CO,) 2 13

Copper sulphate 14-17 88-110 75-90 24-30 10-45 1-45 - -

Cyanide (high efficiency) Sodium cyanide 13 82 140-180 60-80 10-100 1-10 100 2-4 Copper cyanide 10 60 Sodium hydroxide 4 26

Cyanide (Rochelle) Sodium cyanide 6 37.5 125-160 50-70 20-60 2-6 50-60 6 Copper cyanide 4 26 Rochelle salt 8 50 (KNaC,H,O, .4H,O) Sodium carbonate 5 30 Free cyanide 0.5-1 3-6

- Tin (7%) Steel lined Before use, work lead with solution on scrap

antimonial plates until lead (7%) or PVC has been passed

100-150 A h per gal,

Pure copper Lead or The phenol is rubber lined sulphonated by heating wood or steel with its own weight of

sulphuric acid to 120°C for 1 h before use. Agitation is necessary for high current density. Constant filtration is advisable

Chloride content serves as a deposit modifier

- Copper Lead or rubber lined steel

11-12 Pure copper Steel Used to deposit thin rolled or undercoats for other $ extruded metals B

5: - Oxide-free Steel For rapid plating a

copper sheet a E. a

Q

12.2-12.8 Copper, rolled Steel and annealed

w N

i- c

x Operating conditions N

Table 32.5 PLATING PROCESSES-continued c

_______-

2 5 z -

Temperature Current density Current efficiency

Metal Type and composition ozgal-’ g l - ’ “F “C Aft-’ Adm-’ % Voltage pH Anodes Vat Remarks

Copper -continued

Gold

Indium

Iron

Pyrophosphate Copper pyrophosphate (Cu2P,0,. 3H,O) Potassium pyrophosphate Ammonium nitrate Ammonia

Hard Potassium gold cyanide (K@(CN)2) Citnc acid Phosphoric acid Cobalt (as CoK2EDTA)

Alkaline cyanide Potassium cyanide Potassium gold cyanide Potassium carbonate Dipotassium phosphate (K,HPOJ

(1) Indium fluoborate Boric acid Ammonium fluohorate

(2) Indium (as hydroxide) Potassium cyanide Potassium hydroxide o-glucose

Ferrous chloride (FeC1,. 4H’O) Calcium chloride

11

45 1 0.1

2

16 2 0.16

5 2 5 5

38 4.8 7.5

2.5-5 22-25 5-6 3-5

48

50

66 125-140 50-60

300 6 0.6

12 97 35

105 12.5 ml 1

30 120-150 50-65 12 30 30

230 70-90 20-30 30 41

15-30 70-90 20-30 140- 160 30-40 20-30

300 195 90

335

10-80 1-8 100 - 8-8.8 Copper

5-15 0.5-1.5 - - 3-4.5 Insoluble

1-5 0.1-0.5 100 1.5-2 11 Fine gold (24-carat) or insoluble: stainless steel, platinum or graphite

50-100 5-10 75 - 1 Part indium, part insoluble

15-30 1.5-3 50 - 11-12 Steel

U p t o U p t o - - 1.2-1.8 Pure iron 120 12

Steel

-

Enamelled iron

-

-

Lead or rubber lined

s Commonly used for plating printed circuit boards. Use vigorous z agitation 2

3 a_

If insoluble anodes are used, solution must be renewed periodically

Use fluoboric acid to adjust pH

Agitation is desirable for high current densities

Lead Lead fluoborate (Pb(BF,),) 40 240 77-100 25-40 5-70 Fluoboric acid 10 60 Boric acid (H3B0,) free 4.5 27 Glue 0.03 0.2

Nickel Watrs bath Nickel sulphate 50 350 110-150 45-65 50 (NiSQ, .6H,O)

45 Boric acid 6 37 Wetting agent 0.015-0.075 0.1-0.5

Nickel chloride (NiC1, .6H,Q) 7

For plating zinc and zinc-base alloys Nickel sulphate Sodium sulphate (anhydrous) Ammonium chloride Boric acid

Sulphamate bath Nickel sulpbamate (Ni(NH2S03),) Boric acid Nickel chloride

Hard nickel Nickel sulphate Ammonium chloride Boric acid

( I ) Bright Nickel sulphate Nickel chloride Boric acid Sodium naphthalene trisulphonate (CioH,(SQ3)3Na)

(2) Bright (low metan Nickel sulphate Nickel chloride Boric acid

12-17 12-17 2.4-6 2.4

48

4.8 1

28 4 4.8

50 7 6 5.6

9.6 18 8

75-112 70-90 20-32 10-30 75-112 15-37.5 15

300

30 6

180 25 30

330 45 38 35

60 110 50

80-140 25-60 20-250

110-140 43-60 20-100

110-150 45-65 25-100

97-140 35-60 25-100

0.5-7

5

1-3

2-25

2-10

2.5-10

2.5-10

- 100 -

3-4 - 95

- 3-4 5.3-5.8

3.5-4.2

- 6-8 5.6-5.9

3-4 - 95

95 - 3.5-4.2

Pure lead free Rubber lined - from antimony steel

Cast or rolled Lead or Ni (99-100%) rubber lined bagged

Nickel (99-100%)

Nickel (99-100%)

Nickel (99-100%)

Nickel (99-100%)

Nickel

Lead or rubber lined

Lead or rubber lined

-

Rubber lined steel

Rubber lined steel

Agitation desirable for high current densities. Constant filtration desirable. Wetting agent. Sod, lauryl sulphate

Agitation can be used

Air or mechanical agitation

L For building up worn parts A.

N.

a Bright nickel plating a baths are basically e Watts solutions I.

containing brighteners 4

‘9

- a 6 m

W

(0

Agitation constant filtration necessary (r,

N c

Table 32.5 PLATING PROCESSES-continued E

Operating conditions E

s Metal Type and composition ozgal-' g l - ' "F "C Aft-' Adm-l % Voltage pH Anodes Vat Remarks a

3

Temperature Current density Current efficiency

Nickel Woods nickel strike bath a, -continued Nickel chloride 38 240 70-80 21-27 30 3 - - - Nickel Rubber lined Used to strike onto 8'

Hydrochloric acid 13 80 or plastic metals such as stainless n steel or nickel. Pre-etch k in bath at 3 A dm-2 anodic for 2 min before

Palladium

Platinum

Rhodium

Silver

BIaek or grey Nickel chloride 12 Ammonium chloride 4.8 Zinc chloride 4.8 Sodium thiocyanate (NaCNS) 2.4

Palladium (as Pd(NH,),Br,) 4.8 Ammonium bromide 7

Platinum (as dinitrodiamino 1.6 platinum) Ammonium nitrate 16 Sodium nitrite 1.6 Ammonia (s.g. 0.88) 7*

Rhodium (as sulphate 0.32 concentrate) Sulphuric acid 3.2t

Potassium cyanide 8-12 Silver cyanide (80%Ag) 5-9 Potassium carbonate 2.5-14 Free cyanide 5.5-8

75 30 30 15

30 45

10

100 10 44t

2

20$

50-78 31-56

35-50 15-90

Room temperature

120

203

104

70-80

50

95

40

20-27

1.5

40

70

10-40

5-15

0.15

4

7

1-4

0.5-1.5

5 Nickel or Rubber lined - -

insoluble

9.2 Insoluble Glass or - -

rubber lined

10 2-4 - Platinum or Glass or insoluble rubber lined

- 3-6 - Platinum or Glass or insoluble rubber lined

99-100 <1 - Fine silver Lead or rubber lined rolled

Can be used to produce thick deposits for electro forming

Solution maintained by addition of platinum salt

During plating remove bubbles by cathode agitation

Cathode bar may be rocked. Brightener: Carbon bisulphide dissolved in silver solution

High speed Silver cyanide (80%) 1-25 Potassium cyanide (92%) 11-38 Caustic soda 0.6-4.8 Potassium carbonate 2.5-14 Potassium nitrate 6.4-9.6

Strike solution for non-ferrous metals Silver cyanide 0.7 Potassium cyanide 13

Sulphuric acid 8

Stannous sulphate 10

Tin Acid

Cresol sulphonic acid 6.4 (CH, . C,H,OH . SO,H)

(90% SnSO,) Gelatin 0.3 Beta-naphthol 0.16

Alkaline Caustic soda 1.6 Sodium stannate (48% SnO,) 16

44-150 10-240 4-30

4 -60 15-90

4.5 80

50 40

65

2 1

10 100

Immersion (on steel) Stannous sulphate 0.16-0.32 1-2 Sulphuric acid 0.8-2.5 5-15

Tin-nickel Stannous chloride (SnC1,) 8 50 Nickel chloride 48 300 Ammonium hifluoride 9 56 (NH,F . HF)

Tin-lead Tin (as fluoborate) 4 25 Lead (as fluoborate) 2 12

Peptone 0.8 4.5 Fluohoric acid 16 100

Boric acid 5 30

100-120 38-50

Room temperature

68 20

161 15

200-232 90-100

154 68

68-86 20-30

5-100

15-20

10-100

5-30

-

10-30

5-35

0.5-10

1.5-2.0

1-10

0.5-3

-

1-3

0.5-3.5

-

-

- 100

85

-

100

95

- 12 Pure silver Enamelled (bagged) iron or

rubber lined

4-6 - Silver or steel Steel or earthenware

9.4-0.8 - Pure tin Lead or bagged in rubber lined terylene

4-6 13 Pure tin (high Steel speed 1% AI) or insoluble

2-3 2-2.5 Nickel Rubber lined

6-12 - 60/40 tin/lead Rubber lined alloy

Agitation is necessary and is usually effected by solution pumping or cathode movement. Constant filtration advisable

Constant filtration advantageous. Periodic filtration essential. Use agitation at higher current densities

Anode must he filmed for uniform dissolution

Immersion time

immersed in Monel or 2. stainless steel baskets 2 Tin content maintained a by regular additions of $ anhydrous stannous 5, chloride cc,

P This process gives a 60/40 tin/lead deposit. $ Proprietary grain m refiners are available to

5-20 min, work 9

z

w replace peptone h)

w Table 32.5 PLATING PROCESSES-conlinued N e m

Operaring condirion.~

Tcmpcwlure Currenr densiry Currenr F efficiency

ozga l - ' g 1 - l "F "C Adm-z % Volragc pH Anorlrs Val Remarks P g

M e l d Type and composilion

Zinc Acid 'p

Zinc chloride (ZnCI,) 10 60 68-100 20-40 5-50 0.5-5 95 3-8 4.5-5.5 Zinc (99.9%) Lead or Agitation and constant Potassium chloride 25 150 rubber lined filtration necessary for Boric acid 3.7 23 high current densities 2 Proprietary organic additives 3.2-8* 20-50* n a Cyunide (decorative)

Caustic soda 10-20 60-120 Zinc oxide (ZnO) 4-9 25-55 Sodium carbonate 3.2-20 20-120

Sodium cyanide 8-22 50-140 68-120 20-50 25-150 2.5-15 -85 - - Pure zinc Steel -

Cyanide (protective)

Caustic soda 15-22 90-140 from lead

Sodium carbonate 5-12 30-75

Pure zinc free Steel Sodium cyanide 15-25 90-150 68-120 20-50 25-150 2.5-15 - - -

Zinc oxide 9-12 55-75

Zincating (on aluminium) Caustic soda 80 500 77 25 - Zinc oxide 16 100

- - - - - - Improved adhesion by zincating, stripping in 40% HNO, and rezincatine:

p z '9

* 3.2-8 floz gal-' or 20-SO ml I-'.

Electrophttdng process parameters 32-1 7

latinlg processes for magnesium alloys

DOW PROCESS (H. K. DELONG)

This process depends on the formation of a zinc immersion coat in a bath of the following composition:

Component Concentration

oz gal-' p I - '

Tetrasodium pyrophosphate 16 I20 Zinc sulphate 5.3 40 Potassium fluoride I .o 7

The treatment time is 3-5min at a temperature of 175-185°F (80-85T) with mild agitation. The pH of the bath should be 10-10.4.

The steps of the complete process are:

1. Solvent or vapour degreasing. 2. Hot caustic soda clean or cathodic cleaning in alkaline cleaner. 3. Pickle $-1imin in 1% hydrochloric acid and rinse. 4. Zinc immersion bath as above without drying off from the rinse. 5. Cold rinse and immediately apply copper strike as under.

Concentration Component oz gal- ' g 1 - 1

Copper cyanide Potassium cyanide Potassium carbonate Potassium hydroxide Potassium fluoride Free cyanide PM Temperature

4.2 26 7.4 46 2.4 15 1.2 7.5 4.8 30 1.2 7.5 12.8-13.2 - 140°F (60°C) -

CONDITIONS

3040 A ft-' ( 3 4 A dm-') for 9-1 min, reducing to 15-20 A ft-2 (1.5-2 A dm-') for 5 min or longer.

If required, the copper thickness from the above strike can be built up in the usual alkaline or proprietary bright plating baths. Following the above steps, further plating may be carried out in conventional electroplating baths.

ELECTROLESS PLATING ON MAGNESIUM

Deposits of a compound of nickel and phosphorus can be obtained on magnesium alloy components by direct immersion in baths of suitable compositions. Details of the process may be obtained from the inventors, The Dow Chemical Co. Inc., Midland, Michigan, USA.

'GAS PLATING' OF MAGNESIUM (VAPOUR PLATING)

Deposits of various metals on magnesium components (as on other metals) can be produced by heating the article in an atmosphere of a carbonyl or hydride of the metal in question.

32-18 Electroplating and metal .finishing

32.6 Electroplating process parameters

Table 32.6 AVERAGE CURRENT EFFICIENCIES OF PLATING SOLUTIONS The figures given below are ap- proximate

Cadmium (oxide) Chromium Copper (acid) Copper (cyanide) Copper (Rochelle) Gold Indium (cyanide) Indium (sulphate) Iron Lead Nickel Silver Tin (acid) Tin (stannate) Rhodium Zinc (acid) Zinc (cyanide)

0 , /o 85-95 12-16 95-99 30-60 40-65 70-85 30-50

90-95 90-100 94-98 100 90-95 70-85 35-40 97-99 85-90

70-90

Thickness of metal deposited per hour is given in mils (1 mil=O.OOl in) by

CD x W x CE

237 x A

where

CD=current density in A ft-'

CE =current efficiency (Table 32.6) W=g A-' h (Table 32.7)

A=density of metal deposited

Table 32.7 THEORETICAL RELATIONS OF METAL AND CURRENT

Metal deposited Current required

Metal g A-l h oz A-' h A h l b - ' A h kg-'

Aluminium Antimony (antimonious) Cadmium Chromium (hexavalent) Cobalt

Copper (cuprous) Copper (cupric) Gold (auric) Indium Iron (ferrous)

Lead Nickel Palladium Platinum Rhodium

Silver Tin (stannous) Tin (stannic) Zinc

0.335 1.515 2.096 0.323 5 1.099

2.372 1.186 2.452 1.428 1.042

3.866 1.095 1.990 3.642 1.920

4.025 2.215 1.108 1.220

0.011 8 0.053 4 0.073 9 0.0114 0.038 8

0.083 7 0.041 8 0.086 5 0.050 3 0.036 8

0.136 3 0.038 6 0.070 2 0.1284 0.067 7

0.1294 (Troy) 0.078 1 0.039 1 0.043 0

1356 2 989 299 659 216 476 701 1545 413 911

191 42 1 383 844 185 408 318 701 435 959

117 258 414 913 228 503 125 276 236 520

113 (Avoir.) 350 205 451 409 902 372 820

Miscellaneous coating processes 32-19

32.7 Miscellaneous coating processes

(1) AUTOCATALYTIC PLATING

Autocatalytic plating is a form of electroless plating in which metal is deposited via a chemical reduction process (as opposed to immersion plating in which thin coatings are formed by electrochemical displacement of the coating metal).

Processes exist for the autocatalytic deposition of a large number of metals, particularly nickel, gold, silver and copper. Basically, the solutions contain a salt of the metal to be deposited and a suitable reducing agent (most commonly hypophosphite, but also hydrazine and boranes etc.). When a metal substrate, which is catalytic to the solution, is introduced into the bath, it becomes covered with a layer of the coating metal which is itself catalytic and thus the process can continue. This mechanism results in an extremely even distribution of deposit on the substrate, i.e. these solutions have a high 'throwing power'.

The most widely used autocatalytic process is nickel-phosphorus; a typical acid bath is as follows:

nickel chloride 4.8 oz gal-' (30 g I - l )

sodium glycollate 8.0 oz gal - ' (50 g 1-') sodium hypophosphite 1.6 oz gal-' (10 g 1-1)

The solution is operated at temperatures between 75 and 100"C, at pH 4-6, giving deposition rates up to 0.6 thou per hour (15 iun h-l). The deposit is an alloy of nickel and phosphorus, containing about 7-10% phosphorus. A useful property of this material is that it can be hardened (typically by heat treating for 1 hour at 400°C) so as to increase the as-deposited hardness from 400 HV to almost 1000 HV. Thus, autocatalytic nickel coatings find engineering applications, often as a replacement for hard chromium electrodeposits.

(2) COMPOSITE COATINGS

Composite coatings can be electroplated or electroless plated deposits into which a uniform distribution of a second phase material is dispersed. The incorporated material can be hard, ceramic particles for increased wear resistance, as in the Tribomet process carried out by BAJ Ltd. Alternatively, PTFE particles can be used to increase surface lubricity as in the Niflor process from Norman Hay Engineered Surfaces Ltd.

(3) ELECTROSTATIC AND ELECTROPHORETIC METHODS OF PAINT APPLICATION

These are methods which have been developed for the economic application of paint to articles of complicated shapes (and often skeleton structure) in large numbers.

When an article like a metal chair is sprayed by a conventional spray gun procedure, much of the spray overshoots the surfaces and is wasted. In the electrostatic method a very high electrical potential is developed between the gun and the article being painted. The droplets of paint assume a charge of opposite sign to the workpiece and are attracted to it. This ensures more uniform coverage, less overspray, and thus greater economy in operation.

Electrophoresis has been utilized in a somewhat similar way. When a direct current is applied to an aqueous emulsion, large dispersed molecules and even oily particles are caused to move towards one d the electrodes. In the electrophoretic process a paint is provided as an aqueous emulsion and current is applied in such a manner that the globules of paint move towards and attach themselves to the object to be painted. The process can be made automatic and continuous and results in very uniform build-up even on points and sharp edges. It is only suitable for large- scale operations but is very economical in paint.

(4) COATING WITH CERAMIC MATERIAL§

Just as metals can be sprayed, certain refractory oxides and silicates and the like can be applied by flame gun. Coating thickness and uniformity can be controlled by suitable means and hard, dense coatings can be built up. The coatings resemble biscuit-ware rather than a vitreous glaze, that is, they are absorbent: their chief use is to provide abrasion resistance and to delay heat transfer.

32-20 Electroplating and metal jnishing

(5 ) MECHANICAL PLATING

Mechanical plating is a method of plating Which utilizes mechanical energy to deposit metal coatings on to metal parts. Parts, glass beads, water, chemicals and metal powder are tumbled together in a barrel at around room temperature to obtain the desired coating.

The process is used primarily to provide ferrous-based parts with sacrificial coatings of zinc, cadmium, and co-deposits with tin. Parts treated by this method are most often fasteners, springs, clips and sintered iron components which are typically handled in bulk.

Parts which have been degreased, descaled, and copper-flashed are tumbled in rubber-lined barrels with water, glass bead impact media, promoter chemicals, and a finely divided powder of the metal to be plated. The promoter chemical serves to clean the metal powder and controls the size of the metal powder agglomerates that are formed. The mechanical energy generated from the barrel's rotation is transmitted through the glass impact media and causes the clean metal powder to be cold welded to the clean metal parts, thereby providing an adherent, metallic coating.

Due to the absence of an impressed current during coating, the process does not produce hydrogen diffusion into the steel substrate. Thus, a post-electroplating bake, in order to preclude hydrogen embrittlement of high strength steel components, is not required for mechanically plated deposits.

32.8 Plating formulae for non-conducting surfaces

(1) METAL POWDERS

The article to be treated may be coated with a metal powder. The best powder for this purpose is a finely ground copper, which is generally sold under the commercial title of bronze powder. This may be applied by mixing it with a cellulose lacquer to which has been added five parts by volume of thinner and spraying it on the object concerned. Alternatively, the object may first be sprayed with lacquer and before it is quite dry may be brushed over with the bronze powder using a soft camel-hair brush. After this treatment the article can be struck over in an acid copper solution.

Waxes (for gramophone records, etc.) may be coated directly by brushing with bronze powder and a soft brush. After brushing with bronze powder they may be treated in the following manner to improve the conductivity and reduce the time of covering in the plating bath

1. Brush with a soft brush and a 50% mixture of methylated spirit and distilled water. 2. Immerse in a solution containing 30 g I- ' of sodium cyanide and 6 g 1-' of silver nitrate. 3. Make up two solutions as follows: (a) Pyrogallic acid 7 g 1-', citric acid 4 g 1-' and (b) silver

nitrate, 40 g I - ' . Take four parts of solution (a) and one part of solution (b) and mix together and immerse article in this solution for about 10 min.

4. Swill and place in plating bath.

(2) SILVER REDUCTION

A number of articles can be treated by directly reducing silver on the surface. This process is particularly applicable to plastics and glass. Any process which will form a good silver mirror may be used, but the following will be found satisfactory for most purposes.

1. The surface of the article must be very thoroughly cleaned and completely free from grease. Glass and porcelain may be cleaned by using concentrated acid and alkali alternately. Plastics may be treated by brushing or barrelling with a mixture of Vienna lime and pumice, by treating with a suitable solvent or by immersing in a solution of chromic acid.

2. Priming. After cleaning the article is immersed in a 10% stannous chloride solution. Alternately, the solution may be swabbed on to the surface with cotton wool. The article is then thoroughly swilled.

3. The article is then silvered by immersing in a silvering solution, the formula for which is given below. The silvering operation generally takes about 20 min and the temperature must be carefully controlled during this period; usually about 21°C will he found the most satisfactory. The solution should be slightly agitated during the process.

4. The articles are thoroughly swilled and struck over in a copper tartrate bath. After being coated over with copper any desired plating can be made upon it.

Stripping electroplate coatings 32-21

Tte silvering solution is prepared from the following:

Solution (a) 100 g I - ' Rochelle salt. Solution (b) 10 g 1-' silver nitrate. Solution (c] 200 cm3 per litre ammonia (sp. gr. 0.880).

Take 100 cm3 of solution (b) rand add solution (c) carefully a little at a time until the precipitate which first forms just redissolves. If too much is added and the solution becomes quite clear. add a few drops of solution (b) until a very faint turbidity is produced. Then add 20 cm3 of solution (a), thoroughly mix and use immediately.

[N.B. The brown precipitate formed by adding ammonia to silver nitrate is explosive if allowed to dry. Care should be taken therefore to see that this does not happen.]

(3) 'VACUUM METALLIZING'

This process is carried out at less than 0.0007 mmHg pressure and can only be applied to objects which are stable under these conditions. The metal to be deposited is heated until it evaporates and there are several ways in which this is achieved. The vapour recondenses on the first cool surface it encounters, and can be made to form a thick dense coating. The 'throwing power' is very poor since the evaporated metal travels in straight lines and steps must be taken to rotate or xanipulate objects exposed to it in order to achieve uniform coating. By controlling the temperature of the work piece the crystal structure of the deposit can be varied.

32.9 Methods of stripping electroplated coatings

CADMIUM OR TIN FROM STEEL

Coatings may be stripped from steel by immersing the article in a solution containing 1 gal (4.5 litres) of hydrochloric acid, 2 oz (57 g) of antimony trioxide and f pint (280 ml) of water. After stripping and rinsing the article will probably require wiping to remove smuts.

CHROMIUM

Chromium may be stripped from non-ferrous metals by dissolving it in dilute hydrochloric acid. From steel it is best stripped by making it the anode in a solution of sodium hydroxide. If the base metal is zinc or zinc base diecastings, it is best to strip the chromium by making it the anode in sodium carbonate solution as this will not attack the exposed zinc. The conditions of operation are not critical.

COPPER FROM STEEL

Copper can be stripped from steel by immersing in a solution containing 5 lb gal-' (500 g I-') of chromic acid and 8 oz gal-' (50 g I - ' ) of sulphuric acid. This solution will work at room temperature but strips the copper very quickly if heated.

Alternatively, the article can be made anodic (2-6 V) in a solution containing 14 oz gal-' (90 g 1-') sodium cyanide and 2.4 oz gal-' (15 g 1-I) sodium hydroxide.

COPPER FROM ZINC AND ZINC BASE DIECASTINGS

Copper may be stripped from these materials by immersing in a solution prepared by dissolving 18 g of sulphur and 250 g of sodium sulphide (Na2S.9H20) in a litre of solution. The solution works very rapidly if warmed. The sludge formed on the surface of the qbject will require removing from time to time by brushing or immersion in a 120 g I - ' sodium cyanide solution.

32-22 Electroplating and metal jinishing

COPPER, NICKEL, ETC., FROM MAGNESIUM

Most metal deposits can be removed from plated magnesium by submitting the component to the fluoride anodizing process. Alternating current is used in a bath of 10% ammonium bifluoride, in which the plating gradually dissolves without affecting the magnesium. About P 1 0 V are used until most of the plating has disappeared. Finally, the voltage is raised to 120 V to complete the process and cleanse the magnesium from remaining traces of foreign metal. Magnesium hangers must be used with firm connections. The bath should be operated cold. Direct current may be used if the work piece is made the anode using mild steel or magnesium cathodes.

LEAD FROM STEEL, COPPER AND BRASS

Immersion of article in a solution of 95 vol. % glacial acetic acid, 5 vol. % hydrogen peroxide (30 wt %). Dilute solutions may be used although this can lead to pitting of steel.

NICKEL FROM COPPER AND BRASS

Nickel may be stripped from copper by an anodic treatment in either 60 vol. % sulphuric acid or 15 g 1-' hydrochloric acid. Care must be taken with the concentration of the acids as this can affect the pitting of the substrates.

NICKEL FROM STEEL

Nickel can be anodically stripped in sulphuric acid, as for nickel from copper. Copper sulphate (30g 1-') or glycerine (3Ogl-') can be added to reduce pitting of the steel. An immersion process involves the use of fuming nitric acid (85-95% HNO,, sp. gr. 1.50) from which water is excluded.

SILVER FROM BRASS

Silver may be stripped from brass by immersing the object in a mixture of 1 vol. conc. nitric acid and 19 vols. conc. sulphuric acid heated to 175 "F (80 "C). The silver is dissolved in a few minutes. The articles should be immediately removed and swilled.

ZINC FROM STEEL

The reagent used for stripping cadmium may be used. Alternatively zinc may be stripped from steel in either warm dilute hydrochloric or sulphuric acid, or l0-15% ammonium nitrate solution, or hot sodium hydroxide solution.

32.10 Conversion coating processes

(1) PHOSPHATING

Phosphating solutions are used to produce corrosion-resistant coatings on ferrous metals and also zinc, cadmium and aluminium. Probably the most important application for these coatings is to act as bases for subsequent painting operations.

Basically, phosphate solutions comprise metal phosphates dissolved in carefully balanced solutions of phosphoric acid. When a clean metal surface is dipped into the solution, the free acid present reacts with the metal, liberating hydrogen and causing the pH of the solution, adjacent to the metal, to rise. This unbalances the solution, resulting in the precipitation of metal phosphates which form a film, chemically bonded to the substrate.

Due to the complexity of modern phosphate solutions, these processes are normally proprietary, examples of which are listed in section 32.11.

There are four main types of phosphate solution: iron, zinc, heavy zinc and manganese, and these produce increasing weights of coating from 30-90mgft-' for iron phosphate solutions to 1000-4000 mgft - * for manganese phosphate solutions.

Conversion coating processes 32-23

(2) CHROMATING

Chromating solutions contain hexavalent chromium ions and a mineral acid and are used to increase the corrosion resistance of metals, in particular zinc, cadmium, aluminium and magnesium, by forming a surface layer containing chromium compounds.

The process is usually performed by immersion, although spraying or brushing processes are also used. A wide variety of proprietary solutions are available which produce coatings of different thicknesses. These coatings are often distinguishable by their colour which can vary from clear, to blue, to iridescent yellow and finally to black.

(3) COLOURING OF METALS

The following solutions and operating conditions will produce coloured conversion coatings, as detailed:

(i) Copper and Brass Black

Copper carbonate Ammonia 2pt (950 ml) Water 5pt (2.4 1)

1 lb (454 g)

The copper carbonate and ammonia are mixed before adding the water. The solution is operated at 175'F (80°C).

The blue black colour may be fixed by dipping in 2$% sodium hydroxide solution.

Green Water Sodium thiosulphate Nickel ammonium sulphate

or Ferric nitrate Temperature

Potassium chlorate Nickel sulphate Copper sulphate Water Temperature

Brown

(ii) Iron and steel Black

Sodium hydroxide Sodium nitrate Sodium dichromate Water Temperature

Ferric chloride Mercuric nitrate Hydrochloric acid Alcohol Water

Blue

1 gal (USA) 8 oz 8 oz 1 oz 160°F

53 oz 2: 02 24 oz 1 gal (USA) 195-212°F

8 lb 14 oz 14 02. 1 gal. 295°F

2 oz 2 oz 2 oz 8 0 2 8 oz

Room temperature. Parts are immersed for 20 minutes, removed and allowed to stand in air for 12 hours. Repeat and then boil in water for 1 hour. Dry, scratch-brush and oil.

Brown Copper sulphate Mercuric chloride Ferric chloride Nitric acid Alcohol

3 oz gal (20 g 1 - 1 )

0.8 oz gal-' (5gl-I) 5 oz gal-' 25 oz gal-' 93 fl oz gal-'

(30 g 1- ( 150 g 1- ) (700 ml 1 - I )

32-24 Electroplating and metal jinishing

Dip in solution, place in hot box at 175°F (80°C) for 30 minutes, stand in steam box at 150°F (65°C) until coated in red rust, immerse in boiling water to form black oxide, dry and scratch brush. Repeat this operation three times before oiling with linseed oil.

(iii) Stainless steel Black

Sulphuric acid Water Potassium dichromate Temperature

(iv) Zinc Black

Ammonium molybdate Ammonia

180 parts 200 parts 50 parts 210°F (99°C)

4 02 gal-' (24gl-') 6 fl 02 gal-' (45 mll- ' )

Heat solution to obtain a deep black. Rinse in cold and then hot water; allow to dry and harden.

(v) Aluminium Black

Potassium permanganate Nitric acid Copper nitrate

1.6 oz gal-' ( logl-1) 0.5 fl oz gal-' 4 oz gal-'

(4 mll- ' ) (25 g 1-')

Operate at 70°F (24°C) for 10 minutes. Blue

Ferric chloride 60 oz gal-' (360 g 1-') Potassium ferricyanide 60 oz gal-' (360 g 1-') Temperature 150°F (66°C)

32.11 Glossary of trade names for coating processes 32.11.1 Wet processes (1) PHOSPHATE PROCESSES

Processes by which a coating of phosphate is produced on the surface of steel or zinc base alloys by treatment in or with a solution of acid phosphates. For rustproofing, the metal must receive a finishing treatment with paint, varnish, lacquer or oil; examples of typical finishing treatments are given under Parkerizing but it should be understood that firms using or marketing other proprietary phosphate processes may apply different designations or use different media for the necessary finishing treatment.

Bonderizing A proprietary phosphate process applied to steel and zinc, marketed by Ardrox Pyrene Ltd. (similar to Parkerizing for steel but produces a thinner and less protective coating; synonymous with Parkerizing for zinc alloys).

Coslettizing The original phosphate process for steel, introduced in 1903. Electro-granodizing A proprietary phosphate process applied to steel, marketed by IC1 Ltd.

(Paints Division). The chemical action of the solution is assisted by electrolysis. Granodizing Proprietary phosphate processes applied to steel and zinc marketed by IC1 Ltd.

(Paints Division). Lithoform A proprietary phosphate solution applied to zinc, marketed by IC1 Ltd. (Paints

Division). Parkerizing A proprietary phosphate process applied to steel and zinc, marketed by Ardrox

Pyrene Ltd. Examples of subsequent finishing treatments are:

P20 Dewatering black finish P41 Black shellac finish P75 Oiled finish P96 Oiled finish SP55 Mineral oil finish

Walterizing A proprietary phosphate process applied to steel and zinc base alloys, marketed by the Walterisation Co., Ltd.

Glossary of trade names for coating processes 32-25

(2) ALKALINE OXIDATION PROCESSES

Processes by which a black oxide film is formed on steel by treatment in a strongly alkaline solution containing an oxidizing agent. For rustproofing, the metal must receive a finishing treatment which is usually carried out with oil.

Black Magic Blackening processes marketed by M&T Chemicals Ltd. Blakodizing Ebonol

Jerul An American process marketed by Technic Inc.

Black chemical finishes on steel, marketed by Tool Treatments Ltd. Range of conversion coating processes for both ferrous and non-ferrous metals, marketed

by OMI-Imasa (UK) Ltd.

(3) CHROMATE PROCESSES

Alocrom Enthos Chromating solutions marketed by OMI-Imasa (UK) Ltd. Kenoerr Chromating solutions marketed by the 3M Company Ltd.

Chromating solutions marketed by IC1 Paints Ltd.

(4) ANODIC OXIDATION OF ALUMINIUM AND ITS ALLOYS (ANODIZING)

For protection against corrosion and wear, for decoration, for aiding heat emission and for miscellaneous uses based on the absorptive properties of the oxide film when freshly made; used in conjunction with electrolytic ‘polishing’ for producing reflectors. Processes involving electrolytic treatment in solution, generally of chromic, sulphuric or oxalic acid with the production of a relatively thick film of oxide.

Anobrite Bright anodizing process operated by Anobrite Ltd. Bengough-Stuart process (chromic acid) The first anodizing process patented in 1923. Brytul process A process of producing reflectors introduced by British Alcan Aluminium. Eloxal A generic term used in Germany for anodic oxidation. Phosbrite process Chemical polish for bright anodizing marketed by Albright & Wilson Ltd.

(5) IMMERSION PROCESSES FOR THE TREATMENT OF ALUMINIUM ALLOYS

Alocrorn process A process of priming a thin greenish yellow film in a cold acid solution containing chromates. Marketed by IC1 Ltd. (Paints Division).

Alumon Zincating process marketed by Enthone/Imasa Ltd. Bondul Zincating process marketed by W. Canning Ltd. Decorul Oxidizing process giving electrically conducting coatings capable of being coloured by

A4BVprocess (Modified Bauer Vogel) A process of forming a thin oxide film by immersion in

P.vlumin process A similar process marketed by Ardrox Pyrene Ltd.

dyeing. Marketed by Lea Manufacturing Co. Ltd.

an alkaline solution containing chromates.

(6) NON-ELECTROLYTIC PROCESSES

Enplate Electroless nickel plating solutions, marketed by Enthone/Imasa Ltd. lliklud Electroless nickel plating solutions, marketed by Lea Manufacturing Co. Ltd. Sylek Electroless nickel-boron plating solutions, marketed by Imasa Ltd. Transiflo Mechanical plating process, marketed by the 3M Company Ltd.

(7 ) ELECTROPLATING AND ELECTRODEPOSITION PROCESSES

Achrolyte Tin-cobalt alloy plating process marketed by Udylite/Oxy Metals Ltd. Alecra 3000 Brylunizing

Chromonyx

Fescdizing

Trivalent chromium plating process marketed by Albright and Wilson Ltd. Zinc coating of wire by the ‘Bethanizing’ electroplating process of the Bethlehem

Steel Co. Black chromium plating process, often used for coating solar panels. Marketed by

Harshaw Chemicals Ltd. A term applied by FescoI Ltd., to any electrodeposition process carried out by them

(incomplete without mention of the metal referred to, e.g. Fescolizing in chromium, etc.). Now carried out by British Metal Treatments Ltd.

32-26 Electroplating and metal finishing

Listard process-Van der Horst process Patented processes of hard chromium plating for protecting the cylinders of internal combustion and other engines from wear. These processes give an oil-retaining surface to the chromium. The processes are operated by British Metal Treatments Ltd.

Niron Bright nickel-iron plating process, marketed by OMI-Imasa (UK) Ltd. Rovalizing A term applied by International Corrodeless Ltd., to any protective coating process

used or marketed by them. Incomplete without description of the process referred to (e.g. Roval cadmium, etc., see also phosphate processes).

Tryposit A name used by Thomas Try Ltd., to indicate their special process of electrodepositing heavy nickel or hard chromium for engineering purposes.

Zartan Alloy deposit, used as an alternative to decorative chromium. Marketed by M&T Chemicals Ltd.

32.11.2 Dry processes

(1) THERMAL PROCESSES

The processes described below involve heating of the object to be coated in contact with the coating metal (in the form of powder or as a coating to secure inter-penetration) or with a compound of the coating element. Used for coating steel except where otherwise stated.

Aluminizing A process involving spraying with aluminium and heating to cause alloying. Bower Barff A process of coating steel with a black oxide by heating in contact with steam. Calorizing A process of coating with aluminium, similar to sherardizing (see below) but using

Chromizing A process of coating with chromium involving heating to a high temperature in

Galvanizing A process of coating with zinc by dipping pickled steel into molten zinc

Zhrigizing A process of coating with silicon by heating to a high temperature in contact with

Nitriding A process of forming a hard layer on steel involving heating in a suitable atmosphere

Sherardizing A process of coating with zinc involving heating in contact with zinc powder in

aluminium in place of zinc.

contact either with a vapour of chromous chloride or with metallic chromium.

(electrogalvanizing is sometimes used to mean electroplating with zinc).

the vapour of silicon tetrachloride.

(usually ammonia vapour) to form a surface layer rich in nitride.

revolving drums (introduced by Sherard Cowper Coles).

(2) METAL SPRAYING PROCESSES

A method of coating consisting of projecting a stream of molten metallic particles at high velocity against the surface to be coated. Mainly for protection against corrosion but also used for restoring the dimensions of undersized parts.

Wire or Schoop process A process marketed by Metallization Ltd., and Metallizing Equipment Co. Ltd., in which the coating metal in the form of wire is melted and atomized.

Schori or powder process A process marketed by Schori Metallizing Process Ltd., in which a stream of the powdered coating metal is fed into a flame and blown on to the surface to be coated.

Mellosing or molten metal process A process in which a molten metal is fed into a jet of heated compressed air which serves to atomize it and to project it against the surface to be coated.

Arc spray process A process in which the metal feed material is melted by an electric arc and then atomized by a stream of compressed air.

Plasma sprayprocess A process in which a very high temperature plasma is produced by blowing gas through an electric arc. Metal wire or powder is melted by passage through the plasma and is projected by the gas on to the surface to be coated.

Detonation or D-gun process Oxygen, acetylene and the material to be plated, are introduced into a detonation chamber where a spark ignites the mixture. A detonation wave travelling at supersonic speed, forces the powdered material heated to 1 3 5OO0C, on to the substrate. A special building is required for sound insulation. Very high density coatings of refractory materials like tungsten carbide, can be plated by the process.