Example 4 Cadmium Plating of Electrical Outlet Receptacles with Automatic Equipment

A quantity of 12,000 to 14,000 electrical-outlet receptacles per eight-hour day were required in order to justify the use of a small automatic plating system of 3800L (1000 gal) solution capacity with a single lane of rods and workpieces and plating 4 to 5 pm (160 to 200 pin.) of cadmium. When the size and shape of the parts are such that either automatic or still-tank plating processes may be used, the racking requirement is often the most important factor in determining the relative economy of still-tank and automatic plating. Two kinds of automated plating equipment are available, the regular return machine and the programmed hoist unit, which is an automated straight-line unit. The latter equipment is much less expensive to purchase.

Cleaning and rinsing are essential operations in any plating sequence. Figures 2 and 3 show the number of tanks or stations required for such operations in typical barrel and automatic processes. In Fig. 4, where cleaning, rinsing, and postplating operations are indicated for various initial conditions of the work surface, the plating step itself is a rather inconspicuous item in the flow chart of the total finishing process. Table 7 shows variations in processing techniques for still-tank, barrel, or automatic plating to a thickness of less than 13 pm (520 pin.).

Table 7 Conditions for plating cadmium to a thickness of less than 13 pm (520 pin.)

Process variable

Still tank

Barrel

Automatic

Soak cleaning

Alkali, g/L (oz/gal)

53 (6)

106 (12)

70 (8)

Temperature, °C (°F)

82 (180)

82 (180)

82 (180)

Time, min

2-3

5

3-5

Rinsing

Temperature

Ambient

Ambient

Ambient

Time, min

1

3

1

4

2

Electrolytic cleaning

Alkali, g/L (oz/gal)

70 (8)

70 (8)

Temperature, °C (°F)

82 (180)

82 (180)

Time, min

1-1 2

1-3

Rinsing

Temperature

Ambient

Ambient

Ambient

Time, min

1 4

3

1

Acid dipping

HCl, vol%

10-50

10-50

10-50

Temperature

Ambient

Ambient

Ambient

Time, min

1-1 8

3

ito >1 2

Rinsing

Temperature

Ambient

Ambient

Ambient

Time, min

1 4

3

1

Cyanide dipping

NaCN, g/L (oz/gal)

30-45 (4-6)

30-45 (4-6)

30-45 (4-6)

Temperature

Ambient

Ambient

Ambient

Time, min

1 4

3

1

Plating

Temperature, °C (°F)

29 (85)

29 (85)

29 (85)

Current density, A/m2 (A/ft2)

270 (25)

9-15 V

270 (25)

Time, min

10

30

10

Rinsing

Temperature

Ambient

Ambient

Ambient

Time, min

1

3

1

4

2

Rinsing

Temperature

Ambient

Ambient

Ambient

Time, min

1

2

1

4

2

Bright dipping

HNO3, vol%

1 1

1 1

1 1

4 2

4 2

4 2

Temperature, °C (°F)

82 (180)

Ambient

Ambient

Time, min

1

1

1

6

6

2

Rinsing

Temperature, °C (°F)

71-82 (160-180)

82 (180)

Time, min

2

1

2

Drying

Temperature, °C (°F)

82-105 (180-220)

82-105 (180-220)

82-105 (180-220)

Time, min

1-3

5

1-3

Solution No.

Composition

Amount

Temperature

Immersion time

°C

°F

1

H2SO4

8-12 vol%

71-93

160-200

10-120 s

2

HCl

20-50 vol%

RT

RT

10-120 s

3

Na2CO3

75-90 g/L (10-12 oz/gal)

RT

RT

15-60 s(a)

4

Petroleum solvent

—3 mm 2

5

Alkali(b)

60-75 g/L(b) (8-10 oz/gal)

82-93(b)

—3 mm 2

6

Water

82-93(c)

180-200(c)

5-15 s

7

Water(d)

RT

RT

5-15 s

8

Alkali

60-75 g/L (8-10 oz/gal)

66 max

150 max

— 1 min 2

9

(e)

(e)

(e)

(e)

— 1 min 2

10

(e)

(e)

(e)

(e)

30 s

11

NaCN

45-60 g/L (6-8 oz/gal)

RT

RT

5-15 s

Note: For cast iron, the solutions, conditions, and procedure are the same as for steel, except that cast iron parts, after being thoroughly washed in cold water following the acid dip, are dipped for 5 s in a room-temperature (RT) cyanide solution (NaCN, 45 to 60 g/L, or 6 to 8 oz/gal) and then again rinsed in cold water, before proceeding to inspection, plating, and post-treatments.

(a) When solution is sprayed, time is 5 to 15 s.

(b) Heavy-duty cleaner. For electrolytic cleaning, concentration of alkali is 45 to 60 g/L (6 to 8 oz/gal), temperature is 82 °C (180 °F), and time is 1 to 3 min.

(c) When a spray rinse is used, water temperature is 71 to 82 °C (160 to 180 °F).

(d) Immersion or spray rinsing.

(e) Proprietary compounds

Fig. 4 Flow diagram showing cadmium plating operation relative to overall cleaning and post-treatment operations for steel and cast iron components

In the case of Fig. 2, 3, and 4 and Table 7, it is important to consider double or triple overflow rinses to control both water usage and pollution control costs. The use of dead rinses, following process tanks, is equally important.

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