Volume 05 - Surface Engineering Part 4 docx

Equipment Specification Plating tank (1440 L, or 380 gal) 2.7 by 0.76 by 0.76 m (9 by 2 1 2 by 2 1 2 ft) Other tanks (420 L, or 110 gal) 0.91 by 0.76 by 0.76 m (3 by 2 1 2 by 2 1 2 ft) Power rectifier (600 A) 1.5 to 6 V Dimensions of rectifier 0.76 by 0.91 by 2.1 m (2 1 2 by 3 by 7 ft) Total floor space of equipment and access area 2.0 by 4.6 m (6 1 2 by 15 ft) Number of racks 15 Other tanks include a cleaning tank, an acid pickle tank, a hot-water rinse tank, and three cold-water rinse tanks. Table 5 Equipment requirements for cadmium plating of valve bodies and baffle plates in still tanks Production requirements Valve body Baffle plate Weight per piece 1.1 kg (2 1 2 lb) 0.2 kg (0.5 lb) Pieces plated per hour 210 175 Area plated per hour 6.5 m 2 (70 ft 2 ) 11.1 m 2 (120 ft 2 ) Minimum thickness 8 μm (320 μin.) 4 μm (160 μin.) Barrel plating may be used for parts up to 100 mm (4 in.) long and 50 mm (2 in.) thick. Parts such as machine bolts, nuts, and washers are ideal for barrel plating. Conversely, intricate shapes, such as ornaments and complex castings of brittle metals with small sections that fracture easily, should not be barrel plated; the tumbling action may damage these parts, and variation in plating thickness and appearance may result. Intricate designs incorporating recessed or shielded areas may present problems in plating coverage, luster, and appearance. Barrel plating is not applicable for parts requiring heavy plate. Usually, 8 to 13 μm (320 to 520 μin.) is the maximum thickness of plate applied. Example 2: Barrel Plating of Small Coil Springs and Brush Holders. Small coil springs and brush holders are illustrative of parts suitable for barrel plating. Production requirements for plating these parts in horizontal barrels are given in Table 6. Equipment specifications are as follows: Equipment Specification Plating tank (1330 L, or 350 gal) 1.8 by 1.2 by 0.76 m (6 by 4 by 2 1 2 ft) Other tanks (605 L, or 160 gal) 0.91 by 1.2 by 0.76 m (3 by 4 by 2 1 2 ft) Power rectifier (2000 A) 9 to 15 V Dimensions of rectifier 0.91 by 1.2 by 2.4 m (3 by 4 by 8 ft) Centrifugal dryer 0.61 by 0.61 by 0.76 m (2 by 2 by 2 1 2 ft) Baking oven 1.2 by 0.91 by 2.4 m (4 by 3 by 8 ft) Equipment floor space 12 m 2 (125 ft 2 ) Access area behind line 6.3 m 2 (68 ft 2 ) Access area in front 9.3 m 2 (100 ft 2 ) Other tanks in the list above refer to cleaning tanks, acid pickle tanks, hot-water tanks, and three cold-water rinse tanks. Table 6 Production requirements for cadmium plating of coil springs and brush holders in a horizontal barrel Production requirements Coil spring Brush holder Weight per piece 14 g ( 1 2 oz) 9 g ( 5 16 oz) Pieces plated per hour 7200 3800 Area plated per hour 22 m 2 (240 ft 2 ) 17 m 2 (180 ft 2 ) Minimum thickness 4 μm (160 μin.) 8 μm (320 μin.) Automatic Plating. The primary selection factor for automatic plating is cost. The volume of work must be sufficient to warrant installation of the equipment. Example 3: Cadmium Plating of Voltage-Regulator Bases on Automatic Equipment. Voltage-regulator bases were cadmium plated, to a minimum thickness of 3.8 μm (152 μin.), in automatic equipment at the rate of 2640 pieces/h. Production requirements: Factor Specification Weight per piece 170 g (0.37 lb) Pieces plated per hour 2640 Area to be plated per hour 53 m 2 (570 ft 2 ) Minimum plate thickness 4 μm (160 μin.) Equipment requirements: Factor Specification Dimensions of full automatic plating unit 21 by 3.4 by 2.8 m(70 by 11 by 9 ft) Width of access space on sides of unit 0.76 m (3 ft) Width of access space on load end of unit 3.1 m (10 ft) Motor-generator set 15 V, 7500 A Dimensions of motor-generator set 3.1 by 3.1 by 2.4 m(10 by 10 by 8 ft) 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 μm (160 to 200 μin.) 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 μm (520 μin.). Table 7 Conditions for plating cadmium to a thickness of less than 13 μm (520 μin.) 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 4 3 1 2 Electrolytic cleaning Alkali, g/L (oz/gal) 70 (8) . . . 70 (8) Temperature, °C (°F) 82 (180) . . . 82 (180) Time, min 1 2 -1 . . . 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 8 -1 3 1 2 to >1 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/m 2 (A/ft 2 ) 270 (25) 9-15 V 270 (25) Time, min 10 30 10 Rinsing Temperature Ambient Ambient Ambient Time, min 1 4 3 1 2 Rinsing Temperature Ambient Ambient Ambient Time, min 1 4 2 1 2 Bright dipping HNO 3 , vol% 1 4 - 1 2 1 4 - 1 2 1 4 - 1 2 Temperature, °C (°F) 82 (180) Ambient Ambient Time, min 1 6 1 6 1 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 Temperature Solution No. Composition Amount °C °F Immersion time 1 H 2 SO 4 8-12 vol% 71-93 160-200 10-120 s 2 HCl 20-50 vol% RT RT 10-120 s 3 Na 2 CO 3 75-90 g/L (10-12 oz/gal) RT RT 15-60 s (a) 4 Petroleum solvent . . . RT RT 1 2 -3 min 5 Alkali (b) 60-75 g/L (b) (8-10 oz/gal) 82-93 (b) 180-200 (b) 1 2 -3 min 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 2 -1 min 9 (e) (e) (e) (e) 1 2 -1 min 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 s olution (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, concent ration 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. Variations in Plate Thickness For adequate protection of steel, the thicknesses of cadmium in Table 8 are recommended. The shape of a part can markedly influence uniformity of the electrodeposit. Parts of simple design, such as socket wrenches and bathroom hardware, can be plated with a high degree of uniformity of plate thickness. On such parts, about 90% uniformity would be anticipated. Table 8 Recommended thicknesses of cadmium Thickness Environmental exposure Description μm μin. Uses Mild Exposure to indoor atmospheres with rare condensation. Minimum wear and abrasion 5 200 Springs, lock washers, fasteners Moderate Exposure mostly to dry indoor atmospheres. Subject to occasional condensation, wear, or abrasion 8 320 Television and radio chassis, threaded parts, screws, bolts, radio parts instruments Severe Exposure to condensation, infrequent wetting by rain, cleaners 13 520 Washing machine parts, military hardware, electronic parts for tropical service Very severe Frequent exposure to moisture, saline solutions, and 25 1000 . . . Threaded fasteners present a special problem, because of variations in contour and because of tolerance requirements. These items ordinarily are barrel plated, and thicknesses of 3 to 4 μm (120 to 160 μin.) are usually specified. Throwing Power. The effect of shape on uniformity of deposit thickness is exemplified by the open-ended box (100 mm, or 4 in., cube) of Fig. 5. The open end of the box is pointed toward one of the anodes, to produce the most desirable condition for this shape without auxiliary thief rings, shields, bipolar anodes, insoluble anodes, or other devices. Results of plating such boxes with cadmium, silver, and copper, all deposited from cyanide baths, are shown in Fig. 5. These diagrams illustrate two facts: thickness of plate varies significantly from place to place on the simplest shape; and various plating baths have different throwing powers or abilities to plate uniformly over the surface, regardless of shape. Thickness ratio (a) Plating bath Side Bottom Cadmium 1:4.25 1:12 [...]... cyanide 42 5.6 3 0 -4 1 4. 0-5 .5 20 2.7 1 5-2 8 2. 0-3 .7 Sodium hydroxide 79 10.5 6 8- 105 9. 0-1 4. 0 75 10.0 6 0-9 0 8. 0-1 2.0 Sodium carbonate 15 2.0 1 5-6 0 2. 0-8 .0 15 2.0 1 5-6 0 2. 0-8 .0 Sodium polysulfide 2 0.3 2-3 0. 3-0 .4 2 0.3 2-3 0. 3-0 .4 Brightener (g) (g) 1 -4 0. 1-0 .5 (g) (g) 1 -4 0. 1-0 .5 Zinc metal 34 4.5 3 0 -4 8 4. 0-6 .4 17 2.3 1 5-1 9 2. 0-2 .5 Total sodium cyanide 93 12 .4 7 5-1 13 10. 0-1 5.1 45 6.0 3 8-5 7 5. 0-7 .6 Sodium... specifications required to stress relieve cadmium-plated components Hardness, HRC Stress relief before plating Hydrogen embrittlement relief (within 4 h of plating) Temperature Temperature °C °F Minimum time, h °C Minimum h °F time, 3 4- 5 4 17 5- 205 35 0 -4 00 4 3 6 -4 5 17 5- 205 35 0 -4 00 8 23(a) 4 6-5 4 17 5- 205 35 0 -4 00 23 >55 12 0-1 50 25 0-3 00 23 12 0-1 50 25 0-3 00 23 (a) Fasteners and bearings Although the... 10.5 6 8- 105 9. 0-1 4. 0 75 10.0 6 0-9 0 8. 0-1 2.0 Ratio: NaCN to Zn 2.75 0.37 2. 0-3 .0 0. 3-0 .4 2.6 0.3 2. 0-3 .0 0. 2-0 .4 Constituent Low-cyanide bath(c) Microcyanide bath(d) Optimum Range Optimum Range g/L oz/gal g/L oz/gal g/L oz/gal g/L oz/gal Zinc cyanide 9 .4( b) 1.3(e) 7. 5-1 4( b) 1. 0-1 .9 (f) (f) (f) (f) Sodium cyanide 7.5 1.0 6. 0-1 5.0 0. 8-2 .0 1.0 0.1 0.7 5-1 .0 0. 4- 0 .13 Sodium hydroxide 65 8.7 5 2-7 5 6. 9-1 0.0... 8.7 5 2-7 5 6. 9-1 0.0 75 10.0 6 0-7 5 8-1 0 Sodium carbonate 15 2.0 1 5-6 0 2. 0-8 .0 Sodium polysulfide Brightener (g) (g) 1 -4 0. 1-0 .5 (g) (g) 1-5 0. 1-0 .7 Analysis Preparation Analysis Zinc metal 7.5 1.0 0. 8-1 .5 7.5 1.0 6. 0-1 1.3 0. 8-1 .5 Total sodium cyanide 7.5 1.0 6. 0-1 5.0 0. 8-2 .0 1.0 0.1 0.7 5-1 .0 0. 1-0 .13 Sodium hydroxide 75 10 6 0-7 5 8. 0-1 0.0 75 10.0 6 0-7 5 8-1 0 Ratio: NaCN to Zn 1.0 0.1... Composition Amount Immersion time, min(b) g/L oz/gal 1 Ammonium nitrate 10 5- 136 1 4- 1 8 1 0-2 0 2(c) Hydrochloric acid (1.18 sp gr), undiluted 1 0-2 0 Antimony trioxide 15 2 Chromic acid 203 26.8 5-1 0 Sulfuric acid (95%) 48 (d) 6 .4( e) Ammonium persulfate 51 6.7 5-1 0 Ammonium hydroxide 96.8(d) 12.8(e) Sodium cyanide 6 0-9 1 8-1 2 1 0-2 0 3 4 5(f) (a) Solutions are listed in order of preference; all solutions... characteristics of alkaline noncyanide zinc baths Optimum(a) Range(b) g/L oz/gal g/L oz/gal Zinc oxide 9 .4 1.3 7. 5-2 1 1-2 .8 Sodium hydroxide 65 8.6 6 5-9 0 8. 6-1 2 Proprietary additive (c) (c) 3-5 0. 4- 0 .7 7.5 1.0 6. 0-1 7.0 0. 8-2 .3 Constituent Preparation Analysis Zinc metal Sodium hydroxide 75.0 10.0 7 5-1 12 10. 0-1 4. 9 (a) Operating conditions: temperature, 27 °C (81 °F) optimum; cathode current density, 0.6 A/dm2... increasing the total-cyanide-to-zinc ratio of the solution The exact optimum ratio varies slightly for a given proprietary system, as shown in Table 3 Table 3 Effect of bath temperature on total-cyanide-to-zinc ratio Temperature Total-NaCNto-Zn ratio (standard cyanide bath) Total-NaCNto-Zn ratio (midcyanide bath) (standard cyanide bath) (midcyanide bath) 72 2.6 2.2 26 79 2.7 2.3 30 86 2.8 2 .4 34 93 2.9 2.5... satisfactory for steel at 46 HRC After plating, bake parts at 175 to 205 °C (350 to 40 0 °F) for 3 to 24 h The shorter baking periods are generally adequate for parts with a tensile strength below about 1520 MPa (220 ksi); longer baking periods are recommended for steel of tensile strength above about 1520 MPa (220 ksi) or for lowerstrength parts if sharp notches or threads exist Parts greater than 25 mm... to 25 V, barrel (a) Operating temperature: 29 °C ( 84 °F) optimum; range of 21 to 40 °C (69 to 105 °F) (b) Operating temperature: 29 °C ( 84 °F) optimum; range of 21 to 40 °C (69 to 105 °F) (c) Operating temperature: 27 °C (79 °F) optimum; range of 21 to 35 °C (69 to 94 °F) (d) Operating temperature: 27 °C (79 °F) optimum; range of 21 to 35 °C (69 to 94 °F) (e) Zinc oxide (f) Dissolve zinc anodes in solution... content 60.1, 75.2, and 90.2 g/L (8, 10, and 12 oz/gal) Zn (CN); 43 .7, 54. 6, and 65.5 g/L (5.82, 7.27, and 8.72 oz/gal) NaCN; 75.2 g/L (10 oz/gal) NaOH; 2.75-to-1 ratio of NaCN to zinc Temperature: 30 °C (86 °F) (c) Effect of NaOH content 60.1 g/L (8 oz/gal) Zn(CN); 43 .6 g/L (5.8 oz/gal) NaCN; 150 .4 and 75.2 g/L (20 and 10 oz/gal) NaOH; 2.75-to-1 ratio of NaCN to zinc Temperature: 30 °C (86 °F) Sodium carbonate . 8 2- 105 (18 0-2 20) 8 2- 105 (18 0-2 20) 8 2- 105 (18 0-2 20) Time, min 1-3 5 1-3 Temperature Solution No. Composition Amount °C °F Immersion time 1 H 2 SO 4 8-1 2 vol% 7 1-9 3 16 0-2 00. Ambient Ambient Time, min 1 4 3 1 Cyanide dipping NaCN, g/L (oz/gal) 3 0 -4 5 ( 4- 6 ) 3 0 -4 5 ( 4- 6 ) 3 0 -4 5 ( 4- 6 ) Temperature Ambient Ambient Ambient Time, min 1 4 3 1 Plating Temperature,. 16 0-2 00 1 0-1 20 s 2 HCl 2 0-5 0 vol% RT RT 1 0-1 20 s 3 Na 2 CO 3 7 5-9 0 g/L (1 0-1 2 oz/gal) RT RT 1 5-6 0 s (a) 4 Petroleum solvent . . . RT RT 1 2 -3 min 5 Alkali (b) 6 0-7 5 g/L (b) ( 8-1 0