Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 248 of 707

Table I. Concentrations of Fluoboric Acid, Lead Fluoborate, Stannous Fluoborate, and Copper Fluoborate Used in Tin, Lead, and Tin-Lead Alloy Plating Product 48% Fluoboric Acid Fluoboric Acid, 100% Boric Acid 51% Lead Fluoborate Lead Fluoboric Acid, 100% Boric Acid 50% Stannous Fluoborate Stannous Tin Fluoboric Acid, 100% Boric Acid 45% Copper Fluoborate Copper Fluoboric Acid, 100% Boric Acid 656 19 1.710 480 11 48 1.600 320 48 48 1.550 187 30 30 90 Tin/10 Lead Barrel, Still, and High-Speed Baths This bath provides a uniform, smooth matte deposit, which is used for various engi- neering applications. Higher temperatures permit higher current densities, which are required in wire and strip plating. Deposits plated from 93 lead/7 tin baths are harder than those obtained from lead baths. The 93 lead/7 tin bath is used to plate bearings and seals. Since 93 lead/7 tin alloys are soft, slow barrel speeds are recommended in order to prevent heavy parts from bonding to one another. 93 Lead/7 Tin Barrel and Still Baths The operation of the ternary alloy bath is similar to that of the 93 lead/7 tin bath. The ternary alloy deposit results in bearing metals that exhibit a greater resistance to fatigue than do the 93 lead/7 tin alloys. The alloy is used to plate lin- ings in sleeve bearings. 10 Tin/88 Lead/2 Copper Ternary Alloy Barrel and Still Baths FLUOBORATE PLATING Tin fluoborate, lead fluoborate, and fluoboric acid, in various propor- tions (see Tables I and II), can be used for plating all percentages of tin-lead, 100% lead, and 100% tin. Fluoborate baths require boric acid for stability. Anode bags filled with boric acid are hung in the plating tanks. Stabilized liquid peptone, gelatin, resorcinol, or other liquid Concentration (g/L) Specific Gravity (20O 1.365 C) 247

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