Metal Finishing Guide Book

2012-2013

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Table IV. Electrocleaner Operating Parameters���Bath Chemistry (oz/gal) Metal Caustic Silicate Gluconate Phosphate Borates Steel 5-7 2-4 1-3 2-4 ��� Wetters 0.1-0.3 Stainless steel 5-7 2-4 1-3 2-4 ��� 0.1-0.3 Brass 1.5-2.5 1.2-2.4 0.2-0.4 0.8-1.6 0.8-1.6 0.1-0.3 Copper 1.6-3.2 1.2-2.4 0.2-0.4 0.8-1.6 0.4-1.8 0.1-0.3 Zinc 1.2-2.4 1.6-2.4 0.08-0.16 0.4-0.8 ��� 0.1-0.3 White metal 0.8-1.2 1.6-2.4 0.16-0.32 1.2-2.4 ��� 0.1-0.3 Multiply oz/gal by 7.5 to convert to g/L Reducing sugars at 0.2-0.4 oz/gal (1.5-3.0 g/L) reduce hexavalent chromium to the insoluble chromium hydroxide. Polished brass and copper may also be cathodically cleaned as per the specifications given for white metal. The exception is omitting caustic in the electrocleaner solution. and electrocleaning in one step, one tank, or in separate process tanks. In many applications this provides three advantages: simplifies product inventory, eliminates a rinse between soak and electrocleaner, and accomplishes both cleaning steps in one tank. A disadvantage would be shorter service life of the electrocleaner due to oil and grease buildup. Based on the metals electrocleaned, the alkalinity level is critical relative to the caustic (sodium or potassium hydroxide) content. Nonferrous metals, such as copper alloys, brass, and zinc, are best suited to electrocleaning in low- to midrange caustic solutions. These solutions must also contain inhibitors, such as silicate in ratio with caustic, for optimum conductivity with sufficient inhibition of the zinc surface to prevent etching; Borax buffer and silicate inhibitor for copper alloys and brass to prevent dezincification of brass and excess oxidation of copper alloys; high caustic for steel electrocleaning requirements such as conductivity. Table V. Acid Dip Operating Parameters Temperature Base Metal �� �� C Time (min) Steel 75-95 24-35 1-3 Hydrochloric/sulfuric F Acid Type Stainless steel 75-95 24-35 1-3 Hydrochloric/sulfuric Brass 75-85 24-29 2-4 Sulfuric/sulfamic Copper 75-85 24-29 2-4 Sulfuric Zinc 75-85 24-29 1-4 Sulfuric/sulfamic White metal 75-85 24-29 1-4 Sulfuric/sulfamic Table VI. Acid Dip Operating Parameters���Bath Chemistry (oz/gal) Base Metal % v/v (H & S) Acid Concentration Fluorides Chlorides Wetters Inhibitors Steel H(5-50), S(5-15) 0.3-0.7 0.8-1.2 0.03-0.05 0.01-0.03 Stainless Steel H(5-50), S(5-15) 0.3-0.7 0.8-1.2 0.03-0.05 0.01-0.03 Brass S (3-5) 0.2-0.5 ��� 0.03-0.05 ��� Copper S (5-7) 0.2-0.5 ��� 0.03-0.05 ��� Zinc S(1-2), Sul(0.5-0.7) 0.3-0.5 ��� 0.03-0.05 ��� White metal S(1-2), Sul(0.5-0.7) 0.3-0.5 ��� 0.03-0.05 ��� H = hydrochloric acid; S = sulfuric acid; Sul = sulfamic acid. 156

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