Metal Finishing Guide Book


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Table I. Operating Criteria for Soak Cleaners Cleaner Type Concentration Range Temperature Time Agitation Liquid 4-8% v/v 120-185°F (49-85°C) 2-10 min Solution movement Powder 4-10 oz/gal (30-75 g/L) 120-185°F (49-85°C) 2-10 min Solution movement Table II. Soak Cleaner Operating Parameters—Bath Chemistry (oz/gal) Metal Caustic Silicate Gluconate Phosphate Borates Steel 1.8-2.2 1.5-3.0 0.16-3.2 0.4-0.8 — Wetters 0.4-0.8 Stainless steel 1.8-2.2 1.5-3.0 0.16-3.2 0.4-0.8 — 0.4-0.8 Brass 0.0-0.8 2.0-4.0 0.16-0.32 0.8-1.6 0.0-0.8 0.4-0.8 Copper 1.6-3.2 1.2-2.4 0.16-0.32 0.8-1.6 0.0-0.8 0.4-0.8 Zinc 0.0 0.8-1.6 0.16-0.32 1.2-2.4 — 0.4-0.8 White metal 0.0 0.8-1.6 0.16-0.32 1.2-2.4 — 0.4-0.8 Multiply oz/gal by 7.5 to convert to g/L Wetters are usually a balanced blend of anionic and nonionic surfactants. tank weirs, and overflow dams, are mechanical aids to facilitate oil and grease removal from displacement and emulsifying cleaners. Most soak cleaners meet the operating criteria shown in Table I. Aluminum requires a specialized, different approach to cleaning, which will be dealt with separately. Bulk parts may be soak cleaned in line or off line in basket or barrel operations. Table II provides an example of general soak cleaner constituents and applicable concentration ranges. Trial evaluation and testing is required to determine which specific formulation meets the soak-cleaning requirements within the specified cycle limitations. These are some appropriate cleanliness tests to confirm removal of soils: • Absence of water breaks on parts rinsed after a weak post acid dip • Flash rusting of ferrous parts • White towel wipe cleaned surface, confirming absence of smuts, oils, and grease • Absence of UV light fluorescence on cleaned surface previously coated with UV fluorescing oils. • Immersion bronze, copper, or tin deposits on the cleaned, active, appropriately reactive substrate • Mechanical deformation, bending of finished part or grinding of plated deposit • Measure the contact angle of a drop of water on the cleaned metal surface. ELECTROCLEANING This method uses a DC rectifier to provide current, generating gas bubbles that mechanically scrub the part. This is a powerful cleaning method that complements the previous soak-cleaning step. Parts are predominantly positively charged, resulting in anodic or reverse current cleaning. To a lesser degree parts may be negatively charged, resulting in cathodic cleaning. A third option is periodic reverse, which takes advantage of anodic and cathodic cleaning mechanisms. Electrocleaning can be classified into four groups, meeting most cleaning applications. 1 .Anodic. If preceded by a soak cleaner the electrocleaner's main 141

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