Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 121 of 707

Table I. Operating Criteria for Soak Cleaners Cleaner Type Concentration Range Temperature 120-185° Liquid Powder 4-8% v/v 4-10 oz/gal (30-75 g/L) 120-185° Stainless steel Brass Copper Zinc White metal Caustic 1.8-2.2 1.8-2.2 0.0-0.8 1.6-3.2 0.0 0.0 Silicate 1.5-3.0 1.5-3.0 2.0-4.0 1.2-2.4 0.8-1.6 0.8-1.6 Time F (49-85° F (49-85° C) C) Gluconate 0.16-3.2 0.16-3.2 0.16-0.32 0.16-0.32 0.16-0.32 0.16-0.32 2-10 min 2-10 min Agitation Solution movement Solution movement Table II. Soak Cleaner Operating Parameters—Bath Chemistry (oz/gal) Metal Steel — — Phosphate Borates Wetters 0.4-0.8 0.4-0.8 0.8-1.6 0.8-1.6 1.2-2.4 1.2-2.4 0.0-0.8 0.0-0.8 — — Multiply oz/gal by 7.5 to convert to g/L Wetters are usually a balanced blend of anionic and nonionic surfactants. from displacement and emulsifying cleaners. Most soak cleaners meet the oper- ating 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 spec- ified 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 neg- atively 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 appli- cations. 1 .Anodic. If preceded by a soak cleaner the electrocleaner's main 120 0.4-0.8 0.4-0.8 0.4-0.8 0.4-0.8 0.4-0.8 0.4-0.8

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