Metal Finishing Guide Book

2013

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modifications were made which were manifested in pore structure development. Finally, these modifications became the major part of the electrolyte—secondary only in some cases to sulfuric acid—which is in many cases only required due to older specifications where updates may be long overdue. Anodize process procedures using pulse anodizing methodology were investigated and modified by anodizers in the USA and other countries. Several facilities in the USA and Japan provided information which made this universal electrolyte perform better in production. Two different types of pulse gave optimum results: Variable 0.5-2.0-4.0 sec pulses@ 10 -25% Max Current Density Faster Anodize – Pore structure development Prevent pitting and blisters in some cases Reduces burning for Type II and III on difficult alloys Promotes dye penetration Variable 20-30-40 sec pulse @ 25-75% max Current Density (For commercial and architectural anodize where time and energy savings are priorities utilizing the recovery effect) Variable pulse was a major contribution for problem-solving and troubleshooting situations involving galvanic pitting on 7000 series alloys. Pulse anodize methodology was integrated into the system as pulse-stepramp with numerous procedural requirements from 1975-2003. Later, extensive research and development for type IC, including capacitance shunt discharge, was performed3. Eight of these major procedural requirements are presented here. The final development came with the integration of type IC into the universal chrome-free electrolyte, with step-ramp procedure modifications. Pulse capacitance shunt discharge made it possible to achieve anodize pore structure development early during the ramp cycle at 2–3 volts. This final pore structure development initiated at 2–3 volts became a major factor for type IC Anodize. Tartaric, Oxalic, Citric and Boric became the preferred acids for all type IC, II III and the combination Type 123 anodize. Some of the mixed electrolytes used by anodizers have the following formulation: 2 – 10% Sulfuric Acid 2 – 10% Tartaric/Boric 2 – 10% Concentrated Additives or Modifiers (Including Amino Polycarboxylic Acids) Figure 1. One Universal Electrolyte Formulation. 224 This universal electrolyte and variable pulse along with eight key procedural requirements came to be known as the "complete spectrum approach," beginning in 1990 and continuing to the present. Finally, selective brush anodizing was introduced using a super concentrated type IC-IIB- III and type 123 Anodize.

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