Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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SEALER ADDITIONAL INFORMATION Sodium dichromate solution, 5-9 oz/gal Baseline Boiling deionized water Unsealed Baseline Baseline Sodium dichromate solution, 50 parts per million (ppm) COTS permanganate solution COTS low nickel seal solution, with hot water seal COTS low nickel seal solution, without hot water seal Benchmark Candidate Candidate Candidate Table 3. Test Matrix: Sodium Dichromate Sealers and Most Promising Seals to Evaluate for Replacement anodizing at its facility. Therefore, processing and coating requirements for Types II, IIB, and III anodizing at OO-ALC were determined. Based on interviews with OO-ALC personnel, anodizing processes at OO-ALC are used to treat components made from 2000, 6000, and 7000 series Al alloys. The performance require- ments for the three types of anodizing conducted at OO-ALC must meet the requirements of MIL-A-8625F, which are summarized in Table 1 [Ref. 6]. The acceptance criteria recognize that corrosion resistance is determined using the standard salt spray test in accordance with ASTM B117 [Ref. 7], and that paint adhesion is determined in accordance with Federal Test Method Standard 141, Method 6301 [Ref. 8]. (1See Table 2: Acceptance Criteria for Corrosion Resistance.) . SULFURIC ACID (TYPE II AND TYPE IIB) ANODIZING OO-ALC uses sulfuric acid (Type II and Type IIB) anodizing to anodize the components of various aircraft landing gear. Current is applied when parts enter into the solution and is gradually increased to the desired current density (typically 12 to 22 volts). The coatings become harder and denser as the purity of the aluminum in the substrate increases [Ref. 4]. Parts that have been anodized with the Type II and IIB processes are sealed with the sodium dichromate sealer; therefore, these processes were the primary focus of this study. The main Environmental Health and Safety (EHS) concerns expressed by OO-ALC personnel for these processes are the corrosive nature of the sodium dichromate solution and the fact that it contains Cr+6. HARD COAT (TYPE III) ANODIZING OO-ALC performs the hard coat (Type III) anodizing process, after conducting Type II anodizing on a part, as part of their aircraft refurbishment processes. Because Type III anodized coatings are sealed in boiling DI water, the primary EHS 279

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