ASTM B921 PDF

More B Coatings are categorized into four classes according to corrosion protection and finish. The type of conversion coating depends on the composition of the solution and may also be affected by pH, temperature, duration of the treatment, and the nature and surface condition. Films are normally applied by dipping, but may also be applied by inundation, spraying, roller coating, or by wipe-on techniques. Coatings shall adhere to specified electrical resistance, adhesion, and corrosion resistance requirements.

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A number in parentheses indicates the year of last reapproval. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory requirements prior to use.

Referenced Documents2. NOTE 1—Non-rinsed conversion coatings are finding increased usageon fabricated parts and castings. A class twoconversion coating is designed to give painted salt fog corro-sion resistance and some bare salt fog corrosion resistance. Aclass three conversion coating provides little salt fog corrosionresistance, but low electrical contact resistance see MIL-DTL Class four conversion coatings only provide for paintedsalt fog corrosion resistance.

Current edition approved May 1, Published May Originallyapproved in Last previous edition approved in as B — United States Surfaces Preparation5. The parts shall therefore, as far as necessary, becleaned in a non-hexavalent chromium cleaner before conver-sion coating and, if necessary, be pickled.

Methods of Application of Conversation Coatings6. The application methodused shall be taken from the operating instructions for theconversion coating process employed. Conversion coatingsolutions are usually acidic and may contain various salts thatmay be varied to affect the appearance and hardness of the film.

The type of conversion coating depends on the composition ofthe solution and may also be affected by the pH, temperature,duration of the treatment, and the nature and surface conditionof the alloy being treated.

Hot water shall be used only ifallowed by the manufacturer of the conversion coating inquestion. The drying of the coating shall be carried out inaccordance with the specifications of the manufacturer of theconversion or conversion coating in question.

Coating Requirements7. A practical evaluation of the adhesion can be madeby measuring the adhesion of a secondary organic film appliedto the conversion coating in question. When specified, theconversion coating shall pass the organic coating adhesion testin Test Methods D or the equivalent ISO None shall be larger than 1 mmin diameter. Each individual test specimen shall not have morethan 5 isolated spots or pits, none larger than 1 mm in diameteron their respective surfaces.

Spots within 10 mm of the edgesof the panels are not counted. Test specimens shall be by mm. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility. This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters.

Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.

Permission rights to photocopy the standard may also be secured from the ASTM website www.

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