1、Designation: B 630 88 (Reapproved 2006)Standard Practice forPreparation of Chromium for Electroplating with Chromium1This standard is issued under the fixed designation B 630; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the yea
2、r of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice is intended to serve as a process guide (notas a standard procedure) for producing adherent electr
3、odepositsof chromium on chromium for engineering use.1.2 Only well-known, generally practical methods usinghexavalent chromium plating baths have been included. Someof the newer proprietary chromium plating processes producechromium plating for which this process is unsuitable. Suppli-ers of the pro
4、cesses should be consulted.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations p
5、rior to use.2. Referenced Documents2.1 ASTM Standards:2B 177 Guide for Engineering Chromium Electroplating3. Significance and Use3.1 Electrodeposits of chromium on chromium are producedin cases where it is desired to obtain a better performingcoating, to reclaim plated parts that are defective, or r
6、estoreworn chromium coatings to original dimensions.4. Preparation of Surface4.1 Surface FinishingThe smoothness of the chromiumcoating before electroplating with chromium should closelyapproximate the requirements of the finished part. It is usuallyachieved by appropriate grinding with a diamond wh
7、eel.4.2 Stripping and Basis MetalWith previously electro-plated parts where the chromium deposit has been wornthrough, or where grinding has exposed the basis metal,preferred results are obtained by stripping the remainingchromium completely. However, it is possible to obtain satis-factory deposits
8、on such substrates by careful attention todetails in the pretreatment and electroplating process steps.4.3 Stripping may be done by several methods, includingproprietary processes or inhibited hydrochloric acid solution(10 to 20 % by volume), or anodic treatment at 55 to 800 A/m2(5 to 75 A/ft2) in a
9、 solution of 35 to 50 g/L (5 to 7 oz/gal) ofsodium hydroxide or 60 to 75 g/L (8 to 10 oz/gal) of sodiumcarbonate at 20 to 25C (70 to 80F).4.4 Process Outline:4.4.1 Preclean (see 5.1.1 and 5.1.2),4.4.2 Alkaline electrolytic clean (see 5.1.3),4.4.3 Rinse (cold water),4.4.3.1 Rinse (hot water),4.4.3.2
10、Dry,4.4.3.3 Mask (see 5.2),4.4.4 Activate (see 5.3),4.4.5 Chromium electroplate,4.4.6 Rinse (cold water),4.4.7 Rinse (hot water), and4.4.8 Dry.5. Procedure5.1 CleaningThe following cleaning treatments may beused for all conditions and types of electrodeposited chro-mium. The choice of the procedures
11、 will be governed largelyby the condition of the surface.5.1.1 PrecleaningWhen considerable amounts of greaseand oil are present on the surface, precleaning (emulsion oralkaline spray or soak) is necessary to remove the bulk of thesoil.5.1.2 Abrasive CleaningOxide and other films may beremoved by me
12、chanical techniques using such abrasives as fineemery on a cloth or a wheel, pumice slurry, or greaselessbuffing compounds. Grit blasting, shot blasting, wet blasting,or vapor honing may also be used. Abrasive cleaning isgenerally not necessary when suitable mechanical finishingprocedures have been
13、used.5.1.3 Cathodic Alkaline CleaningRemoval of final tracesof dirt, grease, and oil is best accomplished by cathodicalkaline cleaning. Cathodic electrocleaning is necessary be-cause anodic electrocleaning will strip chromium and mayexpose the basis metal. In cathodic cleaning, the parts arenegative
14、ly charged and attract positively charged metallic ions,1This practice is under the jurisdiction of ASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.02 onPre Treatment.Current edition approved April 1, 2006. Published April 2006. Originallyapp
15、roved in 1977. Last previous edition approved in 2001 as B 630 88 (2001).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe A
16、STM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.soaps, and other colloidal materials in the solution, causingthem to “plate out” as loose smut on the surfaces beingcleaned. Thus, do not allow the cleaning solution to beco
17、meheavily contaminated with dirt, grease, or oil.5.2 MaskingRigid, nonconductive materials or stop-offs,which are especially compounded nonconductive tapes, waxes,lacquers, or polymeric materials, will protect areas that are toremain free of chromium. Due to the varying kinds ofchromium electroplati
18、ng solutions and interactions with thesematerials, vendor instructions should be followed.5.3 Activating:5.3.1 The procedure used for etching or activating thechromium surface is most important and usually determines thesoundness of the adhesion. Chromium exhibits a strong ten-dency to acquire surfa
19、ce oxides rapidly (air passivity) thatreduce the adhesion of subsequent chromium deposits. Anodicetching in a chromic acid solution, 250 g/L , at room tempera-ture is recommended. In some instances, this procedure may beperformed in the chromium electroplating solution.5.3.2 Give the part an anodic
20、etch for 5 to 60 s at 6 V. Foreffective control, confirm etch action by visual observation ofuniform gassing; increase etch time if necessary. When basismetal is exposed or high-speed chromium electroplating solu-tions are used, keep the time as short as possible.5.3.3 When the part to be electropla
21、ted has a large mass,allow it to reach the temperature of the electroplating bathbefore etching.5.4 Chromium Electroplating:5.4.1 Make the part cathodic up to 3.0 V. Slowly increasethe voltage in steps of 0.25 V so that gassing and electroplatingstart after 30 to 60 s and full current is reached in
22、5 min.5.4.2 The composition of the ordinary or “conventional”solution is 250 to 400 g/L of chromic acid (CrO3) and sulfateradical (SO4=) to maintain a ratio by weight of CrO3toSO4=of 100 to 1, although many electroplaters prefer ratios aslow as 80 to 1, which facilitates electroplating chromium onch
23、romium. The sulfate is generally added as sulfuric acid (94to 96 mass % H2SO4). Refer to Guide B 177 for moreinformation on the operation of the electroplating solution.5.4.3 Some proprietary baths contain a supplementary cata-lyst in the form of fluorides or other mixed catalysts. Some ofthese bath
24、s are satisfactory, but some could be unsuitable. Thesupplier of any proprietary bath should be consulted forspecific information.6. Keywords6.1 activation; chromium; cleaning; preparation; strikingASTM International takes no position respecting the validity of any patent rights asserted in connecti
25、on with any item mentionedin this standard. 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
26、 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 consi
27、deration 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.This standard is copyrighted by ASTM International, 100 Ba
28、rr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).B 630 88 (2006)2
