1、Designation: B 507 86 (Reapproved 2003)Standard Practice forDesign of Articles to Be Electroplated on Racks1This standard is issued under the fixed designation B 507; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 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 covers design information for parts to beelectroplated on racks. The recommendations contained hereinare no
3、t mandatory, but are intended to give guidance towardgood practice.1.2 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 ap
4、plica-bility of regulatory limitations prior to use.2. Significance and Use2.1 When an article is to be electroplated, it is necessary toconsider not only the characteristics of the electroplatingprocess, but also the design of the part to minimize electro-plating and finishing costs and solution dr
5、agout as well as toimprove appearance and functionality. It is often possibleduring the design and engineering stages to make smalladjustments in shape that will result in considerable benefittoward a better quality part at a lower cost.2.2 The specific property of an electroplating process thatwoul
6、d require some attention to the details of optional designs,is the throwing power of the electroplating solution. Throwingpower is the improvement of the coating distribution over theprimary current distribution on an electrode (usually cathode)in a given solution, under specified conditions.3. Curr
7、ent Distribution and Throwing Power3.1 The apparent current during practical electroplating isnever uniform over the surface of the product. Even parallelplates have a nonuniform distribution of current when freelysuspended in a bath as shown in Fig. 1. In this example, thecurrent lines tend to conc
8、entrate as corners, and edges (high-current density) of the part. Consequently more metal isdeposited at the high-current density areas than at the low-current density areas.4. Relative Throwing Powers of Different Electrolytes4.1 Throwing power is not the same for all metals and allelectroplating b
9、aths. Table 1 lists the commonly used electro-plating processes. They are arranged according to decreasingthrowing power.4.2 A Rochelle-type copper electroplating solution has ex-cellent throwing power compared to the poor throwing powerof a chromic acid solution used to deposit chromium. Thewidely
10、used Watts-type nickel bath has fair throwing power.5. Geometric Factors Determining Deposit Distribution5.1 Since a metal deposits preferentially at protuberances,such as sharp corners, edges, fins, and ribs, these should berounded to a radius of at least 0.4 and preferably 0.8 mm toavoid excessive
11、 buildup. Contouring a base corner in adepression is also recommended to avoid thickness deficiencyat the location.5.2 The width-to-depth ratio of a depression or recessshould be held to more than three as shown in Fig. 2.Otherwise, a special auxiliary anode must be employed insidethe recess to prom
12、ote more uniform current distribution. Anauxiliary anode is usually made of the depositing metal and isplaced close to the low-current density areas to enhance metaldeposition at those regions.5.3 All sharp edges and base angles of a recess should berounded to a radius of 0.25 times or more the dept
13、h of therecess as shown in Fig. 3. When sharp recess angles arerequired for a functional purpose, the electroplater cannot beexpected to meet a minimum thickness at those locationsunless it is specifically required.6. Examples of Distribution of Electrodeposited Nickelon Various Shapes6.1 Fig. 4 thr
14、ough Fig. 52show the kind of nickel distribu-tion that was obtained on several different cathode configura-tions as deposited from a Watts-type bath at normal operatingcurrent densities. The thicknesses illustrated are exaggerated toemphasize the variations that were obtained. The data are1This prac
15、tice is under the jurisdiction of ASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.01 onAncillary Activities.Current edition approved Feb. 10, 2003. Published May 2003. Originallyapproved in 1970. Last previous edition approved in 1998 as B 50
16、7 86 (1998).2Adapted from sketches appearing in Electroplating and Engineering Hand-book, 4th ed, Durney, L. J., ed., Reinhold Publishing Corporation, New York, 1984.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.measurements taken
17、from metallographic cross sections. Ref-erence to the figures enables similar conclusions to be drawnwith most other metals, excluding chromium. The ranges willbe smaller for metals above nickel in Table 1 and larger formetals below nickel.6.2 Improvement in nickel distribution can be gained insidea
18、n angle by increasing the angle size, as shown in Fig. 4.Twosurfaces meeting at an angle of 60 show an average-to-minimum thickness ratio of 3.3, and increasing the angle to 90or 120 the ratio can be reduced to 2.7 or 1.9, respectively.6.3 Sharp corners should be given as large a radius aspractical
19、to improve metal distribution in a recess and avoidexcessive buildup on protuberances. Fig. 6(a) illustrates a partwith a sharp angled recess. Nickel distribution is not veryuniform with practically no deposit down in the corners of therecess. Rounding the corners of the recess on the part, as shown
20、in Fig. 6(b), yields a more uniform nickel thickness in therecess. The average-to-minimum thickness ratio in these ex-amples was 9.2 for the part with sharp corners and 5.6 for thepart with the rounded corners.6.4 Deep recesses will always have a thinner deposit thanthe surrounding external areas, a
21、s shown in the cross section ofa concave part in Fig. 7(a). The average-to-minimum nickelthickness ratio for this example was 6.6. A more uniformdeposit thickness can be obtained on a convex-shaped part, asshown in the example of Fig. 7(b). In this case the average-to-minimum nickel thickness ratio
22、was 2.6.5 Another example of an elongated curved surface (con-vex) is illustrated in Fig. 5(a). The nickel deposit was fairlyuniform with an indicated average-to-minimum thickness ratioof 2. However, when this shape is joined to another like a flatplate, metal distribution is considerably different
23、as illustratedby Fig. 5(b).7. Racking and Rinsing7.1 Other factors besides metal distribution should also betaken into account when designing a part that will be rackelectroplated. The parts must be attached firmly to the rack, sothat all significant surfaces come in contact with the electro-lyte.7.
24、2 The parts must be attached to a rack firmly enough toprevent falling off during electroplating, and the attachmentshould be with enough force to provide a continual low-resistance electrical contact. In many cases, parts are rigidlyfastened to racks through spring clips, prongs or bolts. Little or
25、FIG. 1 Current Density Distribution and Typical Electrodeposit (filled area)TABLE 1 Relative Throwing Powers of Common ElectroplatingBathsBath/Metal RankingRochell copper (cyanide based) ExcellentCyanide cadmium ExcellentCyanide gold GoodCyanide silver GoodAlkaline tin GoodCyanide zinc GoodAlkaline
26、non cyanide zinc GoodFluoborate lead GoodAll chloride nickel FairTin nickel FairSulfamate nickel FairWatts nickelAFairBright nickel FairAcid chloride zinc FairNickel-iron FairChloride iron FairPyrophosphate copper FairAcid copper FairTrivalent chromium PoorHexavalent chromium PoorAUsed for examples
27、illustrated by Figs. 4-5.B 507 86 (2003)2no metal will desposit at the points of contact; therefore, it isimportant to select noncritical areas for attaching parts to racks.7.3 Articles attached to racks should be oriented to permitelectroplating to be free of roughness on significant surfaces.Rough
28、ness comes from insoluble debris suspended in anelectroplating bath that becomes incorporated into the depos-iting metal, especially on upward facing surfaces. Thus, inmany circumstances, it is advisable to have the significantsurfaces in a vertical position, or even be inverted duringelectroplating
29、.7.4 Orientation of a part on a rack is also important toreduce opportunities for air entrapment in cupped areas. Airpockets will prevent metal deposition on the exposed surface.Adequate drainage of parts on racks is also desirable to reducedragout of the electrolyte to the rinses. Engineering desig
30、n canincorporate holes at strategic locations to allow satisfactoryrunoff of solution.NOTE 1Ratio should be a minimum of threeFIG. 2 Width-to-Depth Ratio of a RecessFIG. 3 Rounding Corners to a Radius (r) Related to the Depth of a Recess,r0.25DNOTEAdapted from sketches appearing in Electroplating an
31、d Engineering Handbook, 3rd ed. Reinhold Publishing Corporation, Graham, A. K., andPinkerton, H. L., eds., New York, 1971.FIG. 4 Influence of Increasing Angle to Improve Thickness Distribution of Electrodeposited NickelB 507 86 (2003)3FIG. 5 Nickel Distribution on a Convex Surface (a) aloneCompared
32、to the Same Configuration as Part of a LargerComposite (b)B 507 86 (2003)4ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity
33、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
34、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 r
35、eceived 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 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies
36、) 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).FIG. 6 Improving Nickel Thickness Distribution (Average/Minimum Thickness Ratio) by Rounding CornersFIG. 7 Comparing Nickel Distribution on Concave (a) and Convex(b) SurfacesB 507 86 (2003)5
