1、Designation: B 507 86 (Reapproved 2008)e1Standard 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 la
2、st revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEThe units statement in subsection 1.2 was corrected editorially in April 2008.1. Scope1.1 This practice covers design informa
3、tion for parts to beelectroplated on racks. The recommendations contained hereinare not mandatory, but are intended to give guidance towardgood practice.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does
4、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 prior to use.2. Significance and Use2.1 When an art
5、icle 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 dragout as well as toimprove appearance and functionality. It is often possibleduring the de
6、sign 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 thatwould require some attention to the details of optional designs,is the throwing power of the e
7、lectroplating 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. Current Distribution and Throwing Power3.1 The apparent current during practical electroplatin
8、g 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 concentrate as corners, and edges (high-current density) of the part. Consequently more metal
9、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 baths. Table 1 lists the commonly used electro-plating processes. They are arranged accordi
10、ng 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 used Watts-type nickel bath has fair throwing power.5. Geometric Factors Determining Depos
11、it 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 buildup. Contouring a base corner in adepression is also recommended to avoid thickness d
12、eficiencyat 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 promote more uniform current distribution. Anauxiliary anode is usually made of the depositing
13、 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 depth of therecess as shown in Fig. 3. When sharp recess angles arerequired for a functional p
14、urpose, the electroplater cannot beexpected to meet a minimum thickness at those locationsunless it is specifically required.1This practice is under the jurisdiction of ASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.01 onAncillary Activities
15、.Current edition approved April 1, 2008. Published April 2008. Originallyapproved in 1970. Last previous edition approved in 2003 as B 507 86 (2003).1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6. Examples of Distribution of Elect
16、rodeposited Nickelon Various Shapes6.1 Fig. 4 through 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 vari
17、ations that were obtained. The data aremeasurements taken 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.
18、2 Improvement in nickel distribution can be gained insidean 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 Sh
19、arp corners should be given as large a radius aspractical 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
20、. Rounding the corners of the recess on the part, as shownin 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 ha
21、ve a thinner deposit thanthe surrounding external areas, as 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). I
22、n this case the average-to-minimum nickel thickness ratio 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
23、a flatplate, metal distribution is considerably different as illustratedby Fig. 5(b).2Adapted from sketches appearing in Electroplating and Engineering Hand-book, 4th ed, Durney, L. J., ed., Reinhold Publishing Corporation, New York, 1984.FIG. 1 Current Density Distribution and Typical Electrodeposi
24、t (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 non cyanide zinc GoodFluoborate lead GoodAll chloride nickel
25、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 illustrated by Figs. 4-5.B 507 86 (2008)e127. Racking and Rin
26、sing7.1 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.7.2 The parts must be attached to a rack firmly
27、 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 orno metal will deposit at the points of contac
28、t; 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.Roughness comes from insoluble debris suspended in anelectroplating bath that becomes incorp
29、orated 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.7.4 Orientation of a part on a rack is also important toreduce opportunities for air e
30、ntrapment 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 design canincorporate holes at strategic locations to allow satisfactoryrunoff of solution.N
31、OTE 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,r0.25DNOTE 1Adapted from sketches appearing in Electroplating and Engineering Handbook, 3rd ed. Reinhold Publishing Corporation, Graham, A. K.,and Pi
32、nkerton, H. L., eds., New York, 1971.FIG. 4 Influence of Increasing Angle to Improve Thickness Distribution of Electrodeposited NickelB 507 86 (2008)e13FIG. 5 Nickel Distribution on a Convex Surface (a) aloneCompared to the Same Configuration as Part of a LargerComposite (b)B 507 86 (2008)e14ASTM In
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35、hould 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 S
36、tandards, 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) of this standard may be obtained by contacting ASTM at the aboveaddress or at 6
37、10-832-9585 (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 (2008)e15
