ASTM B320-1960(2003)e1 Standard Practice for Preparation of Iron Castings for Electroplating《电镀用铁铸件的制备》.pdf

1、Designation: B 320 60 (Reapproved 2003)e1Endorsed by AmericanElectroplaters SocietyEndorsed by NationalAssociation of Metal FinishersStandard Practice forPreparation of Iron Castings for Electroplating1This standard is issued under the fixed designation B 320; the number immediately following the de

2、signation indicates the year oforiginal adoption or, in the case of revision, the year 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.e1NOTESection 2.1 was editorially updat

3、ed in May 2003.1. Scope1.1 This practice is intended to assist electroplaters inestablishing and maintaining a satisfactory pre-electroplatingcycle for malleable iron, gray iron, nodular iron, and white ironcastings. It is also intended to indicate certain foundry practiceswhich will facilitate subs

4、equent finishing. Most of the practicesthat follow have been based on experience with malleable andgray iron. However, since they are related to the other forms,the same practices will probably apply. Nodular iron is alsoknown as spheroidal or ductile iron, which is defined as castiron with the grap

5、hite substantially in spherical shape andsubstantially free of flake graphite.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 deter

6、mine the applica-bility of regulatory limitations prior to use. Specific precau-tionary statements are given in 2.1.2. Reagents2.1 Purity of ReagentsAll acids and chemicals used inthis practice are technical grade. Diluted acid solutions arebased upon the following assay materials:Hydrochloric acid

7、(HCl): 31 mass %, density 1.16g/mLHydrofluoric acid (HF): 47 mass %, density 1.186g/mLSulfuric acid (H2SO4): 93 mass %, density 1.83g/mL(WarningUse hydrofluoric acid with extreme care.)(WarningSulfuric acid should be slowly added to theapproximate amount of water required with rapid mixing, andthen

8、after cooling, diluted to exact volume.)2.2 Purity of WaterOrdinary industrial or potable watermay be used for preparing solutions and rinsing.3. Foundry Practices3.1 The seacoal content of the molding and facing sandsshould be maintained at the maximum practicable limits tominimize the occlusion of

9、 sand in the surfaces of the castings.3.2 Upon removal from the molds, castings should besubjected to an abrading action (such as tumbling, grit blasting,or shot blasting) to remove as much as practicable of theoccluded molding sand. Residual sand and scale may beremoved, if necessary, by treatment

10、in various proprietarydescaling baths. These are usually based on fused caustic soda,some of which use chemical oxidizing or reducing agents andothers employ electrochemical action as well. This is particu-larly important in the case of castings that will be annealed, toprevent the burning on of san

11、d during this operation. Castingsthat will be warped or damaged by a blasting operation may bepickled in a solution containing 200 to 250 mL/L of sulfuricacid to remove occluded molding sand. See Warning state-ment in 2.1.3.3 Annealed castings should be given an additional abrad-ing as described in

12、3.2 to remove any scale that may have beenformed, as well as graphitic carbon that may be present at thesurface.4. Nature of Cleaning4.1 The preparation of ferrous castings for electroplatinginvolves the following basic steps in the order named:4.1.1 The removal of oils, greases, residual polishing

13、andbuffing compounds (if any), and shop dirt by cleaning,4.1.2 The removal of oxide films and scales and the loos-ening of surface carbon by pickling or by salt bath treatment(see 3.2),4.1.3 The removal of smut caused by 4.1.2, and4.1.4 Activation for electroplating.4.2 Where excessive amounts of cu

14、tting oils used in ma-chining operations are present, it may be necessary to precleanthe parts before they reach the electroplating room. This may1This practice is under the jurisdiction of ASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.02 o

15、nPre Treatment.Current edition approved April 21, 2003. Published May 2003. Originallyapproved in 1960. Last previous edition approved in 1997 as B 310 60 (1997).1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.require the use of orga

16、nic solvents, vapor degreasers, washingmachines of the power-spray type, emulsion cleaners, orsimple alkaline soak tanks. As short a time as possible shouldelapse between this precleaning and the preplating cleaningcycle so as to prevent rusting of the parts. Where control of theinterval is not poss

17、ible, parts should be left with a slightlyalkaline or very thin organic film.5. Cleaning Solutions and Equipment5.1 The various solutions used for the treatment of mal-leable and gray iron castings should be maintained by chemicalanalysis so far as is practicable, such as determining the freeacid an

18、d iron concentrations of the acid baths and using testsrecommended by the manufacturer, the effective componentsof the proprietary cleaning solutions.5.2 All solutions should be discarded before they lose theireffectiveness, based on tests and experience.5.3 When the amount of soil is excessive, par

19、ticularly whereno precleaning is done, it may be desirable to double thecleaning and pickling facilities. Thus, while the first of any twoparticular solutions becomes heavily contaminated, the secondremains relatively clean and effective for further use. When thefirst of a pair of solutions is disca

20、rded, it is replaced by thesecond solution and a fresh second solution is prepared. Thissystem also reduces the possible carry-over of contaminantssuch as oil and grease into subsequent solutions.5.4 Where doubling the facilities is impossible or impracti-cable, similar economies may be obtained to

21、a degree byproviding cleaner and pickle tanks with overflow dams, sumpsand pumps with which the solution may be recirculated. Thepump intake should be located approximately half-way downthe sump to preclude returning either settled-out solid dirt orsurface oil and grease to the processing tank. The

22、outlet shouldbe near the bottom of the processing tank at the end oppositeto the overflow dam so as to create some solution turbulence(for mechanical scrubbing benefits) and to ensure flow ofcontaminated solution to the dam.5.5 In electrified tanks removable electrodes should beemployed in preferenc

23、e to using the tank as an electrode, tofacilitate inspection and cleaning. To ensure good circuitry,positive contacts such as an inverted V hook for round barsshould be used. In alkaline cleaner tanks, where clean contactis often a problem, submerged oversized steel tank rods areeffective.5.6 All im

24、mersion rinse tanks should be equipped withdam-type overflows to ensure skimming of oil, grease, andlight dirt from the surface of the water. Water inlets should beat the bottom of the tank, and should be of a size sufficient toprovide an adequate flow of water. It is desirable that sub-merged inlet

25、 pipes be equipped with syphon-breakers (asrequired by law in many areas) not only to prevent thebackflow of contaminated water into the mains, but also toproduce a beneficial turbulence or scrubbing action due to theair introduced with the water. Agitation by means of low-pressure, oil-free air thr

26、ough perforated pipes at the bottom ofthe tank may also be used.5.7 Having the heating coils on the working side of tankswill assure a working surface which is free of accumulatedgrease and oil.6. Procedure for Racked Parts6.1 The following cycle may generally be used for rackedparts which will subs

27、equently be electroplated in still tanks,semiautomatic equipment, and full-automatic equipment:6.1.1 PrecleaningWhen castings have been subjected tomachining, polishing, buffing, or similar finishing processes, itis desirable and frequently essential that lubricants and finish-ing compounds be remov

28、ed by precleaning immediately fol-lowing such operations. This is especially important when thelubricants contain unsaturated oils which, upon air oxidation,form films which are extremely difficult to remove. Preclean-ing methods as listed in 4.2 may be employed.6.2 Soak CleaningIn the event preclea

29、ning of a heavilysoiled part is impossible or impracticable, soak cleaning toloosen oils and greases is recommended. The bath may beeither an alkaline solution of such concentration as recom-mended by the supplier, and operated at a temperature as closeto boiling as possible, or an emulsion-type cle

30、aner operated asspecified by the supplier. In either case, agitation of thesolution by air or solution pumping, or movement of the part,will prove beneficial. The time may be 5 min or more.6.3 RinseIf the soak cleaner used is incompatible with thesubsequent cleaner, a rinse is indicated. The supplie

31、r willnormally suggest whether it is to be warm or cold, although awarm rinse (60C) is usually desirable following alkaline soakcleaning. In any case, agitation of the rinse water is desirable;and, in the case of cold-water rinses, a spray upon leaving thetank is beneficial. The time of rinsing depe

32、nds in part upon theshape of the part, but should be no less than 10 s.6.4 Anodic CleaningThe part is made the anode in asolution of a properly compounded alkaline cleaner of aconcentration recommended by the supplier. The cleanershould be free-rinsing, and of high conductivity to permit acurrent de

33、nsity of 6 to 10 A/dm2at a tank potential of 6 to 9 V.The solution temperature should be from 90 to 100C, and thecleaning time from 1 to 2 min.6.5 RinseThe supplier of a proprietary cleaner will usu-ally indicate whether his product rinses more freely in warm orcold water. In general, rinsing should

34、 be done as described in6.3, but preferably in a separate tank. Where practicable to doso, all rinses should be double rinses; that is, two separaterinses in succession, with the second cascading into the first forwater economy.6.6 Acid PicklingThis stage of the cycle is the mostcritical, and its op

35、erating conditions are dependent on the typeof electroplating to follow. Most of the difficulties in electro-plating of gray iron and malleable iron castings are caused bythe free graphitic carbon, flake or nodular, which is present atthe surface of the part. If the subsequent electroplating will be

36、done under conditions causing sufficiently high hydrogenovervoltage (most acid solutions, and such alkaline solutions ascopper, cadmium, or tin), a brief dip (less than 15 s) in a roomtemperature solution containing 200 mL/L of hydrochloric acidor 50 to 100 mL/L of sulfuric acid is usually adequate.

37、 SeeWarning in 2.1. If the electroplating will be done in an alkalinesolution of low hydrogen overvoltage such as cyanide zinc,anodic treatment in acid to remove surface carbon is preferred.This is done by making the part the anode in a solutionB 320 60 (2003)e12containing 250 to 350 mL/L of sulfuri

38、c acid for at least 30 s,preferably more, at a voltage sufficient to provide a currentdensity of at least 10 A/dm2. See Warning in 2.1. A black filmof carbon smut will form during the first 15 to 30 s, then thepart will become passive and the oxygen evolved on the partwill remove the carbon by a com

39、bination of scrubbing andoxidation, leaving the casting relatively clean.6.7 RinseThe part should be rinsed in cold water asdescribed in 6.3, but in a separate tank.6.8 Anodic CleaningThe casting should be subjected toanodic cleaning as described in 6.4, using either the same typeof proprietary clea

40、ner or a room temperature solution consist-ing of sodium cyanide (30 to 45 g/L) and sodium hydroxide (30to 45 g/L).6.9 RinseThe part should be rinsed in cold water asdescribed in 6.3, but in a separate tank.6.10 ActivationIf electroplating is to be done in alkalinesolutions, such as cadmium, copper,

41、 tin, or zinc, no furthertreatment should be necessary. For nearly neutral or acidelectroplating processes, however, parts should be immersedfor 5 to 15 s in a room-temperature solution containing 50 to100 mL of sulfuric acid. See Warning in 2.1.6.11 RinseActivated parts should be rinsed in cold wat

42、eras described in 6.3, but in a separate tank.7. Variation in Procedure for Parts to be Racked7.1 Where parts are subjected to several operations beforeelectroplating, such as machining, forming, polishing, etc.,thought should be given to possible precleaning betweenoperations.7.2 Mineral oils, part

43、icularly in recesses, are best removedby vapor degreasing.7.3 Lubricating oils, buffing compounds greases, and thelike, are best removed by anodic electrocleaning as describedin 6.4. Heavy deposits of dried-on buffing compound may bemore effectively removed by cathodic cleaning under similaroperatin

44、g conditions.7.4 Castings that are heavily rusted can be pickled in asolution containing 50 to 100 mL/L of sulfuric acid and asuitable inhibitor to prevent excessive attack of the basis metal.See Warning in 2.1. Preferably, the solution should beoperated at 65 to 95C, and the time should be as requi

45、red toremove the rust.7.5 Very heavy scale can be removed by making the workanodic in a solution as described in 7.4, but with a suitablewetting agent instead of the inhibitor.7.6 For castings from which molding sand has not beencompletely removed by the abrading processes described in 3.2and 3.3, a

46、 dip in a water solution consisting of 125 mL/L ofsulfuric acid and 125 mL/L of hydrofluoric acid at 20 to 30Cmay be employed. See Warning in 2.1.7.7 A suggested alternative for most of the cycle describedin Section 6 is the use of one of the several proprietaryprocesses involving molten caustics, h

47、ydrides, or alkaline salts,both with and without electrolysis. The suppliers of theseprocesses should be consulted for details.8. Procedure for Parts to Be Processed in Bulk8.1 Castings to be cleaned in cylinders other than those inwhich the electroplating will be done should be processedthrough a c

48、ycle as follows:8.1.1 Tumble CleaningParts are cleaned by tumblingwithout current in a solution of properly compounded alkalinecleaner of 45 to 90 g/L at a temperature of 90 to 100C for atleast 5 min.8.1.2 RinseRinse for at least 1 min by tumbling in warmwater, preferably agitated and overflowing.8.

49、1.3 Acid PickleTumble the parts for at least 1 min in asolution of 250 to 350 mL/L of sulfuric acid at 65C.8.1.4 RinseTumble in cold water, preferably agitated andfreely overflowing, for at least 1 min.8.1.5 ActivationParts to be electroplated in acid solutionsmay be transferred to electroplating cylinders without furtherprocessing. Parts to be electroplated in cyanide solutionsshould be tumbled for at least 1 min in a room temperaturesolution consisting of 15 to 30 g/L of sodium cyanide and 15to 30 g/L of sodium hydroxide.8.1.6 RinseParts activated as in 8