1、Designation: D 6386 99 (Reapproved 2005)Standard Practice forPreparation of Zinc (Hot-Dip Galvanized) Coated Iron andSteel Product and Hardware Surfaces for Painting1This standard is issued under the fixed designation D 6386; the number immediately following the designation indicates the year oforig
2、inal 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.1. Scope1.1 This practice describes methods of preparing surfaces ofnew an
3、d weathered hot-dip galvanized steel for painting.Hot-dip galvanized steel is produced by the immersion offabricated or unfabricated products in a bath of molten zinc, asspecified in Specifications A 123 or A 153/A 153M. Thispractice covers surface preparation on iron and steel productsand hardware
4、that have not been painted previously. Galva-nized surfaces may have been treated with protective coatingsto prevent the occurrence of wet storage stain. This practicedoes not apply to sheet galvanized steel products nor to the coilcoating or continuous roller coating processes.1.2 The values stated
5、 in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.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
6、health practices and to determine theapplication of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A 123 Specification for Zinc (Hot-Dip Galvanized) Coat-ings on Iron and Steel ProductsA 153/A 153M Specification for Zinc Coating (Hot-Dip) onIron and Steel HardwareA 78
7、0 Practice for Repair of Damaged and Uncoated Areasof Hot-Dip Galvanized CoatingsB 201 Practice for Testing Chromate Coatings on Zinc andCadmium SurfacesE 376 Practice for Measuring Coating Thickness byMagnetic-Field or Eddy-Current (Electromagnetic) TestMethods2.2 Society for Protective Coatings Sp
8、ecifications:3Surface Preparation Specification No. 1 Solvent CleaningSurface Preparation Specification No. 2 Hand Tool Clean-ingSurface Preparation Specification No. 3 Power Tool Clean-ingSurface Preparation Specification No. 7 Brush-Off BlastCleaningPaint Specification No. 27 Basic Zinc Chromate-V
9、inylButyral Wash Primer3. Summary of Practice3.1 This practice describes the preparation methods thatprovide clean and suitable galvanized surfaces for painting,specifically so that an applied coating system can develop theadhesion necessary for a satisfactory service life.3.2 The zinc coating is co
10、nstantly in a state of change. Fromthe time the steel part is removed from the galvanizing kettle,the exposed zinc coating interacts with the environment toform, first zinc oxides, next zinc hydroxides, and then zinccarbonates.4The process of complete conversion of the outerlayer of zinc carbonates
11、can take up to two years of exposureto the environment, depending on the local climatologicalconditions. During the first stage, known as newly galvanizedsteel, the exposed surface consists mainly of zinc metal with asmall amount of zinc oxide. During the second stage, known aspartially weathered ga
12、lvanized steel, the exposed surfaceconsists mainly of zinc oxides and zinc hydroxides with somezinc carbonates. At the final stage, known as weatheredgalvanized steel, the exposed surface consists mainly ofwater-insoluble zinc carbonates, some zinc oxides, and rarely,zinc hydroxides. The surface pre
13、paration for each of thesestages must be treated separately.3.3 Variations in surface preparation produce end conditionsthat differ, hence they do not necessarily yield identical resultswhen paints are subsequently applied. Service conditions willdictate the type of surface preparation to be selecte
14、d, although1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings, Materials, and Applications, and is the direct responsibility ofSubcommittee D01.46 on Industrial Protective Coatings.Current edition approved July 1 2005. Published August 2005. Originallyapprove
15、d in 1999. Last previous edition approved in 1999 as D 6386 99.2For 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 ASTM websit
16、e.3Available from Society for Protective Coatings (SSPC), 40 24th St., 6th Floor,Pittsburgh, PA 15222-4656.4This interaction is described in “Duplex Systems,” van Eijnsbergen, J.F.H.,Elsevier Science, New York, NY 1994, and in Zinc Handbook, Porter, F., MarcelDekker, Inc., New York, NY 1991.1Copyrig
17、ht ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the quality produced by any individual process may vary withdifferent compositions of the zinc surface.4. Significance and Use4.1 This practice describes the procedures that can be usedto prepa
18、re new and weathered zinc-coated surfaces on after-fabrication steel products for painting, and that can improve thebond of paint to the zinc surface.5. Processes for Newly Galvanized Steel5.1 Newly Galvanized SteelThe category of newly galva-nized steel refers to zinc-coated steel that has no surfa
19、cetreatment after galvanizing, such as water quenching or chro-mate conversion coating, and has been galvanized within theprevious 48 h. There also should be no visible signs of zincoxide or zinc hydroxide, which first appear as a fine whitepowder.5.2 Surface SmoothingHot-dip galvanized surfaces gen
20、erally are relatively smooth after galvanizing. There may besome thick edges due to excess liquid zinc run-off during thegalvanizing, or high spots in the coating due to includediron-zinc intermetallics (dross) or zinc oxide particles. Thesehigh spots and rough edges, such as the metal drip line, m
21、ustbe smoothed to avoid paint film gaps in the areas of the highspots.5.2.1 Zinc high spots, those that would cause paint film gapssuch as the metal drip line, should be removed by cleaning withhand or power tools as described in SSPC Surface PreparationSpecification 2 or 3. The zinc should be remov
22、ed until it islevel with the surrounding area, taking care that the basecoating is not removed by the cleaning methods. After clean-ing, the surface shall be inspected for conformance to therequired zinc thickness in accordance with SpecificationsA 123 or A 153/A 153M utilizing a magnetic thickness
23、instru-ment in accordance with Practice E 376. Any item fallingbelow the required zinc thickness, before or after removal ofany high spots, shall be repaired in accordance with PracticeA 780.5.3 Surface CleaningHot-dip galvanized surfaces must beclean and free of oil and grease before they are paint
24、ed.Adhesion problems have been experienced with newly galva-nized articles that have been water quenched or treated withchromate conversion coatings. These two post-galvanizingtreatments are not recommended for galvanized articles that areto be painted.5.3.1 Aqueous Alkaline CleaningAn alkaline solu
25、tion, pHin the range of 11 to 12 definitely not greater than 13, can beused to remove traces of oil, grease, or dirt.An alkaline cleaneris unsuitable for removal of heavy build-up of zinc oxide orwet storage stain (see American Galvanizers Publications, WetStorage Stain5, for description of these co
26、nditions). See 5.4 forremoval of zinc oxide layer. The alkaline solution nominally is2 to 5 % sodium compounds, with small additions of emulsi-fying, chelating, or sequestering agents, or a combinationthereof. This solution can be applied through immersion in atank filled with the solution, sprayed,
27、 or brushed with a softbristle brush, usually nylon and not steel or copper. Whendipping or spraying, the solution works best in the temperaturerange from 60 to 85C. After cleaning, rinse thoroughly in hotwater or water under pressure. Allow to dry completely beforeproceeding. Whenever galvanized st
28、eel is rinsed, it is desirableto use heated drying to accelerate the complete removal ofwater from the surface.5.3.2 Solvent CleaningTypical cleaning solvents, such asmineral spirits or high-flash naphtha, can be used to remove oiland grease. The procedure to be used is as specified in SSPCSurface P
29、reparation Specification 1. Proper rags or brushesshould be used to wipe the galvanized parts.NOTE 1Caution: These rags or brushes should be cleaned or recycledoften since oil can accumulate on their surfaces and be transferred back tothe galvanized part. Small parts may be dipped or cleaned in ultr
30、asonicbaths of solvents. After cleaning, rinse thoroughly in hot water or waterunder pressure. Allow to dry completely before proceeding.5.3.3 Hand or Power Tool CleaningHand or power toolcleaning may be used to clean light deposits of zinc reaction byproducts, such as wet-storage stain, as specifie
31、d in SSPCSurface Preparation Specification 2 or 3.5.4 Surface PreparationHot-dip galvanized surfaces havea layer of zinc oxide and zinc hydroxide that must be removedbefore paint will adhere to the zinc coating. Zinc coatingsgenerally are relatively smooth and may be slightly roughenedprior to paint
32、ing. The following four methods may be used toprepare the galvanized surface for painting.5.4.1 Sweep BlastingAbrasive sweep or brush blasting,which uses a rapid nozzle movement will roughen the galva-nized surface profile. The abrasive material must be chosenwith care to provide a stripping action
33、without removing excesszinc layers. One of the materials that has been used success-fully is aluminum/magnesium silicate. Particle size should bein the range of 200 to 500 m (8 to 20 mils). Other materialsthat can be used are soft mineral sands with a MOH hardnessof five or less, organic media, such
34、 as corn cobs or walnutshells, corundum, and limestone. Depending on the value ofhardness for the abrasive medium, blasting pressure may needto be determined for the appropriate nozzle to work-piecedistance, geometry of the component, and blasting medium.For some all-alloy coatings, even the relativ
35、ely low-pressureblast of 0.15 to 0.25 MPa (20 to 40 psi) can be too great,causing cohesion problems. Oil contamination of the com-pressed air will degrade paint adhesion to sweep-blastedhot-dip galvanized surfaces. Care is needed in averting thistype of contamination. Care must be taken to leave zin
36、c layersintact. The purpose of sweep blasting is to deform, not removethe galvanized metal. Any area falling below the required zincthickness, before or after sweep blasting, should be repaired inaccordance with PracticeA 780. The procedure for this processcan be found in SSPC Surface Preparation Sp
37、ecification 7.Sweep blasting of zinc should be not less than 110 m2/h (1200ft2/h) using these abrasive materials. The substrate should bemaintained at a temperature greater than 3C (5F) above thedew point temperature. Following abrasive blast cleaning,surfaces should be blown down with clean, compre
38、ssed air. Insome atmospheric conditions, such as high humidity, or high5Available fromAmerican GalvanizersAssociation, 12200 E. IliffAve., No. 204,Aurora, CO 800145376.D 6386 99 (2005)2temperature, or both, the formation of zinc oxide on the blastedsurface will begin very quickly, so the paint coati
39、ng should beapplied immediately, within 60 min, after sweep blasting. Zincoxide formation is not visible to the naked eye; therefore, inany atmosphere, painting should be stated as soon as possibleafter surface preparation.5.4.2 Zinc-Phosphate TreatmentThis conversion-coatingprocess consists of reac
40、ting the newly galvanized zinc surfacein an acidic zinc phosphate solution containing oxidizingagents and other salts for accelerating the coating action. Thezinc surface is converted to a crystalline phosphate coating ofthe proper texture to inhibit corrosion and increase the adher-ence and durabil
41、ity of the paint film. This process may beapplied by immersion, spray or soft bristle brush application.After a time period of 3 to 6 min, the surface should be washedwith clean water and allowed to completely dry before appli-cation of the paint system. Painting should take place soonafter treatmen
42、t to avoid pick up of surface contaminants.5.4.3 Wash Primer TreatmentThis process involves theuse of a metal conditioner to neutralize surface oxides andhydroxides along with etching the surface. One example of awash primer is SSPC Paint Specification 27. The process isbased on three primary compon
43、ents: a hydroxyl-containingresin: a pigment capable of reacting with resin and acid: and,an acid capable of making the resin insoluble by reacting withthe resin, the pigment, and the zinc surface. The result is a filmof approximately 8 to 13 m (0.3 to 0.5 mils). Failures canoccur if the film exceeds
44、 13 m (0.5 mils). The film usually isapplied by spray but may be applied by soft bristle brush, dip,or roller coater. Using these latter coating methods, it may bedifficult to control the film thickness. For drying time prior totopcoating, follow the manufacturers instructions. This washprimer treat
45、ment may be better suited to certain types of paintsystems. See SSPC Paint Specification 27 for the best match ofthis treatment to a paint system.5.4.4 Acrylic Passivation/PretreatmentThe passivation/pretreatment process consists of applying an acidic acrylicsolution to the newly galvanized surface
46、and then allowing it todry, forming a thin film coating. When applied, the solutionfirst reacts with the zinc surface forming a passivating conver-sion coating while simultaneously forming an acrylic coatingsuitable for painting on top of the passivation layer. Theunderlying conversion coating provi
47、des strong adhesion to thegalvanized surface while the thin film acrylic layer providesbarrier protection, which inhibits corrosion and provides ahighly compatible surface for the application of organic paintfilms. There are versions of these solutions that contain chromeand versions without chrome.
48、 The application methods forthese water based treatments are dipping, flow coating, spray-ing, or other appropriate means. Following application thecoating is dried in an oven or in air. In some instances, thecoating is applied to hot-galvanized articles, in which caseseparate drying is not necessar
49、y. Rinsing is not required. Thecoating is approximately 1-m (0.04-mils) thick. Painting ispossible any time during a period of four months afterapplication, as long as the surface is free of visible zinc oxidesor zinc hydroxides; however, if harmful contaminants, such asdust, dirt, oils, grease or deposits are present, they must beremoved with a mild alkaline degreasing solution (pH 11.5max) followed by a thorough rinse with hot water (60Cmaximum temperature) or a pressure wash, then thoroughlydried. This treatment is applied in the galvanizing plant or laterin
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