1、Designation: D6386 10Standard Practice forPreparation of Zinc (Hot-Dip Galvanized) Coated Iron andSteel Product and Hardware Surfaces for Painting1This standard is issued under the fixed designation D6386; the number immediately following the designation indicates the year oforiginal adoption or, in
2、 the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice describes methods of preparing surfaces ofnew and weathered hot-dip
3、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 A123/A123M or A153/A153M.This practice covers surface preparation on iron and steelproducts and hardware that have not bee
4、n painted previously.Galvanized surfaces may have been treated with protectivecoatings to prevent the occurrence of wet storage stain. Thispractice does not apply to sheet galvanized steel products norto the coil coating or continuous roller coating processes. Sheetand coil surface preparation can b
5、e done in accordance withPractice D7396.1.2 The values stated 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 th
6、e user of this standard to establish appro-priate safety and health practices and to determine theapplication of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A123/A123M Specification for Zinc (Hot-Dip Galvanized)Coatings on Iron and Steel ProductsA153/A153M Specific
7、ation for Zinc Coating (Hot-Dip) onIron and Steel HardwareA780 Practice for Repair of Damaged and Uncoated Areasof Hot-Dip Galvanized CoatingsB201 Practice for Testing Chromate Coatings on Zinc andCadmium SurfacesD7396 Guide for Preparation of New, Continuous Zinc-Coated (Galvanized) Steel Surfaces
8、for PaintingE376 Practice for Measuring Coating Thickness byMagnetic-Field or Eddy-Current (Electromagnetic) Exami-nation Methods2.2 Society for Protective Coatings Specifications:3Surface Preparation Specification No. 1 Solvent CleaningSurface Preparation Specification No. 2 Hand Tool Clean-ingSurf
9、ace Preparation Specification No. 3 Power Tool Clean-ingSurface Preparation Specification No. 7 Brush-Off BlastCleaningSurface Preparation Specification No. 11 Power Tool Clean-ing to Bare MetalPaint Specification No. 27 Basic Zinc Chromate-VinylButyral Wash Primer3. Summary of Practice3.1 This prac
10、tice 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 constantly in a state of change. Fromthe time the steel part
11、 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 can take up to two years of exposureto the environment, de
12、pending 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 galvanized steel, the exposed surfaceconsists mainly of zinc
13、 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,1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coating
14、s, Materials, and Applications and is the direct responsibility ofSubcommittee D01.46 on Industrial Protective Coatings.Current edition approved July 1, 2010. Published July 2010. Originally approvedin 1999. Last previous edition approved in 2005 as D6386 99 (2005). DOI:10.1520/D6386-10.2For referen
15、ced 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 website.3Available from Society for Protective Coatings (SSPC), 40 24th St., 6th
16、Floor,Pittsburgh, PA 15222-4656, http:/www.sspc.org.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 1991.1*A Summary of Changes section appears at the end of this stan
17、dard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.zinc hydroxides. The surface preparation for each of thesestages must be treated separately.3.3 Variations in surface preparation produce end conditionsthat differ, hence they do no
18、t necessarily yield identical resultswhen paints are subsequently applied. Service conditions willdictate the type of surface preparation to be selected, althoughthe quality produced by any individual process may vary withdifferent compositions of the zinc surface.4. Significance and Use4.1 This pra
19、ctice describes the procedures that can be usedto prepare 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-ni
20、zed steel refers to zinc-coated steel that has no surfacetreatment 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 whitepowd
21、er.5.2 Surface SmoothingHot-dip galvanized surfaces gen-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. Thesehig
22、h spots and rough edges, such as the metal drip line, mustbe 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 Pr
23、eparationSpecification No. 2 or No. 3. The zinc should be removed untilit is level 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 Spec
24、ificationsA123/A123M or A153/A153M utilizing a magnetic thicknessinstrument in accordance with Practice E376. Any item fallingbelow the required zinc thickness, before or after removal ofany high spots, shall be repaired in accordance with PracticeA780.5.3 Surface CleaningHot-dip galvanized surfaces
25、 must beclean and free of oil and grease before they are painted.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 ar
26、eto be painted.5.3.1 Aqueous Alkaline CleaningAn alkaline solution, 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 Galvanizer
27、s Publications, WetStorage Stain5, for description of these conditions). 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
28、 through immersion in atank filled with the solution, sprayed, 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. Al
29、low to dry completely beforeproceeding. Whenever galvanized steel 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 gre
30、ase. The procedure to be used is as specified in SSPCSurface Preparation Specification No. 1. Proper rags or brushesshould be used to wipe the galvanized parts. (WarningTheserags or brushes should be cleaned or recycled often since oilcan accumulate on their surfaces and be transferred back to thega
31、lvanized part. Small parts may be dipped or cleaned inultrasonic baths of solvents. After cleaning, rinse thoroughly inhot water or water under pressure. Allow to dry completelybefore proceeding.)5.3.3 Hand or Power Tool CleaningHand or power toolcleaning may be used to clean light deposits of zinc
32、reaction byproducts, such as wet-storage stain, as specified in SSPCSurface Preparation Specification No. 2 or No. 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 coatingsgenerall
33、y are relatively smooth and may be slightly roughenedprior to painting. 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 abras
34、ive material must be chosenwith care to provide a stripping action without removing excesszinc layers, removal of up to 25 microns (1 mil) is acceptable.One of the materials that has been used successfully isaluminum/magnesium silicate. Particle size should be in therange of 200 to 500 m (8 to 20 mi
35、ls). Other materials that canbe used are soft mineral sands with a MOH hardness of five orless, organic media, such as corn cobs or walnut shells,corundum, and limestone. Depending on the value of hardnessfor the abrasive medium, blasting pressure may need to bedetermined for the appropriate nozzle
36、to work-piece distance,geometry of the component, and blasting medium. For someall-alloy coatings, even the relatively low-pressure blast of 0.15to 0.25 MPa (20 to 40 psi) can be too great, causing cohesionproblems. Oil contamination of the compressed air will de-grade paint adhesion to sweep-blaste
37、d hot-dip galvanizedsurfaces. Care is needed in averting this type of contamination.Care must be taken to leave zinc layers intact. The purpose ofsweep blasting is to deform, not remove the galvanized metal.5Available from American Galvanizers Association (AGA), 6881 South HollyCircle, Suite 108 Cen
38、tennial, CO 80112, http:/www.galvanizeit.org.D6386 102Any area falling below the required zinc thickness, before orafter sweep blasting, should be repaired in accordance withPractice A780. The procedure for this process can be found inSSPC Surface Preparation Specification No. 7. Sweep blastingof zi
39、nc should be not less than 110 m2/h (1200 ft2/h) usingthese abrasive materials. The substrate should be maintained ata temperature greater than 3C (5F) above the dew pointtemperature. Following abrasive blast cleaning, surfacesshould be blown down with clean, compressed air. In someatmospheric condi
40、tions, such as high humidity, or high tem-perature, or both, the formation of zinc oxide on the blastedsurface will begin very quickly, so the paint coating should beapplied immediately, within an hour, after sweep blasting. Zincoxide formation is not visible to the unaided eye; therefore, inany atm
41、osphere, painting should be stated as soon as possibleafter surface preparation.5.4.2 Surface GrindingPower tools such as grinders orsanders will roughen the surface of galvanized steel andproduce a surface profile suitable for paint adhesion as perSSPC Surface Preparation Specification No. 11. The
42、grinder orsander shall not be applied with sufficient force to remove allof the zinc coating rather a removal of up to 25 microns (1.0mil) is acceptable. Following grinding or sanding, surfacesshould be blown down with clean, compressed air. In someatmospheric conditions, such as high humidity, or h
43、igh tem-perature, or both, the formation of zinc oxide on the ground orsanded surface will begin very quickly, so the paint coatingshould be applied immediately, within an hour, after grindingor sanding. Zinc oxide formation is not visible to the unaidedeye; therefore, in any atmosphere, painting sh
44、ould be started assoon as possible after surface preparation.NOTE 1This grinding or sanding process may produce a sharpersurface profile if the galvanized steel is over 50C (122F) as the zincmetal is softer at elevated temperatures.5.4.3 Zinc-Phosphate TreatmentThis conversion-coatingprocess consist
45、s of reacting 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 an
46、d durability 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
47、 treatment to avoid pick up of surface contaminants.5.4.4 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 No. 27. The processis based on three p
48、rimary components: 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
49、 film exceeds 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 totop coating, follow the manufacturers instructions. This washprimer treatment may be better suited to certain types of paintsystems. See SSPC Paint Specification No. 27 for the bestmatch of this treatment to a paint system.5.4.5 Acrylic Passivation/PretreatmentThe passivation/pretreatment process consists of applying an a
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