1、Designation: D6386 16Standard 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.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope*
3、1.1 This practice describes methods of preparing surfaces ofnew and 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 A123/A123M or A153/A153M.This practi
4、ce covers surface preparation on iron and steelproducts and hardware that have not been 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 c
5、oating or continuous roller coating processes. Sheetand coil surface preparation can be 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
6、 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 to determine theapplication of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A123/A123M Specificati
7、on for Zinc (Hot-Dip Galvanized)Coatings on Iron and Steel ProductsA153/A153M Specification 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 SurfacesD
8、7396 Guide for Preparation of New, Continuous Zinc-Coated (Galvanized) Steel Surfaces for PaintingE376 Practice for Measuring Coating Thickness byMagnetic-Field or Eddy-Current (Electromagnetic) Test-ing Methods2.2 Society for Protective Coatings Specifications:3Surface Preparation Specification No.
9、 1 Solvent CleaningSurface Preparation Specification No. 2 Hand Tool CleaningSurface 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. 2
10、7 Basic Zinc Chromate-Vinyl Bu-tyral 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
11、.2 The zinc coating is constantly 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 outer
12、layer of zinc carbonates 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
13、 aspartially weathered galvanized steel, the exposed surface1This 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 May 1
14、, 2016. Published May 2016. Originallyapproved in 1999. Last previous edition approved in 2010 as D6386 10. DOI:10.1520/D6386-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume informati
15、on, refer to the standards Document Summary page onthe ASTM website.3Available from Society for Protective Coatings (SSPC), 40 24th St., 6th 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
16、1994, and in Zinc Handbook, Porter, F., MarcelDekker, Inc., New York, NY 1991.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1consists mainly of zinc oxides and zinc hyd
17、roxides 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 preparation for each of thesestages must be treated separately.3.3 Variations in
18、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 selected, althoughthe quality produced by any individual process may vary withdiffere
19、nt compositions of the zinc surface.4. Significance and Use4.1 This practice 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 G
20、alvanized Steel5.1 Newly Galvanized SteelThe category of newly galva-nized 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
21、 of zincoxide or zinc hydroxide, which first appear as a fine whitepowder.5.2 Surface SmoothingHot-dip galvanized surfaces gener-ally are relatively smooth after galvanizing. There may besome thick/rough edges at the drip line due to excess liquidzinc run-off during the galvanizing process, or high
22、spots in thecoating due to included iron-zinc intermetallics (dross) or zincoxide particles. These high spots and rough edges must besmoothed to avoid paint film gaps in the areas of the high spots.5.2.1 Zinc high spots, those that would cause paint film gapssuch as the metal drip line, should be re
23、moved by smoothingwith hand or power tools as described in SSPC SurfacePreparation Specification No. 2 or No. 3. The zinc should beremoved until it is level with the surrounding area, taking carethat the base coating is not removed by the smoothing methods.After smoothing, the surface shall be inspe
24、cted for confor-mance to the required zinc thickness in accordance withSpecifications A123/A123M or A153/A153M utilizing a mag-netic thickness instrument in accordance with Practice E376.Any item falling below the required zinc thickness, before orafter removal of any high spots, shall be repaired i
25、n accordancewith Practice A780 using an appropriate method that iscompatible with the paint system.5.3 Surface CleaningHot-dip galvanized surfaces 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 wa
26、ter 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 solution, pHin the range of 11 to 12 definitely not greater than 13, can beused to remove traces
27、 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 Stain,5for description of these conditions). See 5.4 forremoval of zinc oxide layer. The alkaline solution nominally is2 to 5 %
28、 sodium compounds, with small additions ofemulsifying, chelating, or sequestering agents, or a combina-tion thereof. This solution can be applied through immersion ina tank filled with the solution, sprayed, or brushed with a softbristle brush, usually nylon and not steel or copper. Whendipping or s
29、praying, 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 steel is rinsed, it is desirableto use heated drying to accelerate the complete removal ofwater
30、 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 Preparation Specification No. 1. Proper rags or brushesshould be used to wipe the galvanized p
31、arts. (WarningTheserags or brushes should be cleaned or recycled often since oilcan accumulate on their surfaces and be transferred back to thegalvanized part. Small parts may be dipped or cleaned inultrasonic baths of solvents. After cleaning, rinse thoroughly inhot water or water under pressure. A
32、llow to dry completelybefore 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 specified in SSPCSurface Preparation Specification No. 2 or No. 3.5.4 Surface PreparationHot-dip galvani
33、zed 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 painting. The following four methods may be used toprepare the galvanized surface for paintin
34、g.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 without removing excesszinc layers, removal of up to 25 microns (1 mil) is acceptable.On
35、e 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 mils). 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,
36、 and limestone. Depending on the value of hardnessfor the abrasive medium, blasting pressure may need to bedetermined for the appropriate nozzle 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 MP
37、a (20 to 40 psi) can be too great, causing cohesionproblems. Oil contamination of the compressed air will de-grade paint adhesion to sweep-blasted hot-dip galvanizedsurfaces. Care is needed in averting this type of contamination.5Available from American Galvanizers Association (AGA), 6881 South Holl
38、yCircle, Suite 108 Centennial, CO 80112, http:/www.galvanizeit.org.D6386 162Care must be taken to leave zinc layers intact. The purpose ofsweep blasting is to deform, not remove the galvanized metal.Any area falling below the required zinc thickness, before orafter sweep blasting, should be repaired
39、 in accordance withPractice A780. The procedure for this process can be found inSSPC Surface Preparation Specification No. 7. Sweep blastingof zinc 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) abo
40、ve the dew pointtemperature. Following abrasive blast cleaning, surfacesshould be blown down with clean, compressed air. In someatmospheric conditions, such as high humidity, or hightemperature, or both, the formation of zinc oxide on the blastedsurface will begin very quickly, so the paint coating
41、should beapplied immediately, within an hour, after sweep blasting. Zincoxide formation is not visible to the unaided eye; therefore, inany atmosphere, painting should be stated as soon as possibleafter surface preparation.5.4.2 Surface GrindingPower tools such as grinders orsanders will roughen the
42、 surface of galvanized steel andproduce a surface profile suitable for paint adhesion as perSSPC Surface Preparation Specification No. 11. The 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. Fol
43、lowing grinding or sanding, surfacesshould be blown down with clean, compressed air. In someatmospheric conditions, such as high humidity, or hightemperature, or both, the formation of zinc oxide on the groundor sanded surface will begin very quickly, so the paint coatingshould be applied immediatel
44、y, within an hour, after grindingor sanding. Zinc oxide formation is not visible to the unaidedeye; therefore, in any atmosphere, painting should be started assoon as possible after surface preparation.NOTE 1This grinding or sanding process may produce a sharpersurface profile if the galvanized stee
45、l is over 50C (122F) as the zincmetal is softer at elevated temperatures.5.4.3 Zinc-Phosphate TreatmentThis conversion-coatingprocess consists of reacting the newly galvanized zinc surfacein an acidic zinc phosphate solution containing oxidizingagents and other salts for accelerating the coating act
46、ion. Thezinc surface is converted to a crystalline phosphate coating ofthe proper texture to inhibit corrosion and increase the adher-ence and 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
47、 should be washedwith clean water and allowed to completely dry before appli-cation of the paint system. Painting should take place soonafter 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
48、 andhydroxides along with etching the surface. One example of awash primer is SSPC Paint Specification No. 27. The processis based on three primary components: a hydroxyl-containingresin: a pigment capable of reacting with resin and acid: and,an acid capable of making the resin insoluble by reacting
49、 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 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 bestma
