1、Designation: D 7396 08Standard Guide forPreparation of New, Continuous Zinc-Coated (Galvanized)Steel Surfaces for Painting1This standard is issued under the fixed designation D 7396; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、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 Department of Defense.1. Scope1.1 This guide covers surface
3、 cleaning and various methodsof treating new zinc-coated by the continuous process (galva-nized) surfaces produced by either the hot-dip method or byelectroplating. This guide covers surfaces that have not beentreated previously at the mill to provide temporary protectionagainst staining by moisture
4、 other than by easily removedprotective oils (see Appendix X1). For preparing surfaces ofnew or weathered items of zinc-coated steel produced by batchprocessing, refer to Practice D 6386.1.2 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for info
5、rmationonly.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 health practices and determine the applica-bility of regulatory limitations prior to use.2.
6、Referenced Documents2.1 ASTM Standards:2A 780 Practice for Repair of Damaged and Uncoated Areasof Hot-Dip Galvanized CoatingsD 4285 Test Method for Indicating Oil or Water in Com-pressed AirD 6386 Practice for Preparation of Zinc (Hot-Dip Galva-nized) Coated Iron and Steel Product and HardwareSurfac
7、es for PaintingD 6492 Practice for Detection of Hexavalent Chromium OnZinc and Zinc/Aluminum Alloy Coated Steel2.2 SSPCThe Society for Protective Coatings Standards:3Surface Preparation Specification No. 1 Solvent CleaningSurface Preparation Specification No. 2 Hand Tool Clean-ingSurface Preparation
8、 Specification No. 3 Power Tool Clean-ingSurface Preparation Specification No. 7 Brush-Off BlastCleaningPaint Specification No. 27 Basic Zinc Chromate-Vinyl Bu-tyral Wash Primer3. Summary of Guide3.1 This guide describes surface cleaning and treatmentmethods that provide galvanized surfaces suitable
9、 for painting,specifically so that an applied coating system can develop theadhesion necessary for satisfactory service life.3.2 Eight methods of treatment (Note 1 and Note 2) arecovered as follows:3.2.1 Method AZinc Phosphate Treatment.3.2.2 Method BChromate Treatment.3.2.3 Method CAqueous Chromic-
10、Organic Treatment.3.2.4 Method DAcid-Curing Resinous Treatment.3.2.5 Method EAnnealing Heat Treatments.3.2.6 Method FAmorphous Complex-Oxide Treatment.3.2.7 Method GAbrasive Blast Cleaning.3.2.8 Method HFluro-Titanic/Zirconic Polymer Treat-ment.NOTE 1Materials employed in these methods of treatment
11、are avail-able from a number of sources as proprietary compounds or methods.Selection may be made from available sources.NOTE 2The use of solvents containing volatile organic compounds toprepare or treat the surface of metal components contributes to airpollution in the same manner as the use of sol
12、vent containing paints andcoatings. The user of this guide must determine the applicability ofappropriate regulations governing the volatile organic compound contentof the materials used in a shop application (Miscellaneous Metal Parts),field painting (Architectural), or specific process industry.1T
13、his guide 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 June 1, 2008. Published June 2008. Originallyapproved in 2007. Last pr
14、evious edition approved in 2007 as D 7396 07.2For 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 website.3Available from
15、Society for Protective Coatings (SSPC), 40 24th St., 6th Floor,Pittsburgh, PA 15222-4656, http:/www.sspc.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.3 Variations in surface preparation produce end conditionsthat differ and
16、hence 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 method may vary withdifferent zinc coatings.3.4 Galvanized surfaces are treated by using
17、 various meth-ods and apparatus; satisfactory application may be made at thefollowing locations:Mill Plant FieldMethod A Y Y YMethod B Y Y .Method C Y Y .Method D Y Y YMethod E Y . .Method F Y Y .Method G Y Y YMethod H Y Y .3.5 This guide does not describe the cleaning necessary toprovide a zinc-coa
18、ted (galvanized) surface suitable for theapplication of the treatments. Many cleaning methods areapplicable and the preferred method should be agreed uponbetween the purchaser and the supplier.NOTE 3Most producers of zinc-coated (galvanized) steel sheets andcoils have adopted the practice of applyin
19、g an inhibitor to the zinc surfaceto give temporary protection against staining by moisture during shippingor storage. Some of these inhibitors interfere with proper reaction of mostof the treatments described in these methods, and an unsatisfactory surfacefor painting results. It is strongly recomm
20、ended that the purchaser consultthe supplier of the chemical treatment to be used as to the suitability of thezinc surfaces for treatment by any of these methods.3.6 Surface CleaningGalvanized surfaces must be cleanand free of oil and grease before they are treated. Adhesionproblems have been experi
21、enced with newly galvanized ar-ticles that have been water quenched or treated with chromateconversion coatings. These two post-galvanizing processes,water quenching and chromate conversion coating, are notrecommended for galvanized articles that are to be treatedbefore painting. The presence of chr
22、omate conversion coatingson the surface of the galvanized steel can be detected usingPractice D 6492.3.6.1 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 fo
23、r removal of heavy build-up of zinc oxide orwet storage stain. See the American Galvanizers Publication,Wet Storage Stain,4for description of these conditions. Thealkaline solution is nominally 2 to 5 % sodium compounds,with small additions of emulsifying, chelating, or sequesteringagents, or combin
24、ations thereof. This solution can be appliedthrough immersion in a tank filled with the solution, byspraying, or by brushing with a soft bristle brush, usually nylonand not steel or copper. When dipping or spraying, the solutionworks best in the temperature range from 60 to 85C. Aftercleaning, rinse
25、 thoroughly in hot water or water under pressure.Allow to dry completely before proceeding. Whenever galva-nized steel is rinsed, heated drying to accelerate the completeremoval of water from the surface is desirable.3.6.2 Solvent CleaningTypical cleaning solvents, such asmineral spirits or high-fla
26、sh naphtha, can be used to remove oiland grease. The procedure to be used is as specified in SSPCSurface Preparation Specification 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 s
27、urfaces 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. Allow to dry completelybefore proceeding.3.6.3 Hand or Power Tool CleaningHand or power toolcleaning may b
28、e used to clean light deposits of zinc reactionby-products, such as wet storage stain, as specified in SSPCSurface Preparation Specification 2 or 3.4. Significance and Use4.1 This guide describes procedures that can be used toprepare new zinc-coated surfaces for painting and improve thebond of paint
29、 to the zinc surface.5. Processes5.1 Method A, Zinc Phosphate TreatmentThisconversion-coating method consists of reacting the zinc surfacein a zinc acid phosphate solution containing oxidizing agentsand other salts for accelerating the coating action. The zincsurface is converted to a crystalline ph
30、osphate coating of theproper texture to inhibit corrosion and increase the adherenceand durability of the paint film. Such treatments are recom-mended for product finishes and may be carried out byimmersion, spray, or brush application.5.2 Method B, Chromate TreatmentThis treatment con-sists of a di
31、p or spray with a dilute solution of a mixture ofchromium trioxide and other acids, with the proper accelerator,for a period from 5 to 30 s at room temperature to 55C(130F) to provide a thin amorphous chromate coating thatincreases corrosion resistance and paint adhesion.5.3 Method C, Aqueous Chromi
32、c-Organic TreatmentsCertain water-soluble resins, when properly formulated withchromium compounds, may be applied to zinc surfaces byroller coat or other suitable means, such as dip and squeegeerolls. This may be done over a wide temperature rangeprovided the film is properly baked or cured, or both
33、, asrequired by the paint system to be applied. The resultantcoating provides a corrosion-resistant film that increases theadhesion of applied paint films.5.4 Method D, Acid-Curing Resinous Treatment (Vinyl WashPrimer) (See SSPC-Paint No. 27)This surface treatment isbased on the application of an ac
34、id-curing resinous film ofapproximately 8 to 13-m (0.3 to 0.5-mil) thickness. Thetreatment is based on three primary components: a hydroxyl-containing resin, a pigment capable of reacting with the resinand an acid, and an acid capable of insolubilizing the resin byreacting with the resin, the pigmen
35、t, and the zinc surface. Thefilm is usually applied by spray, but may be applied by brush,dip, or roller coater. Under normal conditions it will drysufficiently for recoating within 30 min, and within8hitwill4Wet Storage Stain (1997), available from American Galvanizers Association,6881 South Holly
36、Circle, Suite 108 Centennial, Colorado 80112,http:www.galvanizeit.org.D7396082not be softened by organic solvents commonly used in paintcoatings. The film has good adhesion to the metal substrate andpromotes good adhesion of most subsequent organic coatingsto itself. Two types of this treatment are
37、available: (1)two-package material to be used the day it is mixed and (2)one-package material that has package stability and does notrequire daily preparation.NOTE 4It may be difficult to control the dry film thickness within theparameters of this specification when applied by brush, roller, or dipc
38、oater.5.5 Method E, Annealing Heat TreatmentsUnder the con-trolled conditions obtainable in a mill, hot-dip galvanizedsurfaces may be converted and alloyed with the base metal tochange the surface character of the zinc coating and make itmore receptive to paint. This surface can be further improvedb
39、y treating in accordance with Methods A, B, C, or D.5.6 Method F, Amorphous Complex-Oxide TreatmentThissurface treatment method consists of reacting the zinc surfacein an alkaline solution containing heavy metal ions for a periodof 5 to 30 s at 45 to 70C (115 to 160F). The surface of thezinc is conv
40、erted to a nonmetallic, amorphous, complex-oxidecoating that inhibits corrosion and increases the adhesion anddurability of paint finishes. The treatment can be carried out byimmersion or spray application.5.7 Method G, Abrasive Blast TreatmentAbrasive sweepor brush blasting which uses a rapid nozzl
41、e movement willroughen the galvanized surface profile. Care must be taken toleave the zinc layers intact. The purpose of the sweep blastingis to deform, not to remove the galvanized metal. Any areafalling below the required zinc thickness, before or after sweepblasting, should be repaired in accorda
42、nce with PracticeA 780.The abrasive material must be chosen with care to provide astripping action without removing excess zinc layers. One ofthe materials successfully used is aluminum/magnesium sili-cate. Particle size should be in the range of 200 to 500micrometers (8 to 20 mils). This correspond
43、s to a #35-70 meshU.S. sieve size. Other materials that can be used are softmineral sands with a Mohs hardness of 5 or less, organic mediasuch as corncobs or walnut shells, corundum, and limestone.Depending on the value of hardness for the abrasive medium,blasting pressure may need to be determined
44、for the appropri-ate nozzle to work-piece distance, geometry of the componentand blasting medium. Typical operating pressures might be lessthan 0.40 MPa (60 psi). For some all-alloy coatings, even therelatively low-pressure blast of 0.15 to 0.25 MPa (20 to 40 psi)can be too great, causing cohesion p
45、roblems. Oil contaminationof the compressed air degrades paint adhesion to sweep-blastedhot-dip galvanized surfaces. Care is needed in averting thistype of contamination. Test Method D 4285 is a method forchecking the cleanliness of compressed air. The procedure forthis process can be found in SSPC
46、Surface PreparationSpecification 7. Sweep blasting of zinc should be not less than110 m2/h (1200 ft2/h) using these abrasive materials. Thesubstrate should be maintained at a temperature greater than3C (5F) above the dew point temperature. Following abra-sive blast cleaning, surfaces should be blown
47、 down with clean,compressed air. In some atmospheric conditions, such as highhumidity and/or high temperature, the formation of zinc oxideon the blasted surface will begin very quickly, so the paintcoating should be applied immediately, within 60 min, ifpractical, after sweep blasting. Zinc oxide fo
48、rmation is notvisible to the naked eye, therefore, in any atmosphere; paintingshould be started as soon as possible after surface preparation.5.8 Method H, Fluro-Titanic/Zirconic Polymer TreatmentThis treatment method is a chromium free analog of thesolutions commonly employed under Method C. It con
49、sists ofa combination of poly(acrylic acid) with copolymer resins and0.01 to 0.1 M H2TiF6or H2ZrF6. The solution can be appliedto the galvanized steel surface by spray, dip, squeegee or rollercoating. The excess solution is spun-off or otherwise removedfrom the metal surface, resulting in a dry in-place surfacetreatment. The finished surface consists of a complex oxidepolymer matrix bound to the zinc metal.6. Keywords6.1 acid-curing resinous treatment; amorphous complex-oxide treatment; annealing heat treatment; chromate; chromatetest; chromic-orga
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