1、Designation: D6386 16D6386 16aStandard 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 adopti
2、on or, in 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.
3、1. Scope*1.1 This practice describes methods of preparing surfaces of new and weathered hot-dip galvanized steel for painting. paintingwith liquid paint and coating products. Preparing surfaces of new and partially weathered galvanized steel for powder coating isaddressed in Practice D7803. Hot-dip
4、galvanized steel is produced by the immersion of fabricated or unfabricated products in abath of molten zinc, as specified in Specifications A123/A123M or A153/A153M. This practice covers surface preparation on ironand steel products and hardware that have not been painted previously. Galvanized sur
5、faces may have been treated with protectivecoatings to prevent the occurrence of wet storage stain. This practice does not apply to sheet galvanized steel products nor to thecoil coating or continuous roller coating processes. Sheet and coil surface preparation can be done in accordance with Practic
6、eD7396.1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to est
7、ablish appropriate safety and health practices and to determine the application of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A123/A123M Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel ProductsA153/A153M Specification for Zinc Coating (Hot-Di
8、p) on Iron and Steel HardwareA780 Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized CoatingsB201 Practice for Testing Chromate Coatings on Zinc and Cadmium SurfacesD4285 Test Method for Indicating Oil or Water in Compressed AirD6492 Practice for Detection of Hexavalent Chromium
9、 On Zinc and Zinc/Aluminum Alloy Coated SteelD7091 Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metalsand Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous MetalsD7396 Guide for Preparation of New, Continuous Zinc-Coated (Galvanize
10、d) Steel Surfaces for PaintingD7803 Practice for Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and Steel Product and Hardware Surfaces for PowderCoatingE376 Practice for Measuring Coating Thickness by Magnetic-Field or Eddy-Current (Electromagnetic) Testing Methods2.2 Society for Protective C
11、oatings Specifications:3Surface Preparation Specification No. 1 Solvent CleaningSurface Preparation Specification No. 2 Hand Tool CleaningSurface Preparation Specification No. 3 Power Tool CleaningSurface Preparation Specification No. 7 Brush-Off Blast CleaningSurface Preparation Specification No. 1
12、1 Power Tool Cleaning to Bare Metal1 This practice is under the jurisdiction of ASTM Committee D01 on Paint and Related Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.46 on Industrial Protective Coatings.Current edition approved May 1, 2016June 15, 2016. Pu
13、blished May 2016June 2016. Originally approved in 1999. Last previous edition approved in 20102016 asD6386 10.D6386 16. DOI: 10.1520/D6386-16.10.1520/D6386-16A.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of
14、ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from Society for Protective Coatings (SSPC), 40 24th St., 6th Floor, Pittsburgh, PA 15222-4656, http:/www.sspc.org.This document is not an ASTM standard and is intended only to provide the
15、user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard
16、 as published by ASTM is to be considered the official document.*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 States1Surface Preparation Specification No. 16 Brush-Off Blast
17、Cleaning of Non-Ferrous MetalsPaint Specification No. 27 Basic Zinc Chromate-Vinyl Butyral Wash PrimerSSPC Guide 15 Field Methods for Extraction and Analysis of Soluble Salts on Steel and Other Nonporous Substrates3. Summary of Practice3.1 This practice describes the preparation methods that provide
18、 clean and suitable galvanized surfaces for painting, specificallyso that an applied coating system can develop the adhesion necessary for a satisfactory service life.3.2 The zinc coating is constantly in a state of change. From the time the steel part is removed from the galvanizing kettle, theexpo
19、sed zinc coating interacts with the environment to form, first zinc oxides, next zinc hydroxides, and then zinc carbonates.4 Theprocess of complete conversion of the outer layer of zinc carbonates can take up to two years of exposure to the environment,depending on the local climatological condition
20、s. During the first stage, known as newly galvanized steel, the exposed surfaceconsists mainly of zinc metal with a small amount of zinc oxide. During the second stage, known as partially weathered galvanizedsteel, the exposed surface consists mainly of zinc oxides and zinc hydroxides with some zinc
21、 carbonates.At the final stage, knownas weathered galvanized steel, the exposed when the part has been openly exposed to the elements for more than twelve months,the exposed surface consists mainly of water-insoluble zinc carbonates, some zinc oxides, and rarely, zinc hydroxides. The surfacepreparat
22、ion for each of these stages must be treated separately.3.3 Variations in surface preparation produce end conditions that differ, hence they do not necessarily yield identical resultswhen paints are subsequently applied. Service conditions will dictate the type of surface preparation to be selected,
23、 although thequality produced by any individual process may vary with different compositions of the zinc surface.4. Significance and Use4.1 This practice describes the procedures that can be used to prepare new and weathered zinc-coated surfaces onafter-fabrication steel products for painting, and t
24、hat can improve the bond of paint to the zinc surface.5. Processes for Newly Galvanized Steel5.1 Newly Galvanized SteelThe category of newly galvanized steel refers to zinc-coated steel that has no surface treatmentafter galvanizing, such as water quenching or chromate conversion coating, and has be
25、en galvanized within the previous 48 h.There also should be no visible signs of zinc oxide or zinc hydroxide, which first appear as a fine white powder.5.2 Surface SmoothingHot-dip galvanized surfaces generally are relatively smooth after galvanizing. There may be somethick/rough edges at the drip l
26、ine due to excess liquid zinc run-off during the galvanizing process, or high spots in the coating dueto included iron-zinc intermetallics (dross) or zinc oxide particles. These high spots and rough edges must be smoothed to avoidpaint film gaps in the areas of the high spots.5.2.1 Zinc high spots,
27、those that would cause paint film gaps such as the metal drip line, should be removed by smoothing withhand or power tools as described in SSPC Surface Preparation Specification No. 2 or No. 3. The zinc should be removed until itis level with the surrounding area, taking care that the base coating i
28、s not removed by the smoothing methods. After smoothing,the surface shall be inspected for conformance to the required zinc thickness in accordance with Specifications A123/A123M orA153/A153M utilizing a magnetic thickness instrument in accordance with Practice E376 and/or Practice D7091.Any item fa
29、llingbelow the required zinc thickness, before or after removal of any high spots, shall be repaired in accordance with Practice A780using an appropriate method that is compatible with the paint system5.3 Surface CleaningHot-dip galvanized surfaces must be clean and free of oil and grease before the
30、y are painted. Solublesalts shall be removed to the degree specified in the painting/coating specification. Removal of Soluble salts can be extracted usingSSPC Guide 15. Adhesion problems have been experienced with newly galvanized articles that have been water quenched ortreated with chromate conve
31、rsion coatings. These two post-galvanizing treatments are not recommended for galvanized articlesthat are to be painted. Practice B201 or D6492 can determine if contamination is on the galvanized surface prior to painting.5.3.1 Aqueous Alkaline CleaningAn alkaline solution, pH in the range of 11 to
32、12 definitely not greater than 13, can be usedto remove traces of oil, grease, or dirt.An alkaline cleaner is unsuitable for removal of heavy build-up of zinc oxide or wet storagestain (see American Galvanizers Publications, Wet Storage Stain, for description of these conditions). See 5.4 for remova
33、l of zincoxide layer. The alkaline solution nominally is 2 to 5 % sodium compounds, with small additions of emulsifying, chelating, orsequestering agents, or a combination thereof. This solution can be applied through immersion in a tank filled with the solution,sprayed, or brushed with a soft brist
34、le brush, usually nylon and not steel or copper. When dipping or spraying, the solution worksbest in the temperature range from 60 to 85C. 85C (140 to 185F). After cleaning, rinse thoroughly in hot water or water underpressure. Allow to dry completely before proceeding. Whenever galvanized steel is
35、rinsed, it is desirable to use heated drying toaccelerate the complete removal of water from the surface.4 This interaction is described in “Duplex Systems,” van Eijnsbergen, J.F.H., Elsevier Science, Elsevier Science, New York, NY 1994, and in Zinc Handbook, Porter, F.,Marcel Dekker, Inc., New York
36、, NY 1991.D6386 16a2NOTE 1 An alkaline cleaner is unsuitable for removal of heavy build-up of zinc oxide or wet storage stain (see American Galvanizers Publications,Wet Storage Stain,5 for description of these conditions). See 5.3.3 or 5.4 for removal of zinc oxide layer.5.3.2 Solvent CleaningTypica
37、l cleaning solvents, such as mineral spirits or high-flash naphtha, can be used to remove oil andgrease. The procedure to be used is as specified in SSPC Surface Preparation Specification No. 1. Proper rags or brushes shouldbe used to wipe the galvanized parts. (WarningThese rags or brushes should b
38、e cleaned or recycled often since oil canaccumulate on their surfaces and be transferred back to the galvanized part.part.) Small parts may be dipped or cleaned inultrasonic baths of solvents.After cleaning, rinse thoroughly in hot water or water under pressure.Allow to dry completely beforeproceedi
39、ng.) Whenever galvanized steel is rinsed, it is desirable to use heated drying to accelerate the complete removal of waterfrom the surface.5.3.3 Hand or Power Tool CleaningHand or power tool cleaning may be used using equipment as specified in SSPC SurfacePreparation Specification No. 2 or No. 3 is
40、one method to clean light deposits of zinc reaction by products, such as wet-storagestain, as specified in SSPC Surface Preparation Specification No. 2 or No. 3.light wet-storage stain.5.4 Surface PreparationHot-dip galvanized surfaces have a layer of zinc oxide and zinc hydroxide that must be remov
41、edbefore paint will adhere to the zinc coating. Zinc coatings generally are relatively smooth and may be slightly roughened prior topainting. The following fourfive methods may be used to prepare the galvanized surface for painting.5.4.1 Sweep BlastingAbrasive sweep or brush blasting, blasting in ac
42、cordance with procedures described in SSPC SurfacePreparation No. 16, which uses a rapid nozzle movement will roughen the galvanized surface profile. The abrasive material mustbe chosen with care to provide a stripping action without removing excess zinc layers, removal of up to 25 microns (1 mil) i
43、sacceptable. One of the materials that has been used successfully is aluminum/magnesium silicate. Particle size should be in therange of 200 to 500 m (8 to 20 mils). Other materials that can be used are soft mineral sands with a MOH hardness of five orless, organic media, such as corn cobs or walnut
44、 shells, corundum, and limestone. Depending on the value of hardness for theabrasive medium, blasting pressure may need to be determined for the appropriate nozzle to work-piece distance, geometry of thecomponent, and blasting medium. For some all-alloy coatings, even the relatively low-pressure bla
45、st of 0.15 to 0.25 MPa (20 to40 psi) can be too great, causing cohesion problems. Oil contamination of the compressed air will degrade paint adhesion tosweep-blasted hot-dip galvanized surfaces. surfaces, Test Method for determining this contamination is D4285. Care is needed inaverting this type of
46、 contamination. Care must be taken to leave zinc layers intact. The purpose of sweep blasting is to deform,not remove the galvanized metal. Any area falling below the required zinc thickness, before or after sweep blasting, should berepaired in accordance with Practice A780. The procedure for this p
47、rocess can be found in SSPC Surface Preparation SpecificationNo. 7. No. 16. Sweep blasting of zinc should be not less than 110 m2/h (1200 ft2/h) using these abrasive materials. The substrateshould be maintained at a temperature greater than 3C (5F) above the dew point temperature. Following abrasive
48、 blast cleaning,surfaces should be blown down with clean, compressed air. In some atmospheric conditions, such as high humidity, or hightemperature, or both, the formation of zinc oxide on the blasted surface will begin very quickly, so the paint coating should beapplied immediately, within an hour,
49、 after sweep blasting. Zinc oxide formation is not visible to the unaided eye; therefore, in anyatmosphere, painting should be stated as soon as possible after surface preparation.This procedure should be completed at the samelocation as the paint application.5.4.2 Surface GrindingPower tools such as grinders or sanders will roughen the surface of galvanized steel and produce asurface profile suitable for paint adhesion as per SSPC Surface Preparation Specification No. 11. The grinder or sander shall notbe applied with sufficient force to remove all of the zinc
