ASTM A385-2005 Standard Practice for Providing High-Quality Zinc Coatings (Hot-Dip)《提供高质量镀锌覆层(热浸)的标准实施规程》.pdf

《ASTM A385-2005 Standard Practice for Providing High-Quality Zinc Coatings (Hot-Dip)《提供高质量镀锌覆层(热浸)的标准实施规程》.pdf》由会员分享，可在线阅读，更多相关《ASTM A385-2005 Standard Practice for Providing High-Quality Zinc Coatings (Hot-Dip)《提供高质量镀锌覆层(热浸)的标准实施规程》.pdf（9页珍藏版）》请在麦多课文档分享上搜索。

1、Designation: A 385 05Standard Practice forProviding High-Quality Zinc Coatings (Hot-Dip)1This standard is issued under the fixed designation A 385; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number

2、 in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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. Scope*1.1 This practice covers the precautions that should be takent

3、o obtain high-quality hot-dip galvanized coatings.1.2 Where experience on a specific product indicates arelaxing of any provision, the mutually acceptable change shallbe a matter for agreement between the manufacturer andpurchaser.1.3 The values stated in inch-pound units are to be regardedas the st

4、andard.2. Referenced Documents2.1 ASTM Standards:2A 143/A 143M Practice for Safeguarding Against Em-brittlement of Hot-Dip Galvanized Structural Steel Prod-ucts and Procedure for Detecting EmbrittlementA 384 Practice for Safeguarding Against Warpage and Dis-tortion During Hot-Dip Galvanizing of Stee

5、l AssembliesA 563 Specification for Carbon and Alloy Steel Nuts3. Steel Selection3.1 The production of a galvanized coating has as its basisthe metallurgical reaction between the steel and the moltenzinc, resulting in the formation of several iron-zinc compoundlayers, for example, gamma (not always

6、visible microscopi-cally), delta, and zeta in Fig. 1. In addition, a layer of themolten zinc adheres to the surface of the compound layers asthe steel is withdrawn from the galvanizing bath. Uponsolidification, this adherent zinc forms the eta layer.3.2 It is known that the exact structural nature o

7、f thegalvanized coating, as typified by Fig. 1, may be modified inaccordance with the exact chemical nature of the steel beinggalvanized. Certain elements found in steels are known to havean influence on the coating structure. The elements carbon inexcess of about 0.25 %, phosphorus in excess of 0.0

8、4 %, ormanganese in excess of about 1.3 % will cause the productionof coatings different from the coating typified by Fig. 1. Steelswith silicon in the range 0.04 % to 0.15 % or above 0.22 % canproduce galvanized coating growth rates much higher thanthose for steels with silicon levels below 0.04 %

9、and between0.15 % and 0.22 %. Recent studies have shown that even incases where the silicon and phosphorous are individually heldto desirable limits, a combined effect between them canproduce a coating as shown in Fig. 2, which typically wouldhave a mottled or dull gray appearance.3.3 These elements

10、 manifest their structural effect as anaccelerated growth of the compound layers, particularly thezeta layer, and the virtual elimination of the eta layer. Cosmeti-cally this accelerated growth is seen as a gray matte finishedcoating as opposed to the usual bright and smooth appearanceof galvanized

11、coatings. Sometimes, a large surface may haveadjacent areas of matte finish and bright finish leading to amottled appearance.3.4 There is some evidence that the coatings resulting fromthis accelerated growth are more brittle and less adherent thannormal coatings. There is also evidence that these co

12、atings aresubject to a premature red staining in atmospheric exposure;however, this staining has been found not to be associated withcorrosion of the substrate steel.3.5 A problem with steel chemistry is not usually apparentuntil after an item has been galvanized. Not all combinations ofsilicon, pho

13、sphorus, carbon, and manganese can be galvanizedsuccessfully. When the steel chemistry is known beforehand,experienced galvanizers can in some, but not all, instancesexercise limited control over the coatings as shown in Fig. 2.Also, the combination of two different steel types or thick-nesses in on

14、e item may result in a nonuniform galvanizingfinish. The experience of the steel supplier, designer, manufac-turer, and galvanizer should determine the steel selection.3.6 In general, galvanized coatings are specified because oftheir corrosion resistance, not because of their appearance. Therelative

15、 corrosion resistance of the normal and abnormalcoatings is, for all practical purposes, equal.1This practice is under the jurisdiction of ASTM Committee A05 on MetallicCoated Iron and Steel Products and is the direct responsibility of SubcommitteeA05.13 on Structural Shapes and Hardware Specificati

16、ons.Current edition approved April 1, 2005. Published April 2005. Originallyapproved in 1955. Last previous edition approved in 2003 as A 385 03.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards

17、volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Assemblies of Different Material

18、s or Different Surfacesor Both4.1 Whenever possible, assemblies should consist of ele-ments of similar steel chemistry and surface condition.4.2 Whenever different analyses of steel or different sur-faces of steel are united in an assembly the galvanized finish isnot generally uniform in appearance.

19、 These differences in-clude:4.2.1 Excessively rusted surfaces.4.2.2 Pitted surfaces.4.2.3 Machined surfaces.4.2.4 Cast iron (especially with sand inclusion).4.2.5 Cast steel.4.2.6 Malleable iron.4.2.7 Hot-rolled steel.4.2.8 Cold-rolled steel.4.2.9 Steel containing chemical elements in excess of thos

20、erecommended in 3.2.4.3 Where combinations are unavoidable, thorough abrasiveblasting of the entire assembly will normally improve galva-nizing quality.5. Overlapping or Contacting Surfaces5.1 Overlapping or contacting surfaces that have not had alledges seal welded are undesirable.5.2 When the dist

21、ance between the overlapping surfaces isless than332 in. 2.38 mm, these surfaces will not normally bewet by molten zinc. Furthermore, cleaning solution compoundsthat remain on these surfaces volatilize during the galvanizingprocess and may interfere with zinc wetting in adjacent areas.Such uncoated

22、surfaces cause a rust staining after exposure tothe environment. Traditionally however, steel grating has beenmanufactured without seal welding and when properly ex-ecuted, this manufacturing means has permitted the galvanizedcoating to satisfy the quality requirements of the applicableASTM specific

23、ations.5.3 When the overlap surface area is large and the edgeshave been seal welded, air or moisture or both entrappedtherein can develop destructive pressures when the assembly isheated to the galvanizing temperature, which is nominally850F 454C. Vent holes or unwelded area around theadjoining sur

24、faces should be provided through one or bothsides into the lapped area per the following tables.FIG. 1 Photomicrograph of Normal Galvanized Coating (X 400)FIG. 2 Photomicrograph of Dull Gray, Thick-Galvanized Coating (X 200)A3850526. Sheet Steel Rolled Over a Wire or Rod Stiffener6.1 All oil or grea

25、se should be removed from both the sheetsteel and wire or rod before rolling (Fig. 3). Grease or oilbecomes volatile at the galvanizing temperature and willgenerate gas which will prevent zinc from sealing the contactedges. All steel should be degreased before pickling and in thecase of folded assem

26、blies, before folding and assembling (seeFig. 4).7. Weld Flux Removal and Welding Rods7.1 Welding flux residues are chemically inert in normalpickling solutions. Thus, they will not be removed by standardgalvanizing cleaning techniques and are best removed at thetime of fabrication by grit or sand-b

27、lasting or by a wire needlegun.7.2 It is desirable to choose a welding rod with a chemicalcomposition as close as possible to the parent metal.7.3 Welding rods high in silicon may cause excessivelythick or darkened coatings or both to form in the welded area.8. Flame Cut Cope Edges Preparation8.1 Fl

28、ame cut copes on beams can be extremely sensitive toresidual stresses in the steel beam and, with the rough surfacefrom the flame cutting operation, can be sources of crackingduring the thermal cycling of the hot-dip galvanizing process.The steel beams start near ambient temperature then areimmersed

29、 in the molten zinc and heated to above 800F forusually 5 to 10 minutes. The steel beams are then cooled backto ambient temperature so the thermal cycling can createthermal stresses in the area of the cope.8.2 One method that has had fairly good success at mini-mizing the cracking at the edges of th

30、e flame cut cope is toweld a bead along the sides of the cope in the area where theflame cutting was done before hot-dip galvanizing. Thiswelding operation will reheat the area and may relieve some ofthe residual stress near the cope edges. The weld bead will noteliminate all incidents of cracking b

31、ut will greatly reduce thelikelihood of cracking.8.3 The weld rod material should be chosen as described inSection 7.9. Cold Forming Before Galvanizing9.1 Refer to the latest revision of Practice A 143/A 143M.10. Shearing, Cutting and Punching Before Galvanizing10.1 Refer to the latest revision of P

32、ractice A 143/A 143M.11. Warpage and Distortion11.1 Refer to the latest revision of Practice A 384.12. Design Recommendations for Providing for the FreeFlow of Cleaning Solutions, Fluxes, Air, and Zinc12.1 All fabricated assemblies shall be so designed withvent and drain holes such that no air is tr

33、apped during theimmersion of the assemblies into cleaning solutions or moltenzinc. Similarly these holes shall allow all solutions and moltenzinc to drain freely from the assemblies. Failure to follow thispractice will result in areas that will not galvanize properly, orthat may retain entrapped flu

34、x or excessive amounts of zinc.12.2 Free flow of cleaning solutions and molten zinc shallalso be provided for in assemblies of hot-rolled shapes. This isaccomplished by cropping the corner to provide an openingwith a minimum area of 0.3 in.21.9 cm2 at the corners of allstiffeners (Fig. 5), gussets,

35、or bracing (Fig. 6).12.3 Air or moisture, or both, entrapped within closedfabricated pipework, such as handrail, can develop destructivepressures when heated to the galvanizing temperature. Pipehandrail shall preferably be vented full open internally, asshown in Fig. 7. In addition, there shall be o

36、ne38-in. 9.5-mmminimum diameter external hole at each intersection to preventany possible explosions in the event that the fabricator neglectsto provide internal venting. Where internal venting is notpossible, external vents shall be provided with one vent hole ineach side of each intersection. The

37、vent openings shall be aminimum of38 in. in diameter or 25 % of the diameter of thepipe that is used, whichever is larger (Fig. 8).12.4 Figs. 9-12 show most of the conditions encounteredwith tubular product assemblies. The venting shall openTABLE 1 Vent Holes for Overlapped Areas for Steels12 in. 12

38、.75mm or Less in ThicknessOverlapped Area in.2cm2 Vent Holes Unwelded Areaunder 16 103 None None16 103 to under 64 413 One38 in. 1 cm 1 in. 2.5 cm64 413 to under 400 2580 One12 in. 1.25 cm 2 in. 5.1 cm400 2580 and greater,each 400 2580One34 in. 1.91 cm 4 in. 10.2 cmTABLE 2 Vent Holes for Overlapped

39、Areas for Steels Greaterthan12 in. 12.75 mm in ThicknessOverlapped Area in.2cm2 Vent Holes Unwelded Areaunder 16 103 None None16 103 to under 64 413 None None64 413 to under 400 2580 One12 in. 1.25 cm 2 in. 5.1 cm400 2580 and greater,each 400 2580One34 in. 1.91 cm 4 in. 10.2 cmFIG. 3 Rolled Surfaces

40、FIG. 4 Folded SurfacesA385053wherever possible. This is the most desirable situation. Aminimum vent opening of 25 to 30 % of the cross-sectionalarea of tubular structure shall be specified where full-openventing is not possible. For small cross sections, larger percentvent openings are recommended.

41、See attached drawings forspecific recommendations. In box sections (Fig. 9) wheregusset plates are used, the gusset plates shall be clipped at thefour corners. In addition, a center hole shall be provided so thatthe cumulative area of the vent holes meets the recommendedminimum. Gusset plates shall

42、not be spaced closer than 36 in.914 mm apart. In the case of columns with end plates (Fig.10) where the end plate must be closed, the shaft of the columnshall be vented. The vent opening shall be a half circle with itsdiameter at the base plate (D, Fig. 10). This is much superiorto putting a hole wi

43、th the circumference of the hole tangentialto the base plate. On trusses (Fig. 11 and Fig. 12) where tubularmembers intersect, vent holes are recommended at both sidesof the intersection.13. Moving Parts13.1 When a galvanized assembly incorporates movingparts (such as drop handles, shackles, and sha

44、fts) a radialclearance of not less than116 in. 1.59 mm must be allowed toensure full freedom of movement following galvanizing.13.2 Moving parts such as handles or hinges should begalvanized separately and assembled after galvanizing. It maybe necessary to post heat these parts in order to have them

45、function freely. This heating may cause discoloration of thegalvanized coating near the heated area.14. Marking for Identification14.1 Paint is not removed by pickling and must not be usedwhen marking for identification material to be galvanized.14.2 Satisfactory identification may be provided by we

46、ldingthe identifying marks on the material, by embossing theidentifying marks on a steel tag of no less than No. 12 gage(0.105 in. 2.69 mm) and securing to the material with a heavywire such as No. 9 gage (0.148 in. 3.76 mm), or by diestamping the identifying marks into the material with charac-ters

47、12 in. 12.7 mm high and a minimum of132 in. 0.79 mmdeep.14.3 All markings shall remain legible after galvanizing.15. Galvanized Nuts, Bolts, and Tapped Holes inGalvanized Products15.1 Oversize tapping or retapping of nuts and tapped holesis required when the bolt or male thread is galvanized. Whilet

48、apping or retapping after galvanizing results in uncoatedfemale threads, the zinc coating on the engaged male threadwill retard corrosion of both components.15.2 Refer to the sections on dimensions of zinc-coated nutsin Specification A 563.15.3 Manufacturers or specifiers are cautioned to considerth

49、e plus tolerance that has been taken on the nominal pitchdiameter of the bolt when establishing the degree of oversizetapping of the nut that is required for proper fit.15.4 Hot-formed heading or bending may cause develop-ment of a scale that requires an extended time of pickling toremove. Should this occur on screws, scale removal prior tothreading is desirable in order to avoid overpickling of thethreaded area.16. Critical Dimensions16.1 When an assembly of steel parts or an individual steel