1、Designation: A 384/A 384M 07Standard Practice forSafeguarding Against Warpage and Distortion During Hot-Dip Galvanizing of Steel Assemblies1This standard is issued under the fixed designation A 384/A 384M; the number immediately following the designation indicates the yearof original adoption or, in
2、 the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 Steel assemblies and subassemblies fabricated by weld-ing, such as composite struc
3、tural members, sash, weldments,etc., that are to be hot-dip galvanized after fabrication, aresubject to warpage and distortion of the material due to theheating and cooling integral to the galvanizing operation,particularly when it is necessary for the assembly to be dippedmore than once to coat the
4、 entire surface.1.2 This specification is applicable in either inch pounds orSI units. Inch pounds and SI units are not necessarily exactequivalents. Within the text of this specification and whereappropriate, SI units are shown in parentheses.2. Referenced Documents2.1 ASTM Standards:2A 143/A 143M
5、Practice for Safeguarding Against Em-brittlement of Hot-Dip Galvanized Structural Steel Prod-ucts and Procedure for Detecting EmbrittlementA 385 Practice for Providing High-Quality Zinc Coatings(Hot-Dip)A 780 Practice for Repair of Damaged and Uncoated Areasof Hot-Dip Galvanized Coatings3. Factors i
6、n Warpage and Distortion3.1 One of the most commonly distorted and warped mem-bers of assemblies is that of sheets or plates from No. 20 gage0.812 mm to14 in. 6.35 mm in thickness which areassembled by welding or riveting to bar-size shapes, angles,channels, tees, etc. The sheets or plates have resi
7、dual stressfrom the welding or riveting as well as stress from rollingoperations to bring the sheet or plate to its final thickness. Asthe sheet or plate is heated to galvanizing temperature, 820 to850F (438 to 454C), the stress can be slightly relieved but theconstraint of the framing does not allo
8、w the stresses to becompletely relieved. The stress relief is minimal and, thus, theinternal stress level of the sheet or plate compounds because ofthe addition of the contraction forces. When the fabricationcools after galvanizing, the framing also restricts the contrac-tion of the sheet or plate f
9、urther increasing internal stresses. Ifthe warpage or distortion is minimal, the fabrication may beacceptable but, if the distortion is significant, the fabricationmay need to be reworked with the sheet or plate attached to theframe after hot-dip galvanizing.3.2 Warpage is accentuated by the use of
10、nonsymmetricalsections such as channels. Regardless of size, channels that aregalvanized by themselves often require straightening aftergalvanizing. This is not true of an I-beam, pipe, H-column, orany other section that is symmetrical about both its major axes.Channels and other nonsymmetrical sect
11、ions should be avoidedfor the framework of a sheet metal assembly that is to behot-dip galvanized whenever it is possible to use symmetricalshapes or sections as framing pieces.3.2.1 Checkered plate may also warp or distort duringgalvanizing due to the asymmetry of the plate design. Since allof the
12、deformations are on one side of the plate, the residualstress from fabricating the checkered plate may cause warpageor distortion. This may be accentuated by attaching checkeredplate to a frame before hot-dip galvanizing.3.3 The use of wide radii bends in corners is recommended.In the case of sheet
13、metal, the product that has a right-anglebend in the sheet metal itself will remain flatter and be freerfrom distortion if the radius of the bend is as large as practical.For extremely tight bends that are integral to the fabrication,stress relieving in accordance with the section on Cold Work-ing a
14、nd Thermal Treatment of Practice A 143/A 143M isrecommended to avoid warpage or distortion.3.4 Certain welding practices, weld sizes and configura-tions, and thickness differences between welded componentscan introduce imbalanced stresses into the weldments. If thesestresses are combined with other
15、stresses during hot-dipgalvanizing, the stress relieving effect of galvanizing maypermit distortion to occur.NOTE 1One example of this situation is the bracing of two largepieces in a fabrication by a smaller piece. The smaller piece is welded at1This practice is under the jurisdiction of ASTM Commi
16、ttee A05 on Metallic-Coated Iron and Steel Products and is the direct responsibility of SubcommitteeA05.13 on Structural Shapes and Hardware Specifications.Current edition approved May 1, 2007. Published June 2007. Originallyapproved in 1955. Last previous edition approved in 2002 as A 384/A 384M -
17、02.This practice is based upon the work of the Technical Services Committee of theAmerican Galvanizers Association.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 t
18、he standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.both ends and during the cool-down after galvanizing it may experiencesignificant stress as it cools more quickly than the two larg
19、er pieces. Theresulting stress may cause warpage or distortion of the smaller, bracingpiece. Another example of imbalanced stresses is the welding of afabrication piece on one edge. When this type of fabrication is hot-dipgalvanized the welding on one edge causes all of the internal stress in thepar
20、t to be concentrated at the edge of the weld and during cool down fromgalvanizing the contraction may cause the part to warp or distort since itcannot move to adjust the internal stresses.3.5 When two pieces of steel are seal welded in an overlap-ping joint, the overlapping section must be properly
21、vented perPractice A 385. If the overlapped area is not properly vented orif it is incorrectly sealed, the pressure from the expansion of thetrapped gases in the overlapped area can distort the two piecesof steel that are welded together and, in the worst case, cancause an explosion underneath the z
22、inc bath surface destroyingthe parts and causing a potential safety problem at the hot-dipgalvanizing facility.3.6 When a fabricated assembly is too large for a particulargalvanizing kettle and the fabrication must be dipped, reposi-tioned, and dipped again, the thermal stresses on the fabricationdu
23、e to the temperature differences from the section inside thezinc bath to the section outside the zinc bath can createwarpage or distortion of the fabrication.3.7 Combining any of these potential causes of warpage, ordistortion, or both, such as non-symmetrical design withdifferent thickness steel pa
24、rts increases the potential forwarpage and distortion to occur.4. Suggested Corrections for Panel Fabrication4.1 The angles selected should be in as perfect alignment asit is practical to obtain.4.2 The angles should be placed in position without clamp-ing or pulling prior to welding so that the cor
25、ners of abuttingedges will lie in position without restraint. Clamps may beapplied to prevent shifting or movement during the weldingoperation.4.3 The stiffening angles should be placed in position andheld down to prevent their being moved when in contact withthe electrode during the welding operati
26、on. In welding anyintermediate lengths along one side of a common member, careshould be taken to prevent warpage of the common memberdue to the application of high heat on the same side at variousintervals along its length.4.4 All edges of tightly contacting surfaces should becompletely sealed by we
27、lding unless the area exceeds therecommended size detailed in PracticeA 385. This will preventthe rusting of the surfaces that are so connected that moltenzinc cannot circulate through the crevices to galvanize thecontacting surfaces.4.5 The sheet steel should not be welded to the angle steelframe p
28、rior to galvanizing if the galvanizing kettle is not ofsufficient size to permit the total immersion in one dip. If theframe has to be dipped one half at a time, it will be better tohave the sheets galvanized, rolled flat after galvanizing, andassembled to the galvanized frame by the use of galvaniz
29、edrivets. These rivets can be countersunk or flat head if theprotruding head of the ordinary button or round head rivet isobjectionable. If the angle steel frame and sheets are punchedprior to galvanizing (the recommended procedure), the use ofdrift pins to bring the holes into alignment should be a
30、voidedas far as possible at the time the sheets and frame areassembled.4.6 If the galvanizing kettle is of sufficient size to permittotal immersion of the assembly in one dip, the riveting offabricated parts prior to galvanizing is not recommendedbecause contacting surfaces will not be coated and ru
31、sting willoccur due to entrapped pickling acid.4.7 Unequal thickness of metal should be avoided whereverpossible due to the different rates of heating and cooling duringthe galvanizing operation and the effect of unequal expansionand contraction.4.8 If the fabrication is non-symmetrical and all othe
32、rattempts to minimize the warpage and distortion have failed,two fabrications may be temporarily connected to make asymmetrical assembly for the hot-dip galvanizing process. Thiscan minimize the warpage and distortion during the thermalcycle of the hot-dip galvanizing. After galvanizing, the tempo-r
33、ary bracing to make the symmetrical assembly can be re-moved and the areas of contact can be repaired or touched-upas described in Practice A 780.5. Embrittlement5.1 Cold working before galvanizing (straightening, spring-ing into position, reforming, etc.) of various steel parts inmaking up an assem
34、bly, or in the cold working of theindividual members of an assembly, punching, cutting, etc.,may result in embrittlement of the base metal following the hotgalvanizing operation. Necessary precautions to fabricate prop-erly and prepare the material for galvanizing to preventembrittlement are describ
35、ed in Practice A 143/A 143M.NOTE 2Welding, if improperly performed, may induce embrittlement.It is recommended that welding procedures be carried out in conformancewith the pertinent specifications of the American Welding Society.6. Keywords6.1 coatings-zinc; galvanized coatings; steel products-meta
36、llic coated; zinc coatings-steel productsA 384/A 384M 072ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such paten
37、t rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited eithe
38、r for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair he
39、aring you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).A 384/A 384M 073
