AWS WZC-1972 Welding Zinc-Coated Steel (First Edition Reprinted August 1983)《镀锌钢焊接 第1版 1983年8月再版》.pdf

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1、AWS WZC/D19.0-72WeldingZinc-Coated SteelAWS WZC/D19.072WeldingZinc-CoatedSteelPrepared byAWS Technical DepartmentJay BlandTechnical Directorin cooperation with theInternational Lead ZincResearch Organization, Inc.Dr. S. F. RadtkeExecutive Vice Presidentand Director ofResearchPublished by AMERICAN WE

2、LDING SOCIETY, Inc.550 N. W. Lejeune Rd. Miami. FL 33126 1972 by American Welding SocietyAU rights reserved.First Edition - 1972Reprint No. I, August 1983Library of Congress No. 72-91061ISBN No. 0-87171-102-8PRINTED IN THE UNITED STATES OF AMERICAiiPREFACEThe excellent long-term protection of steel

3、by galvanizing or metallizing,together with the attendant low maintenance cost, have led to the widespreadapplication of zinc coatings to large structures such as highway bridges,power and television transmission towers, etc.The use of zinc-rich paints in the form of welding primers for thetemporary

4、 protection of shotblasted steel during fabrication and prior to theapplicatio.n of the final paint coating is also increasing each year, typicalapplications being ship hulls and plating and all forms of structural steelwork.To exploit the exceptional advantages of zinc coatings, both for permanenta

5、nd temporary protection, it is essential to be able to weld zinc-coated steeland to produce joints having qualities equal to those of joints in uncoatedsteel.With this objective in mind, the International Lead Zinc ResearchOrganization, Inc. (ILZRO) sponsored a four-year program of work on the arcan

6、d gas welding of zinc-coated steels at The Welding Institute, Cambridge,England. The work identified the problems that can occur when weldingzinc-coated steel; solutions to these problems have been found. The manual isbased on the results of this work and also includes data from other publishedwork.

7、The American Welding Society is grateful to ILZRO for providing most ofthe material used in this manual. The original report has been edited to reflectU.S. terminology in accordance with AWS standards. Some additional textmaterial has been added in several sections for more complete coverage of thes

8、ubject.It should be noted that this manual deals primarily with gas and arcwelding processes used commercially for joining zinc-coated steels. Referenceshould be made to AWS C1.370, Recommended Practices for ResistanceWelding Coated Low Carbon Steels, for information on resistance - spot,resistance

9、- seam and projection welding of zinc-coated (galvanized only)steels.iiiACKNOWLEDGMENTSThe basic report made to ILZRO by the Welding Institute, Abington Hall,Cambridge, England, was prepared by E. N. Gregory. The report alsoacknowledged the financial support of ILZRO on the project, as well asadvice

10、, assistance and cooperation from the following firms and organizations:CanadaEnglandHollandUnited StatesSteel Company of CanadaB. O. C. - Murex, Ltd.Crittal-Hope, Ltd.Imperial Smelting Corp.I. C. I. Paints, Ltd.Metallisation, Ltd.Research Association of British Paint,Colour forexamplesteel beams up

11、 to 80 ft (25 m) longcould be hot-dip galvanized by dipping one end at a time in a 45 ft (17 m)bath.MetallizingZinc in the form of powder or wire is fed into the flame of a metallizinggun where the zinc is atomized and the finely divided droplets of molten zincare projected towards the shotblasted w

12、orkpiece by means of a jet ofcompressed air. A recently developed electric arc metallizing process uses twocoils of wire which are consumed by an electric arc maintained between theends of the wires. Again, the molten zinc is directed onto the workpiece bymeans of compressed air.The zinc coating thi

13、ckness is generally at least 0.004 in. (0.1 mm or 100microns): MetalliZing is used to protect a large variety of components and canbe applied in situ to protect structures such as bridges without any limitationon size.2 IWelding Zinc-Coated SteelPainting with Zinc-rich PaintsZinc-rich or zinc-dust p

14、aints have been developed which have similarproperties to a zinc coating applied by galvanizing or metallizing in that theunderlying steel is to a certain extent protected sacrificially, provided thatsufficient zinc is present in the paint film.Zinc-rich paints are widely used in the form of zinc pr

15、imers or weldingprimers for the temporary protection (up to 12 months) of shotblasted steelduring the period of fabrication by welding, before the final paint coatingsystem is applied. For welding primers, 92-95 weight percent of zinc is used ina variety of binding agents such as sodium silicate, so

16、dium ethyl silicate,epoxy resin or chlorinated rubber. Film thicknesses vary from 0.0005-0.003in. (12-75 microns) depending on the type of paint and method ofapplication. The most Widespread use is for ship hulls and plating, and for allforms of structural steel work. Most shipyards have for some ti

17、meincorporated an automatic shotblasting and painting plant, and a more recenttrend is for steel makers to supply primed plate direct from the steel works.Section 2 - Gas WeldingGas welding uses the heat of combusion of a fuel gas with oxygen, themost commonly used fuel gas being acetylene which giv

18、es a flame temperatureabove 5030 F (3000 C). The oxyacetylene flame may be used for fusionwelding (oxyacetylene welding) (OW) of steel in which the edges of the jointsare melted and a steel filler rod is melted into the joint, or it may be used forbraze welding in which the melting point of the fill

19、er rod is below that of thebase metal but above 800 F (427 C) and in which the edges of the joint are notintentionally melted.Fusion WeldingGalvanized steel may be oxyacetylene fusion welded with copper-coatedmild steel filler rod (e.g., AWS specification A5.2-69; RG45, RG60, RG65:B.S. Specification

20、 1453: 1972; A I, A2). Preparation for welding is similar tothat for welding uncoated steel, i.e., the use of jigs and clamps to preventdistortion caused by heat buildup, and removal of any grease or dirt from theweld area. A neutral flame should be used with no excess of either oxygen oracetylene a

21、nd the size of the nozzle should be the same as that used forwelding uncoated steel of similar thickness.Because of the low travel speed of oxyacetylene welding, necessary to bringthe joint edges to the fusion temperature, the zinc coating is volatilized andcompletely removed for at leastin. on each

22、 side of the weld. For a furtherin. or so on each side, partial volatilization occurs resulting in a reductionin corrosion resistance; beyond this region, for up to -% in., a change in theappearance of the zinc coating due to heat effects has been reported I * butwithout any deterioration in corrosi

23、on resistance. In order to minimize thearea over which the galvanizing is removed and to reduce the amount of repairrequired after welding, the torch should not be moved from side to side. Theleftward or forehand method of welding, Fig. 2.1, should be used in whichthe torch flame points in the direc

24、tion of welding and the welding rodprecedes the torch flame. Compared“ with the rightward or backhand method,in which the torch flame points back at the completed weld with the weldingrod interposed between the flame and the completed weld, more zinc will beburnt off in front of the weld pool and wi

25、ll cause less interference withwelding. Welds should not be remelted by the flame in order to improve theirappearance because this practice, sometimes used when welding uncoatedsteel, will result in additional loss of llvanizing.Repair procedures are described in Section 1. See references at end of

26、manual.41 Welding Zinc-Coated SteelFig. 2.1 - Leftward or forehand welding.Braze WeldingBraze welding is accompanied by a lower heat input than fusion weldingand the base metal is not melted so that there is negligible loss of the zim:coating from the steel. A 60% copper-40% zinc filler rod is gener

27、ally usedwhich melts between 1650 and 1700 F (900 and 930 C) and which flows overthe edges of the joint and alloys with or tins the steel to provide a strongcorrosion-resistant joint. A typical welding technique for braze welding is asfollows:1. Remove grease or dirt from the regions of the joint by

28、 means ofdegreasing agents, wire brushing or steelwool.2. Prepare sheet edges for butt joints as shown in Table 2.1. Lap or teejoints can also be used (Table 2.2).3. Use jigs or clamps to hold the work and prevent distortion duringwelding. Parts that are shown by experience not to suffer fromdistort

29、ion can be held together by tack welding before the joint iswelded.4. Mix braze-welding flux to a stiff paste with water and apply generouslyto upper and reverse sides of the seam and also to the filler rod.5. Use torch nozzle size two times smaller than for fusion welding sheet ofthe same thickness

30、.Gas Welding)S6, Use 60 Cu-40 Zn aHoy filler rod, e.g., AWS Specification A5.7-69, RBCuZn-A*, or B.S. Specification 1453:1957:C2.tThe diameter of thefiller rod should be Itimes the sheet thickness for material up to3/16 in. (4.8 mm). For material over 3/16 in. thick, use ain. (6.4mm) diam rod.7. Adj

31、ust the flame to a slightly oxidizing condition - more so than forwelding uncoated steel.8. When the joint area reaches a dull red heat, deposit the filler metal;direct the flame more on to the rod than the workpiece.9. Use leftwards or forehand technique and avoid any lateral or weavingmotion of th

32、e torch so as to reduce the buildup of heat. Composition: Cu 57-61%; Sn 0.25-1.00%; Al 0.01% max; Pb 0.05% max; total otherelements 0.50% max; Zn remainder.t Composition: Cu 57-63%; Si 0.2-0.5%; Sn 0.5% max; Al 0.03% max; Zn remainder.TABLE 2.1 - Edge preparation for braze welding butt joints ingalv

33、anized sheet.Sheet thicknesslU EdgeJ 0 i nt Des i 9n ( in. ) . ( mm) preparat ionRootopeningRootfaceIIt1/8 max 3.2 maxSquareOver 1/8 Over 3.2 70-90 tr=Jand up to and up togroove 4“(a )1/4 6.4angleNote (a) Root face is not generally specified but sharp cornersshould be rounded off which will result i

34、n a root.face of1/1 6 in. (1. 6 mm).TABLE 2.2 - Examples of lap and tee joints for braze weldinggalvanized steel. (a)Joint Design Type of joi nt Type of weldI.lap Single filletI1Lap Double filletTee Single filletcJ6Tee Double filletNote (a) There is no thicknesslimit and dissimilar thicknesses canbe

35、 joined.61 Welding Zinc-Coated SteelSection 3 - Gas Tungsten-ArcWeldingFusion WeldingIn the gas tungsten-arc welding (GT AW)* process, an arc is maintained be tween a tungsten electrode and the workpiece, and the arc zone is shieldedfrom the atmosphere generally by means of argon or helium or mixtur

36、es ofthese two gases. Argon generally produces an arc which operates moresmoothly and quietly and is less penetrating than helium. The lower arc volt age characteristic of argon facilitates the welding of thin materials because therisk of burn-thru is lessened, and when welding galvanized steel, the

37、 low pene tration obtained with argon reduces the amount of zinc volatilized. WhenGTA welding is applied to galvanized steel, the end of the electrode may rap idly become contaminated by zinc and lose its point, resulting in erratic arcaction. Blocking of the torch nozzle by particles of spatter can

38、 adversely af fect the flow of shielding gas.Electrode contamination can be minimized by holding the torch at an angleof 70 deg to the plate surface instead of the conventional 80 deg and increas ing the gas flow rate from the conventional 15 cth (7 1/min) to 25 cth () 2I/min). This has the effect o

39、f flushing the zinc vapor from the arc area. Minimum currents just sufficient to obtain penetration restrict the amount ofvolatilized zinc and can give neat butt welds. Corner welds in which the sheetedges are sheared and therefore free from zinc should be relatively easy tomake, but tee joints woul

40、d be more likely to give trouble because of the zincat the faying surface. Suitable conditions for making butt joints in 1/16 in.C1.6. mm) sheet are given in Table 3.1.If the base metal is rimming-quality steel, the same precautions must betaken as with uncoated rimming steel, i.e., a deoxidized fil

41、ler wire must beused to prevent the formation of porosity. The following technique factorsmay be considered:1. Use lowest current consistent with adequate penetration.2. Increase gas flow.3. Decrease torch angle to 70 deg.4. Use long are, 3/16 in. (4.8 mm).5. Use deoxidized filler on rimming steel.6

42、. Use uncoated, i.e., sheared edges.7. Use sheet with low zinc coating weight. GTAW is also called TIG welding.Gas TungstenArc Welding 17TABLE 3.1 - Conditions for GTAW butt joints in 1/16 in. continuously galvanized sheet.(alEdgepreparationConditionof edgesRoot opening( ; n.) (mm)Current(A)Torch(de

43、g)Argon flowrate(cfh)(l/min)Square Uncoated(sheared)1/32 60 70 25 12Note (a) Zinc coatingweiht1 1/4 oz/ft2(381 9/m2) including bothsides. 1/8 in. (3.2 mm) thoriated tungsten electrode;direct current straight polarity. 3/64 in. (1.2 mm) diamSi-Mn deoxidized filler rod. Copper backing bar. 3/16x 0.025

44、 in. (4.8 x 0.64 mm) groove.Braze WeldingThe GTAW process can be used to produce braze-welded joints in whichthe amount of base metal melted is minimized by either pushing a filler rodinto the joint or laying the wire flat in the joint and maintaining the arcbetween the tungsten electrode and the fi

45、ller rod. GTA braze welds can becarried out with either alternating current (ac) or direct current-straight polarity(dcsp) and suitable filler rods, e.g., silicon bronze (AWS A5.7-69, RCuSi-A).Suitable conditions for braze welding butt and lap joints in 3/64 in. (1.2mm) galvanized sheet with silicon

46、-bronze or tin-bronze filler rod are given inTables 3.2 and 3.3.2TABLE 3.2 - GTA braze welding conditions for 3/64 in. galvanized sheet. (a)Diameter Argonof tungsten Diameter of flowType of Type of electrode fill er rod ra te Currentjoint current( in. ) (mm) ( in. ) (mm)(cfh)(1jmin) (A)Butt ae 5/64

47、21/16 1.6 17 8 451/32 1n. (1 mm) dc 1/16 1.61/16 1.6 17 8 35root openingLap ac 5/64 2 1/16 1.6 17 845de 1/16 1.6 1/16 1.6 17 8 35Note (a) Filler rod: Copper. 2.5 % tin.81 Welding Zinc-Coated SteelTABLE 3.3 - GTA braze welding conditions for 3/64 in. galvanized sheet. (a)Diameter Argonof tungsten Dia

48、meter of flowType of Type of electrode filler rodra teoCurrentjoint current ( ; n ) (rom)( ; n. )(mm) (efh) (l/min) (A)Butt ac 5/642 3/32 2.5 17 8 481/32 in. (1 mm) de 5/64 2 3/32 2.5 17 833root openingLap ac 5/64 2 3/32 2.5 178 45de 5/64 2 3/32 2.5 17 8 45Note (a) Fillerrod: Copper, 2.5 % tin19Sect

49、ion 4 - Carbon-Arc WeldingCarbon-arc welding (CAW) utilizes the heat from an arc between a carbonelectrode and the workpiece or from an arc maintained between two carbonelectrodes. This process is largely obsolete, having been superseded by moremodern welding methods. A. few small workshops still carry out carbon-arcwelding and carbon-arc torches are available on the market, so that it is worthnoting that galvanized sheet can be joined by means of this process.A braze welding technique should be used with the filler rod held incontact with the joint, either at an