is 2629 (1985): recommended practice for hot-dip
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है”ह”ह
IS 2629 (1985): Recommended Practice for Hot-DipGalvanizing of Iron and Steel [MTD 7: Light Metals andtheir Alloys]
IS : 2629 - 1985( Reaffirmed 1994 )
Indian StandardRECOMMENDED PRACTICE FOR
HOT-DIP GALVANIZING OF IRON AND STEEL
( First Revision)
Third Reprint AUGUST 1997
UDC 6()9.\ : 669.5~o.5
© Copyright 1986
B If I< E A () 0 FIN n I A N S TAN DAR [) SMANAK IHIAVAN, 9 BAIIADUR SHAll ZAFAR MARci
NI~W DFLIII 110002
Gr 7 November 1986
AMENDMENT NO.1 DECEMBER 1988TO
IS : 2629 - 1985 RECOMMENDED PRACTICE FORHOT-DIP GALVANIZING OF IRON AND STEEL
( Pages 15, 16 and 17, Appendix A, last column) - Substitute ' Maybe rejected' for 'Yf'S' and 'May be acc('pted' for' No' whereverappearing.
(SMDC 28)
Printed at Dee Kay Printer•• New Delhi. India
A1\JENDJ\tENT NO.2 MARCH 1995TO
IS 2629: 1985 nECOMMENDED PR~CTICE FORHOT·DIP GALVANIZING OF IRON AND STEEL
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IS I 2629 • 1985
Indian Standard
RECOMMENDED PRACTICE FORHOT-DIP GALVANIZING OF IRON AND STEEL
( First Revision)
Hot-Dip, Sprayed and Diffusion Coatings Sectional Committee, SMDC 28
ChairT1UJn5IUU V. R. SUBIUX"'NI41'I
RepresIIIU"gIndUln Hot Dip Galvanizer's Association, New
Delhi
Karnam Engmcermg Corporal IOn Ltd, Bombay
Steel Authority of India Ltd ( Rourkela SteelPlant), Rourl..l'1a
The Trnplate Co of India Ltd, GolrnurrSteel Authority 01 India Ltd ( R&D Centre for
Iron & St ee l ), RanchiNational Test House, CalcuttaMrmstrv of Railways, Nr-w Delhi
MembersI'ltBl P. K. BA.NERJEES'lRI K.8. BANNINTHAY A
SRBI]. N.BHATTACHAI\YYA
CRUIl8T & ME'l'ALLUR018TA88ISTANTCUEIIl18T&
ME'U.LLUhGIST ( Alternate)SHRI G. GANF8HAN
SHIU B. G. SOBONI ( Allernale )SURI BllIJLAI. KUA8TIlIYA
S14IU J. N. IJIIAMIJIlY I Alternate)SHRI a. A]l[E~1I CUA"IDH.\ l\L\IlAJ 'N I hv Indian ~I{, 1 ..nd
JamdlPdpur\\ II e Products Ltd,
Spr cral Steels LId, Bombay
G'lut, K ..en. \VII .ia ms Lid, CalcuttaInd ian Lead I me Inforrnauon Centre,
New DeihlSHRI B. N, ~ All \ M rrnst ry of Defr-nci (DGI), New Del h.
SHllI A. IlJI,\T'r ALII AllY A ( Alternate )SHRI S. N. SJ'OIl Llc c t nra l Manut.u.turmg Co Lid, Calcutta
SlIlU M. M. MALlIOTJlA ( AllernaJ<JSURI N. K. SINGHAL Indian Iron and Stet I Co Ltd Bur npur
SII/II A. SENGIJPTA ( Alternate)SHRI]. L. SONFJI
SHRI M. R. DOl TOR ( Alternate)
Snur DAIISIIAN ~J"OIl ( Alternate )SUBI S. NEIJ:LAKANTA~ Zc rurh St e<1 PiP" Lid, Hom bay
Dlt A. R. KESKAll ( Alternate)SURI D. PAtH.SHBIL.PUGAZIIENTH)
( C.nllnued lin page 2 )
@ Cop)f1ghl 1986
BUREAU OF INDIAN STANDARDSThis pubhcanon IS protected under thl' Indian Copyrl~ht Acl \ XIV of 1957 ) andreproduction in whole or in part by any means except With wrrtrcn permission of thepublisher .hall be deemed to be aD IOfrmgcmcDt of cop}Tlght Ilnd!r the laid Act.
IS J 2629 .1985
(Ctmli_d!,,,m pa" I )
M,mIH,sSUBI S' G. TUDKKAB
SHRd. C. EaRY (,AI/",IIJ1,)SUBI K. RAOHAVKNDBAN,
Director ( Struc &: Met )
Rt/W'slJl/ingSteel Authority of India Ltd ( Bokaro Steel Ltd ),
Bobro Steel City
Director General, lSI ( Ex-offino MfmM)
S",6ta'JSURI S. K. GUPTA
Deputy Director ( Metal.), lSI
Hot-Dip Galvanizing Subcommittee, SMDC 28 : 1CotJllln"
SaBI V. R. SI1BllAMANUN Indian Hot Dip Galvanizer'. AaociatiOD,New Delhi
Electrical Manufacturing Co Pvt Ltd, Calcutta
Hydel Designs Directorate, ChandigarhHope's Metal Window. ( India) Ltd, Calcutta
Central Electricity Authority, New Delhi
MfmbmSIUn L. PUGAZBII:NTHY ( Altnul' to
Sbri V. R. Subramanian)SSBI V. P. Alf~NJ)
SBBI S. N. SUIOB ( A/I","11, )SBRI B. D. BALISBIUJ. S. B.Df
SlIBI A. K. SOBTI ( AlI"ruJ/, )SURI D. S. hRULLAR General Engineering Works, Bharatpur
StlRI M. S. MIIlUTA (A/I"MI, )DIRECTOR
Dv.PUTY DIRECTOB ( AI'''MI, )SSRI D. DUTTA The Indian Tube Co Ltd, Jam.hedpur
SIIRI N. R. NATARMAH (AI/"nal,)SURI A. K. GUBA The Fort William Co Ltd, Calcutta
SURI S. KUIIAR ( A/I"JllJI, )JOINT DmECTOR ( CHEX' ) Ministry of Railways
JOINT DmEcTOR ( TI )-1 (AII"na/, )SHRI R. C. MABAJAlf The Indian Steel & Wire Products
JamshedpurLtd.
Steel Authority of India Ltd ( Rourkela SteelPlant ), Rourkela
Directorate General of Technical Development,New Delhi
POlIti &. Telegraph Department, Calcutta
The Tata Iron &. Steel Co Ltd, JamshedpurZenith Steel Pipes Ltd, Bombay
Kamani Engineering Corporation Ltd, BombaySpecial Steels Ltd, Rombay
( AI ternat« )The Indian Iron & Steel Co Ltd, BurnpurDirectorate General of Supplies & Disposals,
New Delhi
SBRI AVTA. SUIOH ( .41"'TIIlI,)SHRI B. M.\IIAPATRA
\ SHRI S. S. SINHA ( AII"TIIlI, )S~ru S. MAJUMDAB
SHRI P. G. MUKRER;JKIDSHRI K. MITRA ( AI"'MI,)
DR T. MIJKflKnn:IlISHRI S.NEF.LAKANTAN
DR A. R. KESIUR ( AlI"TIIlI,)SHRI N. D. PAHlKBSURIR.A. SSANBIlAO
Sum S. S. MURANJ~NSHRI ..\. SnHluPTASnur K. M. T ANF.J A
SHill G. M. GUPTA ( .411,,"alt)5l1JU VIJ,\Y KAPoun Guest, Keen, Williams Ltd, Howrah
2
IS : 2629 • 1985
Indian Standard
RECOMMENDED PRACTICE FORHOT-DIP GALVANIZING OF IRON AND STEEL
( First Revision)
O. FOR E \V 0 R D
0.1 This Indian Standard ( FIrst Revision) was adopted by the IndianStandards Jnvututron on 20 June 198'), aflrr the dr ,If t Imahved b) theHot-Dip, Spi avec! and Diffusion (;o,ltln~,> "" I 'LOllal Couunutcc h.id brenapproved by the Strut tural and Metals ])1\ 1'>lllJ} Council
0.2 TIllS standard was first published In 196tJ The present revision hasbeen prepared In the hght of the experrcru c gamed smc e lb first publication and further technical developments in th I~ field I'he continuous galvaniZIng proce~s has been included III this I C\ rsron. The tvprc.il photogI aphsfor the varrou-, dclects In galvaruzcd co,l.lln~~ on iron and steel have alsobeen included In Appendix A.
0.3 Hot-drp ~'llval1l71nb I~ an old .HId w. II known process of applyll1f{ zinccoating to IrOIl or ste-el surface for prou-ctron ,\galll~t (on o-ion The / Inccoatimr hrvtlv proterts the base JIlt tal by acting as an impervious shrcldbetween the metal and the atrnosplu re and secondly affords sacrrhr ra! protection even when moderately siz ed area'> ( ~ mru dia, for example ) 01 thebase metal surface are exposed.
0.3.1 When a thoroughly cleaned article IS immersed In a ~alv,lf\lzlllg
bath, the metal surface reacts with molten 710L to for m a zmc-tro n alloy.As the article is withdrawn Irom the bath, It pick-, lip pure zinc whichsolidifies on cooling and forms tilt' outer layer. The intermediate alloylayer provides a stronu bond f>'etween the ferrous base rnater ial and thepure zinc and also resists corrosion and abrasron III the event of the purezmc layer being removed Under same conditions of prorcss or compo~l·
tion of the material the whole coating may consist of zrnc-iron alloy layers.
0.3.2 The galvaruzmg process can br- grouped under three broad categories, namely (a) the wet process, (0) the dry process, and (c) the contmuous galvamzmq process ContllJUOUS galvamzmz process constvts of (leaningbase steel surface by first oxrchzmg' and subsequently reducing the surface oxides under controlled atmosphere or by any other m-Ime cleaning
3
IS: 2629 • 1985
method. The strip I~ heat- treated in lint" annealing/normalizing furnacefollowed by continuous ff'l'ding through molten zinc bath and passivatingtreatment by suitable agent hkc chromic acid. After g" lvanizing, when thesheet emerges from the zinc bath, the excess molten zinc on them is wipedoff by air or gas jets. There is no fluxing in this process.
0.3.3 Continuous galvanizing process has got advantages over both wetand dry processes with respect to high productivity, control of coatingthickness, uniformity of coating along the length, better coating adherence, less dross formation, better surface appearance, etc.
0.'1 A summary of defects, along with the typical photographs for illustration, commonly met with in the hot-dip galvanizing practice, their causesand remedial measures are given in Appendix A. In this appendix, theinformation given in the last column aids inspectors in interpreting theappearance of the article and help them in arriving at a correct decisionfor accepting or rejecting the finished material.
0.5 Working conditions and safety measures which should be observed ingalvanizing plants are given in Appendix B.
J. SCOPE
1.1 This standard recommends important guidelines for general hot-dipgalvanizing of iron and steel.
2. TERMINOLOGY
2.0 For the purpose of this standard, the following definitions shall apply.
2.1 A.h - A mixture of zinc oxide and varying quantities of metalliczinc. The former is formed as a result of oxidation of clear zinc on thebath surface and when the oxide is skimmed off, a certain amount ofmetallic zinc gets entrapped and removed along with it.
2.2 Dro.. - An interrnetallic compound ( FeZnls ), which is a com piesmixture of zinc and iron, forms in the galvanizing bath as a result of thereaction of molten zinc with iron or iron salts and settles down at thebottom of the bath. Zinc content in dross will vary between 94 to 97 percent depending on the quantity of metallic zinc entrained in dross duringits removal from the pot.
2.3 Flax - A chemical compound applied in the form of an aqueoussolution and dried on to the work in the dry process or spread as a moltenblanket over the zinc bath in the wet process. The primary purpose of theflux is to help in keeping the surface of both work and molten zinc freefrom oxide at the time of reaction. In both the galvanizing processes fluxing helps maintaining the surface of work free from oxides.
4
IS I 2629 • 1985
2.4 Over-Plcklbal - The undue attack of the underlying ferrous surfaceby the pickling solution after the removal of seal e.
2.5 r.hlbltor - A substance added to pickling solution to prevent undueattack on clea.n metal without affecting the scale removing property of thepickling solution.
2.6 White Ruat - A white corrosion product, mainly conta ining zincoxide and basic zinc carbonate, that accumulates on the galvanized surfaceexposed to water film or moist atmosphe, e.
2.7 Wettilll AleDt - A substance added to pickling and prefluxing101utions to facilitate wetting of the work surface.
3. BASE METAL FOR GALVANIZING
3.1 Steel - Mild steel is the most common material that is galvanizedand the variations in the range of compositions used have little influenceon the galvanizing process. The steel, however, should contain minimumamount of segregation, slag inclusions, rolled-in millscale, etc.
3.1.1 Carbon and silicon tend to increase the rate of reaction betweensteel and molten zinc. This effect, however, is not so apparent in the rangeof compositions encountered in mild steels as in high carbon and highsilicon steels.
3.2 Ca.t !rOD - Cast iron react with zinc differently depending on theexact composition, in particular, the silicon and phosphorus contents.
4. PREPARATIONGALVANIZING
OF THE METAL SURFACE FOR
4.1 Cleaalal - If an article is contaminated by oil, grease or paint,pretreatment in special solvents win be necessary for their removal. Several proprietary reagents are available. Generally a sodium hydroxide solution obtained by dissolving 10 to.1..5 kg of sodium hydroxide in 100 litresof water is used.
4.1.1 The work should be so handled in the degreasing bath as to allowfree circulation of liquid over all parts, taking care to clean the scum thatmay collect. If necessary, the work should be raised and lowered in orderto allow the degreasing solution to enter inaccessible areas, threaded sections, etc, for a thorcugh cleaning action. When using sodium hydroxideIOlution, the temperature of the solution may be usually kept between 85and 9000 and the immersion time varying from 1 to 20 minutes dependingon the nature and degree of contamination. When USIng other proprietarydegreasing agents; manufacturers' recommendation should be followed.
s
IS t 2629 • 1985
4.1.1.1 Immediately after degreasing, the work should be rinsed inhot water ( 6DoC ) followed, if possible, by a final rinse in cold runningwater. An Ideal arrangement for rinsing would be to provide an inlet andoutlet on two opposite sides of the rinsing tank; the inlet should be at thebottom of the tank and water should overflow from the top. This way therinse water is in a dynamic state thereby ensuring an efficient and athorough rinsing operation.
4.1.2 When lubricating materials have contaminated with the surfaceof the metal, it may be necessary to heat the part to bluing or scalingtemperature in order to burn off the offending material. Since this is anexpensive and difficult process, prior care should be taken to avoid suchcontamination.
4.2 Cleaning of Castings - Grey iron and malleable iron castings if notproperly cleaned before annealing, develop burnt-on and patches at thesurface which are not removed by normal pickling. Except in the case oflight castings which would be damaged, all castings should be shot or gritblasted prior to galvanizing. It is generally recommended to give a quickrinse in running water followed by cleaning with one of the pickling acids.I t is then processed according to normal fluxing practice
4.2.1 An alternative but less efficient method of cleaning castings withburnt-on sand is to employ a pickle solution containing hydrofluoric acid.For use, the commercial acid is diluted to various strengths, ranging fromone volume of acid and 59 volumes of water for a very weak pickle to onevolume of acid and 9 volumes of water for a very strong solution. With aweak solution pickling may take as long as 24 hours, while the stronli( solution should pickle satisfactorily in 10 to 30 minutes.
4.2.1.1 A hydrofluoric acid pickle leaves a gelatinous layer on thesurface of the castings which shall be thoroughly removed by hosing withwater and scrapping and brushing. The casting shall then go through theordinary pickling process.
4.2.1.2 Solution containing 6 parts by volume of commercial hydrofluoric acid , 4 parts by volume of technical grade hydrochloric acid ( III IS :265-1976. ) and 40 parts by volume of water may also by used for pickling.When pickling of castings is done occasionally, a solution consisting of 4parts of dilute hydrochloric acid ( I : I ) and 1 part of hydrofluoric acidmay be used.
4.3 Pickling - Both hydrochloric acid (St8 4.3.1 ) and sulphuric acid(see 4.3.2) solutions may be used for pickling. Hydrochloric acid is used atroom temperature while with sulphuric acid best results are obtained whenit is hot ( 60 to BO"C )•
• Specrhcarion for hydrochloric acid ( SICIJrld rftlision ).
6
IS 12629· 1985
4.3.1 Hydrochloric Acid Solution ( 100-150 gIL) - Dilute technical gHdcacid conforming to IS : 265-1976* with an equal volume of water. Theactual concentration of hydrochloric acid solutions and the time of immcrsion will depend on the nature of the work to be pickled,
4.3.1.1 A suitable inhibitor should be used with hydrochloric acid,
4.3.2 Sulphuric Acid Solution ( 100-150 gIL) - Dilute 6 to 8 ml of tcchnical grade acid conforming to IS : 266-1 <)77t to 100 ml. The actual concentration of sulphuric acid solutions, the temperature of till' hath .uul thrtime of immersion will depend on the nature of the work to be picl.lcd .
4.3.2.1 A suitable inhibitor should be used with sulphuric acid,
4.3.3 Agitation - Mild agitation of the work in the pir l.Iing tank reduces the time of pickling. Raise or lower the work once or twice to changethe acid layer in contact with the work. Air agitation is not recommended.
4.3.4 Control of the Acid Solution - To make the best use of the solution,reasonably close control of its acid content is necessary. The solutionshould be tested for acid and iron contents at regular intervals in accord.ance with the methods given in Appendix C. The strength of the solutionshould be maintained by periodic addition of fresh concentrated acid. Theiron salt. in the pickling bath gradually accumulate with continued work.in~ and when the iron content reaches to about 100 to 120 gil, thesolution should be discarded.
".3.5 Disposals of Waste Liquor - The acid and iron compounds may berecovered from the waste pickling solution. Where this is not done thepickling solution should be neutralized before dumping into sewers orstreams.
4.f Rinsing - After pickling, the article should be rinsed in runningwater. Two rinse tanks are preferable, the water cascading from one intothe other, that is cascading from the second tank into the first tank.
".5 Cleaning of Strip in the Continuous Galvanizing Process(ARMCO Sendizimir Process) - The cold-rolled strip is passedthrough an oxidizing furnace at temperature around 45()oC where rolhnglubricant is burnt and surface gets slightly oxidized. This is followed byreduction of surface oxides in the annealing/normalizing furnace undercontrolled atmosphere and subsequently allowing the strip to pass throughmolten zinc bath.
·Speclfication for hydroch loric acid ( second rlVlSlon ).tSpecification for sulphuric acid ( secondrtVlJlon ).
7
IS : 2629 - 1985
4.6 Fluxing
4.6.1 The 1 insed article, in the dry process, is dipped in a strong sohition of zinc ammonium chloride ( ZnCI•.3NH. CI), although ammoniumchloride is also used to a certain extent. The actual concentration of theflux solution and its temperature depend on the work being undertakenand on individual circumstances. The working level is generally between200 to 400 g of zinc ammonium chloride per litre. Some wetting agent isusually added to the flux solution. The temperature may range from roomtemperature to 80°C.
4.6.1.1 When dry galvanizing is adopted. the article shall be thoroughly dried after fluxing over a hot-plate or in an air-oven. The temperature should be about 120°C and should not exceed 150°C as the fluxdecomposes above this temperature.
4.6.1.2 In the wet process, a deep flux cover is used on the zincbath and the work is immersed through the flux layer with or withoutfluxing. In this case drying is not considered essential.
4.6.2 The article that has been prefluxed and dried should be galvanized without delay, as the flux coating picks up moisture from the air andalso tends to oxidize. The recommended time limit for galvanizing is within an hour of fluxing.
4.6.3 Control of Fluxing Solution - The specific gravity of the fluxsolution should be controlled by adding requi red quantities of flux crystalsand water to make up for the drag-out losses.
4.6.:to1 Free acid content of the solution should clso be checked,particularly if rinsing is not very thorough and pickle is CArried over. Themethod described in Appendix C may be used for determination of freeacid but the actual titration should be made on a 100 ml sample as theconcentration of acid in the solution will be very low. When more than2 g of free acid per litre of the solution is present, it should be neutralized by adding ammonia solution or addition of zinc spelter.
5. GALVANIZING
5.1 Quality of Zinc - Zinc containing at least 98'5 percent Zn shouldbe used for the purpose of galvanizing.
5.1.1 Galvanizing Bath - The molten metal in the galvanizing bathshould contain not less than 98'5 percent by mass of zinc.
8
IS I 2629 • 1985
5.2 AlaDdDiulD AdditioDs - Aluminium may be added to the galvanizing bath in the dry process to the extent 'of about 0'005 percent ( 0 OCJ'percent Max) ( 0'05-007 g/kg of zinc) to reduce the rate of oxidation ofthe molten metal and brighten the appearance of the article. In the continuous strip galvanizing process, addition of aluminium is made in the bathin the form of Zn-AI alloy to maintain aluminium between 0'12 to 0'20percent to control alloy layer thickness and thereby imparting betteradherence. Lead is also added in the form of Zn-Pb alloy to providespangle on the surface.
5.3 Bath Temperatare - The control of bath temperature IS essentialif the quality of the product is to be consistent and zinc is to be usedeconomically. Articles should be galvanized at the lowest possible temperature which will allow the free drainage of zinc from the work piece duringwithdrawal. A low temperature reduces the formation of ash and dross,besides safeguarding the pot and conserving fuel. The bath temperaturemay vary from 440°C to 460°C and a working temperature of 450"C iscommonly used. The temperature of the molten metal should not ordinarily exceed 475°C to prevent excessive attack of molten zinc on the work.as well as on the pot. In case of high silicon steels, a higher galvanizingbath temperature of 550°C is adopted in order to obtain normal coatingmass - the behaviour of silicon steels at 550°C is similar to that ofordinary steels at the normal galvanizing temperature at 450°C. However,for high temperature galvanizing, top heated ceramic bath are generallyused.
5.4 Suspended Dross - Dross should be allowed to settle at the bottomof the zinc bath, and should not be disturbed more than necessary duringthe dipping operation ( see 5.5 ). As far as practicable the article shouldnot be sunk to the bottom of the bath during galvanizing. After dressingoperations, by dipping the articles once again, some time should be allowed for the dross stiU remaining in the kettle to settle down.
5.5 Rate of IlDlDersiou - The work should be immersed as rapidly aspossible but with due regard.jo operator's safety. This is especially important in wet galvanizing, where the amount of dross increases with the timeof contact with the flux blanket. The speed of immersion also influencesthe uniformity of coating, particularly with long work piece where thedifference in immersion time between the first and the last part to enterthe bath may be considerable.
5.5.1 In case of continuous strip galvanizing the rate of immersion/withdrawal is dependent on the thickness of the strip and line speed governedby furnace design.
9
IS I 2629 • 1985
Top choss is removed at n'~ular interval from the surface of the bath.Coating rolls and grooves are <-I' aru d regularly.
5.5.2 Time of Immersion - The timr- of immersion for a job depends onseveral factors like its chemistry, ~i/,e. thickness, type of job, etc. In mostcases the article shall be left in tl)(' bath until it reaches the temperature ofthe bath which is usually indicated by the stopping of the boiling action.It is thr-n withdrawn without milch delay.
5.6 Withdrawal - The rate of withdrawal, which determines the thickness of the unalloyed zinc layer left on the article, var i-s according to thetype of the process being operated and the form of article, With long article for which withdrawal occupies a large part of the total handling time,speeds are necessarily maintained at higher levels to ensure a reasonablerate of production. It is better to use special jigs and carriers for dippingand withdrawing the work in batches. The rate of withdrawal should becontrolled so that zinc drains freely from the surface.
5.6.1 Articles are withdrawn through a bath of clear zinc to avoid contamination by flux. However, withdrawal through a flux blanket has alsoits advantages in the removal of surplus zinc from the surface and in producing a uniform coatmg at relatively highrr speeds. III the latter case itis recommended to quench the material ( see 5.7 ) to remove fluxresidues,
5.7 Water Quenching - Where the article is withdrawn through a fluxblanket, the quench water needs to be changed flcquently to prevent theaccumulation of corrosive salts. For this purpose tanks having overflowweir may be used with advantage.
5.7.1 Light gauge articles should be spun quickly through the surface ofwater so that they retain sufficient heat after quenching to enable quickdrying. Heavy articles retain sufficient heat for drying.
5.8 Centrifuging - Small articles handled in baskets should be centrifuged to remove excess of zinc immediately after galvanizing while the coating is still in the molten condition. The quality of the finish depends onthe rapidity with which the material is transferred from the galvanizingbath to the centrifuge. It is also important that the centrifuge should bepowered by a high starting torque electric motor to give rapid accelerationto peak speed within 2 to 3 seconds. After centrifuging, the articles shouldbe immediately tipped into water to allow the coating to set and preventthe articles from sticking to each other.
5.8.1 Thread Brushing - Threads on articles which are unsuited forcentrifuging shall be cleaned with a rotating wire brush immediately aftergalvanizing and before the coating sets. This process reduces the thicknessand the protective value of the coating. It should only be confined to thethreaded portions of the article.
10
IS I 2629 • )P8S
5.9 Post-Treatment - The zmc coating on freshly galvanized surface swhen r-xposed to humid, p iorly ventilated conditions during storage and/ortransport react with the moisture, c irbon dioxide, oxygen, etc, m theatmosphere formmg a mixture of salts which are white in colour. Tl1i, ISknown as , white rust' or ' wet storage stam ", Normally a post-treatmentlike chromatmg IS recommended ThIS IS a temporary treatment andretards white rust attack The chrornanng solution contains I percentsodium dichromate and hall percent sulphuric acid solution - the solutionI~ kept at room ternpe ra ture and ItS temperature' should never be allowedto rise above 6°)OC The g,lh -uuz ed articles are dipped mto the chromatmg solution after the galvaruzmg and \\ ater quenchmg operations.
5.9.1 In case of contrnuous str ip ga lvamz.mg the strrp is sprayed withchromatmg solution, such as chromic acid and properly spread uniformlyby means of squee7er rolls Temperature of the chromic acid bath is maintamed around 70-7')oC
5.10 Stacking -Artldr's should not be stacked Immediately after quenchmg (see 5.7) to avoid flakll1g of coatnig I he galvanl7ed articles should beallowed to dry before an; further handhnu operanon
6. TESTING AND INSPECTION
6.1 Freedom from Defects - The zmc cc aung shall be adherent,smooth, rr avonably bllgl-}t, r onunuous and free from such Imperfections asflux, ash and dl oss mclusrons, bare and bl.u k spots, pimples, lumpinessand runs. 11I~t ~t 111\5, bulk) white deposit s and blt\tl I S
6.2 Uniformity in Thickness - G ilvaruv ed articles shall be tested foruruforrmty 111 th rckncss of coatmg in 3( corrlance With preece test given inIS . 2h33-1 CJ86* For quick .ipproxrma«. measurements of thickness, magnetic gauges may be used, hut such mstrurncnts shall be SUItably calibratedbefore use.
6.3 Mass ofCoating - The mass of zrnc coating may be determined In
accordance WIth IS 6745-1972t.
6.4 Adhesion Tests
6.4.1 PIVoted Hammer Test for Zmc Coated Fabricated Products ( Fabricatedfrom Plates, Bars, StYlP, etc) - The adherence of the ZlI1C coat109 on steelshall be deterrnmed by the pivoted hammer test. The hammer used shallconform to the drawmg shown in FII~ 1. The hammer shall be made ofnormalized 0 3-0 4 percent carbon steel The hammer blow shall be controlled by holdmg the pivoted base of the handle on a hor izontal surface
-Method of restmg umforrrury on zmc coated artrcles ( ulond revISIon)tM~lhods for dcterrmnatron of mass of zmc coating on zmr coated Iron and steel
artrcle.
11
IS I 2629 • 1985
of the galvanized member and allowing the hammer head to swing freelythrough an arc from vertical position to strike the horizontal surface. Thetest shall consist of two 01" more standards blows forming parallel impressions with 6 nun spacing and a common axis, as illustrated in Fig. I. Nopart of an impressron shall be closer than 12 mrn to the edge of themember. Removal or hfting of the coating in the area between the impressions shall constitute failure. An extruded ridge less than 2 mm wideimmediately adjacent to the impression shall be disregarded. The specimen is tested in several places throughout its length.
6.4.2 Knife Test for Ziru; Coated Hardware and Assnnbl,d Steel Produ,ts When the coating is cut or pried into, such as with a stout knife appliedwith considerable pressure in a manner tending to remove a portion of thecoating, it shall only be possible to remove small particles of the coatingand it shall not be possible to peel any portion of the coating so as toexpose the underlying iron or steel.
6.4.3 Bifid and Wrapping Tests for Zrn, Coated Sheel and Wire - Thematerial such as sheet or wire shall be tested by bending or wrapping inaccordance with tests given in the relevant Indian Standards.
6.5 In case of continuous galvanized sheets, inspection and testing iscarried out in accordance with IS: 277·1977· or any other standardspecifications.
7. STORING, PACKING AND HANDLING
7.1 Sufficient care should be exercised while storing, packing and handlingof galvanized products. While storing and transporung them, adequateventilation should be provided as otherwise 'while rust' or 'wet storagestain' may result when galvanized coatings react with hwnidity and atmospheric gases. It is sometimes necessary to store galvanized articles withspacers in between them, they are also kept at an inclination to facilitatedrainge of water collected on the articles. In areas where there is a substantial variation in day and night temperatures and hence condensation,the storage area kept warm by provision of heaters. In many cases, it willbe advisable to give a post-treatment like chromating to minimise thechances for formation of white rust.
·Spec::dicatioDfor galvanized deel .beet. ( plaiD and corrugated) ( tlr"d "l1li'011).
12
)00
6mm SPACING SYMMETRICAL
~~"
~
e::pTE S' IMPRESSIONS
PIVOTt:O .BASE
HAIolMEA
EFFECTivE WEIGHT OF HAMMER210 TO 215g
~--.---.-------
JEST POSITION
All dimemloDi in millimetrea.
FIG. I PIVOTED RIVETING HAMIOR
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IS 12629.1985
APPENDIX B( Clause 0.5 )
WORKING CONDITIONS AND SAFETl' MEASURES
B-1. WORKING CONDITIONS
B-I.I The galvanizing shop should be' kept neat and tidy. Where possible,increased use should be made of hoods, extraction ducts and exhaust fansto give as good an atmosphere as possible.
B-2. SAFETY MEASURES
B-2.1 All safety measures should be properly exhibited.
8-2.2 The workers at the galvanizing bath should be provided with:
a) eye or face shield,
b) rubber boots,
c) steel-capped boots,
d) leather or leather on woollen base gloves,
e) rubber and leather aprons, and
f) long rubber or PVC or neoprene gloves.
B-2.3 While cleaning the articles with sodium hydroxide solution, theoperators should be warned that it produces severe flash burns. Specialprecautions should be taken to protect them from splashes of sodium hydroxide solution.
B-2.4 Hydrofluoric acid sometimes used for pickling of castings (see 4.2 )is dangerous and causes very sever burns and sores when it comes in contact with the skin. It should, therefore, be carefully handled by wearingrubber boots, gloves and aprons.
8-2.5 Arrangement should be made to protect the galvanizer from thefumes over the zinc bath.
J9
IS I 2629 • 1985
APPENDIX C( Clauses 4.3.4 and 4.6.3.1 )
TEST METHODS
c.r, QUALITY OF REAGENTS
0.1.1 Unless otherwise specified, pure chemicals shall be employed in testsand distilled water (see IS : 1070.1977-) shall be used when the use ofwater as a reagent is intended.
NOTE - • Pure chemicals' shall mean chemicals that do not contain impuritietwhich affect the results of analysis.
C-2. DETERMINATION OF ACID CONTENT OF THE PICKLINGSOLUTION
0.2.1 Reagents
0.2.1.1 Standard Sodium Carbonate Solution - Approximately 0'5 N.
0.2.1.2 Methyl Orange Indicator Solution - Dissolve 0'05 g of methylorange in 100 ml of alcohol.
C-2.2 Procedure - Filter exactly 25 ml sample of the pickle liquor into250·ml measuring cylinder and make up to 250 ml by adding distilledwater mix thoroughly. Pipette out 25 ml of this solution in a 250 ml conicalflask. Add a few drops of methyl orange indicator and titrate it with thestandard sodium carbonate solution to yellow end point.
C·2.3 Calculation
Mass of hydrochloric acid in gil
Mass of sulphuric acid in gil ....
A X B X 36'52'5~ - -
A X B X 492'5
where
A = volume in ml of the standard sodium carbonate solutionrequired, and
B = normality of the standard sodium carbonate solution.
·Specification for water for general laboratory use ( Sleo"d rms;Dr/ ).
20
IS r 2629 • 1M5
C.:J. DETERMINATION OF IRON CONTENT OF THE PICKUNGSOLUTION
0-3.1 Measure density of the pickling solution with a hydrometer, then onthe corresponding nomograph ( SII Fig. 2 and 3 ) depending on the acidused for pickling, join with a transparent ruler the point representing thisreading shown on the left hand line with the point on the right hand linerepresenting the acid content ofthe pickle. Read off the iron content onthe middle line.
SUL PHUHI(IRON COliTENT ACID CONTHl1
gIl gIl1 a110
2S100
90 SO80
7')70
60 100
SO125
40
30 150
20
100
sp - gr
"30
"lW
~60:;-::r-1.=i'n~-----;-;'ll:n----_--":~
loS
S5
30 ·'·IS
35
40 1·20
OENSll v
50 1·25
25
20 144\40- G Bc
\S
\0 \·OS
5
o ,,00
FlO. 2 NOMOGRAPH RltLATINO THE IRON CONTENT OF SULPHURICActo PICkLE TO THE ACID CONTENT AND DENSITY
21
IS I 2629 • 1985
DE NSIT y
°T W sp - gr
3') -
30
2'i
IRON CONTENTgil
150
- 100
- 50
o
HYDROCHLORICACID CONTENT
9f.f.a
50
100
150
200
250
10 1·05300
o 1·00
FlO. 3 NO\fOORAPH RELATINO THE IRON CONTENT OF HYDROCHLORIO
ACID PICKLE TO THE ACID CONTENT AND DENSITY
22
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