ZINC COATINGS - American Galvanizers Association
ZINC COATINGSA Comparative Analysis of Process andPerformance Characteristics
ContentsINTRODUCTION1BATCH HOT-DIP GALVANIZING2CONTINUOUS SHEET GALVANIZING4ZINC PAINTING6ZINC SPRAY METALLIZING7MECHANICAL PLATING8ELECTROGALVANIZING9ZINC PLATING10SELECTION OF ZINC COATINGS10CONCLUSION11ZINC COATINGS COMPARISON12ACKNOWLEDGEMENTS13Zn3065.4 2011 American Galvanizers Association. The material provided herein has beendeveloped to provide accurate and authoritative information about after-fabricationhot-dip galvanized steel. This material provides general information only and is notintended as a substitute for competent professional examination and verificationas to suitability and applicability. The information provided herein is not intendedas a representation or warranty on the part of the AGA. Anyone making use of thisinformation assumes all liability arising from such use.ZincAmerican Galvanizers Association
INTRODUCTIONZinc, a natural, healthy, and abundant element was firstused in construction in 79 AD; thus, its characteristicsas a well-suited corrosion protective coating for ironand steel products has long been known. The 27th mostabundant element in the Earth’s crust, zinc is naturallypresent in rocks, soil, air, water, and the biosphere, aswell as in plants, animals, and humans. In fact, zinc isessential to life as all organisms require it to survive andcomplete normal physiological functions.Today, more than 13 million tons of zinc are producedannually worldwide, 70% from mined ores, and 30%from recycled sources. More than half of the annualproduction is used in zinc coatings to protect steelfrom corrosion. Because zinc is an infinitely recyclablematerial, the level of recycling increases each year, andcurrently 80% of the zinc available for recycling is indeedreclaimed. However, because of zinc’s excellent fieldperformance as a corrosion protection coating, it oftenremains in service for generations before recycling.Zinc, like all metals, corrodes when exposed to theatmosphere. However, because of its ability to formdense, adherent corrosion byproducts, the rate ofcorrosion is considerably lower than ferrous materials(10 to 100 times slower depending on the environment).Zinc corrosion products develop naturally on the surfaceas the coating is exposed to natural wet and dry cyclesin the atmosphere and are often referred to as the zincpatina. The zinc patina acts as an additional barrierbetween the steel and the environment.In addition to the natural barrier protection of the coatingand patina, zinc also protects the base steel cathodically.The Galvanic Series of Metals (Figure 1) lists metals inorder of their electrochemical potential in the presenceof salt water. When two metals are connected, thosehigher on the list will become anodic and preferentiallycorrode to protect metals lower in the series. Therefore,zinc is anodic to steel and will sacrificially corrode toprotect the underlying steel from corrosion.There are a number of zinc coatings which are oftengenerically termed “galvanizing,” but each has uniquecharacteristics. These characteristics not only affectapplicability, but also economics and performance inthe environment. The method of application, adhesionto the base metal, hardness, corrosion resistance, andthickness (Figure 2) of each zinc coating varies.This practical aid examines the following zinc coatings:batch hot-dip galvanizing, continuous sheet galvanizing,zinc painting, zinc spray metallizing, mechanical plating,electrogalvanizing, and zinc plating; to help architects,engineers, and other specifiers assess and select the mostsuitable zinc coating for corrosion protection.Arrangement of Metals in Galvanic SeriesCORRODED END: Anodic or less noble(ELECTRONEGATIVE)Cathodic protection canMagnesiumoccur when two metalsZincare electrically connected.AluminumAny one of these metalsSteeland alloys will theoreticallyLeadcorrode while offeringTinprotection to any otherNickelwhich is lower in theBrassseries, so long as bothBronzesare electrically connected.CopperStainless Steel (passive) However, in actual practice,Silverzinc is by far the mostGoldeffective in this respect.PlatinumPROTECTED END: Cathodic or More Noble(ELECTROPOSITIVE)Figure 1: Cathodic Protection from Zinc1 milMetallizedHot-Dip GalvanizedFigure 2: Microstructures of Various Zinc CoatingsZinc PaintGalvanized SheetElectroplated1
BATCH HOT-DIP GALVANIZINGZinc Application ProcessBatch hot-dip galvanizing, also known as generalgalvanizing, produces a zinc coating by completelyimmersing the steel product in a bath (kettle) of moltenzinc (Figure 3). Prior to immersion in the zinc bath, thesteel is chemically cleaned to remove all oils, greases,soil, mill scale, and oxides. The surface preparationconsists of three steps: degreasing to remove organiccontaminants, acid pickling to remove scale and rust,and fluxing, which inhibits oxidation of the steel beforedipping in the molten zinc. Surface preparation is criticalas the zinc will not react with unclean steel.After surface preparation, the steel is immersed in themolten (830 F) zinc bath. The bath consists of more than98% pure zinc and less than 2% additives, most commonlyaluminum, nickel, and bismuth, which help with zincfluidity and consumption, coating appearance, etc. Whilein the galvanizing kettle, the molten zinc metallurgicallyreacts with the iron in the steel to form the coating. Afterremoval from the zinc bath, the coating is inspected forconformance to ASTM, CSA, or ISO specifications.Galvanizing lutionDryingZincbathCooling andinspectionFigure 3: Batch hot-dip galvanizing processesCoating Characteristics and PerformanceThe batch hot-dip galvanized coating consists of a seriesof zinc-iron alloy layers with a surface layer of pure zinc(Figure 4). The unique intermetallic layers are tightlybonded (3,600 psi) to and harder than the base steel,offering excellent abrasion resistance. The zinc-iron alloylayers are metallurgically bonded to the steel; and thus,become an integral part of the steel rather than just asurface coating. Furthermore, as mentioned previously,zinc is anodic to steel; therefore, even if the durableintermetallic layers of the hot-dip galvanized coatingare damaged (up to ¼” in diameter) adjacent zinc willsacrificially protect the exposed steel until all of thesurrounding zinc is consumed.Another unique characteristic of the batch hot-dipgalvanized coating is its uniform, complete coverage.During the diffusion reaction in the kettle, the zinc-ironalloy layers grow perpendicular to all surfaces, ensuringedges, corners, and threads have coating equal to orgreater than flat surfaces. Additionally, because hot-dipgalvanizing is a total immersion process, all interior 2Figure 4: Photomicrograph of a Galvanized Coatingsurfaces of hollow structures and difficult to accessrecesses of complex pieces are coated. This complete,uniform coverage means critical points where corrosioncommonly occurs are afforded the same protection asaccessible flat, exterior surfaces.Batch hot-dip galvanizing produces a coating thickerand/or denser than other zinc coating processes. Thegoverning specifications for hot-dip galvanizing; ASTMA123, A153, and A767 as well as CSA specification G 164,and ISO 1461 contain minimum coating thicknessAmerican Galvanizers Association
Time to first maintenance* (years)1009080Key70Rural60SuburbanTemperate Marine50Tropical Marine40Industrial30201001. 01.52.02.53.03.54.0Average Thickness of Zinc (mils)4.55.01 mil 25.4μm 0.56oz/ft2*Time to first maintenance is defined as the time to 5% rusting of the steel surface.Figure 5: Time to First Maintenance Chartrequirements based on steel type and thickness. TheTime to First Maintenance Chart (Figure 5) shows thelinear relationship between zinc coating thickness andmaintenance-free service life. For example, accordingto ASTM A123, structural steel greater than or equalto ¼ inch thick has a minimum coating requirement of3.9 mils, which equates to a maintenance-free life ofaround 72 years in an industrial environment.Applications/Exposure ConditionsHot-dip galvanized coatings are used on a multitude ofmaterials in myriad construction sectors from electricutility to artistic sculptures. Ranging in size from smallparts such as nuts, bolts, and nails to very large structuralshapes, galvanizing is integral to the North Americaninfrastructure. Most commonly batch hot-dip galvanizingis used in atmospherically exposed steel; however, it isalso used in fresh and salt water applications, buried inthe soil, embedded in concrete, and much more. Formore information on the performance of batch hot-dipgalvanizing in various environments, see the AmericanGalvanizers Association’s publication, Performance ofHot-Dip Galvanized Steel Products.BATCH HOT-DIPGALVANIZING SUMMARY Factory controlled Available 24/7/365 Complete coverage Superior bond to steel Coating is harder than the steel Good for exterior and interior useSize can be one limitation to the application of batch hotdip galvanizing; however, the average length of zinc bathsin North America is 40 feet and 55-60 foot kettles arecommon. Utilizing progressive dipping (immersing oneportion of the product and then the other) significantlyincreases the maximum size that can be accommodatedto nearly double the bath size.3
CONTINUOUS SHEET GALVANIZINGZinc Application ProcessContinuous sheet galvanizing is also a hot-dip process,but is only applied to steel sheet, strip, and wire. A coilto coil process, steel sheet from 0.010 to 1.70 inches(0.25 mm to 4.30 mm) thick and up to 72 inches (1,830 mm)wide is passed as a continuous ribbon through cleaningbaths and molten zinc at speeds up to 600 feet per minute.Preparing the steel for the continuous hot-dip coatingbegins with cleaning in an alkaline liquid combined withbrushing, rinsing, and drying. Then, the steel passes intothe heating or annealing furnace to soften it and impartthe desired strength and formability. In this annealingfurnace, the steel is maintained under a reducing gasatmosphere, composed of hydrogen and nitrogen, toremove any oxide that may be on the surface. Just as inthe batch process, the steel must be completely clean ofoxides and contaminants for a successful coating.As the steel exits the furnace, it enters into a vacuumchamber, or snout, before entering the molten zinc bath toprevent any air from reoxidizing the heated steel product.The steel is then sent around a submerged roll in themolten bath to create the bonded coating and removedin a vertical direction. As the product is withdrawn fromthe bath, precisely regulated, high-pressure air (air knife)is used to remove any excess zinc to create a closelycontrolled coating thickness. The steel is then allowed tocool and solidify before contacting another roll to avoidtransferring or damaging the coating.Today, this continuous hot-dip process is used tomake seven different types of sheet products includinggalvanized (zinc), galvannealed (90-92% zinc/8-10%iron alloy), two alloys of zinc and aluminum (55%aluminum/45% zinc alloy and 95% zinc/5% aluminumalloy), two aluminum based alloys (100% aluminum,89-95% aluminum/5-11% silicon alloy), and the ternecoating (85-97% lead/3-15% tin alloy).Continuous Sheet GalvanizingCoating GradeTotal Both SidesPer 0.2706.92G01no minimumContinuous Sheet Galvanizing: The number following the ‘G’ coating grade designation correlates to the total thickness ofzinc applied to both sides of the steel sheet.Table 1: Continuous Sheet Galvanizing Thicknesses 4American Galvanizers Association
Coating Characteristics & PerformanceBecause both are hot-dip processes, continuous sheetand batch hot-dip galvanizing are often confused. Onemajor difference in the two coatings is the thickness. Thecontinuous sheet galvanizing process has greater controland preciseness when it comes to zinc thickness as the airknife used after galvanizing ensures a uniform thicknessacross the steel sheet. The coating is mostly unalloyedzinc, though minimal alloy layers are present, and isductile and able to withstand deep drawing or bendingwithout damage. This is important as the coating isapplied prior to final fabrication such as punching,bending, and cutting.Because of the precise control of coating thickness,continuous sheet is stocked in a variety of coating weights.One of the most common zinc coatings is Class G90,which has 0.9 oz/ft2 of zinc (total both sides) or about0.80 mils (20 µm) per side. Table 1 (page 4) shows theavailable coating grades of continuous sheet galvanizing.As mentioned before, service life for all zinc coatingsis linear to zinc thickness (Figure 5, page 3). Becausethe continuous sheet coating is applied pre-fabrication,final forming and placement often includes punchingholes, bending, cutting, etc., which creates uncoatedareas. Like batch hot-dip galvanizing, the surroundingzinc of continuous sheet coatings will provide cathodicprotection to these uncoated areas; however, as there ismuch less zinc present, best practice is to touch up anyexposed areas after fabrication to extend service life.Applications/Exposure ConditionsAs the name states, the continuous galvanizing processis only applied to sheet steels. The most commonapplications are in car bodies, appliances, corrugatedroofing and siding, duct work, and culvert pipe. Thesmooth coating does allow it to be treated for painting,which will increase service life. Because of the relativelythin coating, unpainted continuous sheet galvanizingis recommended for interior applications or whereexposure to corrosive elements is mild.CONTINUOUS SHEETGALVANIZING SUMMARY Factory controlled Precise and consistent coating thickness Interior applications only(unless painted over) Available in annealed conditionfor formability Mostly pure zinc coating – softer than steel5
ZINC PAINTINGZinc Application ProcessZinc painting, often erroneously termed cold galvanizing,is the application by brush or spray of zinc dust mixedwith organic or inorganic binders. Prior to application,the steel must be cleaned by sand blasting to nearwhite metal (SSPC–SP 10), commercial blast cleaning(SSPC-SP 6) or white metal (SSPC-SP 5). The zinc dustmust be mixed with a polymeric-containing vehicleand constantly agitated during application to producea homogenous mixture and proper adhesion. Zinc-richpaints typically contain 92-95% metallic zinc in dry film.When spray applying, feed lines should be kept as shortas possible to prevent settling of zinc dust and unevenfilm coats. Zinc painting can be applied in either theshop or the field.Coating Characteristics and PerformanceLike all paint coatings, zinc-rich paint is a surfacecoating, mechanically bonded to the steel at a fewhundred pounds per square inch (psi). Zinc-rich paintsare either organic, consisting of epoxies, chlorinatedhydrocarbons, and other polymers, or inorganic basedon organic alkyl silicates. The organic or inorganic paintsare applied to a dry film thickness of 2.5 to 3.5 mils. Ifapplied too thick, cracking may occur.is another reason constant agitation and homogenousmixture is important during application. There is somequestion as to whether cathodic protection is possible atall if the zinc particles are encapsulated in the binder andthe binder is non-conductive.Inorganic and organic zinc-rich paints vary somewhatin their performance. Inorganic zinc-rich paints, whichadhere to the steel with mild chemical reactivity, havegood solvent resistance and can withstand temperatureup to about 700 F (375 C). Inorganic zinc-rich paints donot chalk, peel, or blister readily, are easy to weld andprovide simpler cleanup than organics. The density ofinorganic zinc-rich paints are about half the density ofzinc per mil of batch hot-dip galvanized coatings.The properties of organic zinc-rich paints depend onthe solvent system. Multiple coats may be applied within24 hours without cracking. Organic zinc-rich paints donot have the same temperature resistance of inorganiczincs, as they are limited to 200-300 F. They are alsosubject to ultraviolet (sunlight) degradation, and are notas effective as inorganics in corrosion protection.ApplicationsZinc-rich paint can be applied to steel of any size andshape, though application is difficult on more complexfabrications. Zinc-rich paints are widely used as primersto high-performance two and three coat systems andfor touch-up and repair of batch hot-dip galvanizedcoatings. In mild environments, inorganic zinc paintmay be used independently for corrosion protection, butshould be top coated in more severe environments toextend service life.ZINC PAINTING SUMMARYOne commonality of all zinc coatings examined thusfar is the cathodic protection afforded. Zinc-rich paintcoatings are different than the other coatings as thereis a binding material used to adhere the zinc particles.For cathodic protection to be possible, the zinc dustmust be at a concentration high enough to provide forconductivity between the zinc particles and the steel. This 6 In-shop or field application Weak bond to steel Thinner coating on corners and edges Coating thickness consistency depends onskill of application Durability depends on zinc content in dryfilm conditionAmerican Galvanizers Association
ZINC SPRAY METALLIZINGZinc Application ProcessZinc spraying, or metallizing, is accomplished by feedingzinc powder or wire into a heated gun, where it ismelted and sprayed onto the part usingcombustion gases and/or auxiliarycompressed air to provide the necessaryvelocity (Figure 6). Prior to metallizing,the steel must be abrasively cleaned.The 100% zinc coating can be appliedin the shop or field, but is morecommonly done in the shop where heatfor melting is more readily available.The heat is supplied by combustion ofan oxygen-fuel gas flame or by electricarc. Processes have been developed forfeeding molten zinc directly into thespray nozzle, but only for in shop applications. Followingthe zinc application, the coating is normally sealed witha low viscosity polyurethane, epoxy-phenolic, epoxy, orvinyl resin.Applications/Exposure ConditionsZinc spray metallizing can be applied to materialsof any size, though complexity of the structure isimportant. Metallizing is commonlyused as an alternative to batch hot-dipgalvanizing when the part is too largefor immersion in the galvanizing kettle.And though more often and easilyapplied in the shop, metallizing in thefield is a great option for extending thelife of already erected batch galvanizedstructures. The biggest limitations tometallizing applications are availability(skilled operator and equipment) and asignificant cost premium.Coating Characteristics and PerformanceThe metallized zinc coating is rough and slightly porous,with density about 80% that of batch hot-dip galvanizing.As the metallized coating is exposed to the atmosphere,zinc corrosion products tend to fill the pores providingconsistent cathodic protection. Metallizing covers welds,seams, ends, and rivets well and can be applied in excessof 10 mils (254 µm). However, the mechanically-bondedpure zinc coating can be inconsistent and requires askilled operator for best application. Coatings tend to bethinner on corners and edges, and no coating is applied tointerior surfaces or difficult to access recesses and cavities.ZINC SPRAY METALLIZINGSUMMARY Factory controlled Quality varies by skill of labor Inconsistent coverage and coating thickness Weak mechanical bond of zinc to steel Interior or exterior use Labor intensiveElectric ArcPower SupplyZinc Wire FeederZinc Wire InsideInsulated Flexible ConduitorSpray GunOXY.FUELHeatSourceCompressed Air SourceControlCircuitCableFigure 6: Zinc Spray Metallizing7
MECHANICAL PLATINGZinc Application ProcessMechanical zinc plating is accomplished by tumblingsmall parts in a drum with zinc and proprietarychemicals. Small iron and steel parts – usually limited insize to about 8-9 inches (200-300 mm) and weighing lessthan one pound (0.5 kg) – are cleaned and flash coppercoated before loading into a plating barrel. The barrel isthen loaded with proprietary chemicals, glass beads andzinc powder and tumbled (Figure 7). During tumbling,the glass beads peen zinc powder onto the part. Oncefinished, the parts are dried and packaged, or posttreated with a passivation film, dried, and LPOWDERBecause of the application process (tumbling andpeening), the coating thickness can vary throughout thepart. Complex designs with recesses or blind holes aswell as edges, corners and threads can have inconsistentor non-existent coatings due to inaccessibility to thepeening action of the glass beads. It is also importantthe compaction agents (beads) are large enough to avoidbeing lodged in any cavities, recesses, or small threads inthe part. The coating is mechanically-bonded to the steelwith a similar adhesion to zinc plating.Applications/Exposure ConditionsAs mentioned, mechanical plating can only be appliedto small parts limited to the capacity of the drum.Furthermore, the materials must be simple in design toensure peening to all surfaces. Mechanical zinc platingis most commonly used on high-strength fasteners andother small parts not suitable for hot-dip galvanizing.WATERCLEANED ANDCOPPERED PARTSFigure 7: Mechanical PlatingCoating Characteristics & PerformanceMechanical plating consists of a flash coating ofcopper followed by the zinc coating. Coating thicknessrequirements specified in ASTM B695 range from0.2 to 4.3 mils (5 to 110 µm). While thicker coatingsare possible, the common thickness on commercialfasteners is 2 mils (50 µm). Coating thickness isregulated by the amount of zinc charged to theplating barrel and the duration of tumbling time.The coating has a density of about 70% comparedto a batch hot-dip galvanized coating density. Thehot-dip coating has over 30% more zinc per unitvolume than a mechanical coating. 8MECHANICAL PLATINGSUMMARY Factory controlled Small parts only Poor/no coverage in recesses Variable thickness of coating dependingon tumbling time Inconsistent coating thickness Thinner coating on edges and cornersAmerican Galvanizers Association
ELECTROGALVANIZINGZinc Application ProcessElectrogalvanized (electroplated) coatings are createdby applying zinc to steel sheet and strip by electrodeposition. Similar to sheet galvanizing, the operation iscontinuous and coating thickness is minimal. Applied ina steel mill, sheet or strip is fed through entry equipmentinto a series of washes and rinses then into the zincplating bath.The most common zinc electrolyte-anode arrangementuses lead-silver, or other insoluble anodes and electrolytesof zinc sulfates. Soluble anodes of pure zinc are also used.The coating develops as positively charged zinc ions inthe solution are electrically reduced to zinc metal anddeposited on the positively charged cathode (sheet steel).Grain refiners may be added to help produce a smooth,tight-knit zinc coating on the steel.Coating Characteristics and PerformanceThis electro-deposited zinc coating consists of purezinc tightly adherent to the steel. The coating is highlyductile remaining intact even after severe deformation.Produced on strip and sheet materials, the coatingweight ranges up to 0.2 oz/ft2 (60 g/m2), or thicknessesup to 0.36 mils (9.1 µm) per side, while on wire, coatingweights may reach up to 3 oz/ft2 (915 g/m2). The coatingof pure zinc is thinner than continuous sheet galvanizing,mechanically-bonded, and there are no alloy layers, butprovides a smoother finish. Heat-treated and electrocoated wire can be cold drawn to about 95% reductionin area, depending on the chemical composition of thewire, heat treatment, and diameter.Applications/Exposure ConditionsElectrogalvanized coatings are applied to sheet steelsand wire, and therefore are used in similar applicationsto continuous sheet galvanizing or wire galvanizing.The most common applications are in automobile andappliance bodies and fasteners. Furthermore, to extendthe service life, electrogalvanized coatings can be treatedto make them suitable for painting, and this is oftenrecommended due to the extremely thin zinc coating.ELECTROGALVANIZINGSUMMARY Factory controlled Very thin/consistent coating Interior use only Ductile coating of pure zinc Exposed/bare steel edges when slit orcut-to-length9
ZINC PLATINGZinc Application ProcessZinc plating is identical to electrogalvanizing in principlebecause both are electro-deposition processes. However,zinc plating is used on small parts such as fasteners,crank handles, springs and other hardware items ratherthan sheet metal. The zinc is applied as an expendableelectrode in a cyanide, alkaline non-cyanide, or acidchloride salt solution. Cyanide baths are the mostoperationally efficient but can potentially create pollutionand are hazardous.After alkaline or electrolytic cleaning, pickling to removesurface oxides, and rinsing, the parts are loaded intoa barrel, rack, or drum and immersed in the platingsolution. Various brightening agents may be added tothe solution to add luster, but careful control is needed toensure a quality product. Post-plating treatments may beused to passivate the zinc surface as well as impart varioustranslucent colors or to extend the life of the coating.Coating Characteristics & PerformanceTypical zinc-plated coatings are dull gray with a mattefinish, although whiter, more lustrous coatings can beproduced, depending on the process or agents added tothe plating bath or through post-treatments. The purezinc coating is thin, up to a maximum thickness of 1 mil(25 µm), and mechanically bonded to the surface with ahardness of about a third to a half that of most steels. Thegoverning specification, ASTM B633, lists four classesof zinc-plating: Fe/Zn 5, Fe/Zn 8, Fe/Zn 12 and Fe/Zn25 where the number indicates the coating thickness inmicrons (µm).Applications/Exposure ConditionsZinc plating is typically used for screws and other smallfasteners, light switch plates, and various small partsthat will be exposed in interior or mildly corrosiveconditions. For use in moderate or severe environments,the materials must be chromate-conversion coated foradditional corrosion protection.ZINC PLATING SUMMARY Factory controlled Small parts only Interior use only Very thin coatingSELECTION OF ZINC COATINGSOnce the decision has been made to use a zinc coatingfor corrosion protection, a few additional factors must beconsidered to ensure the proper coating is selected for theapplication and service environment. Each zinc coatingreviewed provides varying degrees of corrosion protectionand it is important to identify the corrosiveness of theexposure environment to ensure the coating selected willprovide adequate service life. Some zinc coatings will beeliminated by their nature alone, e.g. zinc coatings whoseprocesses are limited to small parts or sheet steels cannotbe considered for the protective coating of structural steelmembers; while others may be ruled out based on cost,appearance, availability, performance, etc. The followinginformation examines a few factors in more detail, while 10Table 3 (page 12) provides a snapshot of each of the zinccoatings based on several criteria.Coating Thickness vs. Coating WeightAs has been stated several times throughout this guide,the service life of zinc coatings is linear to zinc coatingthickness. However, zinc coating thickness evaluatedalone can be deceiving when the zinc has been appliedby different processes. In addition to thickness, theamount of available zinc per unit volume, or density, isalso important. Keeping in mind various ASTM and/or other specifications require different weights orthicknesses, it is important to convert all coatings to acommon denominator for comparison.American Galvanizers Association
While coating densities for some types of zinc coatingsare nearly identical, others differ considerably. Onelogical common denominator for comparing zinccoatings would be to convert all coatings into an equalweight per unit area of zinc; which in theory wouldprovide equal service lives. Table 2 represents the coatingthickness required by each zinc application method toequal 1 oz of zinc/ft2 of surface. Therefore, accordingto the conversions, 1.7 mils of hot-dip galvanizedcoating would give the same service life as 2.2 mils ofmechanical plating or 3 to 6 mils (depending on thepaint formulation) of zinc-rich paint.Hot-dip galvanizing(batch or continuous)electrogalvanizing,zinc plating1.7 mils (43 μm)Zinc spraying (metallizing)1.9 mils (48 μm)Mechanical plating2.2 mils (55 μm)Zinc-rich paint3-6 mils (75-150 μm)Table 2: Coating DensitiesIt is also important to remember for all continuousgalvanized sheet materials, including electrogalvanized,the coating weight is given for the total zinc weight for bothsides of the sheet. To obtain the amount of zinc per unitarea of surface, the weight given must be divided in two,assuming equal distribution on both sides. For example,an ASTM A653 Class G90 sheet contains 0.90 oz zinc/ft2 ofzinc or about 0.45 oz/ft2 per side (see Table 1, page 4).Economic ConsiderationsInitial cost will always be considered when specifyingsteel corrosion protection. However, in addition tothe initial cost, evaluating the performance of the zinccoating in the intended environment also impacts theeconomics of the protective system. Hidden costs,such as accessibility of the site, production loss due tomaintenance recoating, and rising wages for laborintensive coatings, such as metal spraying and paintingmust also be considered.The choic
galvanized coating is its uniform, complete coverage. During the diffusion reaction in the kettle, the zinc-iron alloy layers grow perpendicular to all surfaces, ensuring edges, corners, and threads have coating equal to or greater than flat surfaces. Additionally, because hot-d
0.4 0.6 0.8 1 1.2 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Cumulative Zinc Exposure, ppb-months Cumulative Dose Rate Reduction Fraction Alloy 800 w/Depleted Zinc Alloy 600 & 690 w/Depleted Zinc Alloy 600 & 690 w/Natural Zinc Log Alloy 800 Plants w/Depleted Zinc Log Alloy 600 & 690 w/Depleted Zinc Log Alloy 600 & 690 w/Natural Zinc
Iron, zinc plating 2 E3C-S50 (8) E39-L40 Iron, zinc plating 1 Phillips screws M4 25 (with spring and plain washers) Iron, zinc plating 2 E3JK Nuts M4 Iron, zinc plating 2 E39-L41 Iron, zinc plating 2 Phillips screws M3 14 (with spring washers) Iron, zinc plating 4 6 E3C-1 (10) Plain washer M3 Iron, zinc plating 4 E39-L42 Iron, black coating 2
1. AASHTO M111, Zinc (Hot Dip Galvanized) Coatings on Iron and Steel Products 2. AASHTO M232, Zinc Coating (Hot Dip) on Iron and Steel Hardware c. American Galvanizers Association (AGA) 1. The Inspection of Products Hot Dip Galvanized After Fabrication 2. Powder Coating over Hot Dip Galvanized Steel, Powder Coating Journal, Feb 2004,
Chapter 6 Zinc, folate and other B vitamins, vitamin C, vitamin D, calcium, selenium and fluoride 124 6.1 Zinc 124 6.1.1 Choice of zinc fortificant 124 6.1.2 The bioavailability of zinc 124 6.1.3 Methods used to increase zinc absorption from fortificants 125 6.1.4 Experience with zinc fortification of specific foods 125
of zinc in various poultry diets ranges from 40 to 75 ppm [17]. Zinc oxide is the most commonly used zinc . supplement with high antibacterial activity, antifun-gal, and growth promoter ability [18]. Zinc oxide generates hydrogen peroxide which can pass through the cell wall, disrupt metabolic process, and, in turn, inhibit the microbial growth.
1.1 This test method covers procedures for determining the weight [mass] of coating on iron or steel sheet, wire, and other articles in which the coating is zinc or a zinc alloy, such as zinc-5 % aluminum (including zinc-5 % aluminum-mischmetal and zinc-5 % aluminum-0.1 % magnesium) or 55 % aluminum-zinc. In the body of this test method, reference
Production of zinc tablets and zinc oral solutions: guidelines for programme managers and pharmaceutical manufacturers. Produced by the World Health Organization [et al.]. 1.Zinc - standards. 2.Zinc - therapeutic use. 3.Diarrhea - drug therapy. 4.Child. 5.Guidelines. I.World Health Organization. ISBN 92 4 159494 2 (NLM classification: WS 312)
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