Galvanizing Process

TheManufacturing Process of Galvanizing Material by Dwayne A. Rodgers 11/26/02

http://www.galvanizeit.org/process.htm

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Introduction The Galvanizing Process. Typical Steps in the manufacturing process of Galvanizing. The typical characteristics of appearance. Comparative Properties of various Zinc Metal Coating. Corrosion Galvanized Products Summary Definitions Dealing with Galvanizing. Internet References/Bibliography

Introduction: In today's society there are many everyday uses for galvanized products, galvanizing is a process for applying a protective zinc coating over iron or steel to reduce corrosion (McNichols, 2002), where a long life expectancy is important. To view a chart published for Hot Dip Galvanized Coating Service Life click here. Corrosion is a physical and chemical deterioration of a material due to reaction with its environment and especially with oxygen (CRM, 1976). Galvanized products are used everywhere in many different applications where corrosion resistant products are essential. Corrosion resistance can be defined as the ability of the material to resist oxidation (EMT-p177). This report will show how and why galvanizing is important to the life duration of a product that is subject to deterioration caused by the surrounding environment. The Galvanizing Process The process of galvanizing consists of coating metals, such as iron and steel, with a thin protective layer of zinc. The layer of zinc provides protection to the metal from corrosion. The result of galvanizing is a corrosion resistant product to be used for many outdoor applications, where the weather is a factor in the life expectancy of the material. The protective layer of zinc prevents the ferrous material from coming in contact with the oxygen causing oxidation. Oxidation is the combination of a substance with oxygen, in iron and steel the main combination result is rust. Without this contact the ferrous material does not corrode. An example of how this works is when iron reacts with oxygen it forms iron oxide (the main component in corrosion), however if the iron is galvanized the zinc reacts with oxygen causing zinc oxide prior to reaching the iron. There are two types of oxide caused by iron, ferric oxide and ferrous oxide. Ferric oxide (Fe2O3) is a dark red compound occurring naturally as a hematite ore and rust. This material is used in pigments, metal polishes and on magnetic strips. Ferrous oxide (FeO) is a chemically formed powder used in the manufacturing process of steel, heat absorbing glass, and enamels. (AHC-2000). The layer of zinc already has a naturally occurring zinc oxide film which protects the zinc layer against corrosion making it corrosion resistant. If there is a small damaged area or bare spot that exposes the ferrous material, the zinc will sacrifice itself for oxidation. This is a result of the zinc being more electrochemical, attracting oxygen, than the ferrous material causing the zinc to act as a anode protecting the ferrous material. This is the method used in the protection of galvanized products (Geiger, 2002). There are several ways to galvanize steel products, such as hot dip galvanize, electroplating galvanize, mechanical coating, zinc spraying, and zinc dust painting. In hot dip galvanize there are two different processes that are used. One is the process of continuos hot dip galvanizing which consists of a start point and a finish point. In between these two points the material never stops going from a raw material (iron/steel) to a finished good ready to be shipped. The other is stationary hot dip galvanizing in which an individual item is dipped into a pot of molten metal and removed. The following steps are taken in hot dip galvanizing in both hot dip and continuous operations; cleaning, pickling, pre fluxing, galvanizing, cooling, finishing, inspected, and throughout the process the product is rinsed and air blown. The main difference between the two (continuos hot dip and stationary) is that the material on a continuos operation is finished when the cycle is complete versus just dipping the material in most cases is hand finished to remove excess burs, runs, and bumps that are result of no external wipe (air knife, coal, etc.). Top of the page

To view a video on galvanizing click here (quick time must be installed on your computer).

Typical Steps in the manufacturing process of Galvanizing: According to the American Galvanizers Association (2002), the purpose of each of the typical steps in galvanizing are paraphrased below. 1) Cleaning: The step in which the majority of oil, grease, and paints, are removed with a hot alkaline cleaner. This cleaner usually consists of a lead bath or hot soapy water. 2) Rinse/Air Flow: A bath of cooled water to rinse any of the cleaning residue off and air knives to aid in the removing of any additional residue and water that were used on the material before entering the pickling system . 2) Pickling: A bath of diluted hydrochloric or sulfuric acid solutions that serve to remove surface rust and mill scale to provide a chemically clean metallic surface. 3) Rinse/Air Flow: Another water reservoir to dilute the acid concentration that may be left on the material before entering the flux stage and also an air knife to aid in removing un wanted residue. 4) Pre fluxing: The steel is immersed into a liquid flux to remove oxides and to prevent oxidation prior to entering the molten metal. The liquid flux is a concentration that consists usually of zinc ammonium chloride solution. The flux is the key ingredient in aiding in the ability of the zinc to adhere to the iron or steel. 5) Air Flow: Between the pre flux area and the molten metal the material is blown dry using a air knife to remove in moisture that consists prior to entering the liquid metal. Top of the page 6) Galvanizing: The item is immersed in a bath of molten zinc, with a temperature range between 820 and 850 degrees Fahrenheit. The temperature needs to be constantly in this range, if too cold, the zinc freezes, if too hot, the coating consistency is not symmetrical causing low coating, bare spots, or a burnt gray color to exist on the material. With the temperature within range the zinc metallurgic ally bonds to the steel, creating a highly resistant zinc iron alloy layer. The zinc iron alloy is formed in the galvanizing process with pure zinc and the ferrous material being galvanized. This alloy layered is a bond between the iron that is diffused from the steel product being galvanized and the zinc in the molten stage. The layer of coating has several different phases of alloy layers with names such as Alpha, Gamma, Delta, Zeta, and the free Zinc layer. Each of these layers have a different amounts of iron, zinc ratio's. This alloy layer is dependent on the type of steel being used for the galvanizing process. These different alloy layers are what make up the weight of coating that the material receives, determining the finished gauge of the product. The layer gauge to be put on the material is determined by the time in which the material is actually in the zinc bath. 7) Finishing & Cooling: These two steps work together because the cooling of the material results in the finishing of the material. The finishing process consists of removing excess zinc by draining (to aid in the drainage coal and a hard wipe pad are sometimes used), vibrating, and for small items centrifuging (such as with a die in place that is sized according to the desired amount of coating gauge to be applied). While and directly after the finishing process is going on the material is rapidly cooled using different methods to include cold water, high pressure air knives that use nitrogen to form and cool the material. The cool water is aided by chillier units that decrease the temperature of the water before sending it to a quench tank where the material is directly cooled by immersing the completed material directly in the cold water. In many applications the product is also immersed in a wax based substance, applying a light coat to aid in the product being separated when at the end of the continuos run or in use later. 8) Inspection: The inspection process of galvanized material is the simplest and most important means of assessing the quality of the galvanized zinc coating. The inspection process uses some standard testing such as tensile strength, yield strength, hardness, elongation, stress/stain, form/condition, thermal conductivity, electrical resistance, coating weight/gauge, and most importantly the appearance of the finished product. The appearance of the galvanized coat demonstrates the relationship to the coating quality.

The typical characteristics of appearance: There are several characteristics to the appearance to include; dull gray color, rust stains, blisters, texture (smooth, rough), lumps, pimples, bare spots, bulky white deposit, and dark spots. The following information will tell more about these different appearance issues: To view pictures of different coating and more information on the Appearance of galvanized products click here. The information used for inspection was obtained from Wader.com. Top of the page

1. Dull gray coating: This type of coating is normally acceptable and is caused by growth of the zinc iron alloy layers through to the surface of the galvanized coating . 2. Rust stains: The rust stains are acceptable when present as a surface stain, this is usually caused by contact with or drainage with other corroded steel surfaces. 3. Blisters: Small intact blisters in the coating are acceptable and are usually due to absorption of hydrogen by the steel during the pickling process being expelled as a result of the heat put off by the galvanizing process. 4 General roughness and thick coatings: General roughness of the outer material is normally acceptable as long as not otherwise agreed on with the consumer. The cause of rough galvanized coatings is usually a result from uneven growth of zinc iron alloys because of the composition or surface condition of the steel. 5. Lumpiness and runs: Lumps are normally acceptable unless otherwise specified and are caused by uneven drainage. Lumps and runs have no impact on the coating life. 6. Pimples: Pimples are grounds for rejection depending on size and extent. Pimples are caused by inclusions of dross in the coating. Dross, which is a zinc iron alloy particles has a similar corrosion rate to the galvanized coating and its presence as finely dispersed pimples is not objectionable. Gross dross inclusions may be grounds for rejection as they tend to embrittle the coating. 7. Bare spots: Bare spots are generally acceptable if small in area and suitably repaired, depending on the nature of the product. Some reasons for bare spots are faulty processing, rolling defects, laminations and nonmetallic impurities rolled into the surface. 8. Wet storage stain or bulky white deposit: A bulky white or gray deposit, known as wet storage stain may form on the surface of closely stacked freshly galvanized articles which become damp under poorly ventilated conditions during storage or were left damp as a result of the product not being dry before storing. One main reason for wet material being stored is an insufficient wax concentration, either to much was or to little. Top of the page

Comparative Properties of various Zinc Metal Coating . Some of the comparative properties of various zinc metal coating are shown in Table 1 obtained from Senast Zinc Information Site. Zinc coating can be applied to steel by different methods which vary from a zinc containing paint to hot dip galvanizing. All these methods can provide successful protection if you choose the right method corresponding to the environment. In general terms the life of a zinc coating is more or less proportional to its thickness.

The table provides comparative properties of five well known zinc coating methods provided by Senast Corporation.

Table 1: Comparative Properties of various Zinc Metal Coating .

Characteristic of the coatingHot Dip GalvanizingElectro PlatingMechanical CoatingZinc SprayingZinc Dust Painting

AdhesionCoating is integral with the steel because the for-mation process produces zinc/iron alloy layers over coated with zinc.Good, comparable with other electroplated coat-ings.Good, comparable with electroplated coatings.Good mechanical interlock-ing provided the abrasive grit blasting pretreatment is carried out correctly.Good - abrasive grit blasting of the steel gives best results

Hot Dip GalvanizingElectro PlatingMechanical CoatingZinc SprayingZinc Dust Painting

Continuity and UniformityGood - any discontinuities are readily visible as "black spots". Some excess zinc at drainage points on products.Uniform within limita-tions of "throwing power" ot bath. Pores not a problem, as ex-posed steel protected by adjacent zincThin at corners - the the opposite of hot-dip galvanized coat-ings.Depends on operator skill Coating are porous but The pores soon fill with zinc corrosion products and are thereafter impermeable.Good- any pores fill with reaction products. Thin at corners

Top of the pageHot Dip GalvanizingElectro PlatingMechanical CoatingZinc SprayingZinc Dust Painting

ThicknessNormally about 50-125 m on tube and products; thicker coatings up to 250 m obtained by silicon killed steel or grit blasting before galvanizing. Coatings 10 -30 m applied to continuous wire and sheetThickness variable at will; generally 3 - 15 m. Thicker layers are possi-ble but generally uneco-nomical.Variable at will, usually between 10 - 80 m.Thickness variable at will generally 100 - 150 m but coatings of up to 500 m can be appliedUp to 40 m of paint (and more with special formulations) can be applied in one coat


Formability and Mechanical PropertiesConventional coatings ap-plied to finished articles, not formidable; alloy layer is abrasive resistant but brittle on bending. Special coatings with little or no alloy layer readily formed (e.g. on sheet) and resistance welded.Electroplated steel has excellent formability and can be spot welded. Small components are usually finished before plating.Good. Does not cause em-brittlement of high strength steels.When applied to finished articles, forming not re-quired. Can weld through thin coating if necessary but preferable to mask edges to be welded and spray these afterwardsAbrasion resistance better than conventional paints. Painted sheet can be formed and resistance welded with minor damage.


Extra TreatmentsConversion coatings -chromate's prevent wet storage stain; phosphates good on new sheet as a base for paints. Weathered coatings often painted (after 10 - 30 years) for longer service.Conversion coatings (e.g. chromate's used to prevent wet storage stain) Frequently used as a base for paints.Can have conversion coatings applied.Coating with sealant that can provide a base for paints to give long life structures.Can be used alone or as primer under conven-tional paints.

Top of the pageHot Dip GalvanizingElectro PlatingMechanical CoatingZinc SprayingZinc Dust Painting

Other ConsiderationsSize of bath available. Parts up to about 25 meters long can dipped at some works. Care required at design stage for best results. Continuous wire and sheet avail-able.Size of bath available. Process normally used for simple, fairly small components suitable for barrel plating or for con- continuous sheet and wire. No heating except for hydrogen embrittlement relief on high strength steels.Ideal for small parts including washers and springs (e.g. up to 15 cm or 250 g). Access diffi-culties (e.g. inside tubes).No size or shape limitations very economical for work with high weight to area ra-tio. Uneconomical on open mesh. Access difficulties may limit application (e.g. inside tubes). Best method of applying very thick coatings. Little heating on the steel.Suitable for anything that can be painted though there may be difficulties of access in narrow tubular struc-tures. Can be brush, spray or dip applied. No heating involved. Performance varies with media used and percentage of zinc dust

What is Corrosion? Corrosion (rust) is the deterioration of a material that alters its mechanical properties. This is caused by a chemical reaction between the material and oxygen or some other type of type of chemical. Corrosion is one of the most important factors in the breakdown of materials causing a shorter life expectancy than what the product was set out to achieve. This chemical breakdown of the material causes many unfortunate accidents that might have been prevented with the use of a corrosion resistant product (HSC-1999). Top of the page.

Galvanized Products: The following list is some practical uses for galvanized steel products:

Amusement rides Beams Bicycle racks Boat trailers Box rail Bridge rail Bridge substructure Bridge superstructure Cat walks ColumnsConveyor systems Cooling tower parts Dock hardware Dock levelers Fence posts Flag poles Garbage cans Gas turbine skids Grating HandrailsHighway guardrail/posts Ladders Lattice towers Metal sculptures Overhead cranes Overhead sign supports Pedestrian bridges Picnic table frames Pipe Plates PlatformsRebar Signal light poles Stair treads Sound barriers Structural steel Transmission poles Utility trailers Water/waste treatment structures Wheelbarrows Wire mesh

These are a few pictures of different products offered by the Industrial Galvanizers Corporation (Copyright 2002).

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INCLUDEPICTURE "http://www.bsu.edu/web/darodgers/usa.jpg" \* MERGEFORMATINET Summary: Galvanizing (to coat iron or steel with zinc) is today's best way of preserving materials for tomorrow without much environmental impact, due to the recyclable ability of zinc. In today's society the environmental implications of the use of industrial products and processes are essential to the life of all living organisms. With no space left for radioactive waste or other non-biogradeable products something needs to be done to preserve life for tomorrow. Galvanizing is a process that not only works to prevent present day failure but it also looks to the future. Zinc the main ingredient used in the galvanizing process has been found to be essential to humans as well as to the life of many other living organisms. Top of the page

Appendix: Definitions dealing with the galvanizing process. Manufacturing: 1) "A series of interrelated activities and operations that involve product design, and the planning, producing, materials control, quality assurance, management, and marketing of that product" (Biekert, p348). 2) "Building and services products that are not attached to a site" (Flowers, p5). 3) "Systems that transform materials into products in a central location (factory)" (Wright, p25) . 4) "To make or process (a raw material) into a finished product, especially by a large scale industrial operation" (AHC, p826) Galvanizing): 1) "To coat (iron or steel) with rust resistant zinc" (AHC, p558). 2) "The process of coating a metal, usually iron or steel, with a protective covering of zinc (Columbia, 2000). 3) "Is a process for applying a protective zinc coating over iron or steel to reduce corrosion (McNichols, 2002). 4) "The process of coating such metals as iron and steel with a thin protective layer of zinc or zinc alloy" (Geiger, 2002). Corrosion: 1) "The act or process of corroding (To destroy a metal or alloy gradually), the condition caused by corroding" (AHC, p312). 2) "Corrosion is a naturally occurring physical and chemical deterioration of a material due to reaction with its environment and especially with oxygen." (CRM, 1976) 3) "chemical damage" (Geiger, 2002) Corrosion Resistant: 1) "is the ability to resist oxidation" (EMT, p177). 2) "barrier applications used to protect carbon steel, concrete, or other substrates from corrosion by harsh chemicals" (Schweitzer, p1). Anode: 1) "A positively charged electrode, as of a storage battery" (AHC, pg. 55). Electrochemistry 1) "interaction or inter conversion of electric and chemical" (AHC, pg. 441).

Internet References: 1. Senast (2000) "Zinc in the environment" Norden AB http://www.zincinfo.se/english/article.htm 2. Senast (2000) "THE COMPARATIVE PROPERTIES OF VARIOUS ZINC METAL COATING" Norden AB. http://www.zincinfo.se/english/comp.htm 3. Senast (2000) "10 GOOD REASONS FOR HOT DIP GALVANIZING" Norden AB. http://www.zincinfo.se/english/10good.htm 4. Senast (2000) "Case Study Public Infrastructure: Galvanizing Saves Taxpayer $$" Norden AB. http://www.zincinfo.se/english/news.htm 5. Highway Safety Corp. (1999) "Why Galvanize" American Galvinizers Association (AGA) and Structural Steel Fabricators of New England (SSFNE) http://www.galvanizeit.org.htm 6. Highway Safety Corp. (1999) "Service Life Chart for Hot Dip Galvanized Coating" American Galvinizers Association (AGA) and Structural Steel Fabricators of New England (SSFNE) http://www.galvanizeit.org/servicelife/charts.pdf 7. Highway Safety Corp. (1999) "The After Fabrication Hot-Dip Galvanizing Process" American Galvinizers Association (AGA) and Structural Steel Fabricators of New England (SSFNE) http://www.galvanizeit.org/process.htm 8. Trew, Delbert "The Making of Wire" Barb Wire Museum. http://www.barbwiremuseum.com/makingwire.htm 9. The Columbia Encyclopedia, Sixth Edition. Copyright 2002 Columbia University Press. "galvanizing" http://aol.bartleby.com/65/ga/galvaniz.html 10. Reliable Galvanizing "The Galvanizing Process" http://www.reliablegalvanizing.com/steelgalvanizing.htm 11. The Columbia Electronic Encyclopedia Copyright 1994 Columbia University Press "galvanizing" 2001-2002 Family Education Network Inc. http://print.factmonster.com/ce6/sci/A0820097.html 12. Geiger, Gordon H. (2002) "Galvanizing" World Book Online America's Edition http://www.aol.svc.worldbook.aol.com/wbol/wbAuth/jsp/wbArticle.jsp 13. McNichols (2002) "Galvanized/Pre Galvanized" http://www.mcnichols.com/ecommerce/english/pages/products/products/productsupportfiles/mater.. 14. Coating Control, Inc. (2001) "Products" Specialized Machinery for the Coating Process Industry http://www.coatingcontrol.com/page2.html 15. Wader Engineering "Inspection" http://www.wader.com.hk/Inspection.html

Bibliography: 1. Jacob's, James A. & Kilduff, Thomas F. (2001). Engineering Materials Technology 4th Edition. Prentice-Hall, Inc. 2. Mellan, Ibert. (1976) "Corrosion Resistant Handbook". Noyes Data Corporation. 3. De Renzo, D.J. (1986) "Handbook of Corrosion Resistant Coating". Noyes Data Corporation. 4. Berube, Margery S. (2000) "The American Heritage College Dictionary Third Edition". Houghton Mifflin Company. 5. American Society for Metals. (1979) "Coating For Corrosion Prevention" Materials/Metalworking Technology Series. 6. Schweitzer, Philip A. (2001) "Corrosion Resistant Lining and Coating" Marcel Dekker. 7. Flick, Ernest W. (1987) "Corrosion Inhibitors An Industrial Guide". Noyes Publications.

This web site is being manufactured to fulfill part of the course outline objectives in ITDPT 303, Manufacturing Systems at Ball State University. Top of the page

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