Hot-dip galvanization is a form of galvanization. It is the process of coating iron and steel with zinc, which alloys with the surface of the base metal when immersing the metal in a bath of molten zinc at a temperature of around 450 °C (842 °F). When exposed to the atmosphere, the pure zinc (Zn) reacts with oxygen (O2) to form zinc oxide (ZnO), which further reacts with carbon dioxide (CO2) to form zinc carbonate (ZnCO3), a usually dull grey, fairly strong material that protects the steel underneath from further corrosion in many circumstances. Galvanized steel is widely used in applications where corrosion resistance is needed without the cost of stainless steel, and is considered superior in terms of cost and life-cycle. It can be identified by the crystallization patterning on the surface (often called a "spangle").[1]
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Galvanized steel can be welded; however, one must exercise caution around the resulting toxic zinc fumes. Galvanized fumes are released when the galvanized metal reaches a certain temperature. This temperature varies by the galvanization process used. In long-term, continuous exposure, the recommended maximum temperature for hot-dip galvanized steel is 200 °C (392 °F), according to the American Galvanizers Association. The use of galvanized steel at temperatures above this will result in peeling of the zinc at the inter-metallic layer[citation needed]. Electrogalvanized sheet steel is often used in automotive manufacturing to enhance the corrosion performance of exterior body panels; this is, however, a completely different process which tends to achieve lower coating thicknesses of zinc.
Like other corrosion protection systems, galvanizing protects steel by acting as a barrier between steel and the atmosphere. However, zinc is a more electropositive (active) metal in comparison to steel. This is a unique characteristic for galvanizing, which means that when a galvanized coating is damaged and steel is exposed to the atmosphere, zinc can continue to protect steel through galvanic corrosion (often within an annulus of 5 mm, above which electron transfer rate decreases).
The process of hot-dip galvanizing results in a metallurgical bond between zinc and steel, with a series of distinct iron-zinc alloys. The resulting coated steel can be used in much the same way as uncoated.
A typical hot-dip galvanizing line operates as follows:[2]
Lead is often added to the molten zinc bath to improve the fluidity of the bath (thus limiting excess zinc on the dipped product by improved drainage properties), help prevent floating dross, make dross recycling easier and protect the kettle from uneven heat distribution from the burners. Environmental regulations in the United States disapprove of lead in the kettle bath. Lead is either added to primary Z1 grade zinc or already contained in used secondary zinc. A third, declining method is to use low Z5 grade zinc.[3]
Steel strip can be hot-dip galvanized in a continuous line. Hot-dip galvanized steel strip (also sometimes loosely referred to as galvanized iron) is extensively used for applications requiring the strength of steel combined with the resistance to corrosion of zinc, such as roofing and walling, safety barriers, handrails, consumer appliances and automotive body parts. One common use is in metal pails. Galvanised steel is also used in most heating and cooling duct systems in buildings
Individual metal articles, such as steel girders or wrought iron gates, can be hot-dip galvanized by a process called batch galvanizing. Other modern techniques have largely replaced hot-dip for these sorts of roles. This includes electrogalvanizing, which deposits the layer of zinc from an aqueous electrolyte by electroplating, forming a thinner and much stronger bond.
In some cases, it may be desirable to have designated parts of the metal as non-galvanized. This is often desired when metal will be welded after galvanization. To accomplish this, a galvanizer will typically use a masing compound to coat the areas that will not be galvanized during the hot dip process.
In , French chemist Paul Jacques Malouin described a method of coating iron by dipping it in molten zinc in a presentation to the French Royal Academy.
In , Luigi Galvani, for whom galvanizing was named, discovered the electrochemical process that takes place between metals during an experiment with frog legs.
In , Alessandro Volta furthered the research on galvanizing when he discovered the electro-potential between two metals, creating a corrosion cell.
In , French chemist Stanislas Sorel obtained a patent for a method of coating iron with zinc, after first cleaning it with 9% sulfuric acid (H2SO4) and fluxing it with ammonium chloride (NH4Cl).
A hot-dip galvanized coating is relatively easier and cheaper to specify than an organic paint coating of equivalent corrosion protection performance. The British, European and International standard for hot-dip galvanizing is BS EN ISO , which specifies a minimum coating thickness to be applied to steel in relation to the steels section thickness e.g. a steel fabrication with a section size thicker than 6 mm shall have a minimum galvanized coating thickness of 85 μm.
Further performance and design information for galvanizing can be found in BS EN ISO -1 and BS EN ISO -2. The durability performance of a galvanized coating depends solely on the corrosion rate of the environment in which it is placed. Corrosion rates for different environments can be found in BS EN ISO -1, where typical corrosion rates are given, along with a description of the environment in which the steel would be used.
Want more information on GALVANIZED HARDWARE CLOTH? Feel free to contact us.
Hardware cloth is a hot-dipped galvanized woven or welded mesh. The hot-dipped galvanizing process entails the immersion of the metal material into a vat of molten zinc. The metal reacts with the zinc to form a coating on the surface that helps to prevent corrosion. Our galvanized welded mesh features a heavy zinc coating that provides maximum protection and extra durability. Hardware cloth has an unlimited number of applications around the home, business, or farm. It has a light gauge (usually between 2 and 8 mesh).
Use our handy table for sizes:
MeshStandard 100' Long Roll Widths 2 Mesh24"30"36"48"60"72" 3 Mesh24"30"36"48"60"72" 4 Mesh24"30"36"48"60"72" 8 Mesh24"30"36"48"We recommend not sawing or shearing galvanized wire mesh (either hot dip galvanized after or electo-galvanized before) to alter the mesh shape or dimension. This will cause exposed bare metal. This exposure will result in moisture migration (wicking) between the layer of zinc and the bare steel wire beneath. If left exposed (untreated) over time the moisture will continue to travel between the layers as it continues to rust although not visible the rust damage will continue to grow slowly over time until it fails completely and will need to be replaced. This hidden damage can be prevented by applying a generous layer of zinc rich paint that may be applied by brush or spray to seal any exposed bare metal.
Our galvanized steel mesh offers numerous benefits, including:
Galvanized hardware cloth, or hardware cloth as it is sometimes referred to, is one of the most common and recognizable categories of wire mesh. Because hardware mesh is extremely versatile and attractively priced, it is used in thousands of different applications. Aside from its adaptability and price point, another benefit of Marco&#;s hardware cloth is that, due to its zinc coating, it is corrosion resistant and will have a longer life than a comparable plain steel wire mesh.
Marco Specialty Steel has one of the country&#;s most expansive inventories of this product. Below are some of the more popular industries and uses for hardware cloth:
Marco Specialty Steel offers two variations of galvanized hardware cloth, standard and specialty.
All our hardware cloth is constructed in either welded or woven construction, depending upon the opening size and diameter wire.
Generally speaking, all of Marco&#;s hardware cloth are manufactured and stocked in full, 100&#; rolls. Available widths are typically, 24&#;, 36&#;, 48&#;, 60&#; and in some cases, 72&#; wide. Quantity discounts are available for multiple roll purchases. Please contact one of our friendly sales associates with your exact requirements.
Please keep in mind that due to the complexities of the galvanizing process, wires may not be perfectly straight; while straightness may impact the appearance of the mesh, it should not impact its functionality. If &#;straightness&#; is a major concern, we recommend looking at another type of wire mesh, like space cloth.
There are multiple factors to consider when choosing any galvanized steel mesh product. These include mesh size, which affects the product&#;s ability to screen the materials that pass through it; mesh count, which impacts the size of the openings; and weave type, which determines the mesh&#;s filtering ability.
The experts at Marco Specialty Steel will assist you in exploring your options so you can make an informed decision for your company. We&#;ll help you make the ideal match between mesh size, count and weave type and your specific applications.
As a Marco Specialty Steel customer, you will benefit from our quarter-century of steel industry expertise. We also provide a level of customer support that is unmatched in our industry. In addition to our extensive inventory of metal hardware cloth, we&#;ll custom-fabricate our products for your unique applications.
Our 35,000-square-foot Houston, TX facility includes a fully equipped in-house metal fabrication shop staffed by the best metal/steel workers in the business. We feature fast turnaround times so you can keep all your projects on track and deliver timely service to your customers.
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