Galvanized steel
From CollabLandWiki
Manufacturing / extraction processes
These are the steps in the hot-dip galvanizing process:
Firstly the steel is weighed, tagged for temporary identification, then suspended from wire clips. The metal is ready for the galvanizing process.
1. Surface Preparation
Caustic Cleaning- The metal enters into a hot caustic bath which removes the surface soil and grease.
Rinsing- The metal is then rinsed in a bath of water.
Pickling- The metal is dipped into a diluted hydrochloric acid bath which removes the surface rust which makes the steel clean and metallic.
Rinsing- The metal is again rinsed in a bath of water.
Flux Solution- The steel is dipped in flux to remove oxides and to prevent oxidation before the steel gets galvanized. There is dry and wet galvanizing. In the dry process, the steel is dipped in flux, removed, dried, then galvanized. In the wet process, the flux sits above the zinc so it passes through the flux then immediatley to the zinc for galvanizing. At Perry Metal Protection they use the dry galvanizing method.
The galvanizing process is when steel is immersed in a 445-465 C bath of molten zinc. During this process, the steel and zinc metallurgically bond which creates a surface that is free from abrasion, corrosion and forms a barrier of protection against all the elements. The period of immersion in the zinc bath varies from several minutes up to half an hour. It depends on the nature of the steel being galvanized eg- weight and size.
Quenching- The metal is then dipped into a bath of hydrochloric acid. This is the last bath.
3. Inspection
The steel is left to cool off and afterwards, the thickness of the zinc coating and surface are inspected. If there are marks or drips on the surface of the metal, this can be filed off or sanded down.
A Brief History of Galvanizing
The process was first invented by a French chemist in 1742, and first used by Stanilaus Tranquille Modeste Sovel, another French chemist in 1836. By 1850 in Britain the galvanizing industry was using 10,000 tonnes or zinc per year for the protection of steel. For the past 150 years the process of galvanizing has been sucessful as a method of corrosion control.
Material Properties
The hot-dip galvanizing coating is made up of at least 98% zinc metal. The greatest quality of zinc is it's natural capacity to protect. Zinc extends the life of steel which in return protects investments.
The performance varies in different environments. In warm and dry environments the stability of zinc is remarkable. There is no reaction between the galvanized coating and the air so the protection continues.
In the presence of moisture in the atmosphere, the zinc stays stable indefinatley.
In rural areas, the life span of galvanized coatings may be reduced as the effects of aerial spraying and fertilisers. In dry form the fertilisers are harmless, but it is when they get wet that aggressive solutions can be formed which can attack galvanized coatings.
By the sea coast the corrosion rate is increased because of the presence of soluble chlorides. Still, the protection of the galvanized coating is alot better than other protective systems, and can be further increased by a using a duplex galvanizing-plus-paint system.
In industrial areas there are atmospheric impurities in the air. It is advised to reinforce the galvanized coating with a paint system that can resist these atmospheric conditions.
Format & Finish of Materials
Galvanized steel is used where rust, corrosion and abrasion protection is required. It is favoured for the ease of application, low cost and durability.
Successfully painting over hot dipped galvanized steel, known as a duplex system, is an orthodox industrial painting procedure, which in Europe runs into millions of tonnes of steel per annum.
The purpose of the process is to:
- Create an aesthetic or identifying colour
- extends the service life
- add chemical resistance for which galvanizing alone is unsuitable
This system of expanding the fundamental characteristics of galvanizing should not be taken as matching the appearance of painting in terms of high gloss, surface smoothness or paint finishes obtainable over substrates of timber, plaster automotive or white goods sheet metal.
An after-fabrication galvanized surface will retain its cast coating appearance or, in effect, a natural rather than manufactured metallic finish. This distinction is generally the reason for its use to add a specific architectural feature as well as obtain long maintenance free life.
Duplex appearance, in the case of heavy duty coatings, for severe marine or chemical exposure differs little from paint alone and is of little consequence.
Common Fixing Methods
There should be no maintenance problems after the steel has been galvanized. The only problems are when the steel has just been galvanized and there may be some surface dripping which can be easily filed or sanded down.
Galvanized steel is welded together easily and satisfactory by all commonly practiced welding techniques. Closer control of welding conditions than for uncoated steel is usually necessary but procedures are simple and well established.
Durability and Maintenance Requirements
Galvanized steel is chosen because it is very durable. The service life for galvanized steel is over 70 years without maintenance.
In some extreme environments the galvanized coatings can corrode. To avoid this, it is desirable to reinforce the coating with a paint system resistant to the specific conditions.
The durability of galvanizing in the atmosphere is largely due to the corrosion protection afforded by the insoluble corrosion products that slowly accumulate on the surface as it weathers.
Galvanized steel has the least maintenance and lowest long term cost. Even in cases where the initial cost of galvanizing is higher than alternative coatings, galvanizing is almost invariably cheapest in the long term because it lasts longer and needs less maintenance.
Life-cycle / Recycling Possibilities
Galvanized coating can last 70-150 years without maintenance in most urban and rural atmospheres. Yes, the metal can be recycled by either being re-galvanized or taken to a scrap metal yard.
List of manufacturers / contractors / suppliers
Perry Metal Protection, 129 Hutt Park Road, Gracefield, Lower Hutt. ph (04) 568 4139
There are also branches in Hamilton, Auckland, Tauranga and Christchurch.
enquiry@perry.co.nz
http://www.perrymetalprotection.co.nz
Avon Industries Ruatangata Road PO Box 27 Whangarei 0115 Ph 09 435 1033 Fax 09 435 2565 Mob 025 939 060 avonind@xtra.co.nz
CSP Galvanizing 40-44 Gavin Street PO Box 11 165 Ellerslie Auckland 1131 Ph 09 579 0063 Fax 09 579 8907 Mob 021 399 516
ashar@fcsp.co.nz
CSP Galvanizing 27 Washbournes Road PO Box 11 183 Sockburn Christchurch 8030 Ph 03 348 8522 Fax 03 348 5888 Mob 021 341 247
waynesc@fcsp.co.nz
East Tamaki Galvanizing 2 / 33 Springs Road East Tamaki PO Box 58 666 Greenmount Auckland 1730 Ph 09 274 0524 Fax 09 274
0525 Mob 025 906 145 etgalv@xtra.co.nz
Franklin Machinery 37 Subway Road PO Box 445 Pukekohe 1800 Ph 09 238 9289 Fax 09 238 5686 Mob 025 486 243 ianr@gallagher.co.nz
Galvanizing Services 23 Edinburgh Street PO Box 13 181 Onehunga Auckland 1132 Ph 09 636 6003 Fax 09 636 5967 gsl@xtra.co.nz
Galvanizing Hawkes Bay 41 Thames Street PO Box 1114 Napier Ph 06 835 4499 Fax 06 835 9499 dave@galvanising.co.nz
Kibby's Metal Pressings Dawson Street PO Box 75 New Plymouth Ph 06 758 2210 Fax 06 757 5029 kibbys@xtra.co.nz
Taranaki Galvanisers 2003 Ltd Cnr Monmouth Road St H/way 3 RD24 Stratford Ph 06 762 8585 Fax 06 762 8700 taragalv@xtra.co.nz
Product information / specifications
1. Surface finish: The galvanized coating should be continuous, adherent,smooth, as evenly distributed as possible, and free from any surface defects. On silicon killed steels, the coating may be dull grey, provided the coating is sound and continuous. Where a paint finish is to be applied to the galvanized coating, all spikes shall be removed and all edges shall be free from lumps and runs.
2. Adhesion: The galvanized coating should be sufficiently adherent to withstand normal handling during transport and erection.
3. Transport and Storage: Galvanized components should, wherever possible, be transported and stored under dry, well-ventilated conditions to prevent the formation of wet storage staining, also known as 'white rust'.
4. Welding:
Where galvanized steel is to be welded, adequate ventilation should be provided. If adequate ventilation is not available, supplementary air circulation should be provided. In confined spaces a respirator shall be used.
Precedent 1
Sarah I have used three precedents- Civic Square, Waitangi Park and Glover Park. All of these public spaces and parks have used galvanized steel in the construction of the landscape. I chose glover Park because the red galvanized steel tree protectors and lights are a main and striking design feature. I chose the palms in Civic Square as a precedent because they are attractive and they are iconic of the civic Square area. Waitangi Park appealed to me as a precedent because again, there is alot of galvanized steel in the landscape and design of the park. The main designs that attracted me were the skate park graffiti wall and the over bridge in the park.
Precedent 2
Most of the steel structure landscape constructions located in a corrosive environment such as Wellington waterfront,near the open sea. are maded up with Galvanized steel. Since no other protective coating for steel provides the long life, durability and predictable performance of hot dip galvanizing. An alloy of its steel base, a galvanized coating is excellent in matching the design and handling characteristics of steel.
1.Blue flood lamps underneath are shinning up the galvanized steel maded structure.These blue light shaded this structure while itself have been framed.
2.The new extension project of Wellington warterfront are widely used galvanized steel in term of lanscape construction. Those vertical lighting poles which recently mentioned by the newest Topos journal. These vertical strctures are well balanced with the horizontal open space.
3.Galvanized steel has been used in construction of the stage for rollingstone's live concert in westpac stadium.
4.Galvanized steel maybe is the best choice to constructing a steel structure bridge In such corrosive enviroment which near open sea.
5.The ball shaped sculptures are wraping the light with the galvanized steel case.A layer of paint finish applied on these sculptures that reduced the reflectability of the galvanized steel case.Therefore, these cases are nicely shaped inside lights with the exterior contours.
6.This floating structure of sculpture in front of western elevation of the Huttcity gallery,indicates that galvanizing steel are also good for crafting artwork.
See also
References
www.galvanizeit.org
Interview with Graham Black from Perry Metal Protection. We went for a site visit at their Lower Hutt branch on 18/07/06.
J. William Thompson, Sustainable Landscape Construction, Island Press, 2000
Galvanizer's association of Australia, (Gaa) http://www.gaa.com.au/index.html
