Corrugated galvanised iron (CGI) or steel, colloquially corrugated iron (near universal), wriggly tin (taken from UK military slang), pailing (in Caribbean English), corrugated sheet metal (in North America), zinc (in Cyprus and Nigeria) or custom orb / corro sheet (Australia), is a

building material Building material is material used for construction. Many naturally occurring substances, such as clay, rocks, sand, wood, and even twigs and leaves, have been used to construct buildings and other structures, like bridges. Apart from natur ...

composed of sheets of hot-dip galvanised

mild steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobalt ...

, cold-rolled to produce a linear ridged pattern in them. Although it is still popularly called "iron" in the UK, the material used is actually steel (which is iron alloyed with carbon for strength, commonly 0.3% carbon), and only the surviving vintage sheets may actually be made up of 100% iron. The corrugations increase the bending strength of the sheet in the direction perpendicular to the corrugations, but not parallel to them, because the steel must be stretched to bend perpendicular to the corrugations. Normally each sheet is manufactured longer in its strong direction. CGI is lightweight and easily transported. It was and still is widely used especially in rural and military buildings such as sheds and water tanks. Its unique properties were used in the development of countries such as Australia from the 1840s, and it is still helping

developing countries A developing country is a sovereign state with a less-developed Secondary sector of the economy, industrial base and a lower Human Development Index (HDI) relative to developed countries. However, this definition is not universally agreed upon. ...

today.

History

Henry Robinson Palmer Henry Robinson Palmer (1795–1844) was a British civil engineer who designed the world's second monorail and the first elevated railway. He is also credited as the inventor of corrugated metal roofing, which is one of the world's major buildi ...

, architect and engineer to the London Dock Company, was granted a patent in 1829 for "indented or corrugated metallic sheets". It was originally made from

wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.05%) in contrast to that of cast iron (2.1% to 4.5%), or 0.25 for low carbon "mild" steel. Wrought iron is manufactured by heating and melting high carbon cast iron in an ...

produced by puddling. It proved to be light, strong,

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

-resistant, and easily transported, and particularly lent itself to prefabricated structures and improvisation by semi-skilled workers. It soon became a common construction material in rural areas in the United States, Argentina, Spain, New Zealand and Australia and later India, and in Australia and Argentina also became (and remains) a common roofing material even in urban areas. In Australia and New Zealand particularly it has become part of the cultural identity, and fashionable architectural use has become common. CGI is also widely used as building material in African slums and informal settlements. For roofing purposes, the sheets are laid somewhat like tiles, with a lateral overlap of one and half corrugations, and a vertical overlap of about , to provide for waterproofing. CGI is also a common construction material for industrial buildings throughout the world. Wrought iron CGI was gradually replaced by

from around the 1890s, and iron CGI is no longer obtainable, but the common name has not been changed. Galvanised sheets with simple corrugations are also being gradually displaced by 55% Al-Zn coated steel or coil-painted sheets with complex profiles. CGI remains common.

Corrugation today

Today the corrugation process is carried out using the process of

roll forming Roll forming, also spelled roll-forming or rollforming, is a type of rolling (metalworking), rolling involving the continuous bending (metalworking), bending of a long strip of sheet metal (typically coiled steel) into a desired cross-section (g ...

. This modern process is highly automated to achieve high productivity and low costs associated with labour. In the corrugation process

sheet metal Sheet metal is metal formed into thin, flat pieces, usually by an industrial process. Thicknesses can vary significantly; extremely thin sheets are considered foil (metal), foil or Metal leaf, leaf, and pieces thicker than 6 mm (0.25 ...

is pulled off huge rolls and through rolling dies that form the corrugation. After the sheet metal passes through the rollers it is automatically sheared off at a desired length. The traditional shape of corrugated material is the round wavy style, but different dies form a variety of shapes and sizes. Industrial buildings are often built with and covered by

trapezoidal sheet metal In geometry, a trapezoid () in North American English, or trapezium () in British English, is a quadrilateral that has at least one pair of parallel sides. The parallel sides are called the ''bases'' of the trapezoid. The other two sides are ...

. Many materials today undergo the corrugation process. The most common materials for corrugated iron are

ferrous In chemistry, iron(II) refers to the chemical element, element iron in its +2 oxidation number, oxidation state. The adjective ''ferrous'' or the prefix ''ferro-'' is often used to specify such compounds, as in ''ferrous chloride'' for iron(II ...

alloys An alloy is a mixture of chemical elements of which in most cases at least one is a metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have properties ...

(e.g.

stainless steel Stainless steel, also known as inox, corrosion-resistant steel (CRES), or rustless steel, is an iron-based alloy that contains chromium, making it resistant to rust and corrosion. Stainless steel's resistance to corrosion comes from its chromi ...

s), aluminium and copper. Regular ferrous alloys are the most common due to price and availability. Common sizes of corrugated material can range from a very thin 30

gauge Gauge ( ) may refer to: Measurement * Gauge (instrument), any of a variety of measuring instruments * Gauge (firearms) * Wire gauge, a measure of the size of a wire ** American wire gauge, a common measure of nonferrous wire diameter, especia ...

() to a relatively thick 6 gauge (). Thicker or thinner gauges may also be produced. Other materials such as thermoplastic and

fiberglass Fiberglass (American English) or fibreglass (English in the Commonwealth of Nations, Commonwealth English) is a common type of fibre-reinforced plastic, fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened i ...

-reinforced plastic sheets are also produced with corrugations. Clear or translucent products can allow light to penetrate below.

Pitch and depth

The corrugations are described in terms of pitch (the distance between two crests) and depth (the height from the top of a crest to the bottom of a trough). It is important for the pitch and depth to be quite uniform, in order for the sheets to be easily stackable for transport, and to overlap neatly when joining two sheets. Pitches have ranged from 25 mm (1 inch) to 125 mm (5 inches). It was once common for CGI used for vertical walls to have a shorter pitch and depth than roofing CGI. This shorter pitched material was sometimes called "rippled" instead of "corrugated". However nowadays, nearly all CGI produced has the same pitch of 3 inches (76 mm). A design of corrugated galvanised steel sheets "Proster 21", used as

formwork Formwork is Molding (process), molds into which concrete or similar materials are either precast concrete, precast or cast-in-place concrete, cast-in-place. In the context of concrete construction, the falsework supports the shuttering mold ...

, has 21 millimetre deep V-shaped pits.

Corrosion

Although galvanising inhibits the corrosion of steel, rusting is inevitable, especially in marine areas–where the salt water encourages rust–and areas where the local rainfall is acidic. Corroded corrugated steel roofs can nevertheless last for many years, particularly if the sheets are protected by a layer of

paint Paint is a material or mixture that, when applied to a solid material and allowed to dry, adds a film-like layer. As art, this is used to create an image or images known as a painting. Paint can be made in many colors and types. Most paints are ...

References

External links