Building skins: Metallic system By Stephanie Hanlon

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1 Building skins: Metallic system By Stephanie Hanlon There are two major metallic building materials: aluminum and stainless steel. Here we will focus on the metallic system in the building skin rather than the building structural system. Aluminum British scientist Humphrey Davy inscribed the term aluminum in 1807 though he did not discover the element yet. In 1825, Hanse C. Oersted of the University of Copenhagen isolated Metallic aluminum that was a small amount of impure metal. By 1852, the cost of aluminum was $545 per pound. In 1886 Charles Martin Hall and Paul T. Heroult of France independently discovered that metallic aluminum could produced by an electrolytic process. The Hall-Heroult process made it easy to produce metallic aluminum at a reasonable price and in sufficient quantities. As a result, the cost of aluminum was $11.33 per pound in 1885 and down to $0.57 per pound in The known Aluminum Company of America ( ALCOA ), which was formed in 1888, promoted the Hall-Heroult process.

2 Aluminum alloys have been classified as cast and wrought since 1950, and there are two kinds of alloy treatments, non-heat-treatable alloy and heat-treatable alloy. Non-heat-treatable alloy contains trace amounts of manganese and magnesium; used for roofing and cladding. Heat-treatable alloys contain magnesium, silicon, and sometimes copper; used for windows, curtain walls, fasteners, and structural members. Heat-treatable alloys were first manufactured to increase the strength of the metal during WWI. Anodic coatings were created by building up the natural aluminum oxide coating, and it may be transparent or of varying degrees of silver, gray, or brown. However, adonizing did not become available for architectural purpose until after WWII. Adonizing coating became popular after WWII, because of their outstanding resistance to atmospheric corrosion. They are also highly absorptive for dyes and paints. Principal aluminum-finishing process

3 For architectural purposes, after WWI, aluminum and its alloys were used in cast, sheet, and extruded form: which was used for window sash, doors, railings, trim, grilles, and signs. During the 1920 s and 1930 s cast or pressed sheet aluminum spandrel panels were used, the spandrels are set into masonry backup as brick spandrels. The Chrysler and Empire State buildings in New York city are examples. Architectural designers were seeing a vision of the lightweight wall that could be easily fabricated and erected. During WWII, aluminum production and assembly skills increased in order to produce war airplanes, and after the war, the process and the techniques to fabricate aluminum material was available for construction. By 1950, its use became an important component of the glass and metal curtain wall. The Aluminum Company of America building (1953) in Pittsburgh is an aluminum-clad curtain wall that the cladding consists of one story highprefabricated panels of pressed and anodized sheet aluminum penetrated by windows. One other expressive aluminum building is the U.S. Air Forced Academy (1962) in Colorado. Aluminum became the standard building material in a variety of ranges and the new applications like residential siding and sunscreens gained new users. The stamped prismatic panels of the Republic National Bank (1955), Dallas, were insulated and sealed with aluminum foil.

4 Aluminum Company of America building (1953), Pittsburgh, was one of the first to use Prefabricated curtain wall panels Pure aluminum is extremely resistant to corrosion, and an aluminum curtain wall can be cleansed by hand, primed, and recoated with a custom metallic product to match the original appearance. Aluminum requires low-maintenance and low-cost, it is lightweight and has high strength.

5 Stainless Steel In 1821, chromium alloy steels was discovered, but it claimed it was not resistance to corrosion. In 1908, Philipp Monnartz of Germany discovered the role of carbon to block the corrosion resistance of chromium steels. Stainless steel combined with diverse groups of metal alloys containing iron and at least 11 percent of chromium. Chromium allows the alloys to form a tight film of iron-cholomium oxide that resists corrosion and chemical attack. There are four classifications in stainless steel: 1) martensitic stainless steels iron-chromium alloys hardened by heat treatment 2) ferritic stainless steels iron-chromium alloys that cannot be hardened by heat rating 3) austenitic stainless steels iron-chromium-nickel and iron-chromium-nickelmagnanese alloys that are hardened only by cold working which means that the metal will harden only through deformation 4) precipitation hardening stainless steels iron-chromium-nickel alloys, titanium, boron, or beryllium is added as hardeners. Austenitic stainless steels are most often used in architectural purpose as a formed sheet

6 Eduard Maurer of Germany developed austenitic stainless steel, an alloy containing 18 percent chromium and 8 percent nickel (18-8 stainless steel) between 1909 and Stainless steel s surface could be made smoother and shiny so the metal was used for architectural and engineering purposes, the mechanical finishing process and electrolytic process was used to do a job. There were nearly one hundred American patents for electropolishing processes by 1947.

7 In 1927, the Allegheny Steel Company was the first company to advertise stainless steel in sweet s catalogue, and it promoted iron-chromium-nickel alloy. It also promoted every architectural use of stainless steel from structure to decorative application; trim ornament, door, hardware, elevator, light fixture, furniture, and equipment. The manufacturer promoted that stainless steel was corrosion resistance and had high sanitary qualities and a modern look. Even though the price is expensive when compared with aluminum, the maintenance and replacement cost was negligible. The Chrysler building (1930) used about 35,000 square feet of kruppnirosta stainless steel for the dome, spire, gargoyles, storefronts, entrances and doors, and the Empire State Building (1931) used 18-8 stainless steel for vertical trim. The critics praised its low-maintenance. By the 1940s, stainless steel had a reputation as a corrosion-resistant, low-maintenance, visually appealing material. Stainless steel products added extruded shapes for storefronts and trim. In the late 1940s and the beginning of the 1950s curtain wall construction was developed using thin, lightweight panels hung on a structural frame to enclose a building. The curtain wall was composed more of glass, leaving only the mullions as a sheet metal, while the typical building construction in New York city was opaque wire-reinforced a glass spandrel panels set in stainless steel mullions. Overall, aluminum is stainless steel s strongest compatitor because of its lower cost and light weight.

8 The Inland Steel Building (1957), Chicago, an early application of stainless steel in modern architecture, juxtaposes polished stainless steel mullions and spandrel panels with tinted green glass.

9 Resources - Construction Principles, Materials, and Methods 6 th edition by Olin, Schmidt, and Lewis, AIA - Twenty century building materials; history and conservation by Thomas C. Jester, National Park Service