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... n tap water and washing detergents is responsible for pitting in stainless steel cookery. Pitting, small indentations in the surface, is a sign that the chromium-oxide barrier has been dissolved in a localized area, but is purely superficial. (7) Any damage to the oxide barrier is quickly self-repaired. With the now exposed metal, Chromium again reacts with oxygen and forms a new protective coating. Contaminates, such as oil, grease, or particles of standard steel on the metal surface can sometimes interfere with this process.
Pickling is an acid cleaning process that removes this debris, but the chemicals involved include strong hydrofluoric acids and must be used with great care. Reforming of the chromium-oxide usually takes 24 hours, but can be returned instantaneously by the application of nitric acid to serve as a catalyst. Since the Great Chicago Fire of 1871, fire resistance has been an important factor in material selection. The wood frames of the closely spaced structures ignited and spread the flames further until the city was in ashes. The only buildings left were those constructed of steel. Steel will melt, but can not ignite, which prevents steel from conducting any flames to nearby structures.
Low conductivity of steel also slows the transfer of heat to adjoining levels in a structure and can actually contain a blaze within its walls. Fire does still pose a threat to steel and stainless steel none the less. The yield strength of most steel is greatly compromised at 500 0 C. (2) However, measures can be taken to increase both the temperature and amount of time endured before structural failure. Critical temperature can be extended to 600 C by using only 50 % of the load bearing strength, for example. Increases in steel temperature can be slowed by several methods. Spraying with substances such as vermiculite or mineral fiber plaster, while messy, can be applied at the installation site to any steel requiring additional fire protection.
In the 1970 s, asbestos materials were used for this purpose, until it was determined to be a cancer-causing agent. Steel columns can be wrapped in intumescent materials as an alternative to spraying. Intumescent coverings, while normally invisible, swell in a fire and absorb the heat, preventing the steel from reaching destabilizing temperatures. Though steel members can be damage in a fire, they can often be repaired or replaced without damaging the overall building stability. Additionally, steel will not expel any toxic fumes in a fire of any severity. (7) Due to the vast types and applications of stainless steel, numerous installation methods are available for designers. Stainless is often cut or formed to the required size and shape. (5) In thin sheets, the desired form can be stamped or bent to the desired shape, reducing the amount of installation attachments required.
Sinks are commonly formed of grade 316 stainless steel in this method and can be easily installed by a plumber. In the case of structural steel applications, beams are cut to length during fabrication; this reduces cutting and waste at the job site. Since only the required amount is shipped, the transportation costs are reduced. After the materials arrive at the construction site, the pre-fabricated pieces are erected and pre-drilled holes are used for secure connections. With the wide array of stainless steel applications, an understanding of the available attachment methods is more appropriate than an understanding of the installation process of each. Welding is a common method for attaching two metal sheets at a joint.
Arc welding melts the adjacent sheets and allows the steel to intermingle and form a bond as strong as the steel itself. Conversely, soldering uses a second type of metal to form the connection. While requiring less heat and less skilled labor, the filler metal is often weaker than the steel and its lower yield strength must be taken into consideration. As discussed earlier, welding temperatures can cause warping in stainless steel and is not always the best option. Dozens of other methods exist for a designer to choose among.
Rivets are popular when high strength is needed, but the necessary equipment is quite heavy and difficult to use. Rivets are usually limited to structural applications. More delicate work utilizes various machine screws, bolts, or large cap screws. Pre-drilled holes make these attachment methods simple to use. Special epoxy adhesives can also be employed, as well as a joint-and-seam system.
In the joint-and-seam method, the end of the first piece of sheet metal is bent or curved. The second sheet is shaped to the opposite bend and fitted together. Solder can be added for additional strength. As stated earlier, applications for stainless steel span from its beginnings in cutlery and cookware to surgical scalpels. Stainless is the preferred material in many health-care applications because it is non-porous and does not harbor bacteria (7) Due to its durability, harsh chemical disinfectants can be used without damage to the surface.
Possibilities extend from the familiar kitchen sinks to works of art, as show below. Architects often employ stainless steel as structural adornment, not only for the durability of the finish, but its aesthetic qualities as well. In fact Petronas Twin Towers, the tallest building in the world, is one such structure. Notice a majority of the face is stainless steel. Courtesy of Hot Stainless Steel (9) Ease of maintenance is a major advantage of stainless steel.
As mentioned, the chromium oxide barrier makes it ideal for architectural work, since it will not corrode in the environment. Indoors, nearly any chemical cleaner can be used to remove debris without staining or discoloration. When stainless is chosen for an application, the applied finish should be considered. After manufacturing, the mill applies one of three finishes. The mill finishes are listed below. (4) Finish Designation Description Available Forms No. 1 Dull and Mottled Plate, Bar No. 2 D Dull, Matte, Consistent Sheet, Strip No. 2 B Dull, Reflective Sheet, Strip No. 2 BA Highly Reflective Sheet, Strip These finishes are applied either mechanically or chemically.
A secondary plant can then apply a more refined finish at the request of the consumer. Achieved by using a fine-grit abrasive mechanical belt, these polished finishes are described below. Finish Designation Description Available Forms No. 3 Reflective, Course grit lines Plate, Sheet, Strip, Bar No. 4 Reflective, Finer grit lines Plate, Sheet, Strip, Bar Hairline Reflective, Fine parallel lines Plate, Sheet, Strip, Bar No. 6 Reflective, long parallel lines Plate, Sheet, Strip, Bar No. 7 Very reflective, Mirror w / lines Plate, Sheet, Strip, Bar No. 8 Mirror finish Sheet, Strip, Bar No. 9 (a. k. a. Special 8) Buffed mirror finish Sheet, Strip The buffing belt causes the grit or parallel lines mentioned above.
With buffing grains successively finer in each polish, the higher finishes do not show grit lines and can reach a smooth, mirror finish. The No. 9 polish is actually a No. 8 polish, but is nearly perfect showing no grit lines whatsoever. Produced by only Japanese manufactures, it is rare and comparatively more expensive. The up-front cost of stainless steel is usually greater than that of other materials.
Below is a price comparison of general (mild) steel, stainless steel and alternative materials. (7) Material Approximate Price ($/kg) 316 stainless 5. 0 - 6. 0 Redeamingly, the life cycle costs make stainless a cost-effective option. Maintenance costs are negligible and replacement is seldom necessary. After its usefulness is out lived, stainless steel can be resold to manufacturers to be re-smelted and sold. Homes constructed with a steel frame benefit from utility savings as well. An average steel home in Cathedral City, CA has utility costs of $ 41. 54 per month, compared to $ 71. 00 for a wood frame house. (8) It is thought that this is attributed to closer spaced joists in steel construction, providing better insulation. The utility savings quickly offset the 3 - 5 % construction cost increase.
Environmental issues are often thought to be the Achilles heel of steel applications. The contrary is actually true. Steel manufacturing companies have recently adopted environment-friendly philosophies. An excerpt from Avesta Steels website best exemplifies this attitude: (10) Avesta Sheffield's Group Policy for the Protection of the Environment states clearly that attention to environmental protection should be an integral part of the Groups activities. The responsibility for environmental issues has been delegated to the management of individual units. The aim is to achieve a better environmental performance than that required by legislation and other regulations in those countries where the Group operates.
Some of the important strategic objectives set out in the Groups Policy are: -To reduce the consumption of energy and raw materials. -To reduce the production of waste by recycling residual products and byproducts, as well as by other means. -To carry out comprehensive studies to assess the environmental consequences of new or modified processes prior to making such decisions. -To ensure that the environmental performance is audited internally -To assure compliance with environmental laws, directives and other legal requirements made by authorities, as well as with the Group's policy. -To co-operate with local authorities to assess potential risk and to establish contingency procedures for handling environmental incidents. The Avesta Group has made more than a politically correct statement; they have produced actual results as seen in the chart below: While the iron-ore used in steel production is strip-mined, Avesta, among others, is committed to researching safer and more effective mining techniques. Additionally, over 95 % of all discarded steel is recycled; making it the most reused material in the world. Of all steel produced, 30 % is actually recycled material. Advantages of stainless steel are undeniably persuasive. The capacity to create the vast variety of stainless steels translates to the formation of a product with virtually any desired properties.
A custom designable product ensures a growing demand for the employment of stainless steel in a wide array of fields. Rarely is such an aesthetically pleasing material utilized in surgical rooms, automobile factories, home kitchens, architectural adornments, and works of art simultaneously. The combination of strength, corrosion resistance, fire resistance, versatility and beauty of stainless steel has yet to be rivaled by any other material available today. Bibliography: Bibliography 1) Brockenbrough, R.
L. and Johnston, B. G. (1968) U. S.
S. Steel Design Manual. United States Steel Corporation, second printing, 2) Henn, F. Hart and Sontag, H. (1982) Multi-story Buildings in Steel Nichols Publishing Company, New York, Translation by Collins Professional and Technical Books, 3) The Steel Triangle: United States Steel Builds a Corporate Center United Steel Corporation. (1969) 4) Zahner, L. Williams (1995) Architectural Metals: A Guide to Selection, Specification, and Performance. John Wiley & Sons, Inc. 5) Lindbeck, John R. , Williams, Molly W. , and Want, Robert M. (1990) Manufacturing Technology Prentice Hall 6) International Iron and Steel Institute- http//: www.
world steel. org 7) Australian Stainless Steel Development Association- http//: web 8) Georgia Institute of Technology-School of Civil and Environmental Engineering- http//: web 9) Hot Stainless Steel Industries Sdn Bhd- http//: web 10) Avesta Sheffield Steel- http//: web 11) Artist Ulrich Paper. Report- http//: web 12) The Stainless Steel Industry of North America- http: web
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Research essay sample on Stainless Steel Wide Array
