Aluminum Made Harder Than Steel?

By William Gunnar

Anodizing is a common process in the finishing industry for electrolytic treatment of metals to form stable films or coatings on the metal's surface. Anodized aluminum or magnesium, for example, are typically associated with functional coatings like hard anodize, also known as 'hardcoat'.

In this process, unlike electroplating, the work is made the anode, and its surface is converted to a form of its oxide that is integral with the metal substrate.

Generally, it's agreed that the ceramic oxide coating consists of two layers:

The initial layer, which forms right at the surface, is called the barrier layer. It is a comparatively thin, dense, and nonporous form of aluminum oxide.

Next form the outer, heavier layers of the anodic coating. They are more porous and are stacked somewhat like parallel tubes extending through the layer, from the outermost surface down nearly to the barrier layer.

It's important to recognize that, unlike plating, whose thickness accumulates by depositing more and more onto the outermost surface, the anodic layers form by oxygen transfer from the underlying aluminum surface and force existing layers outward.

This means that oxides newest forming are always located between the metal surface and the last, most recently formed alumina oxide. Consequently, the greater the thickness, the lower the density of coating at the outermost surfaces, based on longer solvent action of the electrolyte. Consequently, for maximum wear resistance, more is not always better.

A factor to consider in your design, such as close tolerance bores, bearing diameters, dowel holes or threads, is that the resultant growth portion of the coating is a fractional percentage of the total coating thickness. Hard anodize, for example, will typically result in 50% penetration and 50% buildup.

Keep in mind that buildup is normal or perpendicular to the surface and sharp corners should be rounded to avoid chipping.

To anodize aluminum, one of the most important factors influencing oxide formation is composition of alloy. Reaction of all the various possible alloying or impurity constituents can result in coating voids or disruptions, while other constituents may themselves oxidize in the conditions of anodizing and lessen the intended properties.

Depending on electrolyte, a wide range of thickness can be obtained. Coatings produced in sulfuric acid electrolyte, for example, can be as low as 0.0001 inch (2.5 um) to as high as 0.003 inch (75 um).

Anodic coatings have a definite cellular structure. Imagine individual cells with pores down their centers totaling millions per square inch. This makes for excellent dyeing and sealing. Sealing processes make the coatings non-absorptive and include, immersion in boiling de-ionized water, steam, or nickel acetate.

De-ionized water is often preferred as a sealing solution for its ability to react with anhydrous aluminum in the outer layers of the film. A mono-hydrate of the oxide is formed, which occupies greater volume than the alumina from which it was formed. The result is a reaction to close down and plug the pore structure.

Structures of hard anodizing can be supplemented with a variety of materials, including Teflon (PTFE) waxes, oils and other compounds, to lower friction or add release (nonstick). And because these compounds penetrate the ceramic, their added surface growth is oftentimes negligible.

Want to make a better product? Or simply, make it faster, more reliably, with less scrap? Where ever your surface engineering takes you William Gunnar shares your goal in surface performance!

Article Source: http://EzineArticles.com/?expert=William_Gunnar

Bethlehem Steel- The Steel That Built America

By Adam Singleton

The doors to the steelworks in Bethlehem, Pennsylvania closed for the last time in 1995, bringing to an end 140 years of steel-making in the town. Although no longer in its spiritual home, Bethlehem Steel continues to produce Steel, but its major production facility is now based in Burns Harbor, Indiana. The company has had its ups and downs, has been involved in providing steel for the construction of many railroads, bridges and iconic buildings throughout America and was the forerunner in the production of the steel girders used to build skyscrapers.

The first steel produced in Bethlehem was at the Saucona Iron Company, opened in 1857. Four years later the company changed its name to the Bethlehem Iron Company and in 1863 started mass production of iron railroad rails, used in the building of the Transcontinental Railroad.
Over the next forty years contracts to supply steel were agreed with the US Navy, and by the time that Charles M. Schwab was appointed chairman in 1904 Bethlehem Steel Corporation not only had a huge plant in South Bethlehem, but ironworks in Cuba and shipyards on both US coasts.

In 1908 the company started production of wide-flange structural section steel, leading to a building revolution; those sections being used in the new phenomenon of skyscraper construction. Five years later Bethlehem Steel acquired the Fore Shipbuilding Company in Quincy, Mass. to become one of the country’s largest shipbuilders.

World War I provided Bethlehem Steel with a great opportunity to expand. At the start of the conflict the company had an annual production capacity of 1.1 million tons and employed 15,600 workers. By 1925, after supplying armor, ships, ordnance, guns and munitions for the US and Allied Forces during and immediately after the war, annual production grew to 8.5 million tons and the company’s workforce had grown to 60,000.

In the early thirties Bethlehem Steel continued to grow through acquisition, buying steel companies on the Pacific coast as well as McClintic-Marshall Corp., a major bridge and building construction company. This was the golden era for American construction and Bethlehem Steel was responsible for such landmark constructions as: the Golden Gate Bridge, U.S. Supreme Court, Rockefeller Plaza, Waldorf-Astoria and the George Washington Bridge. During World War II Bethlehem Steel shifted all its production into military hardware, employing close on 300,000 workers of which 180,000 were directly involved in ship-building. Post-war, the company returned to producing steel for US domestic projects, as well as the military, and continued to thrive. The 1960s saw steel imported to the USA reaching record levels, but Bethlehem still home-produced steel for such iconic structures as Madison Square Garden, Newport Bridge and the second Delaware Memorial Bridge.

In 1973 Bethlehem Steel reported an income of $207 million, producing record levels of 23.7 million tons of raw steel and 16.3million tons of finished steel. The company continued to thrive, but in the early 1980s imported steel was making more of an impact, which forced a radical restructure of Bethlehem Steel, resulting in a halving of the workforce over five years in the mid-80s. Consolidation followed over the next ten years and reluctantly the production facility at Bethlehem – where it all began – was shut down in 1995.

Today, Bethlehem has recovered from the loss of its steelworks and is undergoing an economic and cultural renaissance. Hotels in Bethlehem once used by those who had business at the steelworks are now re-inventing themselves as tourist and conference centers. The steel may be long gone in Bethlehem, but the entrepreneurial spirit of its citizens is alive and well.

Adam Singleton is an online, freelance journalist and keen amateur photographer from Scotland. His interests include traveling and hiking.