Alloys, paper machines

Alloy development for suction roll shells has barely kept pace with the ever-increasing performance demands and white water corrosivity in paper machines. Bronze, martensitic stainless steels, early-generation duplex stainless steels, precipitation hardening stainless steels, and later-generation duplex stainless steels have all been used for the manufacture of suction roll shells. Today, the preferred materials for suction roll shells in severe service are duplex... 

Cyclic anodic polarization procedures based upon ASTM G5 (Reference Test Method for Making Potentiostatic and Potentiodynamic Anodic Polarization Measurements) have been used to evaluate the localized corrosion resistance of stainless steel alloys in paper machine white waters. The difference between the open circuit or naturally occurring corrosion potential and the pitting breakdown potential of various materials has been reported by many investigators [lO-Id]. Bowers [14] called the difference between the breakdown potential and the potential of the cathodic/anodic current reversal the margin of safety. He also noted the effect of the sulfate to chloride concentration ratio on localized corrosion of Types 304 and 316L stainless steels, These results permitted alternative materials of construction to be ranked and their limits of resistance to be defined. 

Significant research and testing has been devoted to corrosion fotigue resistance of paper machine suction roll shells [34]. Unfortunately, the results from the various tests used by the various manufacturers have been difficult to compare. Furthermore, their tests do not predict actual performance in the paper machines and cannot be related directly to roll loads or geometries. Experience gained over a long period of time has remained the best guide to selection of suction roU alloys. The tests used are summarized below. 

There are transition metals in many of the products that people use in daily life. Some of these metals have obvious roles, such as the coin metals of gold, silver, and copper. Iron, which makes up 90% of all metal that is refined, or purified for use, is found in everything from tools to paper staples to washing machines. The most important iron product is steel, an iron-based metal alloy. Most steel made for manufacturing purposes is iron alloyed with the element carbon, which makes the steel much harder than iron alone. Several other transition metals are alloyed with iron to make different kinds of steel for different uses. Vanadium, niobium, molybdenum, manganese, chromium, and nickel are all used in steel alloys. For instance, chromium and nickel are alloyed with iron to create stainless steel, a type of steel that does not rust and is used in surgical instruments, cookware, and tools. Some famous landmarks such as the top of the Chrysler skyscraper in New York City and the St. Louis Gateway Arch are covered in stainless steel. 

One of the most important uses of nickel is in making alloys. About 86 percent of the primary nickel used in the United States in 2008 was used to make alloys. About half of that amount went into stainless steel. Stainless steel is common to household appliances (like coffee makers, toasters, and pots and pans), kitchen sink tops and stoves, and medical equipment (X-ray machines, for example). It is also used to make heavy machinery and large containers in which large-scale chemical reactions are carried out. Artists sometimes use stainless steel in sculpture because it does not rust easily. Stainless steel is important to the food and beverage, petroleum, chemical, pharmaceutical (drug), pulp and paper, and textile industries. 

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