Wear Protection
Fig. 3. Magotteaux’ Xwin wear timeline, from new to end of life after 2,117,222 tons and 34,800 hours.
being pulverisered. Te greater the alloy resistance to wear, the longer the grinding element lifetime and conversely, the more abrasive the coal being ground, the shorter the grinding element lifetime. Te primary constituents of coal are
fixed carbon, volatile matter, moisture and ash. Te greatest influence to the grinding element wear life is the abrasivity of the coal, which is a function of the ash content in the coal or more importantly, the silica (SiO2
) content in the ash. Moisture can also be a factor,
particularly if it requires higher amounts of air-flow into the mill that, in the presence of high ash or silica, increases the abrasion on the grinding elements. For this reason low rank coals such as sub- bituminous, lignite or brown coals are the most aggressive and the biggest challenge for grinding element wear life. Indian sub- bituminous and lignite coals are typically the most abrasive due to ash contents as high as 60% and silica in ash as high as 60%. Grinding element lifetimes in India are measured in hours not months. Over the years the primary goal of both utility owners and material suppliers alike
has been for grinding elements with ever increasing wear resistance. Wear-resistant technology advancement has been in the direction of high-chromium, white iron alloys of various compositions; the primary goal being that of increasing alloy hardness while at the same time maintaining the ductility and toughness. In recent years, new wear-resistant technologies, referred to as metal matrix composites, have been developed. Tese composite technologies, dedicated to specific applications, are manufactured by means of a unique casting process. A metal matric composite is made up of ceramic and metal of a certain thickness and design. Te ceramic is located on the external surface of the casting, precisely where the castings tends to wear out. Te resulting product is a one-piece casting that delivers the extreme wear resistance of ceramic with the ductility and durability of high chrome metal. Te interlocking matrix of high
chromium metal with granularised ceramic creates a composite alloy that is no more
susceptible to cracking than a standard high chromium mono-metal casting. Metal matrix composite technologies surpass the invisible ceiling of high chrome mono-metal and high chrome hardsurfacing solutions and permit wear resistant components to achieve new levels of hardness, wear resistance and lifetime. Magotteaux pioneered the
manufacturing of composites in the early 1990s with its Xwin technology, which has been used in severe service applications ever since. It has been widely used for the supply of grinding elements in coal-fired power stations throughout the world. It is greatly extending the grinding element lifetime in coal pulverisers. Within its MMC family, Magotteaux
recently launched its neoX product line. Te neoX line is designed for severe duty applications in which maximum wear resistance is required. Testing has shown neoX grinding elements to perform between 50-100% better than Xwin castings. l
For more information ✔ at
www.engineerlive.com/ipe
Xwin and neoX are patented Magotteaux technologies.
Tis article is based on a presentation given at PowerGen Asia; Kuala Lumpur, Malaysia in September 2014.
Ken Birchett is with Magotteaux International, Vaux-sous-Chèvremont, Belgium.
www.magotteaux.com
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