The Journal of Industry and Technology

Industrial Analytical Instrumentation

Euro Technology

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Precision bearings and condition monitoring

Mancrodur high performance steel doubles life
of Schaeffler axlebox bearings for rail applications

By combining its proprietary Mancrodur case hardening steel with a special hardening process, Schaeffler's new Class K TAROL axlebox bearings offer a 30% increase in load-carrying capacity, which effectively doubles the operating life without taking up any additional space.

Precision bearing manufacturer Schaeffler's proprietary Mancrodur rolling bearing steel, in combination with carbonitriding (a case hardening process that uses carbon and nitrogen), is already proving successful in wind turbines that are subjected to high loads, as well as in steel mills.
With its new High-Capacity TAROL Class K (HCT-K) tapered roller bearings that are used in heavy freight rail traffic, Schaeffler has expanded its range of applications for this high-performance steel. Since April 2016, Mancrodur bearings have been undergoing rigorous testing under actual operating conditions at an Australian customer, and the results have been very promising. According to Alexander Käbe, Project Manager High Capacity TAROL at Schaeffler: "Even when subjected to extreme loads and shocks, this bearing consistently demonstrates its high performance capabilities. Compared to the case hardening steel that is typically used in these applications, we are seeing significant performance gains with bearings made from Mancrodur."

To help rail operators immediately achieve significant gains in the operating life of their fleets and to substantially lower their total cost of ownership (TCO), existing AAR Class K steering knuckles can easily be fitted with Schaeffler's new HCT-K axlebox bearings.
Greater surface hardness, but improved ductility
Compared to standard materials, Mancrodur's load-carrying capacity is approximately 30% higher. As a result, the nominal rating life of Mancrodur is more than twice as long. Combining a high-performance steel with carbonitriding results in the highest load-carrying capacity for a given design envelope. From a materials-engineering perspective, this means this development represents the current state of the art with respect to bearing performance and efficiency. Carbonitriding generates fine carbides and carbonitrides that are evenly distributed throughout the material. This results in a raceway surface that is harder and more resistant to wear. In addition, the heat treatment process increases the ductility of the raceway surface. Consequently, the material is less sensitive to contamination-induced overrolling.

In summary, compared to conventional case hardening, carbonitriding produces a material with high surface hardness
and increased ductility. But only the combination of these two characteristics result in a significant increase in fatigue life.

TAROL bearing assembly: designed for heavy freight traffic
In addition to the new material, Schaeffler development engineers have added a number of other features to ensure that the HCT-K bearings can reliably handle millions of kilometres of use in heavy goods traffic. These innovations include an inner ring that is heat stabilised up to 200°C; a cage made from glass fibre-reinforced polyamide; and a bearing assembly that is fitted with extremely low-friction cartridge seals on both sides. To ensure a reliable automated mounting process, the bearing also features a support ring.

Schaeffler in profile
Schaeffler with its product brands INA, LuK and FAG is a leading global provider of rolling bearing and plain bearing solutions and of linear and direct drive technology, as well as a renowned supplier to the automotive industry of high-precision products and systems for engines, transmissions and chassis. The group of companies with operations around the world generated revenue of approximately 11.2 billion euros in 2013. With around 79,000 employees worldwide, Schaeffler is one of the largest German and European technology companies in family ownership. With approximately 170 locations in 49 countries, Schaeffler has a worldwide network of manufacturing locations, research and development facilities, sales companies, engineering offices, and training centers.

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