Schaeffler has developed a novel high-performance steel it claims can overcome two commonly conflicting objectives in rolling bearing technology: the need for the material to be hard, wear-resistant and capable of supporting heavy loads; and the need for the material to be able to tolerate deformations caused by hard foreign particles during overrolling.
Schaeffler’s carbonitrided Mancrodur high-performance steel resolves these conflicting objectives by offering both a greater surface hardness and a higher ductility compared with other types of steel. This combination results in the operating life of rolling bearings made from Mancrodur being twice as long, particularly in applications with poor lubrication conditions or contamination.
“The new technology is especially relevant to Australia because of the types of applications typically found in heavy processing industries here,” says Martin Grosvenor, Industrial Sector Manager, Schaeffler Australia.
“The type of mixed friction and contamination problems that Mancrodur overcomes typically occur in heavy-duty industries such as steel, mining and rail, where reductions in bearing operating life or premature failure can have disastrous effects on downtime and costs.”
“Additionally, Mancrodur's significantly higher load carrying capacity, and its insensitivity to poor lubrication conditions and contaminants, make it an outstanding material choice for bearings in transmissions in agricultural and construction machinery, automobiles and trucks as well as ships’ propulsion systems.”
Carbonitrided Mancrodur has an exceptional combination of characteristics that make this rolling bearing material particularly suitable for extremely demanding environments.
By using a combination of carbonisation and nitriding for the heat treatment, the surfaces of Mancrodur bearings are, on the one hand, hard and wear-resistant. On the other hand, fine, spheroidal carbides form in carbonitrided Mancrodur, which are uniformly distributed in the material and are less concentrated at the grain boundaries. This reduces the risk of localised weak spots. The raceway surface is therefore not only harder and more wear-resistant but also more ductile.
According to Martin Grosvenor: “Mancrodur is able to level out ridges in the raceway caused by embedded foreign particles, despite its high surface hardness. Material fatigue is considerably reduced, the formation of cracks prevented and the operating life significantly extended.”
“In applications with poor lubrication, the local temperature of the material increases due to increased friction. Compared to other steels, the reduction in strength in Mancrodur due to temperature is less, which considerably reduces the danger of local overloading due to inadequate lubrication.”
Under normal lubrication conditions (full lubrication), carbonitrided Mancrodur increases basic load ratings by 30% compared with standard materials, which equates to an increase in the nominal rating life of 240%. A rating life up to six times longer has been verified in tests when using carbonitrided Mancrodur with full lubrication.
In the harsh and demanding environments encountered in railway technology, mining and the steel industry, tests in actual adverse conditions are vital. The first test bearings from the four-row carbonitrided Mancrodur FAG tapered roller bearing range have been installed at a steel producer in the work rolls on a hot strip mill. The test bearings have achieved twice the standard operating life in this application.
Mancrodur is particularly suitable where greater machine capacity is required under tough operating conditions. In addition to the application areas already tested in steel works, this new high-performance steel has proven itself to be the material of choice in areas such as highly loaded axlebox bearings in freight cars, planetary bearings in wind turbines and bearings in pumps and compressors. The trend towards downsizing means that, in many machines, the bearing supports are approaching the limits of their load carrying capacity.
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