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Until now the estimation of rolling bearing life has been based on engineering models that consider an
equivalent stress, originated beneath the contact surface, that is applied to the stressed volume of the
rolling contact. Through the years, fatigue surface–originated failures, resulting from reduced lubrication or
contamination, have been incorporated into the estimation of the bearing life by applying a penalty to the
overall equivalent stress of the rolling contact. Due to this simplification, the accounting of some specific
failure modes originated directly at the surface of the rolling contact can be challenging. In the present
article, this issue is addressed by developing a general approach for rolling contact life in which the surfaceoriginated
damage is explicitly formulated into the basic fatigue equations of the rolling contact. This is
achieved by introducing a function to describe surface-originated failures and coupling it with the traditional,
subsurface-originated fatigue risk of the rolling contact. The article presents the fundamental theory of the
new model and its general behavior. The ability of the present general method to provide an account for
the surface–subsurface competing fatigue mechanisms taking place in rolling bearings is discussed with
reference to endurance testing data.
Mechatronics simplifies traditional engineering concepts across most
industrial segments. By combining mechanical, electrical and computer technology into a single, integrated solution, products become systems
that are more efficient, reduce
operator error and cost less to
manufacture.
The improvement of the energy efficiency of industrial gear motors and gearboxes is a
common problem for many gear unit manufacturers and end-users. As is typical of other
mechanical components, the radial lip seals used in such units generate friction and heat,
thus contributing to energy losses of mechanical systems. There exist today simulation
tools that are already helping improve the efficiency of mechanical systems — but accurate models for seal frictional losses need to be developed. In this paper SKF presents an engineering model for radial lip seal friction based on a physical approach.
A four-point contact ball bearing makes it easy to simplify
machine designs that combine radial, thrust and moment
loads, because it can handle all three simultaneously. They
are primarily used for slow-to-moderate-speed applications,
or where oscillatory movement is predominant.
Engineers typically learn that the bearing L10 life can be estimated using the so called “C/P method” — or the “basic rating life” of
the bearing, a method rooted in the 1940s. Major developments have since led to the “modified rating life,” released in ISO 281:2007,
which includes the aiso life modification factor. In this paper a succession of equations used for bearing life ratings are reviewed, and
current bearing life rating practices are discussed in detail. It is shown that — despite the introduction more than 30 years ago of
the adjustment factor of the basic rating life, and the standardization in 2007 of the aiso modification factor — use of these improved
calculation methods are not practiced by all engineers. Indeed — many continue referring to the old model as a way of seeking
compliance with existing, established practices.