Introduction
Th e ISO defi nition of a full-complement
bearing states that the bearing does
not have a cage. When that defi nition
was written, it was not technically possible
to have a full-complement bearing
with a cage. But SKF’s new high-capacity
cylindrical roller bearing combines
the load-carrying capacity of a fullcomplement
bearing with the benefi ts
of a bearing with a cage (Fig.1).
History
In 1960, when SKF introduced the
E-design cylindrical roller bearing, it was seen as an important step in the
development of standard cylindrical
roller bearings. Th e bearing was based
on standardized boundary dimensions;
it was the internal macro geometry that
made it diff erent from other bearings.
SKF engineers had found a way to optimize
the number of rollers, the roller
size and the thickness of the inner and
outer rings, leading to an increased loadcarrying
capacity and rated bearing life.
In the 1980s, SKF engineers went
on to develop the EC design, which had
a higher thrust load-carrying capacity, and then the SKF Explorer cylindrical
roller bearings, which were launched in
2002. Th e SKF Explorer bearings benefi
ted from improved material and an
improved heat-treatment process, but it
was mainly the improved micro geometry
that gave these bearings a competitive
advantage. Using knowledge gained
over the years, together with proprietary
software, engineers were able to maximize
the eff ects of the lubricant fi lm
build-up and decrease the friction within
the bearing.

Load-Carrying Capacity
Load-carrying capacity is calculated
using formulas in the standards ISO 76
and ISO 281. According to these formulas,
there are two ways to increase
the load-carrying capacity of a bearing
while maintaining standardized boundary
dimensions:
? Increase the dimensions of the
rollers and maintain the same number
of rollers; or
? Increase the number of rollers and
maintain the roller dimensions.
From a practical point of view, the
fi rst method leads to a technical problem.
Increasing the size of the rollers
will reduce the thickness of the inner
and outer rings and the width of the
side fl anges. Th is has no eff ect on the
theoretical load-carrying capacity calculation.
In reality, however, these changes
will reduce ring stiff ness and fl ange
strength. For the end user, this means a
higher risk of micro movements in the
bearing seating, which causes fretting
corrosion or ring creep. Larger rollers
also increase the risk of smearing damage,
due to their higher moment of inertia.
All in all, the fi rst method, though
impressive on paper, cannot be considered
an improvement. Th e second
alternative, however, does off er viable
alternatives. Based on the former improvements
of the macro and micro
geometries, the roller dimensions and
wall thickness of the bearing rings can
remain unchanged, compared with the
dimensions of the proven 45-year-old
E-design.
However, increasing the number of
rollers within a defi ned envelope is not as easy as it sounds. To make this new
bearing a reality, SKF engineers and scientists
needed to work through a number
of key issues.

“Add More Rollers”—
Easy to Say, Hard To Do
Th ere are two types of rolling element
bearings: caged bearings and fullcomplement
bearings. Full-complement
bearings, which do not use a cage, are
fi tted with a maximum number of rollers.
In this type of bearing, the rollers are
in direct contact with each other, which
causes sliding and increases friction and
heat generation. Under certain circumstances,
this leads to wear and premature
bearing failure, making them unacceptable
for applications where there are
higher speeds. Th is makes a cage essential
for higher-speed applications.
Medium- and large-size cylindrical
roller bearings are equipped as standard
with a machined brass cage, mainly to
keep the rollers from making contact.
Th e cage bars, which usually are orientated
around the roller pitch circle (the
connecting circle of the mid-points of
all rollers), have a defi ned cross section
designed for maximum strength, but
they reduce the number of rollers theoretically
possible. However, by moving
the cage bars away from the roller pitch circle, the rollers can be placed closer to
each other so that more rollers can be
incorporated into the bearing (Fig. 1).
To do this, SKF developed a new window-type
steel cage.
Th is resulted in two basic cage designs—a
JA-style, outer-ring shoulderguided
cage (Fig. 2) and a JB-style, inner-ring
shoulder-guided cage (Fig. 3).

More than Cage Bars
Larger window-type steel cages are
not new. Cage diameters up to 1,300
mm have been used in large-size, tapered
roller bearings for years, with
excellent results. Th e development was
based on the same material thickness as
a comparable tapered roller bearing cage,
using a shoulder guidance of the cage to
provide better performance for occurring
radial accelerations and shocks. But
the development team was faced with
a number of issues. First and probably
most important was how to maximize
cage strength while enhancing the formation
of a lubricant fi lm. Th e team also
needed to fi nd a way to minimize stress
concentrations in the transition between
the cage bars and side rings.
Using proprietary SKF software and
knowledge gained from years of experience,
the team determined that it could
minimize stress concentrations in critiapplied speed corresponds to the limiting
speed of the catalog bearing.
Th e tests were conducted under two
diff erent lubrication conditions. In one
case, oil with a proper viscosity to provide
a suffi cient oil fi lm (κ > 1.5) was
used. In the other case, a low-viscosity
oil to simulate an inadequate lubrication
condition (κ < 0.5) was used. When all
the tests were completed, a 1,000-hour
duration test was conducted. During the
tests, all critical performance parameters
such as temperatures, loads, speed and
vibration levels were monitored continuously.
(Editor’s note: Th e eff ectiveness
of a lubricant is primarily determined by
the degree of separation between the rolling
contact surfaces. If an adequate lubricant
fi lm is to be formed, the lubricant must have
a given minimum viscosity when the application
has reached its normal operating
temperature. Th e condition of the lubricant
is described by the viscosity ratio κ as the
ratio of the actual viscosity ν to the rated
viscosity ν1 for adequate lubrication, both
values being considered when the lubricant
is at normal operating temperature.)