Timken Super Precision Bearings for Machine Tool Applications

A
ENGINEERING
SELECTING THE APPROPRIATE MACHINE
TOOL BEARING
PRECISION TAPERED ROLLER BEARINGS
Angularity (K-factor)
The angled raceways allow the tapered roller bearing to carry
combinations of radial and axial loads. Since load capacities are
intrinsically linked to the bearing stiffness, the selection of the most
appropriate tapered roller bearing cup angle can help optimize the
bearing selection for a given application.
The angularity of the bearing is often described by a factor called
“K.” This factor is the ratio of basic dynamic radial load rating (C 90)
to basic dynamic axial load rating (C a90) in a single-row bearing.
For a bearing with a ribbed cone (the most common design), it is a
function of the half-included cup angle (α) and can be found listed
with the geometry factors in the catalog appendix. The smaller the
K factor, the steeper the bearing angle. (See Figure 12).
Size
Shallow angle for
heavy radial load
K = C 90 = 0.39
tan (α)
C a90
Fig. 12. Designs to support radial and axial loads in any combination.
Optimizing stiffness is often a customer’s primary design goal
when choosing a tapered roller bearing. This usually results in the
determination of a desired spindle diameter. Therefore, meeting a
given envelope narrows the choices for the tapered roller bearing
size selection.
Steep angle for
heavy axial load
Speed
The next most common criteria are the speed capability/limitations
of the remaining potential candidates. This can be challenging, since
the speed rating of a tapered roller bearing is a function of its internal
geometry, the axial setting under operation conditions, the lubricant
used and method of delivery. There is a speed guideline matrix on
page 54 that will aid in determining the speed rating and suggested
lubricant/delivery method for your tapered roller bearing application.
Included in the appendix is a table listing the G 1 and G 2 factors that
can be utilized to compare the relative speed capability and heat
generation between the various tapered roller bearing selections.
Please refer to the topics on permissible operating speeds and heat
generation for further discussion.
Construction
Tapered bearings are uniquely designed to manage both axial and
radial loads on rotating shafts and in housings. The steeper the cup
angle, the greater the ability of the bearing to handle axial loads.
Customized geometries and engineered surfaces can be applied
to these bearings to further enhance performance in demanding
applications.
Timken has designed a variety of tapered roller bearing types to
specifically address various machine tool requirements. Each of
these designs is best suited to a specific set of application needs.
The key features of each type are highlighted below:
TS or TSF Bearing
• Most widely used type of tapered roller bearing.
• Minimum precision grade Level 3 or C (ISO P5).
• TSF has a flanged outer ring to facilitate axial location.
• Available in most bearing series.
• Used in rotating shaft applications.
TSMA Bearing
• Axial oil manifold with axial holes through rib.
• Suitable with circulating oil or oil mist lubrication.
• Centrifugal force distributes oil to critical rib/roller end
contact.
• Available in most precision grades.
• Available in most bearing series.
• Used in rotating shaft applications.
24 TIMKEN MACHINE TOOL CATALOG