Brochure

Mtd. Ball
Bearings
G-223
®
Mounted Ball Bearing Engineering Section
High Speed Applications
Applications where the speed is in the range of 80-
100% of the maximum speeds listed in the rating
tables on pages G-230 to G-233, should be reviewed
and given special consideration.
Modications to consider include:
• Shaft size should be controlled to specications
listed in the installation section. See tables above.
• SKWEZLOC Locking Collar and double lock are
the preferred lock systems for high speed appli-
cations.
• High quality lubricants should be used.
• Grease should be added more frequently and
in small amounts. See Page G-254.
• Care in mounting techniques should be exer-
cised. See Page G-246 to G-253.
Bearing Life In Oscillating
Applications
The equivalent rotative speed (ERS) is used in life cal-
culations when the bearing does not make complete
revolutions during operation. The ERS is then used as
the bearing operating speed in the calculation of the
L10 (Rating) Life. The formula is based on sufcient
angular rotation to have roller paths overlap.
ERS = Equivalent Rotative Speed
N = Total number of degrees per minute
through which the bearing will rotate.
ERS =
In the above formula, allowance is made for the total
number of stress applications on the weakest race per
unit time, which, in turn, determines fatigue life and
the speed factors. The theory behind fretting corro-
sion is best explained by the fact that the rolling ele-
ments in small angles of oscillation retrace a path over
an unchanging area of the inner or outer races where
the lubricant is prevented by inertia from owing in
behind the roller as the bearing oscillates in one direc-
tion. Upon reversal, this small area of rolling contact is
traversed by the same roller in the dry state. The fric-
tion of the two unlubricated surfaces causes fretting
corrosion and produces failures which are unpredict-
able from a normal life standpoint.
With a given bearing selected for an oscillating appli-
cation, the best lubrication means is a light mineral oil
under positive ow conditions. With a light oil, there is
a tendency for all areas in the bearing load zone to be
immersed in lubricant at all times. The full ow lubri-
cation dictates that any oxidized material which may
form is immediately carried away by the lubricant, and
since these oxides are abrasive, further wear tends to
be avoided. If grease lubrication must be used, it is
best to consult with either the bearing manufacturer
or the lubricant manufacturer to determine the best
possible type of lubricant. Greases have been com-
pounded to resist the detrimental effect of fretting
corrosion for such applications.
Static Load Rating
The “static load rating” for rolling element bearings is
that uniformly distributed static radial load acting on a
non-rotating bearing, which produces a contact stress
of 580,000 psi at the center of the most heavily loaded
rolling element. At this stress level, plastic deforma-
tion begins to be signicant. Experience has shown
that the plastic deformation at this stress level can be
tolerated in most bearing applications without impair-
ment of subsequent bearing operation. In certain ap-
plications where subsequent rotation of the bearing is
slow and where smoothness and friction requirements
are not too exacting, a higher static load limit can be
tolerated. Where extreme smoothness is required or
friction requirements are critical, a lower static load
limit may be necessary.
Minimum Bearing Load
Skidding, or sliding, of the rolling elements on the
raceway instead of a true rolling motion can cause
excessive wear. Applications with high speeds and
light loading are particularly prone to skidding. As
a general guideline, rolling element bearings should
be radially loaded at least 1% of Basic Dynamic Rating
for ball bearings. For applications where load is light
relative to the bearings dynamic load rating, consult
Application Engineering for assistance.
Load Ratings and Life Continued
N
360