BEARING ENGINEERING
Schatz Double V Guide Wheel Load Ratings
Basic Load Ratings
Basic Dynamic Radial Load Rating Cr
Schatz Guide Wheel basic dynamic radial load ratings are the radial bearing loads
that will give a basic rating life of 1,000,000 revolutions. The basic dynamic
load ratings have been determined in accordance with the methods prescribed by
ISO, AFBMA, and ANSI.
Basic
Static Radial Load Rating Cor
Basic static radial load rating is the static radial load that creates
a maximum Hertzian
contact stress at the center of the most heavily loaded ball/raceway
contact of 609ksi.
Under this stress, a permanent deformation of rolling element and
raceway will occur.
The depth of the deformation is approximately .0001 times the diameter
of the ball.
Figure 1: Guide Wheel Bearing Under Radial Load
Basic Static Axial Load Rating Coa
Basic static axial load rating is the static axial load that creates
a maximum Hertzian contact stress at the center of the most heavily
loaded ball/raceway contact of 609ksi. Under this stress, a permanent
deformation of rolling element and raceway will occur. 
The depth
of the deformation is approximately .0001 times the diameter of
the ball. For a guide wheel bearing, the axial load is applied
through the V-shaped outer ring and mating guide rail. As shown
in figure 2, this axial load will induce a reactive radial load
and moment load.
Figure 2: Guide Wheel Bearing Under Axial Load
Bearing Fatigue Life
The fatigue life of a guide wheel bearing is defined by the number of revolutions the bearing will operate before the first signs of fatigue occur. The L10 life is the basic rating life in hours that 90% of a sufficiently large group of apparently identical bearings will operate before the first signs of fatigue appear.
Use the formula below to calculate L10 life for bearings operating under radial and axial load as shown:
Life Adjustment Factors
Many life adjustment factors can be applied to the calculated bearing life as stated above. These factors are simply multiplied by the bearing life to determine the final expected operating life of the bearing.
L10 (calculated)*A1*A2*A3 = Adjusted Bearing Life
The three life adjustment factors that Schatz recommends using are:
A1 – life adjustment factor for reliability
A2 – life adjustment factor for material
A3 – life adjustment factor for lubrication
Schatz Double V Guide Wheel Lubrication and Selection Guide
Reliability (A1)
All formulas are based on an L10 life. If a different
life needs to be calculated, use the following
table for the adjustment factor:
Material (A2)
There are several material options for use in linear guide wheel
bearings. The following chart
shows the life adjustment factors for the materials offered:
Lubrication (A3)
Lubrication and the presence of an elasto-hydrodynamic lubrication
film is critical to achieving
proper bearing life. Please consult the Schatz Engineering department for information
on determining
the lubrication factor for a specific application. While the calculation for
the specific lubrication film
thickness is complex, in general, choosing a grease with a base oil that has
a high viscosity is more
suitable for low to moderate speed and high load applications. Alternatively,
grease with a low
viscosity base oil is more suitable for high speed applications with light to
moderate loads.
Schatz’s standard grease for the guide wheel bearings is Chevron
SRI, which is a good general
purpose grease with good water resistance. The following is a table
of other greases that can
be used in guide wheel applications.
