SCHATZ Linear Motion Products
Guide Wheel Bearings | Linear Motion Components

BEARING ENGINEERING

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 609 ksi. 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.

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:

L₁₀ = 16,667/S * (Cr/Fr + ZFa)³

Where:
Fr = Applied Radial Load
Z = Factor
Fa = Applied Axial Load
S = Bearing Speed (RPM)
L₁₀ = Life (hrs.)
Cr = Schatz Bearing
Dynamic Load Rating (see table to above)

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.