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SCHATZ Linear Motion Products
Guide Wheel Bearings | Linear Motion Components

BEARING ENGINEERING

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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.

radialload

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.

Schatz Bearing Basic P/N Cor (lbs.) Coa (lbs.)
W1 320 145
W2 750 300
W3 1,350 600
W4 2,750 1,055

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.

axiallload
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.

Schatz Bearing
Basic P/N
Cr (lbs.) Z
W1 500 2.20
W2 910 2.50
W3 1,740 2.25
W4 3,260 2.45

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

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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:

Reliability (%) 90 ( L10 ) 95 ( L5 ) 96 ( L4 ) 97 ( L3 ) 98 ( L2 ) 99 ( L1 )
Factor (A1) 1.00 .62 .53 .44 .33 .21

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:

Material Type 52100 440C Schatz EMS 138
Factor (A2) 2.2 .6 4.2

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.

Name Manufacturer Mil-SPEC Lube Type Temperature Range (˚F) Oil Type Thickener Type Color Viscosity @ 100˚F Viscosity @ 210˚F Characteristics/ Application
Aeroshell 22 Shell Oil Co. MIL-PRF-81322 Grease -80 to 350 SH Microgel Dark Grey 30.5 cSt 5.7 cSt General purpose
Aeroshell 33 Shell Oil Co. MIL-PRF-23827 Grease -99 to 250 SH/Ester Lithium Green 14.2 cSt 3.4 cSt Aircraft, Gen. purpose, Corrosion-inhibiting
Aeroshell 7 Shell Oil Co. MIL-PRF-23827 Grease -100 to 300 Synthetic Clay Amber 10.3 cSt 3.1 cSt Wide temperature range
Aeroshell 22 Shell Oil Co. Grease -65 to 275 Mineral Lithium Amber 189 cSt 15.6 cSt General purpose
Asonic HQ 72-102 Kluber Grease -40 to 356 Ester Polyurea Beige 100 cSt 12 cSt High temperature
Beacon 325 Exxon Corp. MIL-PRF-23827 Grease -65 to 250 Diester Lithium Light Tan 12 cSt General purpose
Braycote 815 Castrol Oil -100 to 400 PFPE 148 cSt 45 cSt Wide temperature range, Chemically inert
Braycote 601 EF Castrol Grease -112 to 400 PFPE Off-White 148 cSt 45 cSt High-vacuum grease
Braycote Micronic1613 Castrol Grease -99 to 400 PFPE Off-White 148 cSt 45 cSt High-vacuum grease, Long shelf life
Isoflex NBU 15 Kluber Grease -40 to 265 SH/Est./Min. Alkaline Earth Beige 21 cSt 4.7 cSt High speed
Krytox 240 AC Dupont Grease -30 to 550 Fluorinated Fluorotelomer White 270 cSt Stable at high temperatures
Mobil 28 Mobil Oil MIL-PRF-81322 Grease -65 to 350 SH Clay Dark Red 29.3 cSt Wide temperature range
Mobil SHC 220 Mobil Oil Grease -40 to 350 SH Lithium Red 220 cSt 23.8 cSt High wear resistance, Corrosion resistance
RheoTemp 500 NYE Grease -65 to 350 Diester Sodium Dark Blue 51 cSt 8.9 cSt High speed, Moderate temperature
RheoLube 2000 NYE Grease -49 to 257 SH Organic Gel Light Tan 110 cSt 15 cSt Low temp. operation, Vacuum Applications
RheoLube 374-C * NYE Grease -40 to 248 SH Lithium Tan 60.7 cSt 9.5 cSt Superior washout characteristics
RheoTemp 700B NYE Grease -40 to 347 Polyester Lithium Blue Black 51 cSt 8.9 cSt High speed, High temperature
SRI-2 Chevron Oil Co. Grease -20 to 350 Mineral Polyurea Blue/Green 100 cSt 11 cSt General purpose

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