COMPONENTS


TECHNICAL REFERENCE Load/Life Equation – Sizing and Selection


Step 1: Calculate loads on each bearing Given below are force equations for some common configurations.


FA = Axial Force, FR = Radial Force Scenario 1


FA1 = F(x-a) x


FA2 = Fa x


Scenario 2


FA1 = F(x+a) x


FA2 = -Fa x


Scenario 3


FA1 = Fx y


FA2 = -Fx y


FR1 = F


*Note: Since carriages use 4 wheels, 2 wheels absorb the load at both points 1 & 2, divide the calculated load by 2 to obtain the load on each wheel.


Example: Scenario 3 F = 200 lbs x = 15 inches y = 5 inches


FA1 = 200(15) = 600 lbs, or 300 lbs per wheel 5


FA2 = -200(15) = -600 lbs, or -300 lbs per wheel 5


FR1 = 200 lbs, or 100 lbs per wheel Step 2: Calculate the load factor LF


LF = FA / FA(max) + FR / FR(max) LF = 300 / 900 + 100 / 2181 = 0.38


Step 3: Calculate life estimate See page 23 for life constants, AF Life = [LC / (LF)3


] AF = [6.84 x 106 24 © Bishop-Wisecarver Corporation 2011. All rights reserved www.bwc.com 888.580.8272 assumed at 1 / (0.38)3 ] x 1 = 124.7 x 106 inches for the most heavily loaded


bearing using the above example with size W4X guide wheel, FA(max) and FR(max)


from load rating chart pg 6. 2 x Scenario 3 1 x Scenario 2 1 F y 2 F a 1 x Scenario 1 2 a F


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