1413.06.08 Cam Followers.qxd - RBC Bearings

Example 4Estimate the outer ring tensile stress of yoke rollerY 56 L subject to a load of 6,000 lbf. The yoke rollerhas 25 rollers, the outer ring outside diameter = 1.750in., the outer ring raceway diameter =1.125 in., theidealized outer ring width = .690 in.Solution:σ =6 * 6,000 lbf * 1.125 * π = 18,880 psib max225 * .690 in * (1.75 in - 1.125 in )3. Fatigue LifeFatigue life, L 10 [rev, hrs], is a statistical measure ofthe life which 90% of a large group of apparently identicalrolling element bearings will complete or exceed.For a single bearing, L 10 also refers to the life associatedwith 90% reliability.The relationship between fatigue or rating life, capacityand load is:whereL10 rev=(CPe)103L 10 rev = Rating life [10 6 rev]C = Dynamic capacity [lbf]P e = Equivalent radial load(6)In case of constant load, the equivalent radial loadequals the constant load. To compute the equivalentload for all other cases, use:P=eqΣ(qFi * n ti * ine * 100where(9)q = 10/3 for roller bearingsF t = individual radial load [lbf]4. Speed Limit and Maximum Acceleration4.1 Speed Limit)The limiting speed of rolling element bearings isprimarily a function of size and internal design. Thespeed limits given in this catalog should not beexceeded on a continuous basis to prevent prematurefailure due to excessive temperature. Contact RBC forsolutions to high speed applications.4.2 Maximum Acceleration (Deceleration)=qq* 1e *F1n t1 *n 100q+ F + ...2 * n t2 * 2n 100e *To obtain the rating life in hours, use16,667L =n ( C e* Pe10310 hrs)(7)A sufficiently large tangential friction force F t ,acting between outside diameter and track is neededto change the rotational speed of cam follower andyoke roller outer rings.whereL 10 hrs = Rating life [hours]n e = equivalent speed [rpm]In case of constant speed, the equivalent speed equalsthe constant bearing speed. In all other cases theequivalent speed is the weighted average of all individualspeed components.where(nitie Σ 100 )n =* = n t 1* 1+ n t 2* 2+ ...100 100(8)n i = individual speed component [rpm]t i = time interval in percent of total timewhereF = F µ [lbf]t *µ = coefficient of friction(outer ring to track)(10)The force F t produces a moment M t , which mustaccelerate the masses of outer ring and rollers aroundthe bearing axis, plus the rollers in the load zonearound their own axes.43