1413.06.08 Cam Followers.qxd - RBC Bearings

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TECHNICAL DATACam Followers, Yoke,and Track RollersIntroduction to Cam FollowerTechnologySafety PrecautionIn rare cases a bearing failure may cause great mechanicaldamage or even lead to personal injury. To help preventsuch losses, you may contact RBC’s engineeringstaff to review your application details. The engineeringstaff’s review will assist you in identifying potential problemareas and suggest modifications to improve bearingperformance in your application. The engineering staff atRBC has many years of experience with a large variety ofapplications and operating conditions. If you have a safetyrelated application and would like an evaluation by RBC’sengineering department, please submit your applicationdetails in confidence.1. Difference from Standard BearingsThe outer rings of regular ball and roller bearingsare typically mounted in rigid housings providingsupport around the entire circumference. Individualroller forces are transmitted through the outer ringdirectly into the housing with no major deformations.By contrast, cam followers and yoke rollers aresupported at a single point on their circumference.Individual roller forces produce bending moments onRigidlySupportedOuter RingLoad ZoneDeformed Outer RingDeformed Outer Ringthe outer ring around the point of contact. The effectsare outer ring deformation with reversed bendingstresses in dynamic applications, a reduced loadzone, and a higher maximum roller load (see Fig. 1.).To keep deformation to a minimum, the outer ring ofa cam follower must have a considerably heaviercross section than a standard bearing. This requirementconflicts with the desire for maximum dynamicbearing capacity which needs as large a roller diameteras possible. RBC cam followers and yoke rollersprovide an optimum compromise between outer ringstrength and theoretical bearing capacity.2. Capacity and Load LimitsEvaluation of the expected service life and limit loadsof cam followers is more complex than with housedbearings. In addition to the static and dynamic capacityof the rolling elements, outer ring deformation, trackcapacity, and cam follower stud bending stress must beconsidered. In yoke rollers, the pin shear stress must beconsidered.RBC lists the static bearing capacity for referencepurposes only. Typically, the maximum allowable loadis a function of the maximum permissible bendingstress of the stud or the outer ring. For best results, theoperating loads should not exceed the lower of trackcapacity or 50% of the dynamic capacity.2.1 Capacity of Rolling Element BearingEquations for static and dynamic capacities of rollerbearings are given in ANSI/ABMA Standard 11. Themore recent revisions leave it up to the manufacturer tointroduce factors which account for internal designfeatures and operating conditions. For cam followersand yoke rollers RBC has chosen to apply a conservativerating system, so a direct comparison with capacityfigures of competitive products may not be possible.40Contact Stress ProfileRigidly SupportedOuter RingLoad Zone & Maximum Contact StressFig. 1Load ZoneRigidly SupportedOuter RingContact Stress ProfileDeformed Outer Ring2.2 Track CapacityTrack capacity is that load which a track subject to auniform contact stress can withstand without excessiveplastic deformation. It is directly related to track hardness.The published track capacity is based on a hardnessof HRc 40. For other track hardness values the trackcapacity must be modified with factors from Table 1.
Track Hardness Material Strength Modification[HRc] [psi] Factor26 128,000 .4532 146,000 .6136 165,000 .7940 182,000 1.0044 204,000 1.2447 229,000 1.5050 247,000 1.7853 266,000 2.0956 281,000 2.4258 298,000 2.78Table 1. Track Capacity Adjustment Factors.2.3. Bending and Shear Stresses2.3.1 Cam Follower Stud Bending StressIf the load over the width of the outer ring isevenly distributed, it may be replaced by a singleconcentrated force F [lbf] acting at the center of thecam follower (see Fig.2). Assuming that the camfollower stud has been tightly mounted in a housingbore flush with the end plate, this concentrated forcegenerates a bending moment M b .Alternatively, contact stress can be easily calculatedand compared directly to the strength of material.The equation for the Hertz contact stress betweena cylindrical cam follower outer ring and a flatsteel track is given by “Roark, Formulas for Stressand Strain” as:whereMb= F* B 2 + 1 [in lbf]( 32) *B = outer ring width [in]1/32 = cam follower overhang [in]1/32*(2)Bσ = 3,237C max*IeffF* D[psi](1)whereF = radial load [lbf]l eff = length of outer ring contact [in]D = outer ring diameter [in]HousingTrackIt can be shown that for infinite life the ultimatetensile strength of track and roller must be at leastequal to the maximum contact stressExample 1:σ C maxFMoment ArmTheoretical Moment Armwithout stud deflection*sizes 160 and above = 1/16Fig. 2The bending moment generates a bending stressin the cam follower stud of approximate magnitudeDetermine the required minimum track hardnessfor an RBC cam follower S 56 L operating under a3000 lbf radial load.σb= 10 * M bSD 3[psi](3)Solution:σ = 3,237C max3,000 lbf* = 149,800 psi0.8 in * 1.75 inwhereSD=Stud Diameter [in]Referring to Table 1, 149,800 psi is between 146,000 psi(HRc32) and 165,000 (HRc 36). Interpolation yields aminimum track hardness of HRc 33.Standard cam follower studs are heat treated to ahardness of HRc 58 min in the raceway area only.41
Page 1: RBC Roller ® , HexLube ® , CamCen
Page 5 and 6: ApplicationRequirementsDynamicloadi
Page 7 and 8: FEATURED PRODUCTThe RBC ROLLER ® C
Page 9 and 10: RBC Roller ®Long Life Cam Follower
Page 11 and 12: RBC Roller ®Long Life Yoke Rollers
Page 13 and 14: ®HexLubeThe Universal Cam Follower
Page 15 and 16: HexLube ® Universal Cam FollowersS
Page 17 and 18: HexLube ® Universal Cam FollowersS
Page 19 and 20: CamCentric ® Adjustable Cam Follow
Page 21 and 22: HexLube ® Universal Cam FollowersR
Page 23 and 24: HexLube ® Universal Cam FollowersH
Page 25 and 26: Yoke RollersCylindrical and Crowned
Page 27 and 28: Caged Roller Followersr 1BDF wSerie
Page 29 and 30: Precision Ground Inner RingsFor Use
Page 31 and 32: Mast Guide and Carriage RollersTypi
Page 33 and 34: Toothless SprocketsBB 1DdD 1Type A
Page 35 and 36: 35Airframe Needle Roller BearingsCl
Page 37 and 38: 37Airframe Needle Roller Bearings87
Page 39: 39Airframe Track Rollers8002,0003,5
Page 43 and 44: Example 4Estimate the outer ring te
Page 45 and 46: 5.3 Yoke RollersRBC yoke rollers co
Page 47 and 48: TYPICAL APPLICATIONSTable SupportsY
Page 49 and 50: UNIVERSAL SERIES INTERCHANGE TABLE
Page 55 and 56: CUSTOM DESIGNED CAM FOLLOWERSIn add

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