Load Capacity
Understanding the load capacity of a Smalley Retaining Ring assembly requires calculations for both ring shear and groove deformation, with the design limitation being the lesser of the two.
The load capacity formulas do not take into account any dynamic or eccentric loading. If this type of loading exists the proper safety factor should be applied and product testing conducted. In addition, the groove geometry and edge margin (i.e., the distance of the groove from the end of the shaft or housing) should be considered.
Where abusive operating conditions exist, true ring performance is best determined through actual testing.
Ring Shear
Although not commonly associated as a typical failure of Smalley Retaining Rings, ring shear can be a design limitation when hardened steel is used as a groove material. Ring thrust load capacities based on ring shear are provided within this catalog's tables of standard rings. These values are based on a shear strength of carbon steel with the recommended safety factor of 3.
Formula
PR = Allowable thrust load based on ring shear
D = Shaft or housing diameter (in)
T = Ring thickness (in)
Ss = Shear strength of ring material (psi)
K = Safety factor (3 recommended)
Ring shear
Example:
1) WH-550-S16
2) Safety factor = 3
The thrust load based on ring shear above, must be compared to the thrust load based on groove deformation to determine which is the limiting factor in the design.
Groove Deformation (Yield)
Groove deformation is by far the most common design limitation of retaining rings. As permanent groove deformation occurs. the ring beings to twist. As the angle of twist increases, the ring begins to enlarge in diameter. Ultimately the ring becomes dished and extrudes (rolls) out of the groove. As a conservative interpretation the following equation calculates the point of initial groove deformation. This does not constitute failure which occurs at a much higher value. A safety factor of 2 is suggested. Ring thrust load capabilities based on groove deformation are provided within this catalog's tables of standard rings.
Formula
PG = Allowable thrust load based on groove deformation (Ibs)
D = Shaft or housing diameter (in)
d = Groove depth (in)
Sy = Yield strength of groove material(psi), Tabie 1
K = Safety factor (2 recommended)
Permanent groove material deformation
Table 1
Example:
Since ring shear was calculated at 44,787 Ibs., the groove yields before the ring shears. Therefore 28,769 Ibs. is the load capacity of the retaining ring assembly.
Groove Geometry
Groove Radius
To assure maximum load capacity it is essential to have square corners on the groove and retained components. Additionally, retained components must always be square to the ring groove in order to maintain a uniform concentric load against the retained part. The radius at the bottom of the groove should be no larger than Table 2 states.
Table 2
Retained Component
The retained part ideally has a square corner and contacts the ring as close as possible to the housing or shaft. The maximum recommended radius or chamfer allowable on the retained part can be calculated with the following formulas.
Formula
Maximum Radius = .5(b-d) (on retained component)
Maximum Chamfer = .375 (b-d) (on retained component)
where:
b = Radial wall (in)
d = Groove dept (in)
Example
1) WH-100
Maximum Radius = .5(.075-.021) = .027 in.
Maximum Chamfer = .375(.075-.021) =.020 in.
Edge Margin
Ring grooves which are located near the end of a shaft or housing should have an adequate edge margin to maximize strength. Both shear and bending should be checked and the larger value selected for the edge margin. As a general rule, the minimum edge margin may be approximated by a value of 3 times the groove depth.
Shear Formula
Bending Formula
z = Edge margin (in)
P = Load (Ibs)
DG = Groove diameter (in)
Sy = Yield strength of groove material (psi), Table 1
d = Groove depth (in)
K = Safety factor (3 recommended)
Example:
1) VS-125
2) Groove material yield strength = 40,000 psi
3) Safety factor = 3
4) Load = 10001bs.
Therefore the minimum edge margin that should be used is 059 in.