Machinery's Handbook, 31st Edition
1922
RETAINING RINGS
(1) where the speed N is in revolutions per minute, C 1 is the minimum ring cling to groove bottom, E is the ring radial wall, R n is the free neutral ring radius, R o is the free outside ring radius, and R i is the free inside ring radius, all in inches. For external spiral rings, the minimum ring cling is given by: C 1 = ( C − G )/ G , where C is the mean groove diameter in inches, and G is the maximum ring free ID in inches. R C R R C E 1 0466 10 n o i 3 1 3 3 1 3 12 # = + − ^ h^ h . N
(b) (c) Fig. 2. Localized Groove Yielding under Load. (a) Groove Profile before Loading; (b) Localized Yielding of Retained Part and Groove under Load; (c) Groove Profile after Loading beyond Thrust Capacity ( Courtesy Spirolox Retaining Rings ) (a)
Rotation between Parts: The use of spiral-wound rings to retain a rotating part should be limited to applications with rotation in only one direction. The ring should be matched so that the rotation tends to wind the spring into the groove. External rings should be wound in the direction of rotation of the retained part but internal rings should be wound against the direction of rotation of the rotating part. Failure to observe these precautions will cause the ring to wind out of the groove. Spiral-wound rings can be obtained with either right-hand (normal rotation) or left-hand (reverse rotation) wound configurations. Stamped retaining rings do not have these limitations, and may be used for applications that require rotation of the retained part, regardless of the direction of rotation. Retaining Ring Failure.— Failure of a retaining ring application can result from failure of the ring itself, failure of the groove, or both. If a ring fails, the cause is likely to be from shearing of the ring. Shear failure occurs when a ring is installed in a groove and loaded by a retained part with both the groove and the retained part having a compressive yield strength greater than 45,000 psi (310 MPa); or when the load is applied through a retained part and groove, both having sharp corners and line-to-line contact; or when the ring is too thin in section compared with its diameter. To examine the possibility of ring shear, the allowable thrust P s , based on the shear strength of the ring material, is given by (2) where P s is in lb f (N), D is the shaft or housing diameter in inches (mm), t is the ring thick ness in inches (mm), S s is the shear strength of the ring material in lb/in 2 (N/mm 2 ), and K is the factor of safety. Groove Failure: The most common type of groove failure is yielding of the groove mate rial that occurs when the thrust load, applied through the retaining ring against the corner of the groove, exceeds the compressive yield strength of the groove. This yielding of the groove results from a low compressive yield strength of the groove material, and allows the ring to tilt and come out of the groove, as illustrated in Fig. 2(b). When dishing of a ring occurs as a result of yielding in the groove material, a bending moment across the cross section of the ring generates a tensile stress that is highest at the interior diameter of the ring. If the maximum stress is greater than the yield strength of P K DtS s s π =
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