Machinery's Handbook, 31st Edition
RETAINING RINGS 1923 the ring material, the ring ID will grow and the ring will become permanently dished in shape. To determine the thrust load capacity of a ring based on groove deformation, the allowable angle of ring deflection must be calculated, then the thrust load based on groove yield can be determined. However, for spiral-wound rings, the thrust load P G that initiates the onset of groove deformation can be estimated from the following: (3) where P G is given in lb f (N), D is the shaft or housing diameter in inches (mm), d is the groove depth in inches (mm), S y is the yield strength of the groove material in lb/in 2 (N/mm 2 ), and K is the safety factor. For stamped rings, estimate P G by multiplying Equa- tion (3) by the fraction of the groove circumference that contacts the ring. The thrust load capacity of a particular retaining ring application can be increased by changing the workpiece material that houses the groove. Increasing the yield strength of the groove material increases the thrust load capacity of the retaining ring application. However, increasing the strength of the groove material may cause the failure mechanism to shift from groove deformation to ring shear. Therefore, use the lower of the values obtained from Equations (2) and (3) for the allowable thrust load. Groove Design and Machining: In most applications, grooves are located near the end of a shaft or housing bore to facilitate installation and removal of the rings. The groove is normally located a distance at least two to three times the groove depth from the end of the shaft or bore. If the groove is too close to the end of the shaft or bore, the groove may shear or yield. The following equation can be used to determine the minimum safe distance Y of a groove from the end of a shaft or housing: (4) where K is the factor of safety, P t is the thrust load on the groove in pounds (N), S c is the shear strength of the groove material in lb/in 2 (N/mm 2 ), and D is the shaft or housing diameter in inches (mm). A properly designed and machined groove is just as important in a retaining ring application as the ring itself. The walls of grooves should be perpendicular to the shaft or bore diameter; the grooves should have square corners on the top edges, and radii at the bottom, within the tolerances specified by the manufacturers, as shown in Fig. 1 (page 1897 ). Test data indicate that the ultimate thrust capacity for both static and dynamic loading conditions is greatly affected if these groove requirements are not met. For spiral- wound rings, the maximum bottom groove radius is 0.005 inch (0.127 mm) for rings up to 1.000 inch (25.4 mm) free diameter, and 0.010 inch (0.254 mm) for larger rings, internal or external. For stamped rings, the maximum bottom groove radius varies with ring size and style. Table 18. Retaining Ring Standards Military MIL-R-21248B MS-16633 Open-type external uniform cross-section MS-16634 Open-type external uniform cross-section cylindrically MS-3215 Open-type external tapered cross-section MS-16632 Crescent-type external MS-16625 Internal MS-16629 Internal cylindrically bowed MS-16624 Closed-type external tapered cross-section P K = DdS G y π Y DS KP c t π =
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