Machine Design

Stamped Rings

Stamped retaining rings have a tapered radial width that decreases symmetrically from the center section to the free ends. Tapered construction permits the rings to remain circular when they are expanded for assembly over a shaft or contracted for insertion into a bore or housing. This constant circularity assures maximum contact surface with the bottom of the groove.

Stamped retaining rings are classified into three groups: axially assembled, radially assembled, and self-locking rings. Axially assembled rings slip over the ends of shafts or down into bores, while radially assembled rings have side openings and are snapped directly into grooves on a shaft.

Most axially assembled rings have holes in the lugs at the free ends for special pliers that expand or contract the rings for installation or removal. Radially assembled rings are installed with an applicator and removed with a screwdriver or other hand tool. Self-locking rings do not require grooves. They are available for assemblies in which the fastener need not absorb any sizable thrust, but instead serves mainly as a positioning or locking device.

Most stamped retaining rings are made of high-carbon spring steel with corrosion-inhibiting finishes such as phosphate coating, cadmium or zinc plating, and chemical-conversion coatings for special applications. Rings made of aluminum or beryllium copper are available for special assembly requirements, usually without any protective finish. Corrosion-resistant stainless-steel rings are also available.

Design Considerations

Standard ring sizes range from 0.040 to 10 in. in diameter, although rings as large as 40 in. in diameter have been made. Rings are also manufactured for metric shaft and bore diameters. Both ring and groove load capacities should be considered when selecting specific ring types; the lower of the two will be the limiting factor in the assembly. The ultimate thrust load to which a ring may be subjected depends upon the ring's shear resistance; ultimate groove thrust-load capacity depends on a factor of compressive resistance.

For optimum ring performance, the retained parts should have an abutting face that is straight with sharp corners. This enables loads to be transmitted as closely as possible to the groove wall. The thickness of the ring resists shearing and provides maximum uniform compression loading for the groove wall. If the abutting face is curved, and the resultant of the forces is transmitted to the ring at a distance from the shaft or bore circumference, a bending moment is created that will cause the ring to dish. The groove wall will not be loaded uniformly, reducing the ultimate thrust capacity.

Retaining-ring manufacturers specify maximum allowable corner radii and chamfers for each ring size, with corresponding static thrust capacities. If thrust capacities are insufficient for the assembly, a rigid, square-cornered, flat washer should be inserted between the ring and the retained part. The washer is mandatory if the assembly is subject to dynamic loading and the retained part has a corner radius or chamfer.

Clearance depends on the type of ring used. A crescent ring, for example, has a substantially lower shoulder than an E-ring, and for many assemblies supplies a sufficiently large bearing surface. Rings with inverted lugs form a uniformly circular protruding shoulder and provide more clearance than basic internal and external types.

Edge margin is the shoulder between the outer groove wall and the end of the shaft or housing. Minimum is generally considered to be three times the ring's nominal groove depth.

Axial-type rings have generally higher rotational speed limits and present a neater appearance. Radial rings are usually easier to install and remove.

Axial play in the assembly can be compensated for by bowed rings where resilient end-play take-up is permissible. Beveled rings can be used for rigid take-up. Self-locking rings, which can be positioned at any point on a shaft or in a housing, can also compensate for accumulated tolerances.

TAGS: Fasteners
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