Spiral-Wound Rings

Nov. 15, 2002
Spiral-wound retaining rings consist of one or more turns of rectangular edge-wound wire.

Spiral-wound retaining rings consist of one or more turns of rectangular edge-wound wire. This provides a coil which can be installed or removed using automatic equipment or simple hand tools. When required, a 360° uniform thickness can be obtained by offsetting one material thickness at the coil ends.

The standard material for spiral-wound retaining rings is carbon spring steel. Some rings are available in other materials such as 302, 316, and 17-7 PH/C stainless steel, NS A286 alloy, beryllium copper, and Inconel X-750.

Time and stress greatly influence the allowable operating temperature. For those applications near the maximum temperature, the ring stress under load should be minimized by using a sharp-cornered retained part, a groove material with a high yield strength, and a ring from the series that uses the deepest grooves.

Carbon steel rings are normally given an oil-dip treatment to retard rust. Cadmium plating and phosphate coating are other standard finishes readily available. Specials include black oxide and parkerized finishes. Zinc, chrome, copper, and gold plates are also available. Plating adds approximately 0.002 in. to the maximum ring thickness.

Standard rings are available for shafts and bores ranging from 0.46875 to 15 in. in diameter. Rings for shafts and bores ranging from 0.375 to 72-in. diameters can also be manufactured.

Design Considerations

Retaining rings fail in two ways: through shear, or from overstressing due to axial deflection. For shear failure to occur, the groove material must have a compressive yield strength greater than 45,000 psi; the load must be applied through a retained part that has a sharp corner and a yield strength greater than 45,000 psi; the ring must be thin in section compared to the ring diameter.

Under axial deflection the maximum stress on a ring subjected to uniform twisting is a tensile stress at the inner corner of the ring. If the ring is stressed past the yield point it will grow in diameter and become dished.

Retaining-ring manufacturers generally specify the maximum radius of chamfer on the retained part. Excessive chamfer sizes cause drastic reductions in allowable thrust loads.

The shallowest possible groove should be selected to minimize cost of the ring and of machining the groove, and to provide ease of ring installation. The minimum permissible groove depth is determined by the thrust load to be absorbed, size of chamfer on the retained part, and yield strength of groove material in compression.

Rotation of a retained part against a spiral-wound retaining ring must be limited to the direction that would tend to wind the ring into the groove. Spiral-wound rings are available in both left and right-hand winds.

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