Official Answer
Answer
The wire used for spiral rings is cold-rolled from round wire, which naturally produces a 'natural round edge.' If the wire is slit from wider sheets, it will have sharp, 'burred' edges. These burrs act as significant stress concentrators. Under cyclic axial loads, these sharp edges become the initiation points for fatigue cracks. High-quality spiral rings utilize a 'radius edge' or 'round edge' produced during the rolling process. This reduces the stress intensity factor $K_t$ at the edge of the ring, significantly extending the fatigue life. Engineers must specify 'no burrs' and 'radius edges' for any dynamic or safety-critical retaining ring application.
