Edited by Martha K. Raymond
Jonathan Slass
General Manager
Rotor Clip Company Inc.
Somerset, N.J.
Retaining rings are becoming more widely used as a first choice in fasteners. These devices can lower production costs and simplify designs, as well as contribute other benefits to assembly and design. For example, retaining rings function as removable fasteners. During disassembly, their elastic properties let them deform without destroying components. Also, retaining rings often do the job of several parts by replacing more conventional fasteners such as cover plates, cotter pins, and nuts.
Furthermore, assemblies with retaining rings are typically more compact then assemblies joined by other fasteners. Tooling for retaining rings makes assembly quick. Automated methods ensure efficient assembly for both internal and external retaining rings. Internal rings are assembled in holes, bores, or housings and external rings go on shafts, pins, or studs.
In general, the equipment that feeds rings into the assembly machine should be compatible with standard rings. The spring quality of retaining rings permits a standard industry tolerance of three times the thickness for overall height, which is a functionally acceptable dimension. Other qualities include helix and pitch limitations that change for specific applications. But requirements out of the norm, such as material or size, ordinarily require changes in equipment, increasing costs.
Other guidelines include using a tapered mandrel for external retaining rings and a tapered housing for internal retaining rings. When feeding parts onto the tapered mandrel or into the tapered housing, a mechanism called a feed finger carefully transfers the rings, avoiding damage by transferring them with lug holes.
Feeding of rings in the proper direction and manner eliminates ring pitch sensitivity. To ensure proper handling, the feed finger thickness should be such that it is 80% of the ring minimum thickness. For example, if ring thickness is 0.062 in. ±0.003, the feed finger thickness should be 0.059 in. 3 80% or 0.047 in. For easy installation and assembly, another tip is to keep the feed shuttle close to the mandrel.
One precaution to prevent ring failure is to leave out extension sleeves in the tapered mandrel and housing because these sleeves may exceed the expansion/compression limits of the ring. Another way to simplify assembly is to incorporate complementary chamfers to the assembly and installation mandrels.