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Getting more from wave springs and retaining rings
Smalley product manager Simon Ward discusses the characteristics of and applications for small diameter wave springs and retaining rings. In particular he looks at some recent applications for retaining rings, how they can be adapted to different uses, and when it might be better to select a more specialised product.
Wave springs save space without compromising on force or deflection which opens up a whole host of applications where they can be real problem solvers. The same problem solving capability is offered by laminar retaining rings. So how do these components offer their particular benefits, and how does that help in given tasks?
Looking first at the wave spring, we can see that the spring rate (load ÷ deflection) for Smalley wave springs is affected by other characteristics on the spring such as wire thickness, free height and radial wall. Wave springs tend to have constant rates from approximately 20% to 80% deflection. As the spring approaches its solid height, the rate typically grows exponentially and is no longer linear. For this reason, spring applications are toleranced with loads at specified work heights as this is a measurable and more accurate way of determining the functionality of the springs.
What about the impact of overloading? A typical application we were asked about related to a task with 5kg of preload on the spring, but which in use could be five to eight times the calculated load.
The impact of overloading will vary based on the overall size of the spring, spring material, cycles, and the amount of load being applied. All of TFC standard springs are designed to meet a certain load at the listed work height. If you have an application where the spring will see a higher load than what is listed in the data, there is a possibility that the load will over-stress it and the spring may take a set.
Size can also have an impact on the spring’s characteristics. TFC offers off-the-shelf wave springs designed to suit a 6mm diameter bore as standard. If this is too big or the spring characteristics are not quite right, the company can reliably edge-wind custom designed wave springs with diameters as small as 4.5mm. At these small diameters every design parameter has a significant effect on the final design. In any given task, users should carefully consider working lengths, deflection, loads, and the application requirements.
Turning now to retaining rings, TFC offers ranges of both Spirolox retaining rings and laminar seal rings from Smalley. Spirolox retaining rings are manufactured with a circular form to cling in, or on a specified groove diameter, providing a shoulder. Unlike a die stamped equivalent circlip, the retaining ring is produced by edge winding from a continuous coil of single filament pre-tempered round-edge flat wire and does not require heat treatment after forming. This unique process results in a retaining ring that has no 'ears' to interfere with the assembly and, because there is no scrap, they can be produced economically in carbon steel, stainless steel, coppers and many other alloys.
In a typical application for the Spirolox retaining ring, TFC was asked to provide a product to aid in gear assembly, preventing the pinion shafts spinning when the gears are rotating. The ring snaps securely into the external groove of the flanged housing and, because the radial wall is uniform around its total 360º circumference, the flats on the four pinion shafts are able to clear the outer edge of the ring by a consistent 0.50mm in each case.
In some applications, Spirolox retaining rings can also function as a seal, depending on the level of sealing required by the application. A recent sealing application for the Spirolox retaining ring was to clamp a rubber boot onto the groove in a connecting rod. Using a two-turn external XWS series product, the ring provides a full 360° circumferential cover in the groove, a near perfect seal results when the boot is filled with grease. The ring and removal slots are also deburred to ensure the likelihood of the rubber being torn is eliminated.
Smalley’s laminar seal rings utilise different cross sections and a minimal cling to ensure the circumference has maximum engagement with the sealing bore or shaft diameter. A more complete seal can be created using a series of these rings to create a labyrinth. Regardless, neither type of ring is intended to be used to seal against pressurised gas or fluid. They are a primary barrier to restrict the ingress on dirt in harsh environments.
TFC has represented Smalley for over 35 years, with the ability to supply everything from standard products to custom solutions.
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