FEATURE SPRINGS & SHOCK ABSORBERS
ON THE CREST OF A WAVE
Can a wave spring replace a coil spring in your application? Simon Ward, technical
manager at TFC, European partner of Smalley, looks into their benefits
W
hile wave springs and coil springs are both types of compression spring, primarily
used to provide an axial force in either a static or dynamic application, there are differences. Coil springs are typically made of round wire, whereas wave springs are made from flat wire. This provides an opportunity to significantly reduce working heights within any assembly. This is a benefit in key medical applications, for example, such as for handheld instruments like dental tools and insulin pens, which must be lightweight and compact. A wave spring utilises a sinusoidal waveform
to generate the required axial force. A Crest- to-Crest wave spring has multiple turns to build up the free height of the spring to
achieve the required deflection characteristics. Wave and coil springs also store and release
energy in a different way. A coil spring has a pitch angle and is torsional so it can twist as it compresses, meaning not all force is necessarily aligned with the axis. Wave springs rely on bending – as load is applied, the waves begin to flatten, providing an upward force, allowing for complete axial load transmission.
MAKING THE SWITCH For design engineers currently using coil springs, switching to a Crest-to-Crest wave spring needs careful consideration. There is an extensive range of standard sizes that may suit, but in 70-80% of cases we will develop a
bespoke design to maximise the benefits. Before designing any wave spring, it helps
for TFC to understand the space constraints and the spring performance characteristics. The final design is then achieved by modifying the number of waves and turns, adjusting material cross section and wave heights. Choice of material also affects the design and will normally be dictated by the operating temperature and environment where the spring must function. If a Crest-to-Crest spring does not suit the
application, other options including single turn and nested spring are available.
TFC
www.tfc.eu.com
Putting a spring in the step of planer design P
laners are used during road building for a range of applications – extending from complete rehabilitation, through stripping of
individual layers to levelling asphalt and concrete surfaces. Today, these tasks are accomplished mainly with cold milling equipment, in which the milling tools are very hard and the road surface does not have to be heated up. Modern cold milling machines can load a 30-ton truck with asphalt granulate within a few minutes. Failed couplings, unexpected
shutdowns and long traffic delays were just some of the issues a leader in road building and asphalt equipment manufacturing faced on two of its planers. The configuration of the planer included a diesel engine with flange-mounted, torsionally elastic elastomeric coupling supplied by another coupling manufacturer, a clutch, a gearbox and the milling drum. The torsionally elastic coupling was intended to attenuate torsional vibration so as to protect the other elements of the drive train from damaging resonance vibration. This coupling in a planer must also be able to absorb high impact torques which can occur from the driven side during normal operating conditions. However, the elastomeric coupling they were using was unable to meet these requirements. The customer needed a minimum of
22 APRIL 2021 | DESIGN SOLUTIONS
3,000 hours of uptime between overhauls, but the elastomeric coupling failed after just 200 to 1,000 hours of uptime, causing significant extra costs due to downtime. Additional equipment had to be rented to complete the job and the machine had to be removed so the coupling could be replaced. These failures also resulted in disruptive traffic jams and field issues. To overcome the problem, engineers
at TCP completed a torsional vibration analysis of the application to determine the correct performance for the coupling. Within six weeks, the company provided a new helical spring coupling designed specifically for this application. On-site field testing determined if the coupling met the expectations, with the analysis looking at the gearbox, coupling and hydraulic clutch. Ultimately, the helical spring coupling increased the service life of the entire machine. Uptime tripled to more than 3,000 hours with no failures. The equipment change has enabled the planer manufacturer to make substantial cost savings. Their torsional characteristics mean TCP spring couplings are especially
suited to modern diesel engines that produce lower emissions and more power in smaller packages at lower operating speeds. They run reliably and attenuate drivetrain vibration even in the roughest of applications. With their Smart Damping system, the spring couplings can be tuned to supply damping only when needed and to isolate resonance when damping is detrimental. This reduces torsional spikes at startup, shutdown and transient events, which increases the coupling’s lifespan.
Torsion Control Products
www.torsioncontrol.com / DESIGNSOLUTIONS
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