All compression springs basically work in the same manner, but there are still differences between how traditional coil springs and Wave Springs (Flat Wire Compression Springs) operate. Smalley Wave Springs offer the unique advantage of space savings when used to replace coil springs. By reducing the spring operating height, wave springs also contribute to a decrease in the spring cavity. In addition, a smaller assembly size and less material used in the manufacturing process enables a cost savings.
Types of Wave Springs
Smalley offers a variety of wave spring options. Determining which wave spring is right for you depends on your particular application, with each type having its own unique advantages.
Single Turn Wave Springs, in many cases, can replace traditional stamped wave washers which, depending on size, can offer some cost savings. In addition, single turn wave springs can operate in tighter cavities than a wave washer, because the gap or overlapped ends allow the spring to contact the housing without binding. Manufactured by coiling, not stamping, they produce a more accurate, repeatable load than a stamped wave washer.
Multi-turn Wave Springs, also known as Crest-to-Crest Wave Springs, can provide more deflection than single-turn springs and can serve as a replacement for coil springs while occupying up to half as much axial space. Crest-to-Crest wave springs can be designed to operate with the same load and deflection as a coil spring. The lower profile spring also allows for a possible weight savings within the assembly from the reduced spring cavity.
Unlike other wave springs, Smalley’s Wavo Springs are produced from round cross-section wire which helps them to provide higher loads, while occupying significantly less radial space than that required by a Belleville or disc spring.
Linear springs can have similar load and deflection characteristics as a Single Turn Wave Spring. These springs have numerous applications, such as detent preloading and radial loading in a rotary vane pump.
Nested wave springs provide higher loads than single turn springs, these springs are coiled in parallel from one continuous piece of flat wire, eliminating the need to stack individual springs for higher loads. They are particularly useful in static applications requiring high, accurate forces with short deflections.
Interlaced Wave Springs consist of two or three wave springs of the same design, wound and nested together to make one spring. Interlacing them effectively increases the thickness of the spring, providing increased loading that cannot be achieved with a single Crest-to-Crest. This makes interlaced wave springs good for static applications that require high force with more deflection.
Wave Spring Fatigue, Load and Deflections
There are many factors that should be considered when designing with wave spring, such as the housing and/or shaft diameter, load at work height, deflection and cycle life, if required. The load should be specified at a work height as opposed to a deflection from free height.
Calculating fatigue for a wave spring means taking into account the minimum and maximum deflection points, as well as the stresses at those work heights. More specifically, the formula for the fatigue stress ratio is:
Where:
σ = material tensile strength
S1 = calculated operating stress at lower work height
S2 = calculated operating stress at upper work height.
The chart below shows the corresponding estimated cycle life for fatigue stress ratios:
|
Fatigue Stress Ratio (X) |
Estimate Cycled Life (cycles) |
|
X < .40 |
Under 30,000 |
|
.40 < X < .49 |
30,000 – 50,000 |
|
.50 < X < .55 |
50,000 – 75,000 |
|
.56 < X < .60 |
75,000 – 100,000 |
|
.61 < X < .67 |
100,000 – 200,000 |
|
.68 < X < 70 |
200,000 – 1,000,000 |
|
.70 < X |
Over 1,000,000 |
Like many springs used in engineering applications, the linear load range is between approximately 20 percent below the free height at the upper end, and twice the solid height, or about 80 percent deflection, whichever comes first. Although springs can operate outside of this linear “comfort zone,” the loads will be higher than calculated as they approach solid height, as indicated in the graph below:
Wave springs exert a greater force upon loading and a lower force upon unloading. This effect is known as hysteresis. In the figure below, the shaded area shows a graphic representation of the difference between the down-going and upcoming loads.
Wave Springs Save Space and Reduce Weight
Skillful engineering is all about balance, whether you’re weighing price against manufacturability in a pump or force against working height when specifying a wave spring. Dealing with a unique assembly or a one-off production run can compound the challenges of engineering trade-offs. Smalley produces both standard and custom wave springs for just that reason and the company’s engineers can help with your wave spring design.
For more information, visit the Smalley website.
Smalley Steel Ring has sponsored this post. All opinions are mine. –Ian Wright