Engineer's Toolbox: Experts answer questions about retaining rings and wave springs
Every year, hundreds of technical questions are submitted through Smalley's "Ask the Expert" page. The company's team of engineering experts answers the questions directly, but they also post them in a blog for sharing. This selection addresses some commonly asked questions about retaining rings and wave springs.
Retaining ring gaps and performance in high-RPM applications How do Smalley engineers determine the size of retaining ring gaps? What happens if a retaining ring is compressed such that the free ends touch?
Retaining ring gaps are calculated and based on the application dimensions, installation/removal methods, and our manufacturing capabilities. Smalley standard rings are designed such that the gap ends do not touch during installation. If the ring ends touch when compressed, it could jam and possibly deform or damage the ring and/or assembly. Consult Smalley engineering to review your application and installation requirements.
What can Smalley do to improve performance in high-RPM applications?
The rotational capacity is a function of several parameters, including thickness, radial wall, cling (interference fit of the ring as it's installed in/on the groove), diameter, etc. Quite often, the rotational capacity can be increased by increasing the radial wall dimension and/or the amount of cling in the groove.
If after investigating this, the rotational capacity is still not sufficient, then we can add a self-locking feature to the ring. The self-locking feature consists of a tab and a slot so that when the ring expands due to centrifugal force, it is restricted by the tab contacting the edge of the slot. For more information, visit our rotational capacity page.
Wave spring compression and deflection What happens to a wave spring when it gets compressed to solid?
In general, Smalley does not recommend compressing a wave spring below the design work height.
As a wave spring travels close to its solid height, the loads begin to increase exponentially and become unpredictable. The increased loads can cause the spring to relax or to take a set. The amount of relaxation depends on the load and various other factors. The deformation of the material will result in degradation of the performance characteristics of the spring.
An application that requires the spring to be compressed below the work height should be reviewed with Smalley engineering to evaluate the design stress. Many times, we can provide a solution that meets the design requirements. Please contact Smalley engineering to discuss your requirements and the best spring to meet them.
I am considering using the SSR-0225 model wave spring. Your website states, "the calculated spring rate is linear through the first 80% of available deflection." Is the available deflection the free length minus the work height? For example, this spring's available deflection is .170 - .093 = .077 in.?
No. The available deflection refers to the range between the free length and the solid height. The free height is approximate and, therefore, so are the spring rate and available deflection.
Smalley standard springs are inspected only at the load at work height specified in the catalog (for example, the SSR-0225 is checked at a work height of .093 in.). As a general rule, the work height listed in the catalog is the lowest recommended work height for the part.
However, the spring may work at other heights. Contact Smalley engineering to evaluate theoretical spring characteristics at alternate heights.
How do I Measure the Free Height of a Wave Spring?
It's important to know to how to properly measure a wave spring's free height in order to verify that you are using the correct part for your application. When done correctly, it can also save valuable inspection time.
To Measure the Free Height of a Wave Spring:
Ensure the spring is sitting on a flat surface between two parallel plates
Lower the top measuring surface until it touches the spring
Apply a slight force to deflect the spring until the crests of all waves come in contact with the loading surfaces
The distance between the two parallel plates is the free height
Please watch our video for a better understanding of how to measure the free height.
Free Height: The height at which a wave spring is measured in its free state.
Work Height: The designed height at which a desired force/load is delivered.
It is also important to note: the free height of a wave spring is typically a reference dimension. Wave springs are normally designed to provide a specific tolerance/load at a given work height.
Wave spring design What are some overall design limitations on a crest-to-crest wave spring?
Smalley manufactures springs ranging in diameters from about 5 mm, or .197 in., to 3 m, or 9.8 ft, or more. Possible design limitations vary widely and depend on a number of different design requirements, such as load, deflection, free height, cycles, and so on. Contact your Smalley Sales Engineer to discuss potential designs and limitations.
When spec'ing a wave spring, what is the diameter tolerance on a bore or shaft?
Every spring has two diameter measurements: the shaft diameter and the bore diameter.
The shaft diameter is the diameter when measured from the inside edges of spring. It is called the shaft diameter because a common usage of springs is to fit them around a shaft. The bore diameter is the diameter of a spring measured from the outside edges, so called because another common usage of springs is inside a bore, or drilled hole.
The tolerance of a bore or shaft diameter, or any measurement, is the amount of tiny fluctuations in size that are acceptable. Tolerances can account for minute inaccuracies in manufacturing processes and expansion of material while the spring is in use. Tolerances can also help springs to fit a shaft or bore better.
Tools for retaining ring installation and removal What tooling is available to aid in the installation of retaining rings?
More often than not, Spirolox retaining rings can be installed by hand without tooling. This is done by separating the turns, inserting one end of the ring over the shaft (or through the bore) and into the groove, then spiraling the rest of the ring into the groove.
Depending on your application, this process may not be so simple. Heavy-duty single-turn retaining rings and hard-to-reach grooves can make installation difficult. Luckily, Smalley has developed a number of different tools and techniques to assist with rings that are hard to install. Take a look at our comprehensive installation tool guide here.
A popular option is the combination of a plunger and either a tapered sleeve (for internal rings) or plug (for external rings). These parts can be manufactured precisely to fit your application and be integrated into an automated assembly, if desired.
Because every application is different, don't hesitate to contact Smalley Engineering if none of these solutions look like a good fit for you. We will help you to develop the right tool for the job.
We are using your part number WH-56-S02 and would like your recommendation for a removal tool that will not damage the retaining ring.
Smalley part number WH-56-S02 has a removal scallop on the end of the ring. To remove this ring, simply pry out the end using a small screwdriver, and then spiral the ring out by hand.
For larger size rings, Smalley also makes a removal tool, part number RT-107, that can be used to remove the rings. The end of the tool contains a slot to insert the tip of the removal notch. The ring can then be pulled out radially, then up for removal.
Retaining ring material and shear load safety factors I would like to know if you can provide spiral retaining rings made of titanium? We are currently using stainless steel retaining rings within titanium housings and we are experiencing interference and galvanic corrosion between the two metals.
Smalley is able to manufacture spiral retaining rings out of titanium, as well as in a wide range of many other alloys. Contact a Smalley Sales Engineer today to discuss your specific needs and the best material to meet them.
Is the shear load safety factor listed three times the advertised value? For example, the WH-62 lists "2500 (safety factor of 3)" -- does that mean I can expect a failure at a load of around 7,500 lb?
That is correct. The values we list for ring shear have a safety factor of 3, so you can expect the actual ring shear to occur at 3 times the listed value.
However, our experience shows that the failure of a retaining ring is rarely ring shear. More often it is groove deforming, which allows the ring to work its way out of its groove. Groove depth, groove width, and the groove material can all play a part in how well a retaining ring performs.
You can contact a Smalley Sales Engineer today to discuss your axial loading needs and determine the best retaining ring for you.
Installing retaining rings and laminar seal ring application
When installing your retaining rings, does the orientation or direction of loading matter?
Smalley retaining rings are manufactured by edge coiling uniform cross-section flat oil-rolled wire. This process results in a ring with no "wrong side," like there is on a stamped snap ring. Therefore, the orientation of the ring in relation to the direction of loading does not affect performance. Visit the Installation & Removal page for more information.
Have your Laminar Seal Rings been used on reciprocating applications?
Some Smalley clients have successfully utilized Laminar Seal Rings in reciprocating applications. However, because Laminar Seal Rings are not designed for such use, the axial movement in reciprocating applications can have adverse effects on the rings. Therefore, we generally advise against doing so.
Small wave springs and seal rings How small can a wave spring be manufactured and still function in my application?
If our smallest off-the-shelf .235-in. diameter wave spring is too big, Smalley can reliably edgewind custom crest-to-crest wave springs with diameters as small as .180 in. or approximately 4.5 mm.
Depending on the necessary work height(s) and load(s), such small wave springs could be a great fit and perform well. At these small diameters and given the size of the wire relative to the rest of the design and tolerances, every design parameter can have a significant effect on the final design's performance. Smalley's dedicated engineering staff is available to discuss your specific application and help you design the right spring for your needs.
Can a Spirolox retaining ring function as a seal in my application?
Depending on the quality of seal required by the application, it is possible to use a Spirolox retaining ring, although they are not designed for that use.
Smalley's Laminar Seal Rings, however, are designed specifically for sealing against contaminants. In contrast to Spirolox retaining rings, Laminars are manufactured slightly out of round and acquire a circular form when installed. A stronger seal can be created by using a series of these rings or creating a labyrinth. Regardless, neither type of ring should be used to seal against pressurized gas or fluid. For more information, take a look at our Laminar Seal Rings page or contact a Smalley engineer.