When most people think of rings, they think of weddings, circuses or (at least in my case) hobbits, but for a mechanical engineer the word ‘ring’ carries a very different connotation. Retaining rings are one of the most basic ways to control axial movement, but their mechanical simplicity belies the sophistication of their design, not to mention their diversity.
From tapered section snap rings to spiral rings to constant section rings, the sheer number of retaining ring options can be overwhelming. But the old adage about selecting the right tool for the right job still applies, so when it comes to retaining mechanical components when space is at a premium, Hoopster retaining rings are a good option.
Hoopster Retaining Ring Basics
“A retaining ring is a removable shoulder,” explained Benjamin Moskalik, senior research and development engineer for Smalley. “That’s the basic definition of what a retaining ring is. Instead of having to machine in a shoulder, or if you need to be able to place the shoulder in after you’ve inserted a component, that’s where a retaining ring would come into play.”
What sets Hoopster rings apart from other retaining rings is that they do not require a deep groove.
“This is very important for customers who have, for example, a thin-walled tube where they don’t have the option to put a deep groove in because if they do they’ll end up cutting the tube in half,” said Moskalik.
However, it’s important to note that although Hoopster rings can work with a shallower groove than other types of retaining rings, a groove is still necessary. “We’ve been asked if you can use a Hoopster with absolutely no groove at all,” said Moskalik. “That tends to be difficult because there’s not enough cling or friction force to hold the ring in place and really retain anything, but if you have something like a crimped shoulder in the tube, that should be adequate.”
Hoopster Retaining Ring Applications
So where can you find a Hoopster retaining ring in action?
That depends on the size of the ring. Smalley offers standard Hoopsters in sizes ranging from .375” to 3” with a similarly wide range of applications.
“The tiny ones are used in medical applications,” said Moskalik. “Hoopsters are most often used as retaining rings, but they can also hold two radial parts together; think of it as a barrel hoop. Medical devices, surgical tools, things like that are where you find the really tiny rings.”
“As you ramp up to the higher side, you get into industrial equipment,” Moskalik continued. “We’ve seen Hoopsters used in jet engines, for example. That’s where you’re going to find some of the bigger sizes.”
The most common applications involve a tube or a pipe. “Plenty of those types of tools—like a downhole oil tool—use a lot of thin-walled piping or tubing where they just don’t have the option to put in a deep groove,” said Moskalik.
Hoopsters can also be used as endcaps or plugs for a cylinder with a shaft inside it that needs to be removed for cleaning purposes. “I’ve also seen cylindrical applications where there are a lot of components packed in, and at the very end you have a ring holding it all together,” Moskalik added. “Not only does it work in thin-walled applications, but in cases where you have to pass a component through something else. Not having a profile sticking out can really help with the assembly process.”
It’s also worth noting that Hoopster retaining rings can be used in external applications as well. “We have two different series,” explained Moskalik. “There’s the HH [‘Hoopster Housing’] for internal and the HS [‘Hoopster Shaft’] for external.”
Moskalik explained that, in the case of the external rings, there are RPM limits that should be followed:
“It’s very possible to centrifuge the ring out of the groove, but just like any of our retaining rings, we have a formula and we’ve also pre-calculated their rotational capacity. Usually, the rotational capacity of a ring is maximized when you have a bigger radial wall, meaning the width of the material between the inside and outside diameter of the ring. With Hoopsters, there’s not much radial distance between the outside and the diameter, so the rotational capacity on them is lower than a normal retaining ring. It can resist some, but probably not as much as our heavy-duty Spirolox rings.”
Installing and Removing Hoopster Retaining Rings
In addition to their low profile, another benefit of Hoopster retaining rings is that they’re relatively quick to install compared to other retaining ring types. “We’ve found that customers can slide Hoopsters in very easily and they just snap into place because you’re not putting them on with pliers, which they can potentially fall off of. So they should be easier to put on,” said Moskalik.
On the removal side, Hoopster rings are available with or without a removal provision.
“The removal provision is a little bent end that gives you something to grab onto with a plier or to pick underneath to get it started out of the groove. That introduces a bit of a profile that isn’t there without the removal provision, and for some customers it’s important to have a low profile so they go without it. That makes the ring more difficult to remove, but you can still use a pick to get it out of there.”
Indeed, the difficulty of removing a Hoopster ring from an assembly without a removal provision can actually be seen as a kind of tamper proofing. Although it’s not a guarantee, it could reduce the chances of tampering.
“It would require someone to have a dental pick, and how many people have one of those in their back pocket?” Moskalik asked rhetorically.
One Retaining Ring to Rule Them All?
Hoopster retaining rings are a great option in cases where other retaining ring types would be too bulky or when your part can’t support a deep groove. They are available from Smalley in carbon and 302 stainless steel in a variety of sizes, including custom sizes at no tooling charge.
For more information, visit the Smalley website or send a design question to one of the company’s engineers.
Smalley Steel Ring has sponsored this post. All opinions are mine. --Ian Wright