What are Retaining Rings?
Retaining rings, also known as snap rings or circlips rings, are metal fasteners that are installed in a groove on a shaft or in a housing or bore, creating a shoulder that holds an assembly. The devices hold the parts in place with a compact, lightweight design that requires fewer machining operations than other fastening techniques.
The trends in recent years have moved away from threaded fasteners and towards retaining rings. They eliminate the threading, tapping, drilling, and other machining operations associated with more traditional fasteners such as screws, nuts, bolts, cotter pins, washers, and more.
You can significantly reduce manufacturing costs because the grooves can be machined using other manufacturing processes. Overall, they offer a more compact, functional design than their traditional counterparts.
Engineers specify retaining rings based on an application’s:
- Installation and removal requirements
- Rotational speed
- Conditions and operating environment
- Expected force load(s) on the ring
Retaining rings can be 1 mm to 1 m in diameter. Different combinations of size, shape, style, and material result in designs that work in a wide variety of industries and applications. For example, a standard car may have more than 50 retaining rings in powertrain, steering, and passenger safety systems.
Retaining rings are also used in several other applications such as fitness equipment, wind turbines, storage brackets, bicycles, doorknobs, gas pumps, office equipment, and many others.
Types of Retaining Rings
There are four main types of retaining rings available, each of which may then be broken down into sub-types depending on unique application needs:
- Tapered section
- Axially assembled
- Radially assembled
- Axially assembled
- Constant section
- Circular push-on
1. Tapered section retaining rings
Tapered section retaining rings decrease symmetrically from the center to the free ends, remaining circular when contracted or expanded within the limits of normal use. This assures contact with the groove along the entire periphery of the ring.
These rings may be installed axially (horizontally along with the center point of an axis) or radially (externally along the radius of a circle). Depending on the size of the ring in question, it may be manufactured in one of two ways:
- For smaller rings: using a die and stamping on a press from a coil of steel or copper
- For larger rings: wire forming, in which rectangular wire is coiled into the shape of the ring.
1.1 Axially assembled
Axially assembled retaining rings are installed into machined grooves in housings/bores (internal) or on shafts (external). These rings are manufactured with lug holes, small holes in the lugs of both axial internal and external retaining rings, that are used to install/remove them, using pliers designed for this purpose.
1.1.1 Inverted retaining rings
Inverted retaining rings are a variation of axially assembled rings in which the lug holes are inverted to fit in the bottom of the groove. Inverting the lugs allows greater clearance on a shaft or in a housing and forms a higher uniform shoulder good for retaining bearings and other components with large corner radii or chamfers.
1.1.2 Beveled retaining rings
Beveled retaining rings feature a 15° beveled or angled edge. This angle allows the ring to wedge itself between the groove and the retained part until it can go no farther, effectively “locking” everything in place. Think of placing a cork in a bottle. The cork is forced into the opening until it is wedged as far into the opening as possible.
The same thing happens when a beveled retaining ring is installed into an application. The ring is wedging itself into place between the groove wall and the retained part, resulting in what is referred to as rigid end-play take-up.
1.1.3 Bowed retaining rings
Bowed retaining rings are curved versions of standard flat internal and external retaining rings and exert a pre-load on an assembly when installed in the groove. This takes up the end-play and acts like a spring, which keeps the assembly in compression.
In manufacturing, parts can not be produced to an exact dimension; as a result, if they are made on the low side of the tolerance, they will be loose or have a play on the shaft when a standard ring is installed.
If they are made on the high side of the tolerance, they will extend further into the groove and prevent a standard ring from being fully installed. Compensating for accumulated tolerances is what bowed retaining rings are designed to do, by acting as a spring once installed into the groove.
1.2 Radially assembled
Radially assembled retaining rings are installed externally into machined grooves on a shaft. These rings have no lug holes and must be installed using applicators.
Self-locking retaining rings can be installed in a housing/bore or on a shaft that has not had a groove machined into it. Self-locking rings with no lug holes are impossible to remove without either destroying the ring or warping it out of specified tolerances.
2. Constant section retaining rings
Constant section retaining rings (snap rings) feature a uniform, constant section. In other words, the material used to make the ring is the same width at any point along the circumference of the ring.
When they are contracted or expanded, they take on an elliptical deformation. As a result, they contact the groove at three or more isolated points but never continuously around the periphery. These rings are made from either flat or round wire.
3. Spiral retaining rings
Spiral retaining rings are axially installed into housings/bores (internal) or onto shafts (external), making 360° contact with the groove. Spiral retaining rings have no ears or lugs to interfere with the assembly. These rings are manufactured by coiling flat wire into the shape of the finished retaining ring.
Spiral rings are provided with a removal notch to simplify the removal process. Spiral retaining rings can be economically produced in special alloys like stainless steel because the manufacturing process eliminates scrap.
No special tools are required for installation or removal. Duck-billed pliers can be used in installing and removing external spiral rings.
4. Circular push-on
A Circular push-on ring resembles a toothed washer, commonly fabricated in metal. These are installed by pressing onto the end of a grooved shaft until the nut’s inner teeth snap into the groove. The use of push nuts avoids the cost of threading a nut onto the end of the shaft during the manufacturing process.
Advantages of Retaining Rings
- Less shaft/housing preparation (threading, tapping, drilling, etc.)
- Reduced weight and size of finished design
- Lower costs of raw material and labor
- Cheaper compared to other fastening methods
- Use less raw material for a given size
- Reduce and avoid complex machining such as threads and under cuts
- Compact design and Can be assembly quicker
- No special training require for assembly
- Light weight and Easy to install
- Unlike threaded alternatives, significantly reduce production cost