A discussion of retaining rings inevitably must begin with a debunking of myths; namely, that one style of retaining ring will function better than all other types in all instances. No one retaining ring style is better than another. Rather, the parameters of an application actually determine which retaining ring is best to use, and this can vary from assembly to assembly. Selecting the correct type of retaining ring based on variables such as installation/removal requirements, anticipated thrust load, and end-play take-up can ensure the retaining ring chosen will perform reliably, while significantly reducing fastener costs.
There are three main types of retaining rings available to the designer: tapered, constant section, and spiral. These typically are made from carbon steel, stainless steel, or beryllium copper, and feature a variety of finishes for corrosion protection. Again, the final selection of the type and size of retaining ring depends upon these and the previously mentioned parameters.
- Tapered Section Retaining Rings make uniform contact with the groove with a gap between the lugs. The lugs and lug holes are not meant to interfere with the application, but provide a convenient means to install/remove the ring using manual or automated equipment. Tapered rings are used in a variety of automotive applications, including ABS brakes and steering gears.
- Constant Section Retaining Rings are elliptical when installed in the groove, making only three-point contact. As a result, they accommodate less force than a tapered section ring, making them an economic alternative to this type of ring, depending on the application. They also offer more clearance than a tapered ring, but are more difficult to install/remove. Automotive transmissions are typical applications for constant section rings.
- Spiral Retaining Rings make 360° contact with the groove, unlike the other two types. However, they are difficult to install and remove and accommodate less force (on a ring-to-ring comparison). Typical applications include sprinkler valves, clutch drives, and quick-connect devices.
The following application illustrates how the particular requirements of an application will dictate what type of retaining ring to specify. A customer selected a constant section retaining ring to retain a transmission cooling valve located in radiators found in most police cars. This valve, which regulates the oil temperature, is installed in the radiator after an oven brazing operation. A constant section ring was found to be the most economical and effective choice for the application (Figure 1).
However, if a leak is detected in testing, the radiator must go through the brazing operation a second time. Since the valve might melt during this process, it must be removed. The customer would pry the constant section ring off, but this often ruined the groove, causing many valves to be scrapped. In this case, the customer switched to a tapered retaining ring (Figure 2), since the lug holes could be used to easily remove the ring, if necessary. Also, this particular ring featured lugs that are reversed, ensuring there would be enough clearance so the lugs would not interfere with the operation of the valve.
In contrast to the above, a ring that will provide uninterrupted, 360-degree contact is preferred to withstand the rotational speeds of this gear/axle assembly. Removal of the ring is also not a significant consideration. In this instance, a spiral retaining ring is the most cost-effective and logical choice (Figure 3).
To meet today’s stringent standards for cost reduction and value-added design, the designer must consider all options. This includes retaining rings and the flexibility afforded by the different styles when searching for an appropriate fastener to accomplish a given task. Matching this task to the appropriate ring can help you meet your cost reduction targets without sacrificing quality or performance.