What are retaining rings?
Retaining Rings are precision engineered components that are designed to be applied on shafts or in bores and provide a shoulder that accurately positions, locates and retains other parts of an assembly.
The first retaining rings of other than plain wire construction were patented in Germany in 1928 by Seeger-Orbis, and were known as “Sicherungsringes” which, literally translated means “Safety Rings”. The first stamped retaining ring designs were the basic internal (5000) and basic external (5100) series. Radially installed E-Rings (5133) followed, and then came a whole range of design variations to suit specific application needs.
Many different types of retaining rings have been developed over the years, each a solution to a specific problem. Different types of rings are available to solve issues such as: tolerance take-up, clearance diameter, thrust load capacity, flexible installation, rpm capacity, impact loading, non-removable lock-rings, groove-less push-on fastening and radial installation.
As an engineering concept, the retaining ring is still relatively young and has certainly not yet reached it's peak of utilization as a retaining device.
How are retaining rings used?
Retaining Rings work by creating a shoulder that can hold components in place. The retaining shoulder is created when the ring attaches itself to the bore or shaft, typically by snapping into a groove. Ordinarily (however not always) a groove is dug into the shaft or bore, and this groove becomes the seat for the retaining ring. Retaining rings are designed such that their contact diameter has some interference fit with the groove in which they fit. This creates a “snug” fit between the ring and groove. The term used to describe the amount of interference fit is “cling”.
Cling causes the retaining ring to fit tightly and securely against its groove bottom. Without cling a ring would have a loose fit and would “rattle” in its groove. This lack of cling would decrease the retention capacity of the ring because a “cling-less” ring is free to move radially, creating weak retention points that will ultimately cause the assembly to fail. Another key factor is the width of the groove. The groove width is slightly larger than the rings thickness, thus creating a snug axial fit. The tight axial fit along with the cling to the groove bottom create a rigid shoulder which can retain thrust loads.
What advantages does a retaining ring have when compared to a permanent shoulder?
Instead of using a retaining ring, it is possible to machine a permanent shoulder on to a bore or shaft. Creating a permanent shoulder requires one to start with a larger than desired shaft (or a thicker than desired bore), and to machine away material to create the desired size. While removing the material, we would leave untouched the area where we want the shoulder to be. This approach has two disadvantages. First, the initial material will be bigger and therefore more costly. Second, the machining will take time, further adding to the cost.
To use a retaining ring in the same situation, we need only buy a shaft with the desired shaft size, and then machine away a groove for the ring. We then install the ring to create the shoulder. We start with a less expensive piece of material because it is smaller, and machine away only the groove, which is much quicker than machining away large areas of the shaft.
There are some instances where a permanent shoulder is the only solution. One variable to look at is the amount of load that the shoulder will be required to hold. If a retaining ring cannot be found that has a sufficiently high thrust load capacity, a permanent shoulder may be required.
What advantages do retaining rings have over traditional fasteners?
Holding assemblies together using traditional fasteners such as bolts, cotter pins and end caps requires more machining and forethought than assemblies that are secured using retaining rings. The reason is that traditional fasteners often require threaded components, mating threaded holes, counter-bores, and access holes. Retaining rings require only a groove, and in some cases not even a groove is required, such as push on fasteners series 5005
What are some other names for retaining rings?
* snap rings
* wire rings
* lock rings
* retainer clips
* retainer rings
* constant section rings
* tapered section rings
* wire clips
* spiral rings
* round wire rings
* square section rings
What are some places that retaining rings are used?
* piston wrist pins
* drive shafts
* hand tools
* power tools
* agricultural machinery
* torque converters
* speed reducers
* nuclear equipment
* computer equipment
* door handles
* sports equipment
* brake cylinders
* lawn mowers
* lamp assemblies
* hinge pins
* home appliances
* electric motors
* gear retainers
* hydraulic equipment
* photography equipment
* carburetor assemblies
* pressure regulators
Frequently Asked Questions:
How do I measure thickness of a retaining ring?
How to select a retaining ring.
The following design parameters should be considered When selecting a retaining ring:
* Internal or External
* Installation type
* Load capacity
* Tolerance take-up
* Clearance diameter
Internal or External
The two basic families of retaining rings are rings for bores and rings for shafts. Rings for bores are referred to as internal retaining rings, because the ring fits inside a hole (or bore). Similarly rings that fit over shafts are referred to as external retaining rings, because the are installed on the outside (or external) side of a shaft.
: Standard design for retaining rings requires installation from the axial direction, that is along the “axis” of the shaft or bore.
: Problem: Axial access to the shaft is not accessible, or quickness of assembly and disassembly is a factor.
Solution: E or C shaped rings, have a partial open side designed to allow installation from the radial direction.
* Quicker assembly process.
* Larger clearance diameters (installed outside diameter) than axially installed rings.
* Only possible in shaft applications (external).
* Deeper grooves usually required.
Rings usually have two load statistics, thrust load capacity based on ring shear and thrust load capacity based on groove yield. The lower of these two theoretical values is the thrust load capacity of the system, because once the lower value is reached, the system will fail. In most cases, the thrust capacity of the groove is the determining (lower) value. In thrust load calculations, a safety factor is used to account for imperfections in the system. Typically a safety factor between 2 and 4 is used for calculations of thrust load capacities.
Thrust Load Capacity Based on Ring Shear
: The load capacity of the ring. This is the theoretical amount of load that the ring can withstand before it shears (gets cut). The theoretical value is based on the overall thickness of the ring and the shear strength of the ring material.
Thrust Load Capacity Based on Groove Yield
: The load capacity of the groove. This is the theoretical amount of load that the groove can withstand before it deforms and fails. The theoretical value is based on the depth of the groove and the yield strength of the groove material.
How to calculate retaining ring thrust load capacity
Bowed and bevelled-edge retaining rings were designed to provide tolerance take-up. Bowed retaining rings offer resilient end-play take-up while bevelled-edge rings offer only rigid end-play take-up. Resilient end play take-up can be thought of as a spring, adjusting to take up larger or smaller tolerances after installed. Bevelled edge rings offer only rigid end-play take-up because the ring installs to the point where all tolerances are taken up and then locks into place.
Internal Bowed (resilient) Rings
Internal Bevelled (rigid)Edge Rings
External Bowed (resilient)Rings
External Bevelled (rigid)Edge Rings
External Bowed (resilient)E-Rings
Tapered section retaining rings often have lugs that allow for installation via the use of specially designed retaining ring pliers. Lugs can however sometimes interfere with other parts of the assembly, creating a situation where there is insufficient clearance for the other parts in the assembly to operate properly. In such situations, it is common to replace standard tapered section retaining rings (series 5000
) with retaining rings that have inverted lugs (series 5008
). The inverted lugs increase the amount of clearance, effective eliminating the problem described above. Another option in this situation is to choose a spiral wound retaining ring or a constant section retaining ring.