The collar is one of the simplest components in machine design and one of the most integral. Collars can be found on almost any type of machinery and are often accessories to other components. Collars perform multiple functions, typically securing bearings and sprockets to shafts, housing components in motor and transmission assemblies, and acting as mechanical stops.
What are Some Design Considerations for Shaft Collars?
When selecting the proper collar for your application, several factors include material, installation and removal, accuracy, clamping force, finish, bore diameter, and hole pattern.
1. Materials
Material is always a consideration for any application when selecting a fastener, and collars are no exception. Collars are made of aluminum, carbon steel, and stainless steel.
- Aluminum collars are lightweight, durable, and corrosion-resistant. They also have excellent hold power, making them a popular choice for many applications.
- Carbon steel collars provide a durable, economical solution for bearing retention, spacing, and more. However, they are more susceptible to corrosive environmental conditions. Some carbon steel collars are galvanized or coated with a black oxide coating for extra protection.
- Stainless steel collars offer excellent corrosion resistance to salt water, acids, and other corrosive agents. The holding power of stainless steel collars is similar to that of carbon steel collars, but the weak point may be the cap screws. If the cap screws that hold the clips together are made of poor-quality material, it may affect the holding power of the collar and may fail prematurely. This can be avoided by using the same grade of hardware as the collar.
2. Installation and Disassembly
How the collar is fitted and removed in the application helps determine which type of collar to choose. Set-screw, one-piece, and two-piece necklines are the most popular varieties, and each variety installs slightly differently.
How to Install and Remove Set Screw Shaft Collars:
- Unscrew the set screw, so it does not protrude into the inside diameter of the collar.
- Slide the collar over the end of the mating shaft.
- Position the collar at the desired location.
- Tighten the set screw until it engages the mating shaft.
- Do not over-tighten the set screw, as damage to the shaft and collar can result.
- To remove, loosen the set screw and slide the collar off the shaft.
How to Install and Remove Single Split Shaft Collars:
- Loosen the integrated socket head cap screw to allow the shaft collar to expand slightly during installation.
- Slide the shaft collar over the end of the mating shaft.
- Position the collar in the desired location.
- Tighten the screw until the collar is firmly tightened around the shaft.
- Do not over-tighten. The gap in single split collars should not be closed.
- To remove, loosen the cap screw and slide the collar off the shaft.
How to Install and Remove Double Split Shaft Collars:
- Remove both integrated socket head cap screws and separate the two pieces of the shaft collar. If installing radially, steps for installing a single split shaft collar can be followed.
- Position the separate collar pieces adjacent, aligning the mating screw holes onto the intended shaft.
- Reinsert the cap screws into the collar and tighten until the screw threads engage the shaft collars.
- With the collar as one piece, position it to the desired location and finish tightening the cap screws.
- Alternate tightening the screws, so the collar body closes around the shaft uniformly.
- Do not over-tighten the screws. The gaps between the two collar sections should not be closed.
- Loosen or remove the cap screws from the collar to disengage the collar from the shaft.
3. Precision
Accuracy is the relationship between the collar and its perpendicularity to the collar hole. The collar surface is machined with grooves to indicate vertical accuracy and which side of the collar is carrying the load. The load side of the collar should be positioned against the attached gear, sprocket, hub or pulley. If a collar with a precision face is not used, the pressure on the collar will be unevenly distributed, causing the collar to “walk” off-axis.
4. Clamping Force
Clamping force varies by collar type. A strong set screw ring provides the minimal holding force with a single set screw that engages the mating shaft. Monobody provides greater strength by snugly fitting the clamp body to the shaft. Double openings provide slightly greater holding force than single openings and distribute holding force evenly around the shaft. Single and double split rings maintain maximum clamping force. For applications requiring high axial loads, tapped holes are available.
5. Finish
Carbon steel collars are available in black oxide and galvanized. Galvanized for maximum corrosion protection. However, a slippery finish will reduce the collar’s support. Black oxide does not offer as much protection as galvanized. However, its rough finish provides more holding power than galvanized.
6. Bore Size
Bore diameter refers to the inside diameter of the collar. If the hole is too large, the collar will not provide sufficient clamping force on the target shaft and may loosen prematurely. Conversely, if the hole is too small, it will not fit on the shaft.
7. Bore Style
Hole pattern refers to the inside diameter profile of the collar, including the type of hole and whether the hole is threaded. Round is the most popular hole pattern. However, collars with hex holes exist for applications using hex shafts. Threaded and smooth bores are also featured to consider when selecting a collar. Threaded holes provide positive engagement through threads, providing greater retention than smooth eyelets.
A collar is a small component primarily used in the power transmission industry. A collar is also called a retaining ring. There are various “types” of collars, but the two most popular types are “solid” and “split.” Collars hold components in places, such as sprockets, bearings, wheels, or pulleys. Each collar type is available in a variety of hole types, including metric, hex, threaded, square, and Dholes.