Motion systems application examples: Shaft collars and where they work

Mike Santora

8 years ago

By Mike Santora

Shaft collars are part of nearly all types of moving machinery—including designs for mechanical, medical, aerospace, automotive and industrial industries. In electric-motor-driven designs, they’re most common at the gearbox and motor assemblies. Shaft collars satisfy three basic functions:

set shaft position
space components on shafts
limit shaft movement

Some Ruland shaft collars (as the one shown here) attach encoders to shafts. Clamp-style collars need precise face-to-bore mating to meet the demands of medical equipment. Ruland makes their clamp shaft collars with smooth or threaded bores from 3 to 150 mm.

As such, they commonly work as mechanical stops on actuators and cylinders, as locating components for gearboxes and motors, and for keeping sprockets and bearings on shafts. Some shaft-collar variations are more suitable for given applications than others.

Setscrew shaft collars are low cost and install easily, so are quite common despite the fact that clamping collars (with distinct benefits over setscrew designs) have been around for some time. Yet, setscrew shaft collars are still common in today’s applications that don’t need post-installation adjustments and where cost is a concern.

Some Ruland collars function as mechanical stops

Clamp-style shaft collars

Clamp-style collars use compressive forces to secure components to shafts without marring them like setscrews. These collars distribute clamping force uniformly around the shaft (and not at one point) so users can easily adjust them without damaging the shaft. Clamp-style shaft collars are either one-piece or two-piece collars; the two-piece collar most evenly distributes force and creates the strongest hold. While these types of collars are found in nearly any industry where power transmissions are present, they are increasing in medical applications.

In this image we see a hygienic clamping assembly from Ruland on a mozzarella production machine. The collar is located on the outside of the machine and holds the shaft in place in the event of failure. This component is made of a 303 stainless steel shaft collar and other FDA compliant materials. It has none of the surface irregularities, like saw cuts and screw pockets that allow bacterial contamination in other types of shaft collars. This uniform surface allows for easy clean-up around the moving parts of the machine. The collar is also IP69K rated for dust and water up to 176°F/80°C with 10 MPa of pressure.

Clamp-style shaft collars for medical equipment

Clamp-style shaft collars work as guides, spacers, and stops on medical equipment, but only collars with tightly controlled face-to-bore perpendicularity (with a TIR of less than or equal to 0.05 mm) satisfy the design requirements in these critical designs—especially where the collar functions as a load-bearing face or aligns critical motion components such as bearings or gears. Clamp-style shaft collars distribute compressive forces evenly around the shaft for strong hold. Two-piece collars have more holding power than one-piece designs and install in place. In fact, machine integrators can add these collars to a design at any point in the manufacturing process.

Some shaft collars use fastening hardware that tests beyond industry standards for maximum torque capabilities and holding power. For example, some stainless-steel shaft collars sport hardware that can also resist corrosion and satisfy regulatory standards; the stainless hardware undergoes surface treatment to prevent galling. Other clamp-style shaft collars come in steel with a black oxide or zinc finish, aluminum, titanium, and engineered plastic. Black-oxide on steel resists corrosion and smooths screw installation to boost the transfer of screw clamping forces to the collar-shaft interface while preventing stick-slip.