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
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.
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.
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.
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