Pivot Bearings Information
Pivot bearings are frictionless bearings that are suitable for pivotal, angular, or oscillating applications. A cantilevered pivot bearing is a commonly used type of pivot bearing for applications such as:
- gimbal rings
- mirror mounts
- four bar linkages
- vibration isolation systems
Cantilevered pivot bearings, which are sometimes called a single-ended pivot bearing, allow one end to rotate in a limited number of degrees when one end is restrained. Cantilevered flexural pivot bearings are used to support an overhung load. Flexural pivots can also be used in a gimbal type of arrangement. A double-ended pivot bearing is a pivot bearing whose center section rotates a limited number of degrees when both end sections are restrained. Typically, these pivot bearings are used to support an overhung load.
Flexural pivots are pivot bearings that allow mechanical components to pivot about a common axis through a limited angle relative to each other. A flexural pivot is generally frictionless because its flexing elastic elements affect the angular motion rather than displacing the contact surface. Flexural pivots are relatively expensive pivot bearings that are used for specialized high-technology products, such as aircraft control linkages and gimbals for scientific instruments. Torsional spring rate is the amount of torque, measured in Nmm/degree or lb-in/degrees, which a torsion spring needs to create. Torsion springs are used with pivot bearings to provide a circular (torsional) force through the legs of a spring. Examples of torsion springs include:
- axial legs
- tangential legs
- radial legs
- radial over center and one tangential leg springs
Pivot bearings are used to restrain a piston and allow for sufficient clearance for piston expansion to remove the risk of seizure, without incurring damage when the piston runs cold. Pivotal pistons convert combustion pressure into torque by sliding the piston within a cylinder that is restrained and supported by a skirt. Due to the clearance required for expansion, the piston can rock and slap the cylinder, causing the compression seals or rings to become unseated from the surface of the cylinder.