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centrifugal force that can create sudden fatigue failure. While dense material can store more energy than low density material, the flywheel is also subject to higher centrifugal force and thus fails at lower rotational speed than one comprised of low density material. Therefore, the tensile strength of the flywheel material becomes an important reliability consideration. A base failure rate of 0.2 failures per million hours can be assumed for a flywheel based on published failure rate data. Table 23-8 provides service factors to modify the expected failure rate of a flywheel for the expected operating environment. Table 23-8. Service Factors for a Flywheel Driven Machinery Normal Torque, Low Velocity Normal Torque, High Velocity High Torque, Low Velocity High Torque, High Velocity Uniform 1.1 1.3 1.2 1.4 Light shock 1.2 1.4 1.3 1.5 Medium shock 1.3 1.5 1.4 1.6 Heavy shock 1.4 1.6 1.5 1.7 23.8 HINGE A hinge is a joint that holds two parts together so that one can swing relative to the other. Most hinges are separate parts which are added to a completed assembly for further installation. Living hinges, on the other hand, are molded into a part during the forming process. A Butt Hinge is composed of two plates attached to abutting surfaces of a door and door jamb and joined by a pin. A Gravity Hinge closes automatically as a result of the weight of a door to which it is attached. A Strap Hinge is a surface mounted hinge with long flaps of metal on each side, by which it is secured to a door and adjacent post or wall. A Pintle Hinge pivots about an upright pin or bolt. A Spring Loaded Hinge can automatically open or close a door, eliminating the need for a latch to secure the door in its resting position. Rotation of a hinge is permitted along only one axis, and during bending the neutral axis does not change length. Therefore, in the elastic case, the hinge can be considered as a beam undergoing pure bending, and the neutral axis forms a circular arc. Built-in plastic hinges generally undergo some plastic deformation. The hinge Miscellaneous Parts 23-11 Revision B

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