Reliability Analytics Corporation
Previous | Next      Search Home

First 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 Last

First 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 Last

Previous | Next      Search Home

Table 23.12. Typical Failure Modes for a Power Screw FAILURE MODE FAILURE CAUSE FAILURE EFFECT Screw bonded to nut Loss of lubrication Load can not be moved Screw bonded to nut Excessive load pressure Load can not be moved Scored screw shaft Misalignment Eventual power screw failure Fractured nut Excessive Pressure-Velocity Failed power screw operation Worn screw threads Foreign contaminants, loading Unstable power screw operation 23.11.2 Power Screw Failure Rate The number of variables as described previously affecting the failure rate of a drive screw make it extremely difficult to predict. Without some personal experience with the design of the power screw in its intended operating environment, it is normally best to evaluate the individual parts of the power screw using the procedures in Chapters 9 and 16. 23.12 RIVET There are two common types of rivets, lap-joint and butt-joint. In a lap-joint rivet the plates to be joined overlap each other and are held together by one or more rows of rivets. In the butt-joint, the plates to be joined are in the same plane and are joined together with a cover plate which is riveted to both plates by one or more rows of rivets. Factors to be considered in evaluating a riveted joint for reliability include type of joint, spacing of rivets, type and size of rivets, hole-size and rivet material. Both lap-joint and butt-joint rivet assemblies are subject to shear, tension, and crushing. The shearing stress in the rivet will be: P SS= (23-2) As Miscellaneous Parts 23-16 Revision B

Toolkit Home

Reliability Analytics Corporation
reliabilityanalytics.com