Machinery's Handbook, 31st Edition
PLAIN BEARINGS
2399
Methods of Bearing Retention
Fig. 4a. Set Screws
Fig. 4b. Woodruff Key
Fig. 4c. Bolts through Flange Fig. 4d. Bearing Screwed into Housing
Fig. 4e. Dowel Pin Fig. 4f. Housing Cap Two major functions must be achieved by all sealing applications: prevent escape of fluid; and prevent migration of foreign matter from the outside. The first determination in selecting the proper seal is whether the application is static or dynamic. To meet the requirements of a static application there must be no relative motion between the joining parts or between the seal and the mating part. If there is any relative motion, the application must be considered dynamic, and the seal selected accordingly. Dynamic sealing requires control of fluids leaking between parts with relative motion. Two primary methods are used to this end: positive contact or rubbing seals; and controlled clearance noncontact seals. Positive Contact or Rubbing Seals: These seals are used where positive containment of liquids or gases is required, or where the seal area is continuously flooded. If properly selected and applied, contact seals can provide zero leakage for most fluids. However, because they are sensitive to temperature, pressure, and speed, improper application can result in early failure. These seals are applicable to rotating and reciprocating shafts. In many assemblies, positive-contact seals are available as off-the-shelf items. In other instances, they are custom-designed to the special demands of a particular application. Custom design is offered by many seal manufacturers and, for extreme cases, probably offers the best solution to the sealing problem. Controlled Clearance Noncontact Seals: Representative of the controlled-clearance seals, which includes all seals in which there is no rubbing contact between the rotating
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