Machine Design

Spherical plain bearings need no maintenance

The top shaft is supported by angular contact spherical plain bearings in a so-called O arrangement. The bottom illustrations shows the X arrangement.

The weight of the rotary table and anything placed on it is carried by the lower axial spherical plain bearing. The upper plain bearing is a radial spherical design.

Maintenance-free spherical plain bearings boast several advantages over the rolling-element designs. For example, they do not require lubrication because of a hard chromium/PTFE fabric sliding-contact surface. The sliding layer is 0.5-mm thick, asymmetrical, and resistant to moisture. An adhesive bond resists separation. The bearings support high dynamic and static loads such as the basic ISO dynamic load rating of 200 N/mm2 and static load rating Co based on 400 N/mm2. Static loads to 500 N/mm2 are permissible. The bearings have a friction factor of only 0.02 µ at a contact pressure of 200 N/mm2.

There are several variations to the bearing design. Radial spherical plain bearings (RSPB), for instance, are good for supporting radial loads and where bearings must work without maintenance. The design is also recommended where it's suitable to lubricate a metallic sliding-contact surface, as in unilateral loads. The design can be combined with axial spherical plain bearings to support axial loads.

RSPBs are available with lip seals to protect against contaminants and spray. A favorable load-to-mass ratio gives the bearing a compact, high-performance arrangement. The units tolerate alternating loads to 100 N/mm2. Lip seals are fitted on both sides and operating temperatures can range from –50 to 130°C. The devices fit shaft diameters from 17 to 600 mm.

Angular contact spherical plain bearings (ACSPB), another variety, support radial and axial loads. The bearings provide an alternative to tapered roller bearings. ACSPBs are suitable for oscillating dynamic loads, and can be used in paired 0 or X arrangements. (Accompanying illustrations show these arrangements). The bearings fit shafts from 25 to 300-mm diameter.

Axial spherical plain bearings (ASPB), a third variety, are best used to support axial loads but can be combined with radial spherical plain bearings to DIN 648, Series E, to support radial loads. ASPBs are suitable for use as support or base bearings subjected to dynamic loads. These units fit shafts from 10 to 360-mm diameter.

This information provided by INA USA, Fort Hill, South Carolina.

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