Machinery's Handbook, 31st Edition
2452 Ball and Roller Bearings Of additional value are: 1) their resistance to indentation from shock loads or oscillation; and 2) their self-lubricating properties. Usually these bearings are not available from stock, but must be designed and produced in accordance with the data made available by the plastics processor. Pillow Block and Flanged Housing Bearings.— Of great interest in the shop and particu- larly adaptable to “line-shafting” applications are a series of ball and roller bearings sup - plied with their own housings, adapters, and seals. Often called pre-mounted bearings, they come with a wide variety of flange mountings permitting location on faces parallel to or perpendicular to the shaft axis. Inner races can be mounted directly on ground shafts, or can be adapter-mounted to “drill-rod” or to commercial shafting. For installations sensitive to imbalance and vibra tion, the use of accurately ground shaft seats is recommended. Most pillow block designs incorporate self-aligning types of bearings so they do not require the precision mountings utilized with more normal bearing installations. Conventional Bearing Materials.— Most rolling contact bearings are made with all load carrying members of full hard steel, either through- or case-hardened. For greater reliability this material is controlled and selected for cleanliness and alloying practices in conformity with rigid specifications in order to reduce anomalies and inclusions that could limit the useful fatigue life. Magnaflux inspection is employed to ensure that ele - ments are free from both material defects and cracks. Likewise, a light etch is employed between rough and finish grinding to allow detection of burns due to heavy stock removal and associated decarburization in finished pieces. Cage Materials.— Standard bearings are normally made with cages of free-machining brass or low carbon sulfurized steel. In high-speed applications or where lubrication may be intermittent or marginal, special materials may be employed. Iron-silicon-bronze, laminated phenolics, silver-plating, over-lays, solid-film baked-on coatings, carbon- graphite inserts, and, in extreme cases, sintered or even impregnated materials are used in separators. Commercial bearings usually rely on stamped steel with or without a phosphate treat ment; some low cost varieties are found with snap-in plastic or metallic cages. So long as lubrication is adequate and speeds are both reasonable and steady, the materi als and design of the cage are of secondary importance when compared with those of the rolling elements and their contacts with the races. In spite of this tolerance, a good portion of all rolling bearing failures encountered can be traced to cage failures resulting from inadequate lubrication. It can never be overemphasized that no bearing can be designed to run continuously without lubrication! Standard Method of Bearing Designation.— The Anti-Friction Bearing Manufacturers Association has adopted a standard identification code that provides a specific designa - tion for each different ball, roller, and needle bearing. Thus, for any given bearing, a uni- form designation is provided for manufacturer and user alike, so that the confusion of different company designations can be avoided. In this identification code there is a “basic number” for each bearing that consists of three elements: a one- to four-digit number to indicate the size of the bore in numbers of millimeters (metric series); a two- or three-letter symbol to indicate the type of bearing; and a two-digit number to identify the dimension series to which the bearing belongs. In addition to this “basic number” other numbers and letters are added to designate type of tolerance, cage, lubrication, fit up, ring modification, addition of shields, seals, mount ing accessories, etc. Thus, a complete designating symbol might be 50BC02JPXE0A10 , for example. The basic number is 50BC02 and the remainder is the supplementary num- ber. For a radial bearing, this latter consists of up to four letters to indicate modification of design, one or two digits to indicate internal fit and tolerances, a letter to indicate lubri - cants and preservatives, and up to three digits to indicate special requirements.
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