Machinery's Handbook, 31st Edition
2466 Ball and Roller Bearings Design and Installation Considerations.— Interference fitting will reduce bearing ra - dial internal clearance, so it is recommended that prospective users consult bearing man ufacturers to make certain that the required bearings are correctly specified to satisfy all mounting, environmental and other operating conditions and requirements. This check is particularly necessary where heat sources in associated parts may further diminish bear- ing clearances in operation. Standard values of radial internal clearances of radial bearings are listed in AFBMA- ANSI Standard 20. Allowance for Axial Displacement.— Consideration should be given to axial displace ment of bearing components owing to thermal expansion or contraction of associated parts. Displacement may be accommodated either by the internal construction of the bearing or by allowing one of the bearing rings to be axially displaceable. For unusual applications consult bearing manufacturers. Needle Roller Bearing Fitting and Mounting Practice.— The tolerance limits required for shaft and housing seat diameters for needle roller bearings with inner and outer rings as well as limits for raceway diameters where inner or outer rings or both are omitted and rollers operate directly upon these surfaces are given in Table 18 through Table 21, inclusive. Unusual design and operating conditions may require a departure from these practices. In such cases, bearing manufacturers should be consulted. Needle Roller Bearings, Drawn Cup: These bearings without inner ring, Types NIB, NB, NIBM, NBM, NIY, NY, NIYM, NYM, NIH, NH, NIHM, NHM, and Inner Rings, Type NIR depend on the housings into which they are pressed for their size and shape. There- fore, the housings must not only have the proper bore dimensions but also must have suf- ficient strength. Table 18 and Table 19, show the bore tolerance limits for rigid housings such as those made from cast iron or steel of heavy radial section equal to or greater than the ring gage section given in AFBMA Standard 4, 1984. The bearing manufacturers should be consulted for recommendations if the housings must be of lower strength ma- terials such as aluminum or even of steel of thin radial section. The shape of the housing bores should be such that when the mean bore diameter of a housing is measured in each of several radial planes, the maximum difference between these mean diameters should not exceed 0.0005 inch (0.013 mm) or one-half the housing bore tolerance limit, if smaller. Also, the radial deviation from circular form should not exceed 0.00025 inch (0.006 mm). The housing bore surface finish should not exceed 125 micro-inches (3.2 micrometers) arithmetical average. Table 18. AFBMA and American National Standard Tolerance Limits for Shaft Raceway and Housing Bore Diameters—Needle Roller Bearings, Drawn Cup, Without Inner Ring, Inch Types NIB, NIBM, NIY, NIYM, NIH, and NIHM ANSI/ABMA 18.2-1982 (R1999)
Shaft Raceway Diameter a Allowable Deviation from F w
Housing Bore Diameter a Allowable Deviation from D
Basic Bore Diameter under Needle Rollers, F w
Basic Outside Diameter, D
Inch
Inch
Inch
Inch
Over
Incl.
High
Low
Over
Incl.
Low
High
OUTER RING STATIONARY RELATIVE TO LOAD
0.1875 1.8750 0.1875 1.8750
1.8750 3.5000 1.8750 3.5000
+0 +0
0.3750
4.0000
+0.0005
− 0.0005 − 0.0006 − 0.0010 − 0.0011
− 0.0005
… … …
…
OUTER RING ROTATING RELATIVE TO LOAD
0.3750
4.0000
+0 …
− 0.0005 − 0.0005
− 0.0010
… … …
a See text for additional requirements. For bearing tolerances, see Table 10.
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online