National® Industrial Seals 2015 by Timken

More catalogs by Timken | National® Industrial Seals 2015 | 34 pages | 2015-10-07

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Page 26 of National® Industrial Seals 2015

section 1-c technical sealing system preparation and seal installation shaft requirements proper engineering of the components of the assembly is necessary for seal reliability shaft requirements have been determined by the rubber manufacturer’s association through thousands of hours of testing the following items should be considered at the original equipment design stage or whenever anexisting application is to be upgraded shaft finish — shaft finish a prime factor in proper functioning of a lip seal should be specified as 10-25 microinches ra 0.20-0.60 micrometers ra with no machine lead shaft lead — maximum permissible lead angle is 0 ± 0.05° the most acceptable method for obtaining this surface characteristic is plunge grinding shaft diameter — shaft diameter tolerances are shown below tolerances greater than those shown should be used only if agreed upon between user and supplier shaft diameter inches tolerances shaft diameter mm tolerances to and including 4.000 4.001 through 6.000 6.001 through 10.000 10.001 and larger ± .003 ± .004 ± .005 ± .006 to and including 100 100.01 through 150 150.01 through 250 250.01 and larger ± 0.08 ±0.10 ± 0.13 ± 0.15 shaft hardness — radial lip type seals will function satisfactorily on mild steel cast iron or malleable iron shafts under normal conditions however the section of the shaft contacted by the sealing lip should be hardened to rockwell c30 minimum if however the shaft may be nicked or damaged during handling or assembly a rockwell c45 minimum is recommended shaft chamfer — to aid installation and help prevent damage to the seal lip the leading edge of the shaft should have a chamfer or radius which must be smooth and free of nicks or rough spots shaft-to-bore misalignment stbm — the distance the center of rotation is displaced from the center of the bore it usually exists to some degree due to normal machining and assembly tolerances misalignment results in uneven wear and if excessive will shorten seal life to measure attach a dial indicator to the shaft and indicate off the seal bore while rotating the shaft for specific limitations see the national oil seal design type and description charts on page 6 7 dynamic runout — twice the distance the center of the shaft is displaced from the center of rotation it can result from a bent shaft lack of shaft balance or other manufacturing variables to measure find the total movement of an indicator held against the seal area of the slowly rotating shaft for specific limitations see the national oil seal design type and description charts on page 6 7 shaft material — steel stainless steel and certain cast irons all provide good sealing surfaces if finished properly brass or bronze shafts are not recommended nor are alloys of aluminum zinc magnesium and other similar elements if plating is considered it should be hard nonporous chrome plate flaking or plating exposes razor edges which may cut the seal lip xvi