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Preload is an initial load or "negative clearance" given to a bearing before or during operation. This results in the rolling element and raceway surfaces being under constant elastic compressive forces at their contact points. This has the effect of making the bearing extremely rigid so that even when load is applied to the bearing, radial or axial shaft displacement is minimized.
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Deep groove ball bearings are a non-separable type bearing with the line connecting contact points of the inner ring, steel ball, and outer ring of 0º in the radial direction. They are designed to take mainly radial loads but can handle some axial load in either direction. Angular contact bearings are also a non-separable type. The line connecting contact points of the inner ring, steel ball, and outer ring creates an angle with the line drawn in the radial direction called the contact angle. Angular contact bearings can accommodate relatively heavy axial loads in one direction in addition to radial loads. The larger the contact angle, the larger the axial loading capacity becomes.
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Paired arrangements for angular contact bearings are designated as “D2” (universal flush ground pair), “DB” (matched back-to-back pair), “DF” (matched face-to-face pair) and “DT” (matched tandem pair).
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Back-to-back (DB) or face-to-face (DF) are duplex arrangements of angular contact bearings (can also refer to taper bearings). Radial loads and axial loads in either direction can be accommodated by these arrangements. DB arrangements have a large spread between the bearing centers and should be selected when a rigid shaft is required for the application. DF arrangements have a very short spread between centers and should be applied when slight shaft misalignment is needed. The DB arrangement requires the inner rings to be clamped whereas the DF arrangement requires the outer rings to be clamped.
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D1 always denotes a relube feature (any bearing). T is old nomenclature for inch dimensioned bearing units housings with a relube feature.
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BHR follows the ISO precision tolerance classes of P0, P6, P5, P4 and P2, which are equivalent to ABMA classes ABEC 1, ABEC 3, ABEC 5, ABEC 7 and ABEC 9, respectively.
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The "LB" seal is a non-contact seal for reduced torque or higher speed requirements. The "LU" seal is contact seal for better grease contamination control, but the contact friction increases torque and lowers the limiting speed.
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"V1" stands for the first special variation on this basic part number. This suffix lettering does not indicate any specific features. A print will have to be reviewed to see the exact special features.
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The term "electric motor quality" is freely used in describing bearings that meet a perceived "higher" level of quality than the standard ABEC-1 bearing.
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Seals and shields are both in place to keep contaminants out of a bearing. In order of effectiveness, the enclosures that are offered are as follows: metal shields, rubber non-contact seals, Teflon non-contact seals, and rubber contact seals. Not surprisingly, as the sealing performance is increased, the torque required to turn the bearing will also increase due to the increased friction caused by the seal/shield. The application's condition and life requirements are important to know to determine the best shield or seal choice.
