>> P.24
Basic Static Load Rating andStatic Safety FactorBasic static load ratingStatic safety factorThe basic static load rating gives the theoretical allow-able limit of the static equivalent load. Normally, this limit is corrected by considering the operating condi-tions and the requirements for the bearing. The cor-When a bearing at rest sustains a heavy load or a bearing rotating at a relatively low speed receives a rection factor, namely, the static safety factor fs is defined as in the following equation and its general heavy shock load, the contact stress may exceed a values are shown in Table 4.The basic static load rating is the static load that gives For ordinary operation conditionsfs= ………………………………………(9)C0P0where, C0 : Basic static load rating,NP0 : Static equivalent load, NTable 4 Static safety factorOperating conditions of the bearingWhen high rotational accuracy is requiredFor ordinary operation conditions not requiring very smooth rotation When there is almost no rotationfs≧3≧1.5≧1In case of Shell Type Needle Roller Bearings of which outer ring is drawn from a thin steel plate and then carburized and quenched, it is necessary to use a sta-tic safety factor of 3 or more.certain limiting value, producing a local permanent deformation in the raceways or the rolling elements, and subsequently causing noise or vibration or lower-ing the rotating performance. The basic static load rating is, therefore, determined as a guideline for the maximum allowable load for the bearing at rest, under which the permanent deformation will not exceed a certain limit value, and the lowering of the rotating performance will not occur. Its definition is given as follows.the contact stress shown in Table 3 at the center of the contact area of the rolling element and the race-way receiving the maximum load. A radial load con-stant in direction and magnitude is used in the case of radial bearings, while an axial load constant in magni-tude acting along the bearing central axis is used in the case of thrust bearings.Table 3Type of bearingContact stress MPaRoller bearingsSelf-aligning ball bearingsOther ball bearings4 0004 6004 200A21
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