>> P.59
1N=0.102kgf=0.2248lbs.1mm=0.03937inchA56ABCDEFGHIJKLMFriction and AllowableRotational SpeedFrictionAllowable rotational speedAs the rotational speed of rolling bearings is increased, the bearing temperature also increases due to the heat generated at the contact surfaces between the cage, raceways and rolling elements, Compared with sliding bearings, the starting (static) until it nally leads to bearing seizure. It is therefore friction for rolling bearings is small, and the difference necessary to maintain the rotational speed of a bear-between the starting (static) friction and the kinetic ing below a certain limit value to ensure safe opera-friction is also small. The loss of power and tempera-tion for long periods. This limit value is called the ture rise in machines are thus reduced, improving the allowable rotational speed.mechanical efficiency.Since the amount of heat generated is approximately Frictional torque is influenced by the bearing type, proportional to the sliding speed at the contact area, bearing load, rotational speed, lubricant characteris-this sliding speed is an approximate guide indicating tics, etc. It varies according to the lubricant when the limit of the bearing rotational speed.operated under light-loads and high-speed conditions, The allowable rotational speed of bearings thus varies and according to the load when operated under according to the bearing type, size, bearing load, heavy-loads and low-speed conditions.method of lubrication, radial clearance, and other Frictional torque of rolling bearings is complicated such factors.because it is influenced by various factors, but for The allowable rotational speeds shown in the table of convenience, it can be expressed approximately by dimensions are empirical values. They are not absolute values and can be changed according to the bearing use conditions. Depending on the structure and accuracy around the bearing, the lubricant and the lubrication method, it is possible for some bear-ings to be operated at more than twice the allowable rotational speed given in the table without trouble.d2・Radial bearingsM=μP……………………(37)・Thrust bearingsM=μP……………………(38)dm2where,M:Frictional torque, N-mmμ:Coefficient of frictionP:Bearing load, Nddm:Mean value of bearing bore and :Bearing bore diameter, mmoutside diameters, mmThe approximate coefficients of friction of IKO Bearings under operating conditions, in which lubrica-tion and mounting are correct and where loads are rel-atively large and stable, are shown in Table 40.the following equations.Table 40 Coefficient of frictionBearing seriesμNeedle roller bearings with cageFull complement needle roller bearingsThrust needle roller bearingsThrust roller bearings0.0010 〜 0.00300.0030 〜 0.00500.0030 〜 0.00400.0030 〜 0.0040
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