The effect of V should be considered in special cases where the outer race

The effect of v should be considered in special cases

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In this chapter, we will use the above equation for calculating equivalent dynamic load. The effect of V should be considered in special cases, where the outer race rotates and the inner race is stationary. 3.6 Load- life relationship The relationship between the dynamic load carrying capacity, the equivalent dynamic load, and the bearing life is given by, L 10 = ( C P ) p where, P = equivalent dynamic load (N) L10 = rated bearing life (in million revolutions) (3.1) (3.2) (3.3)
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C = dynamic load capacity (N), and p = 3 (for ball bearings) p = 10/3 (for roller bearings) The relationship between life in million revolutions and life in working hours is given by where, L 10h = rated bearing life (hours) n = speed of rotation (rpm) Example 3.1 In a particular application, the radial load acting on a ball bearing is 5 kN and the expected life for 90% of the bearings is 8000 h. Calculate the dynamic load carrying capacity of the bearing, when the shaft rotates at 1450 rpm. Solution Given Fr = 5 kN, L 10h = 8000 h, n = 1450 rpm Step I Bearing life (L 10 ) Step II Dynamic load capacity Since the bearing is subjected to purely radial load, P = Fr = 5000 N From Eq. (3.3), (p = 3, for ball bearings) C = P*(L10) 1/3 = (5000)*(696) 1/3 = 44 310.48 N 3.7 Selection of bearing life While selecting the proper size of a bearing, it is necessary to specify the expected life of the bearing for the given application. The information regarding the life expectancy is generally vague and values based on past experience are used. For all kinds of vehicles, the speed of rotation is not constant and the desired life is expressed in terms of millions of revolutions. The recommended bearing life for wheel applications is given in Table 3.1. Table 3.1 Bearing life for wheel applications Wheel application Life (million rev.) (3.4)
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Automobile cars 50 Trucks 100 Trolley cars 500 Rail-road cars 1000 In the other applications, the speed of rotation is relatively constant and the desired life is expressed in terms of hours of service. The recommended bearing life for some of the applications is given in Table 3.2. Table 3.2 Bearing life for industrial applications 1 Machines used intermittently such as lifting tackle, hand tools and household appliances 4000-8000h 2 Machines used for eight hours of service per day, such as electric motors and gear drives 12000-20000h 3 Machines used for continuous operation (24 h per day) such as pumps, compressors and conveyors 40000-60000h 3.8 Selection of rolling contact bearings from manufacturer’s catalogue The basic procedure for the selection of a bearing from the manufacturer’s catalogue consists of the following steps: (i) Calculate the radial and axial forces acting on the bearing and determine the diameter of the shaft where the bearing is to be fitted. (ii) Select the type of bearing for the given application. (iii) Determine the values of X and Y, the radial and thrust factors, from the catalogue (and also in design data handbook). The values depend upon two ratios, (F a /F r ) and (F a /C 0 ) where C 0 is the static load capacity. The selection of the bearing is, therefore, done by trial and error.
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  • Two '10
  • Ball bearing, contact bearings, Rolling Contact Bearing

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