Machinery's Handbook, 31st Edition
2408
Journal Bearings
Q R = total flow required, gpm r = journal radius, inches
Δ t = actual temperature rise of oil in bearing, ° F Δ t a = assumed temperature rise of oil in bearing, ° F Δ t new = new assumed temperature rise of oil in bearing, ° F t b = bearing operating temperature, ° F t in = oil inlet temperature, ° F T f = friction torque, inch-pounds/inch T' = torque parameter W = load, pounds X = factor Z = viscosity, centipoises ∈ = eccentricity ratio — ratio of eccentricity to radial clearance α = oil density, lbs/inch 3
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l
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Fig. 5. Length, l , of Bearing for Circular Groove Type (left) and Single Inlet Hole Type (right). Journal Bearing Lubrication Analysis.— The following procedure leads to a complete lubrication analysis which forms the basis for the bearing design. 1) Diameter of bearing d: This is usually determined by considering strength and/or deflection requirements for the shaft using principles of strength of materials. 2) Length of bearing L: This is determined by an assumed l / d ratio in which l may or may not be equal to the overall length, L (see Step 6). Bearing pressure and the possibility of edge loading due to shaft deflection and misalignment are factors to be considered. In general, shaft misalignment resulting from location tolerances and/or shaft deflections should be maintained below 0.0003 inch per inch of length. 3) Bearing pressure p b : The unit load in pound per square inch is calculated from the formula: p Kld W b = where K = 1 for single oil hole K = 2 for central groove W = load, pounds l = bearing length as defined in Fig. 5, inches d = journal diameter, inches Typical unit loads in service are shown in Table 3. These pressures can be used as a safe guide in selection. However, if space limitations impose a higher limit of loading, the complete lubrication analysis and evaluation of material properties will determine acceptability.
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