Machinery's Handbook, 31st Edition
Journal Bearings 2409 Table 3. Allowable Sleeve Bearing Pressures for Various Classes of Bearings Types of Bearing or Kind of Service Types of Bearing or Kind of Service Pressure a psi (MPa)
Pressure a psi (MPa ) 100–200 (0.69–1.38)
Electric Motor & Generator Bearings (General)
Diesel Engine Rod
1000–2000 (6.89–13.79) 1800–2000 (12.41–13.79) 500–700 (3.45–4.83) 1500–2500 (10.34–17.24) 80–100 (0.55–0.689) 700–3000 (4.83–20.68)
Turbine & Reduction Gears
Wrist Pins
100–250 (0.69–1.72) 100–150 (0.69–1.03) 300–350 (2.07–2.41) 15–35 (0.103–0.241) 800–1500 (5.52–10.34)
Heavy Line Shafting Locomotive Axles Light Line Shafting Diesel Engine, Main
Automotive, Main Bearings Automotive, Rod Bearings
Centrifugal Pumps Aircraft Rod Bearings
a These pressures in psi (MPa) of area equal to length times diameter are intended as a general guide only. The allowable unit pressure depends upon operating conditions, especially in regard to lubrication, design of bearings, workmanship, velocity, and nature of load. 4) Diametral clearance c d : This is selected on a trial basis from Fig. 6 which shows sug gested diametral clearance ranges for various shaft sizes and for two speed ranges. These are hot or operating clearances so that thermal expansion of journal and bearing to these temperatures must be taken into consideration in establishing machining dimensions. The optimum operating clearance should be determined on the basis of a complete lubrication analysis (see paragraph following Step 23). 5) Clearance modulus m: This is calculated from the formula: m d c d = 6) Length to diameter ratio l/d: This is usually between 1 and 2; however, with the mod ern trend toward higher speeds and more compact units, lower ratios down to 0.3 are used. In shorter bearings there is a consequent reduction in load carrying capacity due to exces sive end or side leakage of lubricant. In longer bearings there may be a tendency towards edge loading. Length l for a single oil feed hole is taken as the total length of the bearing as shown in Fig. 5. For a central oil groove length, l is taken as one-half the total length. Typical l / d ratio’s use for various types of applications are given in Table 4. 7) Assumed operating temperature t b : A temperature rise of the lubricant as it passes through the bearing is assumed and the consequent operating temperature in degrees F is calculated from the formula: t t t b in a ∆ = + where t in = inlet temperature of oil in ° F Δ t a = assumed temperature rise of oil in bearing in ° F. An initial assumption of 20 ° F is usually made. 8) Viscosity of lubricant Z: The viscosity in centipoises at the assumed bearing operat ing temperature is found from the curve in Fig. 6 which shows the viscosity of SAE grade oils versus temperature. 9) Bearing pressure parameter P ′ : This value is required to find the eccentricity ratio and is calculated from the formula:
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