5. A shaft carrying a load P=10kN is supported by two identical plain journal bearings. The shaft, which normally rotates at 3000rev/min has, at the bearing region, a nominal diameter of 50mm and a length of 16mm. Starting with a radial clearance ratio of 0.0015 and neglecting thermal effects: (a) From the load carried calculate the viscosity of the lubricant and from supplied viscosity chart extract the temperature of the lubricant which will produce an eccentricity ratio of 0.7 if the oil used is SAE10. (b) Comment of the necessity to supply lubricant to the bearing and calculate the minimum oil supply rate, assuming that the bearing acts as a 360 bearing. (c) What is the lowest speed at which the shaft can rotate and still maintain a minimum film thickness above an acceptable limit of 3m, at a temperature of 55C ? Hints: a) Using the formulas from the lecture notes: Calculate radial clearance Find velocity Find viscosity from load carried From chart find T b) Look at the lecture notes; c) Write the formula of the minimum film thickness for a journal bearing Calculate a new eccentricity ratio From the diagram, for SAE10 oil, at 55C we get the dynamic viscosity of the oil Load carried is the same, so from this we extract velocity: 5. A shaft carrying a load P=10kN is supported by two identical plain journal bearings. The shaft, which normally rotates at 3000rev/min has, at the bearing region, a nominal diameter of 50mm and a length of 16mm. Starting with a radial clearance ratio of 0.0015 and neglecting thermal effects: (a) From the load carried calculate the viscosity of the lubricant and from supplied viscosity chart extract the temperature of the lubricant which will produce an eccentricity ratio of 0.7 if the oil used is SAE10. (b) Comment of the necessity to supply lubricant to the bearing and calculate the minimum oil supply rate, assuming that the bearing acts as a 360 bearing. (c) What is the lowest speed at which the shaft can rotate and still maintain a minimum film thickness above an acceptable limit of 3m, at a temperature of 55C ? Hints: a) Using the formulas from the lecture notes: Calculate radial clearance Find velocity Find viscosity from load carried From chart find T b) Look at the lecture notes; c) Write the formula of the minimum film thickness for a journal bearing Calculate a new eccentricity ratio From the diagram, for SAE10 oil, at 55C we get the dynamic viscosity of the oil Load carried is the same, so from this we extract velocity