Summer-2017 BME0217-Bloom ME 343

Faculty of Science & Engineering Department of Mechanical Engineering Semester: SUMMER-2017 MID TERM EXAM Section: BME0217-Bloom Course Code: ME 343 Course Title: Machine Design-II Course Teacher: Mahmud Riyad Time: 1 Hour 30 Minutes

Total Marks: 30

[Answer any three out of the four questions. Only use of calculator is allowed for the purpose of calculation. Use of any electronic devices is strictly prohibited in the exam hall. All the questions carrying equal marks]

1. A 5 x 5 – in. full bearing supports a load of 900 lb., Cd / D = 0.0015, n = 400 rpm. The temperature of the SAE 20W oil is maintained at 160o F. Considering the bearing lightly loaded (Petroff), compute the frictional torque, fhp, and the coefficient of friction. 2. The load on a 6-in. full bearing is 1500 lb., n = 320 rpm; L/D =1; Cd/D = 0.0011; operating temperature = 150o F; ho = 0.00088in. (a) Select an oil that will closely accord with the started conditions. For the selected oil determine (b) the frictional loss (ft-lb/min), (c) the hydrodynamic oil flow through the bearing, (d) the amount of end leakage. 3. The radial reaction on a bearing is 1500 lb.; it also carries a thrust of 1000 lb.; shaft rotates 1500 rpm; inner race rotating; smooth load, 8-hr./day service, say 15,000 hr. (a) Select a deep-groove ball bearing. (b) What is the rated 90 % life of the selected bearing? 4. A certain bearing is to carry a radial load of 500 lb. and a thrust of 300 lb. The load imposes light shock; the desired 90 % life is 10 hr./day for 5 years at n = 3000 rpm. Select a deep-groove ball bearing, outer race rotating. Consider all bearings that may serve.