|Lubrication and sliding bearing - Problems, Numericals & mini projects on Machine Design|
|By Prof S S Chauhan, IEC College of Engineering & Technology, Greater Noida|
|Unit-4 Lubrication and sliding bearing Objective: This chapter able the students to understand requirements of lubrication, method of lubrication in journal bearing and design of journal bearing.
Theory and Numerical Problems
1. Define a journal and the bearing.
2. What is the hydrostatic bearing?
3. What are the various type of lubricants used in bearings?
4. What is a hydrodynamic bearing? Define viscosity and viscosity index.
5. Define a short bearing and long bearing.
6. Define sommerfeld number. What is the bearing modulus?
7. What is the condition for full film lubrication How should be the minimum oil film thickness.
8. Name few of the bearing materials. What is the effect of small increase in bearing clearance on film temperature?
9. A 75mm long full journal bearing of diameter 75mm support a load of 12 KN on a journal rotating at 1800RPM. Assume D/C ratio of 1000, and a oil having viscosity 0.01kg/ms at the operating temperature Determine the coefficient of friction. Take L?D ratio 1.
10. In the above problem determine the amount of heat generated
11. A journal bearing 75MM long supports a load of 7.3KN on a 50mm diameter journal turning at 750RPM. The dimeteral clearance is 0.07mm. What should be the viscosity of oil if the operating temperature of the bearing surface is to be limited to 75degree centigrade when in still air at 20 oC.
12. A 100 diameter shaft operating at 2000RPM is supported by means of a 150mm long full journal bearing which is subjected to a radial load of 43KN . Operating temperature of the oil is limited to 80oC and the surrounding air temp. Is 38oC. Assume P=30*10-6 determine the coefficient of friction, bearing pressure, heat generated, heat dissipated, oil use. Is artificial cooling is required.
13. A 50mm medium weight full journal bearing has a length of 100mm and support a load of 2.5KNwhen the shaft rotates at 800RPM. Assuming a temperature difference of 40oC between the operating temps. Of the bearing surface and the surrounding still air , which coefficient of friction .00432,.00615,.00715,.00816 or.00256 will be required in order to eliminate the need for artificial cooling?
14. Explain the mechanism of film lubrication.
15. A full journal bearing has the following specifications
Journal diameter = 75mm
Bearing length = 55mm
Radial clearance = .055mm
Journal speed = 22,000RPM
Radial load = 1 KN
The power loss in the bearing was found to be 3KW find (a) viscosity of the lubricant at effective film temp. (b) The coefficient of friction at the given operating temp.
16. An electric motor whose speed is 1750RPM has bearing 100mm long and 75mm diameter. The oil used has an absolute viscosity of 15 cp under running conditions. The clearance is .0015mmpermm and the load is 0.7MN/m2 . If φ = 90 degree, Determine total power loss in the bearing and the minimum oil film thickness.
17. Design a bearing and journal to support a load of 4KN at 600RPM using a hardened steel journal and a bronze backed Babbitt bearing. The oil viscosity is 250s Saybolt at 37.7oC and specific gravity is 0.90 at 15.6oC . The bearing is relived for 20 degree from normal to the load line. Abundance supply of oil is maintained.
18. Determine the necessary length of bearing, running clearance, side relives, and loss of power due to friction for a journal which has 60mm diameter and rotates at 175RPM. The total load on bearing due to belt pull and the weight of the pulley is 6KN and the load is steady. Use a lubricating oil which has a Saybolt viscosity of 270s at 37.7oC and for which gamma =0.905 at 15.5oC.
19. Design a bearing and journal to support a load of 4900KN at 600RPM using a hardened steel journal and bronze backed Babbitt bearing. An abundance of oil is supplied by means of oiling rings. The oil viscosity is 250s Saybolt at 37.8oC and the specific gravity is 0.90 at 15.6oC . The bearing is relived for 20 degree from normal to the load line.
20. A pressure fed bearing with an annular central groove has a length of 45mm and diameter of 45mm. The bearing supports a load of 4400N at the journal speed of 1000RPM. The radial clearance is 0.025mm and the oil’s SAE30. Determine the equilibrium temperature and minimum oil film thickness. Assume attitude angle 70o.
1. In a journal bearing of 100 mm diameter with a bearing clearance of 0.2 mm, it is found suitable to use lubricating oil with viscosity 60 cP. The shaft runs at 375 r.p.m. and develops a bearing pressure of 1.5 N/mm2. Determine (a) bearing pressure when the shaft speed is increased to 500 rpm, other parameters remaining same. (b) Viscosity at 0.15 mm bearing clearance, 450 rpm of shaft and 2.0 N/mm2 bearing pressure.
2. Following data refers to a 360o(full) hydrodynamic bearing; Journal diameter d = 75 mm, bearing length l = 75mm, radial clearance C = 0.05 mm, minimum film thickness ho= 0.02 mm, Journal speed N =420 rpm, radial load W = 3500 N, Cp for oil = 1.75 kJ/ KgoC, ρ of oil = 0.9 gm/cc.
(a) Required viscosity of oil, Z
(b) The coefficient of friction μ ,
(c) The heat generated, Hg
(d) The amount of oil pumped through the bearing.
3. A 360o hydrodynamic bearing is subjected to a radial load of 10kN. The journal speed is 1500 rpm.The diameter of journal and length of bearing are 60 mm each. The class of fit between journal and bearing is H7e7 (fine), normal running fit with the limits as 60+0.00, +0.03 mm and 60-0.06, -0.09. The minimum oil film thickness is 0.009 mm. Specify the viscosity of lubricating oil required for this application.
4. A 100 mm diameter shaft operating at 2000 rpm is supported in a 150 mm long Full journal bearing subjected to a radial load of 43 kN. Operating temperature of oil is limited to 80oC and surrounding temperature is 38oC, assume ZN/P = 30 x 10-6. Using Mckee and Lasche equation, determine coefficients of friction, bearing pressure, Hg and Hd and viscosity Z of the lubricant.
5. Following data are given for a 360 degree hydrodynamic bearing with usual notations:
D = 50 mm, l =50 mm, C = 0.06 mm, ho = 0.012 mm, N = 1440 rpm, Z = 20 x 10-9 Nsec/mm2, ρ of oil = 900 Kg/m3, Cp of oil = 1.75 KJ/ Kg degreeC . Calculate the maximum radial load that the journal can carry and still operate under hydrodynamic conditions. For this load, calculate power lost in friction and resultant temperature rise.
6. A 50 mm diameter and 75mm long journal bearing is loaded with a bearing pressure 2 Mpa. The journal speed is 500rpm. The heat lost from the bearing surface at the rate of 1.16 x 10-5 (J/s) / ( mm2oC). The housing area is 8 times projected area. If the room temperature is 28oC, Determine the surface temperature of bearing. Co-efficient of friction is 0.0015. Assume Hg = Hd
7. A 90mm shaft rotating at 1200 rpm is supported by 110 mm long bearing. The journal carries 50kN load. Given that To = 70oC , Ta = 250C and ZN/P = 20 x 10-6 Specify the viscosity of the lubricating oil to be used and calculate heat generated. State weather external cooling is required for the bearing.