Question

For the following data for full journal bearing: Shaft diameter of 75.00 mm with a unilateral tolerance of -0.02 mm. • The bushing bore has a diameter of 75.10 mm with a unilateral tolerance of 0.06 mm. • The bushing is 37.5 mm long Supports a load of 2 kN. The journal speed is 1000 rev/min. A decision needs to be made by a designer on choosing the lubricant operating at an average film temperature of 60°C. However, his decision is restricted by the following requirements: • The minimum film thickness must not be less than 0.0175 mm. The maximum pressure developed in the film must not exceed 1.73 MPa. What lubricant would you choose in order to satisfy all the above requirements? For the lubricant that you have chosen, determine the following: The maximum pressure developed in the film, the minimum film thickness, the percentage of side flow and the power loss. Submit a complete calculation and summarize your results as: Lubricant type Maximum pressure in the film Minimum film thickness Percentage of side flow Power loss

Answer 1

Hydrodynamic bearings are bearings in which the load is supported by a thin layer of rapidly moving pressurized liquid or gas between the bearing surfaces. Since there is no contact between the moving parts, there is no sliding friction, allowing fluid bearings to have lower friction, wear and vibration than many other types of bearings, it is possible for some such bearings to have near-zero wear if operated correctly.

Hydrodynamic lubrication

1. A lubricant, which must be a viscous fluid.
2. Hydrodynamic flow behavior of fluid between bearing and journal.
3. The surfaces between which the fluid films move must be convergent.

Know the type Ans To sa satisfy lubricant bearing choose for full journal of So, the requirements to we would is Viscosity of lubricant. (P = f u T DR A C, where, P = Pressure 1.73 MPa to friction form A Contact Area Viscosity Dz Diameter of shaft speed in eps с. Radial clearance 2 uz ? 75 mm aps nz 1000/60 0.08 mm 6 1.73 x 10 3 Ux7 x 75 1000 0.08 x 60 M = 0.0352 Pascal - see Oil lubrication is preffered in journal bearing . At 60°c and 1000 4pm Speed ISO - 68 grade oil are used for in door heating application the film Maximum pressure in pe te P 2x103 Xx75x37.5X106 0.2263 M la

- → Min film thickness ho ho Min. film thickness et R tho R, ho= R-R-e 'The Eau The Ce → (Power loss Tfxw 2x’zn (*)(LD) Rxw Petroff' eguntion Power loss 2x²x x 0.0352 x 1000 bo X 75 0.16 37,5 x 75 х X 75 2 2ax 1000 60 Power loss 60 Watt Ans.