10 Questions You Should to Know about Tilt Pad Bearings

Multiple choice question

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1. A design for a tilting pad thrust bearing, consisting of several pads, is found to have an operating film thickness which is too small. The following corrective actions are possible, select the most appropriate.

&#; Increase the roughness of the pads.

&#; Increase the mean diameter of the bearing.

&#; Reduce the area of the thrust pads.

&#; Increase the temperature of the lubricant sump

2. A single hydrodynamic tilting pad thrust bearing 70mm wide and 50 mm long, is replaced by a pad 50 mm wide and 20 mm long. Which of the following is correct if no other aspect of design is changed and the new bearing is operated at the same load and speed?

&#; Lubricant side flow is unchanged

&#; Load-carrying capacity is increased

&#; The effective viscosity decreases

&#; The maximum temperature of the lubricant under the pad decreases

3. A tilted pad thrust bearing supports a total load of 40 kN. If the shaft rotates at 2.5 revs per second and the pads have a radial width of 8 cm, a mean diameter of 7 cm and operate with an outlet film thickness of 10 µm, what is the pad friction (shear) loss in Watts according to ESDU ?

&#; 6.40 W

&#; 16.20 W

&#; 26.25W

&#; 7.80 W

4. A tilting pad bearing supports a collar on a shaft which is 0.025 m in diameter. The allowable film thickness for a perfectly aligned bearing is 3 µm. What is the minimum operating film thickness required if misalignment is likely according to ESDU ?

&#; 6.75 µm

&#; 13.50 µm

&#; 1.50 µm

&#; 60.00 µm

5. A tilting hydrodynamic pad bearing consisting of four pads of width and length 45mm operates under directed lubrication with a lubricating film thickness of 15x 10-6 m to support the collar of a shaft rotating at 17 revs sec-1. If the bearing has a mean diameter of 110 mm, according to ESDU what is the necessary lubricant flow rate for the whole bearing?

&#; 9.26 x 10-6 m3 s-1

&#; 2.23 x 10-6 m3 s-1

&#; 4.48 x 10-6 m3 s-1

&#; 3.70 x 10-6 m3 s-1

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6. A tilting pad bearing lubricated by flood feed is found to have excessive churning power loss. Which of the following is the most appropriate design adjustment to reduce the power loss?

&#; Increase the runner diameter

&#; Increase the number of pads

&#; Increase the viscosity grade of the lubricant

&#; Use directed lubrication

7. Six nominally square tilting pads of length 0.035 m operate under a load of 735 N. What is the mean pad pressure?

&#; 0.1 MPa

&#; 0.6 MPa

&#; 1 MPa

&#; 2 MPa

8. A designer has produced a design for a tilted pad bearing using ESDU in which the pad operating temperature must be reduced. Which of the following actions will achieve this most effectively?

&#; Decrease the mean diameter of the pads

&#; Reduce the lubricant flow rate

&#; Increase the pad area

&#; Increase the surface roughness of the runner

9. If the total power loss in a flood feed tilting pad bearing is 1 kW and the power loss due to &#;churning&#; is 500 W. What is the power loss due to hydrodynamic shear effects?

&#; 500 W

&#; 2 kW

&#; 0 kW

&#; 1.5 kW

10. The number of pads in a tilting pad thrust bearing is to be selected by the designer. The outer pad diameter to inner pad diameter (D/d) for the bearing 1.6, assuming that a 0.6 complement is required, how many pads will be selected according to ESDU ?

&#; 10

&#; 4

&#; 6

&#; 12

The definitive test of the bearing clearance would be the bench test with a mandrel. The lift test as assembled in the machine is mainly to look for errors such as those we have already discussed. Since the lift test only checks one pad, it is not definitive of the bearing clearance. I would not expect the lift test to exactly match the bench test. Are you using a correction factor (0.) to adjust to the true clearance? Some equipment manufacturers based their clearance on the use of this correction factor. Some do not. You need to know if the manufacturer of your machine uses this correction factor or not when applying their clearance specification.

I assume that you have verified that the mandrel you used has the same diameter as the shaft journal.

Johnny Pellin

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