A study of bearing and its types conference Paper

Fig 1: A Flat Surface Sliding Over a Tapered Land
[Applied Tribology- Bearing Design and Lubrication] 
IV. THRUST BEARING TYPES 
Six common types of thrust bearing are shown in Table 1. The first four are hydrodynamic, with their oil film 
pressure generated by internal pumping action. Hydrostatic bearing uses an external oil pump to supply the 
pressurised supporting film. Since parallel planes do not provide pumping action, Flat land bearings depend 
upon thermal expansion of oil, thermal warping, and irregularities of bearing surfaces, and possibly other 
effects. Characteristic application practices of these various types are as follows: 

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International Journal of Advance Research In Science And Engineering http://www.ijarse.com
IJARSE, Vol. No.4, Special Issue (01), March 2015 ISSN-2319-8354(E) 
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Typical unit load and sizes for each type are listed in Table 1. For the typical Babbitt surface used in most 
machinery thrust bearings, normal upper design load limits are commonly set in the range 250 - 500 Psi to allow 
for uncertainties and load transients. Failure loads in tests are usually in the range 1200 - 1500 psi. At operating 
speeds, these failure loads will commonly involve a peak film pressure of two to three times this normal 
loading. The bearing Babbitt will then flow when local oil film pressure reaches the Babbitt yield strength -as 
temperature rises to 250-300
o 
F range. At very low speeds, Babbitt wear becomes a limiting factor when overall 
film thickness drops to less than 3-10 times overall oil film thickness drops to less than 3-10 times the nominal 
surface roughness of mating runner.
 
Tapered land bearings provide reliable, compact design for variety of midsize to large, high speed machines 
such as turbines compressors and pumps. Flat land extending about 10-20 % of the circumference at trailing 
edge of each segment is commonly included for higher capacity and to minimize wear during starting, stopping, 
and at low speeds. Because the operation of tapered land bearing is sensitive to load, speed, and lubricant 
viscosity, this bearing type is commonly designed to match rated operating conditions of specific machines. 
Pivoted pad thrust bearings are being used more frequently in turbines, compressors, pumps, and marine drives 
in much the same general size and load range as the tapered land designs. Each of the 3-10 or more pads in the 
bearing is commonly supported on a central pivot, which leaves it free to adjust to form nearly optimum oil 
wedge for supporting high loads even with widely varying speeds and lubricants and both directions of 
rotations.
Recent modifications for increasing the load capacity, lowering the temperature and lowering the power loss 
include offsetting the pivots to 60-65 % beyond the leading edge of the pad, replacing steel with copper for 
backing of the Babbitt bearing material to give peak surface temperature, and using non-flooded lubrication to 
minimize parasitic power loss. 
Spring or other flexible supports for the thrust segments are used in some of the largest thrust bearings carrying 
millions of pounds of thrust. This flexible mounting avoids high contact stresses imposed by loading individual 
pivots. 
Step bearing provide a simple design for smaller bearings. With the use of coined or etched step, they are well 
suited to mass production for small bearings and thrust washers for use with low viscosity fluids such as water, 
gasoline and solvents. Step height should be small with the same order of thickness as the minimum film 
thickness for optimum load capacity, yet large enough to allow for some wear.
Flat land bearings will carry only 10-20 % of the load of other thrust bearing types, because flat parallel surfaces 
do not provide pumping action needed to build oil film pressure in a converging wedge shaped clearance. 
Instead, flat land bearing relies on thermal expansion of oil and warping of bearing material by heating from the 
passing oil film. 

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International Journal of Advance Research In Science And Engineering http://www.ijarse.com
IJARSE, Vol. No.4, Special Issue (01), March 2015 ISSN-2319-8354(E) 
1678 | 
P a g e