The Science of Bearing Babbitt Selection
The engineering of a bearing’s Babbitt lining is usually completed during the design of the machine. In selecting the proper type of Babbitt for a particular job there are a number of factors to take into consideration, the most important of which are as follows:
- Surface speed of the shaft
- Load that the bearing is required to carry
There is no doubt that if a bearing is to be highly loaded in relation to its size, a high Tin alloy is desirable; whereas for much slower speed work and less heavily loaded bearings, a Lead-Based Babbitt may be employed, and is far more economical.
1. Surface speed of the shaft: (The number of feet traveled per minute by the shaft circumferentially.)
Formula: (Pi x D x RPM) / 12 = S
Example: Determine the surface of a 2 inch diameter shaft going 1,400 RPM (Pi x D x RPM) / 12 = (3.1416 x 2 x 1,400) / 12 = 733.04 Ft/min
Where: Pi = 3.1416, D = Diameter of Shaft, RPM = Revolutions Per Minute, S = Surface speed of the Shaft
2. Load Bearing is required to carry: (The weight which is being exerted through the combined weights of the shaft and any other direct weights on the shaft and measured in pounds per square inch.)
Formula: W / (I.D x L.O.B.)= L
Example: Determine the load on a bearing of a 2 inch I.D bearing, 5 inches long and carrying a weight of 3,100 lbs W / (I.D x L.O.B.) = 3,100 / (2 x 5) = 310 Lbs/sq.in
Where: W = Total weight carried by bearing,I.D = Inside diameter of bearing, L.O.B = Length of Bearing, L = Load bearing required to carry
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