| In selecting the proper type of Babbitt for a particular job there are a number of factors to take into consideration, the most import of which are as follows: |
Surface speed of the SHAFT
Load bearing is required to carry
Secondly, but no less important, the following points must also be taken into account:
Continuity of service
Bonding possibilities
Cooling facilities
Lubrication
Cleanliness
Attention given to the bearings in question
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There is no doubt that if a bearing 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 leadbase one may be employed, and is far more economical. |
Surface speed of the shaft: (The number of feet traveled per minute by the shaft circumferentially.
| Formula: |
pi x D x RPM 12 |
= S |
pi = 3.14 D = Diameter of Shaft RPM = Revolutions per min S = Surface speed of shaft |
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 |
W = Total weight carried by bearing I.D. = Inside diameter of bearing L= Load bearing required to carry L.O.B. = Length of Bearing |
There are many formulas for standard grade babbitts but they fall into two main classification:
| Babbitt Classification |
Limits |
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Surface Speeds (# of ft/min) |
Load (lbs/sq in) |
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| Min. | Max. | Min. | Max. | |
| Tin-Based Babbitts | 1,000 | 2,400 | 100 | 2,000 |
| Lead Based Babbitts | 100 | 1,000 | 100 | 500 |