In 1839 Isaac Babbitt formulated a metal alloy that would become the standard for fluid film bearings throughout the world, and are in use today in most every heavy industry. The goldsmith from Massachusetts, who also dabbled in brass cannons and dinner ware, developed the metal composition to have some interesting properties.
The base metals of his formulation of tin, lead, or zinc are soft metals. The additives of antimony and copper are harder, and provide a crystalline structure in the alloy to support heavy loads. Today the most common alloy for turbine and heavy industrial bearings is ASTM B23 Grade 2, consisting of 88-90% tin, 7-8% antimony, 3-4% copper, and just trace amounts of lead.
The advantages of a babbitt bearing are numerous. Fluid film bearings by nature can support heavy loads. Once under rotation, the shafts actually ride on a thin film of oil, "floating" on an oil wedge often just a hair in thickness. The oil flowing through the bearing not only provides the support for the shaft so there is no metal to metal contact, but also provides a "shock absorber" and cooling. The bearings can absorb some machine imbalance and vibration by allowing the shaft to move within the oil film of the bearing clearance, allowing a buffer before the actual babbitt bearing is contacted by the rotating shaft. And the constant flow of oil through the bearing provides not only the lubrication but also a cooling medium to remove heat from the friction of the shaft rotating within the bearing housing at quite often high speeds.
Then if any of this operation of the machine goes wrong, the babbitt lining within the bearing shell is designed to be sacrificial. On a small scale, impurities or particles in the oil can become embedded within the soft babbitt rather than scratching or scoring the valuable shaft. Or if oil flow decreases or stops altogether, the friction can cause rapid overheating, melting the sacrificial babbitt rather than damaging the expensive shaft journal or bearing shell. That is where we come in at our Utah shop. When babbitt bearings are damaged, or even just worn from years of use and even abuse, we can replace the babbitt lining of the bearing at a fraction of the cost of new bearings, and at far less than the cost of a shaft that the babbitt bearing is there to protect.
When a damaged bearing comes in to the shop, we do a full inspection, making a drawing of the bearing details if we do not already have it on file. Then the babbitt lining, only ¼" or less in thickness, is machined out of the steel or brass bearing shell. Welding or machine repairs are made to the shell if needed, and then new molten babbitt is cast into place. The bearing bore is then machined to the design dimensions, with oil supply grooves and drains carefully machined into place to provide the design oil flow through the bearing. Oil lips and seals are also machined into place, within tolerances of just .001”, or one thousandths of an inch. Remember, we are creating a flow path for an oil wedge just a few hairs thick.
The newly refurbished bearing will provide the correct tolerances and machine profiles to closely align and support the machine shaft as designed, while still allowing enough clearance between the babbitt lining and the shaft itself for adequate oil flow and cooling. The completed "bearing" is the backbone of the machine, supporting and aligning the shaft to provide many years of smooth and trouble free operation. Our recasting process can provide this service quickly to get our customer's machines back in operation at just a fraction of the cost of new bearings.