Babbitt Bearings: Casting
In 1839, Isaac Babbitt applied for and got a patent on a bearing composed of a white metal alloy of tin, antimony, and copper. This is similar to today’s ASTM B-23 Grade 2 Babbitt. Bearings are cast of this material to prevent direct contact damage while removing or embedding any contaminants during lubrication. Although the formulation of other Babbitt metals has changed, the qualities of embeddability, conformability, and compatibility remain constant.
Before casting Babbitt into a bearing, it is very important to make the proper preparations. No matter what type of casting method you use or what machinery you decide to employ, without pre-casting preparatory work, the chance of the material not achieving its expected quality is high. To make the process a success, it is essential to
- Roughing: Prepare the bearing surface by making certain the surface has a rough or grooved (phonographic) finish. This will create more points for the bonding to occur
- Cleaning: Make certain the bearing surface is clean. Remove all contaminants, e.g. grease, dirt, cutting oils, skin oils. Acidic or caustic baths is the most common way to do so
- Tinning: Place a fine layer of pure tin between the Babbitt and the bearing metal.
All such procedures have two basic purposes – to improve the bonding process and produce quality Babbitt bearings.
Several casting techniques exist. The method depends largely on the type of bearing involved. Essentially, the choices are:
- Hand (Static) Casting
- Centrifugal Casting
- Spray Casting
Each offers its own advantages and disadvantages. None, however, will be able to provide the optimum result unless pre-casting procedures occur first.
Since 1839, fabricators and metalworkers have been working with Babbitt to produce durable, highly machinable and improved bearings. Babbitt bearings, leaded and unleaded, are popular in such equipment as chillers, gear drives, pumps and electric motors. They are also popular for various marine applications.