Page History: Babbitt - What is Babbitt?
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Babbitt metal, also called white metal, is a soft, white non-ferrous alloy used to provide a bearing surface. It has properties that help reduce friction which make it a good material to use in a plain bearing.
Babbitt was first created by Isaac Babbitt. Born July 26, 1799 in Taunton, Massachusetts, Babbitt was well known as an inventor by trade. In 1839, he received a patent for a white metal alloy that showed excellent bearing properties. The original formula for Babbitt's bearing metal was 89.3% tin, 7.1% antimony and 3.6% copper and that formula is still marketed today by some manufacturers as "Genuine Babbitt".
While Babbitt metal is soft and can be easily damaged when treated improperly, and seems at first sight an unlikely candidate for a bearing surface, its appearance is deceptive. The structure of the alloy is made up of small hard crystals dispersed in a matrix of softer alloy. As the bearing wears the harder crystal is exposed, with the matrix eroding somewhat to provide a path for the lubricant between the high spots that provide the actual bearing surface.
Types of Babbitt
The term "Babbitt" is commonly used to describe any kind of "white metal" bearing material no matter the actual composition. Most modern "Babbitt" can be broken into two major categories: tin based or lead based. Here is a breakdown of several common types of Babbitt that are still commercially available and commonly used when restoring old machinery:
Lead Based Babbitt
Lead Based Babbitt is the least expensive babbitt that you can buy. It is also the softest type of Babbitt. One type of lead based babbitt that is still commonly available through McMaster Carr is their Stonewall brand. Composition is 80.25 percent lead, 14.75 percent antimony and 5 percent tin. While this material would work fine for light duty and low speed applications such as a band saw arbor, for just a little more money, you can get a much better quality material. Probably best to shy away from for most machinery applications. Pouring Temperature is 650 degrees F. Prices vary buy expect to pay around $4.50 per pound.
Lead Based Coppered Babbitt
Lead Based Coppered Babbitt is a mid-grade Babbitt product. While still classified as a lead based babbitt, because of the alloy mix, it is generally considered a better material than plain lead based babbitt. An example composition of this type would be approximately 74.5 lead, 14.75 percent antimony, 10 percent tin, 0.25 percent copper and 0.5 percent arsenic. With twice as much tin as plain lead based Babbitt, as well as some copper and arsenic, this Babbitt is stronger and more suited for heavy loads. Still only recommended for low speed applications - not what you would want to use on a jointer or planer head but probably plenty adequate for a band saw with wheels only turning in the 400-500 RPM range. Prices vary but expect to pay around $6.00 per pound. For no more than it cost, this Babbitt would nearly always be preferred over plain lead based. Pouring Temperature is 700 degrees F.
Tin Based Babbitt
Tin Based Babbitt is the best choice for high-speed applications (such as jointers and planers) and hard to lubricate bearings. Composition is approximately 89% tin, 7.5% antimony, and 3.5% copper. In reality, probably overkill for band saw bearings but sure would not hurt to be safe than sorry. While the higher tin content does make this Babbitt more expensive, when you consider the cost of time and labor for pouring bearings, probably money well spent. Cost for tin based products is much higher than the lead based at approximately $16.50 per pound. Pouring Temperature is 725 degrees F.