TIL: Solid Surface Bearing

Today I learned that there exists metal used as a bearing (a mechanism that bears the friction between a rotating part and its housing) that is not in the shape of a ball or a roller and that provides friction reduction through its microstructure. Babbitt metal is a silver alloy consisting primarily of tin or lead, with small percentages of copper and antimony.

Wikipedia article - Babbitt (alloy) on 2025-12-11:

Babbitt metal is most commonly used as a thin surface layer in a complex, multi-metal assembly, but its original use was as a cast-in-place bulk bearing material. Babbitt metal is characterized by its resistance to galling. Babbitt metal is soft and easily damaged, which suggests that it might be unsuitable for a bearing surface; however, its structure is made up of small, hard crystals dispersed in a softer metal, which makes it, technically, a metal matrix composite. As the bearing wears, the softer metal erodes somewhat, creating paths for lubricant between the hard high spots that provide the actual bearing surface. When tin is used as the softer metal, friction causes the tin to melt and function as a lubricant, protecting the bearing from wear when other lubricants are absent.

It's so cool that the soft metal is used because it absorbs debris, provides channels for lubricant, and can even melt and function as lubricant itself, all while remaining a stable material that keeps the rotating part in place. I came across this metal while watching a machinery restoration YouTube channel, Hand Tool Rescue. In the video, you can see the creator melt the babbitt off of the surrounding cast iron:

Even more fascinating is that in the video you can see much of the traditional babbitt bearing creation process described in the wikipedia article:

In the traditional style of a babbitt-metal bearing, a cast-iron pillow block is assembled as a loose fit around the shaft, with the shaft in its approximate final position. The inner face of the cast-iron pillow block is often drilled to form a key to locate the bearing metal as it is cast into place. The shaft is coated with soot as a release agent, the ends of the bearing are packed with clay to form a mold, and molten metal is poured into the cavity around the shaft, initially filling the lower half of the pillow block. The bearing is stripped, and the metal trimmed back to the top surface of the pillow block. Solidified babbitt metal is soft enough to be cut with a knife or sharp chisel.