Rolling elements to move heavy items date back to ancient Egyptians, who used logs to roll stone pieces to pyramid construction sites. Later, Romans used simple ball bearings in nautical applications.
Fast forward 1,500 years: During his employment as a hydraulic engineer for the Duke of Milan, Leonardo da Vinci spent much time analyzing linkages, gears, and other mechanical transmission modes — including bearings. A century later, Galileo detailed a caged bearing system — to prevent the contact and accumulation of bearing rollers. These bearing designs were perfected, patented, and put into large-scale production in the 1700s.
Originally bearings were made of wood — most commonly of heavy, hard, oily Lignum Vitae native to Central America and the West Indies. The natural oils in this wood serve as cutting fluid during manufacture. Once in use, Lignum Vitae bearings were lubricated with animal fats. These bearings were commonly used in wet applications: propeller-driven vessels, water wheels, and pumps.
Today in turbine-type applications, one can still find wooden bearings. But because lignum vitae is not as available as it once was (the trees take hundreds of years to mature) modern companies manufacture bearings out of rock maple impregnated with petroleum wax instead.
During the Industrial Revolution, the steam engine became a practical power source for the newly invented cylinder-boring mill. This machine made large-scale production of quality iron much easier, spurring the development of more precise machine tools and industry in general — and in turn, new bearing designs. Later in the 1800s, Henry Bessemer devised an economical steel-making process that further increased the material's use.
Pedal to the metal
With machines going faster than ever, bearing materials had to withstand resulting heat. In 1839, Isaac Babbitt invented a bearing that included a layer of low-melting tin or lead alloy. This layer goes liquid under high startup temperatures to provide slippery lubrication — and resolidifies once bearing speed stabilizes. Babbitt metal increased the use of metal bearings.
With the inventions of the 1900s — motorcars, robotics, and faster machine tools — bearings have only become more essential on production lines.
Future is plastics
Polymers, from tortoise shell and animal horn to the synthetics first engineered 150 years ago, have been used for myriad applications. But the relatively low cost of many synthetic polymers is what really spurred their use in industry. For example, the nonstick coating polytetrafluoro-ethylene (PTFE) used on pots and pans also works well on increasingly cost-effective bearings.