Despite the latest advances in industrial design and technology, machines still rely on the humble ball bearing to keep everything running smoothly. Basically, bearings are energy-saving devices. They limit friction between the moving parts of all machines and, over hundreds of years, have continually evolved toward greater efficiency and reliability. You can't point to one bearing and say “this is the most frictionless,” so let's take a look at some options.
Building ball bearings is risky. As there is always some variation during production, the balls must be sorted by size. A set of balls for a typical bearing should not vary by more than one micron in diameter. The same applies to track surfaces. After they have been hardened, ground, lapped and sharpened, there are small but measurable variations between the diameters of the inner and outer race rings. In manufacturing, all parts are measured and dimensions recorded, so that the inner and outer rings can later be matched with appropriately sized balls to provide the clearances required to meet exact technical specifications.
Conventional bearings generally use steel cages to hold and guide the balls, preventing them from hitting each other. Steel cages are the cheapest types of deep groove ball bearings, and manufacturers readily stamp their parts from sheet steel to the required profile, rivet the two halves, and insert and secure the balls.
Some well-known bearing manufacturers use polymer cages. It weighs less and generates lower inertial forces. And the fiber-reinforced polyamide material generates less friction than steel and is somewhat self-lubricating. The polymer cage is not simply a copy of the steel version. It has been redesigned to better hold each ball in place and retain and distribute grease where needed. This guides the balls more precisely and helps minimize bearing friction and rolling resistance. Unfortunately, all of this introduces more friction, and to combat this, ball bearings need to be lubricated so they don't seize and break.
A company in Japan solved the problem in an ingenious and innovative way. Instead of forcing the balls apart with a cage or retainer, they insert small points into the track where the balls roll. These fragments speed up and slow down the balls a bit like this, and the end result is balls that will never collide, even without a cage. That means 10 times less friction than traditional bearings and you never need to lubricate them. This small tweak to the design of old technology can result in industrial machines that break down much less frequently, car wheels that need less sustained energy to move forward, or skateboards that roll indefinitely.
This video shows it clearly:
Until the new grease-free bearings are launched on the market, ceramic bearings are the most frictionless. While normal bearings are made from stainless steel, ceramic bearings are made from ceramic silicon nitride (Si2N4). Rolling resistance is the main asset promoted by fans with ceramic bearings. (no pun intended). Because ceramic bearings are rounder, with a smoother surface and a more uniform size, friction is reduced, which can help reduce the energy required to turn the cranks or turn the wheels. A ceramic bearing is also harder than steel bearings (up to 30%), which improves durability and also does not rust, so no maintenance is required.
Most sealed ceramic bearings are actually hybrid ceramic bearings, combining a steel raceway with ceramic ball bearings. All-ceramic bearings use ceramic races, which can be lighter and provide the lowest friction, but have a lifetime cost. Unsealed ceramic bearings can be used to upgrade components that do not use cartridge bearings, such as cup and cone hubs.
