ceramic bearings vs steel bearings

Ceramic bearings vs steel bearings enough has written about this subject so here is gust the fact

first the concept behind a bearing is very simple: Things roll better than they slide. Bearings reduce friction by providing smooth metal balls or rollers, and a smooth inner and outer metal surface for the balls to roll against. These balls or rollers “bear” the load, allowing the device to spin smoothly.

Compared to steel, ceramic materials offer superior corrosion and heat resistance, higher dimensional stability, and lower density, which facilitates high speed. Ortech’s silicon nitride bearings have been used with successful results in machine tool spindles, special operating conditions including corrosive, vaccum, high-temperature, clean, non-lubricated. Ortech’s ceramic bearings are made of silicon nitride, silicon carbide or zirconia Oxide, depending on the application.

High-speed performance
Ceramic balls are about 40% as dense as steel. This means less centrifugal force is developed on the bearings resulting in suppression of heat generation between the balls and outer ring. The result is superior high-speed performance and they can operate at higher speeds.

Ceramic ball have a smoother finish than steel, A high quality steel ball bearing is consider grade 25. The grade number refers to the tolerance per millionth of an inch. A grade 25 is accurate to 25/1,000,000 of an inch. Less expensive ball bearings may be grade 300, which are less round, at 300/1,000,000 of an inch. Ceramic bearings may be grade 5 or 3 , which is a rounder ball bearing. so the vibration and spindle deflection is reduced allowing higher speeds and better performance.

High rigidity. The modulus of elasticity of silicon nitride (Si(sub 3)N(sub 4)), the ceramic material that is most often used in bearings, is about 50% higher than that of steel, leading to a 15 to 20% increase in rigidity.

High hardness. The hardness of ceramic materials runs from about Rc75 to 80, compared to about Rc 58 to 64 for steel.

High compressive strength. The compressive strength of ceramic materials is about 5 to 7 times that of steel.

Low coefficient of friction. A low coefficient of friction reduces rolling resistance, again allowing higher speeds with lower operating temperatures and less wear–and less need for lubrication.

Low thermal expansion. The coefficient of thermal expansion of silicon nitride is about 25% that of typical steel bearings. This property results in less change in bearing preload during spindle operation.

Low electrical conductivity. Since ceramic materials don’t conduct electricity, they are resistant to damage from arcing. Hybrid bearings have a receptivity comparable to the ceramic alone, eliminating the need for special bearing insulation in applications such as traction motors.

Corrosion resistance. The chemically inert nature of ceramic balls makes them resistant to corrosion. They also exhibit a resistance to galling and adhesive wear problems that plague all-steel bearings that are marginally lubricated.

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