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For the SNHB test data. Table 2 summarizes the K-factor and median lifetimes at 50% 90% and 95% confidence levels. Also shown is the ratio of median lifetimes for the SNHBs to the reference steel bearing median life of 587 hours.

The distributions at the 50%, 90%, and 95% confidence levels are obtained by inserting the respective median lives of 7130, 3954, and 3130 hours into TR in Eq. (16). Also plotted in Figure 1 are the experimental data points for the steel and hybrid bearings. As mentioned above, the values from Table 1 allow the ranking and plotting of the hvbrid
bearing data.

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Bearings


Si3N4 bearing parts
Silicon nitride bearings are both full ceramic bearings and ceramic hybrid bearings with balls in ceramics and races in steel. Silicon nitride ceramics have good shock resistance compared to other ceramics. Therefore, ball bearings made of silicon nitride ceramic are used in performance bearings. A representative example is use of silicon nitride bearings in the main engines of the NASA's Space Shuttle.[21][22]

Silicon nitride ball bearings are harder than metal which reduces contact with the bearing track. This results in 80% less friction, 3 to 10 times longer lifetime, 80% higher speed, 60% less weight, the ability to operate with lubrication starvation, higher corrosion resistance and higher operation temperature, as compared to traditional metal bearings.[20] Silicon nitride balls weigh 79% less than tungsten carbide balls. Silicon nitride ball bearings can be found in high end automotive bearings, industrial bearings, wind turbines, motorsports, bicycles, rollerblades and skateboards. Silicon nitride bearings are especially useful in applications where corrosion, electric or magnetic fields prohibit the use of metals. For example, in tidal flow meters, where seawater attack is a problem, or in electric field seekers.[13]

Si3N4 was first demonstrated as a superior bearing in 1972 but did not reach production until nearly 1990 because of challenges associated with reducing the cost. Since 1990, the cost has been reduced substantially as production volume has increased. Although Si3N4 bearings are still 2–5 times more expensive than the best steel bearings, their superior performance and life are justifying rapid adoption. Around 15–20 million Si3N4 bearing balls were produced in the U.S. in 1996 for machine tools and many other applications. Growth is estimated at 40% per year, but could be even higher if ceramic bearings are selected for consumer applications such as in-line skates and computer disk drives.[20]

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