Ceramic bearings for high and very high temperatures

In machinery that must operate in high or very high temperature environments, such as, for example, furnaces for iron and steel industries, furnaces for heat treatments or food furnaces, the choice of the type of bearing and the appropriate lubrication are of fundamental importance and criticality.

Normal steel bearings can operate up to temperatures of 120 ° C. At higher temperatures, the bearing rings must be subjected to a special heat treatment which, however, reduces the hardness of the steel and the load capacity of the bearing. Normally, suffixes are added to the bearing codes to identify the maximum operating temperature, for example:

The suffix S0 is omitted from the bearing code because it represents the standard supply. The other suffixes mean that the bearing is no longer a standard and, therefore, both supply difficulties and high costs can be encountered.

Note that the temperatures indicated are the maximum operating temperatures, not the ambient temperatures in which the bearing is to operate. The latter, in fact, must be lower to take into account the fact that during operation the bearing increases its temperature due to internal friction.

The lubricant must also be adjusted to the required temperature level so that it maintains its tribological characteristics at the highest temperatures. However, as the maximum temperature increases, these lubricants become more and more special and expensive.

Last but not least, the high temperature stabilized bearings have load capacities that can be drastically lower than those of the standard bearing.

The dream of all designers would be to be able to have a bearing that can operate in a high temperature range without having to resort to special treatments, that is, it remains a standard, and that can work even without lubrication.

Full ceramic full complement bearings are the realization of this dream.

These bearings, in fact, have the following characteristics:

1. they are made with materials with one of the highest known temperature resistance. Zirconium Oxide (ZrO2) can operate up to 500 ° C; Silicon Nitride (Si3N4) up to 900 ° C while Silicon Carbide (SiC) has a maximum operating temperature of 1400 ° C.
2. the sliding friction coefficient of ceramic materials is lower than that of steels, resulting in lower heat generation; in essence the maximum acceptable ambient temperature is higher because the heat generation of the bearing is lower
3. ceramic materials are harder than steels and, therefore, the contact area between the rolling element and the raceway is smaller than that which occurs in steel bearings. Since the generation of heat by friction depends on the size of the contact area, the smaller the area and the lower the heat generation, thus allowing higher ambient temperatures
4. ceramic materials can operate without lubrication thus solving the problem of finding special greases for operation at high temperatures
5. the full complement construction allows to eliminate any type of foreign material by maximizing the thermal capacity of the ceramic materials

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