Ceramic Materials Their Properties Part 2
Silicon Nitride Bearings
Silicon nitride has better high temperature capabilities than most metals combining retention of high strength and creep resistance with oxidation resistance. In addition, its low thermal expansion coefficient gives good thermal shock resistance compared with most ceramic materials.
Silicon nitride is the material of choice for vacuum and high speed applications. 58% lighter than traditional steel silicon nitride provide a weight saving benefit and due to the reduction in weight there is a reduction in the centripetal force generated by the rolling elements therefore for similar application when compared to bearing steel silicon nitride offer a significantly increased fatigue life time. Unlike other ceramic materials silicon nitride has the ability to carry similar loads to that of bearing steel however, due to the hardness of the material any application with shock loading is unsuitable for use of silicon nitride or any other ceramic materials for races.
Zirconia (ZrO2) was developed in the 1960s and ’70s and was used to produce the external tiles which created a thermal barrier on the space shuttle that allowed it to re-enter the earth’s atmosphere therefore, zirconia is the material of choice for high temperature applications. The thermal expansion and density of zirconia is close to steel than that of any other ceramic material so it does not have the same weight saving and thermal shock resistance that are found in other ceramic materials.
Best used under low loads, zirconia bearings are used in high temperature and highly corrosive applications.
Silicon Carbide Bearings
Less frequently used than other ceramic materials due to its raw materials cost and difficulty to machine, silicon carbide offers the best heat and corrosion resistance of all the ceramic materials.
Silicon Carbide is best used under low loads and in highly corrosive environments.
M50 Tool Steel Bearings
M50 steel also know as ‘Tool steel’ has high hardness and compressive strength at standard and elevated temperatures with good hot harness and excellent rolling fatigue characteristics it has been a
natural choice for critical aircraft engine bearings being used up to temperatures up to 500°C.
These properties combined with its superior fatigue resistance make it ideal for high temperature high load bearing applications where high precision and stability are paramount, typical applications include
gas turbines and semiconductor assemblies.
Beryllium Copper Bearings
Beryllium copper is high strength alloy comparable to steel with non magnetic properties which can be heat treated for use in bearings.
The use of this material in bearings offers many advantages in extreme environments, excellent heat dissipation with a thermal conductivity between that of steel and aluminium, the material structure
makes it suitable for situations of occasional overload, impact, high temperature, low temperature and marginal lubrication.
The material properties make beryllium copper suitable for use in cryogenic, ultra high vacuum, magnetically sensitive environments as well as certain corrosive applications.
CRONIDUR® 30 X 30 CrMoN Bearings
CRONIDUR® 30 is a martensitic through hardened steel that has a similar corrosion resistance to 316L stainless steel it offers a significant improvement over 440C stainless steel which is typically used in
standard stainless steel bearings.
Other properties that have defined it as material of choice for high speed spindle bearings include high compressive strength, extreme durability, high and low temperature stability.
CRONIDUR® 30 has been proven to provide solutions in applications such as oil exploration down hole equipment, cryogenic pumps and super precision optical equipment. When combined with ceramic balls to form a hybrid bearing life will also be significantly increased.
Stellite is a material which consists of complex carbides in an alloy matrix; it offers a combination of extremely resilient properties which can be used for the components of a rolling element bearing. Advantages include resistance to wear, galling and corrosion even at extremely high temperatures of 500°C while retaining its hardness of 45HRC and non magnetic properties.
Stellite has been extensively used in aerospace applications such inline jet engine valves, landing gear and actuation equipment. This has driven engineers to turn to this material when other exotic alloys and ceramics have not been suitable in bearing applications such as high temperatures valves, equipment operating within range of Tesla magnets, semiconductor applications and cryogenic pumps Speciality Metal & Alloy Bearings.
Speciality Metal & Alloy Bearings
Due to the diversity of environments where engineers & designers are now expecting bearings to operate bearings can be produced in many speciality materials & metal and alloy combinations to produce
Bearings can be produced from the following materials: Inconel, titanium, Monel, XD15NW, BG42 VIM-VAR, M48 Powder Metal High Speed Steel.
Additional speciality ball options are: Ruby, glass, PEEK, NYLON, Toloron, titanium, The above list is not exhaustive as new materials are constantly becoming available.
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