Extreme Temperatures. Zero Compromise.
Bearings are critical components in almost every machine you can think of.
They are essential to wind turbines and electric vehicles, steelmaking equipment and humble household appliances… And all those bearings need to perform reliably, sometimes for years or even decades at a time, no matter the conditions to which they are exposed.
That might mean extremely clean environments, where hygiene is a must. Or perhaps extremely harsh conditions, like those found in mines, quarries, and cement plants. Maybe it is wet environments, where bearings have to deal with a constant influx of water or other liquids. But in this article we are going to explore extreme temperatures, where bearings have to keep on rolling whether no matter how hot or cold it gets.
Whether it is the searing heat of a steelmaking factory or the frigid conditions of arctic exploration, we are talking about temperatures where standard bearings simply cannot be relied upon.
Designing and manufacturing bearings that can withstand such thermal extremes involves years of expertise, specialist materials, advanced lubrication strategies and innovative engineering solutions. Fortunately, these are all things NSK can offer, allowing us to offer performance, durability, and reliability in all temperatures.
Bearings for Hot Environments
At NSK we classify extreme heat as anything above 120°C, the standard operating temperature of an ordinary grease lubricated bearing.
This is obviously scorchingly hot, though many specialist bearings are expected to handle even more extreme temperatures, around 400°C when it comes to steelmaking for instance, and potentially some environments that can reach 1000°C (very briefly) in some aerospace applications (although the bearing will not reach this threshold).
It is important to remember that, if a bearing is going to operate at these extreme temperatures, every aspect of it needs to be able to stand up to the heat.
This does not just mean the material the cages, rings and rolling elements are made from (though this is obviously an important factor) but seals, shields and lubricants as well. Indeed, lubricant is often the limiting factor, with conventional lubricants failing at temperatures above 120 - 150°C.
One option here is Krytox grease, essentially the gold standard for high-temperature, chemically aggressive, or oxygen-rich environments. Krytox offers thermal stability well above 250°C, chemical inertness, and is often used where oxygen compatibility is critical.
Another is to utilise solid lubricants, which essentially provide a slippery layer between two surfaces which prevent them grinding against each other. Essentially it is a solid which plays the exact same role as a liquid or grease.
When it comes to seals, NSK makes use of Viton seals which can handle temperatures of up to 200°C continuously and even up to 250°C in short bursts.
They offer long-life and high performance not just amidst extreme temperatures, but chemicals as well, being highly resistant to oils, fuels, solvents, and acids, offering much more protection than standard rubber seals. They are often found in environments like automotive engines, aerospace, chemical plants, and industrial machinery.
In terms of NSK’s high temperature product offering, we have options starting at 150°C (X26) all the way up to 250°C (X29).
Once you get beyond this then you need to look into our Spacea range, specially designed for extreme environments. As part of this series, our YS and SJ bearings use molybdenum disulfide (MoS2) solid lubricant to withstand temperatures up to 350°C and 400°C, respectively. These solid lubricants enable operation in environments where conventional grease evaporates or decomposes
Bearings for Cold Environments
Bearings for extremely cold temperatures are actually less common then their counterparts for extremely hot environments.
This is largely because extreme cold is much rarer than extreme heat in almost all industrial processes. This doesn’t mean that there is no demand at all, however. Indeed, in some sectors, such as space exploration, medicine, arctic exploration, and cryogenics they are absolutely vital.
Challenges posed by extreme cold are often the inverse of those posed by extreme heat. In the former lubricants fail because oils and greases thicken or freeze. Metal components shrink (rather than expand) which can change internal clearances. Some bearings can become stiff or sluggish, meaning they struggle to start turning when it is cold.
Solutions include using specialist low temperature lubricants or solid alternatives (as with bearings for extreme heat), adopting specialist steels or ceramics like silicon nitride and adjusting internal clearances to account for material contraction. Some bearings are even fitted with flexible cages that can move with thermal changes.
One outstanding example of NSK’s offering for cold environments is our self-lubricating deep groove ball bearings for submersible pumps in cryogenic applications.
These stainless-steel bearings, with cages made from self-lubricating fluoroplastic, are increasingly being adopted by leading manufacturers.
These pumps might need to pump continuously or intermittently, and at temperatures all the way down to -200°C. The pump shaft’s double bearing is an absolutely critical design element and must be resistant to corrosion. No lubrication can be used other than the actual media washing around the bearing.
NSK has therefore developed a series of deep groove ball bearings specifically for these exceptional operating conditions, with a number of key design features which set them apart from conventional pump bearings. These bearings are typically AISI 440C or similar martensitic stainless steels, offering both corrosion resistance and mechanical strength at cryogenic temperatures.
A stable cage that occupies the entire inner volume of the bearing provides guidance for the rolling elements (also made of stainless steel), while the cage material, a self-lubricating fluoroplastic, ensures low friction running of the bearing without external lubrication. In addition, the high-performance fluoroplastic is extremely wear-resistant and offers good low-temperature properties at speeds up to 3600rpm. The cage is made up of two pieces, with the halves joined by stainless steel rivets.
These deep groove ball bearings offer significantly longer service life than other bearings for this type of application, such as those with a cage made from hard phenolic resin. Of course, the bearings are also suitable for pumps handling other cryogenic gases such as nitrogen.
Naturally, as demand for bearing for cold environments continues to grow, we will continue to innovate, just as we have with bearings for extreme heat, so expect more breakthroughs in this space in the years to come.
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