Freezing cold temperatures – A “no-Go” for Bearings?

As human beings, we experience temperatures somewhat between -20°C and +40°C. That is, what we can survive in, at least with the right protective gear. However, things can become at lot hotter than that, which we will address in a later article. And, of course, temperatures can drop below that considerably. Think about the gas that you might use to warm your house. In order to transport it as liquified natural gas, LNG, it is cooled down to -162°C, to make it a liquid. That makes handling it a lot easier, when it is pumped in or out of storage tanks or tankers.

The life of the bearings in the pumps that do that, becomes a lot worse at such low temperatures. The metal becomes brittle and there is no way to use any lubricant. In standard bearings that means that the bearings will fail at very short notice. Brittleness combined with the absence of lubricant causes flaking which in turn will ruin the bearing catastrophically. So how did NSK overcome these challenges?

At first they used a special stainless steel for both the raceways and the balls. Annealing it makes the grain structure more coarse, so that the brittleness, even at low temperatures is reduced.

The other important factor is the cage. It needs to hold the balls in place, avoid any ingress of dirt and have tribological properties that reduce friction to a minimum. PTFE appeared to be the ideal material for the job. The cage in our bearings for very low temperatures is a two piece construction, that is rivetted around the balls into the raceways, so to say. That ticks all the boxes as mentioned above.

The result of combining special stainless steel with a PTFE-cage is, that the bearings can operate in down to -162°C and still run at up to 3600 rpm.? ?

If you want to find out more about our bearings for very low temperatures, check our website at https://www.nsk.com/eu-en/products/data-sheets/lng-pump-bearings/