Bearing selection for extreme operating environments
02 March 2020
Many engineers have at least a basic understanding of rotating bearing technology, and in some cases have become experts in the field as various projects have come and gone over the years. A few design engineers will have hands-on experience too but what happens when the talk – and the project – turns to specifying bearings that must survive in a constant 473°C for three hours, and then continue to perform faultlessly as the temperature plummets to -219°C for another three hours?
For equipment which is going into in space, bearing materials must be well protected against corrosion, but why? What does one need to consider first? Materials technology? Rotating mass? Temperature capability? Lubrication? If your application involves – or might include at some stage in the future – a need to understand how to select and specify bearings that can survive in extremes of heat, cold, or space, bearing industry expert Mike Page provides a summarised oversight.
Of all the elements which are key to specifying the optimum bearing for an extreme application, the most important of these is data, and lots of it. Design engineers must think long and hard about the environment the bearing will operate in, the axial and radial loadings it must cope with, potential variations in these loadings at different rotation speeds, ambient temperature, operating temperatures mindful of frictional forces, the effects of thermal expansion and contraction, protection against the ingress of outside materials, lubrication, life expectancy: the list is extensive. And this is before any manufacturing considerations are embraced, and some of the materials for bearings in extreme applications need specialised manufacturing skills and processes.
So, the more data which can be obtained, the better. Once these variables have been either established or accurately forecast, the importance of materials selection will come to the fore. Designers will be aware that although Martensitic steels have a high carbon content which helps deliver high hardness, these come in different grades and offer different balances of advantages and drawbacks: for example, whereas 440C stainless alloy provides the highest strength and hardest wearing properties, its ability to combat corrosion is compromised compared to lower grades such as 440A and 440B: and there is no escaping the fact that many standard austenitic grades of steel offer much better corrosion resistance.
Read the full article in the March issue of DPA.
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