An important aspect to be carefully considered when machines or systems operate in chemically aggressive environments is the corrosion that occurs in mechanical components. In these environments, bearings can be in direct contact with highly aggressive fluids, gases or vapors such as salt water, chlorinated water, salt spray, water vapor, acid or base vapors, acidic or basic liquids. Corrosion can occur very quickly, thus compromising the functionality of the machine or system.
It has become a good design practice to protect the parts in contact with such aggressive elements by using adequate gaskets (both in terms of shape and material) or by enclosing the sensitive mechanical parts inside protective casings or by replacing normal steel with steels or metals which resist corrosion (in the case of bearings, stainless steels can be used instead of standard 100Cr6 steel).
Each of these solutions, however, has drawbacks that must be carefully evaluated. For example, if you choose to protect the mechanical components by enclosing them in a watertight casing, the possible difficulty of implementation is compounded by cost increases, maintenance difficulties as well as possible operating problems (if we take an electric motor and close it in an enclosure without ventilation, in a short time its temperature will reach an unacceptable value). If, however, as in the case of bearings, you choose to use stainless steel bearings instead of standard steel bearings, you have to accept a reduction in performance for an increase in costs. In fact, it should be remembered that the stainless steels that can be used to make bearings can be of two types:
The fundamental difference between the two steels is that martensitic steel can be hardened obtaining a hardness of the races and rolling elements equal to 52 - 55 HRC while austenitic steel cannot be hardened and, therefore, the hardness is very low, not reaching 20 HRC. This means that stainless steel bearings do not provide the same load capacity as 100Cr6 bearings. In particular, the following applies:
On the other hand, from the point of view of corrosion resistance, austenitic stainless steels are better than martensitic steels thanks to a higher percentage of Cr and the simultaneous presence of Ni.
In summary:
In addition to assessments of load carrying capacity and corrosion resistance, lubrication issues must be considered. In fact, even for stainless steel bearings, lubrication and therefore the choice of the right lubricant and compliance with maintenance instructions are essential for correct operation.
Today, however, there is an alternative and more effective solution to the critical issues highlighted so far: the full ceramic bearing.
The fundamental aspects that make the full ceramic bearing extremely effective in chemically aggressive environments are:
Learn more about fully ceramic bearings, the characteristics of the materials used and how these can be a very effective solution for situations where steel bearings show their limits, download our brochure on ceramic bearings below.