The claimed high performance of NSK's new Robust ultra-high speed machine
tool spindle bearing series is down to the innovative use of materials,
says the company. The graduated construction of these bearings combines,
at its highest level, the high seizure resistance of NSK's SHX steel with
the high speed/high temperature properties of PEEK polymer cage material
and the inherent stiffness of silicon nitride ball material.
Customers can specify different combinations of materials according to
their needs and budgets. For example, at the entry level, Robust users
can specify all-steel bearings that offer 20% higher speed capability
than conventional precision angular contact bearings. These are made from
NSK's Z steel, which features reduced quantities of non-metallic
inclusions and oxides. The next level combines Z steel with silicon
nitride balls, while for the highest speed applications the combination
is as described above.
The heat resistance of SHX is nearly equal to that of M50 steel, a
material used for bearings on the main shafts of jet engines. Top-level
Robust bearings incorporating SHX steel, and used in combination with
NSK's exclusive 'Spinshot' lubrication system, are capable of operating
at peak spindle speeds of 3.5x106dmN.