Avoiding the disadvantages of belt or gear driven spindles, or those
driven directly by a motor via a coupling, the latest generation of
machine tools is increasingly being equipped with motorised spindles -
spindles with their own built-in motors. Unfortunately, motorised
spindles suffer greater exposure to environmental problems such as motor
heating and sleeve cooling, which has profound implications for spindle
bearings.
must be robust enough to resist seizure
and maintain running stability while generating reduced levels of heat
under severe thermal conditions. Answering this need, NSK has introduced
its 'Robust' series precision angular contact bearing, which is supplied
in four types, depending upon the level of performance required. At the
lower end, the 'S' type bearing, with steel balls and rings, and the
hybrid 'H' type with silicon nitride balls and steel rings, are both
capable of speeds 20% higher than conventional precision angular contact
spindle bearings.
Moving up the performance scale, the 'X' type hybrid ceramic bearing is
similar in design to S and H, but has special high-strength polyamide
resin cages and rings made from SHX material - a new steel developed by
NSK with a performance approaching that of M50 steel (gas turbine
bearings). Offering the highest performance of all is the 'EX' series,
which is an X type bearing compatible with NSK's 'Spinshot' lubrication
system. With this system in place the limiting speed of the EX is greatly
increased - up to 3.55 x 10^6 dmN is claimed under conditions of constant
pressure pre-load.
Enter 420