Centrifuge Motor

What's it for?

Would a speed-change-up gearbox be a better bet?

I have some doubts about your power estimations. If the 200 Nm torque has to be maintained (which is exaggerated I am afraid) at the speed you mention then it is over 300kW ( about 500kW).

When a centrifuge works the power requirements are related to frictions in the bearings and between the envelope and environment. For very high speeds the centrifuge which has anyway to be in a protective envelope (for safety in case of accidental destruction) works with a high degree of vacuum in this envelope so that friction with air is drastically reduced.

Let assume that you rotate a thin ring, the maximal radius is :

Rmax<(Re/(Rho*omega^2))^0.5

If the ring is made of high resistance steel at 25000 rpm its diameter has to be <280 mm.

With such a diameter even in air you cannot reach the 300 kW. Some thing is wrong some where. What for do you need such rpm ? isotope separation ?

We use the simple relationship of P=TW to relate the power 300kW to torque of ~120Nm when spinning at 25000RPM.
We can consider a 9000 rpm high with frequency inverter and we can gear up 3x We now need help to find manufacturers that could provide such a motor

How did you come to the 120 Nm ?

If you rotate in air at atmospheric pressure and 20°C such a torque occurs by about 8 to 16 m cylinder length (d=280 mm) depending on the boundary layer thickness.

I am asking myself what for such a device could be used and you did not answer the question in previous comment.

As for the motor you can find it by yourself using google or other search engine.