ground off: to make (something hard) smaller and smoother by gradually rubbing off tiny bits
Schauberger
This results in the spacial separation of the two bipolar substances, i.e. the oxygen proceeds down the centre and the carbones along the sides, where with increasing slip-pressure against the resistances (guide-vanes) and rotating about their own axes, they continue to be ground off. As a result the inner constituents are freed and separated out according to their centrifugal or centripetal characteristics. [The Energy Evolution - Harnessing Free Energy from Nature, The Liquefaction of Coal by Means of Cold Flows]