Filtration method

Claim 1

In a metal working operation including a circuit for recirculating a cutting oil emulsion wherein the cutting oil emulsion contains microorganisms, a process for removing the microorganisms from the cutting oil emulsion recirculated in said circuit by filtering, said process comprising the steps of: providing a filter chamber with an inlet and an outlet, locating within said chamber intermediate said inlet and said outlet a filter medium comprising fibers of at least one inorganic polycrystalline refractory oxide selected from the group consisting of zirconia, alumina and silica, introducing used cutting oil emulsion containing microorganisms into the inlet of said chamber for filtering by said filtering medium, and recirculating the cutting oil emulsion discharged from the outlet of said chamber for reuse in said metal working operation, whereby microorganisms which were contained in said cutting oil emulsion are separated therefrom and prevented from recombining with said emulsion by being retained on said filter medium within said chamber.