The centrifuging machine comprises walls (10) inside the tub which are gently inclined from the bottom towards the top, opening outwards, enabling the separation of phases by means of the component of the centrifugal force which is applied to the inclined surface in the upward direction, with multiple grooves (12) which run from the lower part to the upper part thereof, the bottoms of said grooves being gently inclined outwards. The inner wall (10) of the tub is provided with a coating of synthetic materials to form a single lining (13) and the whole of the internal and external surfaces of the tub are provided with a coating (15,16) of synthetic resin which is resistant to chemical attack.