a pulp mixing apparatus includes a rotor shaft within a housing having a curvilinear inner wall circumferentially disposed about the rotor . a plurality of radially extending , wedge - shaped vanes are rigidly mounted on the rotor and intermesh with a plurality of housing vanes , likewise wedged - shaped , such that in combination , as the rotor vanes are moved into proximity with the stationary housing vanes , a mixing substance is subjected to a compressive and subsequently to a decompressive force whereupon the mixing substance is homogeneously and thoroughly mixed .