Apparatus for processing high viscosity dispersions

Apparatus for dispersing solid constituents into a liquid vehicle employs an immersion mill operating in combination with a low shear mixer blade assembly which sweeps the walls of a tank containing a batch of solid constituents in a liquid vehicle to circulate the batch through the immersion mill to carry out a milling operation to establish a relatively high viscosity mixture having a high degree of uniformity. The immersion mill includes an improvement wherein a helical screw impeller is placed within a tubular inlet passage for moving the batch longitudinally through the tubular inlet passage into the immersion mill, the helical screw impeller including a helical flight extending along the length of the tubular inlet passage and having a diameter complementary to the diameter of the tubular inlet passage and a pitch less than the length of the tubular inlet passage such that the helical flight spans the diameter of the tubular inlet passage along plural turns of the helical flight.