Abstract: A mixing apparatus has a tank for holding a material to be mixed, a drive shaft rotatable in the tank, a radially inner impeller on the drive shaft with blades pitched to produce axial flow of the material in a first direction, and a radially outer impeller with blades pitched to produce axial flow in an opposite direction. The radially inner impeller can be a high solidity impeller disposed in a preferably-stationary flow shield occupying a portion of a circumference between the inner and outer impellers, and providing a barrier between the material flowing axially in opposite directions while leaving spaces for recirculation of material by radial flow at the ends of the opposite axial flows. The outer impeller can be coupled to the drive shaft by connecting members protruding radially through axial spaces provided in or around the flow shield. Baffles are fixed in the tank and support the flow shield.

Abstract: A high solidity impeller has a number of equally spaced blades, each formed from a sheet that is bent to a continuous cylindrical curve along a roll axis that lags (in the rotation direction) the radius at which the blade is attached to the shaft. The blade also is pitched by rotation around the radius, i.e., the leading edge is raised in the flow direction and the trailing edge is lowered. The roll axis preferably lags the radius by 45.degree.. This arrangement provides a good approximation of a true hydrofoil and results in an excellent reconciliation between interests of material and manufacturing cost vs. pumping efficiency. The blades can be formed by rolling asymmetrically shaped contours cut from a flat sheet. A base member and preferably a connecting arm couple each blade to the shaft. The base member abuts the rolled contour along surfaces referenced to the roll axis, which surfaces can be used as a reference for rolling.

Abstract: A hydrofoil impeller includes three impeller blades attached to a hub. Each impeller blade includes a flat section and a curved section which terminates in a tip portion. The flat section has a root portion proximate the hub and which forms a predetermined root angle with respect to a plane perpendicular to the vertical axis of the impeller. The curved section is separated from the flat portion by a bend line. The curved section is bent downwardly from the plane of the flat section along the bend line. The bend line is oriented with respect to the impeller blade such that the blade tip angle is changed as the bend is formed. Accordingly, the bend is used to set the proper tip angle. The blade angle increases from the tip inward to the bend line, then becomes a constant where attached to the hub. The camber increase from the tip inward to the bend line, then falls to zero where attached to the hub.