There are a multitude of mixing impeller designs available for industrial mixing, miscible liquids blending and solids suspension. Good material flow is essential to the successful execution of these processes. Hydrofoil impellers, marine style mixing propellers, axial flow turbines and radial flow turbines are all flow-producing impeller designs. The hydrofoil converts most of the motor’s energy to liquid flow and is therefore the highest efficiency impeller with the least shear. Its blade profile creates nearly uniform flow with the minimum required horsepower. Hydrofoils are fabricated by welding blades formed from flat plate to a cylindrical hub. The marine style propeller performs similarly to the hydrofoil with slightly higher power consumption and resulting shear. At small diameters hydrofoils are more expensive than marine style propellers which are cast and then machined. However, this relationship is reversed when the cost of large castings becomes higher than the fabrication costs of the hydrofoil. Marine style mixing propellers and hydrofoils are common selections for low viscosity mixing. Steep pitch propellers are available where increased flow from a given impeller size is desired. Large diameter hydrofoils driven at low RPM are often selected for agitation of large batches.
Axial flow turbines are fabricated similarly to hydrofoils but with wide, flat blade surfaces at 45-degree angles to contact and therefore push more viscous materials. Primarily used for flow-controlled processes with higher viscosities, the blade edges provide relatively higher shear and require greater horsepower to drive them.
Unlike the previously discussed impellers, radial flow turbines produce a primary flow pattern 90-degrees from the shaft. In order to achieve this motion flat blades are welded to the hub like the axial flow turbine but with a 0-degree angle to the axis of the shaft. These impellers are often used to assist with gas dispersion or to agitate liquids in vessels of large diameter and minimal depth.
Dispersion blades convert input energy primarily to shear and, therefore, produce a different result than flow-driven agitation processes. When used at recommended tip speeds driven by sufficient horsepower these sharp, saw blade-like impellers quickly impart pigments into paints, break down solids into liquids, or create homogeneous emulsions from liquids of dissimilar densities.
Specialty impellers are widely available and include the mixed flow impeller, folding impellers for entry through small openings, and an assortment of laboratory impellers. INDCO can also modify standard impeller designs with options such as polishing and electropolishing, custom keyways, cut or clipped blades, coatings and more.
Each impeller type has unique characteristics and they are not necessarily interchangeable on a given mixer. First, the horsepower required to drive the impeller can change dramatically with changes in diameter, rotational speed and impeller type. Therefore, before increasing the diameter and/or speed of a mixer impeller, horsepower requirements should be evaluated to prevent possible motor failure.
We invite you to contact us with questions at 1-800-851-1049. We can help you select the right impeller for your application.