A: Steve Schloemer, Eirich Machines, says:
A fluidizing paddle blender produces a homogeneous blend by creating mechanical fluidization through the blender’s increased shaft rpm and paddle design. A fluidizing paddle blender has inner and outer paddles similar to a double ribbon blender, which has an inner and outer ribbon. However, the fluidizing paddle blender’s shaft rotational speed is approximately 1.5 times faster than that of a double ribbon blender. The higher shaft speed combined with the inner and outer paddles results in a mechanically fluidized material bed. There are several reasons to consider a fluidizing paddle blender.
Blend quality. A double ribbon blender typically achieves a 5 percent standard deviation, while a fluidizing paddle blender will achieve a 0.5 percent standard deviation with the same blend time.
Blend time. The typical blend time for a double ribbon blender is 5 to 6 minutes for a standard powder blend. The typical blend time for a fluidizing paddle blender is approximately 2 minutes for a standard powder blend.
Fill level. For a double ribbon blender, the inner ribbon needs to engage the material, which requires a recommended minimum fill level of 60 percent of the stated working volume for efficient blending. For a fluidizing paddle blender, the mechanical fluidization of the material allows for greater variance in the blender fill level. The fluidizing paddle blender can efficiently blend material when filled to as low as 25 percent of the stated working capacity.
Liquid addition applications. A fluidizing paddle blender’s mechanical fluidization action brings material to the surface more frequently than the mixing action of the ribbon blender and provides an efficient mechanism to apply liquids to the powder. A proper spray pattern and spray rate will practically prevent the creation of agglomerates. Adding a chopper to a ribbon blender or a fluidizing paddle blender can provide the required shear to “break” agglomerates, if needed.
Friable or shear-sensitive materials. A double ribbon blender imparts higher shear to a material blend than a fluidizing paddle blender, because the outer ribbon imparts shear to the material between the ribbon and the vessel wall. A fluidizing paddle blender’s mechanical fluidization creates space between the particles to allow them to move past one another, which reduces friction or shear and results in little to no attrition to most particles. Slowing the fluidizing paddle blender’s shaft speed increases the amount of shear and attrition to the materials. A fluidizing paddle blender can be very effective with whey protein blends, whole coffee beans, nut-based trail mixes, and spice blends with friable materials such as parsley flakes. A fluidizing paddle blender isn’t a zero-shear blender, however, and will impart attrition to highly friable materials. One or more choppers can be added if additional shear is required.
Dissimilar materials. Particle size variation and material density variation can lead to material segregation during blending and post-blending handling. In general, the larger the differences, the harder it is to blend and maintain homogeneity. A fluidizing paddle blender’s mechanical fluidization allows the blender to efficiently achieve homogeneity even with particle size and density variations. In some extreme situations, the double ribbon blender can allow the materials to segregate during blending. Great care must be taken when particle size and density variations come into play. Any blender must be properly vented, and the shorter the height of the material discharge coming out of the blender, the better. A perfectly blended product can quickly segregate once it exits the blender if it isn’t properly handled.
Eirich Machines, Gurnee, IL, supplies horizontal blenders, vertical, and inclined mixers; dry and wet grinding technology; drying systems; and other equipment for the industrial and chemical, food and beverage, and nutraceutical and pharmaceutical industries.