Ribbon blenders: definition
Helical ribbon blenders are some of the most common mixing equipment, thanks to their versatility and cost-effectiveness. They consist of a stationary U-shaped vessel with a flat top cover and a product discharge point, usually located in the centre of the bottom of the channel.
The mixing shaft is horizontally oriented and rotates on outboard bearings, with radial arms, which support the helical ribbons. The mixer forces the ribbons through the stationary solid material to promote particle dispersion and achieve homogeneous mixtures in very short times.
Although designed for solid-solid processing, they can receive low or high percentages of liquids that are atomised during the processing to produce smooth pastes or slurries.
When purchasing a ribbon blender, one of the factors to consider is the density of the product, the expected mixing volume and the moisture content. The batch volume defines the capacity of the mixer and the bulk density of the mixture, the power required in the motor, so that it generates enough force to move the propellers during the processing.
How does the helical ribbon blender work?
In ribbon blenders, the powder or granular product flows freely inside the vessel. The machine employs an agitator consisting of inner and outer helical ribbons, which force the material to flow in an axial and radial flow pattern at the same time. The outer ribbon moves the material in one direction, while the inner ribbon moves the material in the opposite direction, achieving a high degree of diffusion mixing.
For optimum mixing, helical ribbon blenders require 30 to 80% of the nominal volumetric capacity of the vessel, although these percentages may vary for a particular model. When working with lower volumes, the mixer may not generate adequate contact between the propellers and the mixture.
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