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Fluidized Bed Mixers
Also see: Rotary Batch Mixer and Vee-Cone Blender

Munson Fluidized Bed Mixer MF-5-SS mixes low-to medium-density bulk materials, including liquid additions, in 10 seconds to two minutes, with 30 seconds typical, minimizing degradation of friable materials.
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OVERVIEW

The Munson Fluidized Bed Mixer is a machine of extremes, offering unique benefits within a narrow range of applications in which its limitations are not a factor.

It is among the fastest of all mixers, with cycle times of 10 seconds to two minutes, with 30 seconds typical, yielding a ~5% CV (coefficient of variability).

It also mixes more gently than other agitated blenders, and evacuates blended batches almost instantly through its full-length, drop-bottom gates.

Although it resembles a ribbon, paddle or plow blender from a distance, it differs radically in design and operation. Instead of a single shaft turning agitator blades slowly within a U-shaped trough, the Munson Fluidized Mixer is configured with two counter-rotating shafts turning paddle agitators rapidly within two, parallel U-shaped troughs.

Flat, angular paddles with overlapping paths effectively sweep material from the troughs toward the center and upward, causing it to become airborne in a "fluidized zone" above the longitudinal centerline of the mixing chamber, where discreet particles of batch ingredients readily intersperse, regardless of disparities in particle size, shape or bulk density.

The fluidized zone is also an ideal location in which to spray high- or low-viscosity liquids, which disperse more readily throughout the batch than in ribbon, paddle and plow blenders. As a result, liquids can be added in significantly higher volumes while maintaining free-flowing characteristics of the batch.

This fluidized mixing action also creates less shear than with other agitated blenders, which, together with extremely short mixing times, results in less product degradation.

The fluidized bed mixer also discharges more rapidly, through its full-length, drop-bottom gates (also known as "Bombay Doors"), allowing material to drop from the machine as rapidly as the doors can be opened.

And whereas ribbon, paddle and plow blenders leave a pronounced "heel" of material in the trough following discharge, the fluidized bed mixer evacuates a much greater percentage of material, reducing the need to manually remove — and waste — residual material between product changeovers.

Wash down is nonetheless time-consuming due to the need to access and clean four shaft seals, long gaskets sealing drop-bottom-door perimeters, and multiple paddles extending from twin agitator shafts (although paddle-type agitators are easier to clean than ribbon blades).

Fluidized bed mixers are also more costly than ribbon, paddle or plow blenders initially, due in part to the greater number of components, and to the higher-powered motor needed to drive two paddle agitators through stationary material at start up, and do so against high gear ratios required for high shaft speeds.

Fluidized Bed Mixers are therefore recommended over ribbon, paddle or plow blenders, when mixing low- to medium-density materials (≤50 lbs/ft3 or ≤800 kg/m3) ranging from powders to pellets — particularly friable materials — with or without liquid additions, in applications requiring short cycle times, relatively gentle product handling and infrequent wash downs.