Not All Ribbon Agitators Are Created Equally

By Doug Grunder
President, Marion Mixers, Inc.

A quick search of the internet reveals there are more than 60 companies claiming to build mixers or blenders with ribbon style agitators. The ribbon style of agitator is the most frequently quoted solution by our competitors. In applications involving free flowing solids or slurries of similar particle size, density and shape, the ribbon agitator is a good solution. Ribbon agitators are designed to mix by scrubbing product against product. The inner ribbons pushing product toward the end plates and the outer ribbons moving materials toward the center.

Solid mainshaft

• Provides maximum transfer of torque, minimum shaft deflection and smallest contact surface area. Hollow shafts or stub shafts tend to have greater deflection and fatigue stress.

Solid round spokes

• Provides maximum support of outer ribbon components without interfering with product movement. Plate style spokes tend to stop product movement as materials are forced against the side of each plate spoke.

Large radius fillets

• Spokes are chamfered and then welded with large, smooth fillet to the agitator shaft. Larger radii are easier to clean and cause less stress risers. Drilling and pinning the spoke through the shaft and/or using small fillet welds will make the joint more susceptible to fatigue failure.

Double flight ribbon

• Double inner and double outer ribbon flights are located on the agitator with 1800 of separation. For every revolution of the agitator, particles at any given location inside the blender are manipulated twice as many times with a double helix mixer. Single flight ribbons are much easier and less expensive to fabricate.

Continuous ribbon

• Inner and outer ribbon flights are formed and attached to the spokes of the agitator as a continuous helix from the end-plate to the discharge. Segmented ribbons only span between two spokes. The agitator must turn another 1800 before engaging the next segment of outer flighting. Segmented ribbons create less lateral product movement in the mixer.

Clearance with trough

• Ribbon agitators that are built in unison with a trough assembly can ensure clearances less than 0.25" at the 6:00 position. Tighter clearances result in better incorporation of minor ingredients and more thorough clean-out. Ribbon agitators fabricated separate from the trough are generally sold without a specified clearance.

High speed choppers

• High speed choppers are available for size reduction and/or incorporation of minor ingredient, liquids or shortening. Outer ribbons are designed to pull product into the cutter head(s). Many competitive offerings do not include high intensity choppers with ribbon agitators.

End plate wipers

• Knife edged end-wipers are available to scrape sticky products from the end-plates of the mixer. Cleaning the spoke and end-wipers adjacent the end plate is much easier with round spokes than with plate style spokes.

SOURCE: Marion Mixers