Description

Ribbon mixers are still a very simple and robust solution to mix dry materials offering decent mixing performances which are sufficient for many applications. Ribbon mixers are actually used in many industries and applications : pharmaceuticals, food and bakery, cosmetics, plastics, spices, mixes for drinks, cements grouts and mortars, coffee and tea, tobacco.

A ribbon mixer consists of a U-shape tank and special designed ribbon agitator. A ribbon agitator consists of a set of inner and outer helical agitators.

The mixture movement is forced by the rotation of the ribbon which is circulating the product in 2 directions :

1. The outer agitator circulates the product in one direction while the inner agitator moves the product in the other direction (it can be possible to have even more complex profiles to attempt optimizing the mixing efficiency and thus the mixing time).

2. By mixing enough time, those 2 axial movement, coupled with some radial movement (blades “cutting” the material when rotating), will allow to reach the required degree of homogeneity.

The mixer performance, i.e. time to reach a desired homogeneity, is a function of the following operating parameters :

• Mixing batch size : 70-80% of mixer total volume. Visually, the top of the blades must be slightly above the level of product, and some head space to the top cover must always be available. It is a very common problem to find ribbon blenders overloaded which is strongly decreasing their performance.
• Mixing speed : one should follow the supplier’s recommendation, typical mixing speed for medium size blenders (500-2000kg) is around 50 rpm.
• Small and Minor ingredients to be introduced in the mixer after the main ingredients (or in sandwich), preferably in the central area of the mixer.