131
Mixing
Advantages: 1. Suitable for both dry and wet mixing. 2. Suitable for mixing of fines and particle compositions. 3. Suitable for mixing of cohesive powders. Disadvantages: 1. Undesirable attrition of particles. 2. Sealing problems of the shaft of the Intensifier bar. 3. Cleaning issues
8.13 RIBBON BLENDER Principle The mechanism of mixing is shear which is transferred by moving blades. Construction A ribbon blender consists of a U-shaped horizontal trough or shell containing a helical double-ribbon agitator that rotates inside. The shaft of the agitator is positioned in the center of the trough on which the helical ribbons (also called spirals) are welded. Since the ribbon stirrer consists of a set of internal and external helical ribbons, it is also called a "double" helical ribbon agitator. The counteracting blades are provided for high shear as well as for breaking of lumps or aggregates. The ribbon blenders are powered by a drive system consisting of a motor, a gearbox and couplings. They are generally powered by 10 HP to 15 HP motor for 1000 kg of product mass to be blended. The specific power ranges from 3 to 12 kW / m3 according to the products to be mixed. The area where the shaft exits the container is envisaged with a Sealing arrangement to ensure that the material does not move from the container to the outside. The material is charged into the mixer usually by feed hoppers. It is also equipped with bottom discharge spout. Helical blades Mixer Shell
Drive shaft
Discharge spout Figure 8.5: construction of Ribbon Blender