Knowledge of the material properties allows you to simplify the selection of a blender, allowing you to predict the behavior of the material in different types of blenders. This article focuses on the three conditions necessary for mixing efficiency: no stagnant areas, differences in flow rates and no segregation - and how to match your material properties to a blender to achieve these conditions.
Choosing the right blender for your materials can be difficult and unpleasant work. Suppliers claim that their blenders work efficiently, and their claims are generally correct if the blenders are properly selected for your material. But if you change materials or formulate material, or if you choose a blender designed for materials other than those that you mix, you may encounter problems. Material specialist or calculations based on the material properties of your material. can help you match your material with a blender.
There must be three conditions for effective operation of the blender. First, the blender should not have stagnant areas. Secondly, the blender must promote different flow rates in different parts of the blender. Thirdly, the work of the blender should not separate or mix the ingredients of the mixture.
Prevent stagnant regions
Stagnant areas are areas where materials can sit without moving and not enter the mixing process, thereby preventing complete mixing. They exist in the free-board zone (the area between the bed surface and the top of the blender) and the area between the agitator blades and the walls of the blender. Restricted flow channels, where materials remain separated in layers or channels during mixing, can also create stagnant areas.
The effect of stagnant areas depends on the mixture and flow properties of the individual ingredients. For example, using a mixer with a gravity flow meter to mix cohesive materials leads to the stable formation of ratol around each entrance to the tube and destroys the efficiency of the blender. But mixing free flowing materials in this blender will not lead to the formation of reefs.
An air mixer, plow or paddle mixer, or even a belt mixer operating at a high rpm, can blow small particles into the air and cause them to stick to freeboard surfaces if the thin material is glue. In an air blender, vibrators or special coatings and liners can prevent material accumulation in these regions. These tools are not suitable for plow blades or belt blenders, so it’s best to avoid problems by choosing another blender for adhesive materials.
Draper drums rely on continuous pile formation and avalanche flow in a small area on top of a pile of material in a material mixing vessel. Too cohesive material will create thick layers of avalanches with little interparticle movement. The result is stagnant areas that reduce the effectiveness of the blender. However, a completely free flowing material can have very thin avalanche zones, and also have a less optimal interparticle motion. This also leads to the inefficiency of the blender. A tumbler blender works best with ingredients that have similar resting angles and only enough cohesion to prevent sifting.
Promotion of differences in flow rates
Differences in the advancement of mixing flow rates. Some mixers include mechanisms designed to create different flow rates in the material during operation. For example, a gravitational mass-flow cone-cone blender contributes to a faster rate in the center of the vessel than on the side. This flow rate mixing profile extends from the cone hopper in the cone to about one hopper diameter, which usually results in a short squat with a low mixer volume. Using a modification of the cylinder in the cylinder inside the vertical part of the blender above the section of the hopper of the cone in the cone expands the mixing profile far up to the vertical section. This can maintain the ratio of speed to diameter from 5 to 1. This allows you to increase the volume of the blender.
Differences in flow rates are not enough to ensure efficient mixing. For example, a ribbon mixer lifts and transports only a small amount of material per revolution, and it promises to lift the material more efficiently than transporting material from side to side. The action of the blender creates differences in flow rates, but also leads to poor blender operation: it moves vertically well, but slowly moves to the end. Some users of the ribbon blender found that optimal mixing is possible only when the individual elements are superimposed in the blender, since the overlay, in fact, does some mixing work and then reduces the dependence on the differences in flow velocity.
Segregation prevention
Sometimes the work of the blender separates the individual ingredients during operation and discharge. For example, since the V-blender relies on continuous piling to mix material, segregation can occur if the individual ingredients of the mixture have different abutment angles or if sieving occurs. This gives an uneven mixture. Choosing a different blender can help reduce segregation as well as retrofit a V-blender with a device such as a one-dimensional convergent convergence bin at the output of the V-blender. This device causes flow across the entire width of the blender, which allows to reduce segregation to an acceptable level.
Air flows inside the blender can also separate the ingredients. For example, a tape blender typically has several feed ports. Connecting a single port to the dust collection system results in an accumulation of fines below this port. Since the ribbon blender does not move well from one end to the other, controlling the dust collection system during mixing can cause segregation, reducing the efficiency of the blender and increasing the mixing time.
A list of common blenders and descriptions of their mixing mechanisms, materials that are well mixed in them, and their comparative segregation mechanisms.
