First, an overview of powder mixing
In pharmaceuticals, food additives, powder metallurgy, chemical and many other industries need to be a variety of powder in a certain proportion of uniform mixing together, and then processed into the end product. In this process, the uniform distribution of powder of various components has a direct and important effect on the properties of the final product. The so-called hybrid, that is, powder material in the external force (gravity or mechanical force, etc.) under the action of speed and direction of movement changes, so that the components of the particles evenly distributed operation.
Second, the principle of mixed powder
In the mixer, the mixed use of materials is generally considered the following three:
1, The proliferation of mixed - small-scale layered powder diffusion movement, under the action of external forces separated powder moved to the emerging new level, so that the various components of the powder within the scope of the proliferation of uniform distribution.
2, Convection mixed - a large-scale random movement of powder, the powder produced by the force of the external fluid-like movement, the powder from one place to another material displacement, the powder in a wide range of convection to achieve uniform distribution .
3, Shear mixing - the powder material inside the group cut, under the action of external forces between the powder slip phenomenon occurs, the formation of slip surface, so that the local part of the powder was cut to achieve uniform distribution.
The above three types of mixing are not indiscriminately separated, and all kinds of mixers play a leading role in one of the above three functions. Due to the different structures of various mixing equipment, the mixing effect is significantly different (see table below).
|Mixer||Convection mixing||Diffusion mixing||Shearing mixing|
|Gravity convection diffusion (container rotation)||Big||Medium||Small|
|Forced shear mixing (container fixed)||Big||Medium||Medium|
Third, the mixed principle of mixing equipment
Throughout the mixing process, whether it is artificial or mechanical equipment mixing, according to the working principle is divided into two types of gravity convection diffusion mixing and forced shear mixing.
1, Gravity convection diffusion hybrid principle
Constantly raising the center of gravity of the powder through mechanical force, the use of gravity to force the powder downward repeated flow, diffusion, hedging, folding and other sports hybrid method. Its role is macroscopic powder mixed with each other, infiltration, so as to achieve the purpose of mixing evenly. Representative models: V-type mixer, three-dimensional mixer, double cone machine.
2, Forced shear mixing type mixing principle
The mixing method of forcing the powder to be repeatedly stirred, sheared and the like by forcing the powder with the moving blade in the container is used. Its role is to continuously break up the adjacent relationship between the powder particles microscopically, so that the powder particles fully mobile, interchangeable, to achieve the purpose of powder mixing. Representative models: trough ribbon mixer, single cone screw mixer, coulter mixer.
In practical work, a very good mix of equipment is to achieve a mixed principle based implementation of the operation, but also with other mixed principles.