Understand powder mixing homogenization and horizontal mixer application

Powder mixing is a process of macroscopic distribution of particles with different physical and chemical properties by mechanical or fluid method. In short, it is a process of non-uniformity of more than two kinds of solid powder materials under the action of external force. With the rapid development of new materials and industrial application, the uniform mixing of powder composites is becoming more and more important.

(I) Definition of powder mixture

Powder mixing refers to the process of mixing two or more different components of the powder evenly. Mixing is also the first step in the whole process of product preparation, and it is important to distribute the mass of each component of the mixture evenly, because the uneven mixing cannot be adjusted in the subsequent process.

The mixing mechanism of powder is the mutual diffusion, convection and shear between powder particles. At present, the commonly used mixing methods are: THREE-DIMENSIONAL mixing, double cone mixing, ball grinding mixing and advanced double motion mixing. Double motion mixing is to use the rotation of the barrel and the rotation of the internal blade of the barrel (the rotation speed is 2 times the rotation speed of the barrel) at the same time forced to drive the powder mutual diffusion, convection, shear, the formation of complex movement, so as to achieve the ideal mixing effect.

Two, the factors affecting the mixing homogenization process of powder

(1) Particle size

Coarse powder particles have good compressibility, but poor formability; Fine powder particles have good formability, but poor compressibility, so the appropriate collocation of size particles can improve the filling type of the powder, improve the compressibility of the powder and improve the sintering performance of the powder. However, the larger the particle size difference, the more difficult to mix. Fine powder is easy to "bridge" and mutual adhesion, hinder the mutual movement of particles, not easy to evenly disperse.

(2) Loose packing density (specific gravity)

The greater the density difference of loose packing, the less easy to mix. Loose density of light powder is easy to float, mixing, always floating on the top, it is difficult to mix with heavier powder components, not easy to mix evenly.

(3) Liquidity

Powder fluidity is poor, particles adhere to each other, is not conducive to powder interpenetration movement, convection, not easy to other powder mixing evenly.

(4) Powder properties

Particle properties include particle size and particle size distribution, particle shape, roughness, particle density, static charge, moisture content, brittleness, Angle of repose, fluidity, agglomeration and elasticity. For example, the shape of the particle affects the fluidity of the particle, and density segregation occurs when the density difference of the particle is mixed.

Three, commonly used powder mixer introduction

At present, the commonly used powder mixer is mainly: THREE-DIMENSIONAL mixer, V-type mixer, double cone mixer.

(1) THREE-DIMENSIONAL mixing machine

Working principle: the barrel body of the material is driven by the active shaft, which makes the compound movement of translation rotation and rolling, and makes the material make circular, radial and axial three-way compound movement along the barrel body, so as to realize the mutual flow, diffusion, accumulation and doping of a variety of materials, to achieve the purpose of uniform mixing.

Advantages of 3D mixer: there is no dead Angle of material in the barrel.

Disadvantages are: low loading rate, generally not more than 60%; For ultra-light powder, ultra-fine powder is not easy to mix evenly, easy to float above the barrel, micro is difficult to achieve fully uniform mixing between particles.

(2) V-type mixer

Working principle: using the mixer 2 cylinder barrel length is not equal, line into the principle of asymmetric, as the mixer rolled material from decomposition to combination, from portfolio to decompose, promote material lateral communication, each roll round transverse force that part of the material flow from a bucket to another bucket, such material horizontal radial mixing, decomposition combination to each other, make the material reach uniform mixing effect.

Advantages of V-type mixer: when mixing mixed materials with good fluidity and similar physical properties, better mixing effect can be obtained.

The disadvantage is that: when the material properties of the mixed powder gap is large, generally can not get the ideal mixture; Large energy consumption; The particles impact each other, the friction is large, easy to change the basic characteristics of the powder composition, such as: small particle size, particle shape change.

(3) double cone mixer

Working principle: the powder is added to the double cone bucket, with the continuous rotation of the bucket, the powder material in the container for complex impact movement, to achieve uniform mixing.

Advantages of double cone mixer: it can realize fast mixing between powder.

The disadvantage is that: when the speed is too slow, the material is easy to stratify rolling, can not be quickly and effectively mixed, and easy to form spherical nodules.

4. Application fields of different types of mixers

(1) THREE-DIMENSIONAL mixing machine

3d mixer is widely used in medicine, chemical industry, food, feed, pesticide and other industries. It is not only suitable for mixing ordinary powder materials, but also for mixing materials with oil, sugar, high viscosity, inflammable, explosive, temperature curing and softening. Such as medicine, powder coating (premixing and finished product mixing), leveling agent, food additives, etc., and can be used with production lines.

(2) V-type mixer

V-type mixer is suitable for mixing more than two kinds of dry powder and granular powder materials, especially for trace additives can also achieve good mixing effect, widely used in pharmaceutical, chemical, food, plastic, cosmetics, ceramics, metallurgy and other fields.

(3) Cone mixer

Conical mixer is suitable for mixing solid with solid, solid with liquid, liquid with liquid, widely used in chemical industry, dye, petroleum, metallurgy, building materials, rare earth and other fields. Conical mixer will not produce overheating for heat sensitive materials, will not press feed and grind for granular materials, and will not produce chip segregation phenomenon for mixed materials with different specific gravity and particle size.