Definition
Dispersion mixer is a mechanical equipment used to evenly disperse solid particles in liquid media and achieve mixing, wetting, depolymerization and other processes. It is widely used in laboratories and production links in various industries such as coatings, inks, adhesives, cosmetics, food and chemicals, aiming to obtain stable and uniform dispersion systems.
Principle
Dispersion mixers mainly generate strong shear forces, impact forces, and turbulence through high-speed rotating mixing components. Typically, the core component of the equipment is a high-speed rotating geared disc impeller, and when the impeller rotates, its edge will generate a high linear velocity, driving the surrounding material to form a vortex. Solid particles are broken by shear action in the liquid, and the liquid medium and particles are fully wetted and mixed. The whole process can be seen as the conversion of mechanical energy into surface energy, which reduces particle agglomeration and promotes dispersion.
Among them, the shear rate is related to the linear velocity of the impeller tip, which can be approximated as:
γ = (π * D * N) / (60 * h)
where γ is the shear rate, D is the diameter of the impeller, N is the rotational speed, and h is the clearance distance between the impeller and the vessel wall.
Measurement and evaluation methods
Dispersion is often evaluated in combination with process parameters and final sample performance testing. During operation, preliminary judgments can be made by monitoring power consumption, temperature changes, and visual observation of flow status. After dispersion, the particle size distribution is measured by a commonly used particle size analyzer, the rheological characteristics of the system are measured using a viscometer, and the long-term uniformity of the dispersion system is evaluated by stability tests such as static stratification observation or centrifugation testing. In addition, for specific industries, it may be necessary to refer to relevant national standards or international standards (such as ASTM, ISO) on dispersion, gloss, coloring and other indicators for testing.
Influencing factors
The dispersion effect is affected by multiple factors. Equipment parameters include impeller shape, diameter, speed, and vessel geometry, which directly determine shear strength and flow field distribution. Process conditions such as dispersion time, temperature control, and dosing sequence also significantly affect the final result. In terms of material characteristics, the initial particle size, hardness and concentration of particles, as well as the viscosity and surface tension of the liquid medium are all key variables. In actual operation, the combination of parameters needs to be adjusted according to the characteristics of the system to achieve efficient dispersion.
Applications
Dispersion mixers play a significant role in several industries. In the coatings and inks industry, it is used for the dispersion of pigments and bases, affecting the color and stability of products. In the preparation of adhesives, the equipment can achieve uniform distribution of fillers in the resin. It is commonly used in the cosmetics sector for the dispersion of powders in emulsions. In the food industry, it can be used for mixing and homogenizing sauces and condiments. In addition, it is also widely used in emerging fields such as battery paste, ceramic paste, and nanomaterial preparation.
Selection considerations
When choosing a dispersion mixer, it is necessary to comprehensively consider the processing volume, material characteristics and process requirements. Laboratory scale usually uses small benchtop equipment, focusing on operational flexibility and parameter controllability. Pilot or production needs to pay attention to equipment power, volume and continuous operation capacity. For high viscosity or high solids content systems, the model with strong torque should be selected. Material compatibility is equally important, and parts that come into contact with the material should be made of stainless steel or special coatings depending on their chemical properties. In addition, the ease of cleaning, safety and compliance with relevant industry standards of the equipment are also aspects that need to be evaluated in the selection.