Definition
A high-speed mixer and disperser is a mechanical equipment used for efficient mixing, dispersing, homogenizing and dissolving of liquids, slurries or pastes. It produces strong shear, impact and turbulence in the container through high-speed rotating stirring parts, so that the solid particles or aphrodistic liquid phases in the material are quickly refined and evenly distributed, forming a stable dispersion system. This equipment has a wide range of applications in the sample preparation and process process of many industries and scientific research fields such as chemicals, coatings, inks, food, and new energy materials.
Principle
The core working principle of the high-speed mixer disperser is based on the shear and turbulence effects in fluid dynamics. The equipment is usually composed of a motor, a drive shaft and a mixing head (usually a chainring or vane rotor). The motor drives the mixing head to rotate at high speed in the material, and its linear speed can reach tens of meters per second. The sharp tooth shape or special blade design of the edge of the mixing head exerts a strong mechanical force on the surrounding material when rotating, resulting in the following main effects:
First, a high-shear area is formed between the mixing head and the container wall or the material itself, where solid aggregates or droplets are stretched, divided and refined. Secondly, the high-speed rotation causes violent radial and axial circulation flows, so that all materials in the container are fully involved in the mixing area to avoid dead ends. At the same time, the back of the mixing head is often accompanied by cavitation, and the local high-pressure impact formed when the microbubbles collapse also help the particle depolymerization. The whole process can be simplified to the continuous input of mechanical energy to the material, overcome the cohesion and interfacial tension between particles, and achieve the purpose of dispersion.
Measurement and evaluation methods
The evaluation of dispersion effect should be combined with process parameters and final product indicators. The process parameters mainly include the speed of the mixing line, power input, dispersion time and material temperature, which can be monitored by the equipment instrument or external sensors. Common measurements of product dispersion quality include:
For particle systems, laser particle size analyzers can be used to measure particle size distribution, and dispersion fineness and uniformity can be evaluated by characteristic particle sizes and distribution widths such as D50 and D90. For pigment or filler dispersion, the grind fineness can be determined by a scraper fine meter. For systems such as emulsions, the stability can be measured, such as observing the delamination time through centrifugal settling experiments, or using a viscometer to monitor the change in viscosity before and after dispersion. In addition, microscopic observation (such as light or electron microscopy) can directly determine the agglomeration and dispersion of particles.
Influencing factors
The dispersion effect is affected by multiple factors. The equipment factors include the geometry, diameter, tooth design and linear speed of the mixing head, and the linear velocity v is usually positively correlated with the dispersion strength, and its calculation formula is v = π × d × n, where d is the diameter of the mixing head and n is the rotational speed. The shape and size of the vessel, especially the clearance between the mixing head and the bottom of the vessel, can also affect the flow field and shear efficiency.
In terms of process factors, the dispersion time should be sufficient but not the longer the better, and excessive dispersion may lead to secondary fragmentation of particles or high system temperature. The solid content, initial viscosity, and formulation composition (such as the type and amount of dispersant) are all critical. Appropriate dispersants can reduce the surface energy of particles and promote wetting and stabilization. The order and method of feeding during operation, such as slowly adding powder to the liquid carrier, also help to avoid agglomeration. In addition, temperature control during the dispersion process cannot be ignored, and rising temperature may cause solvent volatilization, resin gelatinization or system instability.
Applications
The application of high-speed mixer dispersers covers many industrial and R&D scenarios that require homogeneity and refinement. In the coatings and inks industry, it is used to fully disperse pigments and fillers in resin solutions to achieve the requirements of color strength, coverage and stability. In the preparation of adhesives and sealants, it is used to mix various bases and additives. In the preparation of lithium battery slurry, it is used to evenly disperse active materials, conductive agents and binders in solvents to form stable slurries. In the food industry, it can be used for the homogenization of sauces, dairy products, etc. In the field of cosmetics, it is used in the preparation of creams and lotions. In addition, it is also a key sample preparation equipment in the laboratory research and development of cutting-edge materials such as nanomaterials and composites.
Selection considerations
Selecting the right high-speed mixer disperser requires a system evaluation. First, it is necessary to clarify the characteristics of the material being treated, such as viscosity range, solids content, corrosiveness, sensitivity to shear forces, and final required dispersion fineness. According to the characteristics of the material and the processing volume, determine the form of equipment, such as a small disperser for laboratories or large dispersers for pilot and production.
In terms of equipment performance parameters, attention should be paid to the power and torque output characteristics of the motor to ensure that it can provide the power needed to overcome material resistance. The speed range should be wide and adjustable to suit the needs of different stages, such as initial wetting and efficient dispersion. The material of the mixing head needs to consider wear resistance and corrosion resistance, and common ones include stainless steel, hardened steel or coating treatment. The stability and sealing of the drive system are important for long-term operation and handling of volatile materials.
In terms of function configuration, it can be considered whether it needs to be equipped with a lifting mechanism, frequency conversion speed regulation, vacuum or pressurization function, cooling jacket and data logging interface. In terms of safety, it needs to have overload protection, emergency braking and other devices. The final selection should take into account the convenience of operation, maintenance cost and long-term operation reliability under the premise of meeting the process goals.