A mixing machine is a machine that uniformly mixes two or more materials by mechanical force, gravity, or the like. Hybrid machines are widely used in various industries and daily life.
The mixing machine can mix a variety of materials into a homogeneous mixture, such as mixing cement, sand, gravel and water into concrete wet materials; it can also increase the contact surface area of ​​the material to promote chemical reactions; it can also accelerate physical changes, such as granular The solute is added to the solvent, and the dissolution and mixing can be accelerated by the action of the mixing machine.
Commonly used mixing machines are divided into four categories: gas and low viscosity liquid mixers, medium and high viscosity liquid and paste mixing machines, thermoplastic material mixers, and powdered and granular solid materials mixing machines.
The gas and low viscosity liquid mixing machine is characterized by simple structure and no rotating parts, small maintenance and repair, and low energy consumption. This type of mixing machine is divided into four types: airflow mixing, pipe mixing, jet mixing and forced circulation mixing.
Medium and high viscosity liquid and paste mixing machinery generally has strong shearing effect; thermoplastic material mixing machine is mainly used for mixing thermoplastic materials (such as rubber and plastic) with additives; powdery, granular solid material mixing machinery For intermittent operation, it also includes machines that combine mixing and grinding, such as rim machines.
All materials involved in the mixing are required to be evenly distributed during mixing. The degree of mixing is divided into three states: ideal mixing, random mixing, and completely unmixed. The degree of mixing of the various materials in the mixing machine depends on factors such as the proportion of the material to be mixed, the physical state and characteristics, and the type of mixing machine used and the duration of the mixing operation.
The mixing of the liquid mainly relies on a mechanical agitator, a gas stream and a jet of the liquid to be mixed, etc., so that the material to be mixed is agitated to achieve uniform mixing. The agitation causes a portion of the liquid to flow, which in turn pushes the liquid around it, with the result that a circulating liquid flow is formed within the solution, and the resulting diffusion between the liquids is referred to as bulk convection diffusion.
When the flow rate of the liquid caused by the agitation is high, shear occurs at the interface between the high-speed liquid stream and the surrounding low-speed liquid stream, thereby generating a large number of local vortices. These vortices rapidly spread around, and more liquid is drawn into the vortex. The turbulent convection diffusion formed in a small range is called eddy diffusion.
The moving parts of the mechanical agitator also shear the liquid when it is rotated. The liquid is also subjected to shearing action when flowing through the wall and various fixing members installed in the container. These shearing actions will cause many Local eddy current diffusion.
The convection diffusion and eddy current diffusion caused by stirring increase the surface area of ​​molecular diffusion between different liquids and reduce the diffusion distance, thereby shortening the time of molecular diffusion. If the viscosity of the liquid to be mixed is not high, it can be brought to a random mixing state within a short stirring time; if the viscosity is high, a longer mixing time is required.
For liquids of different density, composition, and incompatibility, the shearing action caused by the agitation and the strong turbulence shred the dense liquid into small droplets and uniformly disperse it into the main liquid. The flow rate of the liquid produced by the agitation must be greater than the settling velocity of the droplets.
The mixing mechanism of a small amount of insoluble powdery solid and liquid is different from the density component, and the mixing mechanism of the mutually incompatible liquid is the same, except that the stirring cannot change the particle size of the powdery solid. If the solid particles before mixing cannot be made to have a sedimentation rate lower than the flow rate of the liquid, a uniform suspension cannot be formed regardless of the stirring method.
The mixing of different pastes mainly involves repeatedly dividing the materials to be mixed and subjecting them to strong shearing action caused by pressing, squeezing, squeezing, etc., and then repeatedly combining and kneading to achieve the desired degree of mixing.
This kind of mixing is difficult to achieve the ideal mix, only to achieve random mixing. The powdery solid is mixed with a small amount of liquid to form a paste, and the mixing mechanism is the same as that of the paste material.
Different thermoplastic materials and the mixing of thermoplastic materials with a small amount of powdery solids need to rely on strong shearing, repeated kneading and kneading to achieve random mixing.
The granular solid matter with good fluidity is mainly mixed by the rotation of the container itself or by the action of the moving parts contained in the container, and is repeatedly tumbling and blending to be mixed. Such materials can also be convected or turbulent by the air flow to achieve mixing. . Convection or turbulence of solid particles is less prone to eddy currents, and the mixing speed is much lower than the mixing of liquids, and the degree of mixing generally only achieves random mixing.
For fluid particles or powdery solids that are poorly fluid and adhere to each other, it is often necessary to use a mixing machine with mechanical turning, pressing, and twisting.
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