The purpose of granulation can be roughly divided into the following points:
1. Make the material into the desired structure and shape;
2. For accurate quantification, formulation and management;
3. Reduce the dust pollution of the powder;
4. A non-segregation mixture of different types of particle systems;
5. Improve the appearance of the product;
6. Prevent agglomeration during the production of certain solid phase materials;
7. Improve the flow characteristics of the separated raw materials;
8. Increase the volumetric quality of the powder for easy storage and transportation;
9. Reduce the risk during handling of toxic and corrosive materials;
10. Control the dissolution rate of the product;
11. Adjust the void ratio and specific surface area of ​​the finished product;
12. Improve heat transfer and help burn;
13. Adapt to different biological processes.
2 Powder material particle shape property In the granulation process by the strong pressure granulation method, the powder is compacted into a compact state by applying an external force in a defined space. The forces that produce stable agglomeration are bridging forces, low viscosity liquid adhesion, surface forces, and interpolymerization. The success of the agglomeration operation depends, on the one hand, on the efficient use and transfer of the applied external force and on the other hand on the physical properties of the particulate material.
Particle shape refers to the image formed by the contour boundary of a particle or the points on the surface. The shape of the particles directly affects other properties of the powder, such as fluidity, filling, etc., and is also directly related to the behavior of the particles in the mixing, storage, transportation, sintering and other unit processes. In the project, people have different requirements on the shape of the particles according to different purposes. For example, the high-speed dry-pressing method of wall and floor slab powder requires rapid filling and smooth exhaust in the mold, so spherical particles are suitable; concrete aggregate requires high strength and tight filling structure, so the shape of the gravel is hoped. It is a regular polyhedron. Conversely, the shape of the particles varies depending on the process of formation. For example, a simple oscillating jaw crusher produces more flake products; a powder prepared by spray drying is mostly spherical particles. Therefore, various particle shapes need to be quantitatively described to show the difference.
On the other hand, in theoretical research and industrial practice, irregularly shaped particles are often assumed to be spherical to facilitate calculation of particle size, and experimental results are easily reproduced. For this reason, it has become one of the main reasons for the great difference between theoretical calculations and actual situations. Therefore, it is generally necessary to multiply the particle size in the theoretical formula by the coefficient indicating the influence of the shape.
Particles encountered in nature and industrial production are not ideal rule bodies, such as spheres, which vary in shape: spherical, cubic, platy, discs, prismoidal, scaly (flaky), granular, rodlike, needle-like, acicular, fibrous, dendritic, sponge, blocky, sharp angle Sharp, round, porous, aglomelate, hollow, rough, smooth, fluffy, nappy.
Geometry described in mathematical language requires at least two types of data and combinations thereof, in addition to three types of data for special occasions. The commonly used data includes representative values ​​of the particle size in the three-axis direction, a contour curve of the two-dimensional image projection, and related data of the solid geometry such as the surface and the volume. It is customary to refer to various dimensionless combinations of particle sizes as shape indices, and the relationship of various variables of solid geometry is defined as shape factors.
2.1 shape index 1) uniformity (proportion)
The ratio of the two dimensions of the particle - the elongation N and the flatness M can be derived from the ratio between the three axes L, B, T:
Length N = long diameter / short diameter = L / B (≥ 1)
Flatness M = short diameter / thick height = B / T (≥ 1)
When L=B=T, the above two indices of the cube are equal to 1
2) fullness (spacefillingfactor)
The volume fullness Fv, also known as the volume factor, represents the ratio of the volume of the circumscribed cube of the particle to the volume V of the particle, namely:
Fv=LBT/V (≥1)
The reciprocal of Fv can be seen as the extent to which the particles are close to the cube, with a limit of 1.
The area fullness Fb, also known as the shape magnification factor, represents the ratio of the projected area A of the particle to the area of ​​the small circumscribed rectangle of the zui, namely:
Fb=A/LB (≤1)
3) degreeofsphericity
The sphericity or true sphericity indicates the extent to which the particles are close to the sphere:
Ψ0=πDV2/S(≤1)
DV=(6V/Ï€)1/3
Where DV means that the volume of the particles of the particles is comparable, S is the surface area of ​​the particles, and V is the volume of the particles.
For irregularly shaped particles, when it is difficult to determine the surface area, practical sphericity can be used, namely:
Ψ0′= diameter of a circle equal to the projected area of ​​the particle/diameter of the small circumscribed circle of the particle projection (≤1)
4) degreeofcircularity
The circularity, also known as the contour ratio, indicates the extent to which the projection of the particle is close to the circle:
Ψc=πDH/L
DH=(4A/Ï€)1/2
L represents the perimeter of the particle projection.
5) Roundness
Indicates the degree of angular wear of the particle, which is defined as:
Circle angle = ∑ri/NR (≤1)
Where ri is the radius of curvature on the contour of the particle; R is the radius of the large inscribed circle of zui; N is the number of angles.
2.2 Shape factor 1) Surface area shape factor Ф s = surface area of ​​the particle / (average particle size) 2 = S / dp2 (> 1)
2) Volume shape coefficient Фv = volume of particles / (average particle size) 3 = V / dp3 (≤ 1)
3) specific surface area shape coefficient Φ = surface area shape coefficient / volume shape coefficient = Ф s / Ф v (> 1)
For spherical particles, the above three shape factors are:
Фs=πd02/d02=π
Фv=πdo3/6d03=π/6
Φ=Фs/Фv=6π/π=6
It must be pointed out that since the particle size representation method is large, different shape coefficients can be defined by different particle size representation methods. In addition, the particle size value is related to the measurement method of the particle size, and therefore the value of the shape factor varies depending on the measurement method. Therefore, when using the shape factor, it is necessary to pay attention to the specific expression of the particle diameter.
4) Roughness Coefficient The aforementioned shape factor is a macroscopic amount. If you look at the particles microscopically, you will find that the surface of the particles tends to be uneven, with many tiny cracks and holes. The roughness of the surface is expressed by the roughness coefficient R:
R = actual surface area of ​​the microscopic particle / apparently considered as the macroscopic surface area of ​​smooth particles (> 1)
The roughness of the particles is directly related to the particle properties such as friction, adhesion, adsorption, water absorption and porosity between the particles and the solid wall. It is also one of the main factors affecting the wear of the workpiece in the granulation operation equipment. Therefore, the roughness factor is a parameter that cannot be ignored.
1. Make the material into the desired structure and shape;
2. For accurate quantification, formulation and management;
3. Reduce the dust pollution of the powder;
4. A non-segregation mixture of different types of particle systems;
5. Improve the appearance of the product;
6. Prevent agglomeration during the production of certain solid phase materials;
7. Improve the flow characteristics of the separated raw materials;
8. Increase the volumetric quality of the powder for easy storage and transportation;
9. Reduce the risk during handling of toxic and corrosive materials;
10. Control the dissolution rate of the product;
11. Adjust the void ratio and specific surface area of ​​the finished product;
12. Improve heat transfer and help burn;
13. Adapt to different biological processes.
2 Powder material particle shape property In the granulation process by the strong pressure granulation method, the powder is compacted into a compact state by applying an external force in a defined space. The forces that produce stable agglomeration are bridging forces, low viscosity liquid adhesion, surface forces, and interpolymerization. The success of the agglomeration operation depends, on the one hand, on the efficient use and transfer of the applied external force and on the other hand on the physical properties of the particulate material.
Particle shape refers to the image formed by the contour boundary of a particle or the points on the surface. The shape of the particles directly affects other properties of the powder, such as fluidity, filling, etc., and is also directly related to the behavior of the particles in the mixing, storage, transportation, sintering and other unit processes. In the project, people have different requirements on the shape of the particles according to different purposes. For example, the high-speed dry-pressing method of wall and floor slab powder requires rapid filling and smooth exhaust in the mold, so spherical particles are suitable; concrete aggregate requires high strength and tight filling structure, so the shape of the gravel is hoped. It is a regular polyhedron. Conversely, the shape of the particles varies depending on the process of formation. For example, a simple oscillating jaw crusher produces more flake products; a powder prepared by spray drying is mostly spherical particles. Therefore, various particle shapes need to be quantitatively described to show the difference.
On the other hand, in theoretical research and industrial practice, irregularly shaped particles are often assumed to be spherical to facilitate calculation of particle size, and experimental results are easily reproduced. For this reason, it has become one of the main reasons for the great difference between theoretical calculations and actual situations. Therefore, it is generally necessary to multiply the particle size in the theoretical formula by the coefficient indicating the influence of the shape.
Particles encountered in nature and industrial production are not ideal rule bodies, such as spheres, which vary in shape: spherical, cubic, platy, discs, prismoidal, scaly (flaky), granular, rodlike, needle-like, acicular, fibrous, dendritic, sponge, blocky, sharp angle Sharp, round, porous, aglomelate, hollow, rough, smooth, fluffy, nappy.
Geometry described in mathematical language requires at least two types of data and combinations thereof, in addition to three types of data for special occasions. The commonly used data includes representative values ​​of the particle size in the three-axis direction, a contour curve of the two-dimensional image projection, and related data of the solid geometry such as the surface and the volume. It is customary to refer to various dimensionless combinations of particle sizes as shape indices, and the relationship of various variables of solid geometry is defined as shape factors.
2.1 shape index 1) uniformity (proportion)
The ratio of the two dimensions of the particle - the elongation N and the flatness M can be derived from the ratio between the three axes L, B, T:
Length N = long diameter / short diameter = L / B (≥ 1)
Flatness M = short diameter / thick height = B / T (≥ 1)
When L=B=T, the above two indices of the cube are equal to 1
2) fullness (spacefillingfactor)
The volume fullness Fv, also known as the volume factor, represents the ratio of the volume of the circumscribed cube of the particle to the volume V of the particle, namely:
Fv=LBT/V (≥1)
The reciprocal of Fv can be seen as the extent to which the particles are close to the cube, with a limit of 1.
The area fullness Fb, also known as the shape magnification factor, represents the ratio of the projected area A of the particle to the area of ​​the small circumscribed rectangle of the zui, namely:
Fb=A/LB (≤1)
3) degreeofsphericity
The sphericity or true sphericity indicates the extent to which the particles are close to the sphere:
Ψ0=πDV2/S(≤1)
DV=(6V/Ï€)1/3
Where DV means that the volume of the particles of the particles is comparable, S is the surface area of ​​the particles, and V is the volume of the particles.
For irregularly shaped particles, when it is difficult to determine the surface area, practical sphericity can be used, namely:
Ψ0′= diameter of a circle equal to the projected area of ​​the particle/diameter of the small circumscribed circle of the particle projection (≤1)
4) degreeofcircularity
The circularity, also known as the contour ratio, indicates the extent to which the projection of the particle is close to the circle:
Ψc=πDH/L
DH=(4A/Ï€)1/2
L represents the perimeter of the particle projection.
5) Roundness
Indicates the degree of angular wear of the particle, which is defined as:
Circle angle = ∑ri/NR (≤1)
Where ri is the radius of curvature on the contour of the particle; R is the radius of the large inscribed circle of zui; N is the number of angles.
2.2 Shape factor 1) Surface area shape factor Ф s = surface area of ​​the particle / (average particle size) 2 = S / dp2 (> 1)
2) Volume shape coefficient Фv = volume of particles / (average particle size) 3 = V / dp3 (≤ 1)
3) specific surface area shape coefficient Φ = surface area shape coefficient / volume shape coefficient = Ф s / Ф v (> 1)
For spherical particles, the above three shape factors are:
Фs=πd02/d02=π
Фv=πdo3/6d03=π/6
Φ=Фs/Фv=6π/π=6
It must be pointed out that since the particle size representation method is large, different shape coefficients can be defined by different particle size representation methods. In addition, the particle size value is related to the measurement method of the particle size, and therefore the value of the shape factor varies depending on the measurement method. Therefore, when using the shape factor, it is necessary to pay attention to the specific expression of the particle diameter.
4) Roughness Coefficient The aforementioned shape factor is a macroscopic amount. If you look at the particles microscopically, you will find that the surface of the particles tends to be uneven, with many tiny cracks and holes. The roughness of the surface is expressed by the roughness coefficient R:
R = actual surface area of ​​the microscopic particle / apparently considered as the macroscopic surface area of ​​smooth particles (> 1)
The roughness of the particles is directly related to the particle properties such as friction, adhesion, adsorption, water absorption and porosity between the particles and the solid wall. It is also one of the main factors affecting the wear of the workpiece in the granulation operation equipment. Therefore, the roughness factor is a parameter that cannot be ignored.
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