Powder Mixing Overview - This is a scientific real-time operation process, the purpose of which is to evenly mix different types of powder together.
First, the broad spectrum physical characteristics of the powder
At present, we encounter food, chemical, metal powder regardless of the chemical composition of its material, its external physical properties have the following important indicators.
1, the specific gravity of the powder and its effect on mixing
The specific gravity of powder is usually represented as loose specific gravity and vibrated specific gravity.Usually, the specific gravity of the powder is between 0.2g/cm3 and 2.0g/cm3. It is relatively easy to mix such powders with other powders,otherwise it is relatively difficult to mix powders of which the specific gravity is below 0.5g/cm3 or above 2.0g/cm3 with other powders. This is because too light powder floats easily, too heavy powder tends to sink to the bottom, causing difficulties for mixing.
For example, the left picture shows the loose specific gravity of the resin powder is 0.4 g / cm 3. The right picture shows that the vibrated specific gravity of the resin powder is 0.48 g / cm 3. This shows that some powders’ density varies a lot.
2,Fluidity of powder and its impact on the mixing
The fluidity of powder can be expressed in heaps of powder (Left picture above) or it can be measured using a standard flow tester (right picture above). Bad liquidity powder(pile angle bigger than 40 °) because of the powder surface friction is difficult to mix.But there are advantages,once mixed,it is not easy to appear secondary segregation, stratification.Good fluidity powder (heap angle less than 30 °),because the powder is smooth,it is easy to achieve uniform mixing, short mixing time and high efficiency. The disadvantages of the powder with good fluidity is that there will be new segregation and stratification during transportation.
3, The particle size and its impact on the mixing
The particle size is usually expressed by the mesh number, and the particle size suitable for mixing is 50 mesh to 300 mesh.Large powder less than 50 mesh is difficult to be mixed into the main powder, often in the bottom. Small powder more than 300 mesh is so small that it will float above the main powder.
For example, the left picture above is a 20-mesh crystal salt particle,which is easy to remain in the bottom of the container during the mixing process. The right picture above is 2000-mesh pigment powder, which floats above the main powder during the mixing process.
The homogenization is that the density, particle size, fluidity of the several powders prepared to be mixed are basically close , this is the ideal mixing condition.
The left picture above shows the 800-mesh atomized copper powder, the specific gravity is 4.0g/cm3,the right picture abovbe shows the 650-mesh reduced iron powder, the specific gravity is 3.8g/cm3.The difference between the two powders is small,so it is homogeneous mixing. It is quite easy to mix the two powders.
5, Differentiation mixing
Differentiation mixing is common, that is the density, particle size, fluidity of the several powders prepared to be mixed are different,thus causing many mixing problems.Such as light and heavy powder is not easy to mix,ultrafine powder is not easy to mix,bad liquidity powder is not easy to mix and segregation of good liquidity powder.
The left picture above is the 800-mesh flour,the right picture above is the 20-mesh salt granules. Difference of particle size of both powders is big,it belongs to differentiation mixing,so it is difficult to mix the two powders evenly.
In general, whether the powders are easy or difficult to mix evenly is related to the above several physical characteristics.
Second,the steps of powder mixing
1, To confirm the formula and each powder
2, To test and analyze the physical properties of the powders
To register the physical indicators of the powders,analyze the differences between the various powders,if the difference is small,the powders can be mixer directly, otherwise the powders will need pre-treatment.
3, Pre-treatment before mixing
The purpose of pre-treatment is to make the difference between the various powders smaller, make them easier to mix evenly.
Common methods are:
a. Grind the big particle size powder when the difference of particle size is big.
b. Grind the heavy powder when the difference of specific gravity is big.
4, Use advanced mixing equipment
Choose suitable mixing equipment,make right mixing process,define the mixing batch size and mixing time.
5, The analysis after mixing
Accurate judgement of the uniformity after mixing is difficult.
Common detection methods are:
a. End product inspection method.
c. Chemical sampling assay.