Common powders, powders, dry powders, etc. have different names. They actually mean the same thing, but the expression habits in our work are different.
Due to the diversified characteristics of the powder itself, various problems often occur during the seemingly simple powder mixing process. Some problems have complex causes, and the result is that the purpose of uniform mixing cannot be achieved. Ultimately, the product quality of downstream powder products will be reduced, and the product may even be scrapped. These phenomena have attracted great attention from our team, and we are determined to study powder mixing technology and provide technical services to our customers. To this end, we have compiled this small encyclopedia of questions and answers on powder mixing technology, hoping to solve some practical problems for you.
Faced with the above thorny problems, we analyze and judge from the following aspects to find out the specific reasons that affect the uniform mixing.
1. The three major characteristics of powder are the basis for studying powder mixing.
Before looking for the cause of uneven powder mixing, you must understand three major characteristics of powders.
1. Specific gravity (density) of powder
Due to the difference between the loose and tight states of the powder, it can be divided into the following three proportions:
1). Loose packing proportion
2). Tap proportion
3). Free stacking proportion
The free stacking specific gravity refers to the specific gravity of the material when it is actually stacked or the accumulation specific gravity of the material in the mixer barrel. The free stacking specific gravity is between the loose specific gravity and the tapped specific gravity. For details, please refer to topic 2 of the Powder Mixing Encyclopedia.
2. Particle size of powder (particle size)
The particle size of the powder is also an important factor affecting powder mixing. The difference may be very large during the mixing process. For example, salt particles are about 0.6mm and pigment particles are about 0.001mm. The greater the differentiation, the more difficult it is to mix uniformly.
3. Fluidity of powder
The fluidity of powder is also one of the important characteristics. Whether the fluidity is good or not will affect whether the mixing is uniform.
The above three characteristics are the basis for our research on powder mixing technology. Most of the problems encountered in mixing are caused by problems with one characteristic or multiple characteristics at the same time. The methods for analyzing problems are based on these three powders. Start with the characteristics.
2. The greater the difference in the characteristic values of the powders involved in the mixing, the more difficult it will be to mix.
Research has found that the smaller the difference in the characteristic values of various powders in the materials to be mixed, the easier it is to mix uniformly, and the larger the difference in the characteristic values of the powders, the more difficult it is to mix uniformly.
1. For example, if large particle size powder and small particle size powder are mixed together, it will be difficult to mix them uniformly.
2. For example, if a powder with a heavy specific gravity is mixed with a powder with a light specific gravity, it is difficult to mix evenly.
The greater the above-mentioned differentiation, the more difficult it is to mix uniformly.
3. The more extreme the property values of the powders involved in mixing are, the more difficult it is to mix them evenly.
The study found that the characteristic values of the powders participating in the mixing are near the middle value, and it is easy to achieve the purpose of uniform mixing. If its characteristic value is too high or too low, it will cause mixing difficulties. The more extreme the characteristic, the more difficult it will be to mix.
1. Particularly heavy or light specific gravity (heavy powder or light powder) will cause mixing difficulties.
2. Particularly large particle size or extremely small particle size (large particle powder or fine powder) will also cause mixing difficulties.
3. Poor liquidity or excessive liquidity will cause mixing difficulties.
4. Mixing difficulties caused by other special characteristics of the powder to be mixed
Some powders may cause mixing difficulties due to moisture, excessive viscosity, false particles that are difficult to disperse, fiber bundles, etc.
The solution is to perform corresponding pre-mixing pretreatment for such powder before mixing. For details, see topic 7 of Powder Mixing Encyclopedia.
For powders containing fiber bundles and false particles, a dual-motion flying knife dispersing mixer can be used to break up their binding force with a high-speed rotating flying knife.
5. Based on the problems existing in the powder to be mixed, a targeted mixer should be selected.
We need to choose an appropriate mixer to overcome problems with the properties of the powder to be mixed.
1. For example, for food powders with poor fluidity (such as flour, chili powder, plant fiber powder), we need to choose a mixer with forced shearing function to force the materials to overcome the mixing difficulties caused by insufficient fluidity.
2. Materials containing light powder and ultra-light powder (such as plant fiber powder, nano powder, etc.) need to choose a dual-motion mixer. The dual-motion mixer has the entrainment function of barrel motion superimposed with blade motion to overcome the floating of light powder. Not easy to mix with difficulty.
