\    Powder fluidity is a double edged sword

   Liquidity plays an important role in powder mixing. In general, the better the liquidity, the faster the mixing process. In extreme cases, the liquidity is too good, but it will also hinder the mixing process. Therefore, we need to do an in-depth discussion of liquidity.
First, what is liquidity
        Powder under the action of force will occur displacement ability.
        Explain: It shows the performance of the powder flow in mixed motion.
Second, the powder liquidity representation
        The easiest way to express mobility is to use powder piling corners.
        1, powder pile angle (angle of repose / rest angle)
After the natural accumulation of powder, the angle between the slope of the pyramid and the horizontal plane represents the fluidity of the powder. The smaller the angle, the better the fluidity of the powder.
Explanation: The piling angle is also commonly referred to as the angle of repose, which means that the powder is poured onto the plane until it flows around. When the angle is stable, the angle between the inclined plane and the horizontal plane of the powder surface. In practice, powder heap angle is usually used to represent powder flowability, because this method is convenient and intuitive. The smaller the inclination is, the better the fluidity is, whereas the worse fluidity is as shown below.
       2, Powder crash angle
          The powder crash angle will only occur if the powder flowability is particularly poor.
         Powder in the accumulation process due to poor fluidity, there will be constantly piled high - collapse, collapse, then pile up - and then collapse, collapse phenomenon. The angle between the cross section left behind by the powder collapse and the horizontal plane is called the powder collapse angle as shown in the following figure.
       Explanation: Generally, only the powder with poor fluidity will have a breakdown angle; the powder with poor fluidity usually has both the collapse angle and the Piling Angle, that is, the collapsing angle after the collapse of the upper part, and the flow rate after the collapse Piling Angle.
         3, The factors that affect liquidity
         ①.Powder particle shape: the closer the powder particle shape is to the roundness, the better the fluidity of the powder, the more complicated the particle shape of the powder particles (such as the dendritic shape), the poorer the fluidity;
       ②. Powder particle surface smoothness: the smoother the particle surface, the better fluidity, the rougher the particle surface, the greater the flow resistance, the poorer the fluidity;
        ③. There is adhesion between the powder particles, the phenomenon of adsorption will also make mobility worse.
          4, liquidity is double-edged sword
         Poor liquidity and very good liquidity will affect the mixing process. Only the powder with the Piling Angle between 25 ° and 42 ° is suitable for smooth mixing process. As shown below:
       ①. Mobility in the easy-mixing area (pictured above), especially suitable for smooth mixing smoothly.
       ② poor mobility of the powder, such as Piling Angle is greater than 42 degrees, in the mixed movement due to greater friction between the powder particles will slow the uniform mixing process, the mixing time greatly extended, or even can not achieve the purpose of uniform mixing .
        ③. Particularly good liquidity powder, such as Piling Angle less than 23 degrees, due to the friction between the powder particles during mixing is very small, once the rapid movement will produce heavy powder and light powder, between large particles and small particles Segregation phenomenon. As a result, it is difficult to achieve a homogeneous mixture.