The working principle of powder pneumatic conveying equipment can be divided into three types.
1. Gravity slide
Low rotating speed screw and the material on the screw surface is much more affected by gravity than centrifugal force. Because the screw rotating, the material is falling along its direction, the axial displacement is generated. It is basically this principle. At this time ,the filling coefficient of the screw machine is generally less than 05. If excessive filling, the material is not sliding down the screw surface, but is stirred by the screw to make it fall over the axis, and can not obtain a large axial speed. Since the slow screw material is greatly affected by gravity, it is obviously not suitable for the upward pneumatic transportation with a large vertical screw or a large inclined angle.
Although the conveying capacity is low, the material is in a loose and free rolling state, and is less extruded, so it is suitable for the material with easy caking and high grinding property.
When the standard screw is used, it can not only maintain a faster sliding speed, but also have a certain adaptability to the inclined conveying (the inclination angle is generally within 20 degrees).
This method is used for unloading pneumatic conveying screw at the bottom of the silo. The material is often full filled with screw, and the static pressure on the granular material is large. The gravity of each material itself is far less than other forces (screw thrust, friction and static pressure).
This kind of screw resistance is very large, it has to overcome the friction formed under greater pressure. When working, the material seems to be a nut, and the screw acts as a bolts. As long as the nut does not rotate (or rotates slowly), the bolts rotation can make the nut move along the axial direction. The discharge screw at the bottom often adopts the variable pitch screw, and the pitch at the outlet end is larger.
3. Centrifugation induction
It is used for vertical powder conveyor with steep inclination or any powder conveyor with high speed. Its working feature is that the filling quantity of materials is between two types. Under the high speed of screw, loose materials are far more affected by centrifugal force than other external forces such as gravity.