Generally, there are 3 ~ 6 turns in the spiral circle of the spiral sorter. After the slurry is delivered from the upper end, stratification occurs in the process of flowing along the groove. The high-density particles entering the bottom layer tend to move to the inner edge of the groove, and the small-density particles are thrown to the outer edge in the rotary movement of the spiral separator. The heavy materials moving along the inner edge after belt division are discharged through the interceptor.

(1) Flow characteristics of liquid in spiral groove. There are two kinds of liquid flow in the spiral groove, one is the rotary movement along the longitudinal direction of the spiral groove; The other is the circulation movement on the cross section of the spiral groove, also known as the secondary circulation. As shown in the figure, the reason for the secondary circulation is that under the action of centrifugal force, the surface liquid flow has high rotation speed and large centrifugal force, which is thrown to the edge of the groove, while the bottom liquid has small rotation velocity and small centrifugal force, which is greatly affected by gravity and tends to move to the inner edge.

At different radii of the groove surface, the thickness and average velocity of the water layer are different. The thicker the water layer towards the outer edge, the faster the flow continuity and the increase of water supply and inflow. The wet perimeter will expand outward. With the change of velocity, it is close to laminar flow near the inner edge and turbulent flow at the outer edge.

(2) Particles with different densities are sorted in spiral grooves. During the movement of particles with different density in the spiral fine, due to the different magnitude and direction of the force, the vertical and horizontal relative movement is generated, so as to realize the separation. The loose stratification process of particles in the frame rotating groove is the same as that in the Prajna turbulent inclined layer. The particle groups are summarized in the movement process along the bottom of the groove, the high-density particles gradually enter the bottom layer, and the small-density particles enter the upper layer, and the stratification is completed after about one circle.

After stratification, a lower flow layer dominated by heavy materials and an upper flow layer dominated by light materials are formed. At the same diameter position, the lower layer has large particle density, contacts with the groove surface, and is under great pressure from above. Therefore, the movement resistance is also large. On the contrary, the particles in the upper flow layer suffer less resistance. In this way, the velocity difference between the upper and lower flow layers is increased. The small density particles are located in the upper liquid flow with high longitudinal velocity, so they have large inertial centrifugal force. At the same time, the transverse circulation gives them hydrodynamic action in the outward direction. The resultant force of the two exceeds the gravity component and friction of the particles, so that the small-density particles move to the outer edge of the groove. Large density particles are in the lower liquid flow with low longitudinal velocity, so they have small inertial centrifugal force, while the gravity component and transverse circulation of particles give them hydrodynamic action in the direction of inward. The latter two forces exceed the inertial centrifugal force and friction force of the particles, pushing the high-density particles to move to the inner side of the groove and enrich the inner edge area. Other connective particles with intermediate density occupy the middle zone of the groove. This zonal movement lasted about the third and fourth laps and was basically completed