JXSC Mineral

What Are The Main Factors Affecting The Classification?

Many factors affect the classification. Following, we list the main three categories that influence the classifying effect.

Ore properties: The mud content and particle size of the materials fed into the classifier make up the specific gravity and shape of the ore.

Machine structure

  • The size of the inclination angle of the slot
  • The rotation speed of the screw shaft
  • The width of the slot


  • Slurry concentration
  • Ore feeding amount and uniformity
  • Overflow weir height.


Next, we will discuss each influencing factor and its adjustment method in detail.

Ore Properties

  1. What happens when there is a lot of mud or fine particles in the material fed into the classifier? How to adjust?
    When the amount of mud or fine grades in the classified material is more, the viscosity of the pulp is more significant, so the sedimentation speed of the mineral particles in the pulp is lower, and the particle size of the overflow product is also coarser. In this case, to ensure that the particle size in the overflow product meets the requirements, it should reduce the slurry concentration appropriately. Suppose the material contains a small amount of mud or has undergone desliming treatment to avoid the inclusion of too many fine-grained grades in the returned sand. In that case, appropriately increase the graded concentration.
  2. What is the grading effect of different specific gravity of classified materials and shapes of ore particles? How to adjust?
    Under the same concentration and other operating conditions, if the specific gravity of the classified material is smaller, the viscosity of the pulp will be larger, the particle size in the overflow product will become coarser, and the fine-grained content in the returned sand will increase. Therefore, when classifying ores with large specific gravity, the classification concentration should be appropriately increased; it should appropriately reduce the classification concentration when classifying ores with small specific gravity.
    When the ore particles are flat, the sedimentation rate is slower than that of the round or nearly round ore, so the classification concentration of the flat ore is lower, or the discharge rate of the overflow product is accelerated.

sprial classifier

Machine Structure

  1. What is the effect of the speed of the spiral rotation on the classification effect?
    The number of revolutions of the screw should be sufficient to transport the settled coarse particles. The faster the rotating speed of the spiral shaft of the classifier, the stronger the stirring effect on the pulp and the more coarse particles entrained in the overflow product. To obtain a coarser overflow and deal with materials with a larger specific gravity and faster sedimentation, it can appropriately increase the number of revolutions of the screw. Still, it cannot be too large not to damage the classification effect. However, for the classifier used in the second-stage grinding or delicate grinding cycle, it should slow down the screw speed as much as possible.
    In conclusion, spiral classifiers generally use lower revolutions, especially for large spiral classifiers. For example, to obtain a coarse overflow, the speed of the screw with a diameter of two meters should not exceed 6 rpm, and generally, it should control the speed of the screw with a diameter of more than one meter at 2-8 rpm.
  2. What is the relationship between the slot width of the spiral classifier and the processing capacity? How does it relate to grading effects?
    The width of the trough greatly relates to the discharge speed of the overflow product. The wider the trough, the faster the overflow discharge speed, and the greater the possibility that the coarse particles are discharged with the overflow. But on the other hand, the wider the trough, the larger the settlement area of ​​the ore, which is easy to settle. Therefore, the width of the trough has little effect on the classification effect but is closely related to the processing capacity of the classifier. The wider the slot, the greater the processing capacity. On the contrary, the processing power is small. Therefore, the groove width of the classifier shall be compatible with the processing capacity of the grinding machine.



  1. What effect does the slurry concentration have on the classification effect? Why can’t the concentration be too small?
    When the pulp concentration is small, the viscosity of the pulp is also reduced. Therefore, the sedimentation speed of the ore particles is also accelerated, and the particle size of the overflow product obtained is also finer. Conversely, the overflow product particle size is coarser.
    However, it should point out that when reducing the slurry concentration to a certain level, if the concentration continues to decrease, the particle size of the overflow product will become coarser. The main reason is that when reducing a lot of the concentration, the pulp volume (or the amount of pulp) is also large so that the pulp flow rate (upward flow rate and horizontal flow rate) in the classifier also increases. Consequently, the coarser ore particles are also flushed into the overflow product. Therefore, you must reasonably control the pulp concentration according to regulations.
  2. Why is it said that the amount of ore entering the classifier should be appropriate and the ore feeding should be uniform?
    When the slurry concentration is constant, if the amount of ore fed into the classifier increases, the flow velocity of the slurry also increases, thus making the overflow product coarser. When the amount of ore decreases, the particle size of the overflow product becomes finer, and the content of fine particles in the returned sand also increases.
    Therefore, the ore feeding amount of the classifier should be appropriate. In particular, the uniformity of ore feeding should not be large or small. The better, the smaller the fluctuation range. Then the classifier can work under normal processing conditions and obtain a good classification effect.
  3. What is the grading effect of adjusting the overflow weir height?
    When increasing the overflow weir, the settlement area of ​​the ore particles can be increased. At the same time, due to the increase of the pulp surface, the stirring effect of the spiral on the pulp surface is also weakened, which can make the overflow particle size finer.
    On the contrary, lowering the overflow weir will make the overflow particle size coarser.

In a word, many factors affect the spiral classifier’s classification effect, and most restrict each other. Therefore, in the actual production, as a technician, we should observe and analyze more to find the main influencing factors for adjustment to solve the practical problems in production effectively.