In the concentrator, the spiral classifier often carries out pre classification and inspection classification in the grinding circuit. It can also be used in ore washing and desliming operations. It is widely used in major concentrators because of its simple structure, stable operation and convenient operation.
In production, many concentrators more or less encounter the problem of obvious decline in the classification efficiency of spiral classifier, and the root cause of this problem lies in the disordered settlement of fine and heavy ore particles and coarse and light ore particles in the classification process, resulting in equal drop phenomenon, resulting in a large amount of fine sand inclusion in the classifier and overflow coarsening. So, what measures should we take? Next, Fodamon engineer will explain how to improve the classification efficiency of spiral classifier?
- Appropriately increase the screw speed
The rotating speed of the screw shall meet the requirements for transporting coarse particles settled. 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. In order to obtain coarse overflow and deal with materials with high density and rapid settlement, the rotating speed of the screw can be appropriately increased, but it can not be too large to avoid damaging the classification effect. It is generally controlled in the range of 1.5-10r / min.
For the classifier used in the second stage grinding or grinding cycle, the screw speed should be slowed down as much as possible. Generally, lower speed is used in spiral classifier, especially for large spiral classifier. For example, in order to obtain coarse overflow, the screw speed of 2m diameter shall not exceed 6R / min, and generally, the screw speed of 1m diameter shall be controlled at 2-8r / min.
- Reasonably control pulp concentration
When the pulp concentration is small, the viscosity of the pulp also decreases. Therefore, the settling speed of ore particles is also accelerated, and the particle size of overflow products is finer, on the contrary, overflow products are thicker.
However, when the pulp concentration decreases to a certain extent, if the concentration continues to decrease, it will coarsen the particle size of overflow products. This is because when the concentration decreases a lot, the pulp volume (or pulp volume) is also large, which increases the pulp flow rate (rising flow rate and horizontal flow rate) in the classifier. Therefore, the coarser ore particles are also washed into the overflow products, so the pulp concentration must be reasonably controlled according to the regulations.
When there is more mud or fine particles in the graded feed, the make-up water can be appropriately increased to reduce the pulp concentration and obtain the required overflow fineness; When the mud content in the feed is small or has been deslimed, the pulp concentration shall be appropriately increased to reduce excessive fine-grained materials in the return sand.
- Adjust the height of overflow weir
Adjusting the height of overflow weir can change the size of settlement area. When the overflow weir is raised, the settlement area of ore particles and the volume of classification area can be increased. At the same time, due to the rise of the pulp surface, the stirring effect of the screw on the pulp surface is also weakened, which can make the overflow fineness finer. On the contrary, when the overflow particle size is required to be coarse, the height of the overflow weir should be reduced.
Generally, the height range of overflow weir of high weir spiral classifier is controlled within 400-800mm, while the height of overflow weir of submerged spiral classifier is generally between 930-2000mm.
- Maintain proper and uniform ore feeding
When the pulp concentration is constant, if the ore fed into the classifier increases, the flow rate of the pulp also increases, resulting in coarser particle size of the overflow product. When the ore quantity decreases, the particle size of overflow product becomes finer, and the fine particle content in return sand also increases. Therefore, the ore feeding amount of the classifier should be appropriate and uniform, not big or small, and the smaller the fluctuation range, the better. In this way, the classifier can work under normal treatment and obtain good classification effect.
- Bilateral ore discharge mode is adopted
Change the traditional discharge mode at the front end of the spiral classifier and adopt bilateral discharge, which can shorten the movement path of ore particles in the classifier, avoid pulp backflow, discharge fine particle overflow in time and shorten the settling time.
- Add mixing device at the lower end of the classifier
For the fine ore particles that have settled to the bottom of the tank, a stirring device is added at the lower end of the spiral classifier to bring them to the pulp surface again and discharge them with the overflow, so as to reduce the fine inclusion in the grit and improve the efficiency. For example, an automatic sand return lifting device is added at the sand return end of the spiral classifier, and the configuration of the scoop head of the ball mill is cancelled, which greatly improves the classification efficiency.
- Add new force field
It can be considered to change the traditional gravity settlement classification and add a new force field in the classification area, such as adding a cylindrical screen on the upper part of the classifier for secondary classification, which can improve the efficiency of the classifier.
These are the seven measures to improve the classification efficiency of spiral classifier. For spiral classification beneficiation, on the one hand, it is recommended to find a professional equipment manufacturer to purchase and operate according to the technical parameters given by the manufacturer. On the other hand, it is suggested that the spiral classifier operators improve their operation skills, pay attention to every detail in the sorting process, and respond to various emergencies in time to ensure the smooth progress of grading operation.