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Spiral Classifier || Operation and Technique (3rd)
Apr 06, 2018

Second, the nature of ore factors

1) Fineness and mud content of classifying materials

The more sludge or fine-grained grades in the classifying feed, the greater viscosity of the ore slurry, the smaller the settling velocity of the ore particles in the slurry, and the coarser particle of the overflowed product; in this case, the required overflow fineness can be appropriately increased with additional water to reduce the pulp concentration. If the feed contains a small amount of mud, or after the mud removal treatment, the pulp concentration should be increased appropriately.


2) The density of ore

In the same concentration and other conditions, the smaller density of the classifying material, the greater viscosity of the pulp, the coarser particle of the overflow product; Conversely, the higher density of the classifying stream, the smaller viscosity of the pulp, and the smaller overflow particle size. Therefore, when grading ore with a high density, the grading concentration should be appropriately increased; and when grading an ore with a small density, the grading concentration should be appropriately reduced.


Third, the operating factors

1) pulp concentration

Slurry concentration is one of the most important adjustment factors in the operation of the classifier. It is usually controlled by it to control the fineness of the graded overflow. Generally speaking, the slurry has a low concentration, fine overflow, large concentration, and the overflow granularity becomes coarser. This is because the viscosity of the pulp is larger in the thicker ore pulp; the disturbance of the sedimentation of the particles is greater, and the sedimentation rate is slower. Some of the coarser ore particles will be brought out of the overflowing puddle by the horizontally flowing pulp before sedimentation, which make the overflow particle size coarser.

However, when the slurry concentration is very low, the overflow particle size may become coarser. This is due to the fact that the concentration is too low. In order to maintain a certain production capacity calculated in terms of solid mass, the amount of pulp must be very large, resulting in an increase in the flow rate of the pulp in the classifier, and thus flushing the coarser particles to the overflow. Therefore, in actual production, the most suitable grading pulp concentration is for the classifier that processes a given ore, and at this suitable concentration, the maximum productivity can be obtained when maintaining a certain grading particle size; while maintaining a certain productivity, the smallest separation particle size can be obtained. This concentration is called the critical concentration. The actual production critical concentration value is to be determined by testing and referring to the indicators of similar classification operations of the concentrator.


2) The amount of ore given and the uniformity of the ore

When the pulp concentration is constant, if the amount of ore that is fed to the classifier increases, the rising flow rate and the horizontal flow rate of the slurry also increase, thereby making the overflow particle size coarser. On the contrary, if the amount of ore is reduced, the overflow particle size becomes finer. Therefore, the amount of ore to be fed by the classifier should be appropriate, and it should be kept even and stable to enable the classification process to proceed normally and obtain a good classification effect.

When the total load is the same, the return sand of hard ore is larger than that of soft ore. When the amount of return sand increases beyond the prescribed return sand ratio, it may be caused by an increase in the amount of ore, or it may be caused by a decrease in the amount of water causing the overflow concentration to be too low. Therefore, certain amount of ore feed has a certain amount of back-sand, and when a stable overflow concentration is maintained, the amount of back-to-sand volume varies depending on the amount of ore. The change in the amount of sand returned by the classifier can be used to observe the changes in the amount and concentration of the original mill, and other conditions. The change in the amount of sand returned can be judged by observing the height of the sand returned from the top of the classifier.


3) Effect of added chemicals

The chemicals added to the grinding cycle in the flotation plant and the agents brought by the return water affect the grading process and even the grinding operations. The dispersing agent and the coacervating agent cause a large difference in the sedimentation velocity of the particles.


4) Matching of grader model with ball mill

Because ball mills and classifiers are usually produced by two companies, there are often differences in concepts such as production. The output of the ball mill is affected by various conditions, such as feeding fineness, effective diameter after lining the grinding body, rotation speed of the ball mill, selection and grading of the ball grinding medium, loading amount, effective length of the grinding body, and the amount of the feeding amount; The yield is affected by various conditions such as the speed of the grader, the width of the tank, the angle of the tank, and the fineness of the classification. The two equipment should have the following relationship:

Grader throughput = grader throughput - coarse material after classification

Ball mill output = raw material feed amount + coarse material returns after classification

Grader throughput = ball mill output

Therefore, the matching of the two must be considered when selecting the equipment and designing.


5) Classifier Spindle Lift Height

The lifting height of the classifier's spindle is also an important factor affecting the amount of sand returned and grinding fineness. General normal production requires the grader spindle to be in place. Some mills in the beneficiation plant did not fully set down the main shaft because they were not careful because the ore in the grader was not cleaned after the equipment was overhauled. , resulting in less sand return than normal. In addition, if the spindle is not lowered, it may be because the spindle is not cleaned and oiled for a long time, so pay attention to it during the operation.


Fourth, the installation of factors

1) The position and size of the ore port on the top and bottom of the classifier

The bottom of the classifier tank is a semi-circular rectangular long tank, and the bottom of the upper end of the tank is provided with a return sand outlet, and an overflow port is opened at the lower end. The side of the tank near the middle of the tank is open to the mine mouth. In general, the mine mouth is 50mm below the overflow surface. When the flow rate to the slurry is large, the mine mouth should be less than 100mm below the overflow surface to reduce the effect of small flow rate on temperature flow.

The level of the opening under the grading machine, the size of the opening under the grading machine, the opening height of the grading machine, and the opening size of the grading machine are produced on site during the installation of the equipment. In many plants, the size of the grading machine opening has not been adjusted in the equipment installation., And workers in the process of operation and do not pay attention, invisible also affect the grinding operations. Under the grader, the opening is low, and the ore sand sedimentation area is relatively large, so the amount of back sand will be large, the grinding fineness is relatively fine, the grader under the opening is large, relatively large ore sand sedimentation area, the water flow is relatively flat, so the amount of sand back the larger, finer overflow fineness. The grading machine has a low opening, a relatively large amount of return sand, a relatively fine overflowing fineness, a large opening on the grading machine, a relatively large amount of relative sand returning, and relatively fine overflowing fineness.


2) The tilt of the grader tank

The inclination of the bottom of the tank is mainly determined by the necessary lifting height of the returned sand water and is limited to the extent that the ore sand does not fall excessively. The structural parameter that can be changed in production is mainly the overflow weir height, but this factor is determined once in the early stage of production, and it is rarely changed at ordinary times.

The dip angle of the tank also affects the degree of agitation of the slurry by the spiral blade, thus affecting the quality of the overflow product. The dip angle of the tank is small, the settling area of the classifier is large, and the overflow fineness is small; otherwise, the dip of the tank is increased. As the area of settlement decreases, there is more chance of falling coarse materials, and the overflow particle size becomes coarser.

The inclination of the tank body is determined according to the process requirements, generally between 12° and 18° 30′. When the graded grain size is required to be small, it is taken as a small value, and vice versa.

In short, there are many factors influencing the grading effect of the spiral grading machine, and most of them are mutually restricted. Therefore, in the actual production, the technologist needs to observe and analyze more and find the main influence factors to adjust, so as to effectively solve the practical problems in production