Factors affecting the classification effect of spiral classifier and operation method

Spiral classifier mainly used for the production of metal beneficiation process, according to the different settling velocity of the mineral particles, the ore is size classification. The spiral classifier can be divided into three types according to the height of the overflow weir, the low-lying type and the submerged type.

The spiral classifier is composed of a transmission device, a spiral (left or right) and a water tank, a lifting device, a lower support and a feed port.

The water tank is installed obliquely. The inclination angle is determined according to the equipment configuration in the process flow. The transmission device drives the spiral to rotate in the tank. After the fine slurry is fed into the tank from the side feeding inlet, a slurry settlement is formed at the lower end of the tank. The surface area and volume are determined by the sink angle and the weir height. The spiral of low-speed rotation can play a certain agitation. After the slurry is stirred, the light and fine particles are suspended on the upper surface to form an overflow, which overflows from the overflow surface of the trough and flows into the next beneficiation process; the heavy particles sink to the bottom of the trough to form a return. The sand is transported by the screw to the discharge port.

The factors affecting the grading effect are mainly divided into four aspects, equipment factors, ore properties, operating conditions and installation factors.

First, equipment factors

1) Graded area size

In terms of mechanical equipment structural factors, the size of the grading area in the tank is a decisive factor affecting the processing capacity and grading granularity of the classifier. Increasing the width of the groove, increasing the height of the weir or reducing the angle of inclination can increase the graded area.

2) The level of overflow weir.

The level of the overflow of the classifier affects the size of the sedimentation area of ​​the ore. In the production, we can adjust the level of the overflow of the classifier according to the requirements of the fineness of the grinding. If the fineness of the grinding is required to be fine, grader welding two edges of a certain height angle iron, wooden pull plug method to adjust the level of the classifier overflow weir, sometimes after long-term accumulation of sludge, can naturally raise the height of the overflow weir.

The overflow weir height H of the sorghum spiral classifier is 1/4-3/8 of the spiral diameter D, and is mainly used for ore grading of an overflow granularity of 0.83-0.15 mm. The H of the sunken spiral classifier is 3/4-1 of D. It is mainly suitable for ore grading with an overflow particle size of 0.15-0.07mm. When the overflow fineness is high, H takes a small value, and vice versa.

3) The speed of the spiral.

The rotation speed of the spiral affects the degree of agitation of the liquid surface and the ability to transport the sand return. The number of revolutions is related to the diameter of the spiral.

The rotation speed of the spiral should satisfy the coarse particles that can be sent to settle. The faster the speed of the screw shaft of the classifier, the stronger the stirring effect on the slurry, and the more coarse particles are entrained in the overflow product. In order to obtain a thicker overflow and to handle materials that are faster than the major settlement, the rotation speed of the spiral can be appropriately increased, but not too large, otherwise the classification effect will be destroyed. For graders used in two-stage grinding or grinding cycles, the spiral speed is slowed down as much as possible. Lower speeds are generally used in spiral classifiers, especially for large spiral classifiers. If a rough overflow is to be obtained, the 2m diameter screw speed should not exceed 6r/min, and the diameter spiral speed of 1m or more should be controlled at 2~8r/min. For a spiral with a diameter of 0.3 m, the spiral speed can be increased in order to obtain a coarse overflow of the particle size, but it cannot exceed 25 r/min. The appropriate speed should be determined by experiment. The speed of the spiral of the commonly used spiral classifier is selected to be 1.5-10 r/min.

4) Number of classifier blades

Reasonably determine the number of blades. Increasing the number of blades is conducive to increasing the area or aspect ratio, making it easier to meet higher maneuverability requirements and improving the vitality of the equipment, but at the same time making all devices more complicated. Therefore, in addition to meeting special requirements and being limited by pulp, a smaller number of blades should be used. In summary, most graders use single-spiral blades.

In the case of the same flow rate, as the number of blades increases, the area between the blades decreases, the radial velocity increases, and the face tangential velocity decreases, which is caused by the influence of the side wall effect of the blade, which will be beneficial. The particles are only subjected to the inward gas drag and centrifugal force, which reduces the collision of the particles with the blades and facilitates the classification of the particles. Therefore, an increase in the number of blades is advantageous for improving the classification performance of the classifier. In practice, the number of blades should not be excessive due to the influence of the thickness of the blade and the limitation of machining.

5) Pitch of classifier

The pitch is related to the required amount of sand return, the diameter of the helix, and the speed of rotation. The pitch is generally 0.5-0.6 times the diameter of the spiral. A ship adopts an equal pitch, but it can also adopt unequal pitch. For example, the pitch of the overflow end is short, and the pitch of the returning end is long. This can increase the amount of sand return and ensure the amount of sand return. The overflow end is agitated smoothly, which is convenient for improving the overflow quality and the throughput.

6) Width of the classifier tank

The width of the spiral classifier tank has a great relationship with the discharge speed of the overflow product. The width of the overflow is high, and the possibility of coarse particles discharging with the overflow is greater. On the other hand, the wider the trough, the larger the sedimentation area of ​​the ore and the easier it is to settle. Therefore, the effect of the width of the trough on the grading effect is not significant, but it is closely related to the processing capacity of the classifier. The width of the trough is large and the processing capacity is large. On the contrary, the processing power is small. Therefore, the width of the tank of the classifier should be compatible with the processing capacity of the mill. When purchasing the machine, you should pay attention to the width of the classifier and the processing capacity of the mill. Choose the right grader and mill.

The width of the grading tank depends on the spiral diameter of the return sand (ie the size of the classifier) ​​and is 100-200 mm larger than the diameter of the spiral.

7) Spiral diameter of the classifier

The diameter of the spiral indicates the specification of the spiral classifier, which restricts the width of the tank, thereby affecting the size of the trough, affecting the productivity of the overflow and the ability to transport sand. Therefore, the helix diameter of the classifier must be calculated and matched with the capacity of the ball mill , and at the same time meet the classification particle size requirements, select the diameter of the appropriate spiral, so that the classification is carried out under the optimal production state.

8) Guide vane tilt angle

Under the same conditions, the classification accuracy index shows a decreasing trend with the increase of the inclination angle of the guide vanes. Practice has proved that the guiding angle of the guide vane should be between 85 ° and 90 °.

Under the same conditions, with the increase of the angle of the guide vane, the classification accuracy index is reduced, the average particle size is increased, and the output is also increased. The optimum inclination angle of the guide vanes is between 85° and 90°.

9) Blade wear degree

The wear of the classifier blade is a normal production phenomenon. After the blade is worn, the amount of sand return is reduced, resulting in coarser grinding fineness. In addition, if the blade is worn out, it will affect the life of the classifier, so check it in time. Wear the blade and replace the worn blade in time.

Second, the nature of the ore

1) Fineness and mud content of graded feedstock

The more sludge or fine fraction in the graded feed, the greater the viscosity of the slurry, the smaller the sedimentation rate of the ore in the slurry, and the coarser the size of the overflow product; in this case, to ensure compliance The required overflow fineness can be appropriately increased to increase the concentration of the slurry. If the amount of mud in the feed is small, or if it has been desmutted, the slurry concentration should be increased appropriately.

2) Density of ore

In the case of the same concentration and other conditions, the density of the graded material is smaller, the viscosity of the slurry is larger, and the particle size of the overflow product becomes coarser. Conversely, the density of the graded stream is larger, the viscosity of the slurry is smaller, and the size of the overflow is finer. . Therefore, when the ore with a high density is classified, the classification concentration should be appropriately increased; when the ore with a small classification density is used, the classification concentration should be appropriately lowered.

Third, operational aspects

1) slurry concentration

The slurry concentration is one of the most important adjustment factors in the operation of the classifier. It is usually used to control the graded overflow fineness. Generally, the slurry concentration is low, the fineness of the overflow is fine, the concentration is increased, and the overflow is overflow. The particle size becomes coarse. This is because in the thicker slurry, the viscosity of the slurry is larger, the interference of the particle sedimentation is large, and the sedimentation speed is slow. Some of the coarser ore particles are too late to sink, and the horizontally flowing pulp is brought out of the overflow weir. The overflow particle size is made thicker.

However, when the slurry concentration is very low, there may be cases where the overflow particle size becomes coarse. This is because the concentration is too low, in order to maintain a certain capacity calculated according to the solid mass, the amount of slurry is inevitably large, causing the slurry flow rate in the classifier to increase, thereby flushing the coarser ore to the overflow. Go in. Therefore, in actual production, for the classifier that processes the specified ore, there is an optimum graded slurry concentration at which the maximum productivity can be obtained while maintaining a certain graded particle size; while maintaining a certain productivity, The smallest separation particle size is obtained. This concentration is called the critical concentration. The critical concentration value of the actual production shall be determined by testing and referring to the index of similar concentrating operations of the concentrator.

2) Uniformity of ore and ore

When the concentration of the slurry is constant, if the amount of ore fed to the classifier increases, the ascending flow rate and the horizontal flow rate of the slurry also increase, thereby making the overflow particle size coarse. Conversely, if the amount of ore is reduced, the overflow particle size becomes finer. Therefore, the ore-feeding amount of the classifier should be appropriate, and it must be kept even and stable, so that the classification process can be carried out normally, and a good classification effect can be obtained.

When the total load is the same, the sand return of the hard ore is larger than that of the soft ore. When the amount of return sand increases beyond the specified return sand ratio, it may be caused by an increase in the amount of ore, or a decrease in the amount of water caused by a decrease in the overflow concentration. Therefore, a certain amount of ore supply has a certain amount of sand return. When a stable overflow concentration is maintained, the amount of sand return varies with the amount of ore. Through the change of the amount of sand returned by the classifier, it can be observed to determine the change of the original ore amount and concentration of the mill and other conditions. The change in the amount of sand returned can be judged by observing the height of the sand return layer on the upper part of the classifier.

3) Additive effects

The chemicals added to the grinding cycle at the flotation plant and the chemicals brought by the return water have an effect on the classification process and even the grinding operation. The dispersing agent and the coagulating agent cause a large difference in the sedimentation rate of the particles.

4) Matching the model of the classifier with the ball mill

Since 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 the feeding fineness, the effective diameter after the lining of the grinding body, the rotation speed of the ball mill, the selection and grading of the grinding medium, the loading amount, the effective length of the grinding body, and the amount of the feeding; The output is affected by various conditions such as the speed of the classifier, the width of the tank, the angle of the tank, and the fineness of the grade. The two equipments should have the following relationship:

The output of the classifier = the amount of classifier processing - the amount of coarse material after classification

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

Processing capacity of classifier = output of ball mill

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

5) Grader spindle lifting height

The height of the grader's main shaft is also an important factor affecting the amount of sand return and the fineness of grinding. Normal normal production requires the grader spindle to be in place. Some ore dressing mills have not cleaned the ore in the classifier after the equipment has been overhauled. Under the long-term sinking, the mud sinks more. When the grader spindle is lowered, the spindle is not completely lowered because it is not careful. , resulting in less sand than normal. In addition, if the spindle is not lowered, it may be because the spindle has not been cleaned and oiled for a long time, so pay attention to it during the operation.

Fourth, the installation factors

1) Location and size of the upper and lower discharge ports of the classifier

The bottom of the classifier tank is a semi-circular rectangular long groove. The bottom of the upper end of the trough has a returning sand discharge port and the lower end has an overflow port. The side wall near the middle part of the trough body is provided with a feeding port. Generally, the feeding port is 50mm below the overflow surface. When the flow rate of the slurry is effective, the feeding port should be less than 100mm below the overflow surface to reduce The effect of small flow rates on the temperature flow.

The height of the opening under the classifier, the size of the opening under the classifier, the height of the opening on the classifier, and the size of the opening on the classifier are made on site during the installation of the equipment. In many factories, the size of the opening of the classifier is not adjusted during the installation of the equipment. However, the workers did not pay much attention to the operation process, and the invisible also affected the grinding operation. The lower opening of the classifier is relatively large, so the sedimentation area of ​​the ore is larger, so the amount of sand returned will be larger, the fineness of the grinding is relatively fine, and the opening under the classifier is large. The sedimentation area of ​​the ore is larger, the water flow is more gentle, so the amount of sand returned. Will be large, the overflow fineness is relatively thin. The opening on the classifier is low, the amount of sand return is relatively large, the fineness of the overflow is relatively thin, the opening on the classifier is large, the relative amount of sand returned is relatively large, and the fineness of the overflow is relatively thin.

2) Inclination of the classifier tank

The inclination of the bottom of the trough is mainly determined by the necessary lifting height of the returning sand, and the ore is not excessively limited. The structural parameters that can be changed in production are mainly the weir height, but this factor is rarely determined at the initial stage of production.

The inclination of the trough also affects the degree of agitation of the slurry by the spiral blade, thus affecting the quality of the overflow product. The inclination of the trough is small, the settlement area of ​​the classifier is large, and the fineness of the overflow is fine. Conversely, the inclination of the trough is increased. The settlement area is reduced, the coarse grain material has more chances of falling, and the overflow particle size becomes thicker.

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

In short, there are many factors affecting the classification effect of the spiral classifier, and most of them are mutually constrained. Therefore, in the actual production, as a technician, it is necessary to observe more, analyze more, and find the main influencing factors to adjust, so as to effectively solve the practical problems existing in the production.