Guide of Classifing Equipment

2019-06-14 18:06:29xinhai

In the pulverization process, the qualified ore particle size is not formed one-off,but is gradually completed. At each pulverization stage, a portion of the desired fines are always produced. 

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In the grinding process, in order to timely separate the qualified fine particles, prevent over-grinding, and improve the productivity of the grinding mill, classification equipment is essential. The qualified particles are sent to the separation process from the classifier overflow (the sieve is the undersized product), while the coarse particles are returned to the mill for regrinding. Therefore, classifying plays an important role in grinding operations. 

Common Classification Equipment

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The most common classification equipment currently used in concentrators is spiral classifiers and a hydrocyclones.

(1) Spiral Classifier

Spiral classifiers achieve classification function by means of the different sedimentation speed that different-sized ore particles shows in the aqueous medium. Due to their simple structure, stable operation and convenient operation, spiral classifiers are widely used in concentrators. According to the position of the spiral in the water tank and the height of the overflow surface, spiral classifiers can be divided into low spiral classifiers, high spiral classifiers and submerged spiral classifiers. The high spiral classifier is suitable for separating the overflow of more than 0.15 mm, so it is mostly used for the first stage of grinding, while the submerged type classifier is suitable for classifying the product of less than 0.15 mm, thus often used to form closed-circuit grinding with mill in the second stage of grinding process.

(2) Hydrocyclones

The hydrocyclone is a classifying equipment that uses centrifugal force to accelerate these dimentation of ore particles. It requires pressure to feed the ore slurry, so it consumes a large amount of power. But hydrocyclone also has some traits including small installation area, less investment, large capacity and high classification efficiency, and can obtain a fine overflow product. Hydrocyclone is a kind of classification equipment mostly used in the second stage closed-circuit grinding.

hydrocyclone unit


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Working Principle of Spiral Classifiers

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Spiral classifier is a kind of classification equipment manufactured by the principle that the sedimentation speed of solid particle in the liquid varies from their own density. The slurry ground in the mill is sedimented and filtered in the classifier tank, and then the coarse material is screwed into the mill feed port by a spiral blade, and these dimented fine material is discharged from the overflow pipe. The fine ore particles are suspended in the water and discharged as the overflow, and the coarse ore particles are sunk at the bottom of the tank, and are pushed by the spiral rotation to the upper part into the mill. The ore after grinding is fed into the water tank from the feeding port located in the middle of the subsidence zone. The lower end of the inclined installation tank is a classifying and sedimentation zone of the mineral slurry. The spiral rotates at a low speed to agitate the slurry, so that fine and light particles are suspended to the top until they flow out from the overflow end for the next process. The coarse and heavy particles settle to the bottom of the classifier tank and are transported by the screw to the discharge port as sand return. Usually, the spiral classifier and the mill form a closed circuit, in which there turning sand is sent to the mill for re-grinding. 

spiral classifier

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Structure of Spiral Classifiers

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The spiral classifier is mainly composed of a transmission device, a spiral body, a trough body, a lifting mechanism, a lower bearing (bearing bush) and a discharge valve. Take high double spiral classifier as an example. The semi-circular water tank of high double spiral classifier is welded by a steel plate and a profiled steel. The central side wall of the tank body has a feed port, and the lower part of the upper end of the trough body has a sand return port. The bottom of the lower end of the tank body has a drain valve, and the slot is provided with a longitudinal hollow shaft. The shaft is equipped with a bracket frame adapted to the spiral lead angle, and the left and right spiral blades with wear-resistant rubber equipped are fixed on the upper side, and the screw mechanism adopts a double-head uniform pitch. The spiral rotation stirs the slurry on the one hand to float the light and fine particles, and simultaneously discharges the coarse and heavy particles sinking at the tank bottom to the upper end. The hollow shaft is usually made of seamless steel pipe with shaft neck equipped both in the upper and lower end. The upper bearing is located in the rotatable cross-shaped shaft head, and the lower bearing in the lower end support. The shaft heads on both sides of the cross-shaped shaft support are set on the transmission frame,which can make the screw shaft complete both rotation movement and lifting motion.

The bearing support at the lower end requires a good seal because it is immersed in the slurry for a long time. In the past,three commonly used sealing devices were: mechanical seal rolling bearing support, pressure water sealing resin tile sliding bearing support and pressure water seal rubber bearings. Later, the mechanical seal rolling bearing support was improved, and the combination of the packing labyrinth and the high-pressure dry oil combined seal type improved the sealing performance and greatly extended the bearing life.

spiral classifier

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Spiral Classifier Type

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According to the height of (the position of spiral in the classification tank is different from the level of slurry), spiral classifiers can be divided into three types: high spiral classifier, low spiral classifier and submerged spiral classifier. Generally, the overflow of low spiral classifier is usually lower than the bearing center at the overflow end, so the settlement area is too small, the overflow production capacity is too low, and the spiral has a great agitation on the slurry, so in actual production low spiral classifier only used for washing sand minerals with little mud and dehydration of coarse particles, and rarely used in grinding and classification operations. However,the overflow position of high spiral classifier is usually higher than the bearing center at the lower end of the screw shaft, lower than the upper edge, so the subsidence area is larger than that of low spiral classifier, the height of can be adjusted within a certain range. The subsidence area of high spiral classifier can be slightly changed according to the classification requirements to adjust the classification granularity. As for submerged spiral classifier, its overflow end is usually equipped with 4-5 spiral blades, and all the spiral blades are immersed under the liquid level in settlement area, so the settlement area is large and the classification tank is deep.

According to the different structure of the high classifier and submerged spiral classifier, their functions in the classification operation are also different. The high spiral classifier is more suitable for classifying coarse granules larger than 0.15 mm, which is usually used in the first stage of grinding. While the submerge spiral classifiers usually used to classifying overflow product smaller than 0.15 mm because of its stable classifying level, high overflow production and fine particle sizes, which is often combined with mills in the second grinding stage.

According to the spiral axes number, the spiral classifier can be divided into single spiral classifier and double spiral classifier. The classification performances of these two spiral classifiers are basically the same, but the double spiral classifier is significantly larger than the single spiral classifier in terms of sand return treatment capacity,overflow treatment capacity, spiral diameter and other aspects, and the price of double spiral classifier is much higher than the single spiral classifier.Therefore, it is more suitable for combined use with large and even super large grinding machines. The mineral dressing expert recommends that a single spiral classifier should be used as far as possible under a determined processing capacity. According to statistics, the working load of double spiral classifier is 0.6 to 0.75 times that of single spiral classifier, and the efficiency is relatively low. Therefore, when selecting a spiral classifier, it is necessary to determine the appropriate spiral speed and spiral number according to processing capacity.

All classification equipment mentioned above have their own advantages as well as different effects on the classification efficiency of equipment. At present, many classification equipment manufacturers will make corresponding optimization and improvement according to different classification requirements, in order to strive for customer satisfied classification effect. When selecting classification equipment, each mineral processing plant must clearly understand and grasp the spiral classifier characteristics and working principle, and consider the best classification equipment in combination with the production demand of the mineral processing plant.

According to the spiral position in groove and the level of slurry surface, spiral classifiers are divided into low wire spiral classifiers, high wire spiral classifiers and submerged spiral classifiers. At present, low spiral classifiers are rarely used; high spiral classifiers are used for coarse grinding product classification; submerged spiral classifiers are used for fine grinding pulp classification.

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Application of Spiral Classifiers

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Spiral classifiers are mainly used for preliminary classification and inspection classification in the grinding circuit, and can also be used in mineral washing and de-sliming operations.

Advantages: The structure is relatively simple, the installation slope of the classification tank is large, so they are convenient to connect with the self-flow connection configuration of the grinding machine with a diameter less than 3.2 m. Both the classification capacity and the sediment concentration are large, and a high circulating load can be obtained. The production process is stable and easy to handle.

Disadvantages: Due to the influence of spiral disturbance and interference sedimentation, the classification efficiency is low (about 25%-40%). The desilting sands are often mixed with more fine grain heavy minerals. When returned to the grinding machine for re-grinding, over-grinding phenomenon will occur, causing metal loss. In addition, the spiral classifier is cumbersome and has a large area,and it takes time and effort to replace the worn blade and vane-board.

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How to Improve Classification Efficiency of Spiral Classifers?

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The fundamental reason for the low efficiency of spiral classifiers is that the fine- heavy ore particles and the coarse-light ore particles are settled in disorder during the classification process, resulting in an equal drop phenomenon, causing that desilting sand contains huge amount of fine sands and the overflow particles are too coarse. The following measures can be considered to improve the classification efficiency of spiral classifiers:

(1) To change the discharge mode of the traditional spiral classifier and adopt double-sided discharge,which shortens the movement path of the ore in spiral classifier, avoids the reflow of the slurry, discharges the fine-grained overflow in time, and shortens the settlement time.

(2) For the fine ore particles that have settled to the bottom of the tank body, a stirring device can be added at the lower end of the spiral classifier. The fine particles at the bottom will be brought back to the surface of the slurry and discharged with the overflow, thus reducing the fine sand in the bottom and improving classification efficiency. For example, Xinhai spiral classifiers with return sand self-lift device and eliminats big grinding head of its ball mill, which greatly improved the classification efficiency of the spiral classifier.

(3) It is also conceivable to add a new force field to change traditional gravity sedimentation in classification area. For example, adding a trammel screen to the upper part of the classifier for secondary classification can improve the efficiency of the spiral classifier.

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Factors Affecting the Classification Effect of Spiral Classifier

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The classification effect of the spiral classifier has a direct impact on the content of qualified products in the return sand, which has an impact on the efficiency of the grinding operation. When studying this problem, we can start from three aspects: the material of the spiral classifier, the structure of the spiral classifier, and the operation of the spiral classifier.

1. The Material of Spiral Classifier

Regarding the material fed into the spiral classifier, there are two factors that affect the classification effect of the spiral classifier: the mud content of the classifier feedstock and the density of the ore.

If the ore contains a large amount of mud, and the viscosity of the slurry is large, the sedimentation velocity of the ore particles in the slurry would be reduced, causing the overflow product to be coarse. Otherwise, the fine-grained material in the return sand would be more. Therefore, it is necessary to control the concentration of the ore slurry. The particle size of the classifier can be checked regularly, and the concentration of the ore slurry can be appropriately increased or decreased in time to control the classification efficiency of the spiral classifier.

In the case of the same concentration, the smaller the density of the material,the greater the viscosity of the ore slurry, and the coarser the particle sizeof the overflow product; the smaller the density, the higher the fine-grained content in the return sand. Therefore, when dealing with ore of different densities, the density of the material in the classifier should be appropriately increased for the ore with higher density, and the concentration of the classifier should be appropriately reduced for the ore with less density.As for how to know the density of the ore, the determination should be based on the data obtained in the mineral processing test.

2.  Structure of spiral classifier

There are three factors in the structure of the spiral classifier that affect its classification efficiency: the inclination angle of the closed trough of spiral classifier, the height of the overflow , and the revolving speed of the spiral classifier.

The inclination angle of the chute of spiral classifier affects the sedimentation area of the classifier. However, since the closed trough of the spiral classifier is fixed after installation, the angle of the closed trough should be adjusted to an appropriate angle before installation. Generally speaking, when the angle is large, the sedimentation area would be reduced, so the coarse-grained material is easy to slide, and the overflow particle size is coarsened, but the fine-grained material in the return sand would also be reduced correspondingly. On the contrary, when the inclination angle is small, the sedimentation area would be large, and the overflow particle size would be fine, thus the amount of fine-grained material in the return sand will also increase. Therefore, it is important to determine the inclination angle according to the nature of the material, which should be taken into consideration when designing the beneficiation plant.

Spiral classifiers are divided into high spiral classifiers and submerged spiral classifiers. The common feature of these two classifiers is that the overflow height will affect the sedimentation area. If the height of overflow increases, the sedimentation area will increase, the volume of the classifier would increase and the overflow particle size becomes coarse. Generally, the overflow should be adjusted to an appropriate height in the initial stage of production and it is rarely adjusted during the operation. It is customary that the height of the overflow of the high spiral classifier is in the range of 400-800 mm, and the height of the submerged spiral classifier is between 930-2000 mm.

Besides above, the structural factor that can affect the classification effect of classification equipment is the spiral revolving speed. This factor directly affects the degree of liquid surface agitation and the ability to transport return sand. In actual production, both the overflow fineness and the return sand productivity must be met. The faster the revolving speed, the higher the return sand productivity; but the agitation effect will increase the ratio of coarse particles in the overflow. Since the revolving speed is related to the diameter of the spiral, the revolving speed is generally controlled within the range of 1.5-10 r/min.

3.  The Operation of the Spiral Classifier

For a spiral classifier, the operation refers to the concentration of the ore slurry,the amount of ore feeding, and the degree of uniformity of the feeding.

The ore slurry concentration is an important adjustment factor. In actual production,the ore slurry concentration has a great impact on the overflow fineness of the spiral classifier. When the ore slurry concentration is reduced, the overflow particles become finer; while the concentration increases, the overflow particle size will become coarser. Therefore, maintaining a certain concentration and overflow particle size can achieve good production result. It is necessary to do a mineral processing test to determine the appropriate concentration at which the critical separation particle size can be obtained.

The amount of ore feeding is also a factor to be paid attention to. The increase of the ore feeding amount will increase the rising flow rate and the horizontal flow rate of the ore slurry, causing the overflow material particle size to become coarse. Therefore, the amount of ore feeding should be kept proper and uniform, in order to ensure the spiral classifier can work normally and stably.

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The Structure of Hydrocyclone

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The lower part of the hydrocyclone is a conical shell, and the upper part connected to a cylindrical shell. The upper end of the cylindrical casing is sealed, and a bottom plate is arranged in the middle,and a short pipe overflow pipe is inserted in the center of the bottom plate. A feeding pipe is connected to the lower portion of the bottom plate along the tangential direction of the cylindrical shell surface, and an overflow discharging pipe is connected to the upper portion of the bottom plate along the tangential direction of the casing, and the lowermost end of the cone has are placeable sand settling nozzle.

The hydrocyclone is mostly made of wear-resistant cast iron. In order to reduce the wear speed of the inner wall of the body, it is also often lined with wear-resistant materials such as wear-resistant rubber. The specifications of the hydrocyclone are expressed in terms of the diameter of the cylinder. For example, the diameter of the cylindrical portion of the Φ350 hydrocyclone is 350 mm, and the cone angle of the cone can be different, typically a minimum of 10° and a maximum of 45°.


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Hydrocyclone Working Principle

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Hydrocyclones are a kind of equipment for classifying or separating materials based on their particle size and density. The material to be classified or separated is fed at a high speed from the inner wall of the cylinder by a tangential line, and the mixture of medium and particles is rotated to form a centrifugal force field which solid materials or liquid phases of different particle sizes and different densities generate different motion trajectories. Under the action of centrifugal force, medium viscous resistance, buoyancy, gravity and other force fields, coarse particles and large density particles move to the periphery and are discharged from the spigot through the cone; fine particles, low density particles or liquid phase move to the center and discharge by the overflow tube, thus achieving separation of coarse and fine particle or separation of fluids of different densities.

Hydrocyclones are mainly used in the following aspects in mineral processing:

(1) Used as the classification equipment in the grinding circuit, especially for fine grinding;

(2) Used for desliming and concentration of slurry;

(3) Heavy medium hydrocyclones are common heavy media classification equipment.

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Types of Hydrocyclones

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At present, there are many types of hydrocyclones on the market. According to the use function, hydrocyclone can be mainly divided into: classifying hydrocyclone, dewatering hydrocyclone, desliming hydrocyclone, deslagging hydrocyclone and concentrating hydrocyclone. The specific application and use phase of hydrocyclones is as follow:

1. Classifying Hydrocyclone

Classifying hydrocyclone, as its name implies, is to separate and classify the material, such as solid-liquid separation,coarse-fine separation, which is divided into one-stage classification and two-stage classification. One-stage classifying hydrocyclones are widely used in the grinding stage of small and medium-sized processing plant, and forms a closed-circuit grinding and classifying cycle with ball mill. The two-stage classifying hydrocyclones are generally used in the second-stage inspection to achieve the function of controlling classification.

2. Dewatering Hydrocyclone

The dewatering hydrocyclones are mainly used to complete part of the dewatering operation, and the solid-liquid separation cannot be completely realized only by dewatering hydrocyclones. The structure of the hydrocyclone varies depending on the material being processed.

3. Desliming Hydrocyclone

The desliming hydrocyclones are mainly used for material desliming operation.

4. Deslagging Hydrocyclone

Deslagging hydrocyclones are widely used in power plant wet desulfurization, lime pulping, tap water sand removal, sewage treatment and other operations. It is mainly used to remove coarse sand and impurities of large particle sizes. Higher slag removal efficiency can be achieved with a dedicated deslagging hydrocyclone.

5. Concentrating Hydrocyclone

Concentrating hydrocyclone feed port has a unique structure, so it is generally not used alone. It is often used together with thickeners, dewatering screens, filters and other equipment to improve dewatering efficiency and achieve concentration of various minerals before filtration. It is also often used in the concentration operation before the flotation and cyanidation operation, as well as the operation of tailings dry stacking.

Concentrating hydrocyclone is also used for dewatering in nature. However, concentrating hydrocyclone feed port has a unique structure, and the concentration of the underflow slurry is larger.

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Application of Hydrocyclones

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1. Classifying in the grinding circulation system

The hydrocyclone can be used for the classification of the coarse sand and overflow of the ball mill, as well as the pre-classification before the grinding operation. The obtained process effect is almost the same as that of the mechanical classifier, and can basically replace the classifier. Especially when the concentration of the slurry is large and the mechanical classifier cannot obtain a fine overflow, than the hydrocyclone must be used.However, the hydrocyclone wears faster during the working process, and the inner lining needs to be replaced frequently, resulting in high equipment cost. If the high wear resistance material can be used as the lining, the problem can be solved.At present, the most suitable for the hydrocyclone lining is the wear-resistant rubber produced by Yantai Xinhai Wear-resistant Rubber Co., Ltd., which can effectively reduce the wear of the pulp on the lining, and the service life is doubled compared with the ordinary rubber.

2. Desliming operation

The hydrocyclone can be used for desliming operations of various metal and non-metal ore, and can achieve the following purposes: as the preparation operation before the beneficiation operation; improve the beneficiaiton effect; remove the flotation agent on the ore particles; remove the coarse sand from non-metal ores; obtain the finalcon centrate.

3. Concentration operation

In some processes, because the slurry concentration is too low to meet the process requirements, it is necessary to use the hydrocyclone for concentration treatment.For example, Yantai Xinhai Mining Company introduced the tailings dry stacking process. The tailings will be firstly concentrated by hydrocyclone. The high-concentration slurry obtained will be dewatered again by the dewatering screen, and the overflow will be concentrated by the thickener and then sent to dewatering screen. It not only increases the processing capacity of the dewatering screen, but also achieves a better dewatering effect.

4. Sand and impurity removal operation

In the wet beneficiation process, after the raw ore is processed by the mashing process, quartz sand or impurities may be present in the slurry, so sand removal and impurity removal are prerequisites for the beneficiation process.Due to the different nature of the ore, sometimes combination of different sized hydrocyclones will be used to meet the process requirements.

5.Tailings filling and damming

Fine sand less than 37 microns in tailings cannot be used as material for tailings damming. Therefore, when using tailings to build dams, hydrocyclones must be used as classification equipment, at which coarse sands remain near the dam, and fine sands flow to the end of tailings pool. At present, the tailings filling plan is generally pre-concentrated and classified by hydrocyclones, and then dewatered by filters to achieve the best effect.


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Key Operation Point of Hydrocylcones

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1. Select the appropriate hydrocyclone structural parameters (dimensions of each part) based on the classification particle size and the amount of slurry processed.

Firstly, the diameter size of hydrocyclone is determined mainly according to the volume of the slurry to be treated and the classification granularity. Generally, when the overflow is relatively coarse and the classification capacity is large, a large-sized hydrocyclone is suitable; otherwise a small-sized hydrocyclone is better. Under the circumstance of large classification capacity and fine overflow, some hydrocyclones of small sizes can be combined into hydrocyclone clusters.

Secondly, according to the determined hydrocyclone diameter, other structural parameters are selected,such as the overflow pipe diameter, the spigot diameter, the feed port diameter,the cylinder height, the insertion depth of the overflow pipe, and the taperangle.

2. Choose the appropriate hydrocyclone feeding method

Generally, the hydrocyclone feeding methods mainly include the following three types:

Feed ore slurry with the help of height difference. This kind of feeding method requires a large height difference (generally more than 5 m), which is difficult to achieve when terrain conditions are not allowed;

Feed ore slurry with the surge tank. The advantage of this feeding method is that the pressure is stable, but the disadvantage is that there are many pipelines, the slurry reflow is large,and the economic effect is poor;

The advantage of this feeding method is that the pressure is stable, but the disadvantage is that there are many pipelines, the slurry reflow is large, and the economic effect is poor;

Directly feed ore slurry with a sand pump. This kind of feeding method has fewer pipelines and better economic effects, but the ore pressure is fluctuating greatly. At present, most of the dressing plants adopt this kind of feeding method (the so-called dynamic pressure feeding).

3. Stabilize the feeding pressure of the hydrocyclones

Since the hydrocyclone feeding pressure will directly affect the classification capacity and particle size of the hydrocyclone, the greater the feeding pressure, the higher the slurry flow rate, and the greater the hydrocyclone treatment capacity. At the same time,the rotation speed and centrifugal force of the slurry in hydrocyclone are also larger, and the classification particle is also finer. After determining the classification particle size, a certain pressure is required. If the pressure is too large, the fine particles mixed in the desilting sand will increase. If the pressure is too small, the coarse particles mixed in the overflow will increase, which will reduce the classification efficiency of the hydrocyclone.

When the sand pump is used for direct feeding, the head of the selected sand pump (referred to as the effective head) and the flow need to be larger than the normal feeding of the hydrocyclone. If capacity of the sand pump is too large, the sand pump will pant. At this time, a pipe can be installed on the outlet pipe of sand pump,and a part of the slurry is short-circuited back to the pump pool, or a part of the hydrocyclone overflows into the pump pool.

When the sand pump is feeding,the pressure gauge should be installed on the hydrocyclone feeding pipe, so that the hydrocyclone operator can grasp the working condition of the hydrocyclone and the wear condition of the sand pump in time. A larger sand pump pool better, because the pump pool can play a buffering role. At the same time, it is recommended that the sand pump should be lined with a rubber liner to extend the service life.

The feeding pressure of the hydrocyclone can be adjusted by adjusting the opening degree of the gate on the ore feeding pipe.

4. Notice the diameter change of hydrocyclone spigot

When the spigot is increased,the sedimentation volume increases, the concentration decreases, the fine particles in the desilting sand increase, the overflow volume decreases, and the overflow becomes fine. Conversely, when the spigot is reduced, the concentration of desilting sand increases, the coarse particles in the overflow increase and the overflow increases. The change of the spigot can be judged according to the spray angle when the grit is ejected, and the spray angle is generally between 40° and 70°. If the grit is discharged in a rope shape, it means that the spigot is small, and the concentration of grit is higher at this time; if the grit is sprayed in an umbrella shape, the grit is large, and the concentration of grit is the lowest.

The spigot is the most wearable part among the components of the hydrocyclone. Therefore, rubber or other wear-resistant materials are often used to reduce wear and prolong service life, and it is necessary to replace the new spigot regularly.

If the size of the spigot needs frequent adjustment, hydrocyclones with changeable mouthpiece or adjustable spigot device are recommendable.

5. Keep suitable feed concentration

The concentration of feed slurry will directly affect the concentration and particle size of the final product. When raw ore concentration is too low, the classification efficiency of the hydrocyclone is higher but the dry ore treatment capacity is decreased;when the ore concentration is too high, the viscosity of the slurry increases,and the classification efficiency of the hydrocyclone decreases. Generally, the finer the classification particle size, the lower the feed concentration should be.

6. It’s necessary to separate debris such as grass residue and wood chips by means of a sieve before the slurry is fed to the hydrocyclone in order to prevent the hydrocyclone from being blocked. 

For small diameter hydrocyclones, slag removal is especially important. Generally, the size of the slag removal screen is about 1/6 to 5/5 of the diameter of the spigot.

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Advantages and Disadvantages of Hydrocyclones

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Hydrocyclones have the following advantages over other classification equipment:

(1) The classification particle size is fine. Because the hydrocyclone mainly classify minerals by centrifugal force and the centrifugal force can be much larger than gravity. Therefore, the smallest classification particles of hydrocyclone can reach 5 um. Nowadays, hydrocyclones are often used for fine particle classification.

(2) The classification efficiency is high, especially when the classification granularity is very fine (such as 0.037 mm), the classification efficiency is significantly higher than other classification equipment.

(3) Simple structure, no moving parts, easy to manufacture.

(4) The floor space is small. When the processing capacity is the same, the hydrocyclone covers an area of about 1/30-1/50 to a spiral classifier.

The disadvantages of hydrocyclones are as follows:

(1) Power consumption is large. The sand pump used in the cyclone feed station consumes a large amount of electricity, which is about 5-8 times as many as other classification equipment.

(2) The equipment wears out quickly. In particular, the wear around the feed port and the spigot is most severe and needs to be replaced frequently.

(3) The fluctuation of the ore pressure, the ore concentration and the ore particle size is sensitive to the influence of the hydrocyclone's working index.

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Spiral Classifier or Hydrocyclone? Five Major Contrasts Teach You the Correct Selection!

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In the ore beneficiation process, the purpose of the classification is to effectively separate the coarse particles and fine particles, avoiding over-grinding of fine particle minerals, reducing unnecessary energy consumption, and making the coarse particle minerals return to the mill for another effective grinding process. The quality of the classification will directly affect the production capacity of the grinding equipment, the effect of the finished product, and the technical and economic indicators such as the concentrate grade and recovery rate in the subsequent separation process.

Nowadays, spiral classifier and hydrocyclone are considered to be the two most mainstream classification equipment. The spiral classifier can be said to be the first generation of classification equipment, which has been widely used in concentrators for decades. While the hydrocyclone, as the second generation classification equipment, has quickly occupied a place in the classification equipment with its unique advantages. Since both of them are mainstream classification equipment, many people are very confused about what are the differences between these two classification equipment? And Which type of classification equipment should I choose?

1. Material Properties

Commonly, spiral classifiers are consist of high spiral classifier and submerged spiral classifier. The high spiral classifier is generally applied to coarse particle overflow classification, and the diameter of the particle is generally greater than 0.15mm. The submerged spiral classifier is suitable for fine particle overflow classification, and the diameter of the particle is generally less than 0.15mm. Compared with the two spiral classifier, the hydrocyclone has a better classification effect when processing finer particle materials (the classification size range is generally 0.3-0.01 mm).

2. Floor Area

It is obvious that hydrocyclone has a significantly smaller floor area than spiral classifier. Usually, hydrocyclone covers an area of only 1/30 to 1/50 of the spiral classifier. The equipment floor area requirements also limit the application of the spiral classifier to a certain extent.

3.Classification effect

Whether in classification efficiency or product accuracy, spiral classifier is superior to hydrocyclone. A large part of the reason is that if the pressure is not up to standard, the hydrocyclone will change the position of the final material discharge. The spiral rotates at a low speed, and the fine particles are suspended to the top when the slurry is stirred, and then discharge from the overflow , and the coarse particles sink to the bottom of the tank, and are conveyed by the spiral to the discharge port as the return sand. Well, the particle in the hydrocyclone needs to be discharged from the side of hydrocyclone discharge port, and the discharge port is in the opposite side of the inlet, that is, once the pressure is not up to standard, the material separation will be disordered, resulting in the material not being discharged normally from the discharge port. But this is not absolute, especially when the classifying particle is very fine (such as 0.037 mm), the hydrocyclone classification efficiency is significantly higher than spiral classifier.

4. Operation Situation

The biggest reason why the spiral classifier is the most widely used is its simple structure, stable and easy operation. It is also spiral classifiers’ simple operation process and stable working state that not only greatly reduces the funds for maintenance and replacement of equipment, but also guarantees the completion time and makes the classification work more efficiency. In addition, its easy-to-operate feature sallow the operator to perform normal operation of the machine with only short-term training. In other words, selecting a spiral classifier for mineral classifying has relatively low technical requirements for operators. In contrast, the operation of the hydrocyclone is more complicated, and the ore feed pressure, concentration and particle size will greatly affect the classifying index, so higher operation accuracy is required.

5. Investment Cost

But in terms of equipment investment, the price of the hydrocyclone is definitely lower than that of the spiral classifier. However, when using hydrocyclone, there are other additional investment in a series of necessary auxiliary equipment, such as distributors,valves, pumps, etc,. For maintenance, the wear parts like lining and overflow pipes of hydrocyclone need regular maintenance. Of course, the wear frequency and wear degree are determined under the combined effect of these factors such as particle size, shape, and solid content. Therefore, the service life and maintenance cost can only be accurately obtained in the actual ore dressing plant practice. The maintenance aspect of the spiral classifier is mainly to replace the spiral lining, as well as other routine maintenance. However, the spiral classifier maintenance costs are higher for the expensive spiral lining.Overall, the investment price of the spiral classifier is higher than that of the hydrocyclone.

By Contrasts, we found that the two classification equipment, spiral classifier and hydrocyclone, have their own characteristics. Therefore, when selecting the classification equipment, we must consider the material properties, equipment area covered, equipment operation situation, classification efficiency and equipment investment, etc.,and select one that is suitable for the plant. In the meantime, the classification equipment is combined with the grinding equipment in the beneficiation production line to jointly provide the ore of suitable granularity for the ore separation operation. This also requires us to make reasonable choices based on the particle size of the material and the grinding level of the mill when selecting the classification equipment. The choice of any mineral processing equipment will not be unilaterally determined, it must be the result of comprehensive consideration. This will not only help to improve production efficiency, but also strive for the best return on investment for us.

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