A Spiral Classifier is a machine that is primarily used to classify the slimes (fines) from a coarser, sandy sized material. It has a inclined trough with one or two spirals revolving slowly and free from touching the sides or bottom of the tank. The motion of the spiral creates pool hindered settling in the bottom pool area, where the agitation of the water hinder the fines from settling to the bottom, but the coarser particles do settle and are carried up the slope by the revolving spiral, to the discharge, located at the top of the classifier. Then gravity flow or pumps are used to move the coarse material to the next stage in the process, the fines overflow from the pool area. The pool area normally has an adjustable wier, which will determine the amount of time material is in the pool area, and subsequently the coarseness of the discharge from the pool area, with a shorter residence time the coarser the discharge, along with the fines. Therefore, some control of the classification size can be accomplished by adjusting the weir height up or down, to give more of less residence time in the pool area.
The typical range of feed to a spiral is 20 mesh (850 ) to 325 mesh (45 ). The slope of the spirals is 3.5 inches vertical per foot of horizontal distance. These units are primarily constructed from carbon steel, but are available in stainless steel, if required.
1. Coarse particles settle faster, having a faster settling velocity than fine particles under hindered settling conditions. 2. Heavy particles settle faster than lighter particles. 3. Porous or irregular shaped particles settle slower than relatively round and non-porous particles. 4. If fine slimes are present in quantity, it increases the density of the liquid slurry in the pool, rendering all settling velocities slower, as the medium becomes denser. Coarser particles will be in the fines overflow. 5. On the dilute side, (adding water to the pool area) critical dilution is reached when the density approaches that of water, increasing the settling rates and giving a coarser separation. Finer particles will be in the fines overflow. 6. Less water in the pool area with have the effect of giving a coarse separation, by creating a heavy media effect, and allowing coarser particles to overflow.
Experimentation will determine the right conditions to achieve the desired separation in a spiral classifier for a particular material. Overflow from a spiral classifier typically contains from 15% to 25% liquid, while the fines overflow contains from 85% to 75% liquid.
In Mineral Processing, the SPIRAL Classifier on the other hand is rotated through the ore. It doesnt lift out of the slurry but is revolved through it. The direction of rotation causes the slurry to be pulled up the inclined bed of the classifier in much the same manner as the rakes do. As it is revolved in the slurry the spiral is constantly moving the coarse backwards the fine material will flow over the top and be travelling fast enough to be able to work its way downwards to escape. The Variables of these two types of classifiers are The ANGLE of the inclined bed, this is normally a fixed angle the operator will not be able to adjust it.
The SPEED of the rakes or spirals, the DENSITY of the slurry, the TONNAGE throughput and finally the SETTLING RATE of the ore itself.To be effective all of these variables must be balanced. If the incline is too steep the flow of slurry will be too fast for the rakes or spirals to separate the ore. If the angle is too flat the settling rate will be too high and the classifier will over load. The discharge rate will be lower than the feed rate, in this case. The load on the rakes will continue to build until the weight is greater than the rake or spiral mechanism is able to move. This will cause the classifier to stop and is known as being SANDED UP. If the speed of the rakes or spirals are too fast, too much will be pulled, out the top. This will increase the feed to the mill and result in an overload in either the mill or classifier as the circuit tries to process the increased CIRCULATING LOAD.
The DENSITY of the slurry is very important, too high the settling will be hampered by too many solids. Each particle will support each other preventing the heavier material from quickly reaching the bottom of the slurry. This will not allow a separation to take place quickly. The speed at which the slurry will be travelling will be slow and that will hamper effective classification. Another variable is the TONNAGE. All equipment has a limit on the throughput that anyone is able to process, classifiers are no different. This and the other factors will have to be adjusted to compensate for the last variable, the ore itself. Every ore type has a different rate of settling. To be effective each of the previous variables will have to be adjusted to conform to each ones settling characteristics.
The design of these classifiers (rake, spiral, screw) have inherent problems, First, they are very susceptible to wear, caused by the scrubbing action of the ore, that plus all of the mechanical moving parts create many worn areas to contend with. The other problem that these classifiers have is that they are easily overloaded. An overloaded classifier can quickly deteriorate into a sanded-up classifier. Once that happens the results are lost operating time, spillage and a period of poor Mineral Processing and Separation performance.
Another mechanical classifier is the spiral classifier. The spiral classifier such as the Akins classifier consists of a semi-cylindrical trough (a trough that is semicircular in cross-section) inclined to the horizontal. The trough is provided with a slow-rotating spiral conveyor and a liquid overflow at the lower end. The spiral conveyor moves the solids which settle to the bottom upward toward the top of the trough.
The slurry is fed continuously near the middle of the trough. The slurry feed rate is so adjusted that fines do not have time to settle and are carried out with the overflow .liquid. Heavy particles have time to settle, they settle to the bottom of the trough and the spiral conveyor moves the settled solids upward along the floor of the trough toward the top of the trough/the sand product discharge chute.
Spiral Classifiers is art of separating the solid particles in a mixture of solids and liquid into fractions according to particle size or density by methods other than screening. In general, the products resulting, a partially drained fraction containing the coarse material, called the underflow; and a fine fraction along with the remaining portion of the liquid medium called the overflow.
The classifying operation is carried out in a pool of fluid pulp confined in a tank arranged to allow the coarse solids to settle out, whereupon they are removed by gravity, mechanical means, or induced pressure. Underflow materials will be sent back to the ball mill for re-grinding to make a close-circuit, overflow materials will come to next stage of beneficiation.
Normally, there are two types of spiral classifier, high weir type and submersion type. High weir type, the overflow spiral blade is higher than overflow level, but spiral central is lower than overflow surface. The high weir spiral classifier is applied in the classification of minerals with particle size 0.83-0.15mm. Submersion type, spirals are totally under overflow level, which is applied with particle size 0.15 to 0.07mm.
Widely used in chemical industry, minerals (especially suitable for calcium carbonate, kaolin, quartz, talc, mica and other non-metallic mineral product classifying), metallurgy, abrasives, ceramics, refractory materials, medicines, pesticides, food, health products, new materials etc.
Market Study Report has added a new report on Submerged Spiral Classifier market that provides a comprehensive review of this industry with respect to the driving forces influencing the market size. Comprising the current and future trends defining the dynamics of this industry vertical, this report also incorporates the regional landscape of Submerged Spiral Classifier market in tandem with its competitive terrain.
The Submerged Spiral Classifier market report encompasses all the growth drivers and opportunities driving the profitability graph, and also provides valuable insights into challenges that will befall the industry in the ensuing years.
Speaking of the recent developments, the COVID-19 pandemic has drastically changed the market dynamics, causing organizations to alter their entire business structures to stay afloat amid the changing landscape. In this context, the report hosts an in-depth analysis of the implications of the crisis on this vertical to help stakeholders formulate action plans that can effectively manage managing the market contingencies.
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Spiral classifier, also called screw classifier, is widely used for distributing ore in the close circuit with ball mill, grading ore and fine slit in the gravity mill, grading granularity in the flow of metal ore-dressing and de-s and dehydrating in the washing.
According to the principle that different grains are with different specific gravity and sedimentation rate in the liquid, the fine ore flows in the water and the coarse ore sinks in the bottom. The classifier that has machine grading by discharging from the top can filtrate the materials and send coarse materials to the feeding mouth and discharge the fine material from the pipe.
Our spiral classifiers are widely used in the distribution of ore in closed circuits with ball mills, grading ore and fine slit in gravity mills, grading granularity and flow of metal ore-dressing, and de-sliming and dehydrating in washing.
EIMCO-K.C.P. Agidisc Filter is a vertical leaf rotary vacuum filter particularly adapted to filtration of rapid settling solids. It is widely used in dewatering metallurgical slurries of all types, including coal. A horizontal paddle agitator effectively maintains solids in suspension and prevents uneven cake formation. primary application is in the dewatering phase of the flow sheet. Most advantageous applications are dewatering of solids which are free settling and from into an easily discharged, non blinding cake. Maximum filtration area is provided at minimum cost and operating space. Due to its design, utilizing a filtering surface in a vertical plane, washing of the filter cake is very limited. Guided scraper provides for discharge of thin cakes, reduces wear on media. Wide variety of media stainless steel screens, cloth and synthetic fabrics are available. Filtering areas range from 2 to 300 m2.
The EIMCO-K.C.P. equipment product line consists of Liquid Solid Separation products for the Mining, Mineral & Metallurgical Process, Chemical Process, Food Process, Refinery, Pulp and Paper, Power Plant, FGD System, Municipal & Industrial Waste and Water Treatment and with a wide range of related services.