To be successful in a obtaining a uniform grind that is necessary to achieve a high percentage of recovery it is necessary to control the degree of fineness that the ore is reduced to. This is done by separating the fine material from the course and regrinding the coarse until it is fine enough for efficient mineral extraction.
To be able to obtain the necessary control over the amount of grinding required, a method of effective classification and separation by size must be available. For maximum effectiveness it should take place after every stage of grinding.
The types of equipment that are used to accomplish this are called CLASSIFIERS. There are three basic kinds used. The first two, the RAKE classifier and the SPIRAL or screw classifier work on the same principal, and are not often used any more. These two types were popular for many years. It wasnt until the development of the CYCLONE type classifier that their popularity faded. You may still find a few though, in the older mills and the mills that require a classification of the larger ore sizes that the cyclones are not very good at sizing. Both the rake and spiral classifiers take advantage of the natural settling characteristics of ore. Any time that slurry is allowed to flow over a surface the tendency of the ore is to graduate itself into layers of different sized material. The larger sizes will be on the bottom, these are also the ones that are the slowest moving. As you come closer to the surface, the material will become smaller and faster until the very finest and the easiest to wash away is on top.
To understand how these two classifiers make use of this settling action, a description of them is required. First, to have the classification happen, the slurry must be able to flow. This means the classifiers must be inclined. The working portion of these two classifiers are the RAKES or SPIRAL/screw which are placed into the flow of ore. To separate the course material from the fine, the rakes and spiral make use of the same theory, but differ in its application. The theory is, as the slurry flows down the inclined bed of the classifier it will separate into different sizing. The larger ore that is on the bottom will not be flowing as fast as the light ore on top.
To separate the two, the rakes and the spiral will pull the all of the slurry back up the incline, then, let it go to flow back down towards the underflow or in this case the fine ore discharge point. The smaller, faster ore will be able to travel a longer distance than the large particles before the rakes or spiral will pull the ground material back towards the coarse ore discharge. If the Classifier is able to pull the course ore backwards further than it can travel forwards, then eventually the bigger particles will be pulled all the way to the top of the incline where they will be discharged. The smaller faster pieces of ground rock will end up at the bottom of the incline to be discharged as fine material that is ready for the next stage of processing.
This type of classifier will do away with the necessity of pumps. The length of the incline that is needed is long and steep enough to have the material lifted to the feed end of the mill. The flow of the finer ore will run down hill to the next piece of equipment. The concentrator that used this type of classification was built on the side of a hill to make use of gravity to get the material from one stage of production to the next. It was because of this that this type of concentrator was referred to as a GRAVITY FLOW/MILL. I used the past tense in this paragraph because this design of mill is no longer in use.
I want to know what is the range of the % Solids content in overflow from screw/spiral classifier in Hematite Iron ore washing for efficient operation of classifier. I also want to know what is Auto dilution in thickener. Does Auto dilution has any effect on Pumping capacity of clarified water from thickener.
Each operation is different, but the good news is that you can simply determine the solids % wt. in the SOF, try 2 -3 times daily over one week, get a profile. If below 5% wt., you may not need auto dilution, also depending on ore and grind size. This is almost a clarifier regime, often workable without rakes in certain units. Above 5% in general start looking at auto-dilution before adding the flocculant do this off-line. Make sure that the thickener underflow (TUF) discharge comes out continuously, otherwise you may need to play with the lifters, if you have them. The UF solids % wt. must be correlated with the yield stress.look for 30 Pa high-end cut off value for lean operation. When the ore or grind size changes, you need to repeat the evaluation.
My take on these classifiers is that the clear water added to the classifier feed determines the size of the largest heaviest particle going to the overflow. This is the criteria that you should be working to achieve. As you probably have more than one classifier reporting to the thickener you will need to perform the solids percent in each overflow. As you add water to the classifier feed, the separation efficiency increases. You should be raising or lowering the discharge weir to attain the desired size cut. Only if the thickener becomes overloaded should you add water. Pumping excess water adds cost and wear to pump trains.
Pulp density of the Overflow defines % of solids in thickener. This solids% depends also up on quality of recycle water used in spiral processto know quantum of solids..you have to give feed quantity and underflow quantity.
The % solids in classifier overflow may vary in wide range, its all depends on your ore characterisation and operating variables. For the same operation we used to get 15-18% solids as my ore contains too much fines & this is not end process in our case.Try to concentrate on end products. Do not let go valuables in your final tailings.
The Steel Head Rod Mill(sometimes call a bar mill)gives the ore dressing engineer a very wide choice in grinding design. He can easily secure a standard Steel Head Rod Mill suited to his particular problem. The successful operation of any grinding unit is largely dependent on the method of removing the ground pulp. The Steel Head Rod Mill is available with five types of discharge trunnions and each type trunnion is available in small, medium, or large diameter. The types of Rod Mill discharge trunnions are:
The superiority of the Steel Head Rod Mill is due to the all-steel construction. The trunnions are an integral part of the cast steel heads and are machined with the axis of the mill. The mill heads are insured against breakage due to the high tensile strength of cast steel as compared to that of the cast iron head found on the ordinary rod mill. Trunnion Bearings are made of high-grade nickel babbitt, dovetailed into the casting. Ball and socket bearings can be furnished if desired.
Head and shell liners for Steel Head Rod Mills are available in Decolloy (a chrome-nickel alloy), hard iron, electric steel, molychrome steel, and manganese steel. The heads have a conical shaped head liner construction, both on the feed and discharge ends, so that there is ample room for the feed from the trunnion helical conveyor discharge to enter the mill betweenthe rods and head liners on the feed end of the mill. Drive gears are furnished either in cast tooth spur gear and pinion or cut tooth spur gear and pinion. The gears are furnished as standard on the discharge end of the mill, out of the way of the classifier return feed, but can be furnished at the mill feed end by request. Drives may be obtained according to the customers specifications.
The following table clearly illustrates why Steel Head Rod Mills have greater capacity than other mills. This is due to the fact that the diameters are measured inside the liners, while other mills measure their diameter inside the shell.
Rod Mills may be considered either fine crushers or coarse grinding equipment. They are capable of taking as large as 2 feed and making a product as fine as 35-48 mesh. Of particular advantage is their adaptability to handling wet sticky ores, which normally would cause difficulty in crushing operations. Under wet grinding conditions of course the problem of dust is eliminated.
The grinding action of a rod mill is line contact. As material travels from the feed end to the discharge end it is subjected to crushing forces inflicted by the grinding rods. The rods both tumble in essentially a parallel alignment and also spin, thus simulating the crushing and grinding action obtained from a series of roll crushers. The large feed tends to spread the rods at the feed end which imparts still an additional action which may be termed scissoring. As a result of this spreading the rods tend to work on the larger particles and thereby produce a minimum amount of extremely fine material.
The Rod Mill encourages the use of a thick pulp coating both the liners and the rods, thus minimizing steel consumption. Continuous movement of the pulp through the rod mass eliminates the possibility of short circuiting any material. The discharge end of the Rod Mill is virtually open and larger in diameter than the feed end, providing a steep gradient of material flow through the mill. This is described in more detail on pages 20 and 21.
Normally Rod Mills are furnished of the two trunnion design. For special applications they may be furnished of the tire trunnion or two- tire construction. These mills can be equipped with any type of feeder and type of drive, discussed separately in this catalog.
The above tables list some of the most common Open End Rod Mill sizes. Capacities are based on medium hard ore with mill operating in closed circuit under wet grinding conditions at speeds indicated. For dry grinding, speeds and power are reduced and capacities drop 30 to 50%.
The End Peripheral Discharge Rod Mill is designed to produce a minimum amount of fines when grinding either wet or dry. Material to be ground enters through a standard trunnion and is discharged through port openings equally spaced around the mill periphery. These ports are in a separate ring placed between the shell and the discharge head.
The construction of the end peripheral discharge mill emphasizes the principle of grinding. Due to the steep gradient between the point of entry and the point of discharge the pulp flows rapidly through the mill providing a fast change of mill content with a relatively small amount of pulp within the grinding chamber.
The sloping or conical shaped feed head proves ample space for a feed pocket to accommodate large quantities of material and assure their entrance into the grinding rods. Any type of feeder listed on pages 22 and 23 can be furnished for these mills; however, since the mills are not usually operated in closed circuit grinding, the drum or spout feeder is normally preferred.
No other type of mill is so well adapted to dry grinding materials to -4 or -8 mesh in single pass with the production of a minimum amount of fines. A major factor in dry grinding is the rapid removal of finished material to prevent cushioning of the rods. This is accomplished in the End Peripheral Discharge Rod Mill.
The free discharge feature permits the grinding of material having a higher moisture content than with other types of rod or ball mills. Our Peripheral Discharge Mills have found wide application in grinding coke and friable non-metallics, material for glass, pyroborates, as well as gravel to produce sand. Another application is for grinding and mixing sand lime brick materials. The rod action gives a thorough mixture while grinding of the hydrated lime and sand.
For specifications of End Peripheral Discharge Rod Mills use table of standard open end rod mills given on pages 24 and 25. The capacity of the end peripheral discharge rod mill is slightly higher than shown for the Open End Rod Mills.
The CPD (Center Peripheral Discharge) Rod Mill has been developed to produce sand to meet U. S. Government or State specifications. It has also found application in grinding friable non-metallics, and industrial materials and ores which tend to slime excessively. Another application is in the field of abrasion milling on ores such as found on the Mesabi Iron Range. In this latter application true grinding is not desired, but more of a surface scrubbing of the individual particles.
Again with this construction grinding may be done either wet or dry. In this design, however, feed enters both ends by means of feeders and is discharged at the center through rectangular discharge ports equally spaced around the mill periphery. The center discharge openings are generally contained in a separate ring placed between shell halves. The ground material is discharged and directed to either side or directly under the mill by the use of a discharge ring housing.
In standard rod-milling it will be found that rods spread apart at the feed end in the amount of the maximum size of feed entering the mill. In the center peripheral discharge mill the rods are spread at both ends and parallel throughout the length of the mill. This feature results in more space between the rods and thereby lessens the amount of fines produced. Furthermore, fines are also diminished because the material moves rapidly through the mill due to the steep gradient of travel and the distance of travel is reduced by half. Similarly time of contact with the grinding media is reduced by half.
Another center peripheral discharge advantage is that a cubical shaped particle is produced. Maintenance is negligible and grinding media is relatively inexpensive. Other types of sand manufacturing equipment lose efficiency with wear and require excessive maintenance. This loss of efficiency increases rapidly as hardness of feed increases. The Center Peripheral Discharge Rod Mill can be easily maintained at peak operating efficiency by the periodical addition of rods. CPD Rod Mills give a wide range of flexibility to sand plant operation. By changing the rate of feed, pulp dilution (wet grinding), and discharge port area it is possible to produce and blend sand of virtually any fineness modulus and maintain it within Government specifications.
Unlike many crushers or grinders the CPD Mill can easily handle wet or sticky material. When grinding wet, the dust nuisance is completely eliminated. For dry grinding applications the mill is furnished with a dust proof discharge housing.
Various items must be considered in computing the cost of producing manufactured sand. These include wear on the constituent parts, power consumption, lubrication, labor and general maintenance. Maintenance of the center peripheral discharge mill is definitely much lower than that of any other sand manufacturing machine. The greater portion of the wear which takes place is on the inexpensive high carbon steel rods. Field installations show an average of less than 1 # per ton of sand ground as rod consumption, and from 0.08# to 0.10# per ton of sand ground as the steel liner wear. The overall cost of mill operation, exclusive of amortization, is generally less than 30c per ton (year 1958).
Every possible operating convenience has been incorporated in the center peripheral discharge mill design. On most sizes the trunnions are carried in large lead bronze bushed bearings. The interior of the mill is readily accessible through these large trunnion openings. The peripheral ring housing is furnished with a door for inspection and another lower door to facilitate sampling of the mill discharge. Covers for the discharge ports are furnished allowing any variation in discharge area which might be desired.
Given below are approximate capacities for several sizes of the center peripheral discharge mills. Such capacities are expressed in dry tons per hour, based on - x 4 mesh screened feed of medium hard gravel. Mill discharge is generally less than 5% + 4 mesh in wet open circuit operations, for dry grinding work reduce the capacities indicated by approximately 30% to 50%.
A Rod Mill has for Working Principle its inside filledgrinding media, in this case STEEL RODS. These rods run the length of the machine, which is most commonly between eight and sixteen feet in length. The diameter of these rods will range from, when new, between two and four inches. The rods arefree inside the mill. When the mill is turned, the rods tumble against one another grinding all the ore that is between them to aid in the grinding, water is added with the ore as it enters the mill.So from that you can see why it is called a wet tumbling mill. The ore is ground wet and the mill revolves. This causes the grinding media inside of it to tumble grinding the ore.
Historically there has been three basic ways of grinding ore, hammer mills, rolls, or wet tumbling mills. Hammer mills and rolls are not used that often and then usually only for special applications as in lab work or chemical preparation.
The type of mill that is used for grinding ore in a modern concentrator is the wet tumbling mill. These mills may be divided into three types ROD MILLS, BALL MILLS andAUTOGENOUS MILLS. In the first type, the ROD MILL, the ore is introduced into the mill.
From the trunnion liner out wards first we will come to the FACE PLATE. It is slightly concave to create the POOLING AREA for the rock to collect in before entry to the ROD-LOAD. On the outside attached to the face plate is the BULL GEAR. This gear completely circles the mill and provides the interface between the motor and the mill. The bull gear and drive line may be at the other end of the mill instead. There are advantages and disadvantages to either end this will be explained later when we are discussing the motor and drive line. But for now back to the face plate, attached to the other side of the face plate is the SHELL. The shell is the body of the mill. On the inside of the mill there are two layers of material, the first layer is the BACKING for the liners. This is customarily constructed from rubber but wood may be used as well. The purpose of this backing is two-fold, one to absorb the shock that is transmitted through the liners from normal running. And to provide the shell with a protective covering to eliminate the abrasion that is produced by the finely ground rock and water. Without this rubber or wood backing, the life of the mill is drastically reduced due to metal fatigue and simply being worn away.For those of you arent familiar with METAL FATIGUE I will explain. When metal is continually pounded or vibrated, the molecular structure of the metal begins to change, it is said to CRYSTALLIZE, and the metal becomes hard and finally loses all ability to give with the vibration. Thousands of microscopic cracks will begin to appear, as the fatigue of the metal continues, these cracks will grow to become major problems.
Later for interest sake we will explain the difference in some of them, but for now lets stay with identifying the parts of the mill. We have already mentioned the trunnion liner so let start from there.
The trunnion liner may also be referred to as the THROAT LINER. You will find that many of these parts will be called two or even sometimes three names, All I can say is try not to let it confuse you, The name isnt as important as the job that it does. As long as everybody that you work with agree on which name to use, it doesnt matter that much.
Next to this liner is the END LINERS, or to some, the PACE PLATE LINERS.The FILLER RING which is next is not standard in all mills, some mills have them, and some dont. Their job is to fill the corner of the mill up so the shell will not wear at that point. They dont provide any lift to the media, in fact quite often the media will not come into contact with them at all, but what they do is make changing liners that much easier. With different liner designs the replacement of a single liner may be quite difficult and to change one could become a lengthy project.
The liner that butts into the filler liner is known as a BELLY LINER or SHELL LINER, and in some designs LIFTER BARS. These liners and/or lifters give the media its CASCADING action and also receive the most wear. They cover the complete body of the mill and have the largest selection of types to choose from.
As the two ends of the mill are the same there isnt any reason to go over the other face plate. The discharge trunnion assembly is very much like the feed trunnion except that, it wont have a worm as part of the liner. Instead of a feed seal bolted to it, it may have a screen.
This is called a TRUMMEL SCREEN and its purpose is to screen out any rock that didnt get ground as well as any TRAMP METAL or REJECT STEEL that may be coming out of the mill. Reject steel is the old grinding media that has been worn so small that it comes out of the mill. If this tramp metal and steel is allowed to get into pumps and classifiers damage and plug- ups may be caused.
With regards to Rod Mills, let us start by identifying the different portions of the rod load as it goes through one revolution, as you will see, each of these areas will hold interest for the Grinding operator.
As the rod mill turns, the rods are carried by the lifting portion of the liners. The height that they are lifted is referred to as the lift of the liners. As they roll off of the liners, the rods enter the cascade zone. The rods roll through the cascade zone until they come to the toe of the load. At this point the rods come to rest in relation to the shell of the mill. The liners lift the rods back to begin the cascade again. You will notice, that as you go deeper into the rod load, the rod movement becomes less and less until the movement is very slight at the deepest part. This area is called the core of the load. As a description of the normal grinding action, the rods and the ore react together like this. The ore enters-the mill and is deposited in the pooling area directly under the feed trunnion.
This pooling area allows the large rock to fall towards the outside portion of the load, the TOE area. This is the zone with the greatest movement in it, which means the area that will have the highest impact on the ore.
The rock will be carried up by the rods as they go through the CASCADE ZONE reducing the size of the rock. As each particle of ore becomes smaller it will work towards the CORE ZONE while travelling the length of the mill. That makes for a rather neat arrangement doesnt it. The larger rock is deposited in the area where the maximum impact from the rod load occurs and then as each particle gets smaller it slowly travels inwards towards the centre of the load.
This is where the maximum surface contact takes place, producing the finer grind. When the ore has travelled from one end of the mill to the other end it will have completed its grinding cycle in this mill. As it exits the rod load it will be deposited in another POOLING AREA prior to leaving the mill by way of the DISCHARGE TRUNNION. Prom that you can see how a mill will become over loaded. If for some reason the rock begins to separate the rods over their entire length, the larger rock will prevent the intermediate rock from being ground. Which in turn will begin to invade the area that the fine material is being ground in. As the rods become separated through the entire load, the grind will get progressively worse until the unground rock is in the discharge pooling area. At this point, the operator will notice, that large rock is being discharged from the discharge trunnion.
During normal operations there is usually a certain amount of this larger rock that wont get ground. These are known as REJECTS and they serve as one of the tattle tales as to how the mill is grinding. If there is an increase of these rejects then the mill isnt grinding that well and the operator will have to do something about it. If he doesnt the mill load will continue to climb, until the rods in the lifting zone are completely separated. When this happens those rods will have quit grinding.
There is a visual warning of this happening that the operator can take advantage of. The lift on the rods will get higher and higher until they are being carried to the very top of the mill before cascading. I think falling would be a better word for it though. As this is happening, the core of the load will be slowly moving away from the shell towards the center of the mill. This is because the volume of the mill is being filled with unground rock. This will continue until the load hits a critical volume and a critical density. The rock still coming in to the mill will have to have some where to go so it tries pushing the rods out of the mill. Unfortunately they wont make it, the first hunch of rods that get far enough into the discharge trunnion will be- hit by the rest of the load bending and twisting them until they look like SPAGHETTI. This usually shuts the mill down for a couple of days while the millwrights cut the bent rods out of the mill.
On the other end of the scale, if the density is to light, the rod load will become too active, not having the solids in the mill to cushion the impact of rod on rod and rod on liner. As the rods enter the cascade zone, the pattern of the movement of the rods will be different. Instead of having a tightly tumbling mass of rods, the rods will be separated. The lift will be higher and the cascade will form more of an arc. The impact of the rods on the rock will be less because there will be more give in the rod load, with high amount of steel on steel causing the rods to bounce.
Letslook at how these Rod mills work, as I mentioned earlier there are steel rods inside the mill, it is their job to do the actual grinding. If you look at the mill in a cross section of an end view. You will get a very good illustration of the grinding action, of the mill.
The LINERS provide the tumbling action of the rods. When the mill rotates the rods are lifted until they roll off of the liners, this is known as CASCADING. The ore enters the mill at the feed end, as the rods cascade and tumble, the rock is caught between the rods and is ground. The size that the rock will be ground to is dependent on the amount of time the ore is in the mill, how many rods there are in the mill V and the size of the incoming ore.
Fote Machinery is a leading and pioneering enterprise with the most advanced international level in R&D, manufacturing and selling of large-scale crushing & screening plants, mineral procssing equipment and industrial milling equipments.
Ball mill can process barite, slime, potash feldspar, tungsten carbide, copper ore, slag, hematite, white ash, gold ore, aluminum powder, high alumina porcelain, iron powder, fluorite ore Steel slag,dozens or even hundreds of ores
Bar Mill According to the model and size of different prices will vary. If you need the price of a bar grinder, please tell us the specific model and quantity of the mill you need. We will send you the specific price of the mill.
Ceramic ball mill is the necessary grinding equipment in ceramics factory, because it has larger energy consumption, so there is a larger space for saving energy and reducing consumption.
The spiral classifier also named the screw classifier or the spiral classifier machine works as a type of sand classifier or screw sand washer by using the working principle of materials with different particle sizes and weights tending to sink in the liquid at different speeds.
The fine ore particles will swim in the water and then flow out while the coarse ore particles will sink into the bottom of the tank and then be discharged upward by the sand classifier or screw classifier, thus completing the mechanical separating process. Spiral classifier or screw sand washer is one of mineral processing equipment. With the principle of different particle size rate and there is different precipitation speed in the liquid, spiral classifier machine can conduct classifying work.
Fote which is famous for the reasonable spiral classifier price, and has made advanced screw classifiers which are used by the ore beneficiation plant to work together with the ball mill as a closed cycle to realize the classification of the mineral sand, by the gravity mill to classify the mineral sand and fine sand, by the metal beneficiation plant to realize the particle gradation of the ore pulp, and by the ore washing plant to do the desliming and dehydration work.
The spiral classifier machine or sand classifier is mainly made up of transmission gear, spiral device, tank, lifting structure, bottom support (bearing bush) and the ore discharging valve. It features the simple structure, reliable performance and easy operation.
The magnetic separation process, also named the magnetic separating production line and made up of jaw crusher, ball mill, classifier, magnetic separating equipment, concentrator and dryer, is a wet and dry separation combination method of magnetite.
The flotation separation process also known as the flotation separating production line realizes the mineral particle separation based on the working principle of different physical and chemical properties of the minerals leading to different floatability.
Henan Fote Heavy Machinery Co., Ltd.,the former Henan First Machinery Factory,founded in Henan Zhengzhou- China machinery manufacturing capital in 1982,is a large joint-stock company specialized in manufacturing heavy mining machinery and civilian machinery; it has six production bases with an area of 240,000 m, more than 2000 existing employees, 160,000 m standardized....