Successful application of a cone crusher within a crushing circuit is measured by the amount of material passing through the cone, the power draw of the machine, the size distribution of the products coming out of the circuit and the shape of the product. The goal is to efficiently and economically produce the target products, conforming with the required specifications.
A measure of the size reduction achieved for a particular crusher application is the reduction ratio. A cone crusher in a secondary crushing application will typically work with a 3.5:1 to 5:1 reduction ratio. Tertiary cone crusher configurations typically work with a reduction ratio of 2.5:1 to 4:1.
The reduction ratio is defined as the ratio of the feed size for which 80 per cent will pass (F80), divided by the product size for which 80 per cent will pass (P80). The reduction ratio for tough, high strength, damp material is restricted to the low end of the application ranges whereas a soft, low strength, dry material can be successfully crushed at the higher end of the reduction ratio.
The newer, longer stroke, high powered machines of today will outperform the machines in common use 25 years ago. A large stroke provides a greater cross-sectional area for material to pass through the crushing chamber in a given amount of time. The result is that the longer the stroke, the greater the volume of material that can be processed through a given size machine.
The influence of crusher speed, or gyrations of the cone head per minute, is not as well defined as stroke. Depending on the crushing stroke, the CSS and the crushing chamber profile, the effect of increased speed can either increase or decrease the production rate of the crusher. For any combination of these, a different sweet spot in speed will produce maximum throughput for a given feed.
In general, a coarse crusher, such as a secondary cone in open circuit, should be run at the low end of the speed range. As the crushing becomes finer, an increase in speed has been found to be beneficial, especially when shape is a factor. Therefore, it is recommended that tertiary crushers that are operated in closed circuit and at the higher end of the speed range. It needs to be understood that the faster the crusher runs, the faster the manganese wears. The life of other mechanical components will also be reduced. Therefore, the optimum speed for any application is the slowest speed that produces the desired production rate, gradation and shape.
Minimum closed side setting for any cone crusher is that setting just before the factory recommended limit of operating pressure is reached. This is the point at which the hydraulic relief system will act to open the CSS. Minimum CSS may be greater or smaller than published settings based on the conditions and crushing characteristics of the material being processed. Generally, clay or other plastic material in the crusher feed must be eliminated to prevent the formation of compacted material or pancakes, which are non-crushable and will cause activation of the tramp iron relief system.
The breakage of rock in a compression crusher can result in a percentage of flat or elongated product. However, most construction specification rock products require a cubical product. The cubicity of the cone crusher product can be improved with the proper circuit design, screen selection and crusher operating parameters.
When a cubical product shape is required, the following process controls when correctly applied to the crushing circuit will minimize the flat and elongated particles generated inside the cone crusher:
Choke feed means to keep the head covered with at least 150mm of feed material. Conditions that help keep the crusher choked include surge bins, bin level sensors, adjustable speed feeders, and automation.
Keep up to 15 per cent of feed below the CSS to encourage rock on rock attrition crushing. The small particles in the feed fill the voids between the larger particles which increase the density and promote attrition crushing, thereby improving the product shape.
While it is beneficial to retain some feed below the CSS, it is advisable to screen fines (-5mm) out of the feed to minimise compaction and avoid a tramping condition where the crusher will relieve under high pressure.
Crusher feed should be evenly distributed around the centre of the crushing chamber. Avoid feed segregation where the coarse new feed is on one side of the feed opening and the finer recirculated feed is on the opposite side of the feed opening.
The most efficient crushing chamber promotes continual crushing of material as it travels through the chamber. If the liners are too coarse, the material falls too far into the chamber which can lead to packing, increasing crushing pressure, power draw and inducing a bowl float or tramping condition. If the liners are too fine, the feed opening will restrict the larger lump sizes from entering the crushing chamber, resulting in reduced throughput, poor choke condition, decreased power draw and elongated product. In some cone crusher designs the feed opening will reduce as the liners wear.
Operating a secondary cone crusher in closed circuit limits the material top size for processing in the tertiary circuit and allows the near size particles to fill the voids between the larger particles to induce attrition crushing and break flaky elongated particles. Operating a tertiary cone crusher in a closed circuit provides consistent input gradation and improves the shape by attrition crushing.
Running the crusher too fast can generate excessive fines because the material cannot fall as far with each revolution of the eccentric. The material becomes over-crushed and generates excessive crusher dust. Running the crusher too slow will coarsen the output and not allow the attrition rock on rock crushing action that leads to a cubical product.
In any crushing circuit, it is good common sense to get the material to the product piles as quick as possible. This will reduce the wear and tear on the equipment and can lead to increased efficiency and capacity of the circuit because the finished product is not taking up room on the screens, conveyors, and in the crushers.
The size of the raw feed or blasted material and the specification of the final products will dictate the number of crushing stages and screens required. If there is also a shape specification, additional controls and crushing stages may be required. A low reduction ratio application may be able to get by with a jaw/cone/ screen circuit (two-stage crushing). A higher reduction ratio application may require a jaw/ screen/cone/screen/cone circuit (three-stage crushing). A large reduction ratio application may require four or more stages of crushing.
The crusher breaks down the rock to a smaller size. The screen is the cash register of the crushing circuit in that it determines the final gradation of each product pile. In general, it is good practice to oversize the screen to account for changes in environmental conditions that can affect the overall performance of the crushing circuit.
Cone crushers can be categorised into three main design types. With floating bowl and screw bowl cone crushers the upper frame raises to open CSS or relieve crushing pressure. The third type the spider-bearing cone crushers incorporate a shaft supported by a hydraulic piston which controls CSS and crushing pressure. Each machine type has its own features and advantages and each is best suited to particular applications. Terex, through the TC cone, Cedarapids MVP, TG cone and Jaques Gyracone, includes each of these main cone crusher types within its equipment range to ensure it can provide the best option across all crushing applications.
Although past investigations have been conducted to determine crushing relationships, no program which covered a broad range of crushing conditions had been conducted. The previous studies appear to concentrate on small segments of the overall picture and did not fullfill our desired information objectives. Due to the broad range of variables utilized in a production size crusher, is believed to be the most comprehensive study of its kind as of this date.
The principles developed by the Symons brothers in 1925, when they patented the cone crusher as we know it today, are still being used in the machine known as the Symons Cone Crusher. During the development of this novel crushing concept, a technique known as the fall of material (called the Bouncing Ball Theory by some) was used to determine an idea as to the proper head angle, eccentric and speed of eccentric rotation. The final variables used for the Symons Cone Crusher design were, therefore, the logical conditions to start with and use as a reference against which other variables could be compared.
Other tests, conducted in the field and at the MRTC, have confirmed that the eccentric speed should not be reduced below the speed normally used. Similar tests have indicated that the eccentric throw should not be increased significantly above that normally used. It was logical, therefore, that the speed and eccentric should be given significant increases and decreases, respectively during a testing program. The head angles selected were based upon the range of cone crusher head angles being used. It is believed that the majority of the crushing variables used by the various cone crusher manufacturers are covered by the variable ranges selected.
Five hundred tons of 3 (76.2mm) x 1 (31.7mm) limestone was purchased from a limestone quarry near Milwaukee for use as the test material. All the material was obtained on the same day from the same part of the quarry to minimize fluctuations in material characteristics during the test program. Due to the large number of tests (135), no repetitive testing was thought to be necessary.
The material was fed to the crusher at a rate which would either utilize the total horsepower available or fill the crusher cavity. Normally, the horsepower was the limiting factor with the (6.35mm) and 3/8 inch (9.53mm) settings while the cavity capacity was the limiting factor at closed side settings above the 3/8 inch (9.53mm) value.
After either of the two criteria were obtained, the crusher was run until steady operating conditions were achieved. The crushing circuit was then stopped and a belt sample taken. After being weighted, this sample was split to a size convenient for screen size analysis.
Closed side settings were determined by passing a lead slug approximately 2 inches (50.8mm) thick through, the crusher prior to starting the test. This slug was then measured and the value recorded as the crusher setting for that test.
The data from all 135 tests were simultaneously supplied to a canned statistical package known as S.P.S.S. for the equation development. The S.P.S.S. package used was supplied by the Control Data Corporation (CDC) program library. Using a stepwise regression procedure resulted in an indication of each variables importance in relation to the dependent variable, horsepower. Stepwise regression results in each independent variable being entered according to the respective contribution of each to the explained variance (the variability of the dependent variable explained by the regression line)
The R value indicates how well the regression equation fits the sample data. The R value is obtained by dividing the regression sum of squares by the value for the regression sum of squares plus the residual sum of squares. The regression sum of squares being the amount of variation in the independent variables associated with the regression on the dependent variable. The residual sum of squares is the variation of the independent variables not associated with the regression of the dependent variable. This variation is due to the variation in sample data.
C.S.S. = Closed side setting (inches) Eccentric = Eccentric throw (% of normal) Head Angle = Head Angle in degrees from horizontal Speed = Linear Speed in ft./min. of the closed side setting at outermost point of liner Horsepower = Dependent Variable being predicted
The closed side setting therefore accounts for an explained variance of 43%; the eccentric 22%; the head angle 13%; and speed 1%. The R value of .79 indicates that an unexplained variance between the equations developed and the data of 21% exists.
Each of the above were represented by an equation containing the C.S.S. for each eccentric value at the head angle selected. Tables 1-2 show the R values for capacity and horsepower. In nearly all cases the R values for each eccentric value are excellent. Obviously the change in eccentric has a large effect for each head angle as evidenced by the excellent R values developed for the individual eccentrics and the relatively poor R obtained by combining all data for each head angle and developing an equation. This relationship holds true for both the capacity and horsepower predictions.
In tables 1-2 the column labeled Correlation at the 95% confidence level indicates whether a null hypothesis (H0: the values obtained were from a population for which no correlation existed) can be rejected. If a yes is indicated, you can be 95% confident (statistically) that the information used came from a population of data for which a correlation exists. In all but one case, we were able to reject the null hypothesis. Only the correlations obtained from the equations developed using log transformations are presented as the log transformation resulted in the best R values.
Scattergrams for each head angle and eccentric were generated from the equations developed to indicate the predicted horsepower and capacity versus closed side setting. These scattergrams are presented in Figures 1 through 6. Figures 1 through 3 indicate the effect of head angle and eccentric for horsepower consumption versus closed side setting. Figures 4 through 6 show the effects of the same variables on crusher capacity.
Regardless of head angle, eccentric throw, or speed, the closed side setting had the greatest effect on capacity and horsepower. As the closed side setting decreases the capacity decreases and the horsepower increases both changing based upon separate mathematical relationships. It would be logical to assume, therefore, for any given crusher, that an increase in closed side setting will increase capacity (up to the point where the cavity will not accept additional material) and decrease horsepower. There are practical limitations however. We cannot arbitrarily increase the closed side setting (C.S.S.) if we wish to maintain a maximum product top size. At the other extreme there is a physical limitation on how small the setting can be before the mechanical integrity of the crusher in question is violated.
Obviously, we must therefore look at the next variable which contributes to the process. The eccentricity, once again regardless of head angle or speed, has a very significant impact on a crushers capacity. As the eccentricity of the movable crushing member increases, the capacity rapidly increases. (See Figures 4-6) The eccentricity also controls, for any head angle, the horsepower consumption (do not forget the influence of C.S.S.) as shown in Figures 1-3. The horsepower draw will also increase significantly as the eccentricity increases.
It is apparent at this point that for a given closed side setting and head angle that the larger eccentric throws will produce the largest capacities and horsepower consumptions. While it is valid to assume that the amount of work done is related to the horsepower consumption, this assumption is only good up to the point where the added horsepower no longer is doing useful work, but rather is being absorbed in the crushing and supporting structures. Several examples of this wasted horsepower are adjustment ring movement or as seen in a different design the head moving away from the fixed crushing member. It is important therefore, to add horsepower only as long as the work is being done on the material and up to the point where the structural integrity of the machine is not being violated.
The next variable of importance (as per the stepwise regression) is the head angle. It is apparant that as the head angle increases, for a given setting and eccentric, that capacity and horsepower also increase. It has been previously established that a large eccentric is important. A large eccentric coupled with the 60 head angle resulted in a horsepower level far above the maximum acceptable limit at the smaller C.S.S.
An inspection of Figure 3 shows the detrimental effect of the 60 head angle large eccentric on horsepower consumption. In this instance the horsepower draw was high and erratic at the smaller settings. This situation caused a reduction of feed to the cavity to bring the horsepower within acceptable limits. Obviously the head angle must be something less than 60 if we are going to be able to fully utilize the whole crushing cavity at the rated machine horsepower. At the present time there is not enough information available to select the optimum head angle. Another test program concentrating on a broader range of head angles at a large eccentric is needed.
As we have seen, speed increase has been the least contributor to the explained variance. No effect was seen in regard to horsepower consumption. There is some indication that an increase in speed will reduce the crusher capacity (regardless of eccentric or head angle).
Comminutionis the process by which minedoreis reduced in size to make for easier processing. The strict definition is the action of taking a material, specifically mineral ore, and reducing it to minute fragments or particles. This is typically achieved in several stages of a detailed and professionalminingoperation.
Some of the earliest versions ofcrusherswere large stones used by humans to repeatedly hammer rocks placed upon an anvil (a hard stationary surface); the products made from this hammering action were transported by pack animals or humans in sacks. Historically, mining tasks were incredibly labour intensive, and the produced mined products were correspondingly expensive. The only tools available to breakdown ore were adrill bit,sledgehammer, or apickaxe(and the will power of a few tireless workers). The majority of ore sizing and crushing operations were completed by hand until halfway through the 19thcentury. At this time,water powered trip hammersstarted assisting miners; it was roughly the beginning of theindustrial revolution.
During the industrial revolution, commercial mining started seeing the use ofexplosivessuch asgunpowderat the heart of many mining operations; this mining method is known as blasting and it led to ever larger quantities ofrockandmineralsbeing liberated.Steam shovelswere the next tool to revolutionise the mining industry. Over time,larger machinesand moreadvanced mining techniquesstarted making it possible to liberate significantly larger pieces of ore.
The demand for mined minerals and other mined by-products has not reduced over the past 150 years. To ensure supply could meet demand, many differentcrushingandconveyingmachines were invented. Without simultaneous advances within the fields of comminution and conveying, it would not have been possible to mine and convey materials safely and efficiently (even modern conveyors cannot convey single blocks of material weighing many tonnes).
Almost all quarry and mining operations today make use of crushers to reduce the size of larger materials; loose (smaller) sized materials do not typically require a crushing stage. When mining harder rock,jaw crushers,cone crushers, and/orgyratory crushersare usually employed.
Acrusheris a machine designed to reduce the size of large rocks tosmaller rocks,gravel,sand,orrock dust; this is essential for efficient transport of the product via conveyors etc. Crushing is the first of many stages that lead to separation of themineral(s)from thewaste(gangue) material. Waste material can be discarded or recycled allowing the mineral rich product to be further processed at the main plant.
Various types ofcrusherandmineral separatormay be employed depending upon thethroughput,hardness, andpropertiesof the mineral being processed. In all cases, the crushing stage is essentially achieved by transferring a mechanically amplified force (viamechanical advantage)to a material, to breakdown the bonds which hold the material together.
Crushingis achieved by passing the feed between two solid surfaces, then by applying sufficient force to bring the surfaces together so that the molecules of the material being crushed areseparatedfrom (fracture), or,change alignmentin relation to (deform), each other.
Crushers are commonly classified by the degree to which they fragment the starting material, withprimaryandsecondarycrushers handlingcoarse materials, andtertiaryandquaternary crushersreducing particles tofinergradations. Each crusher is designed to work with a certain maximum size of raw material, and often delivers its output to ascreening machine(screener) which sorts and directs the product for further processing. In many cases, initial crushing stages are followed by further milling stages (if the materials need to be further reduced); see ourball millarticle for further details.
Typically, the initial crushing stage is completed using eithergyratory crushersorjaw crushers. It is often the case that there will be only one crusher installed, and this will be referred to as the primary crusher.
The Blake crusher was first patented byEli Whitney Blakein1858and it is the most common type of jaw crusher employed today. The Blake type jaw crusher has afixed feedarea and avariable dischargearea. Blake type crushers come invarious sizesand are commonly used forprimaryandsecondarycrushing roles.
Jaw crushers aresizedbased upon the dimensions of the top feed inlet (gape) or the dimensions of the jaws. For example, a 32 x 54 sized jaw crusher will measure 32 inches from the movable to stationary jaw (when measured at the top i.e. the opening), and each jaw will have a 54-inch width. If a jaw crusher is rated by jaw plate size, a suitable rating maybe 600 x 400, which indicates a 600 mm by 400 mm jaw plate dimension. Sizes may be given inimperial(inches etc.) ormetric(millimetre etc.).
Material is fed into the top feed opening (gape) and gradually moves downwards towards the lower discharge outlet. As the materials passes towards the outlet, it is crushed between the stationary and moving jaws. Thev-shaped areabetween the two jaws is referred to as the crushing chamber. Because the space between the two jaws becomes narrower towards the discharge outlet, the material size is progressively reduced.
Thegapbetween the jaws at the discharge outlet dictates the material output size. A typical jaw crusher will have a crushing ratio of between6:1to8:1i.e. the feed material size is reduced by a factor of 6 or 8.
The process of reducing mined ore for processing is known as comminution, which is defined as the action of reducing a material, especially a mineral ore, to minute particles or fragments; this is normally achieved at mining operations through one or more stages of crushing and milling.
Early mining activities were labour intensive. Ore breakdown occurred via a miners pick, sledgehammer, or drill bit. Until the mid-nineteenth century, most initial ore crushing and sizing continued to be done locally by hand. Later operations were assisted with water powered trip hammers (early-to-middle industrial revolution). The earliest known crushers were hand-held stones, where the weight of the stone increased the force a miner could apply when hammering against a stone anvil. The small volumes of rock and aggregate produced were then typically loaded into sacks for transport by road.
Explosives (gunpowder etc.) were introduced to commercial mining during the industrial revolution; using explosives to mine is referred to as blasting. Blasting came into widespread use for bulk mining in the mid-nineteenth century, followed later by steam shovels. For the first time, new mining techniques and machines began producing ever larger chunks of liberated materials.
Rapid growth in demand over the past century has required considerable upscaling of production tonnages, regardless of the types of ore being mined. To cater for this increase in demand, various crushing and breaking technologies were developed to allow for efficient transport of bulk materials (via conveyors etc.) from the mine to the processing plant.
Today, most mining and quarry operations utilise crushers as part of the front end of the ore beneficiation processes after the ore bed has been liberated by blasting or other techniques. Exceptions include mining of very loose materials such as mineral sands, where this crushing stage is often not needed. Similarly, many coal and lignite beneficiation/washing plants use other technologies such as Bradford Breakers and Mineral Sizers. But for hard rock mining, the use of gyratory crushers, cone crushers, and/or jaw crushers, is the starting point for ore processing.
A crusher is a machine designed to reduce the size of Run of Mine (ROM) large rocks to smaller rocks, gravel, sand, or rock dust; this is essential for efficient transport of the ore via conveyors etc. Crushing is the first of many stages that lead to separation of the ore from the waste (gangue) material. Waste material can be discarded or recycled allowing the ore rich stream to be further processed at the main plant.
Various types of crusher and mineral separator may be employed depending upon the throughput, hardness, and properties of the ore being processed. In all cases, the crushing stage is essentially achieved by transferring a mechanically amplified force (via mechanical advantage) to a material, to breakdown the bonds which hold the material together.
Crushing is achieved by passing ore between two solid surfaces, then by applying sufficient force to bring the surfaces together so that the molecules of the material being treated are separated from (fracture), or, change alignment in relation to (deform), each other.
Crushers are commonly classified by the degree to which they fragment the starting material, with primary and secondary crushers handling coarse materials, and tertiary and quaternary crushers reducing ore particles to finer gradations. Each crusher is designed to work with a certain maximum size of raw material, and often delivers its output to a screening machine (screener), which sorts and directs the product for further processing. In many cases, initial crushing stages are followed by further milling stages using e.g. ball mills etc.
Typically, the initial crushing stage is completed using either gyratory crushers or jaw crushers. It is often the case that there will be only one crusher installed, and this will be referred to as the Primary Crusher. Cone crushers are typically used for 2nd, 3rd & 4th stage crushing steps (although not always).
A primary crusher is designed to receive run-on-mine (ROM) rocks directly from the mines. Gyratory crushers typically crush to reduce the size of aggregate to a maximum of about one-tenth of its original size. Gyratory crushers are always installed vertically orientated.
ROM ore from the mine is typically transferred by haul trucks which discharge into a feed hopper at the upper level; crushed ore is then discharged from the bottom shell assembly. In some cases, a grizzly feeder may be used, and undersize ore can be screened to bypass the crusher (transferred directly to the output conveyor). There is typically also a hydraulic rock breaker to reduce large boulders received from the mine.
The gap between the main shaft and concaves reduces from the top to the bottom of the crusher assembly. The upper concave is lined with hardened steel concave linings and the main shaft is fitted with a mantle liner (sheathe) of similarly hardened material.
Linings are the main wear components of a crusher. Linings wear over time and protect the main casing and shaft from damage. The maintenance strategy for a gyratory crusher will be largely influenced by the rate of wear of the linings, which can be monitored manually (thickness measurements) or by using suitable condition monitoring tools e.g. laser scanning. The liners and mantle are replaced at scheduled intervals or based on the wear rates recorded.
The hydro set system is a hydraulic mechanism which allows the vertical position of the main shaft (and mantle) to be raised and lowered. Changing the position of the mantle changes the gap setting at the outlet of the crusher, and consequently the size of the crushed output. The height of the mantle is often automatically adjusted based upon the torque produced, and has a release mechanism that allows the mantle to drop should the normal workload be exceeded; this is an overload protection feature.
The upper shaft bearing is enclosed within the central spider bushing. This arrangement allows slight oscillation of the upper shaft and limited vertical movement produced by the hydro set. The spider bearing is normally lubricated by grease (manual or automatic).
Crushing action is produced by the oscillation or throw (opening & closing) of the gap between the moving mantle liner, mounted on the central vertical shaft (spindle), and the fixed concave liners mounted on the mainframe (top shell) of the crusher. The mantle and concaves from the working surfaces of the crusher, producing the force required to crush the ore.
Eccentric motion is achieved by the lower eccentric bushing and drive arrangement on the bottom of the main shaft. The input pinion drive countershaft is supported by pinion bearings and powered by an electric motor. An external gearbox or belt drive arrangement reduces the motor speed to approximately 100-200 RPM at the crusher. In some cases, a clutch system may also be used to absorb shocks. The pinion on the countershaft meshes with and turns the eccentric gear drive or crown gear.
The inner surface of the eccentric bushing is machined off-centre from the centre-axis of the crusher. As the eccentric bushing rotates, the lower shaft oscillates in an elliptical orbit around the centreline of the crusher. This action causes the gap between the mantle and concave liners to open and close upon each rotation of the shaft. At the upper end of the mantle this movement is very small, but as the ore falls lower, the throw increases and the crushing force also correspondingly increases.
Crushed ore falls to the bottom shell assembly and is discharged into the crushed ore conveying system for further processing. The lower casing also houses a forced lubrication and hydraulic system, which is critical for the drive arrangement and hydro set mechanism.
Further processing can involve additional crushing stages (secondary, tertiary, quaternary etc.), milling, and other beneficiation steps to suit the ore being processed. It is worth noting that there will often be only a single primary crusher at many mining operations. As such, the primary crusher is a critical and major bottleneck machine for many mining sites, with little, or no bypass opportunities.
Comminutionis the term used to define the process that reduces materials (especiallymined ore). It is the action of reducing a material to minutefragmentsorparticles. The process is typically achieved inminingoperations through stages ofcrushingandmilling.
In the past, mining activities were arduous and labour intensive. Ore breakdown was derived witha miners pick,drill bit, orsledgehammer. Until the mid-1800s,sizingandcrushingoperations relied mostly upon manual labour;water powered trip hammersbecame popular much later, during theIndustrial Revolution. Throughout this early period, only relatively small volumes of rock and aggregate could be produced. These small amounts were then loaded intosacksorwagonsfor transport.
During the Industrial Revolution,explosiveswere first deployed for use in commercial mining. Mining using explosives was referred to asblasting. By the mid-1800s, blasting was a widespread mining technique used forbulk miningand it would be shortly followed bysteam shovelling. These new mining techniques revolutionised the mining industry, allowing for the production of ever larger amounts of liberated materials.
The mining industry has seen growth in the past century due to the rapid increase in demand forminerals; this growth has required significantupscalingof production tonnages. The increase in demand has led to the development of new and more efficient crushers (machines used forsize-reduction). As crushing tonnages increased, so did the requirements to convey and transport their inputs and outputs. To cater for this, items such asflat-bed conveyorsandhaul truckswere introduced.
Thecone crusherwas first developed in United States in the 1920s bySymons Brothersof Milwaukee. Symon Brothers are credited as the first designers and inventors of thespring cone crusher. The Symons Brothers cone crushers biggest advantage was itsdurabilityandsimplicity(the entire machine had only nine moving parts). After further years of research and development (R&D), the spring cone crusher became one of the most efficient -and consequently one of the most widely used-crushing machines.
The spring cone crusher design is able to passuncrushable materialse.g.tramp metal, through thecrushing cavityby using springs. The firsthydraulic cone crusherwas developed in 1948 and this allowed for the opening of the crushing cavity hydraulically, instead of using springs (mechanical actuation). Both the spring and hydraulic cone crusher designs are still in use today.
Cone crushers are capable ofcrushingall types of medium to hard mineral rocks and stones. It also offers many advantages over other crusher designs, such aslow energy consumption, reliability, high efficiency(compared to other crushers), and ahigh reduction ratio(feed/input size compared to product/output size).
Despite being present in many industries, it is most commonly used in theconstructionandminingindustries. Cone crushers are generally found in use for secondary, tertiary, and downstream crushing services, withjaw crushersandgyratory crushersused forprimary crushingoperations.
In some cases, theRun of Mine (ROM)ore from the mine can be fed to a cone crusher via conveyors and screens, but more often, the feed material will come from upstream primary crusher(s) and cone crushers will be used for downstream crushing stages.
Acrusheris a machine designed to reduce the size of large rocks tosmaller rocks,gravel,sand, orrock dust; this is essential for efficient transport of the product via conveyors etc. Crushing is the first of many stages that lead to separation of themineral(s)from thewaste (gangue)material. Waste material can be discarded or recycled allowing the mineral rich product to be further processed at the main plant.
Various types ofcrusherandmineral separatormay be employed depending upon thethroughput,hardness, andpropertiesof the mineral being processed. In all cases, the crushing stage is essentially achieved by transferring a mechanically amplified force (viamechanical advantage) to a material, to breakdown the bonds which hold the material together.
Crushing is achieved by passing the feed between two solid surfaces, then by applying sufficient force to bring the surfaces together so that the molecules of the material being crushed areseparatedfrom(fracture), or,change alignmentin relation to (deform), each other.
Crushers are commonly classified by the degree to which they fragment the starting material, withprimaryandsecondarycrushers handlingcoarse materials, andtertiaryandquaternary crushersreducing particles tofinergradations. Each crusher is designed to work with a certain maximum size of raw material, and often delivers its output to ascreening machine(screener), which sorts and directs the product for further processing. In many cases, initial crushing stages are followed by further milling stages (if the materials need to be further reduced).
Typically, the initial crushing stage is completed using eithergyratory crushersorjawcrushers. It is often the case that there will be only one crusher installed, and this will be referred to as theprimary crusher.
Thefeedis fed by conveyors to afeed binabove the vertically mounted cone crusher. Feed enters the crusher via an opening in theupper shell. Depending upon the cone crusher design, a distribution plate may be used to distribute the feed evenly as it enters the crusher. Aspider cap(if fitted) houses theupper bearingof themain shaft; the shaft is lubricated withgreaseoroildepending upon the design.
Themain shaftis normally manufactured fromhigh grade forged steel(annealed for stress relief). The upper part of the shaft is supported by aself-aligning bearingin the spider cap (if fitted). The self-aligning bearing is designed to cater for the movement generated by theoscillating shaft; thisoscillatingmovement is caused by thelower eccentric drive arrangement. Thejournalof thespider bearingis shrunk onto the top of the main shaft.
Themantleis installed over thehead/cone, which is mounted onto main shaft. The mantle forms part of thereplaceable wear surfacesand it oscillates with the moving shaft (moving wear surface). Mantles are typically manufactured frommanganese steel alloy.
Eccentric motionis achieved by thelower eccentric bushinganddrive arrangementlocated at the bottom of themain shaft. This arrangement is similar in design and principal to that used bygyratory crushers. The eccentric bushing is manufactured fromhigh carbon steelfitted with abronze inner wear sleeve. It is possible to adjust the eccentricthrowby installing different sized sleeves. The throw defines the range of movement of the shaft and consequently the distance between the mantle and bowl liner at any given point, this is particularly relevant at thechoke point(the place where the mantles diameter is largest and where the mantle comes physically closest to the stationary wear surfaces).
An alloy steelpinion gearis mounted onto apinion drive shaft. The pinion drive shaft is supported bypinion shaft bearingsfed from a common lubrication system. An external motor pulley arrangement providesmotive powerto the pinion shaft, which in turn rotates the main shaft via this pinion andcrown geararrangement.
Feed from a feed hopper is fed into a large opening at the top of the cone crusher. Feed then falls due to gravity and iscrushedbetween themantleandconcaves; crushing takes place in thecrushing chamber. As the feed moves towards the drive end of the cone crusher, its size decreases (due to the crushing action), and ever smaller pieces move towards the drive end of the crusher. After passing through the crusher, the product -now at a much-reduced size- is discharged through an opening in the bottom shell.
Crushingaction is produced by theoscillationorthrow(opening & closing) between the moving mantle liner, mounted on the cone, and the stationaryconcave linersmounted within theupper casingof the crusher. Themantleandconcavesform the working surfaces of the crusher, as this is where the crushing action occurs.
Thewidthof the discharge opening dictates the size of a crushers product output. The size of a crushers product output can be varied byraisingorloweringthe upper casing. This adjustment varies the size of a cone crushers product because thegapbetween the mantle and concaves is correspondingly increased or decreased. Raising the concaves (bowl liner) thus increases the products size output, whilst lowering the concaves decreases the products size output.
Because the motion of the mantle iseccentric, the gap between the mantle and concaves on one side is different to the gap on the opposite side, at any given time. When the gap between the mantle and concaves is at its largest, the opposite side gap is at its smallest. The widest gap between the mantle and concaves is referred to as theopen side setting(OSS), whilst the narrowest gap is referred to as theclosed side setting (CSS). Both settings are important because they describe the largest possible product size output(OSS)and smallest possible product size output(CSS). The OSS can be given as:
Eccentric motionis achieved by thelower eccentric bushinganddrive arrangementat the bottom of themain shaft. The inputpinion drive countershaftis supported bypinion bearingsand powered by anelectric motor. An externalgearboxorbelt drivearrangement reduces the motor speed at the crusher; typical crusher speeds range fromseveral hundredrpmup to approx.1000 rpm. In some cases, aclutch systemmay also be used to absorb shocks. Thepinionon thecountershaftmeshes with theeccentric gear drive, orcrown gear.
The inner surface of theeccentric bushingis machined off-centre from the centre-axis of the crusher. As the eccentric bushing rotates, the lower shaft oscillates in anellipticalorbit around the centreline of the crusher. This action causes the gap between the mantle and concave liners to open and close upon each rotation of the shaft. At the upper end of the mantle this movement is very small, but as the feed falls lower, the throw increases and the crushing force also correspondingly increases.
Crushed feed falls to thebottom shell assemblyand is discharged to the product conveying system for further processing. Thelower casingalso houses aforced lubricationandhydraulicsystem, which is critical for the drive arrangement and tramp release cylinders (if fitted).
To calculate the output from a cone crusher, models for size reduction and flow are needed. The interaction between these two models is quite complex as the overall size reduction in a cone crusher is a result of a repeated consecutive comminution process. The flow model is important since it describes how the rock material moves through the crusher chamber. Thereby the flow model provides input to the size reduction model. In turn, the size reduction model predicts the size distribution after compressing the rock material.
Previously presented flow models have only in a simplified way described the material flow. In the present paper the way an aggregate of particles moves down a crusher is described based on the equations of motion. A constitutive relation between size distribution and the uncompressed bulk density of the material is presented. Along with compatibility conditions from the crusher geometry, mass continuity is preserved. This is a very important aspect of flow modelling.
Three different mechanisms are assumed to describe the material flow: sliding free fall and squeezing. For a single particle only one of these three can be active at a time. Sliding occurs when a rock particle is in contact with the mantle and slides downwards. If the mantle accelerates away rapidly enough, the corresponding particle will fall freely. When a particle comes into contact with both mantle and concave or when the density of a material volume exceeds a critical value, squeezing will occur. During squeezing, particles will be compressed and thereby crushed.
The flow model provides detailed information about how different machine parameters affect the flow of the rock material through the crusher chamber. From the model it can be explained why crushers with smaller inclination of the mantle require a larger stroke compared to the ones with steep inclination.
The supply of minerals, ores and aggregates are crucial for the continuous development of todays society. With a rising world population, growing urbanization, and increasing standards of living, the performance and efficiency of existing crushers must be improved in order to meet the escalating demand on these products. The current paper thus presents a comparative study between existing cone crushers and theoretically optimal crushing sequences.
Full scale experiments are conducted in order to examine the effects of Closed Side Setting (CSS), stroke, and eccentric speed on crusher output. The performance of the examined cone crusher is then compared against what is considered as theoretically optimal. The subsequent analysis shows that significant gains can be made in terms of both product yield and overall capacity by adjusting crusher operation depending on the conditions at hand, e.g. increasing the CSS while maintaining the same stroke or decreasing the eccentric speed. It is also shown that a mixture of breakages modes is more optimal than the sole application of one optimized breakage mode.
A cone is a distinctive three-dimensional geometric figure that has a flat surface and a curved surface, pointed towards the top. The pointed end of the cone is called the apex, whereas the flat surface is called the base. This is what a cone looks like: