choosing a mobile impact crusher for recycling what you need to know
RPN connected with product experts and Canadian distributors representing eight of the leading global manufacturers of mobile impact crushers to gain a little more insight into the benefits, features and evolution of this integral tool of today's C&D, concrete and asphalt recycling industries.
Mobile impact crushers, also known as the tracked impact crusher or recycling impactor, are recognizable mainly due to the fact that these crushers are mounted on a tracked undercarriage. Overall range of capacity for mobile impact crushers is roughly about 100 to 500 tons per hour.
Today's mobile impact crushers are especially ideal for smaller-scale recycling operations, for on-site recycling of demolition waste, and for tight-space urban and roadside applications. These units feature a diesel or electric drive system, are transportable by trailer, and can be simply driven off at the location of material that needs to be processed, and go to work very quickly.
With their capability to produce accurately-sized end-product with a cubical end product shape, mobile impact crushers work well as closed circuit stand-alone plants, or they can add significant productivity to any operation, working in tandem with a jaw crusher or screen plant.
Tracked impact crushing plants have evolved greatly over the last several decades, as their designs have been continuously updated and as the crushing market has changed. Major trends include the introduction of electric drive and hybrid systems as opposed to diesel-hydraulic drive systems, and decreases in size, weight, fuel consumption, cost-per-ton, and sound and dust generation.
Today's mobile impact crushers are ideal for use in a wide range of applications, including as a mobile recovered concrete crusher, or for asphalt and mixed C&D waste. They are available compliant to Tier 4 Final emissions standards, and can be equipped with or without a built-in screen, as well as many options specifically geared towards creating recycled materials. Todays mobile impact crushers are safer, more mobile, easier to maintain and operate, and are available with sophisticated machine automation and monitoring.
"The growth in recycling of concrete and asphalt recycling industries has led to higher demand for smaller, more mobile crushers," says John O'Neill, McCloskey International's VP of sales. "Over the last 10 years we have improved our control panel systems to provide operators with more knowledge and information about what is going on inside their machines at all times. The units are also easier and faster to set up."
According to Daryl Todd of B.C.-based Frontline Machinery, the Canadian dealer for Belgium-based crushing and screening plant manufacturer Keestrack, "Wesee a strong movement towards turning concrete and asphalt rubble materials into higher quality recycled materials such as construction sand, washed recycled drain rock, road mulch, RAP (reclaimed asphalt pavement) and a host of other quality products with a much higher value.
"The impact crusher's ability to handle steel-reinforced concrete, along with custom options, such as plastics and wood-waste removal systems, washing systems and more, has enabled recyclers to create much higher quality end products, and crush and process materials previously deemed only waste, or too difficult to process."
"The reason is the quality of the material and very cubical shape produced. The impact crusher is a first- and second-stage crusher in one unit, so you can crush a 600-mm product down to a final product for resale as recycling aggregate.
"Our machines are excellent in recycling asphalt, as we can slow down the rotor speed to crush the asphalt, but not the aggregate inside the asphalt, so the material can be reused in asphalt mixing plants, a huge savings on cost."
According to Norbert Dieplinger, Austria-based SBM Mineral Processing's international business development manager, "Specs are getting tighter so crushers must be much more accurate than in the past. For example, a few years back you could just crush aggregate down to 0- to 3-inch material and use it for road base. Now, engineers are allowing the use of more and more recycled asphalt into their mix, instead of all-natural aggregate and crushed concrete, and not just as road base material. With impact crushers, the shape is exactly what you need, you can get down to smaller sizes and they can process building debris with rebar."
Alexander Taubinger, Rubble Master's managing director and VP sales, says "Cost of ownership and costs per ton are key figures for our customer base." Rubble Master machines feature a diesel-electric drive that burns less fuel, and low maintenance costs are due to the company's latest design and product development.
"Back in the day, it was all about tons per hour. Machines were built overly strong and heavy with large, inefficient power solutions. This is second or third priority these days, since contractors have to meet other job requirements when it comes to most recycling applications."
He adds that with respect to end markets, Rubble Master has always been focused on the final product size and quality. "Lots of contractors still only think about reducing the size of material. It's all about reusable and resalable product size and quality these days."
The changing value of recovered metal, especially over the last decade, is a consideration for all recyclers and contractors managing recycled materials. For users of mobile impact crushers in the processing of concrete and C&D rubble, even with the fluctuating price of recovered steel seen over the last several years, efficient metal separation remains a key component.
"Unfortunately, with the way things have turned as of late, scrap iron is not worth a lot. But I can tell you that having systems in place to remove it is paramount," says Tim Harms, crushing and screening product manager, Kolberg Pioneer (a KPI-JCI & ASTEC Screens company.)
"If you have any metal contamination in your end product, you'll be in trouble trying to resell that product. So it's very important to get it removed. Ten years ago, scrap was of higher value and that was part of the equation. Now it's just the fact that you need to get it out so that you can resell the product. Impact crushers are very good at liberating scrap iron from concrete."
Stephen Whyte, product manager, mobile product development, KPI-JCI & Astec Mobile Screens, adds that the growth of the contractor/rental market has also been key in driving the growth of all tracked crushing and screening plants.
"Guys today can load a tracked impact crusher, go do a job for a week, load it off on the weekend, and they can be set, ready to go on the next site the following week," says Whyte. "It's the contractor/rental market that's really driven the mobile impact crusher market."
He adds that for impact crushing in general, mobile, tracked units are the least path of resistance to get into the business. "You've got the highest reduction ratio. You've probably got the lowest capital investment. And you can get the most bang for your buck'. Almost always you will see entry-level tracked impactors as the first choice for contractors getting into the C&D materials recycling business, no matter the brand."
The stand-out feature of the mobile crusher or tracked impactor for recycling applications, is its mobility, combined with high productivity per hour. Units are fully self-contained on their tracked undercarriage and can easily be driven off a trailer by one operator and quickly put to work, with excellent capability for moving directly to materials. Some models are even capable of tracking (moving about on their tracks) while crushing.
"The ability to move within the job site and job to job is important to the contractor, or other end user, thus driving the demand for portable crushers," says Jody Beasley, national sales director at Screen Machine. "One of the biggest expenses in material processing is physically handling the material. Every time material is moved, labour and expenses are involved. Tracked impact crushers bring the machine to the job site, right to the pile, and allow for very efficient material processing.
"It's all about tons per hour. Our machines have been designed to produce maximum tonnage and one significant way they do that more efficiently is through our patented Crusher Relief System. The Screen Machine Crusher Relief System allows the operator to raise the crusher lid up to six inches while the machine is in operation. This is a huge help in preventing jams inside the crusher and ultimately delivers thousands of additional tons of product over the life of the machine."
According to Stephen Whyte, KPI-JCI and Astec Mobile Screens, "Mobile impact crushers are higher capacity than they were when they first came on. When the first tracked machines came in, they were seen as crushers that were highly portable but would do less weight than the typical portable [trailer-mounted] machine. Whereas now, some of the tracked machines we manufacture can reach those same capacities, and compete with the portable setups.
"Another great feature with our impact crushers is that they allow operators to crush and track at the same time," he continues. "This is why you'll see a lot of these units being used along the highway. One operator can basically load the machine and operate the tracked crusher at the same time."
"This is very important," adds Kolberg-Pioneer's Tim Harms. "You can be crushing and don't have to disengage the crusher to track the machine. You can continue to crush while the machine is being moved around on its tracks, which is a big advantage with respect to time savings. Time is of a huge value. If you lose 10 percent of your time, just because you've got to wait for the crusher to stop so you can move it, those are dollars."
Traditionally, mobile impact crushers have used a diesel-hydraulic engine for the track-drive and power to the crusher. The advent of electric-drive and hybrid systems is one of the main advancements that has occurred over the last decade, and its development is seen by many as one of the most significant trends going forward, especially considering the importance of fuel efficiency, rising transport and operational costs and the global focus on reducing emissions.
"Lowest cost per ton produced is crucial in the customer's business," says Metso Minerals' product manager, Jouni Hulttinen, who adds that main focus areas in their Lokotrack line development have been ease of transport, maintenance and service, as well as safety and energy efficiency.
"Energy efficiency has been a very focused development area," says Hulttinen. "We have reduced fuel consumption up to 20 percent with our tracked impactors." He says one good example is the Lokotrack LT1213(S) (S' designates a built-in screen component) which uses a stand-by function' where the machine switches to idling mode if there is no load on the engine. "Just five minutes on stand-by, per hour, can save 10 litres of fuel per day."
According to Norbert Dieplinger, the drive systems in crushers manufactured by SBM are available as diesel-electric or can be run 100-percent electric. "Not only does electric power reduce the carbon footprint, it can save contractors up to 30 percent on fuel costs when you compare them to the diesel-hydraulic drive systems that were common in the past and are still used by lots of manufacturers," he says.
"This permits high fuel efficiency and allows optimal loading of the crusher," explains Joe Schappert, Kleemann's senior technical sales manager. "Outstanding performance is made possible in part by the extremely efficient direct drive, with which these machines are equipped. A latest-generation diesel engine transmits its power almost loss-free directly to the flywheel of the crusher, via a robust fluid coupling and V-belts. This drive concept enables enormous versatility, as the rotor speed can be adjusted in four stages to suit different processing applications."
A first question to ask when considering a purchase, according to McCloskey's John O'Neill, is: what do you want the machine to do? He says it is necessary for a solid sense of reality to be a big part of the buying decision. "Too many times the customer is upset because they expect peak performance to be the norm, when they need to be looking at all aspects of their operation and how it can support the crusher and the desired end goals or products."
"What kind of support equipment is available and can it support the tonnage capacity of the crusher?" he asks. He adds that other important questions include: Who are the customers? What is the application you intend to use it for? What spec are you working with? How large are the piles to be crushed?"
"If the impact crusher needs a part or maintenance items, can you be confident that the manufacturer will get those parts to you as quickly as possible?" asks Screen Machine's Jody Beasley. "Our machines are manufactured in Ohio, and all parts orders are fulfilled here. We pride ourselves on the fact that more than 97 percent of in-stock parts orders ship the same day."
"All impactors are not created equal, and the differences are significant," says Daryl Todd, Frontline Machinery. "We strongly suggest taking a close look when comparing various models. Start off with the technical specifications, including engine horsepower, the weight of rotor and blow bars, as well as ease of transport, machine weight and dimensions."
Todd says there are many questions to ask, including: Is the rotor direct-drive from the engine, electric drive or hydraulic drive? What is the hopper capacity and feeding height? And what are the after-screen options - single-, double- or triple-deck? Does the machine have the ability to track while in full production? What type / quality are the key components such as hydraulics and electronics? And what is the type and quality of steel used in the frame, crusher housing and rotor? He adds that any mobile impact crusher should also have a user-friendly design, with ease of changing blow bars, and ease of access for maintenance and servicing.
Keestrack's Michael Brookshaw says one of the main questions to ask when considering an impact crusher is: can you transport the unit with your own transport means? "The material that you need to crush in your area is important," he says.
"Look at the costs per ton involved on the purchasing and running of the unit. What are the amounts of material that need to be crushed? Are they large deposits of 30,000 tons or smaller deposits of 500 to 1,000 tons? You should also consider the feed size and capacity that you will need. Would electric drive provide an advantage on the environmental side of the business?"
He adds that the technical aspects of the unit are also very important. Electric drive, pre-screen before the crusher, crusher overload system, pan feeder under the crusher, weight, as well as service and operator friendliness of the unit are all areas that need to be considered. Joe Schappert from Kleemann says that buyers considering a purchase should make sure they choose the correct size for the application and consider how product will flow through the crusher.
"The Kleemann Continuous Feed System (CFS) manages a more equal loading of the crushing area, in which the conveying frequencies of the feeder trough and the pre-screen are adapted independently of each other to the level of the crusher, thus significantly boosting performance.
"Our new impact crushers are differentiated by their size and productivity," continues Schappert. "Our model MR 110 Zsi EVO 2 has a crusher inlet opening of 43.3 inches (1,100 mm), and the MR 130 Zi EVO 2 has a crusher inlet opening of 51 inches (1,300 mm). These provide feed capacities of up to 350 or 450 tph, respectively.
"Consider diesel-electric drives," he adds. "Our latest EVO 2 Mobirex mobile impact crushers utilize direct-drive crushers and electric drives for the vibrating conveyors, belts and the pre-screen. This permits high fuel efficiency and allows optimal loading of the crusher."
Looking ahead, Daryl Todd of Frontline Machinery says there will be more hybrid technology, electric/diesel hybrids, meaning reduced fuel consumption, as well as improved noise reduction. He says that we'll also see advances in contaminant removal systems and washing systems integrated into closed-circuit impact crushers.
GPS systems are another area where Todd expects advances to continue. "GPS systems provide remote monitoring and control, tying in with onboard belt scales," he says. "This allows managers to have total insight into remote operations."
Michael Brookshaw of Keestrack says their telematic system allows customers, distributors and the manufacturer to monitor their machines, inform from distance and advise on capacity, running of the unit and fault finding.
"There has also been much development in the area of wear parts, which are more durable than ever," says Brookshaw. "Our electric-hybrid and full-hybrid system, which we call Keebrid, are excellent in the areas of durability, lower emissions, running costs and all environmental issues."
For McCloskey's John O'Neill, the trend of using one machine to do multiple parts of an operation will continue to decline. "The crusher should crush and the screeners should screen," he says. "Trying to squeeze it all onto one platform is hard and often results in compromises, which if not acceptable to the customer, can be disastrous on the job site."
Rubble Master's Taubinger expects to see improvements in efficiency in all regards. "We expect a very heavy focus on emissions such as dust and noise, as well as more fuel efficiency, safety and ease of operation."
"Advanced diagnostic tools can enable the operator to monitor processes in real time with the ability to adjust settings on a touch screen on the crusher, or even from inside an excavator cab. This leads to further increases in safety and efficiency with a reduction in maintenance, operating costs and downtime.
"Diesel-electric power is the future because of all the advantages it provides with respect to decreased fuel costs and decreased carbon footprint," adds Dieplinger, who also points out that this will make a big difference in years to come, especially considering new carbon taxes being implemented globally.
According to Metso's Jouni Hulttinen, base construction for bikeways, road base and industrial areas are growing end markets for material made from recycled C&D, concrete and asphalt. He says mobile impact crushers, and all types of crushers for recyclable materials, will increasingly move more towards application in the production of high-quality end products.
"Use of the end material has gone from the most basic application to higher-spec building materials," says Hulttinen. "The future trend will go more towards substituting aggregates, new concrete made from recycled concrete, and recycled asphalt added to make new asphalt." RPN
impact crusher working principle
Starting from the base working principle that compression is the forcing of two surfaces towards one another to crush the material caught between them. Impact crushing can be of two variations: gravity and dynamic. An example of gravity impact would be dropping a rock onto a steel plate (similar to what goes on into an Autogenous Mill). Dynamic impact could be described as material dropping into a rapidly turning rotor where it receives a smashing blow from a hammer or impeller. Attrition crushing is the reduction of materials by rubbing; primarily a grinding method. Shear crushing is accomplished by breaking along or across lines of cleavage. It is possible, when required, for a crusherto use a combination of two or three of these principles.
Rapidly increasing operating costs for minerals beneficiating plants continue to be the biggest single problem in maximizing profitability from these operations. The average world inflation rate has been increasing over the last decade and shows little sign of easing. The threat of continued increases in the price of fuel oil will eventually increase the cost of electrical power, in direct proportion for most users. This will undoubtedly cause closure of some lower grade ore bodies unless energy utilization efficiencies, particularly in comminution, can be improved.
Most of the recent literature concerning comminution performance improvement has been directed at grinding mill performance. It can be expected that more refined control systems will improve the overall milling energy efficiency, which is normally the largest single cost component of production. However, published gains by such methods to date appear to be limited to something less than 10%.
The second largest cost for comminution processes is normally that for wear metal consumed in grinding operations.
Allis-Chalmers has continuing -research programs into all forms of comminution processes involving crushing and grinding. Improved crushing technology shows the way to reducing both energy and wear metal consumption mainly by producing finer feed which will improve downstream grinding mill performance.
A new testing procedure for studying crushing phenomena, presently being perfected by Allis-Chalmers, is described for the first time. These bench scale laboratory tests will give more accurate prediction of both energy requirements and size distribution produced in commercial crushing processes. As a direct result, this machine will allow more accurate comparisons to be made in capital and operating cost expenditures for various combinations of crushing and milling processes.
These new testing procedures can be run on small samples including pieces of drill core material. They could be part of testing and feasibility studies for most new concentrators. The same methods can be used to determine likely yield of various sized crushed products and, therefore, benefit crushed stone producers.
The theoretical and practical phenomena concerning comminution processes have received considerable attention in the literature and are not discussed here in any detail. Instead, the breakage studies in this paper are based on an empirical treatment of the fundamental relationships between energy and the size distributions of processed particles that have been observed both in the laboratory and in large-scale, commercial cone-crushing operations.
Because of the bewildering number of variables encountered when studying comminution processes, most investigators have preferred to assume that the size distribution generated in milling and crushing processes bears some relatively fixed relationship such as those described by Gates-Gaudin-Schuhmann1 or Rosin-Rammler.
Fred Bond, in his Third Theory of Comminution, used the former, essentially assuming that size versus cumulative percent passing that size was represented by a straight line of assumed slope 0.5 below the 80% passing size. Based on this assumption, Bond derived his well-known relationship:
The Work Index for rod and ball mills can be determined from laboratory tests and, as demonstrated by Rowland, the relationship gives us a reasonably accurate tool for the design of rotary grinding mill circuits.
Bonds methods have been less successful in predicting fine crushing performance, however, primarily because the typical crusher feed and product distributions do not meet the assumed conditions necessary for the satisfactory application of his equation (see Fig. (1)).
It is most evident that the curved lines appearing on Fig. (1) do not represent a Gates-Gaudin-Schuhmann size distribution. It is therefore not surprising that Bonds procedures do not work well in this situation. The Rosin- Rammler distribution has also been found inadequate to generally describe crusher products.
Work during the early 60s led to the concept of comminution as a repetitive process, with each step consisting of two basic operations the selection of a particle for breakage and the subsequent breakage of this particle by the machine. In this approach, the process under investigation is modelled by combining the particle selection/breakage event with information on material flow in and out of the comminution device.
Most workers who have used this approach have considered size reduction to be the result of the mechanical operation of the comminution device. This mechanical operation consumes the energy, and size reduction is merely a result of this energy consumption. This viewpoint is reasonably valid for tumbling mills where energy input tends to be constant and the proportion of the energy that is usefully consumed in particle breakage is low (<10%). It does not appear to be valid in compression crushers, however, since breakage energy is a significant proportion (>50%) of the total energy input to the crusher and markedly different power rates (energy input per unit of crusher feed) can be obtained by varying ore feedrates and/or crusher parameters such as closed side setting. It will therefore be necessary to include energy information in any model of the crushing process before it will be possible to accurately predict crusher performance. The inclusion of this energy-size information will significantly increase the complexity of these models.
The single-particle breakage event has been the subject of several studies. Most of these have utilized only sufficient energy to break the particle and do not simulate commercial crushing operations where energy levels are such that catastrophic repetitive breakage usually takes place. This approach to the study of comminution processes does yield valuable information, however, and it is unfortunate that it has not received greater attention.
The Bond Impact Work Index method has been an industry standard for the determination of crusher power requirements but was originally developed to ensure, that sufficient power was connected to primary gyratory crushers. In this method, pieces of rock are fractured by trial and error in the test device shown in Fig. (2), until sufficient impact energy has been applied to break the rock.
Normally, the rock breaks in halves, and in most tests only two and seldom more than three large pieces are observed after fracture. No size distribution information is used in calculating the Bond Impact Work Index from the formula:
KWH/tonne). The procedure works quite well for this type of crusher but tends to understate power requirements in fine crushers where power rates are typically much higher (upwards from 0.25 KWH/tonne).
Because of this, a research program was instituted by Allis-Chalmers Comminution Task Force Committee to break rock in a manner more analogous to that observed within commercial fine crushers. A pendulum type test device similar in most respects to that developed by the United States Bureau of Mines and shown diagrammatically in Fig. (3), was built and has been used in an extensive test program to determine whether it would be possible to predict cone crusher performance.
The rock samples selected for crushing in this device are usually minus 38mm (1-), plus 19mm () in size. The sample rock is weighed and then placed between the platens. The end of the rebound platen is placed in contact with the rebound pendulum and the crushing pendulum is raised to a predetermined vertical height which depends on the size of the sample. The crushing pendulum is then released after striking the crushing platen and breaking the rock, the remaining energy is transferred via the rebound platen to the rebound pendulum. The horizontal distance that the rebound pendulum travels is recorded by displacement of a marker and is subsequently converted to a vertical height.
where Ec = crushing energy
E1 = crushing pendulum potential energy (before release)
KE = kinetic energy of the two platens
E2 = rebound pendulum maximum potential energy (after crushing)
EL = system energy loss (sound, heat, vibration)
The system energy loss, EL, is determined by plotting EL as a function of the initial height of the crushing pendulum with no rock present. The major portion of this loss is by vibration. It is felt that the difference between system energy losses with and without rock present in the system is minimal as long as enough initial energy is supplied to result in a small elevation of the rebound pendulum.
The fragments from several rock samples broken under identical conditions were combined for each of the size analyses reported in this paper. Bond Work Indices were also backcalculated from the data using the standard formula, i.e.
Confirmation of the ability of the procedure to provide information suitable for the prediction of crusher performance was obtained by taking feed samples from 31 commercial operations treating a wide range of rocks and ores. At the time of taking a feed sample for laboratory testing in the pendulum device, relevant performance data such as power, feed rate and size distributions for feed and product were taken on the operating crusher. Several thousand rocks have been broken during tests with the device over the past 3 years.
The first thing to notice from these graphs is that there is an extremely good family relationship within each set of size distribution curves. This is somewhat coincidental, since the pendulum curve is the product of a single particle-single impact breakage event and the typical crusher product curve results from multiple particle-multiple impact breakage, but is probably due to two facts:
In order to show that the pendulum product size distribution is sensitive to power rate, several tests have been run on the same feed material at different levels of pendulum input energy. Typical results are shown in Fig. (7) as Schuhmann size distribution (log-log) plots. It can be seen that increasing amounts of fine material are produced with increasing energy input. The same effect was previously demonstrated for an operating crusher in Fig. (1). We can, therefore, conclude from this
that net power rates will be the same in the pendulum and the crusher when the two distributions coincide (as they do in Figs. (4) thru (6). This permits us to determine the efficiency of power utilization in crushers and to predict the product size distribution which will arise from operating crushers at different power rates.
The Bond Work Index figures obtained by backcalculation from the pendulum data are compared with the Net Work Index values obtained from the plants in Fig. (8). The agreement is surprisingly good especially in view of the fact that the 80% passing values do not completely describe the total feed arid product size distributions. This agreement is probably due to the fact that the use of comparable energy levels in both machines gives rise to similar reduction ratios and product size distributions. Because of this, the pendulum test provides a good estimate of the Net Work Index when this is required for current design procedures.
The pendulum product distribution is a breakage function and can be used in models of the process to predict crusher product distributions for different operating conditions. As an example of this approach, Whitens model of the cone crusher, Fig. (9), has been used to simulate the situation given in Fig. (4). The result of this simulation is given in Fig. (10) where it can be seen that very good approximations of crusher performance can be obtained.
The writers are firmly of the opinion that results to date prove that the use of this pendulum device can give more energy-size reduction information in a form readily useable for crusher application. The data can be generated in less time and from a much smaller sample than is required for pilot plant testing. Our present pendulum tester is a research tool and is currently being modified for use in commercial testing of minerals and rocks. More details of this device will be given at a later date.
crusher - an overview | sciencedirect topics
Roll crushers are generally not used as primary crushers for hard ores. Even for softer ores, like chalcocite and chalcopyrite they have been used as secondary crushers. Choke feeding is not advisable as it tends to produce particles of irregular size. Both open and closed circuit crushing are employed. For close circuit the product is screened with a mesh size much less than the set.
Fig. 6.4 is a typical set up where ore crushed in primary and secondary crushers are further reduced in size by a rough roll crusher in open circuit followed by finer size reduction in a closed circuit by roll crusher. Such circuits are chosen as the feed size to standard roll crushers normally do not exceed 50mm.
Cone crushers were originally designed and developed by Symons around 1920 and therefore are often described as Symons cone crushers. As the mechanism of crushing in these crushers are similar to gyratory crushers their designs are similar, but in this case the spindle is supported at the bottom of the gyrating cone instead of being suspended as in larger gyratory crushers. Fig. 5.3 is a schematic diagram of a cone crusher. The breaking head gyrates inside an inverted truncated cone. These crushers are designed so that the head to depth ratio is larger than the standard gyratory crusher and the cone angles are much flatter and the slope of the mantle and the concaves are parallel to each other. The flatter cone angles helps to retain the particles longer between the crushing surfaces and therefore produce much finer particles. To prevent damage to the crushing surfaces, the concave or shell of the crushers are held in place by strong springs or hydraulics which yield to permit uncrushable tramp material to pass through.
The secondary crushers are designated as Standard cone crushers having stepped liners and tertiary Short Head cone crushers, which have smoother crushing faces and steeper cone angles of the breaking head. The approximate distance of the annular space at the discharge end designates the size of the cone crushers. A brief summary of the design characteristics is given in Table 5.4 for crusher operation in open circuit and closed circuit situations.
The Standard cone crushers are for normal use. The Short Head cone crushers are designed for tertiary or quaternary crushing where finer product is required. These crushers are invariably operated in closed circuit. The final product sizes are fine, medium or coarse depending on the closed set spacing, the configuration of the crushing chamber and classifier performance, which is always installed in parallel.
For finer product sizes, i.e. less than 6mm, special cone crushers known as Gyradisc crushers are available. The operation is similar to the standard cone crushers except that the size reduction is caused more by attrition than by impact, . The reduction ratio is around 8:1 and as the product size is relatively small the feed size is limited to less than 50mm with a nip angle between 25 and 30. The Gyradisc crushers have head diameters from around 900-2100mm. These crushers are always operated in choke feed conditions. The feed size is less than 50mm and therefore the product size is usually less than 6-9mm.
Crushing is accomplished by compression of the ore against a rigid surface or by impact against a surface in a rigidly constrained motion path. Crushing is usually a dry process and carried out on ROM ore in succession of two or three stages, namely, by (1) primary, (2) secondary, and (3) tertiary crushers.
Primary crushers are heavy-duty rugged machines used to crush ROM ore of () 1.5m size. These large-sized ores are reduced at the primary crushing stage for an output product dimension of 1020cm. The common primary crushers are of jaw and gyratory types.
The jaw crusher reduces the size of large rocks by dropping them into a V-shaped mouth at the top of the crusher chamber. This is created between one fixed rigid jaw and a pivoting swing jaw set at acute angles to each other. Compression is created by forcing the rock against the stationary plate in the crushing chamber as shown in Fig.13.9. The opening at the bottom of the jaw plates is adjustable to the desired aperture for product size. The rocks remain in between the jaws until they are small enough to be set free through this opening for further size reduction by feeding to the secondary crusher.
The type of jaw crusher depends on input feed and output product size, rock/ore strength, volume of operation, cost, and other related parameters. Heavy-duty primary jaw crushers are installed underground for uniform size reduction before transferring the ore to the main centralized hoisting system. Medium-duty jaw crushers are useful in underground mines with low production (Fig.13.10) and in process plants. Small-sized jaw crushers (refer to Fig.7.32) are installed in laboratories for the preparation of representative samples for chemical analysis.
The gyratory crusher consists of a long, conical, hard steel crushing element suspended from the top. It rotates and sweeps out in a conical path within the round, hard, fixed crushing chamber (Fig.13.11). The maximum crushing action is created by closing the gap between the hard crushing surface attached to the spindle and the concave fixed liners mounted on the main frame of the crusher. The gap opens and closes by an eccentric drive on the bottom of the spindle that causes the central vertical spindle to gyrate.
The secondary crusher is mainly used to reclaim the primary crusher product. The crushed material, which is around 15cm in diameter obtained from the ore storage, is disposed as the final crusher product. The size is usually between 0.5 and 2cm in diameter so that it is suitable for grinding. Secondary crushers are comparatively lighter in weight and smaller in size. They generally operate with dry clean feed devoid of harmful elements like metal splinters, wood, clay, etc. separated during primary crushing. The common secondary crushers are cone, roll, and impact types.
The cone crusher (Fig.13.12) is very similar to the gyratory type, except that it has a much shorter spindle with a larger-diameter crushing surface relative to its vertical dimension. The spindle is not suspended as in the gyratory crusher. The eccentric motion of the inner crushing cone is similar to that of the gyratory crusher.
The roll crusher consists of a pair of horizontal cylindrical manganese steel spring rolls (Fig.13.14), which rotate in opposite directions. The falling feed material is squeezed and crushed between the rollers. The final product passes through the discharge point. This type of crusher is used in secondary or tertiary crushing applications. Advanced roll crushers are designed with one rotating cylinder that rotates toward a fix plate or rollers with differing diameters and speeds. It improves the liberation of minerals in the crushed product. Roll crushers are very often used in limestone, coal, phosphate, chalk, and other friable soft ores.
The impact crusher (Fig.13.15) employs high-speed impact or sharp blows to the free-falling feed rather than compression or abrasion. It utilizes hinged or fixed heavy metal hammers (hammer mill) or bars attached to the edges of horizontal rotating discs. The hammers, bars, and discs are made of manganese steel or cast iron containing chromium carbide. The hammers repeatedly strike the material to be crushed against a rugged solid surface of the crushing chamber breaking the particles to uniform size. The final fine products drop down through the discharge grate, while the oversized particles are swept around for another crushing cycle until they are fine enough to fall through the discharge gate. Impact crushers are widely used in stone quarrying industry for making chips as road and building material. These crushers are normally employed for secondary or tertiary crushing.
If size reduction is not completed after secondary crushing because of extra-hard ore or in special cases where it is important to minimize the production of fines, tertiary recrushing is recommended using secondary crushers in a close circuit. The screen overflow of the secondary crusher is collected in a bin (Fig.13.16) and transferred to the tertiary crusher through a conveyer belt in close circuit.
Primary jaw crushers typically operate in open circuit under dry conditions. Depending on the size reduction required, the primary jaw crushers are followed by secondary and tertiary crushing. The last crusher in the line of operation operates in closed circuit. That is, the crushed product is screened and the oversize returned to the crusher for further size reduction while the undersize is accepted as the product. Flow sheets showing two such set-ups are shown in Figs. 3.1 and 3.2.
Jaw crushers are installed underground in mines as well as on the surface. When used underground, jaw crushers are commonly used in open circuit. This is followed by further size reduction in crushers located on the surface.
When the run of mine product is conveyed directly from the mine to the crusher, the feed to the primary crusher passes under a magnet to remove tramp steel collected during the mining operation. A grizzly screen is placed between the magnet and the receiving hopper of the crusher to scalp (remove) boulders larger than the size of the gape. Some mines deliver product direct to storage bins or stockpiles, which then feed the crushers mechanically by apron feeders, Ross feeders or similar devices to regulate the feed rate to the crusher. Alternately haulage trucks, front-end loaders, bottom discharge railroad cars or tipping wagons are used. In such cases, the feed rate to the crusher is intermittent which is a situation generally avoided. In such cases of intermittent feed, storage areas are installed and the feed rate regulated by bulldozers, front loaders or bin or stockpile hoppers and feeders. It is necessary that the feed to jaw crushers be carefully designed to balance with the throughput rate of the crusher. When the feed rate is regulated to keep the receiving hopper of the crusher full at all times so that the volume rate of rock entering any point in the crusher is greater than the rate of rock leaving, it is referred to as choke feeding. During choke feeding the crushing action takes place between the jaw plates and particles as well as by inter-particle compression. Choke feeding necessarily produces more fines and requires careful feed control. For mineral liberation, choked feeding is desirable.
When installed above ground, the object of the crushing circuit is to crush the ore to achieve the required size for down stream use. In some industries, for example, iron ore or coal, where a specific product size is required (iron ore 30+6mm), careful choice of jaw settings and screen sizes are required to produce the minimum amount of fines (i.e. 6mm) and maximum the amount of lump ore within the specified size range. For hard mineral bearing rocks like gold or nickel ores where liberation of minerals from the host rock is the main objective, further stages of size reduction are required.
A gold ore was crushed in a secondary crusher and screened dry on an 1180micron square aperture screen. The screen was constructed with 0.12mm diameter uniform stainless steel wire. The size analysis of the feed, oversize and undersize streams are given in the following table. The gold content in the feed, undersize and oversize streams were; 5ppm, 1.5ppm and 7ppm respectively. Calculate:
The self tuning control algorithm has been developed and applied on crusher circuits and flotation circuits [22-24] where PID controllers seem to be less effective due to immeasurable change in parameters like the hardness of the ore and wear in crusher linings. STC is applicable to non-linear time varying systems. It however permits the inclusion of feed forward compensation when a disturbance can be measured at different times. The STC control system is therefore attractive. The basis of the system is:
The disadvantage of the set up is that it is not very stable and therefore in the control model a balance has to be selected between stability and performance. A control law is adopted. It includes a cost function CF, and penalty on control action. The control law has been defined as:
A block diagram showing the self tuning set-up is illustrated in Fig. 18.27. The disadvantage of STC controllers is that they are less stable and therefore in its application a balance has to be derived between stability and performance.
Bone recycling is a simple process where useful products can be extracted. Minerals such as calcium powder for animal; feed are extracted from the bone itself. The base material for cosmetics and some detergent manufacturing needs are extracted from the bone marrow.
The bone recycling process passes through seven stages starting from crushing and ending with packing. Figure 13.14 gives a schematic diagram showing the bone recycling process which goes through the following steps:
Following the standard procedures in the Beijing SHRIMP Center, zircons were separated using a jaw crusher, disc mill, panning, and a magnetic separator, followed by handpicking using a binocular microscope. The grains were mounted together with the standard zircon TEM (417Ma, Black etal., 2003) and then polished to expose the internal structure of the zircons. Cathodoluminescence (CL) imaging was conducted using a Hitachi SEM S-3000N equipped with a Gatan Chroma CL detector in the Beijing SHRIMP Center. The zircon analysis was performed using the SHRIMP II also in the Beijing SHRIMP Centre. The analytical procedures and conditions were similar to those described by Williams (1998). Analytical spots with 25m diameter were bombarded by a 3nA, 10kV O2 primary ion beam to sputter secondary ions. Five scans were performed on every analysis, and the mass resolution was 5000 (at 1%). M257 standard zircon (561.3Ma, U=840ppm) was used as the reference value for the U concentration, and TEM standard zircons were used for Pb/U ratio correction (Black etal., 2003). Common Pb was corrected using the measured 204Pb. Data processing was performed using the SQUID/Isoplot programs (Ludwig, 2001a,b). Errors for individual analyses are at 1, but the errors for weighted average ages are at 2.
A stockpile can be used to blend ore from different sources. This is useful for flotation circuits where fluctuations ingrade can change the mass balance and circulating loads around the plant. Blending can also be done on the ROMpad.
The lowest cost alternative is to have no surge at all, but rather to have a crushing plant on line. This is workable for small-scale plant with single-stage jaw crushers as the availability of these simple plant is very high provided control over ROM size is maintained.
The second alternative is to use a small live surge bin after the primary crusher with a secondary reclaim feeder. Crushed ore feeds this bin continuously and the bin overflows to a small conveyor feeding a dead stockpile. In the event of a primary crusher failure, the crusher loader is used to reclaim the stockpile via the surge bin, which doubles as an emergency hopper.
For coarse ore, the next alternative is a coarse ore stockpile. Stockpiles of this type are generally 1525% live and require a tunnel (concrete or Armco) and a number of reclaim feeders to feed the milling circuit.
Multi-stage crushing circuits usually require surge capacity as the availability of each unit process is cumulative. A fine-ore bin is usually required. Smaller bins are usually fabricated from steel as this is cheaper. Live capacity of bins is higher than stockpiles but they also require a reclaim tunnel and feeders.
what is a vertical shaft impactor (vsi) primer? | stedman machine company
All roads, you might say, lead to the Vertical Shaft Impactor (VSI) because these crushers make it possible to create roadways and just about everything else. Francis E. Agnew of California patented one of the first Vertical Shaft Impactors in 1927. His configuration stacked three VSIs atop each other to produce sand, thus starting the VSI evolution.
Today, VSI crushers and the folks who rely on them have produced many configurations to include everything from the addition of cascading material into the crushing chamber, to air swept separation of lighter product. One version suspends the shaft from above like a sugar centrifuge. Its also one of the most feature-patented crushers, so some of the things mentioned here might be unique to a single manufacturer. VSIs apply a large amount of energy to crush material and thats why its one of the most versatile crusher configurations today.
When it comes to producing materials such as aggregate for road making, VSI crushers use a high-speed rotor and anvils for impact crushing rather than compression force for the energy needed for size reduction. In a VSI, material is accelerated by centrifugal force by a rotor against the outer anvil ring, it then fractures and breaks along natural faults throughout the rock or minerals. The product is generally of a consistent cubical shape, making it excellent for modern Superpave highway asphalt applications. The rotor speed (feet per minute) controls final particle size.
The VSIs high cubical fracture percentage maximizes first-pass product yield and produces tighter particle size distribution. It has a high-throughput capacity ideal for beneficiation (elimination of soft material). Properly configured the VSI accepts highly abrasive materials. It has simple operation and maintenance. You can quickly change product size by changing rotor speed or cascade ratio. Some models have reversible wear parts to reduce downtime. The VSI typically has low operating costs even in high-moisture applications because of reduced energy costs and low wear cost per ton.
There are some feed size limitations with a VSI because of the small feed area available in the center of the rotor. Tramp material in the feed such as gloves, tools, etc. can cause problems with imbalance. The high RPM and HP require careful balance maintenance such as replacing shoes on both sides of the rotor at the same time. High wear part cost may be a problem for some hard abrasive materials, but the VSI may still be the best option.
Major limestone applications are for Superpave asphalt aggregates, road base, gravel, sand and cement. Industrial uses include: corundum, corundite, ferro silicon, glass, refractories, silicon carbide, tungsten carbide and zeolite. Mining applications include: bauxite, burnt magnesite, iron ore, non-ferrous metal ore, perlite and trona sulfate. VSIs are excellent for everything from abrasive materials to waste and recycling applications.
Feed size and characteristics will affect the application of a VSI. The feed size is limited by the opening in the center of the rotor. Normally less than 5-inch material is desired, but very large VSIs can handle up to 12-inch feed. Another feature that will affect application is moisture, which can make the feed sticky. Required production capacity is the final limiting criteria. Large primary horizontal shaft impactors can output up to 1600 TPH and more. 1000 TPH is about the maximum for a VSI because of the limiting motor size and the rising G-force of a high-speed rotor, which is calculated by multiplying the radius times the square of the RPM.
Shoe configurations are many: rock on rock, groups of rollers, special tip wear parts and many others. The metallurgy of the shoes is also highly varied. Rotors can have three to six shoes. The number of shoes is typically governed by the diameter of the rotor. The larger the diameter rotor, the more openings are possible. Computational Fluid Dynamics (CFD) mathematical models are utilized to simulate the flow and collision forces to reveal solutions for lower wear cost, consistent final product, and higher energy efficiency.
The material to be crushed is fed into the center of an open or closed rotor. The rotor rotates at high rpm, accelerating the feed and throwing it with high energy into the crushing chamber. When the material hits the anvil ring assembly, it shatters, and then the cubical shaped product falls through the opening between the rotor and the anvil and down to the conveyor below.
The typical VSI is fed, from above, into the center of its rotor. The material is then flung across an open void to the crushing chamber. It then impacts the outer anvil ring. This crushing action imparts very high energy to the material and is very effective on most types of material. It gives a very uniform and consistent grade of product.
In cascade feeding, material bypasses the rotor and enters the crushing chamber from above. Its called cascade feeding because as material fills up a large feed bowl, with an outer diameter larger than the outer diameter of the rotor, it spills over the side and falls into the crushing chamber from above, bypassing the rotor. The effect of increasing feed through cascade is similar to slowing the rotor. Cascade feeding in amounts up to 10 percent may have no effect on particle size distribution or quality. The product gradation curve and product shape will change, if an increased amount of cascade feeding is used.
The VSI features multiple rotor/anvil configurations for various applications. From open or enclosed rotors to the tubular rotor, each machine is configured for their unique application. In many cases the rotor table, rotor assemblies, anvil ring or rock shelf are interchangeable, allowing maximum application flexibility.
The open top metal rotor is good for large feed or medium to very hard material, but it will work best for softer materials. It can handle medium abrasive, dry or wet, but not sticky materials. High reduction ratios are common, which are excellent for sand and gravel production in closed loop systems. Shoe shape can change the production size range. A straight shoe face design produces finer product, and a curved shoe face design produces coarser material.
The tubular rotor creates higher tip-speeds, which increases first pass yield with tighter particle size distribution and also reduces the recirculation loads. One unique feature is that the rotor rotation is reversible, allowing wear on both sides of the tube. Rotating the tube itself one-quarter turn also doubles the wear.
Any time the material or rock is used as an impact wear surface the term autogenous is used. Putting a top on the rotor table and shoes allows autogenous use. During operation of the VSI, a bed of material can be designed to build up inside the rotor against each of the shoe wall segments. The bed, which is made up of material that has been fed to the rotor, extends to a wear tip. The bed protects the shoe wall segment from wear.
Concerning the rock shelf anvil, it forms a near vertical wall of material upon which the accelerated material impacts. Rock-on-rock crushing reduces maintenance but can require up to 30 percent of material recirculation before meeting size requirements. Also, the rock shelf anvil absorbs energy that could otherwise be used for breaking, which may reduce efficiency. More RPM may be needed to achieve the same result as a solid metal anvil.
Good for medium abrasive materials, rock-on-rock configurations of either or both rotor and anvil may produce consistent material with low-wear cost and can handle wet but not sticky conditions. Reduction ratios from 2:1 to 5:1 can be expected. Its widely used for quarried materials, such as sand and gravel.
The VSI is one of the most versatile crushers available on the market today. Even with some limitations, like feed size and output capacity, VSI features have been and continue to be developed to maximize first-pass yields and lower operating costs. If you test your process on full-scale equipment before choosing your VSI, you wont be disappointed.
Stedman Machine Company works closely with its customers to determine the best, most cost-effective, efficient size reduction method and equipment for specific applications. Stedmans line of equipment includes: Cage Mills, Grand Slam and Mega Slam Horizontal Shaft Impactors, V-Slam Vertical Shaft Impactors, Hammer Mills, Aurora Lump Breakers, Micro-Max and Vertical Roller Mill Air Swept Fine Grinders. Stedman operates a complete testing and toll processing facility staffed by experienced technicians with full-scale equipment, allowing customers to witness accurate crushing test results, predicted output capacities and processing data. Support services include system design and 24-hour parts and service.
why are my impact crusher blow bars breaking?
Problem: The customer was experiencing breakage. When we went to the site, we found that the wedges were loose, causing the bar to move up in the rotor station, causing pressure on the locating nose. This pressure lead to a break in a blow bar. A new person was in charge of the crusher and did not realize they could loosen.
Are the wedges tightened properly? What is the condition of the wedges?Are they being checked periodically for tightness, especially after initial installation?Image 1 & 2Here is an example of wedges not being used properly; user was forcing old nuts/bolts under wedges to push them up instead of jacking bolts/ set screws. These wedges need to be replaced with new ones!
Rock Crusher Maintenance
impact crusher | description | advantages | types of impact crusher | engineering intro
The word impact makes sense that in this particular type of crusher some impaction is being used for crushing of rocks. In normal types of crusher pressure is generated for the crushing of rocks. But, impact crushers involve an impact method.
There is a hopper one side that takes the crushing material into the machine. All material is carried only within a cage. This cage has an opening on the end, bottom and on the side. These openings help in escaping the pulverized material from the impact crusher. Normally such type of crusher is used for crushing of materials that are not very hard say soft material and materials that are non-abrasive. For example limestone, coal, gypsum, seeds etc.
Horizontal shaft impactor (HSI) crusher consists of hammers that are fixed to the spinning rotor. Hammers are utilized for the breaking of these rocks. Normally horizontal shaft impactor crusher is used for soft materials and materials like gypsum, phosphate, limestone and weathered shales.
Working principle of vertical shaft impactor is totally different than horizontal shaft impactor. It has a high speed rotor with wearing resistant tips and main chamber (crushing chamber) is designed in such a way so that speed rotor throw the rocks against the high crushing chamber. In vertical shaft impactor crusher predominant force is the velocity of speed rotor.
Rock from ores has an irregular uneven shape. If crushers that used pressure force is used then it results in unpredictable and even more uneven, jagged shape particles. Therefore, use of VSI crusher results in more cubical and even shapes particles. This is so, because vertical shaft impactor crusher utilizes the velocity force that is applied evenly to the surface and the mass of rock.
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tips to maximize crushing efficiency - pit & quarry : pit & quarry
To apply what this means to your crusher, operations produce the exact sizes in the reduction process that their market demands. In the past, quarries produced a range of single-size aggregate products up to 40 mm in size.
In practice, many jaw crushers are not fed to their designed capacity. This is because the subsequent processing plant does not have sufficient capacity to handle the volume of material that would be produced if the jaw crusher was working to capacity.
If you seek fewer fines, trickle feeding material into the jaw crusher could achieve this. But this would have an adverse effect on particle shape, and it also reduces throughput capacity, hindering the crushers efficiency.
Ideally, the feed rate should not be switched from choke to non-choke, as this can cause problems downstream at the secondary processing plant. In practice, many jaw crushers are fed in this intermittent fashion due to gaps in the delivery of feed material from the quarry.
The reduction ratio is then calculated by comparing the input feed size passing 80 percent versus the discharge size that passes 80 percent. The finer the closed-side setting, the greater the proportion of fines produced.
The closed-side setting of a jaw crusher helps determine the nip angle within a chamber, typically 19 to 23 degrees. Too large of an angle causes boiling in the crushing chamber. This is where the jaw plates cannot grip onto the rock, and it keeps slipping up and down, avoiding being crushed. The nip angle gets flatter as the machine is set tighter.
The settings on a jaw crusher are designed to produce material ideal for secondary crushing. The best particle shape is typically found in material that is about the same size as the closed-side setting.
Smaller sizes will contain a higher proportion of elongated particles because they have passed through the crusher without being touched. Larger sizes may also contain a higher proportion of elongated particles because they are further from the closed-side setting. This can cause bridging issues in downstream machines.
It is critical that a cone-type crusher be choke fed to produce the best product shape and quality. It is not as important in a jaw, as material is not generally stockpiled after the jaw. Because the cone is part of the secondary and tertiary stations, particle shape assisted by a choke-fed chamber is important because finished products are created in these stages.
Choke feeding is important for cone crushers because it maintains a good particle shape by facilitating an inter-particle crushing action. Trickle feeding is not the best option because it increases the proportion of flaky material in the crusher product, hindering its efficiency.
It is a good rule to maintain about 10 to 15 percent of material finer than the closed-side setting in the feed to assist crushing action. More than 10 to 15 percent will likely cause ring bounce due to the pressures in the chamber.
Its important to find the right liner for the feed gradation and desired product. If the liner is too large, feed material will drop too far in the chamber before being crushed. Too fine of a liner will prevent material from entering the chamber at all.
Monitoring the crushing force as registered through the load on the crusher motors, as well as the pressure on the hydraulic mantle adjustment mechanism, will give forewarning of crusher packing problems before they affect your efficiency.
Try to match the closed-side setting of the crusher to the top size of the product to be produced. If closing the circuit at 1 in. to produce a 1-in.-minus product, set the crusher at or near 1 in. or slightly below.
The initial impact is responsible for more than 60 percent of the crushing action, with the remainder made up of impact against an adjustable breaker bar and a small amount of inter-particle collision.
This is why it is vitally important that the feed arrangement to an impact crusher ensures an even distribution of feed material across the full width of the rotor. This will allow for even distribution of energy into the feed material and uniform wear patterns, ensuring consistent product gradation and power consumption.
Slower rotor speeds can be used as a means of reducing fines but may result in a product with more oversize or return than is desired. Slower rotor speeds are preferable as a means of minimizing the wear on crusher components, as well as for achieving less fines production and optimal product size.
The product grading from an impact crusher will change throughout the life of the wear parts, particularly the impact hammers or blow bars. As the profile of the hammer changes with increased wear, the product grading becomes coarser. Many modern impact crusher installations have a variable speed drive arrangement that allows an increase in the rotor speed to compensate for wear on the impact hammers.
In many impact crushers, a third curtain or crushing chamber can be added to increase reduction in every pass through the machine. This can be important in finer product applications where the third chamber can provide the desired output gradation. A third chamber that increases the reduction will also increase the power needs and, normally, the wear cost.
One tip to consider: Decreasing the gap between the hammers and impact curtain increases particle retention in the chamber. This increases the size reduction ratio, but it also reduces efficiency throughput capacity and increases fines production.
Follow the steps outlined in this article to achieve the best crushing efficiency for jaw, cone, gyratory and impact crushers and to ultimately increase profits and reduce fines production. By taking these steps, youre reducing the amount fines produced and adding dollars to your pocket.