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.
what is impact crusher|working principle, parts and types | quarrying & aggregates
The impact crusher is a highly efficient coarse, medium and fine crusher for medium-hard and softer rocks. Whether in a quarry, mining or Construction waste recycling, the impact crusher can efficiently crush the stone, so that the particle shape, particle size distribution and cleanliness are in line with the strict standards of concrete and asphalt aggregate. Impact crushing equipment not only achieves first-class product quality but also a remarkable throughput.
When the stone falls into the working area of the blow bar (hammer), it is crushed by the impact of the blow bar on the high-speed rotating rotor, and is thrown to the apron for a second impact, and rebounds until the rotating blow bar (hammer) is hit again. This process is repeated until the material is crushed to the required size and discharged from the machine outlet.
Aiming at the problems of the previous generation of impact crushers in terms of crushing efficiency and processing capacity, the CI5X impact crusher optimizes the crushing cavity type, rotor speed and power curve, improves the crushing efficiency and crushing ratio, and makes the finished product The aggregate shape is further optimized, and the gradation curve is more reasonable.
The comprehensive processing capacity of the equipment is increased by more than 15% compared with the previous generation products, which can meet the requirements of high-grade concrete for the preparation of aggregates.
PFW impact crusher is a new type of high-performance hydraulic crusher developed with internationally advanced impact crusher technology. It is very suitable for coarse, medium and fine crushing of various soft and medium-hard minerals and rocks.
PF impact crusher adopts traditional impact crushing technology. After years of design optimization, it has more excellent performance and reliable use. It is the most common medium-hard and soft material fine crushing equipment.
The PF impact crushing cavity and rotor have been optimized in design, and the production capacity and finished product particle size have been improved compared with traditional impact crushing. The counterattack frame and rotor are mechanically adjusted, which is simple and reliable.
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 - an overview | sciencedirect topics
The impact crusher (typically PE series) is widely used and of high production efficiency and good safety performance. The finished product is of cube shape and the tension force and crack is avoided. Compared with hammer crusher, the impact crusher is able to fully utilize the high-speed impact energy of entire rotor. However, due to the crushing board that is easy to wear, it is also limited in the hard material crushing. The impact crusher is commonly used for the crushing of limestone, coal, calcium carbide, quartz, dolomite, iron pyrites, gypsum, and chemical raw materials of medium hardness. Effect of process conditions on the production capacity of crushed materials is listed in Table8.10.
Depending on the size of the debris, it may either be ready to enter the recycling process or need to be broken down to obtain a product with workable particle sizes, in which case hydraulic breakers mounted on tracked or wheeled excavators are used. In either case, manual sorting of large pieces of steel, wood, plastics and paper may be required, to minimise the degree of contamination of the final product.
The three types of crushers most commonly used for crushing CDW materials are the jaw crusher, the impact crusher and the gyratory crusher (Figure 4.4). A jaw crusher consists of two plates, with one oscillating back and forth against the other at a fixed angle (Figure 4.4(a)) and it is the most widely used in primary crushing stages (Behera etal., 2014). The jaw crusher can withstand large and hard-to-break pieces of reinforced concrete, which would probably cause the other crushing machines to break down. Therefore, the material is initially reduced in jaw crushers before going through any other crushing operation. The particle size reduction depends on the maximum and minimum size of the gap at the plates (Hansen, 2004).
An impact crusher breaks the CDW materials by striking them with a high-speed rotating impact, which imparts a shearing force on the debris (Figure 4.4(b)). Upon reaching the rotor, the debris is caught by steel teeth or hard blades attached to the rotor. These hurl the materials against the breaker plate, smashing them into smaller particle sizes. Impact crushers provide better grain-size distribution of RA for road construction purposes, and they are less sensitive to material that cannot be crushed, such as steel reinforcement.
Generally, jaw and impact crushers exhibit a large reduction factor, defined as the ratio of the particle size of the input to that of the output material. A jaw crusher crushes only a small proportion of the original aggregate particles but an impact crusher crushes mortar and aggregate particles alike and thus generates a higher amount of fine material (OMahony, 1990).
Gyratory crushers work on the same principle as cone crushers (Figure 4.4(c)). These have a gyratory motion driven by an eccentric wheel. These machines will not accept materials with a large particle size and therefore only jaw or impact crushers should be considered as primary crushers. Gyratory and cone crushers are likely to become jammed by fragments that are too large or too heavy. It is recommended that wood and steel be removed as much as possible before dumping CDW into these crushers. Gyratory and cone crushers have advantages such as relatively low energy consumption, a reasonable amount of control over the particle size of the material and production of low amounts of fine particles (Hansen, 2004).
For better control of the aggregate particle size distribution, it is recommended that the CDW should be processed in at least two crushing stages. First, the demolition methodologies used on-site should be able to reduce individual pieces of debris to a size that the primary crusher in the recycling plant can take. This size depends on the opening feed of the primary crusher, which is normally bigger for large stationary plants than for mobile plants. Therefore, the recycling of CDW materials requires careful planning and communication between all parties involved.
A large proportion of the product from the primary crusher can result in small granules with a particle size distribution that may not satisfy the requirements laid down by the customer after having gone through the other crushing stages. Therefore, it should be possible to adjust the opening feed size of the primary crusher, implying that the secondary crusher should have a relatively large capacity. This will allow maximisation of coarse RA production (e.g., the feed size of the primary crusher should be set to reduce material to the largest size that will fit the secondary crusher).
The choice of using multiple crushing stages mainly depends on the desired quality of the final product and the ratio of the amounts of coarse and fine fractions (Yanagi etal., 1998; Nagataki and Iida, 2001; Nagataki etal., 2004; Dosho etal., 1998; Gokce etal., 2011). When recycling concrete, a greater number of crushing processes produces a more spherical material with lower adhered mortar content (Pedro etal., 2015), thus providing a superior quality of material to work with (Lotfi etal., 2017). However, the use of several crushing stages has some negative consequences as well; in addition to costing more, the final product may contain a greater proportion of finer fractions, which may not always be a suitable material.
Reduction of the broken rock material, or oversized gravel material, to an aggregate-sized product is achieved by various types of mechanical crusher. These operations may involve primary, secondary and even sometimes tertiary phases of crushing. There are many different types of crusher, such as jaw, gyratory, cone (or disc) and impact crushers (Fig. 15.9), each of which has various advantages and disadvantages according to the properties of the material being crushed and the required shape of the aggregate particles produced.
Fig. 15.9. Diagrams to illustrate the basic actions of some types of crusher: solid shading highlights the hardened wear-resistant elements. (A) Single-toggle jaw crusher, (B) disc or gyrosphere crusher, (C) gyratory crusher and (D) impact crusher.
It is common, but not invariable, for jaw or gyratory crushers to be utilised for primary crushing of large raw feed, and for cone crushers or impact breakers to be used for secondary reduction to the final aggregate sizes. The impact crushing machines can be particularly useful for producing acceptable particle shapes (Section 15.5.3) from difficult materials, which might otherwise produce unduly flaky or elongated particles, but they may be vulnerable to abrasive wear and have traditionally been used mostly for crushing limestone.
Reduction of the broken rock material, or oversized gravel material, to an aggregate-sized product is achieved by various types of mechanical crusher. These operations may involve primary, secondary and even sometimes tertiary phases of crushing. There are many different types of crusher, such as jaw, gyratory, cone (or disc) and impact crushers (Figure 16.8), each of which has various advantages and disadvantages according to the properties of the material being crushed and the required shape of the aggregate particles produced.
Fig. 16.8. Diagrams to illustrate the basic actions of some types of crusher: solid shading highlights the hardened wear-resistant elements (redrawn, adapted and modified from Ref. 39). (a) Single-toggle jaw crusher, (b) disc or gyrosphere crusher, (c) gyratory crusher, and (d) impact crusher.
It is common, but not invariable, for jaw or gyratory crushers to be utilised for primary crushing of large raw feed, and for cone crushers or impact breakers to be used for secondary reduction to the final aggregate sizes. The impact crushing machines can be particularly useful for producing acceptable particle shapes (section 16.5.3) from difficult materials, which might otherwise produce unduly flaky or elongated particles, but they may be vulnerable to abrasive wear and have traditionally been used mostly for crushing limestone.
The main sources of RA are either from construction and ready mixed concrete sites, demolition sites or from roads. The demolition sites produce a heterogeneous material, whereas ready mixed concrete or prefabricated concrete plants produce a more homogeneous material. RAs are mainly produced in fixed crushing plant around big cities where CDWs are available. However, for roads and to reduce transportation cost, mobile crushing installations are used.
The materiel for RA manufacturing does not differ from that of producing NA in quarries. However, it should be more robust to resist wear, and it handles large blocks of up to 1m. The main difference is that RAs need the elimination of contaminants such as wood, joint sealants, plastics, and steel which should be removed with blast of air for light materials and electro-magnets for steel. The materials are first separated from other undesired materials then treated by washing and air to take out contamination. The quality and grading of aggregates depend on the choice of the crusher type.
Jaw crusher: The material is crushed between a fixed jaw and a mobile jaw. The feed is subjected to repeated pressure as it passes downwards and is progressively reduced in size until it is small enough to pass out of the crushing chamber. This crusher produces less fines but the aggregates have a more elongated form.
Hammer (impact) crusher: The feed is fragmented by kinetic energy introduced by a rotating mass (the rotor) which projects the material against a fixed surface causing it to shatter causing further particle size reduction. This crusher produces more rounded shape.
The type of crusher and number of processing stages have considerable influence on the shape and size of RA. In general, for the same size, RAs tend to be coarser, more porous and rougher than NAs, due to the adhered mortar content (Dhir etal., 1999). After the primary crushing, which is normally performed using jaw crushers (Fong etal., 2004), it is preferable to adopt a secondary crushing stage (with cone crushers or impact crushers) (CCANZ, 2011) to further reduce the size of the CDW, producing more regularly shaped particles (Barbudo etal., 2012; Ferreira etal., 2011; Fonseca etal., 2011; Pedro etal., 2014, 2015; Gonzlez-Fonteboa and Martnez-Abella, 2008; Maultzsch and Mellmann, 1998; Dhir and Paine, 2007; Chidiroglou etal., 2008).
CDW that is subjected to a jaw crushing stage tends to result only in flatter RA (Ferreira etal., 2011; Fonseca etal., 2011; Hendriks, 1998; Tsoumani etal., 2015). It is possible to produce good-quality coarse RA within the specified size range by adjusting the crusher aperture (Hansen, 1992). In addition, the number of processing stages needs to be well thought out to ensure that the yield of coarse RA is not affected and that the quantity of fine RA is kept to the minimum (Angulo etal., 2004). This is because the finer fraction typically exhibits lower quality, as it accumulates a higher amount of pulverised old mortar (Etxeberria etal., 2007b; Meller and Winkler, 1998). Fine RA resulting from impact crushers tends to exhibit greater angularity and higher fineness modulus compared with standard natural sands (Lamond etal., 2002; Hansen, 1992; Buyle-Bodin and Hadjieva-Zaharieva, 2002).
One of the commonly known issues related to the use of RCA is its ability to generate a considerable amount of fines when the material is used (Thomas etal., 2016). As the RCA particles are moved around, they impact against one another, leading to the breakage of the friable adhered mortar, which may give rise to some technical problems such as an increase in the water demand of concrete mixes when used as an NA replacement (Thomas etal., 2013a,b; Poon etal., 2007).
The coarse fraction of RMA tends to show a higher shape index owing to the shape of the original construction material (e.g., perforated ceramic bricks) (De Brito etal., 2005). This can pose a problem in future applications as RMA may not compact as efficiently as RCA or NA (Khalaf and DeVenny, 2005). Its shape index may be reduced if the material is successively broken down to a lower particle size (De Brito etal., 2005).
Impact crushers (e.g., hammer mills and impact mills) employ sharp blows applied at high speed to free-falling rocks where comminution is by impact rather than compression. The moving parts are beaters, which transfer some of their kinetic energy to the ore particles upon contact. Internal stresses created in the particles are often large enough to cause them to shatter. These forces are increased by causing the particles to impact upon an anvil or breaker plate.
There is an important difference between the states of materials crushed by pressure and by impact. There are internal stresses in material broken by pressure that can later cause cracking. Impact causes immediate fracture with no residual stresses. This stress-free condition is particularly valuable in stone used for brick-making, building, and roadmaking, in which binding agents (e.g., tar) are subsequently added. Impact crushers, therefore, have a wider use in the quarrying industry than in the metal-mining industry. They may give trouble-free crushing on ores that tend to be plastic and pack when the crushing forces are applied slowly, as is the case in jaw and gyratory crushers. These types of ore tend to be brittle when the crushing force is applied instantaneously by impact crushers (Lewis et al., 1976).
Impact crushers are also favored in the quarry industry because of the improved product shape. Cone crushers tend to produce more elongated particles because of their ability to pass through the chamber unbroken. In an impact crusher, all particles are subjected to impact and the elongated particles, having a lower strength due to their thinner cross section, would be broken (Ramos et al., 1994; Kojovic and Bearman, 1997).
Figure 6.23(a) shows the cross section of a typical hammer mill. The hammers (Figure 6.23(b)) are made from manganese steel or nodular cast iron containing chromium carbide, which is extremely abrasion resistant. The breaker plates are made of the same material.
The hammers are pivoted so as to move out of the path of oversize material (or tramp metal) entering the crushing chamber. Pivoted (swing) hammers exert less force than they would if rigidly attached, so they tend to be used on smaller impact crushers or for crushing soft material. The exit from the mill is perforated, so that material that is not broken to the required size is retained and swept up again by the rotor for further impacting. There may also be an exit chute for oversize material which is swept past the screen bars. Certain design configurations include a central discharge chute (an opening in the screen) and others exclude the screen, depending on the application.
The hammer mill is designed to give the particles velocities of the order of that of the hammers. Fracture is either due to impact with the hammers or to the subsequent impact with the casing or grid. Since the particles are given high velocities, much of the size reduction is by attrition (i.e., particle on particle breakage), and this leads to little control on product size and a much higher proportion of fines than with compressive crushers.
The hammers can weigh over 100kg and can work on feed up to 20cm. The speed of the rotor varies between 500 and 3,000rpm. Due to the high rate of wear on these machines (wear can be taken up by moving the hammers on the pins) they are limited in use to relatively non-abrasive materials. They have extensive use in limestone quarrying and in the crushing of coal. A great advantage in quarrying is the fact that they produce a relatively cubic product.
A model of the swing hammer mill has been developed for coal applications (Shi et al., 2003). The model is able to predict the product size distribution and power draw for given hammer mill configurations (breaker gap, under-screen orientation, screen aperture) and operating conditions (feed rate, feed size distribution, and breakage characteristics).
For coarser crushing, the fixed hammer impact mill is often used (Figure 6.24). In these machines the material falls tangentially onto a rotor, running at 250500rpm, receiving a glancing impulse, which sends it spinning toward the impact plates. The velocity imparted is deliberately restricted to a fraction of the velocity of the rotor to avoid high stress and probable failure of the rotor bearings.
The fractured pieces that can pass between the clearances of the rotor and breaker plate enter a second chamber created by another breaker plate, where the clearance is smaller, and then into a third smaller chamber. The grinding path is designed to reduce flakiness and to produce cubic particles. The impact plates are reversible to even out wear, and can easily be removed and replaced.
The impact mill gives better control of product size than does the hammer mill, since there is less attrition. The product shape is more easily controlled and energy is saved by the removal of particles once they have reached the size required.
Large impact crushers will reduce 1.5m top size ROM ore to 20cm, at capacities of around 1500th1, although units with capacities of 3000th1 have been manufactured. Since they depend on high velocities for crushing, wear is greater than for jaw or gyratory crushers. Hence impact crushers are not recommended for use on ores containing over 15% silica (Lewis et al., 1976). However, they are a good choice for primary crushing when high reduction ratios are required (the ratio can be as high as 40:1) and the ore is relatively non-abrasive.
Developed in New Zealand in the late 1960s, over the years it has been marketed by several companies (Tidco, Svedala, Allis Engineering, and now Metso) under various names (e.g., duopactor). The crusher is finding application in the concrete industry (Rodriguez, 1990). The mill combines impact crushing, high-intensity grinding, and multi-particle pulverizing, and as such, is best suited in the tertiary crushing or primary grinding stage, producing products in the 0.0612mm size range. It can handle feeds of up to 650th1 at a top size of over 50mm. Figure 6.22 shows a Barmac in a circuit; Figure 6.25 is a cross-section and illustration of the crushing action.
The basic comminution principle employed involves acceleration of particles within a special ore-lined rotor revolving at high speed. A portion of the feed enters the rotor, while the remainder cascades to the crushing chamber. Breakage commences when rock enters the rotor, and is thrown centrifugally, achieving exit velocities up to 90ms1. The rotor continuously discharges into a highly turbulent particle cloud contained within the crushing chamber, where reduction occurs primarily by rock-on-rock impact, attrition, and abrasion.
This crusher developed by Jaques (now Terex Mineral Processing Solutions) has several internal chamber configurations available depending on the abrasiveness of the ore. Examples include the Rock on Rock, Rock on Anvil and Shoe and Anvil configurations (Figure 6.26). These units typically operate with 5 to 6 steel impellers or hammers, with a ring of thin anvils. Rock is hit or accelerated to impact on the anvils, after which the broken fragments freefall into the discharge chute and onto a product conveyor belt. This impact size reduction process was modeled by Kojovic (1996) and Djordjevic et al. (2003) using rotor dimensions and speed, and rock breakage characteristics measured in the laboratory. The model was also extended to the Barmac crushers (Napier-Munn et al., 1996).
Figure 9.1 shows common aluminum oxide-based grains. Also called corundum, alumina ore was mined as early as 2000 BC in the Greek island of Naxos. Its structure is based on -Al2O3 and various admixtures. Traces of chromium give alumina a red hue, iron makes it black, and titanium makes it blue. Its triagonal system reduces susceptibility to cleavage. Precious grades of Al2O3 are used as gemstones, and include sapphire, ruby, topaz, amethyst, and emerald.
Charles Jacobs (1900), a principal developer, fused bauxite at 2200C (4000F) before the turn of the 20th century. The resulting dense mass was crushed into abrasive particles. Presently, alumina is obtained by smelting aluminum alloys containing Al2O3 in electric furnaces at around 1260C (2300F), a temperature at which impurities separate from the solution and aluminum oxide crystallizes out. Depending upon the particular process and chemical composition there are a variety of forms of aluminum oxide. The poor thermal conductivity of alumina (33.5W/mK) is a significant factor that affects grinding performance. Alumina is available in a large range of grades because it allows substitution of other oxides in solid solution, and defect content can be readily controlled.
For grinding, lapping, and polishing bearing balls, roller races, and optical glasses, the main abrasive employed is alumina. Its abrasive characteristics are established during the furnacing and crushing operations, so very little of what is accomplished later significantly affects the features of the grains.
Aluminum oxide is tougher than SiC. There are four types of gradations for toughness. The toughest grain is not always the longest wearing. A grain that is simply too tough for an application will become dull and will rub the workpiece, increasing the friction, creating heat and vibrations. On the other hand, a grain that is too friable will wear away rapidly, shortening the life of the abrasive tool. Friability is a term used to describe the tendency for grain fractures to occur under load. There is a range of grain toughness suitable for each application. The white friable aluminum oxide is almost always bonded by vitrification. It is the main abrasive used in tool rooms because of its versatility for a wide range of materials. In general, the larger the crystals, the more friable the grain. The slower the cooling process, the larger are the crystals. To obtain very fine crystals, the charge is cooled as quickly as possible, and the abrasive grain is fused in small pigs of up to 2ton. Coarse crystalline abrasive grains are obtained from 5 to 6ton pigs allowed to cool in the furnace shell.
The raw material, bauxite, containing 8590% alumina, 25% TiO2, up to 10% iron oxide (Fe2O3), silica, and basic oxides, is fused in an electric-arc furnace at 2600C (4700F). The bed of crushed and calcined bauxite, mixed with coke and iron to remove impurities, is poured into the bottom of the furnace where a carbon starter rod is laid down. A couple of large vertical carbon rods are then brought down to touch and a heavy current applied. The starter rod is rapidly consumed, by which time the heat melts the bauxite, which then becomes an electrolyte. Bauxite is added over several hours to build up the volume of melt. Current is controlled by adjusting the height of the electrodes, which are eventually consumed in the process.
After cooling, the alumina is broken up and passed through a series of hammer, beater, crush, roller, and/or ball mills to reduce it to the required grain size and shape, producing either blocky or thin splintered grains. After milling, the product is sieved to the appropriate sizes down to about 40 m (#400). The result is brown alumina containing typically 3% TiO2. Increased TiO2 content increases toughness while reducing hardness. Brown alumina has a Knoop hardness of 2090 and a medium friability.
Electrofused alumina is also made using low-soda Bayer process alumina that is more than 99% pure. The resulting alumina grain is one of the hardest, but also the most friable, of the alumina family providing a cool cutting action. This abrasive in a vitrified bond is, therefore, suitable for precision grinding.
White aluminum oxide is one of the most popular grades for micron-size abrasive. To produce micron sizes, alumina is ball-milled or vibro-milled after crushing and then traditionally separated into different sizes using an elutriation process. This consists of passing abrasive slurry and water through a series of vertical columns. The width of the columns is adjusted to produce a progressively slower vertical flow velocity from column to column. Heavier abrasive settles out in the faster flowing columns while lighter particles are carried over to the next. The process is effective down to about 5 m and is also used for micron sizing of SiC. Air classification has also been employed.
White 99% pure aluminum oxide, called mono-corundum, is obtained by sulfidation of bauxite, which outputs different sizes of isometric corundum grains without the need for crushing. The crystals are hard, sharp, and have better cleavage than other forms of aluminum oxides, which qualifies it for grinding hardened steels and other tough and ductile materials. Fine-grained aluminum oxide with a good self-sharpening effect is used for finishing hardened and high-speed steels, and for internal grinding.
Not surprisingly, since electrofusion technology has been available for the last one hundred years, many variations in the process exist both in terms of starting compositions and processing routes. For example:
Red-brown or gray regular alumina. Contains 9193% Al2O3 and has poor cleavage. This abrasive is used in resinoid and vitrified bonds and coated abrasives for rough grinding when the risk of rapid wheel wear is low.
Chrome addition. Semi-fine aloxite, pink with 0.5% chromium oxide (Cr2O3), and red with 15% Cr2O3, lies between common aloxite, having less than 95% Al2O3 and more than 2% TiO2, and fine aloxite, which has more than 95% Al2O3 and less than 2% TiO2. The pink grain is slightly harder than white alumina, while the addition of a small amount of TiO2 increases its toughness. The resultant product is a medium-sized grain available in elongated, or blocky but sharp, shapes. Ruby alumina has a higher chrome oxide content of 3% and is more friable than pink alumina. The grains are blocky, sharp edged, and cool cutting, making them popular for tool room and dry grinding of steels, e.g., ice skate sharpening. Vanadium oxide has also been used as an additive giving a distinctive green hue.
Zirconia addition. Aluminazirconia is obtained during the production process by adding 1040% ZrO2 to the alumina. There are at least three different aluminazirconia compositions used in grinding wheels: 75% Al2O3 and 25% ZrO2, 60% Al2O3 and 40% ZrO2, and finally, 65% Al2O3, 30% ZrO2, and 5% TiO2. The manufacture usually includes rapid solidification to produce a fine grain and tough structure. The resulting abrasives are fine grain, tough, highly ductile, and give excellent life in medium to heavy stock removal applications and grinding with high pressures, such as billet grinding in foundries.
Titania addition. Titaniaaloxite, containing 95% Al2O3 and approximately 3% Ti2O3, has better cutting ability and improved ductility than high-grade bauxite common alumina. It is recommended when large and variable mechanical loads are involved.
Single crystal white alumina. The grain growth is carefully controlled in a sulfide matrix and is separated by acid leaching without crushing. The grain shape is nodular which aids bond retention, avoiding the need for crushing and reducing mechanical defects from processing.
Post-fusion processing methods. This type of particle reduction method can greatly affect grain shape. Impact crushers such as hammer mills create a blocky shape while roll crushers cause splintering. It is possible, using electrostatic forces to separate sharp shapes from blocky grains, to provide grades of the same composition but with very different cutting actions.
The performance of the abrasive can also be altered by heat treatment, particularly for brown alumina. The grit is heated to 11001300 C (20152375 F), depending on the grit size, in order to anneal cracks and flaws created by the crushing process. This can enhance toughness by 2540%.
Finally, several coating processes exist to improve bonding of the grains in the grinding wheel. Red Fe2O3 is applied at high temperatures to increase the surface area for better bonding in resin cut-off wheels. Silane is applied for some resin bond wheel applications to repel coolant infiltration between the bond and abrasive grit, and thus protect the resin bond.
A limitation of electrofusion is that the resulting abrasive crystal structure is very large; an abrasive grain may consist of only one to three crystals. Consequently, when grain fracture occurs, the resulting particle loss may be a large proportion of the whole grain. This results in inefficient grit use. One way to avoid this is to dramatically reduce the crystal size.
The earliest grades of microcrystalline grits were produced as early as 1963 (Ueltz, 1963) by compacting a fine-grain bauxite slurry, granulating to the desired grit size, and sintering at 1500C (2735F). The grain shape and aspect ratio could be controlled by extruding the slurry.
One of the most significant developments since the invention of the Higgins furnace was the release in 1986, by the Norton Company, of seeded gel (SG) abrasive (Leitheiser and Sowman, 1982; Cottringer et al., 1986). This abrasive was a natural outcome of the wave of technology sweeping the ceramics industry at that time to develop high strength engineering ceramics using chemical precipitation methods. This class of abrasives is often termed ceramic. SG is produced by a chemical process. In a precursor of boehmite, MgO is first precipitated to create 50-m-sized aluminamagnesia spinel seed crystals. The resulting gel is dried, granulated to size, and sintered at 1200C (2200F). The resulting grains are composed of a single-phase -alumina structure with a crystalline size of about 0.2m. Defects from crushing are avoided; the resulting abrasive is unusually tough but self-sharpening because fracture now occurs at the micron level.
With all the latest technologies, it took significant time and application knowledge to understand how to apply SG. The abrasive was so tough that it had to be blended with regular fused abrasives at levels as low as 5% to avoid excessive grinding forces. Typical blends are now five SGs (50%), three SGs (30%), and one SG (10%). These blended abrasive grades can increase wheel life by up to a factor of 10 over regular fused abrasives, although manufacturing costs are higher.
In 1981, prior to the introduction of SG, the 3M Co. introduced a solgel abrasive material called Cubitron for use in coated abrasive fiber discs (Bange and Orf, 1998). This was a submicron chemically precipitated and sintered material but, unlike SG, had a multiphase composite structure that did not use seed grains to control crystalline size. The value of the material for grinding wheel applications was not recognized until after the introduction of SG. In the manufacture of Cubitron, alumina is co-precipitated with various modifiers such as magnesia, yttria, lanthana, and neodymia to control microstructural strength and surface morphology upon subsequent sintering. For example, one of the most popular materials, Cubitron 321, has a microstructure containing submicron platelet inclusions which act as reinforcements somewhat similar to a whisker-reinforced ceramic (Bange and Orf, 1998).
Direct comparison of the performance of SG and Cubitron is difficult because the grain is merely one component of the grinding wheel. SG is harder (21GPa) than Cubitron (19GPa). Experimental evidence suggests that wheels made from SG have longer life, but Cubitron is freer cutting. Cubitron is the preferred grain in some applications from a cost/performance viewpoint. Advanced grain types are prone to challenge from a well-engineered, i.e., shape selected, fused grain that is the product of a lower cost, mature technology. However, it is important to realize that the wheel cost is often insignificant compared to other grinding process costs in the total cost per part.
The SG grain shape can be controlled by extrusion. Norton has taken this concept to an extreme and in 1999 introduced TG2 (extruded SG) grain in a product called ALTOS. The TG2 grains have the appearance of rods with very long aspect ratios. The resulting packing characteristics of these shapes in a grinding wheel create a high strength, lightweight structure with porosity levels as high as 70% or even greater. The grains touch each other at only a few points, where a bond also concentrates in the same way as a spot weld. The product offers potential for higher stock removal rates and higher wheelspeeds due to the strength and density of the resulting wheel body (Klocke and Muckli, 2000).
Recycling of concrete involves several steps to generate usable RCA. Screening and sorting of demolished concrete from C&D debris is the first step of recycling process. Demolished concrete goes through different crushing processes to acquire desirable grading of recycled aggregate. Impact crusher, jaw crusher, cone crusher or sometimes manual crushing by hammer are preferred during primary and secondary crushing stage of parent concrete to produce RA. Based on the available literature step by step flowchart for recycling of aggregate is represented in Fig. 1. Some researchers have also developed methods like autogenous cleaning process , pre-soaking treatment in water , chemical treatment, thermal treatment , microwave heating method  and mechanical grinding method for removing adhered mortar to obtain high quality of RA. Depending upon the amount of attached mortar, recycled aggregate has been classified into different categories as shown in Fig. 2.
Upon arrival at the recycling plant, CDW may either enter directly into the processing operation or need to be broken down to obtain materials with workable particle sizes, in which case hydraulic breakers mounted on tracked or wheeled excavators are used. In either case, manual sorting of large pieces of steel, wood, plastics and paper may be required, to minimize the degree of contamination.
The three types of crushers most used for crushing CDW are jaw, impact, and gyratory crushers (Fig.8). A jaw crusher consists of two plates fixed at an angle (Fig.8a); one plate remains stationary while the other oscillates back and forth relative to it, crushing the material passing between them. This crusher can withstand large pieces of reinforced concrete, which would probably cause other types of crushers to break down. Therefore, the material is initially reduced in jaw crushers before going through other types. The particle size reduction depends on the maximum and minimum size of the gap at the plates. Jaw crushers were found to produce RA with the most suitable grain-size distribution for concrete production (Molin etal., 2004).
An impact crusher breaks CDW by striking them with a high speed rotating impact, which imparts a shearing force on the debris (Fig.8b). Materials fall onto the rotor and are caught by teeth or hard steel blades fastened to the rotor, which hurl them against the breaker plate, smashing them to smaller-sized particles. Impact crushers provide better grain-size distribution of RA for road construction purposes and are less sensitive to material that cannot be crushed (i.e. steel reinforcement).
Gyratory crushers, which work on the same principle as cone crushers (Fig.8c), exhibit a gyratory motion driven by an eccentric wheel and will not accept materials with large particle sizes as they are likely to become jammed. However, gyratory and cone crushers have advantages such as relatively low energy consumption, reasonable amount of control over particle size and production of low amount of fine particles.
Generally, jaw and impact crushers have a large reduction factor, defined as the relationship between the input's particle size and that of the output. A jaw crusher crushes only a small proportion of the original aggregate particles but an impact crusher crushes mortar and aggregate particles alike, and thus may generate twice the amount of fines for the same maximum size of particle (O'Mahony, 1990).
In order to produce RA with predictable grading curve, it is better to process debris in two crushing stages, at least. It may be possible to consider a tertiary crushing stage and further, which would undoubtedly produce better quality coarse RA (i.e. less adhered mortar and with a rounder shape). However, concrete produced with RA subjected to a tertiary crushing stage may show only slightly better performance than that made with RA from a secondary crushing stage (Gokce etal., 2011; Nagataki etal., 2004). Furthermore, more crushing stages would yield products with decreasing particle sizes, which contradicts the mainstream use of RA (i.e. coarser RA fractions are preferred, regardless of the application). These factors should be taken into account when producing RA as, from an economical and environmental point of view, it means that relatively good quality materials can be produced with lower energy consumption and with a higher proportion of coarse aggregates, if the number of crushing stages is prudently reduced.
considerations when choosing a concrete crusher
Because concrete and rebar construction is extremely strong, it is used in all kinds of buildings and infrastructure from residences to storefronts to factories and roadways. Rather than send all of this valuable material to landfills, concrete demolition contractors and recyclers can turn this waste product from demolition sites into a valuable end product, that may be used in a variety of projects.
Below, we provide a basic guide for demolition contractors and concrete recyclers on how to select the best concrete crusher for the project at hand. We begin with an overview of the three basic types of crushers on the market.
Jaw crushers. At their most basic, jaw crushers use the same technology as a nutcracker. They crush debris between two vertically oriented jaws, which are tapered to allow only smaller material to pass through. A flywheel powers the jaws, which open and close just like a mouth. The ability to process extremely hard and abrasive materials, ability to accept a large infeed size, and lower operating costs are advantages to jaw crushers. However, they are a primary crusher and can only crush down to a 3 or 4 minus, which is often sold or used as a lower value fill type material, so not suitable if trying to achieve a smaller and higher value end product.
Impact crushers. While jaw crushers use compression to break up concrete, impact crushers use impact (as their name implies). Material is introduced into the crushing chamber, which houses a heavy rotor spinning at a high RPM. The rotor has blowbars or hammers which impact the material, causing it to break apart, and further propels the material at high speed against an impact curtain wall(s), further crushing the material. Impact crushers can be highly productive in recycling applications, and are available in closed circuit configuration with an integrated screening deck, allowing users to achieve a final product as small as 3/4' or even less if required. In our professional opinion, an impact crusher is the best choice for most concrete, or asphalt recycling applications.
Cone crushers. These are less common in recycling applications. Their basic crushing chamber shape is a cone whose open top accepts rock. As the aggregate moves down toward the base of the cone, they are crushed between two internal liners one that is fixed and another that is moving in an eccentric motion. Cones are best used in hard, abrasive rock and are not ideal in recycling applications, as they have low tolerance to tramp iron and other contaminants found in demolition materials, and can only be used in secondary and tertiary crushing applications.
Once you understand these basic types of crushers, you can proceed to more specific characteristics of the machine at hand. Here are the qualities concrete demolition contractors typically review when choosing a new crusher:
Feed material type and size Can the machine process only concrete, or may other materials be mixed in? What is the max feed size that can be processed safely and cost effectively by the machine? These are important questions that need answering when choosing the right machine for your application.
Output size. This determines what type of products may be produced from the crusher. A jaw will produce a coarse 3 8 minus, while with a closed circuit impactor you can make minus or even smaller if required.
Production rates. Each machine has its own productivity pace, typically described in tons of material processed per hour. Be wary of stated claims on brochures, you should check with users who operate the equipment in question who have verified means of measuring realistic production numbers.
Equipment size. Machine dimensions determine storage and transportation options. Before purchasing a crusher, you should assess where you will be moving the crusher, and what the weight and size restrictions are for that region.
Specification Comparisons We recommend creating a spreadsheet when assessing various brands of a similar type of crusher. The initial purchase price means very little in the overall picture, so start to look and compare important specifications.
Dealer support With any equipment, its often only as good as the dealer that stands behind it. When considering a major investment such as a crusher, you should visit the dealer and ask for a tour of their offices and facility. You can get a feel for the type of people and company by viewing how clean and professional of an operation they run, as well as how well stocked they are for spare parts and wear parts. Also request contact info for other customers who have purchased the same machine you are considering. If you can meet with these existing customers onsite and view the machine(S) in action and speak to someone who has operated the machine for a good period of time, this can prove to be extremely valuable and save you tens, if not hundreds of thousands, as making a poor choice when choosing a crusher can prove to be very costly.
used impact crushers for sale. kinglink equipment & more | machinio
Secondary Mobile Impact Crushing Plant
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Impact Crusher can crush the large, medium and small size materials (granite, limestone, concrete ,etc.)With max feed size less than ...
Impact Crusher can crush the large, medium and small size materials (granite, limestone, concrete ,etc.)With max feed size less than 500mm and compression strength less than 350Mpa. Presently, by practices, its c...
Impact Crusher can crush the large, medium and small size materials (granite, limestone, concrete ,etc.)With max feed size less than 500mm and compression strength less than 350Mpa. Presently, by practices, its c...
High qulaity mobile crusher for aggregates, hard stone, granite, pebble, ore crushing
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impact crusher blow bars, hammers material and manufacturer | quarrying & aggregates
Different working conditions need to choose different types of blow bars, from high manganese steel, martensitic alloy steel to high-chromium iron. These types of blow bar can ensure that the impact crusher always maintains the best operating condition with the best cost performance.
High manganese steel has high impact resistance and excellent wear resistance under strong impact abrasive wear conditions. The high manganese steel hammer hardly breaks, so high manganese steel is suitable for primary crushing applications.
Martensitic alloy steel can achieve a good balance between impact resistance (toughness) and hardness, and is often used in secondary crushing applications that require better impact resistance and hardness, such as quarrying and construction waste recycling.
Compared with martensitic alloy steel, the brittleness (fragility) of high chromium iron determines that it is not suitable for crushing large or super large hard materials. Therefore, high-chromium iron blow bars are the most commonly used type in secondary crushing applications.
jaw crusher vs impact crusher | what's the difference | m&c
Jaw crusher and impact crusher are the main crushing equipments in the ore crushing production line. Jaw crusher is mainly used for the process of high hardness materials, mainly for the coarse crushing of ore, while the impact crusher for the treatment of medium hardness and brittleness stones, mainly for the medium crushing and fine crushing of stones.
Jaw crusher is mainly composed of frame, eccentric wheel, flywheel, moving jaw, side guard plate, elbow back seat, reset spring, fixed jaw plate and movable jaw plate etc. The jaw crusher uses power to drive the jaw plate to move periodically to extrude the material to achieve the crushing effect.
Impact crusher is mainly composed of reaction liner, feed port, plate hammer, rotor frame etc. When the impact crusher is working, the plate hammers that distributed on the rotor according to different rules will hit the material on the reaction liner for crushing.
a. Jaw crusher is a primary crusher, which is the first equipment to crush the raw stone. It has simple and reasonable structure, high hardness of wear-resistant parts, and is suitable for the primary crushing of high hardness stone;
b. Impact crusher is a two-stage crushing equipment, which is the equipment for crushing the discharged material of jaw crusher again. It is not suitable for crushing high hardness stone such as granite and basalt, and has good crushing effect for brittle and soft stone.
Jaw crusher is mainly used for crushing all kinds of ores and bulk materials into medium particle size and crushing materials whose compressive strength 320Mpa. The feed size of jaw crusher is 125mm 750mm, which is the preferred crushing equipment for primary crushing.
The feed size of the impact crusher 500mm and the compressive strength 350MPa. It is suitable for all kinds of coarse, medium and fine materials (granite, limestone, concrete, etc.). The discharge particle size can be adjusted and the crushing specifications are diversified.
a. When jaw crusher working, the motor drives the belt and pulley to move the moving jaw up and down through the eccentric shaft. When the moving jaw rises, the angle between the elbow plate and the moving jaw increases, so as to push the moving jaw plate close to the fixed jaw plate. At the same time, the material is crushed to achieve the purpose of crushing;
When the moving jaw goes down, the angle between the elbow plate and the moving jaw becomes smaller. Under the action of the pull rod and spring, the moving jaw plate leaves the fixed jaw plate. At this time, the crushed materials are discharged from the lower opening of the crushing chamber.
Under the action of centrifugal force, the materials will collide with the materials strongly that distributed around the turntable, and then break. After the two parts of materials collide and crush, they will form eddy current movement between the turntable and the shell, resulting in many times of friction and smashing. After many times of circulation crushing, they will be discharged from the discharge port.
a. Jaw crusher is coarse crushing equipment, the discharge size is generally large, and the size of finished product is generally 10-350mm; due to the crushing principle of jaw crusher, there are many needle and flake finished aggregate;
b. Impact crusher, as a medium and fine crushing equipment, has a finer discharging particle size; the impact crusher has the function of shaping, with good discharging particle shape of finished aggregate, less water chestnut angle, and the particle shape is better than the cone crusher.
a. Jaw crusher has a deep crushing cavity without dead zone, so it has a large crushing ratio, strong production capacity, simple and reasonable structure, reliable work, low operating cost, high efficiency in operation, environmental protection, large adjustment range of discharge port, which can meet the requirements of different demands;
b. Impact crusher has the advantages of large feed inlet, high crushing chamber, impact resistance and wear resistance, economic and reliable operation, strong crushing capacity, good comprehensive benefit, and the finished aggregate has uniform particle size, beautiful particle shape and good selling price;
c. The crushing efficiency of the jaw crusher is lower than impact crusher. Its because the jaw crusher does not work when discharging, but the rotor of the impact crusher keeps rotating, whenever the material enters the crushing chamber, it will be crushed.
In short, the production capacity of jaw crusher is larger than that of impact crusher. The output of jaw crusher can reach 600-800t per hour (depending on the different manufacturers and product model), and the output of impact crusher is about 260-450t per hour.
The sales of jaw crusher in the market is higher than that of impact crusher, the main reason is that the price of jaw crusher is more favorable. Secondly, jaw crusher is a more traditional crushing equipment, and its performance, quality, power consumption and other aspects can meet the application requirements of users, it is more cost-effective and easy to attract users attention
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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